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Umgang mit Nagetieren und Fixierungstechniken

Umgang mit Nagetieren und Fixierungstechniken

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Lab Animal Research
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JoVE Science Education Lab Animal Research
Rodent Handling and Restraint Techniques

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April 30, 2023

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Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN 

It has been demonstrated that even minimal handling of mice and rats is stressful to the animals. Handling for cage changing and other noninvasive procedures causes an increase in heart rate, blood pressure, and other physiological parameters, such as serum corticosterone levels. Fluctuations can continue for up to several hours. The methods of restraint required for injections and blood withdrawals also cause physiological changes that can potentially affect scientific data. Training in the proper handling of mice and rats is required to minimize the effects to the animals.1 Mice and rats can be restrained manually with restraint devices, or with chemical agents. Manual methods and the use of restraint devices are covered in this manuscript. All restraint methods include the process of lifting the animals from their home cage.

Princípios

Common methods for removing either a mouse or a rat from its cage involve lifting the animal by the tail, using forceps to grab the scruff of the neck or base of the tail, using a tube or other enrichment device,2 grasping around the body, or scooping the animal into the palm.3,4

When lifting a mouse or rat by the tail, it is imperative that the tail be grasped at the base near the rump of the animal. Should the animal be lifted from the end of the tail, the skin of the tail can deglove and be pulled off by the stress of the body weight; a degloving injury will result in the tail being amputated. 3 Moving an animal from one cage to another, or to a working surface, should be done quickly and steadily. Suspending the animal in the air for any length of time will not only cause distress, but can also cause the animal to twist or struggle, possibly resulting in harm to the tail. The handler should not place their hand under the animal because-as it is lifted by its tail-it is instinctive for the animal to try to grasp the hand for security, resulting in a bite.

In many mouse production facilities, forceps are used to remove animals from their cages. This is done for biosecurity, as it is believed that there is less chance for cross-contamination from animal to animal. The forceps tips should be stored in alcohol between handling of individual animals, or groups of animals. There are a variety of forceps used to grasp mice. The most commonly used include long dressing forceps with atraumatic tips-or with rubber, plastic, or silicone tubing placed over the ends of the forceps to provide a cushion-or tongue forceps with rubber grips.4

Forceps can grasp a mouse either at the scruff of the neck or at the base of the tail. Most mice become accustomed to this method quickly and do not struggle. However, patience and practice is necessary to become adept at catching the animals. Beginners will need to be trained on how tightly to grasp the mice, especially at the scruff, as this could interfere with breathing. When using forceps on the tail, care must be taken to place the forceps near the base of the tail to avoid injury.

For animals that are anxious or exhibit stereotypies, placing tubes into the cage may decrease handling difficulty, and reduce the flight/fright response to daily animal husbandry. A tube made of a nonporous material can be added for enrichment, and serve as a place for the animal to shelter or seek safe refuge. Such tubes can be open-ended or capped on one end. Most mice or rats will willingly go into the tubes when their cage is opened, or they can be easily guided to the tube. Once the animal is inside the tube, the open end is covered to transport the animal to the new location. When placed in a fresh cage, the tube can be gently tipped upward to encourage the animals to leave it. Animals are easily conditioned to this method of cage changing and will immediately enter the tubes, making this method as quick and easy as others for moving animals from one place to another. Although tubes do not have to be present in the home cage to be effective, having a tube in the primary enclosure increases recognition of a familiar safe site, as well as provides cage enrichment.2

Some institutions prefer that animals be lifted by the body for routine handling, especially for handling rats. Animals must be habituated to this method from an early age. Young rats between 2-4 weeks of age tend to jump straight up. Placing a hand over the rat's back will cause it to jump into the palm of the handler, allowing it to be grasped. A second hand may be needed to prevent the rat from squirming out of grasp before placing it into another cage. Adult rats are gently grasped around the thorax, lifted, and quickly placed into another cage, or onto a surface.

When changing cages with neonate mice or rats, it is often necessary to remove them while keeping the nest intact. With the use of two hands to scoop the nest and neonates from the bottom of the cage, the intact nest is moved into a new cage. However, to avoid dropping pups, the fingers of each hand must be held closely together. Once moved to a new cage, it is important to verify that the pups are all present. It is advisable to count the pups before and after moving them. A plastic scoop may be used instead of the hands. If this method is used, a hand should be placed over the top of the scoop to prevent neonates from wiggling or jumping out of the scoop. This method of transferring pups, compared to the individual handling of the pups, is less distressing to both the pups and the dams.

Restraint for technical procedures requires a confident and firm, but gentle, touch. Tentative approaches can result in handler bites. If the handler recoils as an animal squeals, that animal quickly learns how to avoid restraint. However, aggressive handling can result in the injury or death of rodents. A balance of an assertive yet gentle approach is the goal for rodent handling.

Mice and small rats can be restrained by grasping the skin at the nape of the neck, referred to as scruffing. Precautions for this method include both grasping the skin too firmly or too loosely. If the skin is grasped too tightly, the airway can become constricted, which can lead to death. If grasped too loosely, the animal will be able to turn its head and potentially bite the handler.

Animals that are agitated or extremely fearful are much more likely to bite. It is best to calm the animal prior to handling. There are various calming techniques that have been tried with varying success. The most reliable method is to use some sort of chemical restraint, most often an inhalation anesthetic. Isoflurane or sevoflurane are short-acting inhalation anesthetics that can be delivered with only the handling required to transfer the animal from its cage to an induction chamber. Once the animal is anesthetized, they can be manipulated or manually restrained for the procedure.

A method for calming a rat is to wrap it in a thick terry towel, allowing it to hide under the towel. Placing it on a lab coat sleeve so that they can bury their head in the folds at the elbow may also provide a sense of safe security to the animal. This same result can be achieved by placing the animal in a dark area for a few minutes.

Procedimento

1. Scruffing

Mice are most often restrained using the scruffing technique, but young rats can also be restrained with this method. Adult rats are more difficult to restrain with this technique due to a more muscular neck, a reduced amount of loose skin, and an aversion to this method.

  1. The one-handed restraint method is utilized most often in mouse strains that are very calm, such as the athymic nude, SCID, and some GEM strains. However, there is a greater risk for being bitten with this method. Novice animal handlers should become comfortable with the two-handed restraint technique before attempting the one-handed method.
    1. Place the animal on a surface that they can grip, such as a wire bar cage top or a mat.
    2. Hold the tail between the third and fourth fingers of the nondominant hand, and apply gentle backward traction. This causes the animal to hold onto the surface, and results in the body being stretched and elongated.
    3. Turn the hand so that the palm is facing the body of the animal.
    4. With the index finger and thumb, pin the rodent over the shoulders.
    5. Gently slide the thumb and index finger forward, and position them at the base of the skull. Grasp the loose skin at the neck and lift the animal.
    6. Use the middle finger to stabilize the animal along the back by pinning the dorsal skin against the base of the thumb.
  2. Two-handed restraint
    1. Place the animal on a surface that they can grip.
    2. Hold the tail at the base (within 1-2 cm of the body) with the dominant hand, and apply gentle backward traction. This causes the animal to hold onto the surface, and results in the body being stretched and elongated.
    3. With the index finger and thumb of the other hand, pin the rodent over the shoulders.
    4. Gently slide the thumb and index finger forward, and position them at the base of the skull. Grasp the loose skin at the neck and lift the animal.
    5. Use the remaining fingers to stabilize the animal along the back by pinning the dorsal skin against the base of the thumb.
    6. Secure the hindquarters by pinning the tail against the palm with the fourth finger, or by allowing the hind limbs to rest on a solid surface.

Figure 1
Figure 1: One-handed and two-handed restraint method for mice

2. Gloves

There are a variety of gloves available for handlers to wear for protection from rat bites. They are generally unsuitable for work with mice due to the loss of dexterity. Often, the disadvantages of many glove types outweigh the advantages.

  1. Cotton canvas work gloves are not bite resistant, but provide a small amount of protection from teeth and nails. They do not provide good grip as they slide easily over the fur.
  2. Good quality leather gloves are bite resistant. However, their stiffness causes a reduction in dexterity. The thickness of the leather, though protective, reduces tactile acuity and hand mobility.
  3. Chain mail gloves provide a psychological sense of security for the animal handler. However, they are heavy and most rats' teeth can penetrate between the links. In addition, these gloves decrease manual dexterity, and if used improperly are more dangerous for both the animal and the handler.
  4. Rubber-insulated gloves that are commonly used in homes for washing dishes provide a textured palmar surface, and allow for a secure grip on the hair coat of rodents. The stretchy latex surface is thick enough to resist puncture by rodent incisors, and thin enough to be able to feel and control the animal. The major disadvantage is that they are made of latex, which is a concern for persons with latex allergies. Furthermore, these gloves deteriorate in light, and need to be replaced regularly.

3. Body Restraint

  1. The "T. rex grip" is a two-handed restraint method for rats.
    1. Place a rat on a surface that can be gripped.
    2. Holding the base of the tail with one hand, bring the other hand up and over the back with the index and middle fingers split.
    3. Place the hand over the shoulder with the index finger on one side of the head, and the middle finger on the other side. The fingers on each side of the head restrict side-to-side movement of the head.
    4. Encircle the body behind the forelegs with the third finger, the fourth finger, and the thumb. Care must be taken to avoid compressing the chest and compromising respirations. This grip prevents the rat from moving forward or backward out of the hand.
    5. Stabilize the tail and hindquarters by grasping the base of the tail with or without holding onto the hind feet.
    6. This restraint works well with larger rats, and when access to the head is needed.
  2. The forelimb crisscross method is a two-handed restraint method.
    1. Place the animal on a surface that they can grip.
    2. Hold the tail at the base (within 1-2 cm of the body) with the dominant hand and apply gentle backward traction. This causes the animal to grip onto the surface, and results in the body being stretched and elongated.
    3. Bring the other hand from behind over the back.
    4. Grasp the rat directly behind the shoulders, with the fingers on one side and the thumb on the other side of the chest, and slide the hand forward, thus forcing the forelegs forward.
    5. The forelegs will cross under the rat's chin, creating a physical barrier and preventing the rat from moving its head down toward the fingers.
    6. Take care to avoid compressing the chest and compromising respirations.

Figure 2
Figure 2: T-rex grip and forelimb crisscross method for restraining rats

4. Restraint devices

Figure 3
Figure 3: Broome-style restraining device

Figure 4
Figure 4: Flat-bottomed rodent restrainer

  1. Rigid devices come in a variety of types, and are generally made of nonporous material that is easily disinfected.
    1. The Broome-style restraint is designed to provide access to the tail for intravenous injections. It is constructed with a slot that runs along the full length of the device, which allows the animal to be pulled into the restrainer hindquarters first. A plastic nosepiece is inserted to hold the animal in place.
      1. Remove the nosepiece from the body of the restraint tube by loosening the screw.
      2. Grasp the animal at the base of the tail, and orient the restraint tube so that the slit that runs the length of the tube is facing up. Gently pull the animal into the restraint device hindquarters first.
      3. It is often advantageous to place the animal on a smooth surface to facilitate its placement into the tube.
      4. Once the animal is fully in the tube-and has been drawn to the closed end-slide the plastic nosepiece into the tube to occlude the opening.
      5. Place the nosepiece assembly so that the animal's nose is in the center opening. Do not position the nosepiece so tightly that the animal cannot breathe.
    2. The flat-bottomed rodent restrainer is a half cylinder with openings that allow access from the top and the bottom of the restraint device. A rigid plastic gate is inserted into one of several graduated slots to hold the animal within the device.
      1. Hold the animal by the base of the tail with the dominant hand on a smooth surface, or on a cage top.
      2. Hold the flat-bottomed restraint tube in the other hand, and angle it so that the open end is at the animal's head at a 45° angle to the table/cage top surface.
      3. Some animals will immediately enter the tube, while others are reluctant and require the handler to steer them into the tube.
      4. Place the tube over the animal's head. Immediately tap the animal's rump and maintain pressure to prevent the animal from backing up.
      5. Once the animal is in the restraint device, slide the plastic gate into the appropriate slot to hold the animal in the restraint device.
    3. Tube restraints are Plexiglass cylinders with one closed end containing holes or slits for air circulation. Some are modified with a wide slothalf the length of the cylinderto accommodate exposure of a hind limb for intramuscular injections, saphenous and femoral blood collection, or access to the dorsal surface for subcutaneous injections.
      1. Grasp the animal by the base of the tail with the dominant hand on a smooth surface, or on a cage top.
      2. Hold the restraint tube in the other hand and angle it so that the open end is at the animal's head at a 45° angle to the table/cage top surface.
      3. Some animals will immediately enter the tube. Other animals are reluctant and require the handler to steer them into the tube.
      4. Place the tube over the animal's head. Immediately tap the animal's rump and maintain pressure to prevent the animal from backing up.
      5. Scruff and manually guide unmanageable animals into the tube, allowing the skin being held to slide through the slit in the tube.
      6. Once the animal is in the restraint device, it is necessary to occlude the opening to prevent the animal from backing up.
      7. Depending on the procedure, several fingers are placed across the opening.
      8. Stuff a large latex glove into the opening. The gloves are usually textured and will grip the Plexiglass surface.
      9. Some restraint tubes will have closures specific to that style or size.

Figure 5
Figure 5: Tube restraining device

  1. Flexible restrainers are disposable flexible plastic cones. They are available in either transparent or opaque plastic. The plastic is thin enough to allow penetration by a needle to accomplish injections without removing the animal from the restraint device. They come in a variety of sizes to fit mice and rats, both adult and weanling.
    1. Cut the plastic with scissors to allow access to the limbs, the tail, and other injection sites.
    2. Select a cone size appropriate for the animal. The cone should be long enough to extend 2-3 inches beyond the animal's rump.
    3. Insert the animal into the cone
      1. Open the cone and grasp it around the upper half.
      2. Grasp the animal by the base of the tail with the dominant hand, placing it on a smooth surface or a cage top.
      3. Hold the restraint cone in the other hand, and angle it so that the open end is at the animal's head at a 45° angle to the table/cage top surface.
      4. Some animals will immediately enter the cone. Other animals are reluctant and require the handler to steer them into the restraint cone.
      5. Place the cone over the animal's head. Immediately tap the animal's rump and maintain pressure to prevent the animal from backing up. Due to the larger diameter of the cone opening, animals are much more likely to turn around to exit the cone.
      6. As soon as the animal enters the cone, grasp the open end and seal it to force the animal to the end.
      7. Secure the opening by folding the plastic to one side of the tail and applying the binder clip to the folded plastic, being careful to avoid clamping the tail or skin. Alternatively, gather the plastic around the tail evenly, and place the twist tie as close to the body as possible to secure the opening.

Figure 6
Figure 6: Flexible restrainer

5. Restraint methods for specific technical procedures

  1. Ventral exposure is required for intraperitoneal injections.
    1. Scruffing
      1. Scruff the animal and turn the hand so that the abdomen is exposed.
      2. Tilt the animal so that the head is pointing downward at a 30° angle.
      3. Secure the hindquarters by pinning the tail against the palm using the fourth finger.
      4. Alternatively, the hindquarters can be immobilized by pinning the excess skin along the back between the fingers and the base of the thumb.
    2. T. rex grip and forelimb crisscross restraint methods
      1. Grasp the animal (rats only) using either of the above techniques.
      2. With the free hand, grasp both hind legs above the hock, and extend them caudally.
      3. Support the weight of the animal with the palm of the hand on the back.
      4. Tilt the animal so that the head is pointing downward at a 30° angle.
      5. A second person performs the injection.
    3. Rigid restrainer
      1. Most rigid restraint devices cannot prevent the animal from instinctively rolling to remain upright.
      2. If a rigid restrainer is employed, turn the animal so that its head is pointed down and is perpendicular to the tabletop.
    4. Flexible restrainer
      1. When placed properly in a flexible plastic cone, the animal is unable to turn over or around.
      2. Care must be taken to position the animal such that the hind limbs are sufficiently separated to allow access to the abdomen.
      3. As the animal is compressed, it is imperative that the injection be low enough on the ventral surface to avoid puncture of the spleen, liver, kidney, or stomach.
  2. Dorsal exposure is required for injections into the subcutaneous space.
    1. Scruffing
      1. Scruff the animal and allow its hind legs to rest on a solid, flat surface.
      2. Lift the scruff to create a tent of skin over the neck and shoulders.
      3. Place the weight of the hand on the table when injecting mice. Placing weight on the mouse can cause suffocation.
      4. Hold rats in place with weight on the hindquarters, but never the chest.
      5. Inject the substance into the space below the fingers on the body of the animal.
    2. Rigid restrainers
      1. Place the animal in a restraint device with an opening large enough to pull the skin up.
      2. It may be necessary to use forceps to grasp the skin.
      3. Most animals remain in the proper posture unless the restraint is rotated.
      4. Do not inject a volume that prevents the skin from receding from the opening once the injection is complete.
  3. The restraint of the hind limb is necessary for intramuscular injection; blood withdrawal from the saphenous vein, femoral vein, or femoral artery; and injection into the footpad.
    1. Scruffing of mice and small rats (under 200 g)
      1. Scruff the animal and turn the hand so that the abdomen is exposed.
      2. Access the hind foot by placing the foot between the fingers.
      3. This method is best used only for footpad injections.
    2. T. rex grip or forelimb crisscross
      1. This method requires two people: one for restraint of the body, and one for restraint of the limb and the performance of the injection.
      2. Extend the rat's hind leg by grasping the foot for access to the saphenous vein, femoral vein or artery, or the muscle for injection.
      3. Hold the leg just above the hock for injection of the footpad.
    3. Rigid restrainers
      1. Place the animal in a restraint tube head first.
      2. Expose the tail and hindquarters by gently pulling them backward from the tube.
      3. Immobilize the leg by grasping the skin of the flank and locking the knee straight. This provides access to the quadriceps muscle for injection in the mouse or rat, and prevents the animal from exiting the restraint device.
      4. In devices with large slots, position the leg outside the tube for access to the blood vessels for sampling or footpad injection.
      5. Those restraint tubes with flat end pieces allow the tube to rest on the table and stabilize the device during the procedure.
      6. Because the animal is secured in this manner, it is possible to perform injections or blood sampling of rats by a single technician.
    4. Flexible restraint
      1. Flexible plastic restraints can be modified by cutting openings to accommodate the exposure of limbs.
      2. The openings made can be customized for each animal, or for specific procedures.
      3. As the animal is secured in this manner, it is possible for a single technician to perform injections or blood sampling of rats.

Rodents are widely used model organisms to investigate diverse scientific questions, and it has been demonstrated that even minimal handling is stressful for these animals.

Handling for simple tasks such as cage changing may cause an increase in heart rate, blood pressure, and serum corticosterone levels, and these fluctuations can continue for several hours. The methods of restraint required for common injection and blood withdrawal procedures can also cause physiological changes, which can potentially affect the scientific data. Therefore, training for proper handling of mice and rats is required to minimize these effects on animals.

In this video, we will first review the basic techniques for handling rodents, and then we'll discuss the rodent restraint procedures including manual techniques and methods involving usage of restraining devices.

Let's begin by discussing the basics of rodent handling. One of the most common methods for moving either an adult mouse or rat is by lifting the animal by its tail. While doing this, it is imperative that the tail be grasped at the base near the rump. If the animal is lifted by the end of its tail, the skin can be pulled off due to the body weight and may lead to an injury resulting in tail amputation. Importantly, moving an animal from one place to another should be done quickly and steadily. Suspending the animal in air for any length time will not only cause distress, but will also cause the animal to twist or struggle, possibly causing harm to the tail. Also, the handler should not place a hand under the animal, because it may try to grasp it for security, resulting in a bite.

Another method for handling adult rodents is to use forceps. Types of forceps commonly used are long-dressing forceps or tongue forceps with rubber, plastic, or silicone tubing placed over the ends to provide a cushion. The forceps can grasp the mouse either at the scruff of the neck or at the base of the tail. The use of forceps minimizes cross contamination from animal to animal, and it is quicker and less expensive than changing gloves between each animal cage. Beginners will need to be trained on how tightly to grasp the mice with forceps, especially at the scruff as it could interfere with breathing. When using the forceps on the tail, care must be taken to place the forceps near the base of the tail to avoid injury. Remember to store them facedown in 70% ethanol between handling of different groups of animals.

Also, one can use tubes made of a non-porous material to transfer animals. These tubes can be added to a cage as a place for the animal to shelter or seek safe refuge. Most mice or rats would willingly enter the tubes when their cage is opened, or they can be easily guided into the tube. When the animal is inside, cover the open ends with your palm and fingers. Next, to encourage the animal to leave, gently tip the tube upward in the new cage. Animals are easily conditioned to this method of cage changing, making this a quick and easy process for moving animals from one place to another.

Some institutions prefer that animals-especially rats-be lifted by their body, even while routine handling. Adult rats are gently grasped around the thorax, lifted, and quickly placed into another cage. It is important that animals are habituated to this method of handling from an early age. When working with young rats, placing a hand over the rat's back will cause it to jump into the palm of the handler allowing it to be grasped. A second hand may be needed to prevent the rat from squirming from the grasp.

When changing cages with neonate mice or rats, it is often necessary to remove them while keeping the nest intact. Use two hands to scoop the nest and pups from the bottom of the cage into a new cage. Hold your fingers close together to avoid dropping the pups. Once the nest has been moved to a new cage, it is important to verify that all the pups are present. Alternatively, a plastic scoop may be used to move neonate rodents in their nests. While doing this, it is important that you place your hand over the top of the scoop to prevent neonates from wiggling or jumping out. Compared to the individual handling of the pups, scooping the entire nest is less distressing to both the pups and the dams.

Now that we have discussed the basics of rodent handling, let's delve into detailed procedures for rodent restraint. First we will outline how to restrain these animals manually. Mice and young rats can be restrained using the one handed or the two-handed technique. However, for adult rats, full body restraint using the T-rex grip or the forelimb crisscross method, are the preferred techniques.

Let's begin by learning the two-handed restraint method. First, place the animal on a surface they can grip, such as the wire bar lid. With your dominant hand, hold the tail at the base and gently tug the mouse backwards. This causes the animal to hold onto the surface and allow its body to be stretched. Next, gently pin the rodent with your non-dominant index finger and thumb positioned at the base of the skull, and grasp the loose skin on the neck to lift up the animal. Use your remaining fingers to stabilize the animal with its back against the base of your thumb. You can secure the hindquarters by pinning the tail with your ring finger against the palm of your hand.

For the one-handed restraint method, again place the animal on a surface that it can grip. Hold the tail between the third and fourth fingers of your non-dominant hand and apply gentle backward traction. With your index finger and thumb of the same hand, pin the rodent over the shoulders. Gently slide your thumb and index finger forward and grasp the loose skin at the neck and lift the animal. Use your middle finger to stabilize the animal along the back by pinning the dorsal skin against the base of the thumb.

The third restraint method we will discuss is the T-rex grip- a two-handed restraint method for rats. First, place the rat on a solid surface, like a mat, that it can grip. While holding the base of the tail with one hand, place your other hand over the rat's shoulder with your index and middle finger split on either side. This is to restrict the side-to-side head movement. Once the head is stabilized, encircle the body behind the forelegs with the middle and ring fingers and the thumb. Avoid compressing the chest so that it does not compromise the animal's breathing. Finally, stabilize the tail and hindquarters by grasping the base of the tail WITHOUT holding onto the hind feet, if you plan to administer an oral gavage; or WITH holding onto the hind feet, if the intention is to inject the animal.

Lastly, to restrain a rat using the forelimb crisscross method, place the animal on a surface it can grip. Then with your dominant hand, hold the tail at the base and apply gentle backward traction so that the animal's body elongates. Next, with your other hand, grasp the animal directly behind the shoulders, with your fingers on one side and thumb on the other side of the chest, and slide the hand forward. This motion will force the animal's forelegs to cross under its chin, creating a physical barrier that prevents the animal from moving its head down. Take care to avoid compressing the chest, which will lead to difficulty in breathing.

Now that we have reviewed the manual restraint techniques, let's learn how to restrain rodents using specialized devices.

The first device that we'll learn about is the Broome-style restraint device. It has a slot that runs along the full length of the device and a plastic nosepiece, which is inserted to hold the animal in place. Start by loosening the screw to remove the nosepiece. Then, orient the restraint tube such that the slit is facing up. Grasp the animal at the base of the tail and gently pull the animal into the restraint device, hindquarters first. Once the animal is inside, slide the plastic nosepiece back into the tube to prevent it from opening. Place the nosepiece such that the animal's nose is centered in the opening. Do not position it so tightly that the animal cannot breathe.

Another example of a restraint device is the flat-bottomed rodent restrainer, which is a half cylinder with openings that allow access from the top and the bottom of the device. It also has slots in which a rigid plastic gate can be inserted to hold the animal in place. To use this restrainer, grasp the rodent by the base of the tail with your dominant hand and place it on a smooth surface. Using your other hand, hold the flat-bottomed restraint tube so that the open end is at the animal's head at a 45° angle to the surface. Place the tube over the animal's head, and immediately tap the rump to prevent the animal from backing up. Once it is in the device, slide the plastic gate into the appropriate slot to secure the animal's position.

The third type of device that we'll discuss is tube restraints. These are Plexiglass cylinders with one closed end containing holes for air circulation, and a slit at the open end. To use a tube restraint, grasp the animal and place it on a smooth surface. Next, place the open end of the tube at the animal's head at a 45° angle. As soon as the rodent enters the tube, tap the rump to prevent it from backing up. Finally, occlude the opening by stuffing a large latex glove, which will grip the Plexiglass surface and prevent the animal from exiting the tube.

Lastly, we will discuss how to use flexible restrainers, which are disposable flexible plastic cones available in different sizes. Selection of a cone depends on the animal size. Ideally, it should be long enough to extend 2-3 inches beyond the animal's rump. Like previous methods, place the animal on a smooth surface and place restraint cone at a 45° angle over the animal's head. As soon as the animal enters the cone, grasp the open end and seal it to force the animal to the end. Secure the opening by folding the plastic to one side of the tail and applying a binder clip to the folded plastic being careful to avoid clamping the tail or skin.

After discussing the basics of handling and different restraining techniques, let's review why having an understanding of these procedures is necessary for any in vivo scientist.

The knowledge and rationale behind these basic handling procedures is at the core of maintaining animal's health. From the time the animals are born, they are handled for simple, day-to-day activities like weighing, inspection and cage changing, which ought to be performed irrespective of the scientific objective.

The restraining procedures are also useful for marking purposes. For example, in order to perform procedures like ear punching the animal need to be restrained by scruffing. On the other hand, a restraint device should be used when inserting a microchip in rats so that they can be tagged permanently.

Lastly, the manual restraining methods are used for common injection procedures like subcutaneous and intraperitoneal administration. And the knowledge of restrain devices is useful when performing intravenous administration, which demands minimal animal movement during the injection.

You've just watched JoVE's introduction to basic handling and restraint techniques for rodents. These procedures require a confident and firm, but gentle touch. Tentative approaches can result in handler bites, while aggressive handling can cause injury to the rodent. Therefore, it is important to learn these techniques thoroughly and find a balance of an assertive yet gentle grip. As always, thanks for watching!

Applications and Summary

Routine handling for cage changing and technical procedures is a cause of stress for experimental animals. Although this type of stress is not a threat to the overall wellbeing of the animal, it can cause fluctuations in physiologic parameters that can have an adverse effect on the research data. The use of skilled personnel, proper techniques, and equipment can mitigate some of the stress.

Referências

  1. Balcombe, J.P., Barnard, N.D., and Sandusky, C. 2004. Laboratory routines cause animal stress. Contemporary Topics. 43:6. 42-51
  2. Gouveia, K. and Hurst, J.L. 2013. Reducing mouse anxiety during handling: effect of experience with handling tubes.
  3. AALAS Learning Library*. Animal handling and restraint in: Working with the laboratory rat. https://www.aalaslearninglibrary.org/Pages/Courses/CourseAllPages.aspx?intLessonID=27691
  4. AALAS Learning Library*. Animal handling and restraint in: Working with the laboratory mouse. https://www.aalaslearninglibrary.org/Pages/Courses/course.aspx?intCourseID=2451&intPageID=94993

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Rodents are widely used model organisms to investigate diverse scientific questions, and it has been demonstrated that even minimal handling is stressful for these animals.

Handling for simple tasks such as cage changing may cause an increase in heart rate, blood pressure, and serum corticosterone levels, and these fluctuations can continue for several hours. The methods of restraint required for common injection and blood withdrawal procedures can also cause physiological changes, which can potentially affect the scientific data. Therefore, training for proper handling of mice and rats is required to minimize these effects on animals.

In this video, we will first review the basic techniques for handling rodents, and then we’ll discuss the rodent restraint procedures including manual techniques and methods involving usage of restraining devices.

Let’s begin by discussing the basics of rodent handling. One of the most common methods for moving either an adult mouse or rat is by lifting the animal by its tail. While doing this, it is imperative that the tail be grasped at the base near the rump. If the animal is lifted by the end of its tail, the skin can be pulled off due to the body weight and may lead to an injury resulting in tail amputation. Importantly, moving an animal from one place to another should be done quickly and steadily. Suspending the animal in air for any length time will not only cause distress, but will also cause the animal to twist or struggle, possibly causing harm to the tail. Also, the handler should not place a hand under the animal, because it may try to grasp it for security, resulting in a bite.

Another method for handling adult rodents is to use forceps. Types of forceps commonly used are long-dressing forceps or tongue forceps with rubber, plastic, or silicone tubing placed over the ends to provide a cushion. The forceps can grasp the mouse either at the scruff of the neck or at the base of the tail. The use of forceps minimizes cross contamination from animal to animal, and it is quicker and less expensive than changing gloves between each animal cage. Beginners will need to be trained on how tightly to grasp the mice with forceps, especially at the scruff as it could interfere with breathing. When using the forceps on the tail, care must be taken to place the forceps near the base of the tail to avoid injury. Remember to store them facedown in 70% ethanol between handling of different groups of animals.

Also, one can use tubes made of a non-porous material to transfer animals. These tubes can be added to a cage as a place for the animal to shelter or seek safe refuge. Most mice or rats would willingly enter the tubes when their cage is opened, or they can be easily guided into the tube. When the animal is inside, cover the open ends with your palm and fingers. Next, to encourage the animal to leave, gently tip the tube upward in the new cage. Animals are easily conditioned to this method of cage changing, making this a quick and easy process for moving animals from one place to another.

Some institutions prefer that animals-especially rats-be lifted by their body, even while routine handling. Adult rats are gently grasped around the thorax, lifted, and quickly placed into another cage. It is important that animals are habituated to this method of handling from an early age. When working with young rats, placing a hand over the rat’s back will cause it to jump into the palm of the handler allowing it to be grasped. A second hand may be needed to prevent the rat from squirming from the grasp.

When changing cages with neonate mice or rats, it is often necessary to remove them while keeping the nest intact. Use two hands to scoop the nest and pups from the bottom of the cage into a new cage. Hold your fingers close together to avoid dropping the pups. Once the nest has been moved to a new cage, it is important to verify that all the pups are present. Alternatively, a plastic scoop may be used to move neonate rodents in their nests. While doing this, it is important that you place your hand over the top of the scoop to prevent neonates from wiggling or jumping out. Compared to the individual handling of the pups, scooping the entire nest is less distressing to both the pups and the dams.

Now that we have discussed the basics of rodent handling, let’s delve into detailed procedures for rodent restraint. First we will outline how to restrain these animals manually. Mice and young rats can be restrained using the one handed or the two-handed technique. However, for adult rats, full body restraint using the T-rex grip or the forelimb crisscross method, are the preferred techniques.

Let’s begin by learning the two-handed restraint method. First, place the animal on a surface they can grip, such as the wire bar lid. With your dominant hand, hold the tail at the base and gently tug the mouse backwards. This causes the animal to hold onto the surface and allow its body to be stretched. Next, gently pin the rodent with your non-dominant index finger and thumb positioned at the base of the skull, and grasp the loose skin on the neck to lift up the animal. Use your remaining fingers to stabilize the animal with its back against the base of your thumb. You can secure the hindquarters by pinning the tail with your ring finger against the palm of your hand.

For the one-handed restraint method, again place the animal on a surface that it can grip. Hold the tail between the third and fourth fingers of your non-dominant hand and apply gentle backward traction. With your index finger and thumb of the same hand, pin the rodent over the shoulders. Gently slide your thumb and index finger forward and grasp the loose skin at the neck and lift the animal. Use your middle finger to stabilize the animal along the back by pinning the dorsal skin against the base of the thumb.

The third restraint method we will discuss is the T-rex grip- a two-handed restraint method for rats. First, place the rat on a solid surface, like a mat, that it can grip. While holding the base of the tail with one hand, place your other hand over the rat’s shoulder with your index and middle finger split on either side. This is to restrict the side-to-side head movement. Once the head is stabilized, encircle the body behind the forelegs with the middle and ring fingers and the thumb. Avoid compressing the chest so that it does not compromise the animal’s breathing. Finally, stabilize the tail and hindquarters by grasping the base of the tail WITHOUT holding onto the hind feet, if you plan to administer an oral gavage; or WITH holding onto the hind feet, if the intention is to inject the animal.

Lastly, to restrain a rat using the forelimb crisscross method, place the animal on a surface it can grip. Then with your dominant hand, hold the tail at the base and apply gentle backward traction so that the animal’s body elongates. Next, with your other hand, grasp the animal directly behind the shoulders, with your fingers on one side and thumb on the other side of the chest, and slide the hand forward. This motion will force the animal’s forelegs to cross under its chin, creating a physical barrier that prevents the animal from moving its head down. Take care to avoid compressing the chest, which will lead to difficulty in breathing.

Now that we have reviewed the manual restraint techniques, let’s learn how to restrain rodents using specialized devices.

The first device that we’ll learn about is the Broome-style restraint device. It has a slot that runs along the full length of the device and a plastic nosepiece, which is inserted to hold the animal in place. Start by loosening the screw to remove the nosepiece. Then, orient the restraint tube such that the slit is facing up. Grasp the animal at the base of the tail and gently pull the animal into the restraint device, hindquarters first. Once the animal is inside, slide the plastic nosepiece back into the tube to prevent it from opening. Place the nosepiece such that the animal’s nose is centered in the opening. Do not position it so tightly that the animal cannot breathe.

Another example of a restraint device is the flat-bottomed rodent restrainer, which is a half cylinder with openings that allow access from the top and the bottom of the device. It also has slots in which a rigid plastic gate can be inserted to hold the animal in place. To use this restrainer, grasp the rodent by the base of the tail with your dominant hand and place it on a smooth surface. Using your other hand, hold the flat-bottomed restraint tube so that the open end is at the animal’s head at a 45° angle to the surface. Place the tube over the animal’s head, and immediately tap the rump to prevent the animal from backing up. Once it is in the device, slide the plastic gate into the appropriate slot to secure the animal’s position.

The third type of device that we’ll discuss is tube restraints. These are Plexiglass cylinders with one closed end containing holes for air circulation, and a slit at the open end. To use a tube restraint, grasp the animal and place it on a smooth surface. Next, place the open end of the tube at the animal’s head at a 45° angle. As soon as the rodent enters the tube, tap the rump to prevent it from backing up. Finally, occlude the opening by stuffing a large latex glove, which will grip the Plexiglass surface and prevent the animal from exiting the tube.

Lastly, we will discuss how to use flexible restrainers, which are disposable flexible plastic cones available in different sizes. Selection of a cone depends on the animal size. Ideally, it should be long enough to extend 2-3 inches beyond the animal’s rump. Like previous methods, place the animal on a smooth surface and place restraint cone at a 45° angle over the animal’s head. As soon as the animal enters the cone, grasp the open end and seal it to force the animal to the end. Secure the opening by folding the plastic to one side of the tail and applying a binder clip to the folded plastic being careful to avoid clamping the tail or skin.

After discussing the basics of handling and different restraining techniques, let’s review why having an understanding of these procedures is necessary for any in vivo scientist.

The knowledge and rationale behind these basic handling procedures is at the core of maintaining animal’s health. From the time the animals are born, they are handled for simple, day-to-day activities like weighing, inspection and cage changing, which ought to be performed irrespective of the scientific objective.

The restraining procedures are also useful for marking purposes. For example, in order to perform procedures like ear punching the animal need to be restrained by scruffing. On the other hand, a restraint device should be used when inserting a microchip in rats so that they can be tagged permanently.

Lastly, the manual restraining methods are used for common injection procedures like subcutaneous and intraperitoneal administration. And the knowledge of restrain devices is useful when performing intravenous administration, which demands minimal animal movement during the injection.

You’ve just watched JoVE’s introduction to basic handling and restraint techniques for rodents. These procedures require a confident and firm, but gentle touch. Tentative approaches can result in handler bites, while aggressive handling can cause injury to the rodent. Therefore, it is important to learn these techniques thoroughly and find a balance of an assertive yet gentle grip. As always, thanks for watching!

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Rodent HandlingRestraint TechniquesStress In RodentsPhysiological ChangesTraining For Handling RodentsManual Restraint TechniquesRestraining DevicesBasics Of Rodent HandlingLifting Rodents By The TailInjury PreventionMoving Rodents Quickly And Steadily