The intravenous self-administration (IVSA) paradigm is considered to be the gold standard in examining the reinforcing properties of drugs of abuse in rodents. This manuscript outlines the experimental procedures and surgical techniques necessary to obtain reliable IVSA data. In particular, meticulous catheter implantation and maintenance are highlighted.
Animal models have been developed to study the reinforcing effects of drugs, including the intravenous self-administration (IVSA) paradigm. The advantages of using an IVSA paradigm to study the reinforcing properties of drugs of abuse such as cocaine include the fact that the drug is self-administered instead of experimenter-administered, the schedule of reinforcement can be altered, and accurate measurement of the quantities of drug consumed as well as the timing and pattern of IV injections can be obtained. Furthermore, the intravenous route of administration avoids potential confounds related to first pass metabolism or taste, and produces rapid increases in blood and brain drug levels. As outlined in this video, intravenous self-administration can be obtained without prior food restriction or prior drug training following careful catheter placement during surgery and meticulous daily catheter flushing and maintenance. Experimental procedures outlined in this paper include a description of animal housing and acclimation methods, operant training using sweetened milk solutions, and catheter implantation surgery.
1. Animal Housing and Acclimatization Procedures
2. Operant Training
3. Preparation of Equipment to be Used during Surgery
Required equipment – 20, 23 and 26 gauge needles, grinder, 1 cc syringes, tygon tubing, soldering iron, heparin, antibiotics and analgesic.
4. Catheter Implantation Surgery
Required equipment and reagents: Isoflurane, sterile saline, alcohol (70%), 1 and 3 cc syringes filled with sterile saline, 1-cc adapted syringes, antibiotic and analgesic solutions prepared in section 3 above, mouse catheters (CamCaths, Cambridgeshire, UK), catheter covers (crystal caps from HRS Scientific, Montreal, Quebec), eye lubricant, 4 cm plastic bar to elevate vein (this can be constructed from a plastic Q-tip), polysporin, sterile swabs and gauze, curved and straight forceps, artery clamps, fine scissors.
5. Behavioural testing – Intravenous Self-Administration
Figure 1. The pattern of responding for Intravenous drug self-administration will vary by drug, dose range and mouse strain employed. The figure presented shows cocaine self-administration data following successful catherization surgeries using the procedure described in the video. The figure shows the mean (±SEM) cocaine infusions earned and mean (±SEM) cocaine consumption (mg/kg body weight) across a range of 4 cocaine doses presented in a random order on a FR1 schedule of reinforcement. Abscissa: dose of self-administered drug per infusion. Left Ordinate: total number of infusions earned during the 2-hr operant session. Right Ordinate: total cocaine intake in mg/kg during the 2-hr testing session. All 13 catheters remained patent for the duration of the study (4 weeks). A one-way ANOVA conducted on dose revealed that mice were administering cocaine in a dose-dependent fashion [F (1,12) = 42.8 , p<0.05]. There is an increase in cocaine consumption over the dose-response curve [F (3,36) = 29.6, p<0.05] despite a decrease in lever pressing at the higher doses. Each data point represents the average of 3 testing sessions at each cocaine dose (±SEM) collected in CD-1 mice (n=13/ dose, males and females combined). Comparisons of active (drug-reinforced) vs inactive lever responding across the dose response curve were made using two-way ANOVA to ensure that mice were discriminating between the two levers. For the CD1 mice, the analysis revealed a preference for the active lever [F (1,12) = 10.255 , p<0.05] over the entire dose-response curve (data not shown here).
Animal models of drug abuse are particularly useful in understanding the genetic basis of drug-related behaviours. For instance, mice with different genetic profiles show heritable differences in their sensitivity to cocaine 6-8 and help identify potential gene candidates mediating the phenotypic variability observed 9. The intravenous catheterization procedures described in this paper have been used with considerable success to examine drug IVSA in various strains of mice as well as mice of different genetic backgrounds 10.
The procedures shown in this video highlight important factors to focus on during and following the catherization surgery in order to obtain reliable intravenous self-administration data. First, the placement of the catheter tubing within the right atrium is vital, in order to prevent catheter failure from blot clots. During surgery it is important to make sure that the catheter end is unimpeded, and not occluded by either the heart or vein tissue. Second, daily catheter flushing is required both before and after operant sessions in order to prevent blockages. Finally, the catheter cannula must be covered constantly with both the cannula caps and crystal covers when the animals are in their home cages, to prevent the entry of debris. Minor blockage of the catheter cannula may be dislodged using a fine 26 gauge needle, however daily flushing with the heparinized antibiotic solution is required, particularly on days when the animals are not tested for IVSA.
To perform animal survival surgery, a good knowledge of aseptic techniques, analgesia and anaesthesia is necessary. While this video does not replace proper surgical training, it may be used as a guide for researchers wishing to acquire the techniques necessary for this paradigm.
The authors have nothing to disclose.
Experiments on animals were performed in accordance with the guidelines and regulations set forth by the Canadian Council of Animal Care and the McGill University Animal Care Committee. This research was supported by funds awarded to KG from the Canadian Institutes of Health Research (CIHR). No conflicts of interest declared.
Name of the reagent | Company | Catalogue number | Comments (optional) |
Ticarcillin Disodium Salt | Sigma-Aldrich | T5639-1G | 1 gram bottle |
Tears Naturale P.M (Eye lubricant) | Alcon | N/A | 3.5 gram tube This eye lubricant can be found in most pharmacies. Any ophthalmic eye lubricant can be used. |
Cocaine | Medisca Pharmaceutique | 0723-06 | 1 gram bottle |
Ketamine | Medisca Pharmaceutique | 1754-04 | 25 gram bottle |
Midazolam | Medisca Pharmaceutique | 2519-06 | 1 gram bottle |
Heparin sodium salt | Sigma-Aldrich | H4784-250MG | 250 gram bottle |
Ketoprofen | Sigma-Aldrich | K1751-1G | 1 gram bottle |
Amikicin Sulphate salt | Sigma-Aldrich | A2324-5G | 5 gram bottle |
Sucrose ACS Reagent | Sigma-Aldrich | S5016-500G | 500 gram bottle |
Standard mouse catheters with soft mesh | CamCaths | MIVSA/20/26/BC-1S | Tubing specifications: 26SWG;0.451;0.254 |
Crystal cap applicator | HRS Scientific | 313CAC | This is the white catheter cap. |
Tygon Micro Bore Tubing | Thomas Scientific | 9561S41 | Tubing specifications (bore x o.d. x wall thickness in inches): .01 x .03 x .01 |