Rodents are an appropriate model to investigate the molecular substrates of behavior and complex psychiatric disorders. Brain microinjection in awake rodents can be used to elucidate disease substrates. An efficient and customizable brain microinjection method as well as the execution of an operant paradigm that quantifies motivation is presented.
Brain microinjection can aid elucidation of the molecular substrates of complex behaviors, such as motivation. For this purpose rodents can serve as appropriate models, partly because the response to behaviorally relevant stimuli and the circuitry parsing stimulus-action outcomes is astonishingly similar between humans and rodents. In studying molecular substrates of complex behaviors, the microinjection of reagents that modify, augment, or silence specific systems is an invaluable technique. However, it is crucial that the microinjection site is precisely targeted in order to aid interpretation of the results. We present a method for the manufacture of surgical implements and microinjection needles that enables accurate microinjection and unlimited customizability with minimal cost. Importantly, this technique can be successfully completed in awake rodents if conducted in conjunction with other JoVE articles that covered requisite surgical procedures. Additionally, there are many behavioral paradigms that are well suited for measuring motivation. The progressive ratio is a commonly used method that quantifies the efficacy of a reinforcer to maintain responding despite an (often exponentially) increasing work requirement. This assay is sensitive to reinforcer magnitude and pharmacological manipulations, which allows reinforcing efficacy and/ or motivation to be determined. We also present a straightforward approach to program operant software to accommodate a progressive ratio reinforcement schedule.
Rodents and humans respond in remarkably similar ways to behaviorally relevant stimuli1-3. This suggests that rodents are appropriate subjects for elucidating the molecular substrates of behavior and complex psychiatric conditions4. Understanding the molecular substrates of complex behavioral processes, such as motivation, frequently requires brain microinjection. Both the brain microinjection technique and a primary motivation assay will be presented here. Rats will be used as subjects, but these procedures can readily be adapted to well-handled mice. Included herein are procedures for the manufacture of the required cannulae, obturators (dummy cannulae or stylets), and microinjectors. The method presented is significantly more flexible and more cost-efficient than prefabricated implements. This flexibility will prove valuable when optimizing conditions. Importantly, because the microinjection procedure can be used to test a myriad of hypotheses; the techniques presented here should be broadly applicable. For example, receptor ligands can be microinjected to understand neurochemistry3,5,6; cell-permeable peptides and small-molecules can be microinjected to understand intracellular signaling pathways7-10; toxins, ion channel blockers, or antagonist cocktails can be microinjected to understand circuitry1,11,12.
While the generic protocol presented here can be readily adapted by the user for their particular needs, the procedure is particularly well suited for behavioral assays since microinjection occurs in awake rodents that are only under mild hand restraint. No anesthesia or special restraints are required. This is possible because the brain itself lacks pain sensation. However, if anesthesia is not used, microinjection must occur through cannulae that were previously stereotaxically implanted. This is because nociceptors are present on the scalp, meninges,13 which are the membranes surrounding the brain, and the periosteum,14 which is the membrane covering the skull. It should be noted that microinjection under anesthesia is sometimes desirable. One example is when the virus is being injected, and one may wish to inject virus directly through either stainless steal needles15 or glass pipettes because this can reduce tissue damage and improve transduction efficiency.16,17 The microinjectors described below can be modified for this purpose and suggestions on how to do this can be found in the Discussion. Because other JoVE articles have demonstrated stereotaxic brain cannula implantation,18-20 these procedures will not be covered here.
We present these microinjection procedures together with an assay that quantifies motivation. Several rodent models of motivated behavior are currently in use, such as the runway box and barrier scaling. Here, we describe how to use an operant progressive ratio schedule of reinforcement to quantify motivation where operant responding is being maintained by a reinforcer. Responding on the progressive ratio is responsive to reinforcer magnitude.21,22 Accordingly, this assay is routinely used as a proxy for motivation and/or reinforcing efficacy. 21,23-30 Because several excellent reviews have covered this topic in detail,21,24 we will focus mainly on practical concerns.
这里介绍的方法是制造显微注射插管和microinjectors将阐明的动机的行为的分子底物辅助的有效手段。此方法提供了几个优点。首先,通过制造自己的植入物和microinjectors,新颖的实验参数可以迅速地优化;也就是,一个不需要等待定制组件到达。第二,由于小直径的套管,多个套管可以同时注入。这缩短了所需的手术时间,从而可提高生存性,而且还允许每只动物的多个植入物。第三,用于控制操作室的软件容易地适应渐进比时间表自一个固定的比率范例可以迅速地通过简单地施加含有所需强化程序的事件过渡参数列表转换为渐进比范例。
成为广泛有用的,但是一般的显微注射过程被提出,应该是广泛地适用于现有的几乎任何试剂的显微注射。因此,我们预期,这种技术将继续以类似的高实用程序在将来有轻微变形。通过只改变几个变量,这种方法可以应用到试剂的宽数。这将最常被操纵参数包括该微量从套管伸出的长度,注射的体积,以及注射速度。例如,人们可能想要喷射器,以进一步从套管末端突出,以避免神经胶质疤痕,通常形成围绕慢性植入物。此外,人们可能希望注入量较大。为纹状体病毒显微注射,1微升的体积中通常使用这种卷典型地注入在一段较长的时间(通常10 – 10分钟加3 – 10分钟额外扩散时间)相比,使用d表示药物试剂(通常为0.3 – 0.5微升了2 – 3分钟加1 – 3分钟附加的扩散时间)。用户应该查阅文献和/或凭经验确定最适合自己需要的参数。无论如何,这个过程的成功是关键取决于4个变量:1)套管的长度,2)微量长度,3)微量喷雾图案的注射前的质量,以及4)系统的完整性。因为显微注射位置取决于该微量从套管伸出的深度,当务之急是两插管(步骤1.2.8)和微量长度(后弯曲,步骤2.2.1)都精确所有受试者之间已知的和均匀的。这可以容易地通过容易地拒绝任何实施不是在最终重新测量所需的长度来控制。此外,注射位置只能如果它立即发生的引导套管下方预测。因此,任何微量能源部在测试不是喷长,细流(步骤2.4.6),应予以拒绝。甲质量注射还涉及该系统的完整性在注射前。如果分配所有的水从注入后(装填试剂之前)多点是在实验室观察擦拭,然后泄漏需要纠正(请注意:步骤2.4.8)。此外,如果气泡(步骤2.4.9),其从水在PE20管分离所述药物是不是一个,单泡(填充试剂的微量之后),则喷射器部分堵塞。这种堵塞既可以防止或转移注射。这也可以很容易地补救(注上的步骤2.4.8)。
如果一个希望microinject而动物是在立体框架有三个备选方案。首先,人们可以增加微量颈圈,使得它可以通过立体定向操纵器牢固地保持并延伸得足够远以允许连接到PE20管道的长度。第二,上Ë可以暂时植入插管,并使用标准的微量这里介绍。第三,人们可以使用拉伸和抛光玻璃吸管16,17
这里提出的步骤的一个显著限制是,最好是在良好的处理大鼠中所熟悉的方法进行。因为同样的调查处理的大鼠,每天超过2个月的用于在结果部分中描述的数据大鼠不需要特别的处理程序。这包括每日观察手术植入物和操纵至少2周。然而,大鼠可迅速通过多种技术,用于前预脉冲抑制试验,这可受应力习惯于。这些特殊习惯化技术已被很好地先前详述。43除了这些程序,可取的做法是可以的大鼠习惯于其中缩短microinjectors使用杜显微注射过程环'假'注射。在这些假注射剂,可以认为微量不会突出到组织,以限制组织损伤是至关重要的。换句话说,该微量应不超过14毫米弯曲。因此,需要对这种技术的最佳实施彻底的习惯可能被视为一种限制。
虽然若干行为范例存在测量动机,所述进行比通常用于量化该受试者愿意施加以获得加强件的工作。渐进比范例产生被称为断点的量度,其通常被定义为在最后一个完整比杠杆压力机的最大数目; 即 ,最大响应生成一个加强件21的渐进比是敏感的加强件大小。例如,更高的可卡因(或蔗糖)的剂量产生较高的断点和低级可卡因(或蔗糖)的剂量得到降低breakpoint。21,22因此,断点为动机和/或增强功效的常规使用的代理。21,23-26由于断点的意图是确定当动物停止响应,逐步比范例的一个重要参数是会议的长度。有限会话长度可以穿上断点值的假帽,这可以通过预治疗,异常降低的自我管理,或增加后加固暂停的速度加剧。这变乱可以通过任何数目的方法来克服。 例如 ,会话终止时动物已经版主由平均内输注间隔的某一倍数响应44这种方法的一个更普遍应用于变型是终止会话一次响应具有被扣缴一些保持跨学科常凭经验确定的值。我们已经提供了应用这种方法的步骤4.4.9.11的方法。
The authors have nothing to disclose.
MSB is supported by the Alcohol Beverage Medical Research Foundation, a Center for Translational Research Award (UL1 TR000058), the National Institutes for Alcohol Abuse and Alcoholism (P50 AA022537), and startup funds provided by the Virginia Higher Education Equipment Trust Fund and the VCU School of Medicine.
Cannula Tubing | Amazon Supply/ Small Parts | HTXX-26T-60 | 26 gauge, Hypotube S/S 316-TW 26GA |
Obturator | Amazon Supply/ Small Parts | GWXX-0080-30-05 | 33 gauge, Wire S/S 316LVM 0.008 IN |
Microinjector Wire | MicroGroup | 33RW 304 | 33 gauge |
Super Glue | Loctite | 3924AC | Liquid, Non-gel, can be autoclaved |
Microinjector Plastic Tubing | Becton Dickson | 427406 | PE20 |
Medium Weight Hemostats | World Precision Instruments | 501241-G | |
Ruler | Fisher | 09-016 | 150 mm |
#7 Forceps | Stoelting | 52100-77 | Dumont, Dumostar |
Rotary Tool | Dremmel | 285 | Two-speeds |
Cut-off Disc | McMaster Carr | 3602 | 15/16" x 0.025" |
Microinjection Pump | Harvard Apparatus | PhD 2000 | |
1 ul Glass Syringe | Hamilton | 7001KH | Needle Style: 25s/2.75"/3 |
Cotton Tipped Applicator | Fisher | 23-400-101 | |
Lab Wipes | Kimwipes | 34133 | |
Operant Software | Coulbourn | Graphic State | |
Operant Chambers | Coulborun | Habitest |