このプロトコルでは、マウスでの強化子として感覚刺激を用いたオペラント学習の方法を説明します。それは事前のトレーニングや食事制限を必要とせず、そしてそれは、食品などの薬理学的または自然的強化子を使用せずに、やる気のある行動の研究が可能になります。
Operant methods are powerful behavioral tools for the study of motivated behavior. These ‘self-administration’ methods have been used extensively in drug addiction research due to their high construct validity. Operant studies provide researchers a tool for preclinical investigation of several aspects of the addiction process. For example, mechanisms of acute reinforcement (both drug and non-drug) can be tested using pharmacological or genetic tools to determine the ability of a molecular target to influence self-administration behavior1-6. Additionally, drug or food seeking behaviors can be studied in the absence of the primary reinforcer, and the ability of pharmacological compounds to disrupt this process is a preclinical model for discovery of molecular targets and compounds that may be useful for the treatment of addiction3,7-9. One problem with performing intravenous drug self-administration studies in the mouse is the technical difficulty of maintaining catheter patency. Attrition rates in these experiments are high and can reach 40% or higher10-15. Another general problem with drug self-administration is discerning which pharmacologically-induced effects of the reinforcer produce specific behaviors. For example, measurement of the reinforcing and neurological effects of psychostimulants can be confounded by their psychomotor effects. Operant methods using food reinforcement can avoid these pitfalls, although their utility in studying drug addiction is limited by the fact that some manipulations that alter drug self-administration have a minimal impact on food self-administration. For example, mesolimbic dopamine lesion or knockout of the D1 dopamine receptor reduce cocaine self-administration without having a significant impact on food self-administration 12,16.
Sensory stimuli have been described for their ability to support operant responding as primary reinforcers (i.e. not conditioned reinforcers)17-22. Auditory and visual stimuli are self-administered by several species18,21,23, although surprisingly little is known about the neural mechanisms underlying this reinforcement. The operant sensation seeking (OSS) model is a robust model for obtaining sensory self-administration in the mouse, allowing the study of neural mechanisms important in sensory reinforcement24. An additional advantage of OSS is the ability to screen mutant mice for differences in operant behavior that may be relevant to addiction. We have reported that dopamine D1 receptor knockout mice, previously shown to be deficient in psychostimulant self-administration, also fail to acquire OSS24. This is a unique finding in that these mice are capable of learning an operant task when food is used as a reinforcer. While operant studies using food reinforcement can be useful in the study of general motivated behavior and the mechanisms underlying food reinforcement, as mentioned above, these studies are limited in their application to studying molecular mechanisms of drug addiction. Thus, there may be similar neural substrates mediating sensory and psychostimulant reinforcement that are distinct from food reinforcement, which would make OSS a particularly attractive model for the study of drug addiction processes. The degree of overlap between other molecular targets of OSS and drug reinforcers is unclear, but is a topic that we are currently pursuing. While some aspects of addiction such as resistance to extinction may be observed with OSS, we have found that escalation 25 is not observed in this model24. Interestingly, escalation of intake and some other aspects of addiction are observed with self-administration of sucrose26. Thus, when non-drug operant procedures are desired to study addiction-related processes, food or sensory reinforcers can be chosen to best fit the particular question being asked.
In conclusion, both food self-administration and OSS in the mouse have the advantage of not requiring an intravenous catheter, which allows a higher throughput means to study the effects of pharmacological or genetic manipulation of neural targets involved in motivation. While operant testing using food as a reinforcer is particularly useful in the study of the regulation of food intake, OSS is particularly apt for studying reinforcement mechanisms of sensory stimuli and may have broad applicability to novelty seeking and addiction.
求めているオペラント感覚は、マウスが好きな動物である静脈内薬物自己投与する代わりに使用すると便利です。手術もカテーテルの維持管理のいずれも必要になる、ということは、これらのマウスにおいて重要な技術的なハードルであるため、有利である。それは、食品など他の自然な強化子とは別の補強の側面を測定することがありますので、OSSにも魅力的です。
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The authors have nothing to disclose.
このプロジェクトは、NIHの助成金DA19112(DGW)とDA026994(CMO)によってサポートされていました。イラストは、キャサリン心苦しくによって提供されていました。実験は、ヴァンダービルトマウス神経行動学研究室で行った。
Material Name | Type | Company | Catalogue Number | Comment |
---|---|---|---|---|
Drug self-administration test package for mouse: extra-wide chamber and retractable levers | Med Associates, Inc | MED-307W-CT-D1 | Levers are ultra-sensitive (require ~2 grams force) and are mounted 2.2 cm above the floor. Yellow stimulus lamps are mounted 2 cm above each lever. | |
Interface and software package | Med Associates, Inc | MED-SYST-16 | This is the package for up to 16 chambers. |