Pain is a multi-faceted, complex disease that affects all humans. Unfortunately, progress in pain management has been met with limited success. However, considerations of the multiple components of pain have suggested that targeting non-conventional sites could strongly impact the pain management field. The endocannabinoid (eCB) system is one of several lipid signaling systems in the brain and in the body. Verified components of this system include two G-protein coupled receptors, their signaling pathways, two predominant endogenous ligands [anandamide (AEA) and 2-arachidonyl glycerol (2-AG)], and their synthetic and metabolic pathways. The system plays an important modulatory role in many crucial CNS processes (e.g., brain reward, appetite regulation, cognition). Consequently, it is not surprising that this system has been implicated in the pathophysiology of a variety of health problems related to these processes, including pain management. This application is largely based on the idea that a clinically significant component of pain is behavioral depression (i.e., pain-depressed behaviors). In humans, this is indicated by absences from work or school, lack of interest in customary activities, overall decreases in motor activity, and is most often associated with clinical depression. In animals clinical approximation of pain is through decreases in locomotion or grooming and interest in feeding or social interaction. Given these, a promising new strategy for comprehensive treatment of pain is an adjunct focus on pain-depressed behaviors and depressed mood. With this application we plan to evaluate eCB modulation of pain-depressed behaviors using intracranial self-stimulation (ICSS) and drug discrimination (DD) in mice. ICSS has been widely used to study modulation of motivated behavior (i.e. reward) and affect by drugs whereas DD is primarily used to model the subjective/intoxicating effects of drugs. We propose utilizing these well-established operant procedures to evaluate the eCB's effects on pain-induced behavioral depression, affect and intoxication. To complement these behavioral measures, we will determine mechanistic characteristics of affective cannabinoid analgesia versus reward in selected brain regions such as the nucleus accumbens, a brain area implicated in reward and affective pain, through the use of well- established neurochemical analyses such as mass spectrometry and [35S]GTPgS G-protein binding studies. Given the clear need to explore novel therapeutic targets, improve upon existing preclinical pain assays, and incorporate the affective component of pain, we propose that studying the eCB system's modulation of pain-depressed behavior will meet these needs. We feel these studies have significant public health implications and offer a large degree of innovation while relying upon well-established behavioral and neurochemical measures. In summary, considering the paramount public health concern regarding effective pain management this application promises to establish whether the eCB system is a viable and attractive therapeutic means to effectively reduce the great societal burdens associated with pain management.

Public Health Relevance

Pain is a public health concern of utmost importance and is typicaly accompanied by behavioral depression that results in absences from work/school, lack of interest in customary activities, overall decreases in activity, and is most often associated with depresion. Given the clear need to explore novel therapeutic targets, improve upon existing preclinical pain assays, and incorporate the affective component of pain, we propose a thorough evaluation of the endogenous cannabinoid system's ability to ameliorate pain-depressed behavior, while taking into account critical factors relevant to this system such as modulation of reward and intoxication.

National Institute of Health (NIH)
National Institute on Drug Abuse (NIDA)
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Biobehavioral Regulation, Learning and Ethology Study Section (BRLE)
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Thomas, David A
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Virginia Commonwealth University
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Negus, S Stevens (2018) Addressing the Opioid Crisis: The Importance of Choosing Translational Endpoints in Analgesic Drug Discovery. Trends Pharmacol Sci 39:327-330
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