BRAIN CANNABINOID RECEPTOR SIGNALING AND PHARMACOLOGY

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DESCRIPTION: (Applicant's Abstract) Marijuana (Cannabis sativa) has had long history of use for both medicinal and recreational purposes. Since the cloning of a central nervous system cannabinoid receptor and its localization in specific brain areas; questions concerning the role of this receptor in normal brain function have arisen. Since little is known about the role of the cannabinoid receptor in normal brain function, our long term goals are to understand the basic cell biology of this receptor with the idea that this may help us understand the role of the cannabinoid receptor in learning and memory, sensory perception including pain, appetite and nausea. The first aim of our proposed research is to investigate the function of the rat brain cannabinoid receptor at the cellular electrophysiological level using a novel neuronal expression system. Preliminary experiments demonstrate that dissociated adult rat sympathetic ganglion neurons microinjected with cRNA in vitro transcribed from rat brain cannabinoid receptor cDNA express a functional cannabinoid receptor within 18 hours. Expression is both robust and reliable. The heterologously expressed rat brain cannabinoid receptor inhibits voltage-dependent calcium channel activity. This is the first demonstration of expression and functional coupling of the cloned rat brain cannabinoid receptor in an adult neuron. The ability to express an identified cannabinoid receptor and receptor mutants in normal adult mammalian neurons will facilitate identification of ion channel targets, cellular pathways and structure/function studies of the cannabinoid receptor. The second aim of our proposed research is to test the hypothesis that the cannabinoid receptor is spontaneously active and can couple to G proteins in the absence of endogenous ligands. The role of spontaneous cannabinoid receptor activity in normal brain function or drug abuse behavior is completely unknown. Our experiments will address the functional consequences of spontaneous activity of both cloned and native cannabinoid receptors. The third aim of our research is to test the functional coupling and spontaneous activity of the cannabinoid receptors in their native environment. Native cannabinoid receptors in both central and peripheral nervous system neurons will be studied using cellular electrophysiological techniques. If the cannabinoid receptor is spontaneously active in its native environment, this activity will change both normal physiology and the outcome of antagonist signaling. A spontaneously active cannabinoid receptor will have important functional consequences and negative antagonists could have potential therapeutic benefits.