The search for the neurobiological processes that underlie chemical dependence has entered the fourth decade of heightened investigation. The proliferation of neurotransmitter receptor subtypes has initiated a renaissance in potential new, more selective therapies for a number of neurological disorders. Hopefully, the definition of the subclasses of neurotransmitter receptors underlying cocaine self-administration will lead to new pharmacotherapeutic adjuncts for the treatment of these debilitating disorders. The overall goal of the research outlined in this competitive renewal application is to investigate the role of cholinergic neurons in intravenous cocaine self-administration. Recently completed acetylcholine (ACh) turnover rate studies implicate cholinergic innervations of several brain regions in cocaine self-administration. Cholinergic neurotoxin induced lesions that effect three of these regions [nucleus accumbens (NAcc), ventral pallidum (VP) and medial septum- (MS) vertical limb of the diagonal band (vlDA)] resulted in a shift to the left in the dose-intake relationship for self-administered cocaine. Experiments proposed in this next funding period will concentrate on the characterization of the role of cholinergic neurons in the NAcc, VP, vIDA and MS in cocaine self-administration using intracranial administration of receptor sub-type selective agonists, a selective cholinergic neurotoxin, in vivo microdialysis, targeted gene expression and immunohistochemistry. The overall research strategy will be first to administer muscarinic and nicotinic receptor agonists directly into the NAcc and assess effects upon the threshold for cocaine self-administration and extracellular fluid levels of dopamine, glutamate and gamma-aminobutyric acid. Agonists selective for the M4 muscarinic and alpha7 nicotinic receptors wilt be administered into the NAcc of cocaine self-administering rats to assess effects upon the threshold for cocaine self-administration and extracellular fluid levels of dopamine, glutamate and gamma-aminobutyric acid .This will be followed by similar experiments in the ventral pallidum. A transgenic mouse strain developed in Japan that utilizes immunotoxin mediated cell targeting to selectively remove cholinergic cells will be used to determine if NAcc cholinergic neuronal systems are also involved in mouse cocaine self-administration. This will be followed by experiments using a selective cholinergic neurotoxin, 192 IgG-saporin, to selectively remove cholinergic neurons in the vlDB and the MS and assess effects upon thresholds for intravenous cocaine self-administration. Targeted gene expression with real time reverse transcriptase polymerase chain reaction followed by Western blot analysis will then be used to identify the up or down regulation of cholinergic receptor subtypes potentially involved. This approach should result in the characterization of the specific cholinergic neuronal systems and receptors responsible for the shift to the left in the dose intake relationship and further define the importance of cholinergic cell systems in drug self-administration.
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