Cocaine positive reinforcement and its withdrawal: consequences in the muscarinic cholinergic system

Abstract

Positive and negative drug reinforcements are consequences that will strengthen the frequency of an organism's future behavior, preceded by the presence or removal of an antecedent stimulus, respectively. Both effects are associated with addiction caused by several drugs of abuse, such as cocaine, changing dopamine levels in the striatum. However, little is known about how cocaine self-administration/cocaine binge and its withdrawal change the muscarinic cholinergic system, neither their correlation with the dopaminergic system, the aim of this project. The focus of this study is to understand how the neuroadaptative changes caused by cocaine positive reinforcement effects and its withdrawal modulate acetylcholine and the muscarinic cholinergic system. In in vitro assays, hippocampal and striatal slices will be used to study the effect of an intermittent dopamine exposure (six exposures), at different concentrations, on the muscarinic cholinergic system and dopaminergic system, immediately after and one hour after the last exposure. This assay will simulate a common mechanism among several drugs of abuse: the intermittent dopamine increase in the mesocorticolimbic system and its decrease during withdrawal. In vivo assays will mimic or show both cocaine positive reinforcement effects and its withdrawal: cocaine self-administration and escalating dose 'binge' cocaine administration paradigm (craving/bingeing) and elevated plus maze (during withdrawal). After the behavioral studies, caudate-putamen, amygdala and hippocampus will be removed for analysis. Both assays accomplishes the same techniques: immunoblotting and real time PCR for dopaminergic system (D1 and D2 subtype receptors, dopamine-related enzymes for in vivo assays: AADC, VMAT2 and MAO-A/B), acetylcholine-related enzymes (ChAT, VAChT and AChE) and the muscarinic cholinergic system (M1, M2, M3, M4 and M5 subtype receptors). Proteomic analysis by mass spectrometry, a powerful technology, will also be applied as a confirmatory and complementary parameter to elucidate the function of the muscarinic cholinergic system against cocaine reinforcement effects. (AU)