Mechanisms underlying neuropeptide release in the extended amygdala

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Although endogenous neuropeptide transmitters play critical roles in the reinforcing effects of ethanol consumption and the aversive effects of ethanol withdrawal, we have a poor understanding of mechanism(s) underlying central neuronal release of neuropeptides. This gap in our knowledge critically undermines our abilities to elucidate the biological effects of ethanol (EtOH), as 1) multiple studies have demonstrated that acute and chronic EtOH induces release of neuropeptides in brain regions associated with EtOH reinforcement and withdrawal-induced aversion, and 2) one of the very few medications (naltrexone) commonly used to treat EtOH craving is assumed to act by antagonizing effects of endogenously-released opioid peptides. Multiple behavioral studies document involvement of endogenous neuropeptides in response to stress, drugs and other behavioral states, but we still know very little about the physiological mechanisms underlying neuropeptide release. Howevever, this knowledge could significantly enhance our ability to create novel pharmacotherapies for alcohol dependence. Previous studies from our lab and others have shown enhanced release of neuropeptides in the central nucleus of the amygdala (CeA) by acute EtOH exposure. In addition, several studies have shown persistent release of specific peptides following withdrawal from chronic intermittent EtOH; these peptides may mediate the “anxious-like” withdrawal behaviors. However, our current preliminary data suggest that many conventional notions of peptide release may be inaccurate or incomplete; specifically, high-frequency activity is neither sufficient nor necessary for peptide release. We have recently begun exploring potential cellular phenomena that could regulate peptide release and our preliminary data demonstrate that we can relatively selectively induce release of the neuropeptide corticotropin-releasing factor (CRF) using optogenetic methods. In addition, we have characterized the potential role of the BK potassium channel in mediating EtOH effects. Proteomic analysis has shown that the BK channel is linked to the intracellular enzyme dynamin-1, a protein essential for mediating peptide release. We hypothesize that in contrast to fast synaptic transmission at axonal terminals, central neuropeptide release is mediated by a mechanism dependent on both the BK channel and dynamin-1. Because of the wealth of preclinical data implicating endogenous neuropeptides in effects of ethanol consumption and the clinical experience with naltrexone (which acts by blocking effects of endogenous opioid peptides), we believe that mechanistic studies of the physiological and ethanol-induced release of peptides in the extended amygdala may facilitate development of novel pharmacotherapies for the treatment of alcoholism.