Neuropeptide Y system in accumbens shell mediates ethanol self-administration in posterior ventral tegmental area

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Abstract

Although modulatory effects of neuropeptide Y (NPY) on ethanol consumption are well established, its role in ethanol reward, in the framework of mesolimbic dopaminergic system, has not been studied. We investigated the influence of nucleus accumbens shell (AcbSh) NPYergic system on ethanol self-administration in posterior ventral tegmental area (p-VTA) using intracranial self-administration paradigm. Rats were stereotaxically implanted with cannulae targeted unilaterally at the right p-VTA and trained to self-administer ethanol (200 mg%) in standard two-lever (active/inactive) operant chamber, an animal model with high predictive validity to test the rewarding mechanisms. Over a period of 7 days, these rats showed a significant increase in the number of lever presses for ethanol self-administration suggesting reinforcement. While intra-AcbSh NPY (1 or 2 ng/rat) or [Leu31, Pro34]-NPY (0.5 or 1 ng/rat) dose-dependently increased ethanol self-administration, BIBP3226 (0.4 or 0.8 ng/rat) produced opposite effect. The rats conditioned to self-administer ethanol showed significant increase in the population of NPY-immunoreactive cells and fibres in the AcbSh, central nucleus of amygdala (CeA), hypothalamic arcuate nucleus (ARC) and lateral part of bed nucleus of stria terminalis as compared with that in the naïve rats. Neuronal tracing studies showed that NPY innervations in the AcbSh may derive from the neurons of ARC and CeA. As NPY and dopamine systems in reward areas are known to interact, we suggest that NPY inputs from ARC and CeA may play an important role in modulation of the dopaminergic system in the AcbSh and consequently influence the ethanol induced reward and addiction.

Rats were conditioned to self-administer ethanol directly in the posterior ventral tegmental area (p-VTA). Intra-accumbens shell (AcbSh) injection of neuropeptide Y (NPY) agonists potentiated, while antagonist decreased ethanol self-administration. Expression of NPY in the AcbSh, central nucleus of amygdala (CeA), bed nucleus of stria terminalis and arcuate nucleus (ARC) was increased in the conditioned rats. Additionally, AcbSh receives NPY fibers from ARC and CeA. NPYergic innervation to the dopamine system in AcbSh seems important to ethanol reward and reinforcement.

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