Effects of chronic alcohol consumption, withdrawal and nerve growth factor on neuropeptide Y expression and cholinergic innervation of the rat dentate hilus

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Several studies have demonstrated the vulnerability of the hippocampal formation (HF) to chronic alcohol consumption and withdrawal. Among the brain systems that appear to be particularly vulnerable to the effects of these conditions are the neuropeptide Y (NPY)-ergic and the cholinergic systems. Because these two systems seem to closely interact in the HF, we sought to study the effects of chronic alcohol consumption (6 months) and subsequent withdrawal (2 months) on the expression of NPY and on the cholinergic innervation of the rat dentate hilus. As such, we have estimated the areal density and the somatic volume of NPY-immunoreactive neurons, and the density of the cholinergic varicosities. In addition, because alcohol consumption and withdrawal are associated with impaired nerve growth factor (NGF) trophic support and the administration of exogenous NGF alters the effects of those conditions on various cholinergic markers, we have also estimated the same morphological parameters in withdrawn rats infused intracerebroventricularly with NGF. NPY expression increased after withdrawal and returned to control values after NGF treatment. Conversely, the somatic volume of these neurons did not differ among all groups. On other hand, the expression of vesicular acetylcholine transporter (VAChT) was reduced by 24% in ethanol-treated rats and by 46% in withdrawn rats. The administration of NGF to withdrawn rats increased the VAChT expression to values above control levels. These results show that the effects of prolonged alcohol intake and protracted withdrawal on the hilar NPY expression differ from those induced by shorter exposures to ethanol and by abrupt withdrawal. They also suggest that the normalizing effect of NGF on NPY expression might rely on the NGF-induced improvement of cholinergic neurotransmission in the dentate hilus.

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