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Alcohol withdrawal increases neuropeptide Y immunoreactivity in rat brain
1Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, USA.
Background:
Neuropeptide Y (NPY) is widely expressed in the brain and is known to affect consummatory behaviors including drinking alcohol as well as to play a role in seizures. We investigated the effects of a 4 day binge ethanol treatment model that is known to induce physical dependence and withdrawal seizures to determine the effects of ethanol dependence and withdrawal on NPY expression.
Methods:
Male Sprague Dawley rats were treated with ethanol or control nutritionally complete diets by intragastric treatment three times per day for 2 or 4 days with an average daily dose of approximately 8 g/kg ethanol per day. Ethanol-fed rats treated for 4 days and then withdrawn for 24, 72, and 168 hr also were studied. Brains were perfused and sectioned for immunohistochemistry for NPY, phospho-cyclic adenosine monophosphate responsive element binding (pCREB), and other proteins.
Results:
NPY immunoreactivity (NPY-IR) was found in several brain regions, with the hippocampus and cerebral cortex showing the most pronounced changes. NPY-IR was reduced by ethanol treatment in hippocampus and cortex, although at 72 hr of withdrawal there was a dramatic increase in NPY-IR in the hilus of the dentate gyrus and in CA3 and CA2 fields of hippocampus. Ethanol withdrawal seizures occurred around 12 to 24 hr of withdrawal, preceding the changes in NPY-IR at 72 hr. pCREB immunoreactivity (pCREB-IR) tended to decrease during ethanol treatment but showed a dramatic increase in dentate gyrus at 72 hr of withdrawal. Parvalbumin immunoreactivity indicated that some of the pCREB-IR and NPY-IR were within inhibitory interneuron basket cells of the hippocampal hilus. NPY-IR returned to control levels by 168 hr of withdrawal.
Conclusions:
These studies suggest that hippocampal NPY is reduced during the development of ethanol dependence. Ethanol withdrawal seizures precede a dramatic increase in hippocampal NPY-IR. Previous studies have suggested that NPY in the hippocampus reduces seizure activity and that NPY is induced by seizure activity. Thus, the increase in NPY-IR at 72 hr of withdrawal after binge ethanol treatment may be protective against prolonged withdrawal seizure activity.