Vasoactive intestinal peptide and corticotropin-releasing hormone increase β-endorphin release and proopiomelanocortin messenger RNA levels in primary cultures of hypothalamic cells: Effects of acute and chronic ethanol treatment

Background: β-Endorphin (β-EP) neurons are involved in ethanol's action on a variety of brain functions, including positive reinforcement. These neurons are innervated by vasoactive intestinal peptide (VIP)-containing and corticotropin-releasing hormone (CRH)-containing neurons in the hypothalamus. Whether these neuropeptides affect β-EP neuronal function in the presence or absence of ethanol has not previously been determined. Methods: The authors determined the effects of VIP and CRH on gene expression and peptide release from β-EP neurons in primary cultures of mediobasal hypothalamic cells. The effects of receptor antagonists on VIP- and CRH-induced β-EP release was determined. Furthermore, the authors studied the effects of acute and chronic treatment with ethanol on the response of β-EP neurons to VIP and CRH. Real-time reverse-transcription polymerase chain reaction was used for messenger RNA (mRNA) detection, and radioimmunoassay was used for hormone measurements. Results: We show that β-EP neurons responded concentration dependently to VIP and CRH treatments by increasing both β-EP release and proopiomelanocortin mRNA expression. Simultaneous treatment with a nonspecific receptor antagonist reduced the ability of CRH or VIP to induce ß-EP release from mediobasal hypothalamic cells. Acute treatment with ethanol increased β-EP neuronal gene expression and the secretory response to CRH and VIP. However, previous exposure to chronic ethanol reduced the CRH and VIP responses of these neurons. Conclusions: These results indicate that VIP and CRH stimulate β-EP release from hypothalamic cells in primary cultures and that the stimulatory and adaptive responses of β-EP neurons to ethanol may involve alteration in the responsiveness of β-EP-secreting neurons to CRH and VIP.