Stress-induced secretion of alpha-melanocyte-stimulating hormone is accompanied by a decrease in the activity of...

The purpose of the present study was to examine the acute effects of stress on the secretion of alpha-melanocyte-stimulating hormone (alpha MSH) and the activity of tuberohypophysial dopamine (DA) neurons in female and male rats. The activity of tuberohypophysial DA neurons was estimated by measuring the accumulation of 3,4-dihydroxyphenylalanine (DOPA) following administration of the decarboxylase inhibitor NSD 1015, and the concentrations of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the intermediate and neural lobes of the posterior pituitary. The combination of brief (2 min) ether exposure followed by 30 min of supine restraint (immobilization in the supine position) decreased the rate of DOPA accumulation in the intermediate, but not in the neural lobe of both female and male rats. Similarly, brief ether exposure followed by 10, 20 or 30 min of supine restraint increased plasma alpha MSH concentrations and decreased DOPAC concentrations in the intermediate lobe of female and male rats. In the absence of ether, tube restraint (confinement in a cylindrical acrylic tube) increased alpha MSH secretion and decreased intermediate lobe DOPAC concentrations, whereas ether in the absence of physical restraint had no effect. These results suggest that the stress-induced activation of alpha MSH secretion in both female and male rats may be due, in part, to a decrease in the activity of tuberohypophysial DA neurons in the intermediate lobe of the posterior pituitary.