A melanocortin agonist reduces neuronal firing rate in rat hypothalamic slices

Bath application of cr-melanocyte stimulating hormone (alpha-MSH) to rat hy pothalamic slices inhibited the spontaneous firing rate of continuously fir ing neurons in the ventromedial hypothalamic nucleus or paraventricular nuc leus. This inhibitory effect is most likely direct and independent of synap tic transmission. The cr-MSH-responsive neurons tested did not respond to n europeptide Y (NPY) application. On the other hand, a-MSH did not inhibit t he intraburst firing rate of phasic bursting neurons, although these bursti ng neurons were highly responsive to a serotonin 5HT2a/2b/2c agonist with a change of firing pattern to continuous firing and an increase in firing ra te which was reversed by NPY. These results suggest that a change of neuron al firing rate may represent a neural correlate of satiety induced by anore xic agents. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.