[Effects of 5-HT on activity of arcuate neurons of rat hypothalamic slices]

Extracellular recordings were made from 176 spontaneous discharging units in the arcuate nucleus of rat hypothalamic slices. Depending on the patterns of discharge, the units were divided into three types; slow irregular (76%), fast continuous (26.5%) and phasic units (6.3%). The effect of 5-HT on the different types of units were observed. The results indicated that most of neurons were inhibited by 5-HT, and only a small portion of the cells showed excitation and a few of the slow irregular units showed "excitation after inhibition". With 5-HT 10(-6) mol/L we found that 12 units inhibited by 5-HT could not be reversed by CHD, while the 4 inhibited units could be partly or completely reversed by MSG. 4 of the 7 neurons inhibited by 5-HT were partly blocked by Pindobind-5-HT1A but not for the remaining 3 neurons. The results suggest that the inhibitory effect of 5-HT on arcuate neurons may be mediated by 5-HT1 receptor, while some by 5-HT1A receptor.