Effects of progesterone on thermosensitive neurons in preoptic slice preparations.

Single neuronal activities in preoptic (PO) slice preparations from both male and female rats were recorded and examined for their responses to 3 ng/ml or 30 ng/ml progesterone (P). Of 31 warm-sensitive neurons, 19 (61.3%) were inhibited by P, 5 (16.1%) were excited, and 7 (22.6%) did not respond to P. Of 26 thermally insensitive neurons, 4 (15.4%) were inhibited by P, 3 (11.5%) were excited, and 19 (73.1%) did not respond to P. Of 4 cold-sensitive neurons, 3 were inhibited and one was excited. These results demonstrate that P inhibits most warm-sensitive neurons directly or indirectly via local neuronal circuits in the slice.