Effects of estradiol treatment on responses of rat preoptic warm sensitive neurons to progesterone in vitro

Single unit activity was recorded extracellularly in preoptic slice preparations from ovariectomized female rats. The rats were pretreated daily with (1) estradiol benzoate ( 20 μg 0.1 ml sesame oil) for 3 consecutive days just prior to the experiment (OVX + E_72h), (2) sesame oil (OVX + Oil), or (3) untreated (OVX). In the preparations from OVX rats, 12 (50%) of 24 warm-sensitive neurons were inhibited and 2 (8%) were excited by the application of progesterone (P) in perfusion medium (30 ng/ml). In OVX + Oil preparations, 4 (40%) of 10 warm-sensitive neurons were inhibited and none was excited by P. In OVX + E_72h preparations, however, only 4 (10%) were inhibited by P and 16 (38%) of 42 warm-sensitive neurons were excited. When Ru38486, a P-receptor antagonist, was applied together with P, no excitation was observed in warm-sensitive neurons in OVX + E_72h preparations. These findings suggest that the P-induced excitation of preoptic warm sensitive neurons is mediated through the estrogen-induced P-receptors.