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 + E72h), (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 + E72h 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 + E72h preparations. These findings suggest that the P-induced excitation of preoptic warm sensitive neurons is mediated through the estrogen-induced P-receptors.
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