Effect of Mating Behavior on Luteinizing Hormone-Releasing Hormone Release in Female Rabbits as Monitored with Push-Pull Cannulae

Abstract

To examine the effect of mating behavior on luteinizing hormone-releasing hormone (LHRH) release, intact New Zealand female rabbits were implanted with push-pull cannulae (PPC) aimed at the tuberal region of the hypothalamus and perfused with modified Krebs-Ringer phosphate medium at 11–13 µl/min. In the mating experiments, does (n = 10) were initially perfused for a control period of 60–170 min followed by a mating period (100–160 min) which included the introduction of the male rabbit for an average time period of 30 min. Two groups of LHRH release patterns were observed: positive and negative responders. In the positive LHRH responders (n = 5), a clear rapid increase in LHRH release following mounting by the male occurred with a significant increase in the mean LHRH release (1.83 ± 0.33 to 3.27 ± 0.80 pg/10 min, p < 0.040), in the mean LHRH amplitude (1.97 ± 0.46 to 4.33 ± 1.29 pg, p < 0.022) and in the amplitude of the largest LHRH pulse (2.13 ± 0.43 to 7.58 ± 3.65 pg, p < 0.022). In the negative LHRH responders (n = 5), no changes in LHRH release were detected although all rabbits ovulated, with some becoming pregnant. It appears from histological analysis that the difference between these two patterns of responses following mating are due to different cannula placements. In the positive responders, the tip of the PPC was localized in the tuberal region whereas in the negative responders, the placements were more dorsal and, in some cases, anterior. Therefore, in contrast to basal pulsatile LHRH release that can be measured in widespread areas in the hypothalamus, the postulated LHRH surge following coitus in the intact female rabbit can be detected only when a specific area of the hypothalamus (tuberal portion) is perfused, indicating activation of a particular set of LHRH neurons following sexual stimulation.