Effects of various types of hypothalamic deafferentation on luteinizing hormone pulses in ovariectomized rats

Abstract The pulsatile luteinizing hormone (LH) secretion in chronically ovariectomized rats bearing various types of hypothalamic deafferentation was examined. Ovariectomized rats were subjected to complete, anterolateral or anterior hypothalamic deafferentation and bled every 6 min for 3 h through an indwelling atrial cannula 5 days after the brain surgery. Another group of ovariectomized animals was subjected to posterior-anterior hypothalamic deafferentation (PAD), which cut off the anterior part of the arcuate nucleus from the mediobasal hypothalamus, and bled 1, 3 or 5 weeks after the deafferentation. Coronal sections of the brain were immunostained with anti-LH-releasing hormone (LHRH) serum. The pulsatile LH secretion was observed in rats bearing anterior, anterolateral or complete hypothalamic deafferentation and these types of deafferentation did not affect the frequency of LH pulses. The mean LH level during the 3-h sampling period and the amplitude of LH pulses decreased as the incision extended postero-laterally. Rats bearing PAD showed an irregular fluctuating pattern in plasma LH concentration 1 week after PAD. Parameters of LH pulses were restored with time after PAD. This suggests that the system generating LHRH pulses severed by PAD had been reorganized. LHRH-immunopositive neuronal fibres were found in the external layer of the median eminence in the rats bearing any type of deafferentation. The present results suggest that the frequency of LH pulses could be controlled by the LHRH pulse generator, which consists of non-LHRH neurons and is located in the mediobasal hypothalamus.