Effects of Hypothalamic Deafferentation on the Pulsatile Rhythm in Plasma Concentrations of Luteinizing Hormone in Ovariectomized Rats1

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Abstract
Plasma LH concentrations were measured by radioimmunoassay in blood collected at 10-min intervals through atrial cannulas implanted in long-term ovariectomized rats. Regular fluctuating levels of the hormone were recorded in which plasma LH concentration rose rapidly to a peak every 20–40 min. Interruption of the anterior nerve projections to the medial basal hypothalamus (MBH) by deafferentation with a small stereotaxic knife rendered rats acyclic and resulted in a persistently cornified vaginal epithelium (constant estrus). Although these neural afferents were necessary for an ovulatory discharge of LH, the anterior deafferentation procedure did not block either the post-castration rise in plasma LH or the pulsatile discharge of hormone in the same rats when they were ovariectomized 4–6 weeks after deafferentation.Similarly, an extended frontal or an anterior-lateral cut resulted in constant estrus and permitted the pulsatile circulating levels of LH after ovariectomy. Posterior-lateral deafferentation did not interrupt the estrous cycle or alter LH release after ovariectomy. Complete deafferentation of the MBH caused rats to become either constantestrus or constant-diestrus (persistently leucocytic vaginal epithelium). Although histological study did not reveal anatomical differences in the brains of the complete cut subjects which could be correlated with their responses to deafferentation, only the constant estrus animals showed the post-castration rise in LH and a regular fluctuating pattern in plasma LH concentration. These differential responses to complete deafferentation were considered in relation to other cuts which caused the constant diestrus state. The data suggest that control of the high plasma LH concentration, which shows a regular fluctuating pattern in ovariectomized rats, may be autonomously inherent to the MBH-hypophysial unit. (Endocrinology94: 730, 1974)