Immunofluorescence study of the hypothalamo-infundibular LRH tract and serum gonadotropin levels in the female squirrel monkey during the estrous cycle.

The study of LRH reactive neurons of the medial basal hypothalamic group was made with rabbit antisera to unconjugated synthetic LRH, in normally cycling female squirrel monkeys. The specifically immunoreactive material present along the hypothalamo-infundibular LRH tract shows significant modifications that are particularly distinct in the lateral, posterior and anterior labia of median eminence, with a maximum concentration during the early and middle follicular phases, a sudden fall to a minimum concentration during the late follicular and ovulatory phases and with a progressive increase during the luteal and early follicular phases. Serum FSH and LH levels show a progressive decrease from the luteal phase to the late follicular phase, with differential modifications suggesting that a double regulation might take place in cycling squirrel monkeys. A parallel is suggested between the specifically reactive material along the hypothalamo-infundibular tract, serum gonadotropin levels and variations in the medial basal hypothalamic and infundibular LRH concentrations during the estrous cycle in the squirrel monkey.