Immunofluorescence study of the preoptico-terminal LRH tract in the female squirrel monkey during the estrous cycle

Reactive LRH neurons of the preoptico-terminal trace were studied with rabbit antisera to unconjugated or conjugated synthetic LRH in normally cyclic female squirrel monkeys. The specific immunoreactive material present along the preoptic-terminal LRH tract showed significant modifications that were particularly distinct (1) at the level of the perikarya, and (2) in the axons and axonal endings situated around the short and long capillary loops of the lamina terminalis. Conspicuous variations were observed during the luteal phase (with distinct and fast refilling), and the early and mid-follicular phases (suggesting a pulsatile mode of release); minimum concentrations were attained during the late and peri-ovulatory phases. A comparison is made between these modifications and those observed along the hypothalamo-infundibular LRH tract in the same animals. The preoptico-terminal LRH tract is thought to be one of the possible mechanisms controlling the sensitivity of gonadotropic cells to LRH, and the synthesis and storage of gonadotropins before their mid-cycle discharge.