FOS EXPRESSION IN LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS OF GUINEA-PIGS, WITH KNIFE CUTS SEPARATING THE PREOPTIC AREA AND THE HYPOTHALAMUS, DEMONSTRATING LUTEINIZING-HORMONE SURGES

LHRH neurons in guinea pigs, as in primates and other non-rodent speci es, are broadly distributed in the basal forebrain. In this study, kni fe cuts were made in the anterior hypothalamus, effectively separating more caudally positioned hypothalamic LHRH neurons from those in rost ral preoptic areas. Guinea pigs with knife cuts displayed an LH surge in response to steroid administration, There was no significant differ ence in the number of LHRH neurons that expressed Fos in conjunction w ith an LH surge, although fewer total LHRH neurons were detected in th e forebrain of knife-cut versus sham-cut animals, Knife-cut animals di splayed a larger percentage of LHRH/Fos neurons in one region of the c audal hypothalamus than sham-cut animals, The area and perimeter of th e LHRH reaction product within the cytoplasm of LHRH/Fos neurons were smaller than those of single-labeled LHRH neurons in sham-cut animals and in the caudal hypothalamus, but not the rostral preoptic area, of knife-cut animals, We conclude that caudal hypothalamic LHRH neurons s eparated from rostral preoptic regions are capable of sustaining an LH surge in guinea pigs. This finding is important, as LHRH neurons are present in the caudal hypothalamus, as well as in preoptic areas, of a large number of mammalian species, including humans.