SUBGROUPS OF LUTEINIZING-HORMONE-RELEASING HORMONE PERIKARYA DEFINED BY COMPUTER ANALYSES IN THE BASAL FOREBRAIN OF INTACT FEMALE RATS

The hypothesis that the basal forebrain population of LHRH perikarya is composed of heterogeneous subgroups was examined in this study. We used three-dimensional computerized reconstruction to examine populations of LHRH-immunopositive neurons detected in noncolchicine treated cycling female rats. Perikarya were detected with two antisera capable of detecting LHRH decapeptide within larger mol wt species, i.e. Millar's (RM) 1076 and Arimura's (AA) 419. No immunopositive perikarya were detected with antiserum AA 422, which requires the fully processed decapeptide for binding. A more broadly distributed population of LHRH neurons was detected in females killed on proestrus than in females killed on estrus or the other days of the cycle. These relationships were observed with both antisera, RM 1076 and AA 419. Subgroups of cells were clearly defined when the population of LHRH neurons detected on proestrus was simultaneously displayed with the population detected on estrus. Strikingly similar subgroups were revealed by simultaneous displays of populations of LHRH neurons detected by the antisera RM 1076 and AA 419 in proestrous females. This study revealed a three-dimensional onion skin-like laminar organization of LHRH subgroups expanding from the ventricle outward laterally and from the diagonal band of Broca to the hypothalamus caudally. We propose that these subgroups vary in their metabolic activity of biosynthesis, processing, transport, or release of LHRH in relation to the proestrous preovulatory release of LH.