TOPOGRAPHY OF NEURONS EXPRESSING LUTEINIZING-HORMONE-RELEASING HORMONE GENE TRANSCRIPTS IN THE HUMAN HYPOTHALAMUS AND BASAL FOREBRAIN

The distribution of neurons expressing luteinizing hormone-releasing h ormone (LHRH) gene transcripts was mapped in the human hypothalamus an d basal forebrain by in situ hybridization and computer-assisted micro scopy. Hypothalamic blocks were dissected from five adult males and on e adult female and snap frozen in isopentane. The blocks were serially sectioned either in the coronal or in the sagittal plane at a thickne ss of 20 mu m. Approximately every twentieth section was incubated wit h a S-35-labeled cDNA probe complementary to LHRH mRNA. Specificity wa s confirmed by hybridization of adjacent sections with a probe targete d to the gonadotropin-associated protein (GAP) region of LHRH messenge r ribonucleic acids (mRNA). Maps of neurons containing LHRH mRNA were manually digitized with the aid of an image-combining computer microsc ope system. We report a much wider distribution and greater numbers of LHRH neurons than have been previously described in the human brain. Three morphological subtypes were observed based on cell size and labe ling density: 1) small, heavily labeled, oval or fusiform neurons, loc ated primarily in the medial basal hypothalamus, ventral preoptic area , and periventricular zone; 2) small, oval, sparsely labeled neurons l ocated in the septum and dorsal preoptic region and scattered from the bed nucleus of the stria terminalis to the amygdala (''extended amygd ala''); and 3) large round neurons (>500 mu m(2) sectional profile are a), intermediate in labeling density, scattered within the magnocellul ar basal forebrain complex, extended amygdala, ventral pallidum, and p utamen. The pronounced differences in morphology, labeling density, an d location of the three subtypes suggest that distinct functional subg roups of LHRH neurons exist in the human brain.