LHRH neurons and their projections in humans and other mammals: species comparisons.

Using light microscopic immunocytochemistry, we have identified LHRH neurons and their projections in humans, monkeys, ferrets, bats and rats. In all these species, LHRH neurons project to the vascular contact zone of the ME, but positions of perikarya vary. This cell population, confined largely to rostral forebrain regions in rats, expands into the medial basal hypothalamus in humans, rhesus monkeys, ferrets and bats. Accompanying this expansion is an augmentation of extrahypothalamic LHRH projections. In rats, LHRH projections are primarily confined to the ME and OVLT. In humans, monkeys, ferrets and bats, however, there are also substantial projections to the posterior pituitary, habenular complex and amygdala. Although the significance of these extrahypothalamic projections is unknown, LHRH may function at some of these sites as a neuromodulator. Humans, monkeys, ferrets and bats further differ from rats in the apparent presence of mature decapeptide within perikarya. Whether variations in the dynamics of maturation of LHRH are related to differences in location of these neurons is currently under investigation.