In primates, the importance of the preoptic area (POA) and mediobasal hypothalamus in mediating the positive feedback action of E2 on LH release continues to be debated. Nevertheless, kisspeptin neurons, which have been implicated in mediating this action of E2, are present in both these hypothalamic areas in the female. Since E2 induced LH surges may be elicited in adult male primates following castration it seemed reasonable to posit that the distribution of hypothalamic kisspeptin neurons might be similar in the male and female monkey. The present study investigated this notion for the POA.
A group of follicular phase females (N=4) and three groups of adult male rhesus monkeys were studied; intact (N=3), castrate (N=3), and castrate implanted sc for up to 48 hours with E2-containing Silastic capsules to produce circulating E2 levels of 200-500 pg/ml (N=6). The brains were perfused with 4% paraformaldehyde and hypothalami were serially sectioned at 25 um. Nickel-diaminobenzidine immunostaining was performed using the sheep anti-human kisspeptin-54 antibody, GQ2 at 1:60,000. Kisspeptin-54 was used to preadsorb GQ2 for control purposes.
In follicular phase females and intact males, immunoreactive kisspeptin perikarya were seen in the anteroventral periventricular nucleus and medial POA, and robust fibers were seen throughout the POA. Typically, kisspeptin immunoreactivity was not homogenously distributed throughout the cell body, but instead exhibited either a cytoplasmic granular pattern or appeared as a cytoplasmic
"cap". In male castrates, immunoreactive kisspeptin perikarya were rarely observed and fiber staining was diminshed: E2 treatment restored immunoreactive kissppetin in both cell bodies and fibers. These findings suggest, perhaps not unexpectedly, that the distribution of kisspeptin neurons in the POA of the male and female monkey is similar, and that testicular hormones maintain kisspeptin expression in this region of the hypothalamus by a mechanism that is dependent on, or may be mimicked by, ER signaling.