Kisspeptin neurons in the arcuate nucleus (ARC) regulate prolactin secretion
and are in physical contact with tuberoinfundibular dopaminergic (TIDA) neurons
which inhibit prolactin secretion. Prolactin levels in the blood are increased with advancing age in rats; therefore
we investigated the interactions with TIDA neurons and kisspeptin neurons in aged female rats (24 months of age)
relative to those of young adult female rats (9-10 weeks of age). Plasma prolactin levels in the aged rats were significantly higher than those of young adult rats. Tyrosine hydroxylase (TH)-immunoreactive (ir) cell bodies and kisspeptin-ir nerve fibers were found in the dorsomedial ARC of both groups. The number of TH-ir cell bodies in the dorsomedial ARC did not differ significantly between groups. Additionally
no significant differences in the number of TH-ir cells in contact with kisspeptin-ir fibers was observed between groups. However
the number of kisspeptin-ir or Kiss1 mRNA-expressing cells in the ARC was significantly reduced in the aged rats compared with that of the young rats. These results suggest that the contacts between TIDA neurons and kisspeptin neurons are maintained after reproductive senescence
while production of kisspeptin in the ARC decreases significantly during aging.
