Kisspeptin neuron is a critical regulator of reproductive functions. We previously showed that kisspeptin neurons innervate not only GnRH neurons but also hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons, which inhibit prolactin (PRL) secretion, in adult female rats. This study aimed to examine the interactions between kisspeptin and TIDA neurons in aged female rats.

8-week-old (8W) female rats whose estrous cycle was diestrus and 24-month-old (24M) female rats were perfused with 4% paraformaldehyde. After removing brains, coronal cryosections were cut and used for dual immunofluorescent histochemistry and in situ hybridization.

Apparent TH-ir cell bodies and kisspeptin-ir fibers were found in the dorsal ARC of both 8M and 24W. The number of TH-ir cells in the dorsal ARC did not differ significantly between groups. Moreover, no significant differences were observed in the number of TH-ir cells contacting with kisspeptin-ir fibers between groups. On the other hand, the numbers of ARC kisspeptin-ir and Kiss1-expressing cells in 24M was significantly fewer than those in 8W. Plasma levels of PRL in 24M were significantly higher than that in 8W.

This study revealed that the contacts between TIDA neurons and kisspeptin neurons are maintained after menopause. Since both kisspeptin-ir and Kiss1-expressing cells were decreased in 24M compared with 8W, the decreased expressions of ARC kisspeptin neuron might be involved with higher PRL level through TIDA neurons in aged female rats.