Dual phenotype kisspeptin-dopamine neurones of the rostral periventricular area of the third ventricle project to gonadotrophin-releasing hormone neurones.

The neuropeptide kisspeptin and its G-protein-coupled receptor, Gpr54, are critical regulators of fertility. Two major populations of kisspeptin neurones exist in the rodent: one in the rostral periventricular area of the third ventricle (RP3V) and another in the arcuate nucleus. The RP3V population of kisspeptin neurones is crucial for the generation of the luteinising hormone surge that drives ovulation in females. The RP3V kisspeptin neurones are sexually dimorphic, with many more neurones in females than males, and they project to gonadotrophin-releasing hormone (GnRH) neurones. Tyrosine hydroxylase (TH) expressing neurones in the RP3V are also sexually dimorphic and are assumed to project to GnRH neurones. In the present study, we examined the coexpression of kisspeptin and TH peptides in the RP3V of dioestrous and pro-oestrous female mice. We also investigated whether kisspeptin and TH peptides colocalised in terminal appositions with GnRH neurones in the rostral preoptic area (rPOA). Approximately half of the kisspeptin neurones in the RP3V were found to also express TH and vice versa, although there was no difference between mice in dioestrus or pro-oestrus. The majority (95%) of GnRH neurones in the rPOA exhibited a close apposition from a kisspeptin fibre, whereas only one quarter exhibited a close apposition from a TH fibre. Many of the TH close appositions with GnRH neurones coexpressed kisspeptin (62-86%), although these dual-labelled appositions comprised <20% of all kisspeptin appositions on GnRH neurones. The percentage of GnRH neurones with kisspeptin, TH and double-labelled appositions did not differ between dioestrous and pro-oestrous mice. These findings indicate that a subpopulation of kisspeptin neurones expressing dopamine innervate GnRH neurones in the rPOA.