Abstract
[Introduction] Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) of the hypothalamus are considered to regulate gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) surge in female rodents. Our previous studies showed that purinergic signaling involves GnRH/LH surge and then ovulation in female rats. The present study, thus, aims to identify the purinergic neurons that project to the vicinity of AVPV kisspeptin neurons.[Materials and method] Adult Wistar-Imamichi female rats (n = 4) were stereotaxically injected with fluorogold (FG), a retrograde tracer, into the AVPV. Then, the animals were ovariectomized and primed with diestrous levels of estradiol-17β (E2) for 5 days followed by proestrous levels of E2 for 2 days. Seven days after the FG injection, the animals were perfused with 4% paraformaldehyde and 50-μm brain sections including the hypothalamus and hindbrain were made using a cryostat. The brain sections were subjected to double-immunohistochemistry for FG and vesicular nucleotide transporter (VNUT), a marker of purinergic neurons. [Results] VNUT-immunoreactive cells were mainly found in the hypothalamic arcuate nucleus and medial part of supramammillary nucleus (SuM), and brainstem A1, A2, A6 regions and area postrema (AP). FG- and VNUT-co-immunoreactive cells were found in the majority of VNUT-ir cells in the A1, around one-third of VNUT-ir cells in the A2, one-tenth of VNUT-ir cells in the A6, and few VNUT-ir cells in the SuM. These results suggest that the purinergic neurons located in the A1, and A2 may project their axons to the vicinity of AVPV kisspeptin neurons and possibly play a role in an induction of GnRH/LH surge, and then ovulation in female rats.
