Poster Presentation The International Congress of Neuroendocrinology 2014

Prolactin-regulating dopaminergic neurons in the hypothalamus express neurokinin-B receptor and are innervated by neurokinin B- and kisspeptin-immunopositive fibers in rodents. (#231)

Nobuhiko Sawai 1 , Norio Iijima 2 , Hitoshi Ozawa 2 , Toshiyuki Matsuzaki 1
  1. Gunma University Graduate School of Medicine, Maebashi
  2. Graduate School of Medicine, Nippon Medical School, Tokyo

Neurons co-expressing kisspeptin, neurokinin B (NKB), and dynorphin in the hypothalamic arcuate nucleus, named KNDy neurons, are directly affected by sex hormones, and are well known for regulating the secretion of gonadotropin-releasing hormone. However, recent studies have shown that KNDy neurons also project and terminate to tuberoinfundibular dopaminergic (TIDA) neurons, suggesting a role in prolactin secretion. Besides the TIDA neurons that project to the median eminence, there is a possibility that periventricular hypophyseal dopaminergic (PHDA) neurons projecting to the intermediate lobe (IL) of the pituitary gland may also be directly innervated by KNDy neurons. Dopamine release by PHDA neuron at the IL is suggested to inhibit secretion of PRL and alpha-MSH, thus the pathway needs to be investigated. Moreover, whether these neurosecretory dopaminergic neurons possess receptors for receiving signals of any neuropeptides from KNDy neurons remains to be elucidated. In the present study, by means of double immunohistochemistry and retrograde neural tracer, we examined whether KNDy neurons project directly to PHDA neurons that project to blood vessels, as well as to TIDA neurons. The results revealed that KNDy neurons are widely projecting to neurosecretory dopaminergic neurons of the PHDA and TIDA neurons in rats and mice. Secondary, presence of a major receptor for NKB, neurokinin-3 receptor (NK3R), in PHDA and TIDA neurons was examined and it appeared that most TIDA and PHDA neurons possess NK3R. These findings indicate that, in rodents, KNDy neurons widely project to neurosecretory dopaminergic neurons distributed in the hypothalamus, and may affect them via the NKB-NK3R signaling pathway.