GnRH and testosterone treatment generate GnRH neurons in the hypothalamus of adult zebrafish (Danio rerio)

Abstract

Gonadotropin-releasing hormone (GnRH) is an essential in the control of reproduction of vertebrates. A decrease in the secretion of GnRH causes reproductive disorders called congenital idiopathic hypogonadotropic hypogonadism (IHH), which is characterized by absence of puberty. Once diagnosed, IHH patients can be treated with reproductive hormone therapy to restore the disease. Interestingly, studies have documented a reversion of the disease after discontinuation of hormone treatment, which improves the reproductive capacities. We suggest the hormone treatment stimulate the neurogenesis of GnRH neurons in the hypothalamus in such a way to produce reversion in IHH patients. Here, we characterized the neurogenesis in the preoptic area (POA) of adult zebrafish. Our results showed that GnRH and not testosterone treatment, significantly increased the neurogenesis in the POA. In addition, results obtained by in situ hybridization to gnrh3 and MALDI TOF, did not detect any GnRH isoform in the hypothalamus. Therefore, our results and recent publications show that GnRH does not affect the control of reproduction in zebrafish. In order to find a potential candidate to replace GnRH, we cloned and characterized phoenixin/smim20 expression, which has a reproductive role in mammals. phoenixin/smim20 is widely expressed in the brain especially in the hypothalamus of adult zebrafish.