Sexual Dimorphic Distribution of Hypothalamic Tachykinin1 Cells and Their Innervations to GnRH Neurons in the Zebrafish

Abstract

Substance P (SP) and neurokinin A (NKA), encoded by TAC1/Tac1 gene are members of the tachykinin family, which exert their neuromodulatory roles in vertebrate reproduction. In mammals, SP and NKA have been shown to regulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion via kisspeptin neurons. On the other hand, the role of SP/NKA in the regulation of reproduction in non-mammalian vertebrates is not well known. In the present study, we first localized expression of tac1 mRNA in the brain of male and female zebrafish, Danio rerio. Next, using an antibody against zebrafish tachykinin1 (Tac1), we examined the neural association of SP/NKA neural processes with GnRH3 neurons, and with kisspeptin (kiss2) neurons, in the brains of male and female zebrafish. In situ hybridization showed an apparent male-dominant tac1 expression in the ventral telencephalic area, the anterior and posterior parts of the parvocellular preoptic nucleus, and the suprachiasmatic nucleus. On the other hand, there was female-dominant tac1 expression in the ventral periventricular hypothalamus. Confocal images of double-labeled zebrafish Tac1 and GnRH3 showed associations between Tac1-immunoreactive processes and GnRH3 neurons in the ventral telencephalic area. In contrast, there was no apparent proximity of Tac1 processes to kiss2 mRNA-expressing neurons in the hypothalamus. Lastly, to elucidate possible direct action of SP/NKA on GnRH3 or Kiss2 neurons, expression of SP/NKA receptor, tacr1a mRNA was examined in regions containing GnRH3 or Kiss2 neurons by in situ hybridization. Expression of tacr1a mRNA was seen in several brain regions including the olfactory bulb, preoptic area and hypothalamus, where GnRH3 and Kiss2 cells are present. These results suggest that unlike in mammals, Tac1 may be involved in male reproductive functions via direct action on GnRH3 neurons but independent of kisspeptin in the zebrafish.

The Effects of Tachykinin1 Gene Products on Prepubertal Dabry’s Sturgeon (Acipenser dabrynus) Pituitary Hormone Secretion and Gene Expression

“…Early studies have found that SP injection could enhance the learning ability of goldfish through dopamine mediation [30]. Another research showed that the SP/NK1R system is involved in osteogenesis and sexually differential localized expression of tac1 in the brain in zebrafish [31,32]. Recent studies have found that SP and NKA can promote the Lh and Prl secretion through NK1R and NK2R at the grass carp pituitary cells, which proves that tac1 encoding products are involved in the regulation of reproductive function in fish [33].…”

Transcriptome analysis reveals pituitary lncRNA, circRNA and mRNA affecting fertility in high- and low-yielding goats

“…SP and NKA can regulate the secretion of GnRH and LH. They play a neuromodulatory role in reproductive processes in vertebrate animals ( Arisawa et al, 1989 ; Ogawa et al, 2021 ). SP signaling in TAC1 neurons is linked to kisspeptin signaling at the level of GnRH neurons to regulate fertility in male mice ( Maguire et al, 2017 ), but the regulation of GnRH by SP may be the opposite in different species; for example, in crested newt, SP has been shown to downregulate GnRH and attenuate the pituitary secretion of LH ( Gobbetti et al, 2000 ).…”

Sex‐specific differences in the circadian pattern of action potential firing by rat suprachiasmatic nucleus vasopressin neurons

“…22 Because VP release from SCN neurons is activity dependent, 19,20 these observations suggested there might be differences in the firing pattern of SCN VP neurons in the two sexes. Indeed, sexually dimorphic features of the SCN have been reported in several species, [28][29][30][31][32][33][34] including humans, 35 and sex differences in circadian physiology are well documented. [35][36][37][38][39][40] Therefore, the goal of this study was to characterize and compare the circadian profiles of electrical activity in identified SCN VP neurons of male and female rats.…”