Female reproductive state is associated with changes in distinct arginine vasotocin cell types in the preoptic area of Astatotilapia burtoni.

Nonapeptides play a crucial role in mediating reproduction, aggression, and parental care across taxa. In fishes, arginine vasotocin (AVT) expression is related to social and/or reproductive status in most male fishes studied to date, and is linked to territorial defense, paternal care, and courtship. Despite a plethora of studies examining AVT in male fishes, relatively little is known about how AVT expression varies with female reproductive state or its role in female social behaviors. We used multiple methods for examining the AVT system in female African cichlid fish Astatotilapia burtoni, including immunohistochemistry for AVT, in situ hybridization for avt-mRNA, and quantitative PCR. Ovulated and mouthbrooding females had similar numbers of parvocellular, magnocellular, and gigantocellular AVT cells in the preoptic area. However, ovulated females had larger magnocellular and gigantocellular cells compared to mouthbrooding females, and gigantocellular AVT cell size correlated with the number of days brooding, such that late-stage brooding females had larger AVT cells than mid-stage brooding females. In addition, we found that ventral hypothalamic cells were more prominent in females compared to males, and were larger in mouthbrooding compared to ovulated females, suggesting a role in maternal care. Together, these data indicate that AVT neurons change across the reproductive cycle in female fishes, similar to that seen in males. These data on females complement studies in male A. burtoni, providing a comprehensive picture of the regulation and potential function of different AVT cell types in reproduction and social behaviors in both sexes.

Expression of tachykinin3 and related reproductive markers in the brain of the African cichlid fish Astatotilapia burtoni.

Neurokinin B, encoded by the tachykinin3 gene, plays a crucial role in regulating reproduction in mammals via KNDy neurons and interaction with GnRH. Previous work in teleost fishes has focused on hypothalamic tac3 expression for its role in reproduction, but detailed studies on extra-hypothalamic tac3 expression are limited. Here, we identified two tac3 genes in the social African cichlid fish Astatotilapia burtoni, only one of which produces a functional protein containing the signature tachykinin motif. In situ hybridization for tac3a mRNA identified cell populations throughout the brain. Numerous tac3a cells lie in several thalamic and hypothalamic nuclei, including periventricular nucleus of posterior tuberculum, lateral tuberal nucleus (NLT), and nucleus of the lateral recess (NRL). Scattered tac3-expressing cells are also present in telencephalic parts, such as ventral (Vv) and supracomissural (Vs) part of ventral telencephalon. In contrast to other teleosts, tac3 expression was absent from the pituitary. Using double-fluorescent staining, we localized tac3a-expressing cells in relation to GnRH and kisspeptin cells. Although no GnRH-tac3a colabeled cells were observed, dense GnRH fibers surround and potentially synapse with tac3a cells in the preoptic area. Only minimal (<5%) colabeling of tac3a was observed in kiss2 cells. Despite tac3a expression in many nodes of the mesolimbic reward system, it was absent from tyrosine hydroxylase (TH)-expressing cells, but tac3a cells were located in areas with dense TH fibers. The presence of tac3a-expressing cells throughout the brain, including in socially relevant brain regions, suggest more diverse functions beyond regulation of reproductive physiology that may be conserved across vertebrates.