Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana.
J Comp Neurol. 2019 May 1;527(7):1210-1227. doi: 10.1002/cne.24622. Epub 2019 Jan 15.
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.
神经激肽 B 由速激肽 3 基因编码，通过 KNDy 神经元和与 GnRH 的相互作用在哺乳动物的生殖调控中发挥关键作用。先前的硬骨鱼类研究集中在下丘脑 tac3 的表达，以研究其在生殖中的作用，但关于额外下丘脑 tac3 表达的详细研究是有限的。在这里，我们在社会性非洲丽鱼 Astatotilapia burtoni 中鉴定了两个 tac3 基因，只有其中一个产生含有标志性速激肽基序的功能性蛋白。tac3a mRNA 的原位杂交鉴定了整个大脑中的细胞群。许多 tac3a 细胞位于几个丘脑和下丘脑核中，包括后结节室旁核、外侧结节核（NLT）和外侧 recess 核（NRL）。分散的 tac3 表达细胞也存在于端脑部分，如腹侧（Vv）和上丘（Vs）腹侧端脑。与其他硬骨鱼类不同的是，垂体中没有 tac3 表达。使用双荧光染色，我们定位了 tac3a 表达细胞与 GnRH 和 kisspeptin 细胞的关系。虽然没有观察到 GnRH-tac3a 共标细胞，但密集的 GnRH 纤维环绕并可能与视前区的 tac3a 细胞形成突触。在 kiss2 细胞中仅观察到最小的（<5%）tac3a 共标。尽管在中脑边缘奖励系统的许多节点中都有 tac3a 表达，但在表达酪氨酸羟化酶（TH）的细胞中却没有，而 tac3a 细胞位于密集的 TH 纤维区域。tac3a 表达细胞存在于大脑的许多部位，包括与社会相关的脑区，这表明其具有更多的功能，不仅仅是调节生殖生理，这些功能可能在脊椎动物中是保守的。
