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

Abstract

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.

The entire trajectories of single pontocerebellar axons and their lobular and longitudinal terminal distribution patterns in multiple aldolase C‐positive compartments of the rat cerebellar cortex

“…A recent anterograde labeling study indicated that LRN axons terminate mostly in aldolase C-negative areas, while BPN axons terminate in aldolase Cpositive areas . However, in previous studies, it was not clear whether a given pontocerebellar axon innervates aldol- (Table 1), and those in the mouse (83.9%) were slightly lower (Biswas et al, 2019). Whether such simple correlation of a single mossy fiber axon to aldolase C expression pattern is generalized to other mossy fiber axons partly remains a question, since single neurons innervate both aldolase C-positive and -negative bands in some mossy fiber systems such as external cuneate neurons (Ji & Hawkes, 1994) and spinocerebellar neurons (Luo et al, 2018).…”

“…The present study extends this single axonal reconstruction analysis to single neurons in various parts of the BPN that project to various lobules and aldolase C compartments of the bilateral cerebellar cortices of rats. The present results obtained in the rat will be compared with those in the mouse (Biswas, Luo, Sarpong, & Sugihara, 2019).…”

“…Single spinocerebellar neurons such as noncrossed Clarke column cells pass through the ipsilateral inferior cerebellar peduncle and project bilaterally in multiple parasagittal bands with ipsilateral dominance in the mouse (Luo, Patel, Sarpong, Sasamura, & Sugihara, 2018). Single BPN axons pass through either the ipsilateral or the contralateral MCP and mainly spread bilaterally in the cerebellum of the mouse (Biswas et al, 2019). Therefore, based on these data of single axonal morphologies of the different and representative mossy fiber systems in the rat and mouse, it is safe to conclude that the branching and termination pattern of single mossy fiber axons is common to different mossy fiber systems as schematically represented before (Shinoda & Sugihara, 2013), and multiple cerebellar collateral branches of single pontocerebellar mossy fibers is a basis of a neural scaffolding underlying discrete, symmetrically disclosed multiple longitudinal zonal organization of pontocerebellar axon terminals described before (Serapide et al, 2001).…”

“…The present data support the conclusion of Rosina and Provini (1984) in that many single BPN axons double cross the midline in the pons and the cerebellum, and project bilaterally with a larger number of axon terminals in the contralateral than the ipsilateral cerebellum (see Table 1). However, the result by Rosina and Provini (1984) (Biswas et al, 2019). Although it is known that some BPN neurons send their axons to the cerebellum through the ipsilateral MCP (Biswas et al, 2019;Brodal & Jansen, 1946;Voogd, 1964), the exact proportion of such neurons that send their axons to the ipsilateral MCP among the total BPN neurons has not been determined.…”

“…However, the result by Rosina and Provini (1984) (Biswas et al, 2019). Although it is known that some BPN neurons send their axons to the cerebellum through the ipsilateral MCP (Biswas et al, 2019;Brodal & Jansen, 1946;Voogd, 1964), the exact proportion of such neurons that send their axons to the ipsilateral MCP among the total BPN neurons has not been determined. By staining practically all fibers in the MCP, the present study could determine that less than 10% of the BPN neurons send their axons through the ipsilateral MCP ( Figure 10).…”