Male-predominant galanin mediates androgen-dependent aggressive chases in medaka.

Junpei Yamashita,Kataaki Okubo,Yoshitaka Nagahama,Thomas Fleming,Akio Takeuchi,Kohei Hosono

doi:10.7554/elife.59470

Junpei Yamashita, Kataaki Okubo + Show 4 more

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https://doi.org/10.7554/elife.59470

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Abstract

Recent studies in mice demonstrate that a subset of neurons in the medial preoptic area (MPOA) that express galanin play crucial roles in regulating parental behavior in both sexes. However, little information is available on the function of galanin in social behaviors in other species. Here, we report that, in medaka, a subset of MPOA galanin neurons occurred nearly exclusively in males, resulting from testicular androgen stimulation. Galanin-deficient medaka showed a greatly reduced incidence of male-male aggressive chases. Furthermore, while treatment of female medaka with androgen induced male-typical aggressive acts, galanin deficiency in these females attenuated the effect of androgen on chases. Given their male-biased and androgen-dependent nature, the subset of MPOA galanin neurons most likely mediate androgen-dependent male-male chases. Histological studies further suggested that variability in the projection targets of the MPOA galanin neurons may account for the species-dependent functional differences in these evolutionarily conserved neural substrates.

Highlights

Almost all animals interact socially with conspecifics at some stage of their lives (Hofmann et al, 2014; Chen and Hong, 2018)
Neurons expressing gal were observed in the anterior part of the parvocellular portion of the magnocellular preoptic nucleus/anterior parvocellular preoptic nucleus (PPa), the posterior part of the parvocellular portion of the magnocellular preoptic nucleus, and the posterior parvocellular preoptic nucleus (PPp) in the medial preoptic area (POA) (MPOA), and the anterior tuberal nucleus (NAT)/ ventral tuberal nucleus (NVT)/lateral recess nucleus (NRL) in the hypothalamus of the adult brain of both sexes (Figure 1D–G; abbreviations for medaka brain nuclei are given in Supplementary file 1)
We have shown that the parvocellular portion of the magnocellular preoptic nucleus (pPMp) population of medaka MPOA neurons expresses Gal nearly exclusively in males

Summary

Introduction

Almost all animals interact socially with conspecifics at some stage of their lives (e.g. for territorial/ resource disputes, mating, and parenting) (Hofmann et al, 2014; Chen and Hong, 2018). GAL-expressing neurons are commonly found in the MPOA of vertebrates, including teleost fish, the majority of which do not provide parental care (Fischer and O’Connell, 2017). Neuroscience species have consistently shown that males have many more MPOA Gal neurons than females (Cornbrooks and Parsons, 1991; Rao et al, 1996; Rodrıguez et al, 2003; Tripp and Bass, 2020) This contrasts with the situation in mammals, where either there is no sex difference in the number of these neurons, or the direction of the sex difference (if any) varies among species and even within strains in mice (Bloch et al, 1993; Park et al, 1997; Mathieson et al, 2000; Wu et al, 2014). We have further explored the mechanism underlying this differential gal expression and provide direct evidence that Gal has a male-biased, but unexpected, behavioral role in medaka

Results

Discussion

Materials and methods

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