Social stress impacts spexin functioning by receptor, GALR2b, downregulation in the Nile tilapia brain

Spexin is a relatively new neuropeptide that has been implicated in various neuroendocrine functions including as an appetite-limiting factor and reproductive function inhibitor. Spexin has also been attributed to stress response in the brain, although the information is limited and its downstream targets and effects are still unclear. For example, social stress in the Nile tilapia upregulated the expression of spexin in the brain but it is unknown if its receptors are also affected. Here we studied spexin’s receptors, galanin receptor 2a (GALR2a) and GALR2b, in the Nile tilapia. We performed a chronic social defeat paradigm to induce social stress on subordinate males. This employs the natural social hierarchy among male tilapia, which leads to the formation of dominant and subordinate males. A subordinate male was paired with an aggressive, dominant male for five days straight. Brain tissues from the subordinate males were sampled on the fifth day. Using gene expression analysis, we found that galr2b receptor was highly expressed in the brain compared to galr2a. In socially stressed males, galr2b expression was downregulated in the brain, when compared to unstressed control males. No change in galr2a was observed under social stress. Social stress-induced regulation of spexin-GALR2b activity may indicate spexin as a neuromodulator of social stress.