Issa, F. A. | bioRxiv Science

bioRxiv2026

Cellular mechanisms underlying social regulation of the posterior tubercular nucleus in zebrafish (Danio rerio)

Social status profoundly influences animal behavior through neural plasticity, yet the cellular mechanisms that mediate reconfiguration of neuromodulatory systems remain poorly understood. Here, we investigated status-dependent structural changes in the posterior tubercular nucleus (PTN) of adult zebrafish. Animals were assigned to four social conditions: communal, isolated, dominant, or subordinate. Using markers for cell proliferation (PCNA) and birth-dating (BrdU), we demonstrate that social dominance significantly enhances cell proliferation, leading to an increased population of PTN dopaminergic neurons. In contrast, subordinate and isolated fish exhibited suppressed proliferation and elevated expression of superoxide dismutase 1 (SOD1), suggesting that chronic social stress induces an oxidative burden that may lead to neuronal loss. Furthermore, we identified evidence of neurotransmitter phenotypic plasticity; subordinate fish displayed a significantly higher ratio of glutamatergic (vglut2a) to dopaminergic (dat) expression in PTN neurons compared to dominants, suggesting a status-dependent shift in neuromodulatory identity. Multivariate principal component analysis showed distinct neurobiological profiles that separate social ranks, suggesting that status-dependent plasticity is a coordinated multi-modal response whereby increased BrdU and PCNA expression clustered with the dominant profile while increased expression of cellular stress and shift to glutamate cellular identity clustered with social subordinate and isolate profiles. Collectively, our results improve our understanding of how social experience reshapes the zebrafish brain through integrated changes in cell proliferation, cellular shift in neurotransmitter identity and regulation of cellular viability; thus, providing a potential mechanism for the maintenance of stable behavioral phenotypes in competitive social environments.

neuroscience↗

bioRxiv2023

The effects of social experience on host gut microbiome in male zebrafish (Danio rerio)

Although the gut and the brain vastly differ in physiological function, they have been interlinked in a variety of different neurological and behavioral disorders. The bacteria that comprise the gut microbiome communicate and influence the function of various physiological processes within the body including nervous system function. However, the effects of social experience in the context of dominance and chronic stress on gut microbiome remain poorly understood. Here, we examined whether social experience impacts the host zebrafish (Danio rerio) gut microbiome. We studied how social dominance during the first two weeks of social interactions changed the composition of zebrafish gut microbiome by comparing gut bacterial composition, diversity and relative abundance among socially dominant, submissive, social isolates, and control group-housed communal fish. Using amplicon sequencing of the 16S rRNA gene, we report that social dominance significantly affects host gut bacterial community composition but not bacterial diversity. At the genus-level, Aeromonas and unclassified Enterobacteriaceae relative abundance decreased in dominant individuals while commensal bacteria (e.g., Exiguobacterium and Cetobacterium) increased in relative abundance. Conversely, the relative abundance of Psychrobacter and Acinetobacter was increased in subordinates, isolates, and communal fish compared to dominant fish. The shift in commensal and pathogenic bacteria highlights the impact of social experience and the accompanying stress on gut microbiome with potentially similar effects in other social organisms. IMPORTANCEDisruptions in the gut microbiome negatively impact various systems in the body. Recently, the gut microbiome has been associated with neurological deficits in both behavioral and neurodegenerative disorders. Given the increasing prevalence in diagnosis of both neurological disease and behavioral disorders, researching the link between social behaviors and the gut microbiome is critical to better understand how the gut and the brain communicate during healthy and diseased states. Our research findings demonstrate the effects of social dominance and chronic stress on host gut microbiome composition. By identifying variations in bacterial relative abundance based on social experience and associated stress, a broader understanding of pathogenic (e.g., Enterobacteriaceae, Aeromonas) versus commensal communities (e.g., Exiguobacterium, Cetobacterium) and related host physiology can be inferred.

microbiology↗