Glutamatergic projections from the substantia nigra pars reticulata to the dorsal raphe nucleus regulate male social hierarchies

Social hierarchy constitutes a fundamental organizational characteristic
among various social species, significantly influencing individual
survival, health, and reproductive success within these societies. Neurons
in the substantia nigra pars reticulata (SNr) exhibit extensive
connectivity with the dorsal raphe nucleus (DRN), a critical structure
implicated in social interaction, reward processing, and the establishment
of social rank. However, the specific neuronal types within the SNr, as
well as the associated neural circuits that regulate social dominance,
remain inadequately characterized. This study aims to elucidate the
crucial role of SNrGlu neurons in the establishment and maintenance of
social hierarchy in male mice. Employing fiber photometry, we observed
that the activation of SNrGlu neurons increased during the initiation of
effortful behaviors in the tube test. Further investigations revealed that
optogenetic activation or chemogenetic inhibition of the glutamatergic
neurons in the SNr induced upward or downward shifts in social ranks,
respectively. Additionally, our findings indicate that the activation of
SNr glutamatergic terminals in DRN elevated social status and reduces
anxiety levels in mice. Collectively, these results broaden our
understanding of the functions associated with SNr glutamatergic neurons
and underscore their critical role in regulating social hierarchy among
male mice. This work enhances our understanding of the functions of SNr
glutamatergic neurons in both physiological contexts and neurological
disorders.