Oxytocin receptor distribution reflects social organization in monogamous and polygamous voles.

TLDR

Oxytocin is implicated in affiliative behaviors such as parental care, grooming, and sex behavior. The study demonstrates that vole species with differing social affiliations display contrasting patterns of oxytocin receptor expression in the brain. The authors used in vitro receptor autoradiography with an iodinated oxytocin analogue to map receptor binding in prairie and montane voles. Prairie voles show high oxytocin receptor density in limbic and cortical regions, while montane voles have receptors mainly in septal and hypothalamic areas, a pattern replicated in pine and meadow voles, and receptor distribution in montane voles shifts within 24 h of parturition, suggesting that differential oxytocin receptor expression may drive species‑specific social bonding.

Abstract

The neuropeptide oxytocin has been implicated in the mediation of several forms of affiliative behavior including parental care, grooming, and sex behavior. Here we demonstrate that species from the genus Microtus (voles) selected for differences in social affiliation show contrasting patterns of oxytocin receptor expression in brain. By in vitro receptor autoradiography with an iodinated oxytocin analogue, specific binding to brain oxytocin receptors was observed in both the monogamous prairie vole (Microtus ochrogaster) and the polygamous montane vole (Microtus montanus). In the prairie vole, oxytocin receptor density was highest in the prelimbic cortex, bed nucleus of the stria terminalis, nucleus accumbens, midline nuclei of the thalamus, and the lateral aspects of the amygdala. These brain areas showed little binding in the montane vole, in which oxytocin receptors were localized to the lateral septum, ventromedial nucleus of the hypothalamus, and cortical nucleus of the amygdala. Similar differences in brain oxytocin receptor distribution were observed in two additional species, the monogamous pine vole (Microtus pinetorum) and the polygamous meadow vole (Microtus pennsylvanicus). Receptor distributions for two other neurotransmitter systems implicated in the mediation of social behavior, benzodiazepines, and mu opioids did not show comparable species differences. Furthermore, in the montane vole, which shows little affiliative behavior except during the postpartum period, brain oxytocin receptor distribution changed within 24 hr of parturition, concurrent with the onset of maternal behavior. We suggest that variable expression of the oxytocin receptor in brain may be an important mechanism in evolution of species-typical differences in social bonding and affiliative behavior.