Central distribution of oxytocin and vasopressin 1a receptors in juvenile Richardson’s ground squirrels

Abstract

Oxytocin and vasopressin are well‐conserved peptides important to the regulation of numerous aspects of social behavior, including sociality. Research exploring the distribution of the receptors for oxytocin (Oxtr) and for vasopressin (Avpr1a) in mammals has revealed associations between receptor distribution, sociality, and species’ mating systems. Given that sociality and gregariousness can be tightly linked to reproduction, these nonapeptides unsurprisingly support affiliative behaviors that are important for mating and offspring care. We localized these receptors in juvenile Richardson’s ground squirrel brains to determine whether distribution patterns of Oxtr and Avpr1a that are associated with promiscuous mating systems differ in rodents that also exhibit non‐reproductive affiliation. These squirrels are social, colonial, and engage in nepotistic alarm calling behavior and affiliation outside of a reproductive context. Juveniles are the most affiliative age‐class and are non‐reproductive; making them ideal for examining these associations. We found that juveniles had dense Oxtr binding in the dentate gyrus of the hippocampus, amygdala, lateral septum, bed nucleus of the stria terminalis and medial geniculate nucleus. Juveniles had low to modest levels of Avpr1a binding in the medial preoptic area, olfactory bulbs, nucleus accumbens, superior colliculus, and inferior colliculus. We noted Oxtr and Avpr1a binding in the social behavior neural network (SBNN), further supporting a role of these nonapeptides in modulating social behavior across taxa. Oxtr and Avpr1a binding was also present in brain regions important to auditory processing that have known projections to the SBNN. We speculate that these neural substrates may be where these nonapeptides regulate communication.

Characterization of oxytocin and vasopressin receptors in the Southern giant pouched rat and comparison to other rodents

“…Nonetheless, like the pouched rat, some species do not demonstrate sex differences in OTR or V1aR density. In particular, no evidence of a sex difference has been found for V1aR in prairie and montane voles ( 9 ), V1aR in the jerboa ( Jaculus orientalis ) ( 49 ), OTR and V1aR in Richardson’s ground squirrels ( 23 ), or OTR and V1aR in Mongolian gerbils ( 25 ). We note that OTR in the dorsal HPC appears to differ between the sexes in prairie voles ( 50 ), and V1aR can differ between sexes in prairie voles that experienced different rearing conditions ( 51 ).…”

“…We also found an unusual pattern of relatively light OTR binding in the LS compared to relatively dense binding in the BST. In most rodent species, if OTR density is abundant in the BST, it is also abundant in the LS (e.g., California mouse ( 17 ), deer mouse ( 17 ), Alston’s singing mouse ( 8 ), long-tailed singing mouse ( 8 ), Richardson’s ground squirrel ( 23 ), colonial ice rat ( 61 ), vlei rat ( 61 ); but see rat ( 52 )). The pattern of relatively dense binding in the BST but little in the LS has only been reported in two species thus far: the prairie vole ( 28 ) and the naked mole-rat ( 10 ).…”

“…These differences between the sexes are region-specific, and are thought to support sex-specific behaviors ( 16 ). However, other species lack sex-differences in receptor distribution in OTR or V1aR in the brain ( 9 , 23 – 25 ). Not surprisingly, sex differences are only observed if both sexes are studied, and they require measurement of purported sexually dimorphic brain regions.…”

Call‐specific patterns of neural activation in auditory processing of Richardson’s ground squirrel alarm calls

“…The experimenter was blind to the treatment group of each animal during enumeration. Regions were identified using anatomical landmarks (see Figure S2) using the Allen mouse brain atlas as a reference (Lein et al, 2007), and previously published Nissl‐stained sections of the Richardson's ground squirrel (Freeman, Hare, & Caldwell, 2019), since a Richardson's ground squirrel brain atlas does not exist. Therefore, some ground squirrel brain region boundaries may differ from those depicted in Figure 1.…”

“…Image credit: Allen Institute, http://atlas.brain -map. org (Lein et al, 2007) Nissl-stained sections of the Richardson's ground squirrel (Freeman, Hare, & Caldwell, 2019), since a Richardson's ground squirrel brain atlas does not exist. Therefore, some ground squirrel brain region boundaries may differ from those depicted in Figure 1.…”