Distribution of vasopressin in the brain of the eusocial naked mole‐rat

Abstract

Naked mole-rats are eusocial rodents that live in large subterranean colonies in which one queen breeds with one to three males. All other animals are nonbreeding subordinates. The external features of male and female subordinates, including their genitalia, are remarkably monomorphic, as is their behavior. Because vasopressin (VP) is associated with social behaviors and sex differences in other species, its distribution in naked mole-rats was of interest. We used immunohistochemistry to examine VP in the brains of subordinate and breeding naked mole-rats of both sexes. As in other mammals, VP-immunoreactive (-ir) somata were found in the paraventricular (PVN) and supraoptic nuclei (SON) and VP-ir projections from these nuclei ran through the internal and external zone of the median eminence. However, naked mole-rats had very few VP-ir cells in the bed nucleus of the stria terminalis (BST) and none in the suprachiasmatic nucleus (SCN); the extensive network of fine-caliber VP-ir fibers usually seen in projection sites of the BST and SCN were also absent. Equally unexpected was the abundance of large-caliber VP-ir fibers in the dorsomedial septum. VP immunoreactivity was generally similar in all groups, with the exception of VP-ir cell number in the dorsomedial hypothalamus (DMH). Breeders had a population of labeled cells in the DMH that was absent, or nearly absent, in subordinates. Future studies on the function of VP in these areas are needed to determine how the atypical distribution of VP immunoreactivity relates to eusociality and the unusual physiology of naked mole-rats.

Social control of brain morphology in a eusocial mammal

“…If sexual dimorphisms do exist in the naked mole-rat brain, however, they appear to be more subtle than the effects of social status, which are detectable at a gross level using even small sample sizes. Taken together with reports on spinal motoneurons innervating perineal muscles (21,23), and vasopressin innervation of the naked mole-rat brain (19), in which no sex differences were found, these data suggest that neural sex differences are attenuated in naked mole-rats compared with other mammals.…”

“…Increases in immediateearly gene expression are observed in gonadotrophin-releasing hormone (GnRH) neurons within minutes of a relevant social stimulus, suggesting that this is a very early event in a molecular cascade presumably leading to longer-term changes (16). Breeding status is also reflected in altered neuropeptide expression in naked mole-rats, with subordinates exhibiting less vasopressin in the dorsomedial hypothalamus (19). GnRH neurons have not yet been examined in naked mole-rats, but subordinates release less pituitary luteinizing hormone in response to a GnRH pulse than do breeders (47).…”

“…Studies of the naked mole-rat brain have been conducted only very recently and have focused on the organization of somatosensory cortex and the visual system (e.g., 17, 18). We recently described the distribution of vasopressin, a neuropeptide associated with social behaviors, in the naked mole-rat brain (19). Morphometric comparisons between the brains of breeders and subordinates, however, have not been made.…”

Exploring Spatiotemporal Organization of SCN Circuits

“…The study of core-shell functional specializations has been hampered by the fact that there is significant diversity among species in the peptidergic phenotypes of SCN cells (Morin and Allen 2006). The SCN shell contains neurons expressing arginine vasopressin (AVP) in most species, including mouse, rat, hamster, lemur and humans, although not in mink (Larsen and Mikkelsen 1993) or mole rat (Rosen et al 2007). The SCN core is rich in vasoactive intestinal polypeptide (VIP) and gastrin-releasing peptide (GRP) in mouse, rat, and hamster (Morin et al 1992;Moore 1996;Abrahamson and Moore 2001).…”

Hormones, reproduction and disease in the longest-lived rodent: the naked mole rat

“…The distribution pattern of vasopressin (a neuropeptide involved in social recognition memory, i.e. the ability to remember a previously-encountered conspecic, at the base of all mammalian social relationships 25 ) immunoreactivity in the dorsomedial septum of the brain of NMR, 26 suggests that his could be related to social recognition memory. The neuropeptide oxytocin, which also modulates social bonding and other social behaviors in many vertebrates, was found to have a localization pattern in the central nervous system on NMR subordinates similar to other species.…”