Density‐induced social stress alters oxytocin and vasopressin activities in the brain of a small rodent species

Abstract

It is known that social stress could alter oxytocin (OT) and arginine‐vasopressin (AVP) expression in specific regions of brains which regulate the aggressive behavior of small rodents, but the effects of density‐induced social stress are still unknown. Brandt's voles (Lasiopodomys brandtii) are small herbivores in the grassland of China, but the underlying neurological mechanism of population regulation is still unknown. We tested the effects of housing density of Brandt's voles on OT/AVP system with physical contact (allowing aggression) and without physical contact (not allowing aggression) under laboratory conditions. Then, we tested the effects of paired‐aggression (no density effect) of Brandt's voles on OT/AVP system under laboratory conditions. We hypothesized that high density would increase aggression among animals which would then increase AVP but reduce OT in brains of animals. Our results showed that high housing density induced more aggressive behavior. We found high‐density‐induced social stress (with or without physical contact) and direct aggression significantly increased expression of mRNA and protein of AVP and its receptor, but decreased expression of mRNA and protein of OT and its receptor in specific brain regions of voles. The results suggest that density‐dependent change of OT/AVP systems may play a significant role in the population regulation of small rodents by altering density‐dependent aggressive behavior.

Population Variation Altered Aggression-associated Oxytocin and Vasopressin Expressions in Brains of Brandt’s Voles in Field Conditions

“…In this study, we found that, in two eld experiments, high population density was associated with increased AVP/AVPR expression, and decreased the OT/OTR expression, which correspond well to the increased frequency of aggression and chasing behaviors. These results are exactly consistent with our previous study under laboratory condition [12]. In another study, we found aggression of Brandt's voles was reduced by injection of OT but increased by injection of OT antagonists and OTR antagonists [24].…”

“…crowding or aggression, food or space shortage). Our previous study indicated that high housing density could decrease OT or its receptor but increase AVP of its receptors [12], but it is not clear whether such associations operate in eld conditions. In this study, we showed that high population density increased AVP/AVPR expression but decreased the OT/OTR expression, and aggression behavior of voles was also increased in semi-natural conditions.…”

“…Based on manipulation experiments of OT or its receptor of voles [24] as well as many previous studies on rodents (see above), the high density induced decrease of OT or increase of AVP could increase aggressive behaviors of voles. Based on our ghting experiments of Brandt's voles in the laboratory [12], aggression behavior as a stressor would further decrease OT expression, but increase AVP expression. Thus, the reciprocal facilitation between OT/AVP expression and aggressive behavior could be an important component of population regulation in small rodents (Fig.…”

“…High density is often accompanied by an increase in crowding, unfamiliar encounters and shortages of food or shelter, which may act as social or physiological stressors in animals. Our recent study indicates that under laboratory condition, high density as an environmental stressor could decrease OT expression, but increase AVP expression of Brandt's voles; ghting could decrease OT expression but increase AVP expression of voles [12]. In another experiment, injection of OT in brains reduced aggression of Brandt's voles, but injection OT and OTR antagonists increased aggression of Brandt's voles [24].…”

“…Both extrinsic and intrinsic factors would affect their population uctuations [31][32][33]. Our previous study on Brandt's voles in laboratory condition demonstrated that at high density, AVP expression increased, and OT expression decreased in association with the observed increase of aggression behavior [12]. We now test whether such associations occur in eld conditions.…”