![]() ![]() ![]() In fact, recent publications have shown that 4 weeks social isolation leads to increased passive coping in female prairie voles ( Grippo et al, 2007a, b). Thus, we predicted that even a short separation from a partner may be aversive and lead to an alteration in emotionality as reflected by increased passive stress-coping or anxiety-like behavior in male voles. Although the formation of pair bonds is thought to be based on brain circuitries mediating reward and reinforcement ( Young and Wang, 2004 Nair and Young, 2006 Aragona et al, 2003, 2006), an aversion to prolonged partner separation may help preserve the bond over time by inducing proximity-seeking behaviors. Unlike 95% of all mammalian species, prairie voles are socially monogamous, forming enduring and selective pair bonds with their mates ( Carter and Getz, 1993). Prairie voles ( Microtus ochrogaster) have served as an excellent animal model for examining the neurobiological mechanisms underlying social bonding ( Carter and Getz, 1993 Carter et al, 1995 Aragona and Wang, 2004) and for investigating the physiological consequences of social loss ( Grippo et al, 2007a, b). Thus, understanding the neurobiological consequences of partner loss, particularly with respect to increased susceptibility to depression, may be informative for developing strategies for coping with the loss of a loved one. In humans, bereavement is a highly disruptive experience that is usually followed by a painful period of acute grief ( Shear and Shair, 2005). In contrast, the absence or sudden disruption of those bonds increases susceptibility to diseases ( House et al, 1990 Kirschbaum et al, 1995 Uchino et al, 1996 Capitanio et al, 1998 for review see Biondi and Picardi, 1996 DeVries et al, 2003), including depression ( Zisook et al, 1997 Watanabe et al, 2004 Grippo et al, 2007a, b). There is increasing evidence that social bonds have a positive impact on health and buffer against stressors ( Kikusui et al, 2006). Hence, the prairie vole model may provide insights into brain mechanisms involved in the psychopathological consequences of partner loss. We speculate that the CRF system may mediate an aversive affect following separation from the female partner, which may facilitate proximity seeking between the pair-bonded individuals. Furthermore, pairing with a female was associated with elevated CRF mRNA in the bed nucleus of the stria terminalis, and partner loss elicited a pronounced increase in circulating corticosteroid and adrenal weight. Both CRF type 1 and 2 receptors were involved in the emergence of passive stress-coping behavior. This effect was abolished by long-term intracerebroventricular infusion of a nonselective corticotropin-releasing factor (CRF) receptor antagonist without disrupting the bond itself. Following 4 days of separation from the female but not the male partner, experimental males displayed increased passive stress-coping. Elevated plus-maze, forced swim, and tail suspension tests were used to assess anxiety-like and passive stress-coping behaviors indicative of depressive-like behavior. After 5 days, half of the males of each group were separated from the partner. Male prairie voles were paired with a novel female or male sibling. As the monogamous prairie vole forms enduring, selective pair bonds with the mating partner, they provide an animal model to study the physiological consequences of pair bonding and, thus, the loss of the bonded partner. Disruption of social bonds through separation or death often results in profound grieving, depression, and physical illness. Social relationships significantly influence physiology and behavior, including the hypothalamo–pituitary–adrenal axis, anxiety, and mental health. ![]()
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