Robyn J. McQuaid

A paradoxical association of an oxytocin receptor gene polymorphism: early-life adversity and vulnerability to depression.

Several prosocial behaviors may be influenced by the hormone oxytocin. In line with this perspective, the oxytocin receptor (OXTR) gene single nucleotide polymorphism (SNP), rs53576, has been associated with a broad range of social behaviors. In this regard, the G allele of the OXTR SNP has been accompanied by beneficial attributes such as increased empathy, optimism, and trust. In the current study among university students (N = 288), it was shown that early-life maltreatment was associated with depressive symptoms, and that the OXTR genotype moderated this relationship, such that under high levels of childhood maltreatment, only individuals with GG/GA genotype demonstrated increased depressive symptomatology compared to those with the AA genotype. In addition, the role of distrust in mediating the relation between childhood maltreatment and depression seemed to be more important among G allele carriers compared to individuals with the AA genotype. Thus, a breach in trust (i.e., in the case of early-life abuse or neglect) may have a more deleterious effect among G carriers, who have been characterized as more prosocial and attuned to social cues. The data suggested that G carriers of the OXTR might favor social sensitivity and thus might have been more vulnerable to the effects of early-life adversity.

Making room for oxytocin in understanding depression

Depression is accompanied by an array of neurobiological variations, including altered HPA axis activity, monoamine, growth factor and inflammatory immune functioning. In addition, a recent perspective has entertained the possible role for oxytocin in depressive disorders. Given the involvement of oxytocin in prosocial behaviors such as attachment, affiliation, trust, and social support seeking, it is not surprising this neuropeptide might be involved in the development or maintenance of depressive disorders. This view is supported by evidence that oxytocin interacts with various neuroendocrine, neurotransmitter, and inflammatory processes that have previously been implicated in depression. Thus, it might be profitable to consider the contribution of oxytocin in the context of several neurobiological changes provoked by stressors. The current review examines the relation between oxytocin and depression with a specific focus on the interactions between the oxytocinergic system and stressor-provoked biological and psychosocial responses. The possibility is also considered that oxytocin might increase the salience of social cues, such that positive or negative experiences result in exaggerated responses that may influence affective states.

Social Agonistic Distress in Male and Female Mice: Changes of Behavior and Brain Monoamine Functioning in Relation to Acute and Chronic Challenges

Stressful events promote several neuroendocrine and neurotransmitter changes that might contribute to the provocation of psychological and physical pathologies. Perhaps, because of its apparent ecological validity and its simple application, there has been increasing use of social defeat (resident-intruder) paradigms as a stressor. The frequency of stress-related psychopathology is much greater in females than in males, but the typical resident-intruder paradigm is less useful in assessing stressor effects in females. An alternative, but infrequently used procedure in females involves exposing a mouse to a lactating dam, resulting in threatening gestures being expressed by the resident. In the present investigation we demonstrated the utility of this paradigm, showing that the standard resident-intruder paradigm in males and the modified version in females promoted elevated anxiety in a plus-maze test. The behavioral effects that reflected anxiety were more pronounced 2 weeks after the stressor treatment than they were 2 hr afterward, possibly reflecting the abatement of the stress-related of hyper-arousal. These treatments, like a stressor comprising physical restraint, increased plasma corticosterone and elicited variations of norepinephrine and serotonin levels and turnover within the prefrontal cortex, hippocampus and central amygdala. Moreover, the stressor effects were exaggerated among mice that had been exposed to a chronic or subchronic-intermittent regimen of unpredictable stressors. Indeed, some of the monoamine changes were more pronounced in females than in males, although it is less certain whether this represented compensatory changes to deal with chronic stressors that could result in excessive strain on biological systems (allostatic overload).

Distress of ostracism: Oxytocin receptor gene polymorphism confers sensitivity to social exclusion

A single-nucleotide polymorphism on the oxytocin receptor gene (OXTR), rs53576, involving a guanine (G) to adenine (A) substitution has been associated with altered prosocial features. Specifically, individuals with the GG genotype (i.e. the absence of the polymorphism) display beneficial traits including enhanced trust, empathy and self-esteem. However, because G carriers might also be more socially sensitive, this may render them more vulnerable to the adverse effects of a negative social stressor. The current investigation, conducted among 128 white female undergraduate students, demonstrated that relative to individuals with AA genotype, G carriers were more emotionally sensitive (lower self-esteem) in response to social ostracism promoted through an on-line ball tossing game (Cyberball). Furthermore, GG individuals also exhibited altered blood pressure and cortisol levels following rejection, effects not apparent among A carriers. The data support the view that the presence of the G allele not only promotes prosocial behaviors but also favors sensitivity to a negative social stressor.

Environmental enrichment in male CD-1 mice promotes aggressive behaviors and elevated corticosterone and brain norepinephrine activity in response to a mild stressor

Housing rodents in an enriched environment (EE) has been typically considered to have positive effects on well-being and cognitive functioning of the animals. However, in some strains of mice, EEs have also been reported to elicit aggression and to promote stress-related outcomes. In the current investigation, we examined whether environmental enrichment would elicit aggression among CD-1 male mice and thus sensitize responses to a subsequent mild stressor. It was first observed that mice housed in an EE for 2 weeks displayed more aggressive behaviors than did mice that had been housed in a standard environment (SE). In the second experiment, it was noted that after 4 weeks of EE or SE housing, mice exhibited comparable plasma corticosterone concentrations as well as levels of brain norepinephrine and its metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), in the absence of a challenge. However, upon exposure to mild stressor (placement in a novel cage), relative to their SE counterparts, EE mice were more active and displayed higher plasma corticosterone concentrations and enhanced MHPG accumulation in the prefrontal cortex and hippocampus. It seems that enrichment in male CD-1 mice promotes aggression, and may sensitize biological processes, possibly increasing vulnerability to stressor-related outcomes.

Chronic Pharmacological mGluR5 Inhibition Prevents Cognitive Impairment and Reduces Pathogenesis in an Alzheimer Disease Mouse Model

Beta-amyloid (Aβ) oligomers contribute to the pathophysiology of Alzheimer disease (AD), and metabotropic glutamate receptor 5 (mGluR5) has been shown to act as a receptor for both Aβ oligomers and cellular prion proteins. Furthermore, the genetic deletion of mGluR5 in an APPswe/PS1ΔE9 mouse model of AD improves cognitive function and reduces Aβ plaques and Aβ oligomer concentrations. Here, we show that chronic administration of the orally bioavailable mGluR5-selective negative allosteric modulator CTEP, which is similar in structure, potency, and selectivity to Basimglurant (RO4917523), which is currently in phase II clinical development for major depressive disorder and fragile X syndrome, reverses cognitive decline in APPswe/PS1ΔE9 mice and reduces Aβ plaque deposition and soluble Aβ oligomer concentrations in both APPswe/PS1ΔE9 and 3xTg-AD male mice. These findings suggest that CTEP or its analogue Basimglutant might potentially be an effective therapeutic for the treatment of AD patients.

The differential impact of social defeat on mice living in isolation or groups in an enriched environment: plasma corticosterone and monoamine variations

Social defeat in mice is a potent stressor that promotes the development of depressive- and anxiety-like behaviours, as well as variations of neuroendocrine and brain neurotransmitter activity. Although environmental enrichment may protect against some of the adverse behavioural and biological effects of social defeat, it seems that, among male group-housed mice maintained in an enriched environment (EE), aggressive behaviours may be more readily instigated, thus promoting distress and exacerbating psychopathological features. Thus, although an EE can potentially have numerous beneficial effects, these may depend on the general conditions in which mice were raised. It was observed in the current investigations that EE group-housed BALB/cByJ mice displayed increased anxiety-like behaviours compared to their counterparts maintained in a standard environment (SE). Furthermore, in response to social defeat, EE group-housed male mice exhibited decreased weight gain, exaggerated corticosterone elevations and altered hippocampal norepinephrine utilization compared to their SE counterparts. These effects were not apparent in the individually housed EE mice and, in fact, enrichment among these mice appeared to buffer against serotonin changes induced by social defeat. It is possible that some potentially beneficial effects of enrichment were precluded among group-housed mice, possibly owing to social disturbances that might occur in these conditions. In fact, even if social interaction is an essential feature of enrichment, it seems that some of the positive effects of this housing condition might be optimal when mice are housed individually, particularly with regard to buffering the effects of social defeat.

Environmental enrichment influences brain cytokine variations elicited by social defeat in mice.

Environmental enrichment may protect against some of the adverse behavioural and biological effects of stressors. However, unlike the effects seen in some species, among male mice housed in groups, enrichment may alter social stability, encourage competition and aggression, and thus promote the establishment of a stressful environment. A potent psychosocial stressor such as social defeat in mice promotes brain neurochemical changes as well as pro-inflammatory cytokine variations in the prefrontal cortex (PFC) and hippocampus. The present investigation demonstrated that enrichment in group-housed male mice, even in the relatively nonaggressive, although highly anxious BALB/cByJ strain encouraged the effects of a repeated social defeat stressor experienced 4 weeks later, especially with respect to corticosterone as well as hippocampal corticotropin-releasing hormone (CRH) and interleukin (IL)-6 variations. Moreover, within the hippocampus, enrichment itself was accompanied by modest reductions in the expression of the IL-1β receptor (IL-1r1). Thus, it seems that living in an enriched environment among group-housed male mice might promote a stressful environment that enhances basal hippocampal CRH and cytokine variations and increased vulnerability to further changes upon subsequent exposure to a social stressor.

The Role of the Val66Met Polymorphism of the Brain Derived Neurotrophic Factor Gene in Coping Strategies Relevant to Depressive Symptoms.

Disturbances of brain derived neurotrophic factor (BDNF) signalling have been implicated in the evolution of depression, which likely arises, in part, as a result of diminished synaptic plasticity. Predictably, given stressor involvement in depression, BDNF is affected by recent stressors as well as stressors such as neglect experienced in early life. The effects of early life maltreatment in altering BDNF signalling may be particularly apparent among those individuals with specific BDNF polymorphisms. We examined whether polymorphisms of the Val66Met genotype might be influential in moderating how early-life events play out with respect to later coping styles, cognitive flexibility and depressive features. Among male and female undergraduate students (N = 124), childhood neglect was highly related to subsequent depressive symptoms. This outcome was moderated by the BDNF polymorphism in the sense that depressive symptoms appeared higher in Met carriers who reported low levels of neglect than in those with the Val/Val allele. However, under conditions of high neglect depressive symptoms only increased in the Val/Val individuals. In effect, the Met polymorphism was associated with depressive features, but did not interact with early life neglect in predicting later depressive features. It was further observed that among the Val/Val individuals, the relationship between neglect and depression was mediated by emotion-focused styles and diminished perceived control, whereas this mediation was not apparent in Met carriers. In contrast to the more typical view regarding this polymorphism, the data are consistent with the perspective that in the presence of synaptic plasticity presumably associated with the Val/Val genotype, neglect allows for the emergence of specific appraisal and coping styles, which are tied to depression. In the case of the reduced degree of neuroplasticity expected in the Met carriers, early life adverse experiences are not tied to coping styles, and hence less likely to be translated into depressive states.

The moderating role of an oxytocin receptor gene polymorphism in the relation between unsupportive social interactions and coping profiles: implications for depression

Oxytocin is a hormone that is thought to influence prosocial behaviors and may be important in modulating responses to both positive and negative social interactions. Indeed, a single nucleotide polymorphism, rs53576, of the oxytocin receptor gene (OXTR) has been associated with decreased trust, empathy, optimism, and social support seeking, which are important components of coping with stressors. In the current study, conducted among undergraduate students (N = 225), it was shown that parental and peer social support was related to fewer depressive symptoms through elevated problem-focused coping and lower emotion-focused coping, and these effects were independent of the OXTR polymorphism. Unsupportive social interactions from parents were associated with more severe depressive symptoms through the greater use of emotion-focused coping, and this relation was moderated by the OXTR genotype. Specifically, individuals who carried the polymorphism on one or both of their alleles demonstrated increased emotion-focused coping following unsupportive responses compared to those without the polymorphism. Likewise, lower problem-focused coping mediated the relation between parental and peer unsupportive responses to depressive symptoms, but this mediated relation was only evident among carriers of the polymorphism. These findings suggest that carrying this OXTR polymorphism might favor disadvantageous coping styles in the face of negative social interactions, which in turn are linked to poor mood. Regardless of genotype, parental, and peer social support are fundamental in determining stress-related coping and well-being.