Anxiety and Stress Responses in Female Oxytocin Deficient Mice

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Abstract
Oxytocin is believed to attenuate the response of the hypothalamic-pituitary-adrenal axis to stress and to be anxiolytic. Stressors with a psychological component evoke both central and peripheral secretion of oxytocin in laboratory rodents. Oxytocin gene deletion mice provide a novel way to understand the role of oxytocin in stress and anxiety-related behaviours. We present our experience with female oxytocin deficient mice that were tested in an elevated plus maze (EPM), a behavioural test of anxiety, or exposed to psychogenic stressors (platform shaker or novel environment). Oxytocin-deficient mice not only displayed more anxiety-related behaviour, but also released more corticosterone after a psychogenic stressor and manifested greater stress-induced hyperthermia compared to wild-type mice. The diurnal variation of corticosterone and the response of corticosterone to corticotropin-releasing factor were not significantly different between genotypes. We also measured Fos-immunoreactive protein, an index of neuronal activation, in the medial amygdala of female mice after EPM testing. The medial amygdala is important for processing of psychogenic stress and anxiety and also contains oxytocin pathways and oxytocin receptors. The expression of Fos in the medial amygdala of mice not exposed to the EPM was not different between genotypes. Following EPM exposure, Fos expression was greater in oxytocin null compared to wild-type mice. Our findings support the hypothesis that central oxytocin is anxiolytic, and attenuates the stress response to psychogenic provocation in female mice.