Hippocampal microinfusion of oxytocin attenuates the behavioural response to stress by means of dynamic interplay with the glucocorticoid-catecholamine responses

Abstract

The neurohypophysial hormone oxytocin acts as a central nervous system neurotransmitter/neuromodulator. We evaluated the effects of oxytocin on behavioural responses to stress, as well as associated biophysiological responses, in a controlled, prospective animal model. The long-term effects of exogenous oxytocin microinjected to the hippocampus of male rats were assessed. Animals were exposed to predator scent stress and treated 1 h or 7 days later with oxytocin or vehicle. Behaviours were assessed with the elevated plus-maze and acoustic startle response tests, 7 days after microinjection and freezing behaviour upon exposure to a trauma-related cue on day 8. These data served for classification into behavioural response groups. Trauma cue response, circulating corticosterone and oxytocin, hippocampal expression of glucocorticoid and mineralocorticoid receptors, and oxytocin receptor mRNA levels were assessed. The interplay between oxytocin, corticosterone and norepinephrine was assessed. Microinfusion of oxytocin both immediately after predator scent stress exposure or 7 days later, after exposure to trauma cue significantly reduced the prevalence rates of extreme responders and reduced trauma cue freezing responses. Post-exposure treatment with oxytocin significantly corrected the corticosterone stress response, decreased glucocorticoid receptor expression and increased mineralocorticoid receptor expression in the hippocampus compared to vehicle treatment. High-dose corticosterone administration together with norepinephrine caused release of plasma oxytocin and hippocampal oxytocin receptor. Oxytocin is actively involved in the neurobiological response to predator scent stress processes and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety-related disorders.