Physiological role of the ascending monoaminergic system in hypothalamo-hypophysial responses to emotional stress

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Effects of monoaminergic receptor antagonists or a benzodiazepine were studied on neuroendocrine responses to fear stimuli of anxiety-producing novel stimuli in male Wistar rats.1.Dopaminergic D1 receptors were found to mediate facilitatory vasopressin response to noxious stimuli but not the suppressive vasopressin response to conditioned fear stimuli.2.Anxiogenic novel environmental stimuli were shown to suppress vasopressin secretion.3.Histaminergic H2 receptors were shown to mediate the suppressive vasopressin response to novel stimuli and to inhibit, in an activity-dependent manner, the facilitatory oxytocin response to the stimuli.4.The noradrenergic system was demonstrated to mediate the responses in vasopressin, oxytocin and prolactin secretion to conditioned fear stimuli but not to the responses to unconditioned fear stimuli or anxiogenic novel environmental stimuli.5.Chlordiazepoxide, one of the benzodiazepines which are known to ameliorate an anxiety state as a result of modulating noradrenergic neuron activity, was found to block the responses in vasopressin and oxytocin secretion to unconditioned or conditioned fear stimuli but not the responses to anxiety-producing novel environmental stimuli.6.Serotonergic 5-HT_<1A> receptors were demonstrated to be involved in the vasopressin and oxytocin responses to conditioned fear stimuli but not to novel stimuli.