The effect of lysine-8-vasopressin (300 mU/kg b.w.) has been tested in a single-trial step-down passive avoidance test. Vasopressin treatment resulted in an improvement of step-down latency in normal rats, but this action disappeared when the animals were pretreated with 80 mg/kg alpha-methyl-p-tyrosine (α-MT). Vasopressin treatment decreased the hypothalamic, septal and striatal dopamine (DA) levels. Following vasopressin, the turnover of norepinephrine (NE) increased in the hypothalamus, as did these of DA in the septum and striatum. The data suggest that the cerebral catecholaminergic system might be one of the important mediators of the behavioural action of vasopressin.
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