Facilitatory effects of caerulein on hypothalamic defensive attack in cats.

Effects of intraventricularly microinjected caerulein (0.1, 1.0 and 10.0 micrograms) on the thresholds for hypothalamically elicited defensive attack and influences of haloperidol (0.5 mg/kg, i.p.) on the effects were studied in chronic cats. Directed attack and hissing were selected for threshold determination, and thresholds for these responses were measured under two situations: one with provocations by a human, and the other without such provocation. Results were as follows. (1) Caerulein lowered all thresholds in generally equal decrements and in a dose-related manner, accompanied by a general behavioral arousal. (2) Prior injection of haloperidol prevented the effects of caerulein, suggesting an antagonism-like interaction between haloperidol and caerulein. (3) Observed facilitatory effects of caerulein on the hypothalamic defensive attack were very similar to those observed with dopamine (DA) agonists such as methamphetamine and apomorphine and opposite to those with DA antagonists such as haloperidol and chlorpromazine. These findings suggest that caerulein exerts its facilitatory effects on the excitability of the ventromedial hypothalamic nucleus through its synergistic interaction with DA.