Effects of the opiate antagonist naloxone upon hypothalamically elicited affective defense behavior in the cat.

The opiate antagonist naloxone hydrochloride was employed in order to determine whether endogenous opioids play a role in the control of affective defense behavior elicited from the medial hypothalamus in the cat. The effects of naloxone upon quiet biting attack behavior elicited from the lateral hypothalamus were also assessed. A comparison of the differences in response latencies or thresholds before and after naloxone (i.p.) administration was made. Naloxone (1, 4 and 10 mg/kg) was found to significantly facilitate affective defense behavior in a dose- and time-dependent manner. The duration of facilitation ranged from 30 min after a 1 mg/kg injection to 180 min after a 10 mg/kg injection. The data also suggest that the effects of naloxone upon affective defense behavior are opposite to those seen with quiet biting attack. In two animals, quiet biting attack behavior was suppressed for 30 min following a 10 mg/kg injection of naloxone. Naloxone was also administered to cats in which hypothalamic stimulation elicited predatory responses coupled with components of affective defense behavior. In these cases, naloxone was ineffective in altering latencies for this 'mixed' response. These findings suggest that the opiate peptide system selectively inhibits affective defense behavior elicited from the medial hypothalamus of the cat.