Potentiation of total horizontal activity and ambulation in rats treated with combinations of beta-phenylethylamine and naloxone.

The effects of beta-phenylethylamine (PEA) (6.25-50 mg kg-1) and of naloxone (1-10 mg kg-1), administered alone and in combination, were studied in the rat. Adult, male rats were individually tested in a novel enclosure over a 30 min period, after administration of drugs. Measures of total horizontal activity, ambulation and rearing activity were counted automatically on the basis of interruptions of photobeams. In addition, observational data were collected, using behavioural categories which have previously been used to characterize the behavioural stereotypy syndrome induced by phenylethylamine in large doses. The results showed that certain combinations of phenylethylamine and naloxone produced striking increases in total horizontal activity and ambulation scores, but not in vertical activity scores. Furthermore, naloxone antagonized hyperreactivity and splayed-hindlimb components of the stereotypy syndrome induced by phenylethylamine, but not the head-weaving component. The behavioural specificity of the potentiation of total horizontal activity and ambulation by phenylethylamine in combination with naloxone is emphasized, and the enhancement of activity is contrasted with previous reports of the effects of naloxone administered in conjunction with d-amphetamine.