Behavioral effects of amantadine, especially on abnormal behavior in mice and rats, were reevaluated, in comparison with those of tricyclic antidepressants, methamphetamine and L-DOPA. 1) Amantadine at 10~50 mg/kg, i.p., tended to decrease ambulation and rearing in rats and mice. The drug at 50 mg/kg, i.p., caused piloerection and hyperirritability and at doses over 80 mg/kg, i.p., it impaired coordinated motor activity in rats. 2) Amantadine inhibited methamphetamine-induced hyperactivity, but apomorphine-induced stereotyped behavior was unaffected in rats. 3) Amantadine was equipotent to imipramine in suppressing haloperidol-induced catalepsy in rats, but L-DOPA was without effect. On the other hand, amantadine was 40 and 400 times as potent as imipramine and L-DOPA, respectively, in suppressing Δ9-tetrahydrocannabinol (THG)-induced catalepsy in rats. 4) Amantadine was as potent as imipramine in suppressing the muricide of olfactory bulbectomized rats, but was 3.5, 8.8 and 225.5 times as potent as methamphetamine, imipramine and L-DOPA, respectively, in inhibiting THC-induced reversible muricide in rats. 5) Amantadine at 50 mg/kg did not elicit circling behavior in the rat with unilateral nigral lesion induced by 6-hydroxydopamine. 6) Amantadine at high doses caused irritable aggression characterized by squealing in rats pretreated with intraventricular 6-hydroxydopamine. The most important characteristic of amantadine is its prominent effect suppressing the THC-induced catalepsy and muricide. This may be a reflection of the feature of amantadine activating the dopaminergic as well as the serotonergic systems.
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