Centrally acting non-narcotic antitussives prevent hyperactivity in mice: Involvement of GIRK channels

We have previously reported that centrally acting non-narcotic antitussives inhibited G protein-coupled inwardly rectifying potassium (GIRK) channel-activated currents, and that the antitussives had multiple pharmacological actions on various models of intractable brain diseases in rodents. In this study, the question of whether these antitussives inhibit drug-induced hyperactivity in mice was investigated. Antitussives, such as cloperastine and tipepidine, at cough suppressant doses, inhibited an increase in ambulation of mice neonatally treated with 6-hydroxydopamine. In addition, all antitussives studied inhibited an increase in methamphetamine-induced hyperactivity in mice. Methylphenidate, which is used for treatment of ADHD, inhibited 6-hydroxydopamine-lesion-induced, but not methamphetamine-induced, hyperactivity in mice. By the rota-rod test, the drugs had little effect on motor coordination of the hyperactive mice. Significant correlation was found between the ameliorating effects of antitussives on methamphetamine-induced hyperactivity and their inhibitory actions on GIRK channel currents (coefficient factor, 0.998). Furthermore, tertiapin, a GIRK channel blocker, prevented an increase in methamphetamine-induced hyperactivity of mice. These results demonstrated that antitussive drugs (cloperastine, tipepidine and caramiphen) possessing inhibitory action on GIRK channels inhibit drug-induced hyperactivity in mice, suggesting that such antitussives may potentially be therapeutic for patients with ADHD.