- Abstract Two antibiotic tetracyclines, demeclocycline (DMC) and minocycline, share several biochemical and behavioral properties with lithium (Li). DMC inhibited both noradrenaline- and chloradenosine-sensitive cyclic AMP accumulation in rat cerebral cortical slices both in vitro and ex vivo following two weeks of chronic dietary treatment. Minocycline, a lipophilic tetracycline, produced similar results in vitro. Both DMC and minocycline reduced open-field activity levels in rats following acute treatment, four hours prior to testing. Moreover, both drugs inhibited amphetamine-induced hyperactivity in the open field. Chronic treatment with 0.4% and 0.8% dietary DMC for two weeks attenuated amphetamine hyperactivity without affecting baseline activity levels in the open field. Neither DMC nor minocycline attenuated apomorphine-induced stereotypy at doses that attenuated amphetamine hyperactivity, a profile which is similar to that of lithium. Unlike lithium, however, DMC did not reverse reserpine-induced hypoactivity.