A single injection of amphetamine or nicotine (as previously described) or eserine were able to induce a significant increase in the RNA levels of hippocampus but not in neocortex of rats. A pretreatment with α-MT, a specific inhibitor of the catecholamine synthesis, blocked the RNA increase produced by these drugs. These results suggest a common adrenergic mechanism for the effect of amphetamine, nicotine and eserine on hippocampal RNA levels.