MECAMYLAMINE REVERSES PHYSOSTIGMINE-INDUCED ATTENUATION OF SCOPOLAMINE-INDUCED HYPERACTIVITY

It has previously been demonstrated that the muscarinic antagonist sco polamine induces hyperactivity in rodents, which is reversed by physos tigmine but not by directly acting agonists such as pilocarpine. This may suggest that non-muscarinic actions of physostigmine may be respon sible for its reversal of scopolamine-induced hyperactivity. We have f ound, in male Wistar rats, whose activity was measured on electromagne tic detector plates, that the central nicotinic receptor antagonist me camylamine (3 mg/kg) reverses the blockade of scopolamine-induced beha vioural activation induced by physostigmine. This suggests that activa tion of nicotinic receptors can counteract the effects of muscarinic b lockade. Interestingly, however, treatment with nicotine does not bloc k scopolamine-induced hyperactivity, suggesting that the exogenous and endogenous ligands may have different receptor or neuronal substrates .