Memory facilitation with posttrial injection of oxotremorine and physostigmine in mice.

The immediate posttrial injection of oxotremorine (0.125, 0.250 and 0.500 muMol/kg i.p.) and equimolecular doses of physostigmine can facilitate the retention of a passive avoidance response in mice. Injections given 10 min after training also significantly facilitate retention, but injections given 30 or 120 min after training do not affect retention. These findings suggest an action of oxotremorine and physostigmine on mechanisms involved in memory storage. The enhanced retention produced by oxotremorine and physostigmine was blocked by pretreatment with atropine (2 muMol/kg, 20 min, i.p.) but was not affected by methylatropine (2 muMol/kg, 20 min, i.p.). The retention was not modified by posttrial injection of metoxotremorine (0.25 muMol/kg i.p.) or neostigmine (0.250 muMol/kg i.p.), quaternary analogs of oxotremorine and physostigmine, respectively. The results suggest a central action of both cholinergic agents attributable to an activation of muscarinic brain receptors.