Effects of agonists and antagonists of cholinergic receptors on self-stimulation of the medial prefrontal cortex of the rat.

The effects of agonists and antagonists of muscarinic and nicotinic receptors on self-stimulation (SS) of the medial prefrontal cortex (MPC) were investigated. Rats, implanted chronically with monopolar electrodes in the MPC, received subcutaneous injections of nicotine (0.2, 0.4 and 0.8 mg/kg), mecamylamine (2.0, 4.0 and 8.0 mg/kg), pilocarpine (0.5, 1.0, 2.0 and 4.0 mg/kg), scopolamine (0.05, 0.1, 0.2, 0.4 and 0.8 mg/kg) and physostigmine (0.1, 0.2 and 0.4 mg/kg). In order to assess the possible non-specific effects of drugs such as sedation or motor dysfunction, spontaneous locomotor activity (SLA) was used as control. In those groups of rats in which the drugs produced an effect on SS, an operant behaviour for drinking (DB) on an FR-10 schedule was also used as control. Nicotine and mecamylamine had no effect on SS. Both pilocarpine and physostigmine produced a decrease in SS, SLA and DB. Scopolamine, on the contrary, produced a dose-related decrease on SS rate, which was accompanied by a facilitatory effect on SLA and DB. These results suggest that only muscarinic receptors could play a specific role on SS of the MPC.