THE ROLE OF THE MEDIAL PREFRONTAL CORTEX OF RATS IN SHORT-TERM-MEMORYFUNCTIONING - FURTHER SUPPORT FOR INVOLVEMENT OF CHOLINERGIC, RATHER THAN DOPAMINERGIC MECHANISMS

The putative involvement of the dopaminergic innervation of the medial part of the prefrontal cortex (PFC) in short-term memory functioning was investigated by evaluating the effects of local infusions of dopam inergic drugs into the ventral part of the medial PFC of rats in an op erant delayed-matching-to-position (DMTP) task. Two separate groups of rats were tested after bilateral microinfusion of several doses of ei ther the dopamine receptor agonist apomorphine (APO) or the dopamine r eceptor antagonist cis-flupenthixol (FLU) into the ventromedial PFC. I n addition, all animals were tested after infusion of several doses of the muscarinic receptor antagonist scopolamine (SCO) and the dopamine D1 receptor antagonist SCH-23390 (SCH). The drugs tested affected DMT P performance differentially. APO had no effect on response accuracy, although it dose-dependently affected nose poke activity and response latencies. FLU and SCH both induced a dose-dependent, but delay-indepe ndent deterioration of response accuracy that was parallelled by incre ases in response latencies and decreases in nose poke frequencies, cau sing some animals to stop responding after infusion of the highest dos es of both drugs. In contrast, SCO infusions into the ventromedial PFC induced a dose- and delay-dependent deterioration of response accurac y, that was accompanied by an increase in response latencies only. Tak en together, these results provide additional support for the involvem ent of cholinergic, rather than dopaminergic mechanisms in short-term memory processes supported by the medial PFC of the rat, and they are not in favor of a functional dissociation between the dorsomedial PFC and the ventromedial PFC in this role.