Posttraining infusion of cholinergic drugs into the ventral subiculum modulated memory in an inhibitory avoidance task: Interaction with the bed nucleus of the stria terminalis

The ventral subiculum (vSUB), a hippocampal efferent target implicated in learning and stress coping, receives cholinergic input and sends glutamatergic output to the bed nucleus of the stria terminalis (BNST). This study examined the roles of vSUB muscarinic activation and its interaction with BNST N-methyl- d-aspartate and noradrenergic receptors in formation of aversive memory. Male Wistar rats with cannulae implanted into the vSUB or BNST were trained on a step-through inhibitory avoidance task. Shortly after training, they received cholinergic drugs infused into the vSUB and/or glutamatergic or noradrenergic drugs infused into the BNST. Results of the 1-day retention tests showed that intra-vSUB infusion of oxotremorine (0.01 μg) or scopolamine (0.3 or 3.0 μg) enhanced or impaired retention, respectively. Both effects were dose- and time-dependent, and 0.001 μg oxotremorine attenuated the amnesia induced by 3.0 μg scopolamine. The oxotremorine-induced memory enhancement was blocked by intra-BNST infusion of dl-2-amino-5-phosphonovaleric acid or propranolol at a dose not affecting retention; the amnesia induced by scopolamine was blunted by intra-BNST infusion of glutamate or norepinephrine at a dose with a negligible effect on retention. These data suggest that in an inhibitory avoidance task muscarinic activation of the vSUB modulated memory formation by interacting with the BNST glutamatergic and noradrenergic functions.