CONTRIBUTION OF THE VAGUS NERVE IN MEDIATING THE MEMORY-FACILITATING EFFECTS OF SUBSTANCE-P

The present study determined whether the effects of peripherally administered substance P on memory are mediated via activation of the vagus nerve. Rats were submitted to subdiaphragmatic vagotomy, sham vagotomy or non-operated, and trained in a step-down inhibitory avoidance task and tested 24 h later. Posttraining administration of 50 mu g/kg of SP facilitated retention performance in non-operated and sham-operated groups. The facilitating effects of 50 mu g/kg of SP was blocked by vagotomy, although vagotomy did not attenuate the memory-enhancing effects of larger doses (250 and 500 mu g/kg). These results suggest that the mnemotropic effects of peripherally administered SP are sensitive to the functional integrity of the vagus nerve. Alternatively, the vagus nerve ma p be one pathway but not the only pathway by which systemic SP influences the memory storage processes in the brain.