ENHANCEMENT OF MEMORY PROCESSING IN AN INHIBITORY AVOIDANCE AND RADIAL MAZE TASK BY POST-TRAINING INFUSION OF BOMBESIN INTO THE NUCLEUS-TRACTUS-SOLITARIUS

Bombesin is a peptide known to modulate memory storage when given eith er systemically or intraventricularly immediately after training. Two experiments were conducted to determine whether the nucleus of the sol itary tract (NTS) mediates the effects of bombesin on memory. In the f irst experiment male Sprague-Dawley rats were trained in an inhibitory avoidance task (0.35 mA, 0.5 s footshock) and bombesin or vehicle was infused unilaterally into the NTS through implanted cannulae immediat ely after training. Retention was assessed either 2 or 7 days later. D oses of 25 or 50 ng of bombesin significantly enhanced retention on th e 2 day test (P < 0.05 and 0.01 compared with vehicle controls, respec tively). There were no differences between the drug and control groups on the 7 day retention test. In the second experiment, bombesin (25, 50, or 250 ng) or vehicle was infused unilaterally into the NTS immedi ately after the animals were trained in a win-shift radial arm maze ta sk. On retention tests given 18 h later, groups that received 25 ng or 50 ng of bombesin made a significantly greater percentage of correct choices on the retention test than did the vehicle-treated controls (P < 0.02 and P < 0.05, respectively). The findings indicating that bomb esin influences retention by activating the NTS is consistent with rec ent evidence suggesting that the NTS is involved in regulating memory storage.