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 either systemically or intraventricularly immediately after training. Two experiments were conducted to determine whether the nucleus of the solitary tract (NTS) mediates the effects of bombesin on memory. In the first 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 immediately after training. Retention was assessed either 2 or 7 days later. Doses of 25 or 50 ng of bombesin significantly enhanced retention on the 2 day test (P < 0.05 and 0.01 compared with vehicle controls, respectively). 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 immediately after the animals were trained in a win-shift radial arm maze task. 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 bombesin influences retention by activating the NTS is consistent with recent evidence suggesting that the NTS is involved in regulating memory storage.