Reversible lesions of the nucleus of the solitary tract attenuate the memory-modulating effects of posttraining epinephrine.

Rats implanted with cannula tips placed above the nucleus of the solitary tract (NTS) were trained to obtain food pellets placed in 2 arms of a Y maze and then given a footshock in 1 arm of the maze. The rats then received bilateral injections of lidocaine or buffer into the NTS and peripheral injections of saline or epinephrine (0.01 or 0.05 mg/kg ip). Two tests were given 24 and 48 hr after training to assess retention in the presence and absence of contextual cues (the stainless steel floor) associated with the footshock training trial. Epinephrine (0.05 mg/kg) produced a significant enhancement in retention, which was attenuated by injections of lidocaine into the NTS. These findings indicate that the NTS is involved in mediating the memory-modulating effects of peripheral epinephrine and that such effects are initiated at least in part by activation of vagal afferents projecting to the NTS.