Brain stem mechanisms of conditioned taste aversion learning in rats.

Acquisition of conditioned taste aversion (CTA) in rats is not prevented by functional decortication, anesthesia or hypothermia applied after intake of the flavored fluid and maintained throughout the action of the poison but is disrupted by bilateral application of 10 ng tetrodotoxin (TTX) into the parabrachial nuclei. The blockade is directly proportional to TTX dosage, indirectly proportional to distance of the injection site from parabrachial nuclei and equally affects CTAs using different CS (saccharin, NaCl) and different US (LiCl, carbachol, amphetamine, cycloheximide). CTA is disrupted by TTX applied up to 4 but not 8 days after a single CS-US pairing. TTX fails to disrupt overtrained CTA and elicits only a weak anterograde amnesia when applied 1 but 2 or more days before CTA acquisition. It is concluded that the parabrachial nuclei and the adjacent reticular formation probably represent the neural substrate of the permanent CTA engram the protracted consolidation of which is disrupted by prolonged cessation of impulse which is disrupted by prolonged cessation of impulse activity in the information storing network.