Post-training nucleus basalis magnocellularis functional tetrodotoxin blockade effects on passive avoidance...

The tetrodotoxin (TTX) functional ablation technique was employed in order to evaluate the temporal coordinates of the rat's nucleus basalis magnocellularis (NBM) involvement in memory trace processing. Under ketamine general anesthesia, TTX (10 ng in 1 microliter saline) was stereotaxically administered to rats, either in one or both NBMs. TTX was injected to different groups of rats, respectively 15 min, 6, 24, 48, 96 h after passive avoidance acquisition testing. The rats underwent retrieval testing 48 h later, i.e. after full recovery from TTX effects. Results show that: (1) monolateral TTX blockade significantly impairs PAR conditioned responding if induced up to 6 h but not 24 h after acquisition testing; (2) bilateral TTX blockade dramatically impairs passive avoidance responding up to a 48-h delay but not 96 h after acquisition testing. The results indicate a very profound involvement of NBM in passive avoidance response consolidation. The experimental evidence is discussed together with previous functional ablation findings concerning amygdala, parabrachial nuclei and neocortex.