Time-dependent deficits of rat's memory consolidation induced by tetrodotoxin injections into the caudate-putamen, nucleus accumbens, and globus pallidus.

In order to better define corpus striatum involvement in memory processing, tetrodotoxin functional ablation was employed to assess the respective roles of the caudate-putamen as a whole and of its anterior, median, and posterior regions, of the nucleus accumbens, and of the globus pallidus during early passive avoidance response consolidation of the rat. Under general ketamine anesthesia (100 mg/kg) by means of microinjections, tetrodotoxin (10 ng/microliter) was bilaterally administered at the appropriate stereotaxic locations of the chosen sites and subsites at different postacquisition delays (0.25, 1.5, and 6 h). Saline solution was administered to control subjects in the same sites. Rats always underwent retrieval testing 48 h after treatment, i.e., when tetrodotoxin blockade had completely disappeared. The results show that both total caudate-putamen and median caudate-putamen blockades caused passive avoidance responding impairment when performed at 0.25- and 1.5-h postacquisition delays, that caudate-putamen anterior and caudate-putamen posterior blockades were never followed by passive avoidance impairment, and that both nucleus accumbens and globus pallidus blockades were followed by passive avoidance impairment when performed at 0.25- and 1.5-h postacquisition delays. In all structures, tetrodotoxin administration caused no impairment at the 6-h delay. The results are discussed with reference both to previous results obtained after reversible or irreversible lesions of the same structures and to the functional mnemonic relationships of the corpus striatum and its components with other subcortical structures, particularly the substantia nigra.