Role of dorsal hippocampus in acquisition, consolidation and retrieval of rat's passive avoidance response: a tetrodotoxin functional inactivation study

• Published in: Brain research Vol. 730; no. 1; pp. 32 - 39
• Main Authors: Lorenzini, Carlo Ambrogi, Baldi, Elisabetta, Bucherelli, Corrado, Sacchetti, Benedetto, Tassoni, Giovanna
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 19.08.1996; Amsterdam Elsevier; New York, NY
• Subjects: Acquisition; Anatomical correlates of behavior; Animals; Avoidance Learning - physiology; Behavior, Animal - physiology; Behavioral psychophysiology; Biological and medical sciences; Conditioning (Psychology); Consolidation; Dorsal hippocampus; Functional inactivation; Fundamental and applied biological sciences. Psychology; Hippocampus - drug effects; Hippocampus - physiology; Male; Memory - physiology; Nerve Block; Passive avoidance; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Rats, Wistar; Retention (Psychology) - physiology; Retrieval; Tetrodotoxin; Tetrodotoxin - pharmacology; Retrieval; Tetrodotoxin; Consolidation; Functional inactivation; Passive avoidance; Acquisition; Dorsal hippocampus; Memory retrieval; Rat; Rodentia; Central nervous system; Male; Learning; Vertebrata; Mammalia; Acquisition process; Animal; Lesion; Avoidance; Hippocampus; Brain (vertebrata)
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/0006-8993(96)00427-1

By means of local administration of tetrodotoxin (TTX) fully reversible functional inactivation of rat's dorsal hippocampus (DH) was obtained in order to define the role of this structure in the memorization of a conditioned passive avoidance response (PAR). In Experiment 1, on permanently cannulated animals, TTX (10 ng in 1.0 μ1 saline) or saline (1.0 μ1) was injected uni- or bilaterally in the DH, respectively 1 h before PAR acquisition, immediately after PAR acquisition, and 1 h before PAR retrieval, always performed 48 h after the acquisition trial. It was shown that both pre-acquisition and pre-retrieval DH uni- or bilateral blockades were followed by significant PAR retention impairment, while in post-acquisition only the bilateral blockade determined PAR retention impairment. In Experiment 2, on three different groups of rats, TTX (10 ng in 1 μ1 saline) was bilaterally administered, under general ketamine anesthesia (100 mg/kg), into the DH at different post-acquisition delays (0.25, 1.5, 6 h). Retrieval testing, 48 h after treatment, showed that post-acquisition bilateral DH blockade caused PAR impairment only when performed 0.25 or 1.5 h after acquisition. The results indicate a well defined mnemonic role of DH during the acquisition, consolidation and retrieval of PAR engram. The experimental evidence is discussed in relation to other reports and to DH connectivity with the medial septal area and the amygdala.