Effects of hippocampal lesions on lever-press learning in rats

• Published in: Japanese Journal of Pharmacology 1993, Vol.61 (suppl.1), p.182-182
• Main Authors: Matsumoto, Akira, Kubo, Taizo, Ishikawa, Koichi
• Format: Article
• Language: eng ; jpn
• ISSN: 0021-5198
• DOI: 10.1016/S0021-5198(19)51604-3

Local microinjection of kainic acid (KA) or colchicine (CO) caused degeneration of the pyramidal layer of the hippocampus or granular layer of the dentate gyrus, respectively, and simultaneous application of KA and CO degenerated both structures. The involvement of hippocampal formation in the processes of learning and memory was investigated in Wistar rats which received KA and/or CO. The animals were trained to press the lever for getting food pellets when either the light (15 lux) or sound (80 dB) was presented as a cue. If CO was bilaterally applied, the animal showed significant impairment in the acquisition of lever-press responding, in which light was used separately as a cue, in comparison with that of the control (local application of saline). However, this substance did not cause significant impairment when sound was used as cue stimuli. Furthermore, KA did not cause significant impairment for both cues, light and sound. Simultaneous application of KA and CO caused significant impairment in this learning. When the correct response was reached to a criterion level for a single cue, the task was progressed to a combined learning with two cues, where the animal could receive food by lever-pressing when either light or tone was presented separately, but not when both cues were presented simultaneously. Both KA- and CO-treated animals could not learn this paradigm. These results suggest that the hippocampus is necessary for lever-press learning and that degeneration of pyramidal or granular cells caused different effects on acquisition in memory formation but not on their retention.