Two-way active avoidance learning following medial, dorsolateral, or total septal lesions in rats: Effect of intensity of discontinuous shock

Abstract

Effects of medial, dorsolateral, or total septal lesions on the acquisition of two-way active avoidance behavior at different shock levels were studied in Wistar rats. Intermittent shocks (0.2 sec every 2 sec) and six levels of intensity (0.25, 0.4, 0.7, 1.0, 1.3, and 1.9 mA) were employed. Each rat was run only one session with a single-shock intensity. Following total and dorsolateral septal lesions, rats accepted more weak shocks on Trial 1 and during the whole session than rats with medial septal lesions which, in turn, did not differ from control animals. Rats with dorsolateral septal lesions showed fast acquisition and, when shocks were weak, rats with medial septal lesions showed slow acquisition of the task. The results were interpreted the following way: (i) Medial septal lesions, depleting hippocampal acetylcholinesterase (AChE), produce slow acquisition when shocks are weak; (ii) dorsolateral septal lesions, not interfering with hippocampal AChE, produce a learning enhancement which probably was due to increased locomotor activity and a reduced reactivity to weak electric shocks; and (iii) total septal lesions produce reduced reactivity to weak electric shocks.