Modulation of working memory and of long- but not short-term memory by cholinergic mechanisms in the basolateral amygdala

Abstract

Male Wistar rats were exposed to one-trial step-down inhibitory avoidance training using a 0.5 mA footshock. Through bilaterally implanted indwelling cannulae, they received bilateral 0.5 μl infusions of saline, oxotremorine (0.06 or 0.3 μg) or scopolamine (0.25 or 2.0 μg) into the basolateral complex of the amygdaloid nucleus (BLA). Infusions were either 10 min before training (experiment 1) or 4 min after training (experiment 2). In experiment 1, the animals were tested three times: first for working memory (WM) 2 s after training, then for short-term memory (STM) 1.5 h later, and finally for long-term memory (LTM) 24 h later. Oxotremorine enhanced and scopolamine depressed WM and LTM while leaving STM unaffected. In experiment 2, the treatments were given after WM was presumably over. Again, oxotremorine again enhanced and scopolamine depressed LTM, and neither had any effect on STM. The results fit with the suggestion by Beninger and his co-workers that cholinergic synapses in the BLA regulate WM, generalize that finding to a different task, and show that this mechanism uses muscarinic receptors. In addition, they indicate that the well-known effects of intra-amygdala oxotremorine and scopolamine on LTM are independent of those that the drugs have on WM.