Differential effects of inactivation of the right and left basolateral amygdala on spatial memory in place avoidance task in rats

There is strong evidence that two cerebral hemispheres are differentially involved in emotional memory and that amygdala is a key subcortical structure for emotional experience. The present research investigated the possible involvement of lateralization of basolateral amygdala (BLA) and central amygdala (CEA) in place avoidance memory. For this purpose, male Long-Evans rats (280-320 g) were implanted bilaterally with cannulae aimed at the BLA and CEA. One week later, the rats were trained in place avoidance apparatus as a spatial learning model. During the training session (30 min), the animal learned to avoid and recognize the places with a possibility of shock. One day later, bilateral or unilateral injection of TTX (5 ng/ml/side) were performed to inactivate temporarily the BLA and CEA during retrieval of the place avoidance task. Control rats were injected with the same volume of saline. Place avoidance training occurred in a single 30 min session and one day later, the avoidance memory was assessed during a 30 min extinction trial. The time to the first entrance and the number of entrances into the punished sector during extinction were used to measure the avoidance memory. The results indicated that bilateral or only right BLA inactivation significantly impaired retrieval of memory, although inactivation of the CEA and left BLA had no significant effect. Taken together, these results suggested that the right and left BLA make differential contribution to the expression of spatial memory and that the contribution of the right BLA may be more important.