Post-training stimulation of the basolateral amygdala improves spatial learning in rats with lesion of the fimbria-fornix.

PURPOSE

To evaluate the capacity of amygdala stimulation to improve neural plasticity in animals bearing lesions of the fimbria-fornix (FF) system.

METHODS

The animals were lesioned under narcosis (chloral hydrate, 420 mg/kg ip.) using a bilateral transection of the FF procedure. During the same surgery some animals were implanted with an electrode in the right basolateral amygdala (BLA) to allow the electrical stimulation of this structure. Training was carried out one week after surgery using a Morris water maze. Animals were trained in four consecutive days (8 trials/day) in the non-visible platform condition except in the fourth day in which only 4 trials were performed followed by a probe trial in which the escape platform was removed. On day 5 of training 8 trials with visible platform were performed. After each of the first 3 training days one group of animals received trains of electrical stimulation to the BLA, while control groups were not stimulated. A group of non-lesioned animals served as control. The location of the electrode was confirmed histologically after the end of the experiments.

RESULTS

The learning capacity of the lesioned animals was improved by the electrical stimulation of the amygdala. The latency to find the submerged platform within this group approaches that of the non lesioned animals in the course of training (2-way ANOVA with repeated measures), while other lesioned animals continued to show severely impaired learning abilities.

CONCLUSIONS

This is the first evidence that stimulating the BLA can positively influence the learning abilities of lesioned animals. Further experiments should contribute to improve the stimulation paradigms to make it more effective, if possible.