Long-term improvement of learning after early electrical stimulation of some central nervous structures: Is the effect structure and age-dependent?

Abstract

The experiments reported here point out the effect of an imposed electrical stimulation of certain brain structures on the subsequent acquisition of a food-reinforced operant task performed four weeks later. In the first experiment, we compared the effect induced by electrical stimulation of the lateral hypothalamus, the nucleus accumbens and the parietal cortex. The stimulation was bilaterally applied on 15 day-old rats of the Sprague-Dawley strain, and the behavioral test was performed 28 days later. As already reported, the lateral hypothalamic stimulation induced an important improvement of performance immediately from the beginning of the acquisition session. Stimulation of neither the nucleus accumbens nor the parietal cortex had any effect on learning. In the second experiment, we compared the effect of lateral hypothalamic stimulation to the effect induced by the stimulation of the substantia nigra and locus coeruleus, applied under the same conditions as in the first experiment. Stimulation of the locus coeruleus induced the same improvement of learning as the lateral hypothalamic stimulation, whereas stimulation of the substantia nigra had no effect on learning. In the third experiment in order to know if this improvement was influenced by the age of the animal at the time of stimulation, we stimulated the lateral hypothalamus of rats aged 10, 15, 30 and 90 days and tested their performances 28 days later. The behavioral improvement was not age-dependent since it was observed in all animals stimulated between 10 and 90 days. The possible implication of the dorsal noradrenergic bundle arising in the locus coeruleus is discussed.