[Effect of sleep on cerebral DNA synthesized during learning]

Female Wistar rats weighing 200 g were implanted with cortical electrodes and with an intraventricular cannula. Five days later they were injected with 3H-thymidine and subjected to a two-way active avoidance session lasting four hours. During the following three hours they were left free to sleep while their EEG activity was being recorded. Biochemical analyses carried out in different brain regions and in liver indicated that the concentration of cerebral radioactive DNA was markedly lower in non-learning rats as compared to learning animal and to the control group. An increase in synchronized sleep and in paradoxical sleep was observed in learning animals, whereas non-learning rats exhibited an increment of synchronized sleep only. On the basis of these results and of previous data obtained with rats analyzed soon after the training session, it is concluded that the effect observed in non-learning animals stems from a loss of radioactive DNA synthesized during training. Such a loss takes place in the following resting period and is to be related to the variations of sleep pattern recorded. The process of DNA degradation might reflect the elimination of molecules associated with neural information non longer usable for adaptive aims.