Functional development of the visual system in normal and protein-deprived rats. VI. Evoked responses in adult rats, protein deprived in early life and nutritionally rehabilitated from weaning.

Previous studies have shown an increase in latency of the visual evoked response (VER) recorded from the cortical surface of adult rats subjected to protein deprivation (PD) during pre- and postnatal development. This alteration has been shown to originate mainly from the cortex itself. In the present study the possibility of normalizing such VER alterations by nutritional rehabilitation after early protein deprivation (R-PD) was investigated. Male rats were subjected to pre- and early postnatal protein deprivation through their mothers. Nutritional rehabilitation was started from weaning. The rats gained weight rapidly compared with rats subjected to protein deprivation throughout postnatal development but never reached the weight of controls (C) of the same age. Food consumption in relation to body weight was similar to that of controls. Rehabilitation continued until adult age when neurophysiological experiments were performed. The VER recordings from the dorsal lateral geniculate nucleus (dLGN) showed latencies similar to those reported previously for adult C and PD rats. The latencies of onset and first peaks of the cortical response recorded from the surface were increased by 5-6 ms in R-PD compared with C rats and hence similar to the latencies of adult PD rats. Intracortical responses to electrical stimulation in the dLGN were also similar to those of adult PD rats showing an normal onset latency but an increased latency of the peaks of the monosynaptic and late responses compared with C rats. The present results imply that the increased VER latencies noted in adult PD and R-PD rats are due to changes installed by protein deprivation during early development since they can not be reversed by nutritional rehabilitation starting at weaning.