Functional development of the visual system in normal and protein deprived rats. III: Recordings from adult optic nerve in vitro.

A persistent increase in the latencies of the visual evoked response recorded from the cortical surface of protein deprived adult rats was described recently (Sjöström et al. 1984). The morphological correlate to this alteration is unknown. Previous studies on malnourished rats have shown a reduction of axonal diameters and in the number of myelin lamellae in relation to axonal circumference, and hence the possibility of a decrease in fibre conduction velocity must be considered. In parallel study, we have established that changes in diameters and myelination of optic nerve fibres similar to those previously reported in malnourished rats are present in adult protein deprived (PD) rats (Conradi et al. 1985). In the present paper, recordings of optic nerves in vitro from adult normal (C) and protein deprived (PD) rats are described. The compound action potentials were very similar in the two groups. Three positive peaks were easily defined, probably corresponding to three functional groups of optic nerve fibers. No significant differences in amplitudes or conduction velocities for the three peaks were found between the C and PD rats. It is concluded that the increased latencies of the evoked response are not caused by a decrease in conduction velocity.