[Postnatal development of evoked potentials in the rat somatosensory cortex].

The developmental changes of evoked potentials in the somatosensory cortex were studied using Long-Evans rats of postnatal age from day 2 to day 55. A hole of appropriate size was made in the skull under urethane anesthesia (1.4 g/kg) and somatosensory evoked potentials (SEPs) were recorded with a silver-ball electrode. Electrical stimulation was applied to whisker C 3 follicle. The electrode was moved on the dura over the hemisphere and SEPs were displayed on an oscilloscope. When a maximum SEP was obtained 100 successive responses were digitally processed with a time resolutions of 100 microseconds and averaged. From the averaged SEP, various peak latencies and amplitudes were calculated. In response to electrical stimulation of the whisker follicle, a short-latency positive wave appeared on postnatal day 2 (PND 2) and the second positive wave was recorded on PND 8 and a negative wave appeared on PND 10. The latency of these waves shortened, while the amplitude increased with age. SEPs in developing rats attained adult pattern on PND 17, although both the values of latency and amplitude reach the limit on PND 55. The placing reaction was also tested from PND 9 to PND 15 to examine the functional development of whisker. All subjects displayed positive placing reaction of chin hair on PND 10. At this age all components appeared in the SEP, 1st positive, 2nd positive and negative waves.