The surface evoked potential and parvalbumin-immunoreactivity in the somatosensory cortex of the developing rat.

The development of the rat somatosensory system was followed electrophysiologically and immunohistochemically. In the surface evoked potential elicited in the primary somatosensory cortex by electrical stimulation of the whisker C3 follicle, a short-latency positive wave was first recorded on postnatal Day 2. A long-latency positive wave was recorded in some pups on postnatal Day 7 and in most pups on postnatal Day 8. On postnatal Day 10, a P/N complex appeared between the short- and long-latency positive waves. Parvalbumin, believed to appear with functional maturation, appeared mainly after postnatal Day 7 in Layer V in the underlying area, although a few weakly stained cells appeared on postnatal Day 5. On postnatal Day 10, weakly stained cells appeared in the area containing barrels; their staining increased with time. In this system, electrophysiological and immunohistochemical parameters changed by the 3rd postnatal week with the most marked changes occurring within 2 postnatal weeks.