The development of laminar staining for neuron-specific enolase in the rat somatosensory cortex

The expression of the enzyme neuron-specific enolase (NSE) in the central nervous system (CNS) has been used as a developmental marker based on observations that it is expressed shortly after the arrival of afferent inputs. The immunostaining pattern of NSE was examined in the laminae of the somatosensory cortex of the rat and the relationship of this staining pattern with previous data on the timing of afferent and efferent arrival was determined. Male rat pups were sacrificed on postnatal days 1 (24 h after birth), 3, 5, 8, 10, 12, 15 and 20, and as an adult (over 90 days of age). Sections were stained with an anti-NSE antibody using the avidin-biotin immunocytochemical method. Sections from day 1 animals revealed stained cells in the subplate layer and cortical plate, presumably in cells destined to form layers VI and V. By day 8 there was staining in layers II, III, V and VI, the same layers that exhibited staining in the adult rat. This appears consistent with the arrival of afferents and efferents which is completed by approximately postnatal day 7. On day 10, there was a change in the staining pattern: cell staining in layer VI was decreased and then increased gradually up to adult levels by day 20. A stable pattern of NSE staining was not observed previous to day 20. These results suggest that changes in NSE expression following the initial arrival of afferents may relate to maturation of the neurons.