EXPRESSION OF THE EXTRACELLULAR-MATRIX GLYCOPROTEIN TENASCIN IN THE SOMATOSENSORY CORTEX OF THE MOUSE DURING POSTNATAL-DEVELOPMENT - AN IMMUNOCYTOCHEMICAL AND IN-SITU HYBRIDIZATION ANALYSIS

Layer 4 of the rodent somatosensory cortex contains the barrel field w hich is the cortical representation of the whisker pad loca ted on the contralateral side of the face. Each barrel within the barrel field i s related one to one to its corresponding whisker both anatomically an d physiologically. The astrocyte-derived extracellular matrix glycopro tein tenascin has been shown by immunocytochemistry to delineate the b oundaries between barrels during their formation until the end of the second postnatal week. The present study describes the anatomical loca lization of tenascin mRNA expressing cells in the somatosensory cortex of the mouse from birth to postnatal day 15. During this time, a gene ral down-regulation of tenascin-specific message was observed as a fun ction of the state of maturation, with layers 5 and 6 down-regulating the message earlier than layers 1 and 213. Tenascin (as detected by im munocytochemistry) also revealed this gradual down-regulation with mat uration. Layer 4 of the somatosensory cortex was different in that, wi th the onset of formation of barrel field boundaries at postnatal day 3, tenascin protein and mRNA were down-regulated more in layer 4 than in the upper and the lower layers of the soma tosensory cortex and, in terestingly, not in layer 4 of adjacent cortical areas. At postnatal d ay 6 tenascin immunoreactivity was most clearly distinguished in the b arrel field boundaries while tenascin-specific mRNA was no longer dete ctable in layer 4. Down-regulation of tenascin message was also seen a t P6 at the level of the enlarged barrel corresponding to an early pos tnatal lesioned row of whiskers. At postnatal day 15, tenascin protein and mRNA were no longer detectable in the somatosensory cortex. Distr ibution of glial fibrillary acidic protein immunoreactivity did not re veal any preferential accumulation of GFAP-positive radial glial proce sses in barrel field hollows versus barrel field boundaries at any sta ge.