Lectins demarcate the barrel subfield in the somatosensory cortex of the early postnatal mouse.

Plant lectins were used to examine the disposition of glycosylated molecules in vibratome sections through the barrel subfield of mouse somatosensory cortex at selected times during postnatal development. The peroxidase conjugates of peanut agglutinin (PNA, specific for N-acetylgalactosamine), concanavalin A (specific for mannose), and wheat germ agglutinin (specific for N-acetylglucosamine and N-acetylneuraminic acid) were used to study lectin binding in aldehyde-fixed tissue sections of cortex. Following peroxidase cytochemistry and light microscopy, it was found that all three lectins bound in the region of the barrel subfield as early as postnatal day 3 (day of birth = postnatal day 1). The lectins bound to the prospective sides and/or septae of individual barrels in preference to the prospective hollows. This lectin demarcation of the barrel field occurred prior to the detection of this region with cresyl violet staining and was still demonstrable on postnatal day 6, when the individual barrels became discernible with cresyl violet. This suggests that the lectin binding material is present before the barrel field becomes a fully formed and organized region. A decrease in lectin affinity for binding sites in these tissue sections occurs during postnatal development (Cooper and Steindler: Soc. Neurosci. (Abstr.) 10: 43a, '84) and this study demonstrates that lectins do not delineate the barrel field of more mature animals (2-3 months old), whereas barrels can be detected with cresyl violet at this time. A preliminary electron microscope analysis of the postnatal day 6 somatosensory cortex demonstrates that the lectin PNA binds to elements of the forming neuropil and also to Golgi apparatus intermediate saccules in neuronal cells. The prospective barrel field can be detected with lectins during a critical period in development in which alterations can occur in the barrel field in response to peripheral deprivation (Jeanmonod et al: Neuroscience 6:1503-35, '81) and therefore we suggest that the glycans visualized with lectin-peroxidase conjugates denote possible candidates for molecules involved in shaping barrel structure.