PATTERNING OF LOCAL INTRACORTICAL PROJECTIONS WITHIN THE VIBRISSAE REPRESENTATION OF RAT PRIMARY SOMATOSENSORY CORTEX

Anterograde and retrograde tracing with biotinylated dextran amine and Phaseolus vulgaris leukoagglutinin was used to assess projection patt erns within the vibrissae representation of the rat's primary somatose nsory cortex (S-I). Large and small injections of either tracer into t he center of the vibrissae representation yielded dense anterograde an d retrograde labelling throughout much of the tangential extent of the vibrissae representation within S-I. In all layers, the pattern and e xtent of retrograde and anterograde label was in rough congruence. The organization of this labelling varied across cortical layers. In laye rs II and III, labelled fibers extended away from injection sites in a ll directions and yielded a uniform pattern, which decreased in densit y with increasing distance from the tracer injection. There was a tend ency for labelling to be more extensive along the representation of th e row of vibrissae follicles that included the injection site than acr oss rows. There was also a tendency for anterograde labelling to be mo re extensive in the direction of the representation of follicles more rostral on the face than that injected. In lamina IV, both labelled fi bers and cells were restricted for the most part to the septa regions between the barrels. However, a small number of retrogradely labelled neurons were also located in the barrels (approximately one-ninth of t he number found in the septa). The pattern observed in laminae II-III was repeated in layers V and VI. In these laminae, there was no eviden ce of a pattern of intracortical connections related to the vibrissae representation in overlying lamina IV. (C) 1995 Wiley-Liss, Inc.