Early development of the representation of the body surface in SI cortex barrel field in neonatal rats as demonstrated with peanut agglutinin binding: evidence for differential development within the rattunculus

Physiological studies have demonstrated a highly organized somatotopic representation of the body surface in SI cortex of rat. This representation is correlated morphologically with the presence of barrel-shaped structures in layer IV. Conventional staining techniques reveal barrels in the latter part of the first postnatal week. Recently, the peroxidase conjugates of lectins, which recognize glycosylated molecules, have been used to study barrel field formation. Con A, for example, has been shown to bind primarily to prospective barrel sides and septa as early as postnatal day 3 (PND-3) in mouse. To date, investigations of SI cortex using the lectin (Arachis hypogaea) peanut agglutinin (PNA) have been confined to the study of the barrel field representation of the face and mystacial vibrissae in the mouse. In the present study we extend these findings to the development of the representation of the entire body surface called the rattunculus. Rats ranging from PND-1 (first 24 h after birth) to PND-12 were anesthetized with Nembutal and perfused with 4% paraformaldehyde and 2% glutaraldehyde in 0.2 M sodium cacodylate buffer. Brains were removed, flattened tangentially, and sectioned on a vibratome at 30-120 microns. Sections were blocked in TRIS-buffered saline (TBS) plus 2% bovine serum albumin and incubated in peanut lectin at 4 degrees C. Following incubation, sections were washed with TBS and processed using peroxidase histochemistry. Lectin binding in the prospective forelimb representation was apparent by PND-5 whereas lectin binding to the prospective face-mystacial vibrissae representation occurred before PND-4. These results suggest that body part representations show individual variations during early pattern formation.