Differential distribution of immunoreactivity in the developing rat spinalcord revealed by the monoclonal antibody Py

Monoclonal antibody Py was developed as a useful tool for the identificatio n of large diameter neurons of the adult rat central nervous system [Woodha ms et al., J. Neurosci., 9 (1989) 2170-2181]. Here, we present a detailed l ight-microscopic study of the distribution of Py-immunoreactivity in the de veloping rat spinal cord. The first cells which demonstrated Py-immunoreact ivity were the motoneurons in layer IX of the gray matter at embryonic day 15. These cells, including their axons and dendrites, remained Py-immunorea ctive throughout subsequent developmental stages into adulthood and were th e most intensely stained cells in the adult rat spinal cord. Other cell pop ulations which became Py-immunoreactive during development were neurons in layers III-VIII, and large-to-medium diameter neurons of the dorsal root ga nglion (DRG). Transient Py-immunoreactivity was observed in the distal port ions of DRG axons as well as in the ascending fibers in the dorsal funiculu s. Py-immunoreactive fibers could be detected in the ventral most part of t he dorsal funiculus (corticospinal tract area), even at embryonic ages prio r to the arrival of corticospinal fibers. The localization and transient ex pression of the antigen recognized by the Py-antibody in developing rat spi nal cord strongly suggests an important role of this molecule in stabilizat ion and/or plasticity of the neuronal cytoskeleton. The results presented h ere form the foundation for the use of Py-immunocytochemistry to study well -defined cell populations under a range of experimental and pathological co nditions. (C) 1999 Elsevier Science B.V, All rights reserved.