Developmental expression of alpha-, beta- and gamma-subspecies of protein kinase C in the dorsal corticospinal tract in the rat spinal cord.

Developmental expression of alpha-, beta- and gamma-subspecies of protein kinase C in the dorsal corticospinal tract was immunohistochemically investigated at the cervical level of the postnatal rat spinal cord. On postnatal day 0, immunoreactivity for these subspecies was uniformly distributed throughout the posterior funiculus. On postnatal day 7, immunoreactivity for this enzyme in the posterior funiculus began to decline. On postnatal days 14 and 21, the immunoreactivity in the posterior funiculus became weak, while the dorsal corticospinal tract forming in the most ventral portion of the posterior funiculus exhibited strong immunoreactivity for these three subspecies of protein kinase C. Thereafter, immunoreactivity in the corticospinal tract rapidly declined, and on postnatal days 28 and 35, weak immunoreaction was demonstrated as very fine granular deposits in the tract. Expression of this enzyme in the dorsal corticospinal tract at these stages resembled that in the adult rat. Electron microscopically, growth cones and nascent axonal shafts were first noted on postnatal day 2 in the most ventral portion of the posterior funiculus, and thereafter, the axonal shaft gradually thickened and on postnatal day 14 some axons began to be myelinated. The growth cones and thin axonal shafts randomly exhibited weak immunoreactivity in the axoplasm. The thicker unmyelinated axonal shafts showed distinct immunoreactivity uniformly throughout the axoplasm and along the axolemma as granular deposits. In these developing axons, intensity and distribution of immunoreactivity for all three subspecies were principally similar. In the mature myelinated axons, the intensity and distribution of immunoreactivity for each subspecies of protein kinase C were quite different, i.e. immunoreactivity for alpha-subspecies was randomly distributed on some cytoskeletal elements, and that for beta-subspecies was uniformly detected on most of the cytoskeletal elements. In contrast, immunoreactivity for gamma-subspecies was distributed mainly on the endoplasmic reticulum. These findings suggest that in growing corticospinal axons protein kinase C might be involved in several important aspects of axonal development, and that in mature axons this enzyme might participate in different aspects of axonal function.