A Comparative Distribution of Parvalbumin-Immunopositive Neural Elements in the Spinal Cord of Newborn and Adult Cats

Abstract

We performed a comparative immunohistochemical analysis of parvalbumin, a calcium-binding protein, expression in the lumbosacral spinal cord of newborn and adult cats. In contrast to adult animals, parvalbumin immunostaining in newborn kittens was mainly detected in the sensory fibers located in the dorsal horns and medial part of the intermediate gray matter. The location of these fibers partially recapitulates the position of the Clarke’s nuclei, but is not limited by their classical boundaries, spanning the entire length of the lumbar spinal cord and transitioning into the putative Stilling’s nuclei in the sacral region. Thus, in newborn kittens, in contrast to adult animals, parvalbumin-immunopositive proprioceptive fibers appear to make up a single network. We hypothesize that with age, this continuous system of fibers undergoes restructuring due to maturation and spreading of the neuronal and neuropil components of the lumbar enlargement, responsible primarily for the locomotor control. As a result, two local groups of interneurons, the Clarke’s and Stilling’s nuclei, form. The only parvalbumin-immunopositive spinal neurons in newborn kittens are premotor interneurons located along the lamina IX curvature. These neurons are characterized by a weak or no immunolabeling of the neuronal marker protein NeuN, which is indicative of a special neurochemical status of these neurons.