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

We performed a comparative immunohistochemical analysis ofparvalbumin, a calcium-binding protein, expression in the lumbosacralspinal cord of newborn and adult cats. In contrast to adult animals,parvalbumin immunostaining in newborn kittens was mainly detectedin the sensory fibers located in the dorsal horns and medial partof the intermediate gray matter. The location of these fibers partiallyrecapitulates the position of the Clarke’s nuclei, but is not limitedby their classical boundaries, spanning the entire length of thelumbar spinal cord and transitioning into the putative Stilling’snuclei in the sacral region. Thus, in newborn kittens, in contrastto adult animals, parvalbumin-immunopositive proprioceptive fibersappear to make up a single network. We hypothesize that with age,this continuous system of fibers undergoes restructuring due tomaturation and spreading of the neuronal and neuropil componentsof the lumbar enlargement, responsible primarily for the locomotorcontrol. As a result, two local groups of interneurons, the Clarke’sand Stilling’s nuclei, form. The only parvalbumin-immunopositivespinal neurons in newborn kittens are premotor interneurons locatedalong the lamina IX curvature. These neurons are characterized bya weak or no immunolabeling of the neuronal marker protein NeuN,which is indicative of a special neurochemical status of these neurons.