Immunohistochemical detection of calcium/calmodulin‐dependent protein kinase II in the spinal cord of the rat and monkey with special reference to the corticospinal tract

Calcium/ calmodulin‐dependent protein kinase II is a prominent enzyme in the mammalian brain that phosphorylates a variety of substrate proteins. In the present study, monoclonal antibodies that specifically recognize either the α or the β isoforms of this enzyme were used to determine the distribution of these isoforms within the rat and monkey spinal cord. In the rat, the corticospinal tract consists of two components: the dorsal corticospinal tract, which occupies the ventralmost aspect of the dorsal funiculus; and the ventral corticospinal tract, which occupies an area adjacent to the ventral median fissure. Both dorsal and ventral corticospinal tract fibers were strongly immunopositive for the α‐antibody. Unilateral ablation of the sensorimotor cortex of the rat eliminated the α‐immunoreactive staining in the contralateral dorsal corticospinal tract. The neuropil in the superficial laminae of the dorsal horn (Rexed's laminae I and II) was densely stained with the α‐antibody, whereas the neuropil in laminae IV‐X was immunonegative. Dense α‐immunopositive neurons were also distributed in the head of the dorsal horn (laminae I‐IV). In contrast to the strong α‐immunoreactivity seen in the dorsal corticospinal tract fibers, only very weak β‐immunoreactivity was observed in this tract. Moderate β‐immunoreactive products were distributed homogenously throughout the neuropil of the gray matter, although the neuropil of the superficial laminae of the dorsal horn (laminae I and II) was stained more strongly than the other regions of the gray matter (laminae III‐X). Neuronal components in all laminae were immunopositive for the β‐antibody. Thus, motoneurons in the ventral horn, which were immunonegative for the α‐antibody, were immunopositive for the β‐antibody. This selective distribution pattern of immunoreactivity of α‐ and β‐antibodies in the rat was also present in the monkey spinal cord, although the α‐immunopositive corticospinal tract fibers in the monkey descended in the lateral funiculus as the lateral corticospinal tract instead of passing through the dorsal funiculus, as is the case in the rat. The differential distribution of immunoreactivity in the spinal cord suggests that these two isoforms of calcium/ calmodulin‐dependent protein kinase II may have different functional roles in the spinal cord. © Wiley‐Liss, Inc.