LOCALIZATION OF THE CALCIUM CALMODULIN-DEPENDENT PROTEIN PHOSPHATASE,CALCINEURIN, IN THE HINDBRAIN AND SPINAL-CORD OF THE RAT/

The calcium/calmodulin-dependent protein phosphatase calcineurin was l ocalized at the light microscopic level in the rat hindbrain and spina l cord by using an antibody against the alpha-isoform of the catalytic subunit. Calcineurin was highly concentrated in axons, dendrites, and cell bodies of a subpopulation of alpha-motoneurons in hindbrain moto r nuclei and the lateral motor column along the length of the spinal c ord. These calcineurin-positive alpha-motoneurons appeared to be rando mly distributed and represented approximately 25% of the total alpha-m otoneuron pool in the motor trigeminal nucleus and the spinal cord lat eral motor column. Within the facial nucleus, calcineurin-containing m otoneurons were present in the medial and dorsal subdivision but not i n the lateral and intermediate subdivision. In addition to the enrichm ent in motoneurons, calcineurin was enriched in cells of the superfici al laminae of the spinal cord dorsal horn and its extension into the m edulla, the caudal spinal trigeminal nucleus. Axonal staining in the w hite matter of the spinal cord was generally weak, except in the dorso lateral funiculus, where strongly calcineurin-positive axons formed a putative ascending tract that appeared to terminate uncrossed in the c audal lateral reticular nucleus of the medulla. This tract may origina te from calcineurin-positive cells in the dorsolateral funiculus. We a lso compared the distribution of calcineurin with calcium/calmodulin-d ependent kinase II in the spinal cord and found that the kinase is mor e widely expressed. Thus, calcineurin is highly restricted to a few lo cations in the hindbrain and spinal cord. Selective staining in facial subnuclei that innervate phasically active muscles suggests that calc ineurin-positive motoneurons represent a subset of alpha-motoneurons i nnervating a metabolic subtype of muscle fibers, possibly fast-twitch fibers. (C) 1996 Wiley-Liss, Inc.