Distribution of Protein I, a Synapse‐Specific Phosphoprotein, and Adenylate Cyclase in the Rat Spinal Cord

The longitudinal and transverse distributions of the synapse‐specific phosphoprotein Protein I and adenylate cyclase in the rat spinal cord were studied. Protein I was found to be enriched in all cervical and midlumbar (L 3 ‐L 5 ) segments, and sparse in midthoracic and sacral segments. Adenylate cyclase activity was high in all cervical and lumbosacral segments, and low in mid‐thoracic segments. Cross‐sectionally, both Protein I and adenylate cyclase were more enriched in the dorsal half than in the ventral half in the various segments studied. The similar topographical distributions of Protein 1 and adenylate cyclase in the spinal cord support the idea that adenylate cyclase may be intimately associated with Protein I in the nervous system, and could thereby regulate the state of in vivo phosphorylation of Protein I through formation of cyclic AMP.