cGMP accumulation by spinal cord neurons during the period of neuromuscular junction formation.

A 4--5-fold increase in cGMP levels in spinal cord neurons has been demonstrated in vitro and in vivo upon association with skeletal muscle. The increase on cGMP was temporally coincident with the onset of neuromuscular junction formation and independent of any concomitant change in cAMP. The response was specific for spinal cord neurons cocultured with skeletal muscle; glial cells could not be substituted for spinal cord neurons nor could fibroblasts be substituted for muscle cells. The response was not dependent upon action potential activity, synaptic transmission or muscle contractile activity. Muscle conditioned medium was found to produce the largest increase of cGMP in spinal cord neurons of 23-fold.