(284) Persistent electrical activity in primary nociceptors after spinal cord injury is maintained by scaffolded adenylyl cyclase and protein kinase A and is associated with altered adenylyl cyclase regulation

Abstract

Little is known about intracellular signaling mechanisms that persistently excite neurons in pain pathways. We found recently that persistent spontaneous activity (SA) generated in the cell bodies of primary nociceptors within dorsal root ganglia (DRG) makes major contributions to chronic reflex hypersensitivity and to spontaneous pain in a rat model of thoracic spinal cord injury (SCI). The occurrence of SCI-induced SA in a large fraction of DRG neurons at and below the injury level for months after SCI, and the persistence of this SA long after dissociation of the neurons provide a special opportunity to define intrinsic cell signaling mechanisms that chronically drive SA at the first stage in pain pathways. We have found that SCI-induced SA generated in small dissociated DRG neurons requires continuing activity of adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA), as well as a scaffolded complex containing AC5/6, A-kinase anchoring protein 150 (AKAP150), and PKA. SCI caused a small but significant increase in the expression of AKAP150 but not other AKAPs. DRG membranes isolated from SCI animals revealed a novel alteration in the regulation of adenylyl cyclase (AC) activity. Membrane AC activity stimulated by added Ca2+-calmodulin increased modestly, while the inhibition of G(alpha)s-stimulated AC activity by G(alpha)i showed an unexpected and dramatic decrease after SCI. Localized enhancement of the activity of AC within scaffolded complexes containing PKA is likely to contribute to chronic pathophysiological consequences of SCI, including pain, that are promoted by persistent hyperactivity in DRG neurons.