Modulation of presynaptic activity by phosphorylation in cultured rat spinal dorsal horn neurons.

Phosphorylation, in particular by protein kinase C (PKC), modulates spinal sensory transmission and nociceptive behaviors. Whereas PKC's postsynaptic actions are well established, its presynaptic effects in spinal sensory neurons are mostly inferred from postsynaptic recordings. Here we first show that the amphipathic styryl dye FM 1-43 can be used to image presynaptic activity in cultured spinal dorsal horn cultures and then test whether PKC modulates presynaptic activity in cultured spinal dorsal horn neurons. Pretreatment with the broad-spectrum kinase inhibitor staurosporine (2 micromol/L) inhibited dye release. Bisindolylmaleimide I, a PKC inhibitor, potentiated dye release at low doses (200 nmol/L and 1 micromol/L), while inhibiting it at a higher dose (5 micromol/L). Activating PKC with phorbol dibutyrate (0.5 micromol/L) induced an increase in exocytosis, which is partially blocked by bisindolylmaleimide I. These results indicate that styryl dyes can be used to observe presynaptic regulation of spinal dorsal horn neurons, and that PKC acts presynaptically to modulate spinal sensory transmission. PERSPECTIVE: With dye imaging technique, we demonstrate here that PKC presynaptically regulates sensory transmission in spinal dorsal horn neurons. In combination with conventional whole-cell patch-clamp recording technique, the present study provides a new methodology for studying spinal sensory transmission and modulation and facilitates our understanding of pain mechanism.