PKC and PKA, but not PKG mediate LPS-induced CGRP release and [Ca2+]i elevation in DRG neurons of neonatal rats

Calcitonin gene-related peptide (CGRP), is produced in dorsal root ganglia (DRG) neurons and released from primary afferent neurons to mediate hemodynamic effects and neurogenic inflammation. In this work, we determined whether lipopolysaccharide (LPS), an inflammatory stimulator, could trigger CGRP release from cultured DRG neurons and if so, which cellular signaling pathway was involved in this response. Cytoplasmic concentration of calcium ([Ca2+](i)) plays a key role in neurotransmitter release, therefore [Ca2+](i) was also determined in cultured DRG cells using fluo-3/AM. The results showed that LPS (0.1-10 mug/ml) evoked CGRP release in a time- and concentration-dependent manner from DRG neurons. LPS also increased [Ca2+](i) in a concentration-dependent manner. The protein kinase C (PKC) inhibitors, calphostin C 0.5 muM or RO-31-8220 0.1 muM, and the cAMP-dependent protein kinase (PKA) specific inhibitor RP-CAMPS 30 muM or nonspecific inhibitor H8 1 muM inhibited 1 mug/ml LPS-evoked CGRP release and [Ca2+](i) increase from DRG neurons. The cGMP-dependent protein kinase (PKG) inhibitor Rp-8-pCPT-cGMPS 30 muM did not block the LPS response. These data suggest that LPS may stimulate CGRP release and [Ca2+](i) elevation through PKC and PKA but not PKG signaling pathway in DRG neurons of neonatal rats. J. Neurosci. Res. 66:592-600, 2001. (C) 2001 Wiley-Liss, Inc.