抄録
Nerve growth factor (NGF), one of the neurotrophins, facilitates sensitivities to noxious stimuli in primary sensory neurons in inflammation. Although endogenous glutamate modulates pain reception mediated by metabotropic glutamate receptors 1 and 5 (mGluR1/5) in primary sensory afferents, it has not been clarified whether NGF signaling modulates mGluR1/5-mediate response. In this study, we examined the effect of NGF on mGluR1/5-mediated responses in cultured dorsal root ganglion (DRG) neurons.
Intracellular calcium concentration in control DRG neurons was scarcely changed under perfusion of DHPG, an mGluR1/5 agonist. On the other hand, treatment of NGF for 3 days markedly increased the proportion of neurons responding to DHPG (increase in calcium concentration), which was abolished in calcium free extracellular solution. In addition, DHPG-induced calcium current was blocked by 5'-iodoresiniferatoxin, a transient receptor potential V1 (TRPV1) antagonist, in NGF-treated DRG neurons. Therefore, the functional interaction between mGluR1/5 and TRPV1 seems to facilitate in NGF-treated DRG neurons. To evaluate underlying molecular mechanism, we examined the expression of mGluR1/5, TRPV1 and A-kinase anchoring protein 5 (AKAP5; the scaffolding protein). NGF increased expression of TRPV1 and AKAP5 protein, while expression of mGluR1 and mGluR5 protein showed no significant change. Immunoprecipitation experiments showed that TRPV1-AKAP5 complex and phosphorylation of TRPV1 at S800 increase by the treatment of NGF, while amount of mGluR1/5-TRPV1 complex remained unchanged.
These results suggest that NGF sensitizes mGluR1/5-mediate response in primary sensory neurons possibly through increase in TRPV1 and/or the phosphorylation.
