Effects of insulin-like growth factor-1 on neurochemical phenotypes of cultured dorsal root ganglion neurons with excitotoxicity induced by glutamate.

Insulin-like growth factor-1 (IGF-1) is a neurotrophic factor and plays an important role in promoting axonal growth from dorsal root ganglion (DRG) neurons. The neuropeptide- and neurofilament (NF)-immunoreactive (IR) neurons are two major phenotypical classes in DRG. Whether IGF-1 affects neurochemical phenotypes of DRG neurons remains unknown. In the present study, primary cultured DRG neurons were used to determine the effects of IGF-1 on neurochemical phenotypes of the neurons with excitotoxicity induced by glutamate (Glu). DRG neurons were dissociated and cultured for 48 hours and then exposed to IGF-1 (20 nmol/L), Glu (0.2 mmol/L), Glu (0.2 mmol/L) plus IGF-1 (20 nmol/L) for additional 24 hours. The DRG neurons were continuously exposed to culture media as control. After that, all above cultured DRG neurons were processed for detecting mRNA levels of calcitonin gene-related peptide (CGRP) and neurofilament-200 (NF-200) by real time-PCR analysis. CGRP and NF-200 expression in situ was determined by fluorescent labeling technique. The results showed that CGRP mRNA, but not NF-200 mRNA, increased after IGF-1 administration in the absence or presence of Glu. IGF-1 could increase the percentage of CGRP-expressing neurons, but not NF-200-expressing neurons, in the absence or presence of Glu. The ability of IGF-1 on CGRP expression may play a role in neurogenic inflammation or nociception.