Acute and chronic effects of neurotrophic factors BDNF and GDNF on responses mediated by thermo-sensitive TRP channels in cultured rat dorsal root ganglion neurons.

Neurotrophic factors (NTFs), beside regulating neuronal survival in the central and peripheral nervous system, are also involved in the modulation of neuronal function in the adult animal. Both brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) levels are altered in pathological pain states, and exogenous BDNF and GDNF have multiple effects on pain behavior, depending on the animal model (i.e. inflammatory vs. neuropathic). Thermally gated TRP channels TRPM8, TRPA1 and TRPV1 play a significant role in pain signaling and their pattern and level of expression as well as their biophysical properties are altered in chronic pain states. Our aim was to investigate the effect of long-term and acute exposure to BDNF and GDNF on the functional expression of these thermoTRP channels in cultured rat dorsal root ganglion (DRG) neurons. We found that while BDNF treatment primarily increased the fraction of capsaicin-sensitive (TRPV1-expressing) neurons, GDNF exposure led to an increase in the allyl isothiocyanate (AITC)-responding (TRPA1-expressing) population. Moreover, BDNF treatment increased the amplitude of the response to both AITC and capsaicin. Acute treatment with both NTFs leads to a reduction in the magnitude of tachyphylaxis to noxious stimuli (heat and AITC). Overall, our data provides evidence for a role of BDNF and GDNF in regulating the pattern of expression and level of activity of the transducer channels TRPA1 and TRPV1, leading to enhanced neuronal sensitivity to painful stimuli and increased co-expression of thermoTRP channels.