Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, C42
Acute and chronic effects of GDNF and BDNF on thermoTRPs from rat dorsal root ganglion (DRG) neurons
C. Ciobanu1, A. Babes1, G. Reid2
1. Department of Animal Physiology and Biophysics, University of Bucharest, Bucharest, Romania. 2. Department of Physiology, University College Cork, Cork, Ireland.
TRPA1, TRPV1 and TRPM8 are cation channels expressed in sensory neurons involved in thermal perception and pain sensing. Neurotrophins (NTFs) Brain Derived Neurotrophic Factor (BDNF) and Glial cell line-Derived Neurotrophic Factor (GDNF) are essential for neuronal development and survival but they are also involved in pain signaling and neuronal modulation. The aim of this study was to assess effects of chronic and acute treatment with BDNF and GDNF on functional expression and activation of TRPM8, TRPA1 and TRPV1 in rat DRG neurons. Calcium Green-1 imaging was used to monitor responses of neurons stimulated with specific activators for TRP channels. Primary cultures of adult Wistar rat DRG were split in two; half of the neurons were incubated with 100ng/ml NTF for 12-24h, and the other half used as control. For acute effects, neurons were treated for 7 minutes with 100ng/ml BDNF or GDNF between two consecutive stimuli (MO or heat). For all experiments, serum free medium (Bottenstein et al., 1980) was used. Chronic treatment with NTFs changed the pattern of functional expression of TRP channels. Thus, GDNF increased the population of MO-sensitive neurons from 28% to 37% (141/513 to 117/313, χ2 test, p < 0.01) and BDNF increased the fraction of CAP-sensitive neurons from 61% to 76% (312/513 to 208/274, χ2 test, p < 0.001). BDNF also increased the amplitude of the responses to Me (from ΔF/F0 = 0.20 ± 0.02, mean ± S.E.M., n = 69 up to 0.26 ± 0.02, n = 53, p<0.05, Student t test), MO (from 0.46 ± 0.01, n = 141, to 0.54 ± 0.02, n = 78, p<0.01, Student t test) and CAP (from 0.62 ± 0.01, n = 312, up to 0.68 ± 0.02, n = 208, p<0.01, Student t test). The fraction of neurons co-expressing TRPV1 and TRPA1 (neurons activated by both MO and CAP) was increased by chronic GDNF from 24% to 34% (χ2 test, p < 0.001). Acute treatment with both GDNF and BDNF significantly reduced the magnitude of TRPV1 and TRPA1 desensitization induced by repeated applications of heat and MO. The ratio between the amplitudes of the second and the first response to heat (used as a measure of desensitization) was 0.68 ± 0.05, n = 28 for control compared to 1.10 ± 0.13, n = 33 for BDNF treated neurons (Student t test, p < 0.01). GDNF had the same effect (ratio control 0.74 ± 0.1, n = 15 vs. 1.20 ± 0.11, n = 36, Student’s unpaired t test, p < 0.05). GDNF also reduced the magnitude of AITC-induced TRPA1 desensitization (ratio 0.81 ± 0.07, for control vs. 1.00 ± 0.05, p < 0.05). Our results suggest that NTFs regulate the expression and activity of the transducer channels TRPA1 and TRPV1, leading to enhanced neuronal sensitivity to noxious stimuli. Acute treatment with these neurotrophins abolishes desensitization of TRPA1 and TRPV1 which are both involved in pain sensing. Thus, BDNF and GDNF may be involved in induction and maintenance of chronic pain in the peripheral nervous system.
Where applicable, experiments conform with Society ethical requirements