Inhibitory Effect Of Electrical Stimulation On GABA-induced Depolarization In Rat Dorsal Root Ganglion Neurons

Object: By using different frequencies of electrical stimulation on sciatic nerve, we observe the effect of GABA-induced depolarization on rat dorsal root ganglion neurons. In order to investigate the effect of electrical stimulation on nociceptive information in DRG.Methods: We dissociated the DRG attached dorsal roots of sciatic nerve. With intracellular microelectrode recording method, different frequencies of electrical stimulation (0.02~5 ms, 2 V) were applied to neurons freshly dissociated from rat sciatic nerve by Powerlab recording system, stimulus intensity was higher than threshold intensity. Conduction velocity (CV) was measured by relative value between conduction distance and latency to onset of the evoked somatic action potential (AP), this was a method to know the cell size and classification of the excited fiber. Then different frequencies of electrical stimulation (1 Hz, 2 Hz, 5 Hz, 10 Hz and 50 Hz) with duration (5 ms) and intensity (2 V) were applied to the distal end of sciatic nerve in rat. We observed the variation of membrane potential amplitude of GABA (3×10-4 mol/L)-induced depolarization in rat dorsal root ganglion neurons before and after electric al stimulation.Results: 1. To measure the conduction velocity of nerve fibers: Totally 40 cells can produce AP, 70% (28/40) fibers belong to Aδfibers and 30% (12/40) are Aβfibers. 2. Compare depolarization amplitude before and after stimulation at different times: Each frequency of electrical stimulation (1 Hz, 2 Hz, 5 Hz, 10 Hz and 50 Hz) can inhibit GABA-induced membrane potential in dorsal root ganglion neurons 2 min after stimulation. The amplitude of inhibitory membrane potential was different when the stimulation frequencies were different, and the time course of maximum inhibitory effect also was different. When the frequencies of stimulation were 1 Hz, 2 Hz, 5 Hz, 10 Hz and 50 Hz, the maximum inhibitory effect separately happened at 2 min, 2 min, 24 min, 12 min, 2 min, inhibitory ratio were 16.78%±3.64%, 19.80%±3.80%, 24.68%±3.99%, 29.20%±3.36% and 20.44%±3.12%(n=4~5)for each stimulation frequency;and the depressant effect persistent to 24 min, 24 min, 48 min,﹥72 min and 48 min after electrical stimulation for each stimulation frequency. 10 Hz stimulation's depressant effect persistent the longest. 3. Compare depolarization amplitude of different stimulation frequencies at the same time: Compare the inhibitory depolarization amplitude of GABA-induced membrane potential in dorsal root ganglion neurons by different frequencies of stimulation at same time course, after 2 min, 12 min, 24 min, 36 min, 48 min, 60 min and 72 min stimulation, 5 Hz and 10 Hz stimulation's depressant effect on GABA-induced dorsal root ganglion neurons membrane potential were stronger than other stimulation frequencies, and the depressant effect of 10 Hz stimulation was stronger than 5 Hz stimulation. Conclusion: Each frequency of electrical stimulation on sciatic nerve in rat can inhibit the depolarization amplitude of GABA-induced membrane potential in dorsal root ganglion neurons, and 10 Hz electrical stimulation depressant effect was the strongest. It is possible that electrical stimulation make nociceptive information transmit easily by activate Aδ-fiber nociceptors, or it may phosphorylate GABAA receptor to compress GABA-induced"presynaptic inhibition", thus facilitated release of the excitatory transmitter, leads to the pain.