Local injection of alpha, beta-methylene ATP induces excitation of primary afferent fibers in rats

Abstract

Abstract: Objective To observe the excitation and sensitization of dorsal cutaneous primary afferent fibers induced by P2X agonist alpha, beta-methylene ATP (αβme-ATP) in rats. Methods By means of single fiber electrophysiological recordings on the nerve filaments isolated from the dorsal cutaneous branches of the T₉-T₁₃ spinal nerves, the effects of αβme-ATP (100 μmol/L, 10 μl) injection into the cutaneous receptive field on the mechanical threshold and spontaneous discharge of rat primary sensory afferent units were observed. Results The mean mechanical threshold of Aδ and C fibers prior to αβme-ATP injection were 0.384±0.018 and 0.943±0.102 mN, and lowered to 0.304±0.013 and 0.659±0.071 mN after the injection, respectively (P<0.05, P<0.01). The mechanical threshold of the Aβ fibers before αβme-ATP injection was 0.301±0.019 mN, and slightly lowered to 0.288±0.018 mN after the injection (P>0.05). Injection of αβme-ATP (10 μl) into the receptive fields evoked spontaneous discharge in 7.7% of the Aβ fibers, 66.7% of Aδ fibers and 75.0% of C fibres, respectively, and the proportions of Aδ and C fibers with spontaneous discharge evoked by αβme-ATP were significantly greater than that of Aβ fibers (P<0.05). In the control experiments, injection of saline did not significantly affect spontaneous discharge or excite the nerve fibers. The mean discharge frequency of Aδ and C fibers increased from 0.73±0.24 and 0.54±0.21 impulses/min before injection to 3.05±0.65 and 8.53±2.04 impulses/min during the injection, with subsequent reduction to 2.40±0.60 and 6.68±1.68 impulses/min in the following 5 min (P<0.05). In contrast to Aδ and C fibers, Aβ fibers exhibited no significant changes in the mean discharge frequency in response to αβme-ATP (0.23±0.09 impulses/min before injection, 0.28±0.09 impulses/min during injection and 0.22±0.14 impulses/min after injection, P>0.05). The excitatory effects of αβme-ATP on the discharge rate in Aδ and C primary afferent terminal could be observed in the entire course of experiment. Conclusion Peripheral application of αβme-ATP, an ATP analogue, excites and sensitizes a subpopulation of Aδ and C fibers but not Aβ fibers of rat dorsal cutaneous primary afferent fibers.

CLC Number:

ZHANG Qi, ZHAO Yan, TIAN Yu-ling, GUO Yuan, CAO Dong-yuan, WANG Hui-sheng. Local injection of alpha, beta-methylene ATP induces excitation of primary afferent fibers in rats[J]. Journal of Southern Medical University, 2005, 25(10): 1256-1260.

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