Involvement of peripheral ionotropic glutamate receptors in activation of cutaneous branches of spinal dorsal rami following antidromic electrical stimulation of adjacent afferent nerves in rats

The aim of the present study was to investigate the role of peripheral ionotropic glutamate receptors in the process of signal transmission between adjacent different peripheral sensory nerves. The T9 and T10 cutaneous branches of spinal dorsal rami were dissociated and cut proximally in pentobarbital anesthetized rats. Eighty-seven single afferents from T10 nerve filaments were recorded and characterized by assessing their spontaneous activities. Following 30 s antidromic electrical stimulation (intensity: 1 mA; duration: 0.5 ms; frequency: 20 Hz) of T9 cutaneous branches, the spontaneous activities of Aβ, Aδ and C fibers of T10 nerve were significantly enhanced from 2.00 ± 0.34, 2.42 ± 0.33, and 2.19 ± 0.32 impulses/min to 4.31 ± 0.58, 5.22 ± 0.55, and 5.27 ± 0.69 impulses/min, respectively (n = 29 for each type, P < 0.05). These enhanced spontaneous discharges of T10 nerve were significantly blocked by local treatment of its receptive field with either N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 or non-NMDA receptor antagonist DNQX (0.1 mM, 10 μl for each drug) (P < 0.05). These results suggest that peripheral ionotropic glutamate receptors are involved in the activation of peripheral nerves following the antidromic stimulation of adjacent afferents from different spinal segments. We further provide the direct evidence that neurotransmitters released from adjacent peripheral nerves may also contribute to the occurrence of allodynia as well as secondary hyperalgesia during the pathological nociception.