Tetrodotoxin block of A-fibre afferents from skin and muscle – a tool to study pure C-fibre effects in the spinal cord

Abstract

The properties of tetrodotoxin (TTX)-resistant C-fibre afferents of the dorsal roots were tested in Sprague-Dawley rats. Dorsal roots (L4-L6) were blocked with TTX (0.5-1 micro M) and the amplitude of the first response of the dorsal horn superficial interneurones (cord dorsum potential, CDP) to electrical stimulation of peripheral C-fibres in combination with natural noxious stimulation was taken as measure for intact conductivity of different kinds of noxious input by means of the C-fibre refractory period. After blockade of dorsal roots with TTX, formerly masked CDPs from muscle C-fibre afferents were uncovered. Noxious pressure to the gastrocnemius soleus muscle belly and noxious pinch to the calcanean tendon proved to be TTX resistant and therefore was propagated centrally. For cutaneous heat nociceptors it could also be shown that conductivity was intact after blockade of the dorsal roots with TTX. However, we could not exclude the TTX resistance of non-nociceptive receptors of muscle or skin. Nevertheless, blockade of afferents with TTX together with suitable stimulation techniques proves to be a reliable method to investigate central effects from C-fibre afferents without contaminating effects from A-fibres in the rat.

Noxious Stimuli Evoke a Biphasic Flexor Reflex Composed of Aδ-Fiber-Mediated Short-Latency and C-Fiber-Mediated Long-Latency Withdrawal Movements in Mice

“…4), confirming the involvement of myelinated fibers in this movement. The remaining movement was solely the long-latency movement, which was considered to be mediated by TTX-resistant C-fibers (3,4,12). Consistent with the study in cats shown by Schomburg et al (3), we observed the concomitant increments of the long-latency movement with the TTX-induced suppression of the short-latency movement.…”

“…We next further characterized the afferent fibers involved in the biphasic movement using TTX, which selectively blocks myelinated A-fibers, leaving unmyelinated C-fibers intact (3,4,12). A small peace of cotton was soaked with TTX (1 -10 mM, 50 ml) and then placed onto the sciatic nerve, which had been exposed by removing the perineural sheath.…”

“…This is supported by the results obtained using focal application of TTX to the sciatic nerve. TTX is used to achieve a selective and reliable blockade of the myelinated Afibers (3,4,12). Upon application of TTX, the shortlatency movement was selectively suppressed and finally abolished (Fig.…”

Changes in Tetrodotoxin-Resistant C-Fibre Activity during Fatiguing Isometric Contractions in the Rat

“…The heterogeneous family of small-diameter afferent fibres embraces a particular fraction of fibres expressing a high density of tetrodotoxin-resistant (TTX-R) voltage-gated sodium channels (VGSC) with a conduction velocity predominantly within the C-fibre range [19]; [20], see also [21]–[23]. The projection zone of TTX-R gastrocnemius–soleus (GS) afferent fibres in the rat spinal cord has been described recently, the synaptic field potential of the TTX-R muscle afferents reached their maximum value in lamina IV-VI of the dorsal horn [24].…”

“…In the rat, TTX-R afferent fibres respond to pinch and heat within the noxious range [20]. VGSC-Na v 1.8 (which give rise to the TTX–R inward sodium current) is shown to be substantial for pain sensation at low temperatures [26].…”