Selective Activation of Primary Afferent Fibers Evaluated by Sine-Wave Electrical Stimulation

Abstract

Transcutaneous sine-wave stimuli at frequencies of 2000, 250 and 5 Hz (Neurometer) are thought to selectively activate Aβ, Aδ and C afferent fibers, respectively. However, there are few reports to test the selectivity of these stimuli at the cellular level. In the present study, we analyzed action potentials (APs) generated by sine-wave stimuli applied to the dorsal root in acutely isolated rat dorsal root ganglion (DRG) preparations using intracellular recordings. We also measured excitatory synaptic responses evoked by transcutaneous stimuli in substantia gelatinosa (SG) neurons of the spinal dorsal horn, which receive inputs predominantly from C and Aδ fibers, using in vivo patch-clamp recordings. In behavioral studies, escape or vocalization behavior of rats was observed with both 250 and 5 Hz stimuli at intensity of ~0.8 mA (T5/ T250), whereas with 2000 Hz stimulation, much higher intensity (2.14 mA, T2000) was required. In DRG neurons, APs were generated at T5/T250 by 2000 Hz stimulation in Aβ, by 250 Hz stimulation both in Aβ and Aδ, and by 5 Hz stimulation in all three classes of DRG neurons. However, the AP frequencies elicited in Aβ and Aδ by 5 Hz stimulation were much less than those reported previously in physiological condition. With in vivo experiments large amplitude of EPSCs in SG neurons were elicited by 250 and 5 Hz stimuli at T5/ T250. These results suggest that 2000 Hz stimulation excites selectively Aβ fibers and 5 Hz stimulation activates noxious transmission mediated mainly through C fibers. Although 250 Hz stimulation activates both Aδ and Aβ fibers, tactile sensation would not be perceived when painful sensation is produced at the same time. Therefore, 250 Hz was effective stimulus frequency for activation of Aδ fibers initiating noxious sensation. Thus, the transcutaneous sine-wave stimulation can be applied to evaluate functional changes of sensory transmission by comparing thresholds with the three stimulus frequencies.

Sensory afferents regenerated into dorsal columns after spinal cord injury remain in a chronic pathophysiological state

“…When we recorded from single fibers ( figure 4C), the CV of the uninjured segment was well within this range for Aβ fibers (Feasby et al, 1981,Shin et al, 1997. The regenerated axon segments did not conduct slower than 2m/sec, the upper CV of C-fibers (Leem et al 1993) and these axon segments were able to follow reliably at stimulation frequencies of up to 10 Hz, a frequency at which C-fibers show conduction changes (Koga et al 2005). Since we stimulated regenerated fibers at spinal level T9, it is also unlikely that the fibers were displaced Ia afferents that normally terminate in Clarke's column.…”

Epigenetic Gene Silencing Underlies C-Fiber Dysfunctions in Neuropathic Pain

“…Using the EPW test to evaluate C-, A␦-, and A␤-fiber functions after nerve injury (Koga et al, 2005;Matsumoto et al, 2008;Ueda, 2008), we found that AS-ODN significantly blocks hypoesthesia, seen in response to 5 Hz (Cfiber) stimuli, but does not block hypersensitization, seen in response to 250 Hz (A␦-fiber) or 2000 Hz (A␤-fiber) stimuli (Fig. 5A-C).…”

Efficacy of a Novel Device for Assessment of Autonomic Sensory Function in the Rat Bladder

“…The Neurometer® electrodiagnostic stimulator (Neurotron, Inc, Baltimore, MD), through the application of a constant current neuroselective electrical stimulus, provides reliable measures of spinal sensory and peripheral sensory nerve function for both large and small myelinate, as well unmyelinated nerve fibers [6][7][8][9] . The Neurometer® delivers sine-wave stimuli at frequencies of 2000, 250, and 5 Hz that have been shown to selectively stimulate large myelinated (Aβ), small myelinated (Aδ), and small unmyelinated (C) fibers, respectively 10,11 . This easy to conduct electro diagnostic procedure has been used in the evaluation of bladder sensory function in humans 12 .…”