Microneurographic identification of spontaneous activity in C-nociceptors in neuropathic pain states in humans and rats

Abstract

C-nociceptors do not normally fire action potentials unless challenged by adequate noxious stimuli. However, in pathological states nociceptors may become hyperexcitable and may generate spontaneous ectopic discharges. The aim of this study was to compare rat neuropathic pain models and to assess their suitability to model the spontaneous C-nociceptor activity found in neuropathic pain patients. Studies were performed in normal rats (n=40), healthy human subjects (n=15), peripheral neuropathic pain patients (n=20), and in five rat neuropathic pain models: nerve crush (n=24), suture (n=14), chronic constriction injury (n=12), STZ-induced diabetic neuropathy (n=56), and ddC-induced neuropathy (n=15). Microneurographic recordings were combined with electrical stimulation to monitor activity in multiple C fibers. Stimulation at 0.25 Hz allowed spontaneous impulses to be identified by fluctuations in baseline latency. Abnormal latency fluctuations could be produced by several mechanisms, and spontaneous activity was most reliably identified by the presence of unexplained latency increases corresponding to two or more additional action potentials. Spontaneous activity was present in a proportion of mechano-insensitive C-nociceptors in the patients and all rat models. The three focal traumatic nerve injury models provided the highest proportion (59.5%), whereas the two polyneuropathy models had fewer (18.6%), and the patients had an intermediate proportion (33.3%). Spontaneously active mechano-sensitive C-nociceptors were not recorded. Microneurographic recordings of spontaneous activity in diseased C-nociceptors may be useful for both short- and long-term drug studies, both in animals and in humans.

Microneurographic recording from unmyelinated nerve fibers in neurological disorders: An update

“…The same result was found in a different study in patients with small-fiber neuropathy (Fig. 4) (Serra et al, 2012).…”

Exploration of the conditioning electrical stimulation frequencies for induction of long-term potentiation-like pain amplification in humans

“…Therefore, the 200 Hz with 5 ms intervals in the present study might potentially be associated with less efficiency of afferent input to the spinal neurons compared with the lower frequencies. Compared with A-fiber nociceptors, C-nociceptors are not capable of following the high frequency electrical stimulation (100 Hz and 200 Hz) used in the present study leading to direct conduction failure (Raymond et al, 1990;Weidner et al, 1999;Serra et al, 2012).…”

Gabapentin reduces allodynia and hyperalgesia in painful diabetic neuropathy rats by decreasing expression level of Nav1.7 and p-ERK1/2 in DRG neurons

“…A prominent feature of PDN is neuropathic pain, which is typically characterized in its early phase by hyperalgesia, allodynia, spontaneous pain (Serra et al, 2012;Clark and Lee, 1995). It is well known that the anti-epilepsy drug GBP has a wide use in the treatment of chronic pain conditions, particularly neuropathic pain (Rosenberg et al, 1997;Lin et al, 2005;Jones and Sorkin, 1998).…”