Development of spontaneous activity and mechanosensitivity in axotomized afferent nerve fibers during the first hours after nerve transection in rats

Abstract

1. Spontaneous activity and ectopic mechanical excitability of axotomized unmyelinated and myelinated fibers in the sural nerve were examined in anesthetized rats. The analysis was performed within 30 h after the nerve lesion using single-fiber recordings that were performed proximal to the severed nerve end. 2. Among all unmyelinated fibers tested (n = 865), 4-8% exhibited persistent spontaneous activity of low and irregular frequency. The percentage of spontaneously active C fibers did not change significantly during the first 30 h. Only 6 of 796 A fibers had spontaneous activity. 3. Mechanical stimulation of the cut nerve end excited 5-8% of all C fibers under investigation. No development with time could be detected in the frequency of mechanically excitable C fibers. In contrast, beginning 6 h after nerve transection, the number of mechanically excitable A fibers rose with time, reaching 27% after 22-30 h. 4. Among the A fibers (C fibers) that exhibited mechanical excitability or spontaneous activity, only 4% (25%) had both properties, whereas 96% (75%) were either mechanosensitive or spontaneously active. 5. With time after the nerve lesion, the mean discharge rate of all spontaneously discharging C fibers decreased significantly from 49 imp/min (0.5-9 h after nerve lesion) to 11 imp/min after 22-30 h. The mean discharge rate of C fibers exhibiting solely spontaneous activity and those C fibers that were additionally mechanosensitive did not differ significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotherapy-evoked neuropathic pain: Abnormal spontaneous discharge in A-fiber and C-fiber primary afferent neurons and its suppression by acetyl-l-carnitine

“…The recording method involves cutting the nerve in preparation for microfilament dissections and it is well known that axons discharge when transected. However, this "injury discharge" lasts for no more than a minute or two in the vast majority of fibers (Wall et al, 1974;Devor and Bernstein, 1982;Michaelis et al, 1995;Blenk et al, 1996). The nearly complete absence of spontaneous discharge in the control animals is consistent with our procedures.…”

Multiple Interacting Sites of Ectopic Spike Electrogenesis in Primary Sensory Neurons

“…Together, these observations indicate that the original spontaneous singlet spiking arose at the cut end of the sciatic nerve (Michaelis et al, 1995) and that, when the soma was depolarized, the invading axon spike triggered DAP-evoked spike bursts that originated in the cell soma. Note that under these conditions, individual bursts were of hybrid origin, the first spike in each burst being axonal and subsequent spikes somatic.…”

Sensory Transduction in Peripheral Nerve Axons Elicits Ectopic Action Potentials

“…These sensory properties included the development of spontaneous ectopic discharge (Michaelis et al, 1995), axonal sensitivity to a variety of algesic agents such as bradykinin (BK), prostaglandin E2, acidic pH, and capsaicin (Michaelis et al, 1997;Moalem et al, 2005), and the appearance of mechanosensitivity and thermosensitivity along the axon itself at the developing neuroma site (Koschorke et al, 1991;Michaelis et al, 1995Michaelis et al, , 1997Blenk et al, 1996). The common hypothesis explaining these observations is that anterograde axonal transport of sensory transducer molecules such as heatactivated channels or of voltage-gated ion channels causes an accumulation of these membrane proteins at the lesioned site.…”