Increased conduction velocity of nociceptive primary afferent neurons during unilateral hindlimb inflammation in the anaesthetised guinea-pig
Section snippets
Animals and Complete Freund’s Adjuvant treatment
Experiments were carried out on young female Dunkin Hartley guinea-pigs (weight 150–300 g). Two main groups were used. In the first (treated) group, a unilateral hindlimb inflammation was induced under anaesthesia with 4% halothane. Two intradermal injections of CFA (Sigma), one (70 μl) into the plantar surface of the left hindpaw and another (70 μl) into the lateral region of the leg beside the left knee, were given two or four days prior to the electrophysiological recordings. These injections
Results
CFA treatment produced an area of erythema and oedema in the ipsilateral (left) foot and leg. Compared with the non-injected right foot, the girth of the injected (ipsilateral) foot measured near the first site of CFA injection was significantly increased (in animals from which intracellular recordings were made) from 263±24 to 315±25 mm, i.e. by 19.3±1.0%, at two days after CFA (mean±S.E.M., n=24), and from 274±32 to 329±29 mm, i.e. by 21.7±1.3%, at four days (n=16).
Discussion
We have presented evidence of increased single-point CVs in both central (DR) and peripheral sural nerve fibres of primary afferents after CFA treatment. Single-unit recordings demonstrated increases in single-point CVs in all CV groups (C, Aδ and α/β) in nociceptive but not in LTM neurons. These increases were confirmed by CAP recordings, which showed increases in single-point CVs in the DR and sural nerve, despite the presence of non-nociceptive afferent fibres in both nerve as well as
Conclusion
The present experiments demonstrate a significant increase in DR single-point CVs of nociceptive but not of LTM primary afferent neurons. This was confirmed in whole nerves using CAP recordings from S2 DRs or sural nerves. The shift in single-point CV may be due to alterations in the density and/or efficacy of certain ion channel types, such as Na+ channel subunits and/or other factors that are correlated with CV. The decreased threshold and increased single-point CV of nociceptors seen in the
Acknowledgements
This work was supported by the Wellcome Trust UK. Thanks for technical asistance go to Carol Berry and Barbara Carruthers.
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2016, Neuroscience LettersCitation Excerpt :Intracellular voltage recordings were made from neuronal somata of L4/L5 C-fiber DRG neurons using sharp glass microelectrodes filled with 1 M KCl, (see Refs. [19,20]). Somatic action potentials (APs) evoked antidromically by stimuli applied to the dorsal root were recorded on line, but analyzed offline using the CED Spike II program and scripts (see Refs. [21–23]). The CV for each neuron was estimated (offline) by dividing the conduction distance by latency (in ms) from the stimulus artifact to the AP onset.
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2016, Neuroscience and Biobehavioral ReviewsCitation Excerpt :The CV for each unit (afferent neuron/fiber) is estimated by the latency from the electrical stimulus artifact to the onset of the evoked AP/spike (Fig. 2), and the approximate conduction distance which is usually measured, at the end of the experiment, from the stimulating electrode site to the recording site. The CV (m/s) is estimated by dividing the conduction distance (in mm) by latency (in ms) (see e.g. Djouhri and Lawson, 2001a; Fang et al., 2005a). The boundary between Aαβ- and Aδ-fibers is species dependent (see below).
Persistent hindlimb inflammation induces changes in activation properties of hyperpolarization-activated current (I<inf>h</inf>) in rat C-fiber nociceptors in vivo
2015, NeuroscienceCitation Excerpt :This was based on dorsal root compound APs recorded from rats with same sex, age and weight and under the same conditions (see Fang et al., 2002). As described previously (Djouhri and Lawson, 2001), the dorsal root of the DRG under investigation (L4 or L5) was sectioned close to its entry to the spinal cord, and placed over a pair of bipolar platinum stimulating electrodes. Somatic APs were evoked in DRG neurons by stimulation of the dorsal root with single rectangular pulses (0·3 ms duration) (see Fig. 2).
Chronic inflammatory pain is associated with increased excitability and hyperpolarization-activated current (I <inf>h</inf>) in C- but not Aδ-nociceptors
2012, PainCitation Excerpt :This is why only about 2 C-nociceptors per experiment are recorded in normal and CFA rats. Previous studies showed several changes in the membrane properties of C- and Aδ-nociceptive neurons in guinea pig, 2 to 4 days after CFA-induced inflammation [13,15,16]. These included decreases in AP duration at base, AP rise time and fall time, and increased maximum rate of AP rise and fall [13,15] and increased CV [16].