Actions of capsaicin on mouse dorsal root ganglion cells in vitro

doi:10.1016/0304-3940(93)90733-2

Neuroscience Letters

Volume 157, Issue 2, 23 July 1993, Pages 187-190

https://doi.org/10.1016/0304-3940(93)90733-2 Get rights and content

Abstract

The effects of capsaicin were investigated on different populations of dorsal root ganglion cells in the in vitro mouse spinal cord-dorsal root ganglion preparation using intracellular electrodes. Dorsal root ganglion cells were characterised by the conduction velocity of their propagated action potential evoked by electrical stimulation of the dorsal root, and by the shape of their action potential. All cells with C-fiber characteristics (conduction velocity < 0.6 m/s; broad action potential with shoulder on the descending slope) were depolarised and generated action potentials when capsaicin (100–700 nM) was added to the bathing solution for 30 s. At these concentrations the membrane potential of DRG cells with myelinated fibers (conduction velocity > 2.0 m/s) was unaffected. Concentrations of capsaicin of 1.0–5.0 μM depolarised 50% of cells with conduction velocity > 10 m/s. During the depolarization of the membrane no action potentials were generated. In 50% of the capsaicin-sensitive neurons with conduction velocity faster than 10 m/s there was an initial hyperpolarization. Electrical stimulation of the dorsal root failed to evoke action potentials during the depolarization in 38% of the DRG cells with myelinated fibers and in all C-fibers tested within 10 min of the onset of the capsaicin effect. Passive depolarization of the membrane by intrasomal current injection mimicked the conduction block in neurons with large myelinated fibers. These observations confirm that capsaicin applied directly to the dorsal root ganglion affects, in a dose-dependent manner, both myelinated and unmyelinated primary afferents with a higher potency for C-neurons. Capsaicin evoked action potentials in C-neurons but not in neurons with myelinated fibers. Action potential block by capsaicin was a common feature in all types of fibers, indicating that capsaicin may impair the propagation of sensory signals generated from the periphery.

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Cited by (22)

Synergistic antinociceptive effect of a calcium channel blocker and a TRPV1 blocker in an acute pain model in mice
2017, Life Sciences
Citation Excerpt :
Ascending of nociceptive signals triggered by capsaicin is dependent upon activation nociceptive fibers by capsaicin. In fact, capsaicin induces membrane depolarization in nociceptive neurons that, in turn, triggers the firing of action potentials that leads to calcium and sodium influx at nerve terminals [23–25]. The amount of calcium entering through the TRPV1-associated pore is relatively low as shown by electrophysiological records [26], but larger amounts of extracellular Ca2 + may enter the cell when VGCCs are activated by action potential discharges [27].
Extensive evidence supports a role for voltage-gated calcium channels (VGCC) and TRPV1 receptors in pain transmission and modulation. We investigated the profile of analgesic interaction between Phα1β toxin (a VGCC blocker) and SB366791 (selective TRPV1 antagonist) in a model of acute pain induced by capsaicin. Changes in body temperature induced by combination regimens were also evaluated.
Isobolographic approach with a fixed dose-ratio of combined drugs was used to determine whether antinociceptive interaction of Phα1β and SB366791 are subadditive, additive or synergic. Body temperature was obtained by thermal infrared imaging.
Phα1β and SB366791 interact in a synergistic manner to cause antinociception. We found an interaction index (α) of 0.07 for Phα1β and SB366791 when these drugs were injected together intraplantarly, which indicates that in vivo interaction between these drugs is greater than additive interaction. Synergism also occurred when intraplantar SB366791 was administered simultaneously with intrathecal Phα1β (interaction index α = 0.06) suggesting a 15 fold rise in potency on the analgesic effect of these drugs when they are added together. It was observed no significant alterations in body temperature of animals treated with this combination regimen.
Our data reveal that Phα1β toxin potentiates in 15 fold the antinociceptive action of the TRPV1 blocker SB366791. Therefore, lower doses of these drugs are required to achieve antinociceptive effects when these agents are given in combination.
Phα1β toxin prevents capsaicin-induced nociceptive behavior and mechanical hypersensitivity without acting on TRPV1 channels
2013, Neuropharmacology
Citation Excerpt :
Conversely, the TRPV1 antagonist SB366791 reduced Ca2+ transients with lower potency but higher efficacy, moreover the inhibitory effect of SB366791 and Phα1β did not overlap but were additive. It is well known that capsaicin induces membrane depolarization and can trigger the firing of action potentials in DRG cells (Heyman and Rang, 1985; Petruska et al., 2000; Urban and Dray, 1993). Furthermore, the amount of calcium entering through the TRPV1-associated pore is relatively low in voltage-clamp experiments at −80 mV (Zeilhofer et al., 1997), whereas larger amounts of extracellular Ca2+ may enter the cell when VGCCs are activated e.g., by action potential discharges (Greffrath et al., 2001).
Phα1β toxin is a peptide purified from the venom of the armed spider Phoneutria nigriventer, with markedly antinociceptive action in models of acute and persistent pain in rats. Similarly to ziconotide, its analgesic action is related to inhibition of high voltage activated calcium channels with more selectivity for N-type. In this study we evaluated the effect of Phα1β when injected peripherally or intrathecally in a rat model of spontaneous pain induced by capsaicin. We also investigated the effect of Phα1β on Ca²⁺ transients in cultured dorsal root ganglia (DRG) neurons and HEK293 cells expressing the TRPV1 receptor. Intraplantar or intrathecal administered Phα1β reduced both nocifensive behavior and mechanical hypersensitivity induced by capsaicin similarly to that observed with SB366791, a specific TRPV1 antagonist. Peripheral nifedipine and mibefradil did also decrease nociceptive behavior induced by intraplantar capsaicin. In contrast, ω-conotoxin MVIIA (a selective N-type Ca²⁺ channel blocker) was effective only when administered intrathecally. Phα1β, MVIIA and SB366791 inhibited, with similar potency, the capsaicin-induced Ca²⁺ transients in DRG neurons. The simultaneous administration of Phα1β and SB366791 inhibited the capsaicin-induced Ca²⁺ transients that were additive suggesting that they act through different targets. Moreover, Phα1β did not inhibit capsaicin-activated currents in patch-clamp recordings of HEK293 cells that expressed TRPV1 receptors. Our results show that Phα1β may be effective as a therapeutic strategy for pain and this effect is not related to the inhibition of TRPV1 receptors.
PLC-β3 signals upstream of PKCε in acute and chronic inflammatory hyperalgesia
2007, Pain
While protein kinase Cε has been shown to contribute to acute and chronic mechanical hyperalgesia, its upstream signaling pathway has received little attention. Since phospholipase C can signal to PKCε and has been implicated in nociceptor sensitization, we tested if it is upstream of PKCε in mechanisms underlying primary mechanical hyperalgesia. In the rat, the PKCε-dependent mechanical hyperalgesia and hyperalgesic priming (i.e., a form of chronic latent enhanced hyperalgesia) induced by carrageenan were attenuated by a non-selective PLC inhibitor U-73122. A lipid mediator of PLC signaling, l-α-lysophosphatidylcholine produced dose-dependent mechanical hyperalgesia and hyperalgesic priming, which was attenuated by EAVSLKPT, a selective PKCε inhibitor. However, U-73122 did not attenuate hyperalgesia induced by ψεRACK, a selective PKCε activator. Antisense to PLC-β3 isoform, which was found in small-diameter dorsal root ganglion neurons, also attenuated carrageenan-induced acute and chronic-latent hyperalgesia. These studies support the suggestion that PLC-β3 is an important upstream signaling molecule for PKCε-mediated acute and chronic inflammatory pain.
Differential pH and capsaicin responses of Griffonia simplicifolia IB4 (IB4)-positive and IB4-negative small sensory neurons
2004, Neuroscience
Protons play a key role in nociception caused by inflammation and ischaemia, but little is known about the relative sensitivities of different dorsal root ganglion (DRG) neurons. We have therefore examined the responses in vitro of rat DRG cells classified according to whether or not they bind Griffonia simplicifolia IB4 (IB4), a lectin which is widely used to distinguish between two major populations of small diameter neurons. Under voltage-clamp conditions, proton-activated inward currents were found in approximately 90% of small DRG neurons and showed one of three waveforms: transient, sustained or mixed. The majority of IB4-positive (IB4+) neurons (63%) gave rise to sustained inward currents that were sensitive to capsazepine. In contrast, the most prevalent waveform in small IB4-negative (IB4−) neurons (69%) was a mixed response containing transient and sustained components. The transient component was inhibited by amiloride whilst the sustained component showed a variable sensitivity to capsazepine. We also found that more IB4+ cells responded to capsaicin and, on average, gave rise to a larger magnitude of response than small IB4− neurons, consistent with their higher prevalence and greater amplitude of vanilloid receptor 1 (TRPV1)-like acid responses. The increase in intracellular Ca²⁺ induced by capsaicin was also slightly greater in IB4+ neurons and in these cells its magnitude correlated with the level of TRPV1 immunoreactivity.
Our data suggest that acid-sensing ion channels (ASICs) and TRPV1 are the major acid-sensitive receptors in small IB4− neurons, whilst TRPV1 is the predominant one in IB4+ neurons. Because ASIC-like responses were approximately 10-fold more sensitive to changes in H⁺ than TRPV1-like responses, we speculate that small IB4− rather than IB4+ neurons play an essential role in sensing acid. Our results also highlight differences in capsaicin responses between IB4+ and IB4− small neurons and reveal the close link between capsaicin responses and levels of TRPV1 expression.
Electrophysiological properties of identified trigeminal ganglion neurons innervating the cornea of the mouse
2000, Neuroscience
The cornea is innervated by three functional types of neurons: mechanosensory, polymodal and cold-sensitive neurons, all of which are presumed to be nociceptive. To explore if corneal neurons constitute a heterogeneous population according to their electrophysiological properties, intracellular recordings were made in vitro from trigeminal ganglion neurons innervating the cornea of the mouse. Corneal neurons were labelled with FluoroGold applied after a corneal epithelial wound. Five days later, the trigeminal ganglion attached to the eye by its nerves was removed and placed in a superfusion chamber. FluoroGold-positive cells that also responded to electrical stimulation of the cornea were considered corneal neurons. Non-corneal neurons were also studied. Based on their conduction velocity at room temperature, corneal neurons were classified as myelinated A (>1.5 m/s) or non-myelinated C (≤1.5 m/s) neurons. A and C neurons differed significantly in their passive and active electrical properties. Virtually all corneal C neurons and about two-thirds of A neurons exhibited a hump in the falling phase of the action potential (S neurons), while the remaining A neurons (F neurons) showed faster and narrower action potentials without a hump. Among non-corneal neurons, A neurons of the F type were found in a proportion of about 50%. Based on their ability to produce somatic action potentials in tetrodotoxin (0.1 μM), non-corneal neurons were classified as fully or partially tetrodotoxin sensitive, which were mainly of the Aδ type, and tetrodotoxin resistant, which were C neurons. Among the corneal neurons, those with a faster action potential, possibly associated to the expression of tetrodotoxin-sensitive Na⁺ channels, may be pure corneal mechanosensory neurons, all of which are known to belong to the Aδ type. Neurons with a slower action potential showing a hump in the repolarization phase are both corneal Aδ and C polymodal nociceptive neurons, a type of cell in which tetrodotoxin-resistant Na⁺ channels have been identified. The possibility is raised that the small population of neurons with a very high input resistance are cold-sensitive neurons.
From the present results, we suggest that the electrophysiological properties of primary sensory neurons innervating the cornea are attributable not only to their conduction velocities, but also to the functional characteristics of their peripheral nerve terminals.
Action of capsaicin on dorsal root-evoked synaptic transmission to substantia gelatinosa neurons in adult rat spinal cord slices
1999, Brain Research
An action of capsaicin was investigated on dorsal root-evoked synaptic transmission to substantia gelatinosa (SG) neurons in adult rat spinal cord slices by use of the whole-cell voltage-clamp technique. In 79% of neurons examined, superfusing capsaicin (1 μM) for 30 s depressed a C-fiber-evoked excitatory synaptic current in a manner sensitive to a capsaicin-receptor antagonist, capsazepine (10 μM). On the contrary, Aδ-fiber-evoked excitatory and inhibitory synaptic currents were unaffected by capsaicin in all of cells tested. It is concluded that capsaicin specifically acts on C-afferents, resulting in an inhibition of evoked excitatory transmission to the SG; this may contribute to, at least in part, an acute analgesic action of capsaicin.

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Actions of capsaicin on mouse dorsal root ganglion cells in vitro

Abstract

Brain Res.

Neurosci. Lett.

Brain Res.

Neurosci. Lett.

Neuroscience

Eur. J. Pharmacol.

Brain Res.

Brain Res.

Brain Res.

Neurosci. Lett.

Neuroscience

Pain

Brain Res.

The site of action of capsaicin on the guinea-pig isolated ileum

Naunyn-Schmiedeberg's Arch. Pharmacol.