Noxious heat-induced CGRP release from rat sciatic nerve axons in vitro (original) (raw)
Related papers
1997
Noxious heat is able to activate heat-sensitive nociceptors in the skin very rapidly, but little is known about the mechanisms by which heat is transduced. We used the whole-cell patch-clamp technique to study the effects of noxious heat and capsaicin on freshly dissociated rat dorsal root ganglion neurons in vitro. Using temperatures between 41°C and 53°C, 8 of 19 small neurons (ø ≤ 30 mm) exhibited a heatevoked inward current. All heat-sensitive neurons tested were also capsaicin-sensitive. Moreover, the heat response tended to be enhanced after capsaicin (360 ± 150 pA versus 125 ± 45 pA, P Ͻ 0.1, n = 7). Two of five heat-insensitive neurons were excited by capsaicin; both neurons developed a heat response after capsaicin. Large neurons (ø Ͼ 30 mm) did not respond to heat (0/7), and were not sensitive to capsaicin either. These findings indicate that heat stimuli may directly activate capsaicin-sensitive primary nociceptive afferents.
European Journal of Neuroscience, 2007
We have previously shown that isolated rat sciatic nerve axons express capsaicin, heat and proton sensitivity and respond to stimulation with a Ca ++-dependent and graded calcitonin gene related peptide (CGRP) release. There is morphological evidence for stimulated vesicular exocytosis and for capsaicin receptor, transient receptor potential vanilloid type-1 (TRPV1, formerly VR1) translocation in the axolemma of unmyelinated nerve fibres. In sensory nerve terminals CGRP release in response to noxious heat can be sensitized by activation of G-protein-coupled receptors and related protein kinases. We present evidence that also in isolated mouse sciatic nerve axons the intracellular protein kinase A (PKA)-and C (PKC)-dependent transduction pathways modulate heatinduced (45°C) CGRP release. This is demonstrated using the direct activators, forskolin and phorbol 12-myristate 13-acetate (PMA), as well as prostaglandin E2 (PGE 2) and bradykinin acting through G-protein-coupled receptors. Inhibition at rest of protein kinases A or C left heat-induced CGRP release unchanged. In TRPV1 knockout animals no sensitization to heat was observed using a combined stimulation by prostaglandin E2 and bradykinin. To a surprising degree, peripheral nerve axons resemble peripheral sensory terminals in their common properties of sensory and signal transduction.
European Journal of Neuroscience, 1999
Capsaicin (CAPS) as well as acidic pH induces Ca 2+ in¯ux in a subset of rat dorsal root ganglion neurons. Here we show that CAPS as well as three different approaches to induce experimental tissue acidi®cation (phosphate buffered solution pH 5.4, CO 2 -gassed solution pH 6.1 and NPE-caged protons) yielded a transient heat sensitization of peripheral nociceptive terminals in rat skin in vitro. The heat sensitization induced by CAPS (1 mM) could be prevented by preloading the neurons with the neuroprotective calcium chelator BAPTA-AM (1 mM). However, this pretreatment had no effect on the sensitization following exposure to acidic solutions (pH 5.4 and pH 6.1). Therefore, the membrane-permeant proton buffer SNARF-AM (200 mM) was used together with BAPTA-AM in order to prevent changes in intracellular pH. Under these conditions heat sensitization by low pH did not occur. To investigate the underlying membrane mechanisms, current recordings together with simultaneous calcium measurements using FURA-2 were performed in neurons isolated from rat dorsal root ganglia. In a subset of these neurons, an increase in [Ca 2+ ] i and concomitant facilitation of heat-activated ionic currents was observed after application of CAPS as well as pH 5.6. Rises in [Ca 2+ ] i thus appear to play an essential role in plastic changes not only of central neurons but also of peripheral nociceptive terminals which may account for heat hyperalgesia.
European Journal of Pharmacology, 1988
Field stimulation (10 Hz for 10 s, 0.5 ms pulse width, 60 V) of the guinea-pig isolated main bronchi (atropine plus indomethacin in the bath) produced reproducible contractions which were abolished by tetrodotoxin or in vitro capsaicin desensitization. These responses were almost abolished by ~-conotoxin GVIA (CTX), a peptide modulator of neuronal calcium channels which, however, did not affect the bronchial contraction due to neurokinin A or to capsaicin. Field stimulation (10 Hz for 2.5 s, 1 ms, 60 V) of the electrically driven, isolated guinea-pig left atria excised from reserpine-pretreated animals (atropine in the bath) produced a delayed positive inotropic response which was abolished by tetrodotoxin or in vitro capsaicin desensitization. This response was abolished by CTX, which did not affect the response to exogenous calcitonin gene-related peptide nor that to capsaicin. These findings indicate that CTX-sensitive mechanisms (presumably Ca channels regulating the release of transmitters) are activated upon antidromic invasion of sensory terminals and consequent production of the 'efferent' response while the activation of sensory nerve endings by capsaicin occurs through CTX-resistant mechanisms.
Neuroscience, 1991
Ah&e&-Protons can release in a Ca2+-dependent manner, calcitonin gene-related peptide (CGRP)-like immunoreactivity from peripheral endings of capsaicin-sensitive afferents. Here we have studied the mechanism by which proton promotes CGRP-like immunoreactivity release and whether the neuropeptide released might exert a biological action. In muscle slices of guinea-pig urinary bladder high pH (PH 8 or 9) media neither enhanced CGRP-like immunoreactivity outflow nor affected the caps&in-evoked CGRP-like immunoreactivity release. The CGRP-like immunoreactivity release evoked by superfusion with pH 5 medium was not affected by tetrodotoxin (0.3 PM) indomethacin (10 PM) or the protein kinase C inhibitor H-7 (30pM). However, it was reduced by 35% in the presence of the voltage-sensitive Ca*+-channel antagonists nifedipine (1 PM) and omega-conotoxin (0.1 PM) and by 80% in presence of the capsaicin "antagonist" Ruthenium Red (10 PM). The CGRP-like immunoreactivity release by capsaicin (10 FM) was reduced by 80% in the presence of Ruthenium Red, and not affected by voltagesensitive Ca*+-channel blockers, while that evoked by 80 mM K+ was decreased by 82% in the presence of nifedipine and omega-conotoxin. The Ca*+-channel agonist Bay K 8644 enhanced the high K+-evoked CGRP-like immunoreactivity release but not that induced by capsaicin or pH 5 medium. Exposure to pH 6 solution of one half of the neck of guinea-pig urinary bladder induced a slowly developing inhibition of electrically evoked contractions, that was absent in the half pre-exposed in vitro to a desensitizing dose of capsaicin. The low pa-evoked CGRP-like immunoreactivity release from capsaicin-sensitive sensory nerves is: (i) like that evoked by capsaicin, largely sensitive to Ruthenium Red; (ii) only in a minor part dependent on voltage-sensitive Ca*+-channels; and (iii) associated with a biological action.
2020
ABSTRACTVoltage-gated CaV2.2 calcium channels are expressed in nociceptors, at pre-synaptic terminals, soma, and axons. CaV2.2 channel inhibitors applied to the spinal cord relieve pain in humans and rodents, especially during pathological pain, but a biological function of nociceptor CaV2.2 channels in processing of nociception, outside pre-synaptic terminals, is not explored. Here, we demonstrate that functional CaV2.2 channels in skin are required for thermal hyperalgesia following intraplantar capsaicin exposure. We provide evidence that CaV2.2 channels at nociceptor free endings release inflammatory signals, ATP and IL-1β. We assess the role of CaV2.2 splice isoforms to capsaicin-induced hyperalgesia measured by thermal and mechanical stimuli. Our data reveal a critical role for peripheral CaV2.2 channels in skin in neurogenic thermal hyperalgesia but not in mechanical hypersensitivity. Inhibition, or the complete lack, of peripheral CaV2.2 channels blunts the hyperalgesia resp...
We investigated the regulation by nerve growth factor of the response of sensory neurons to noxious heat (>43 8C). In dissociated dorsal root ganglion neurons (<30 mm) from adult rat we demonstrated, using perforated patch clamp recording, that the inward current elicited in response to noxious heating is enhanced by nerve growth factor and reduced by capsazepine. The tachyphylaxis observed in response to the second of two heat pulses was reversed in most cells when nerve growth factor was introduced into the medium during the 5 min between the two heat stimuli, similar to ®ndings using capsaicin [X. Shu & L.M. Mendell (1999) Neurosci. Lett. 274, 159±162]. The threshold temperature did not change systematically after nerve growth factor. Using antibodies to TRPV1 and trkA in a subset of cells from which we recorded, we found a virtually perfect correlation between expression of TRPV1 and sensitivity to noxious heat. In addition, trkA expression was perfectly correlated with the ability of nerve growth factor to reverse tachyphylaxis. Thus, this physiological test is a reliable measure of trkA expression in cells sensitive to noxious heat. In agreement with studies in heterologous cells expressing trkA and TRPV1, pharmacologically blocking phospholipase C abolished the effect of nerve growth factor on heatevoked currents in cells veri®ed to express trkA. We conclude that the response of dorsal root ganglion neurons to noxious heat is conditioned by nerve growth factor in the same way as their response to capsaicin and that these responses require the presence of trkA and TRPV1.
Journal of Neurophysiology, 2003
It is well established that the vanilloid receptor, VR1, is an important peripheral mediator of nociception. VR1 receptors are also located in several brain regions, yet it is uncertain whether these supraspinal VR1 receptors have any influence on the nociceptive system. To investigate a possible nociceptive role for supraspinal VR1 receptors, capsaicin (10 nmol in 0.4 μl) was microinjected into either the dorsal (dPAG) or ventral (vPAG) regions of the periaqueductal gray. Capsaicin-related effects on tail flick latency (immersion in 52°C water) and on neuronal activity (on-, off-, and neutral cells) in the rostral ventromedial medulla (RVM) were measured in lightly anesthetized rats. Administration of capsaicin into the dPAG but not the vPAG caused an initial hyperalgesic response followed later by analgesia (125 ± 20.96 min postinjection). The tail flick–related burst in on-cell activity was triggered earlier in the hyperalgesic phase and was delayed or absent during the analgesic...
A rapid capsaicin-activated current in rat trigeminal ganglion neurons
Proceedings of the National Academy of Sciences, 1994
A subpopulation of pain fibers are activated by capsaicin, the ingredient in red peppers that produces a burning sensation when eaten or placed on skin. Previous studies on dorsal root ganglion neurons indicated that capsaicin activates sensory nerves via a single slowly activating and inactivating inward current. In rat trigeminal neurons, we identified a second capsaicin-activated inward current. This current can be distinguished from the slow one in that it rapidly activates and inactivates, requires Ca2+ for activation, and is insensitive to the potent capsaicin agonist resiniferatoxin. The rapid current, like the slower one, is inhibited by ruthenium red and capsazepine. The two capsaicin-activated inward currents share many similarities with the two inward currents activated by lowering the pH to 6.0. These similarities include kinetics, reversal potentials, responses to Ca2+, and inhibition by ruthenium red and capsazepine. These results suggest that acidic stimuli may be an endogenous activator of capsaicingated currents and therefore may rationalize why pain is produced when the plasma acidity is increased, as occurs during ischemia and inflammation.