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48 THE MOLECULAR BASIS OF COLD SENSATION AND COLD PAIN
Invited Presentations / Workshop – Mechanisms And Translational Research 2 / European Journal of Pain 11(S1) (2007) S1–S57
ably, when both receptors were activated, by ET-1 alone, the separate inhibitors of PKA and of PKC suppressed pERK, by 50% and 100%, respectively. Blockade of post-synaptic neurotransmitter receptors, or inhibition of TRPV1, did not lower ET-1-elevated pERK; the relevant ET receptors are thus post-synaptic. There appears to be a contradiction between antinociceptive effects of i.t. ET-1 in vivo and its activation of pro-nociceptive spinal pERK in vitro.
S19
domains I and II of Nav1.8 prevents p38-mediated increase in current density in transfected DRG neurons. Our study shows that the effect of p38 MAPK on Nav1.8 is direct and suggests that one mechanism by which inhibitors of p38 reduce inflammatory and neuropathic pain may be through preventing p38-mediated increase of Nav1.8 current density. doi:10.1016/j.ejpain.2007.03.060
doi:10.1016/j.ejpain.2007.03.059
Workshop – Mechanisms And Translational Research 2: COLD PAIN – FROM SKIN TO BRAIN
46 PHOSPHORYLATION OF SODIUM CHANNEL NAV1.8 BY P38 MAPK INCREASES CURRENT DENSITY IN DRG NEURONS A. Hudmon a,c,d, J. Choi a, L. Tyrrell a, J.A. Black a, A.M. Rush a,e, S.G. Waxman a, S.D. Dib-Hajj *,a,b a
Department of Neurology and the Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, United States b Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT, United States c Biochemistry, STARK Neuroscience Research Institute, Indianapolis, IN, United States d Molecular Biology, STARK Neuroscience Research Institute, Indianapolis, IN, United States e NeuroSolutions Ltd., Coventry, UK Sensory neuron-specific sodium channel Nav1.8 and p38 mitogen-activated protein kinase are wellrecognized targets in inflammatory and neuropathic pain. Nav1.8 channels produce the slowly inactivating, tetrodotoxin-resistant (TTX-R) current in dorsal root ganglia (DRG) neurons which contribute most of the inward current underlying the depolarizing phase of action potentials. Nerve injury or inflammation of peripheral tissues activates p38 in DRG neurons which acutely impact nociceptive neuron excitability. We investigated the potential association and modulation of Nav1.8 by activated p38 in DRG neurons. We used molecular, cellular and electrophysiological methods to investigate co-localization of Nav1.8 and p38, and the effect of activation of p38 on Nav1.8 current, in DRG neurons. We demonstrate that Nav1.8 and p38 are co-localized in DRG neurons and more importantly, that activated p38 increases Nav1.8 current density in these neurons. The increase in current density is not accompanied by changes in gating properties of the channel. We now establish for the first time that Nav1.8 is directly phosphorylated by p38, and show that alanine substitution of two p38 phospho-acceptor serine residues on the loop joining
47 Workshop Summary: COLD PAIN – FROM SKIN TO BRAIN A. Binder Department of Neurology, Christian-Albrechts-Universita¨t Kiel, Klinik Fu¨r Neurologie, Sektion Fu¨r Neurologische Schmerzforschung Und Therapie, Kiel, Germany Evoked pain is known to be a striking symptom of neuropathic pain. However, the importance of cold hyperalgesia and cold hypersensitivity has been recognized just recently. Multiple underlying mechanisms are suspected to explain the variety of clinical pictures presenting pathological cold sensation and cold (evoked) pain. Thus, the aims of this workshop are to highlight: the molecular logic for the perception of cold-evoked pain, the current understanding of cold thermoreceptors, the controversy regarding TRPA1 and cold signaling, the human surrogate models of cold hyperalgesia, the phenomenology of cold hyperalgesia in clinical pain states, the brain mechanisms implicated in acute and chronic physiological and pathophysiological cold sensation and pain.
doi:10.1016/j.ejpain.2007.03.061
48 THE MOLECULAR BASIS OF COLD SENSATION AND COLD PAIN D.D. McKemy Department of Biological Sciences, Neurobiology Section and School of Dentistry, Division of Diagnostic Sciences, University of Southern California, Los Angeles, USA The perception of temperature is a fundamental part of sensory perception and allows us to evaluate both our
S20
Invited Presentations / Workshop – Mechanisms And Translational Research 2 / European Journal of Pain 11(S1) (2007) S1–S57
external and internal environments. Thermosensitive nerves can be segregated into those that detect either innocuous or noxious (painful) temperatures; the latter being nociceptors. Over the last decade, ion channels of the transient receptor potential (TRP) family have been identified and shown to respond at distinct temperature thresholds, thus establishing the molecular basis for thermosensation. While much is known of those channels mediating the perception of noxious heat, those proposed to be involved in cool to noxious cold sensation, TRPM8 and TRPA1, have only recently been described. The former channel is a receptor for menthol, and links the sensations provided by this and other cooling compounds to temperature perception. While TRPM8 almost certainly performs a critical role in cold signaling, its part in nociception is still at issue. The latter channel, TRPA1, is activated by many pungent compounds, but has also been postulated to mediate our perception of noxious cold temperatures. However, a number of studies of the thermosensory properties of TRPA1 both in vitro and in vivo have been contradictory. Thus, the molecular logic for the perception of cold-evoked pain remains enigmatic and this part of the workshop will summarize our current understanding of these cold thermoreceptors, as well as address the current controversy regarding TRPA1 and cold signaling. doi:10.1016/j.ejpain.2007.03.062
49 TOWARDS SURROGATE MODELS OF COLD HYPERALGESIA N. Attal INSERM U 792, Hopital Ambroise Pare, AP-HP, Boulogne-Billancourt, France Cold hyperalgesia is a clinically important phenomenon and is observed in a number of peripheral or central nervous system lesions, particularly complex regional pain syndrome, oxaliplatin induced neuropathies and central post-stroke pain. In a prospective cohort of patients treated with chemotherapy, we have shown that cold hyperalgesia may be the unique expression of oxaliplatin-induced neurotoxicity. The mechanisms of cold hyperalgesia due to a nerve lesion are not clearly elucidated and have been suggested to involve a central lack of inhibition exerted by cold-specific afferents on nociceptors, a central sensitization to non-nociceptive coldfiber input or a peripheral sensitization of cold-sensitive C nociceptors. One possible model for studying cold hyperalgesia in humans is represented by topical menthol. We will present the results of recent psychophysical studies in healthy subjects indicating, that topical menthol modulates selectively the responses to noxious cold
(Hatem et al., 2006; Wasner et al., 2004). These models may be suitable for use in painful patients and their possible applications for the study of cold hyperalgesia in humans will be discussed. References Hatem, S., Attal, N., Willer, J. C., & Bouhassira, D. (2006). Psychophysical study of the effects of topical application of menthol in healthy volunteers. Pain, 122, 190–196. Wasner, G., Schattschneider, J., Binder, A., & Baron, R. (2004). Topical menthol – a human model for cold pain by activation and sensitization of C nociceptors. Brain, 127, 1159–1171. doi:10.1016/j.ejpain.2007.03.063
50 BRAIN MECHANISMS OF COLD-PAIN AND COLD HYPERALGESIA A. Binder Division of Neurological Pain Research and Therapy, Department of Neurology, Christian-Albrechts-Universitaet Kiel, Germany Brain-imaging techniques using functional MRI, PET and magnetencephalography (MEG) have opened new emerging insights in exploring brain mechanisms implicated in the processing of acute and chronic coldpain and cold-evoked pain. Furthermore, translational research, i.e. implementing human surrogate models of cold-pain and cold allodynia/hyperalgesia into functional imaging studies and the comparison with results derived from studies in clinical pain states, have enriched the knowledge. Using two different surrogate models of cold allodynia in healthy volunteers, i.e. topical application of menthol or the peripheral A-fiber block, experimental cold allodynia was shown to be processed in different cerebral areas depending on the underlying mechanism of generation. Peripheral sensitization favoured a preferential activation of the thermoreceptive spinothalamic pathway in the menthol model that did not differ from the activation matrix of physiological cold-pain. A-fiber block attenuated the thermoreceptive input through the lateral pain pathway and produced a consistent increase in cold-induced activity within the medial pain system pointing to a pathological disinhibition of activity in the ascending polymodal nociceptive channel following A-fiber block. These results will be compared with the different patterns of brain activity associated with cold-pain and cold-evoked pain studied in patients suffering from chronic neuropathic pain, e.g. syringomyelia. doi:10.1016/j.ejpain.2007.03.064
ably, when both receptors were activated, by ET-1 alone, the separate inhibitors of PKA and of PKC suppressed pERK, by 50% and 100%, respectively. Blockade of post-synaptic neurotransmitter receptors, or inhibition of TRPV1, did not lower ET-1-elevated pERK; the relevant ET receptors are thus post-synaptic. There appears to be a contradiction between antinociceptive effects of i.t. ET-1 in vivo and its activation of pro-nociceptive spinal pERK in vitro.
S19
domains I and II of Nav1.8 prevents p38-mediated increase in current density in transfected DRG neurons. Our study shows that the effect of p38 MAPK on Nav1.8 is direct and suggests that one mechanism by which inhibitors of p38 reduce inflammatory and neuropathic pain may be through preventing p38-mediated increase of Nav1.8 current density. doi:10.1016/j.ejpain.2007.03.060
doi:10.1016/j.ejpain.2007.03.059
Workshop – Mechanisms And Translational Research 2: COLD PAIN – FROM SKIN TO BRAIN
46 PHOSPHORYLATION OF SODIUM CHANNEL NAV1.8 BY P38 MAPK INCREASES CURRENT DENSITY IN DRG NEURONS A. Hudmon a,c,d, J. Choi a, L. Tyrrell a, J.A. Black a, A.M. Rush a,e, S.G. Waxman a, S.D. Dib-Hajj *,a,b a
Department of Neurology and the Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, United States b Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT, United States c Biochemistry, STARK Neuroscience Research Institute, Indianapolis, IN, United States d Molecular Biology, STARK Neuroscience Research Institute, Indianapolis, IN, United States e NeuroSolutions Ltd., Coventry, UK Sensory neuron-specific sodium channel Nav1.8 and p38 mitogen-activated protein kinase are wellrecognized targets in inflammatory and neuropathic pain. Nav1.8 channels produce the slowly inactivating, tetrodotoxin-resistant (TTX-R) current in dorsal root ganglia (DRG) neurons which contribute most of the inward current underlying the depolarizing phase of action potentials. Nerve injury or inflammation of peripheral tissues activates p38 in DRG neurons which acutely impact nociceptive neuron excitability. We investigated the potential association and modulation of Nav1.8 by activated p38 in DRG neurons. We used molecular, cellular and electrophysiological methods to investigate co-localization of Nav1.8 and p38, and the effect of activation of p38 on Nav1.8 current, in DRG neurons. We demonstrate that Nav1.8 and p38 are co-localized in DRG neurons and more importantly, that activated p38 increases Nav1.8 current density in these neurons. The increase in current density is not accompanied by changes in gating properties of the channel. We now establish for the first time that Nav1.8 is directly phosphorylated by p38, and show that alanine substitution of two p38 phospho-acceptor serine residues on the loop joining
47 Workshop Summary: COLD PAIN – FROM SKIN TO BRAIN A. Binder Department of Neurology, Christian-Albrechts-Universita¨t Kiel, Klinik Fu¨r Neurologie, Sektion Fu¨r Neurologische Schmerzforschung Und Therapie, Kiel, Germany Evoked pain is known to be a striking symptom of neuropathic pain. However, the importance of cold hyperalgesia and cold hypersensitivity has been recognized just recently. Multiple underlying mechanisms are suspected to explain the variety of clinical pictures presenting pathological cold sensation and cold (evoked) pain. Thus, the aims of this workshop are to highlight: the molecular logic for the perception of cold-evoked pain, the current understanding of cold thermoreceptors, the controversy regarding TRPA1 and cold signaling, the human surrogate models of cold hyperalgesia, the phenomenology of cold hyperalgesia in clinical pain states, the brain mechanisms implicated in acute and chronic physiological and pathophysiological cold sensation and pain.
doi:10.1016/j.ejpain.2007.03.061
48 THE MOLECULAR BASIS OF COLD SENSATION AND COLD PAIN D.D. McKemy Department of Biological Sciences, Neurobiology Section and School of Dentistry, Division of Diagnostic Sciences, University of Southern California, Los Angeles, USA The perception of temperature is a fundamental part of sensory perception and allows us to evaluate both our
S20
Invited Presentations / Workshop – Mechanisms And Translational Research 2 / European Journal of Pain 11(S1) (2007) S1–S57
external and internal environments. Thermosensitive nerves can be segregated into those that detect either innocuous or noxious (painful) temperatures; the latter being nociceptors. Over the last decade, ion channels of the transient receptor potential (TRP) family have been identified and shown to respond at distinct temperature thresholds, thus establishing the molecular basis for thermosensation. While much is known of those channels mediating the perception of noxious heat, those proposed to be involved in cool to noxious cold sensation, TRPM8 and TRPA1, have only recently been described. The former channel is a receptor for menthol, and links the sensations provided by this and other cooling compounds to temperature perception. While TRPM8 almost certainly performs a critical role in cold signaling, its part in nociception is still at issue. The latter channel, TRPA1, is activated by many pungent compounds, but has also been postulated to mediate our perception of noxious cold temperatures. However, a number of studies of the thermosensory properties of TRPA1 both in vitro and in vivo have been contradictory. Thus, the molecular logic for the perception of cold-evoked pain remains enigmatic and this part of the workshop will summarize our current understanding of these cold thermoreceptors, as well as address the current controversy regarding TRPA1 and cold signaling. doi:10.1016/j.ejpain.2007.03.062
49 TOWARDS SURROGATE MODELS OF COLD HYPERALGESIA N. Attal INSERM U 792, Hopital Ambroise Pare, AP-HP, Boulogne-Billancourt, France Cold hyperalgesia is a clinically important phenomenon and is observed in a number of peripheral or central nervous system lesions, particularly complex regional pain syndrome, oxaliplatin induced neuropathies and central post-stroke pain. In a prospective cohort of patients treated with chemotherapy, we have shown that cold hyperalgesia may be the unique expression of oxaliplatin-induced neurotoxicity. The mechanisms of cold hyperalgesia due to a nerve lesion are not clearly elucidated and have been suggested to involve a central lack of inhibition exerted by cold-specific afferents on nociceptors, a central sensitization to non-nociceptive coldfiber input or a peripheral sensitization of cold-sensitive C nociceptors. One possible model for studying cold hyperalgesia in humans is represented by topical menthol. We will present the results of recent psychophysical studies in healthy subjects indicating, that topical menthol modulates selectively the responses to noxious cold
(Hatem et al., 2006; Wasner et al., 2004). These models may be suitable for use in painful patients and their possible applications for the study of cold hyperalgesia in humans will be discussed. References Hatem, S., Attal, N., Willer, J. C., & Bouhassira, D. (2006). Psychophysical study of the effects of topical application of menthol in healthy volunteers. Pain, 122, 190–196. Wasner, G., Schattschneider, J., Binder, A., & Baron, R. (2004). Topical menthol – a human model for cold pain by activation and sensitization of C nociceptors. Brain, 127, 1159–1171. doi:10.1016/j.ejpain.2007.03.063
50 BRAIN MECHANISMS OF COLD-PAIN AND COLD HYPERALGESIA A. Binder Division of Neurological Pain Research and Therapy, Department of Neurology, Christian-Albrechts-Universitaet Kiel, Germany Brain-imaging techniques using functional MRI, PET and magnetencephalography (MEG) have opened new emerging insights in exploring brain mechanisms implicated in the processing of acute and chronic coldpain and cold-evoked pain. Furthermore, translational research, i.e. implementing human surrogate models of cold-pain and cold allodynia/hyperalgesia into functional imaging studies and the comparison with results derived from studies in clinical pain states, have enriched the knowledge. Using two different surrogate models of cold allodynia in healthy volunteers, i.e. topical application of menthol or the peripheral A-fiber block, experimental cold allodynia was shown to be processed in different cerebral areas depending on the underlying mechanism of generation. Peripheral sensitization favoured a preferential activation of the thermoreceptive spinothalamic pathway in the menthol model that did not differ from the activation matrix of physiological cold-pain. A-fiber block attenuated the thermoreceptive input through the lateral pain pathway and produced a consistent increase in cold-induced activity within the medial pain system pointing to a pathological disinhibition of activity in the ascending polymodal nociceptive channel following A-fiber block. These results will be compared with the different patterns of brain activity associated with cold-pain and cold-evoked pain studied in patients suffering from chronic neuropathic pain, e.g. syringomyelia. doi:10.1016/j.ejpain.2007.03.064