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343 PHARMACOLOGICAL CHARACTERIZATION OF A NEW SELECTIVE SIGMA-1 RECEPTOR ANTAGONIST SHOWING ANTIHYPERALGESIC AND ANTIALLODYNIC ACTIVITY IN DIFFERENT PAIN MODELS IN MICE
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Poster Sessions / European Journal of Pain 13 (2009) S55–S285
340 REDUCED NEUROPATHIC PAIN BEHAVIOURS AND ACTIVITY-INDUCED SPINAL SENSITIZATION IN SIGMA-1 RECEPTOR KNOCKOUT MICE 1 B. De la Puente1 , X. Nadal2 , E. Portillo-Salido1 , R. Sanchez-Arroyos ´ , 1 1 1 1 3 S. Ovalle , G. Palacios , Ao. ´ Muro , L. Romero , J.M. Entrena , J.M. Baeyens3 , J.A. Lopez-Garc´ ´ ıa4 , R. Maldonado2 , D. Zamanillo1 , 1 1 J.M. Vela *. Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain; 4 Department of Physiology, Faculty of Medicine, Universidad de Alcal´ a de Henares, Alcal´ a de Henares, Spain In the present study we investigated the relevance of sigma-1 receptor (s1 R) in modulating nerve injury-evoked pain and spinal sensitization-related events. For this purpose, wild-type mice and mice lacking the s1 R gene were exposed to partial sciatic nerve ligation and neuropathic pain-related behaviors were investigated. To explore underlying mechanisms, spinal processing of repetitive nociceptive stimulation and expression of extracellular signalregulated kinase (ERK) were also investigated. Sensitivity to noxious heat of homozygous s1 R knockout mice did not differ from wildtype mice. Baseline values obtained in s1 R knockout mice before nerve injury in the plantar, cold plate and von Frey tests were also indistinguishable from those obtained in wild-type mice, suggesting that basic mechanisms for perception of sensory and nociceptive inputs are intact in mice lacking s1 Rs. However, cold and mechanical allodynia did not develop in s1 R null mice exposed to nerve injury. Using isolated spinal cords we found that mice lacking s1 R showed reduced wind-up responses respect to wild-type mice, as evidenced by a reduced number of action potentials induced by trains of C-fiber intensity stimuli. In addition, in contrast to wild-type mice, s1 R knockout mice did not show increased phosphorylation of extracellular signal-regulated kinase (ERK) in the spinal cord after sciatic nerve injury. Both wind-up and ERK activation have been related to mechanisms of spinal cord sensitization. Our findings identify s1 R as a constituent of the mechanisms modulating activity-induced sensitization in pain pathways and point to s1 R as a new potential target for the treatment of neuropathic pain. 341 POTENTIATION OF MORPHINE ANALGESIA BUT INHIBITION OF ITS REWARDING EFFECTS FOLLOWING COADMINISTRATION OF A NEW SELECTIVE SIGMA-1 RECEPTOR ANTAGONIST A. Vidal1 *, C. Tourino ˜ 2 , L. Romero1 , J.M. Baeyens3 , D. Zamanillo1 , R. Maldonado2 , J.M. Vela1 . 1 Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain Opioids are widely used in the management of pain, but side effects limit their use. The addictive liability is one among the undesirable effects of opioids that limits their widespread use for routine prescription to manage pain outside the clinical practice. Herein we describe a new selective sigma-1 receptor (s1 R) antagonist (S1RA) that, when administered in combination with morphine, potentiated morphine analgesia and reduced its rewarding effects. S1RA was evaluated in the acute thermal nociceptive tests (tail-flick and hot plate) in mice and it did not increase significantly the response latency except for the highest dose tested. Interestingly, at subactive doses when administered alone, S1RA was able to potentiate the analgesic effect of morphine. This opioid-potentiating effect is s1 R-mediated as S1RA was unable to enhance morphine analgesia when administered to mice lacking s1 R. In order to evaluate the capability of S1RA to modify the
rewarding properties of morphine we used the conditioned place preference paradigm in mice. S1RA did not produce any effect in place conditioning when administered alone, suggesting that S1RA did not exert neither rewarding nor aversive effects. However, S1RA attenuated the rewarding effects induced by morphine. We conclude that combination of S1RA with morphine results in potentiation of analgesia and parallel blocking of the rewarding effects of morphine. These pharmacological results underline the potential usefulness of combining S1RA with morphine and other opiods and points to selective sigma-1 receptor antagonists as a new strategy to increase efficacy and safety when used in combination with opiods. 342 CSF2RB, A GENE IN THE PAIN1 AUTOTOMY LOCUS IN MICE, IS ASSOCIATED WITH NEUROPATHIC PAIN IN HUMANS AND IN MICE M. Yarkoni-Abitbul1 *, S. Zhang2 , D. Tichauer1 , T. Elahipanah1 , R. Dorfman3 , Z. Seltzer1 . 1 University of Toronto, Toronto, Canada; 2 Zhejiang University, Hangzhou, China; 3 Hospital for Sick Children, Toronto, Canada Background and Aims: Pain1 is a genetic locus on mouse chromosome 15 harbouring yet unidentified gene(s) for autotomy variability following peripheral neurectomy, a model of spontaneous neuropathic pain (NP). We conducted a genomewide analysis to identify genes in Pain1 and other loci whose expression levels in dorsal root ganglia (DRGs) and spinal cord (SC) are correlated with autotomy levels in mice, and to test whether these genes correlate with human NP. Methods: The hindpaw of 35 A/J (‘A’) and C57BL/6J (‘B’) inbred mice was denervated by sciatic and saphenous neurectomy, or sham-operated, or left intact (5 mice/group/strain). Using 70 Agilent microarrays, we profiled the expression levels of all genes in L3-L6 DRGs and SC (1 array/tissue/mouse). Results: The expression of Csf2rb, encoding GM-CSF (granulocytemacrophage-colony stimulating factor) receptor 2-beta and located in Pain1, had a 1.7 fold-change between naïve A and B mice in DRG (p = 0.03), and a 1.9 fold-change between A mice expressing high versus low autotomy (p = 8.7×10−5 ) in SC. The human Csf2rb was then genotyped in 85 traumatic leg amputees and 336 women post-mastectomy (with or without NP) using 13 tagging SNPs. Two SNPs (rs2075943 and rs960739) were significantly associated with phantom limb pain (p = 0.007 and p = 0.045), and post-mastectomy pain (p = 0.047 and p = 0.04, respectively). Conclusions: Csf2rb is a good candidate for the gene in Pain1 that controls autotomy variability in mice and NP in humans. 343 PHARMACOLOGICAL CHARACTERIZATION OF A NEW SELECTIVE SIGMA-1 RECEPTOR ANTAGONIST SHOWING ANTIHYPERALGESIC AND ANTIALLODYNIC ACTIVITY IN DIFFERENT PAIN MODELS IN MICE ˜ 1 , X. Nadal2 , A. Dordal1 , G. Gris1 , A. Vidal1 , D. Zamanillo1 , J. Burgueno L. Romero1 *, M. Laloya1 , B. Aubel1 , C. Segales ´ 1 , J.M. Baeyens3 , 4 2 J.A. Lopez-Garc´ ´ ıa , R. Maldonado , J.M. Vela1 . 1 Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain; 4 Department of Physiology, Faculty of Medicine, Universidad de Alcal´ a de Henares, Alcal´ a de Henares, Spain Previous studies using sigma-1 receptor (s1 R) knockout mice identify s1 R as a constituent of the mechanisms modulating activity-induced sensitization in nociceptive pathways. Given the attractive therapeutic potential, we have developed a selective s1 R antagonist (S1RA). Herein, we describe for the first time the main pharmacological properties of S1RA, a new compound
Poster Sessions / European Journal of Pain 13 (2009) S55–S285
with analgesic properties acting on s1 R. S1RA shows high affinity for the s1 R and does not show significant affinity for a panel of more than 150 other receptors, enzymes and ion channels tested. The IC50 of binding to s1 R was not significantly different in the presence of phenytoin in competition assays, which identifies S1RA as an antagonist at s1 R. In isolated spinal cords from mice, S1RA produced clear inhibition of the wind-up responses, as evidenced by a reduced number of action potentials induced by trains of C-fiber intensity stimuli. SR1A was active in pain models involving sensitization and chronic pain. Acute administration of S1RA reduced capsaicin-induced mechanical hypersensitivity, formalin-induced pain behaviours and allodynia and hyperalgesia in the neuropathic pain model of partial sciatic nerve ligation. In addition, chronic administration of S1RA during 11 and 21 days significantly reduced the expression of thermal hyperalgesia, mechanical allodynia and cold allodynia in nerve-injured mice. No tolerance to the analgesic effect of S1RA was found after repeated administration. Altogether, these pharmacological results confirm the therapeutic potential of blocking s1 R for the treatment of pain and identify S1RA as a new analgesic compound with a new mechanism of action. 344 PERIPHERAL INJURY REGULATES OPIOID RECEPTOR EXPRESSION IN DORSAL ROOT GANGLIA AND NERVE PAW OF RATS V.O. Zambelli1 *, V.P. Gutierrez1 , C.A. Parada2 , Y. Cury1 . 1 Laboratory of Pathophysiology, Butantan Institute, S˜ ao Paulo, Brazil; 2 Departament of Physiology and Biophysics de Fisiologia e Biof´ısica, UNICAMP, Campinas, Brazil Aims: The efficacy of opioid drugs is enhanced in the presence of tissue injury and inflammation. Previous data of our group demonstrated that, in rats, prostaglandin E2 (PGE2 , intraplantar/i.pl.) and chronic constriction injury (CCI) of the sciatic nerve increase the peripheral antinociceptive efficacy of opioid agonists. The aim of this study is to characterize the effect of PGE2 - induced hyperalgesia and CCI on opioid receptor expression in dorsal root ganglia (DRG) and nerve paw (NP). Methods: The expression of m, k and d-opioid receptors was evaluated by immunoblotting, in DRG or NP (ipsilateral and contralateral to injury) 3 h after i.pl. injection of PGE2 (100 ng/paw) or 14 days after CCI. Results: PGE2 increases the expression of m- and k-opioid receptors in NP (43% and 71%, respectively) and decreases (30%) the expression of d-opioid receptors. m-opioid receptor expression is also increased in the ipsi and contralateral DRG (79 and 27%, respectively), while k-opioid receptor expression is increased only in the ipsilateral DRG (168%). CCI up-regulates m-opioid receptors in NP (27%) and DRG (ipsi and contralaterally, 49 and 20%, respectively) and d-opioid receptors in the ipsilateral DRG. On the other hand, k-opioid receptors are down-regulated by CCI in both NP (51%) and DRG (21%). Conclusion: Peripheral opioid receptor expression is distinct regulated by the presence of acute and chronic tissue injury. The upor down-regulation of opioid receptors can contribute to alterations in the peripheral efficacy of opioids in different pain conditions. Financial Support: FAPESP (07/03404–4, 07/00135–2)
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345 LACK OF INTERACTION BETWEEN CUTANEOUS C-NOCICEPTORS AND SYMPATHETIC EFFERENT FIBRES IN PATIENTS WITH COMPLEX REGIONAL PAIN SYNDROME M. Campero1 *, H. Bostock2 , T. Baumann3 , J. Ochoa4 . 1 Departamento de Neurolog´ıa, Facultad de Medicina Cl´ınica Alemana-Universidad del Desarrollo, Santiago, Chile; 2 Institute of Neurology, University College London, Queen Square, London, United Kingdom; 3 Department of Neurological Surgery, Oregon Health & Science University, Portland, United States; 4 Good Samaritan Hospital & Medical Center and Oregon Health & Science University, Portland, United States Background and Aims: Although ‘reflex sympathetic dystrophy’ has been replaced by ‘complex regional pain syndrome’ (CRPS) type I, there remains a widespread presumption that the sympathetic nervous system is actively involved in maintaining chronic neuropathic pain (sympathetically maintained pain, SMP), in absence of detectable nerve damage. Different sites have been entertained for abnormal interaction between sympathetic and somatosensory pathways. Recent data from a patient with SMP has suggested that silent cutaneous nociceptors are activated by catecholamines released from sympathetic efferents in peripheral nerves. Methods: We have used microneurography to evaluate possible electrophysiological sympathetic/nociceptor interactions in 25 patients diagnosed with CRPS I (n = 14) and II (n = 11) by recording from single identified C nociceptor subtypes. Results: Potential effects of sympathetic activity upon 28 polymodal nociceptors and 13 silent nociceptors, recorded in CRPS patients, were assessed but no evidence of activation of nociceptors related to sympathetic discharge was found, even though nociceptors in 6 CRPS II patients exhibited pathological behavior. Conclusions: We conclude that activation of nociceptors by sympathetic efferent discharges is not a common pathogenic event in either CRPS I or CRPS II patients. 346 EVALUATION OF THE SUDOMOTOR C-FIBER FUNCTION WITH TRANSCUTANEOUS ELECTRICAL STIMULATION IN NORMAL SUBJECTS P. Kokotis1 , A. Fyllos1 *, A. Papagianni1 , N. Karandreas1 , M. Schmelz2 . 1 EMG Laboratory, Department of Neurology, Aeginition Hospital, University of Athens, Athens, Greece; 2 Department of Anesthesiology, University of Heidelberg, Mannheim, Germany Aim: Transcutaneous electrical activation of thin efferent sympathetic sudomotor fibers results in sweating. We determined normal values of the quantitive sweating response as an objective functional parameter of the autonomous nervous system. History: Originally the sudomotor responses were chemically induced by acetyl choline – electrical stimulation is suggested to be better controlled. Method: Electrodes and a sweat capsule are fixed on the left medial forearm, with a reference on the right. The skin is stimulated for 30 seconds by constant current stimulus (7.5 mA, 0.5 ms) at 3 frequencies (5, 20, 100 Hz) in random order with an interval of 3 minutes. As possible confounding variables we included in the study: gender, age, height, weight, room and skin temperature. Results: The majority of subjects (70 healthy subjects, 36 men, mean age: 41.67, range: 19–73) responded to electric current of 5 Hz frequency with sweating. Only in 10% a higher threshold (5 Hz10 mA) was found. We evaluated the area under the curve of the responses (AUC), the mean derivative of the single responses, and the slope (b) of the three derivative values of the sweat response increasing with increasing stimulation frequency. Normal values were established and significant correlations were found between age and the log of the maximum area (p = 0.0366) and the log of (b) (p = 0.0038).
Poster Sessions / European Journal of Pain 13 (2009) S55–S285
340 REDUCED NEUROPATHIC PAIN BEHAVIOURS AND ACTIVITY-INDUCED SPINAL SENSITIZATION IN SIGMA-1 RECEPTOR KNOCKOUT MICE 1 B. De la Puente1 , X. Nadal2 , E. Portillo-Salido1 , R. Sanchez-Arroyos ´ , 1 1 1 1 3 S. Ovalle , G. Palacios , Ao. ´ Muro , L. Romero , J.M. Entrena , J.M. Baeyens3 , J.A. Lopez-Garc´ ´ ıa4 , R. Maldonado2 , D. Zamanillo1 , 1 1 J.M. Vela *. Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain; 4 Department of Physiology, Faculty of Medicine, Universidad de Alcal´ a de Henares, Alcal´ a de Henares, Spain In the present study we investigated the relevance of sigma-1 receptor (s1 R) in modulating nerve injury-evoked pain and spinal sensitization-related events. For this purpose, wild-type mice and mice lacking the s1 R gene were exposed to partial sciatic nerve ligation and neuropathic pain-related behaviors were investigated. To explore underlying mechanisms, spinal processing of repetitive nociceptive stimulation and expression of extracellular signalregulated kinase (ERK) were also investigated. Sensitivity to noxious heat of homozygous s1 R knockout mice did not differ from wildtype mice. Baseline values obtained in s1 R knockout mice before nerve injury in the plantar, cold plate and von Frey tests were also indistinguishable from those obtained in wild-type mice, suggesting that basic mechanisms for perception of sensory and nociceptive inputs are intact in mice lacking s1 Rs. However, cold and mechanical allodynia did not develop in s1 R null mice exposed to nerve injury. Using isolated spinal cords we found that mice lacking s1 R showed reduced wind-up responses respect to wild-type mice, as evidenced by a reduced number of action potentials induced by trains of C-fiber intensity stimuli. In addition, in contrast to wild-type mice, s1 R knockout mice did not show increased phosphorylation of extracellular signal-regulated kinase (ERK) in the spinal cord after sciatic nerve injury. Both wind-up and ERK activation have been related to mechanisms of spinal cord sensitization. Our findings identify s1 R as a constituent of the mechanisms modulating activity-induced sensitization in pain pathways and point to s1 R as a new potential target for the treatment of neuropathic pain. 341 POTENTIATION OF MORPHINE ANALGESIA BUT INHIBITION OF ITS REWARDING EFFECTS FOLLOWING COADMINISTRATION OF A NEW SELECTIVE SIGMA-1 RECEPTOR ANTAGONIST A. Vidal1 *, C. Tourino ˜ 2 , L. Romero1 , J.M. Baeyens3 , D. Zamanillo1 , R. Maldonado2 , J.M. Vela1 . 1 Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain Opioids are widely used in the management of pain, but side effects limit their use. The addictive liability is one among the undesirable effects of opioids that limits their widespread use for routine prescription to manage pain outside the clinical practice. Herein we describe a new selective sigma-1 receptor (s1 R) antagonist (S1RA) that, when administered in combination with morphine, potentiated morphine analgesia and reduced its rewarding effects. S1RA was evaluated in the acute thermal nociceptive tests (tail-flick and hot plate) in mice and it did not increase significantly the response latency except for the highest dose tested. Interestingly, at subactive doses when administered alone, S1RA was able to potentiate the analgesic effect of morphine. This opioid-potentiating effect is s1 R-mediated as S1RA was unable to enhance morphine analgesia when administered to mice lacking s1 R. In order to evaluate the capability of S1RA to modify the
rewarding properties of morphine we used the conditioned place preference paradigm in mice. S1RA did not produce any effect in place conditioning when administered alone, suggesting that S1RA did not exert neither rewarding nor aversive effects. However, S1RA attenuated the rewarding effects induced by morphine. We conclude that combination of S1RA with morphine results in potentiation of analgesia and parallel blocking of the rewarding effects of morphine. These pharmacological results underline the potential usefulness of combining S1RA with morphine and other opiods and points to selective sigma-1 receptor antagonists as a new strategy to increase efficacy and safety when used in combination with opiods. 342 CSF2RB, A GENE IN THE PAIN1 AUTOTOMY LOCUS IN MICE, IS ASSOCIATED WITH NEUROPATHIC PAIN IN HUMANS AND IN MICE M. Yarkoni-Abitbul1 *, S. Zhang2 , D. Tichauer1 , T. Elahipanah1 , R. Dorfman3 , Z. Seltzer1 . 1 University of Toronto, Toronto, Canada; 2 Zhejiang University, Hangzhou, China; 3 Hospital for Sick Children, Toronto, Canada Background and Aims: Pain1 is a genetic locus on mouse chromosome 15 harbouring yet unidentified gene(s) for autotomy variability following peripheral neurectomy, a model of spontaneous neuropathic pain (NP). We conducted a genomewide analysis to identify genes in Pain1 and other loci whose expression levels in dorsal root ganglia (DRGs) and spinal cord (SC) are correlated with autotomy levels in mice, and to test whether these genes correlate with human NP. Methods: The hindpaw of 35 A/J (‘A’) and C57BL/6J (‘B’) inbred mice was denervated by sciatic and saphenous neurectomy, or sham-operated, or left intact (5 mice/group/strain). Using 70 Agilent microarrays, we profiled the expression levels of all genes in L3-L6 DRGs and SC (1 array/tissue/mouse). Results: The expression of Csf2rb, encoding GM-CSF (granulocytemacrophage-colony stimulating factor) receptor 2-beta and located in Pain1, had a 1.7 fold-change between naïve A and B mice in DRG (p = 0.03), and a 1.9 fold-change between A mice expressing high versus low autotomy (p = 8.7×10−5 ) in SC. The human Csf2rb was then genotyped in 85 traumatic leg amputees and 336 women post-mastectomy (with or without NP) using 13 tagging SNPs. Two SNPs (rs2075943 and rs960739) were significantly associated with phantom limb pain (p = 0.007 and p = 0.045), and post-mastectomy pain (p = 0.047 and p = 0.04, respectively). Conclusions: Csf2rb is a good candidate for the gene in Pain1 that controls autotomy variability in mice and NP in humans. 343 PHARMACOLOGICAL CHARACTERIZATION OF A NEW SELECTIVE SIGMA-1 RECEPTOR ANTAGONIST SHOWING ANTIHYPERALGESIC AND ANTIALLODYNIC ACTIVITY IN DIFFERENT PAIN MODELS IN MICE ˜ 1 , X. Nadal2 , A. Dordal1 , G. Gris1 , A. Vidal1 , D. Zamanillo1 , J. Burgueno L. Romero1 *, M. Laloya1 , B. Aubel1 , C. Segales ´ 1 , J.M. Baeyens3 , 4 2 J.A. Lopez-Garc´ ´ ıa , R. Maldonado , J.M. Vela1 . 1 Department of Pharmacology, Laboratorios ESTEVE, Barcelona, Spain; 2 Laboratory of Neuropharmacology, Facultat de Ci`encies de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain; 3 Department of Pharmacology and Institute of Neuroscience, Faculty of Medicine, Universidad de Granada, Granada, Spain; 4 Department of Physiology, Faculty of Medicine, Universidad de Alcal´ a de Henares, Alcal´ a de Henares, Spain Previous studies using sigma-1 receptor (s1 R) knockout mice identify s1 R as a constituent of the mechanisms modulating activity-induced sensitization in nociceptive pathways. Given the attractive therapeutic potential, we have developed a selective s1 R antagonist (S1RA). Herein, we describe for the first time the main pharmacological properties of S1RA, a new compound
Poster Sessions / European Journal of Pain 13 (2009) S55–S285
with analgesic properties acting on s1 R. S1RA shows high affinity for the s1 R and does not show significant affinity for a panel of more than 150 other receptors, enzymes and ion channels tested. The IC50 of binding to s1 R was not significantly different in the presence of phenytoin in competition assays, which identifies S1RA as an antagonist at s1 R. In isolated spinal cords from mice, S1RA produced clear inhibition of the wind-up responses, as evidenced by a reduced number of action potentials induced by trains of C-fiber intensity stimuli. SR1A was active in pain models involving sensitization and chronic pain. Acute administration of S1RA reduced capsaicin-induced mechanical hypersensitivity, formalin-induced pain behaviours and allodynia and hyperalgesia in the neuropathic pain model of partial sciatic nerve ligation. In addition, chronic administration of S1RA during 11 and 21 days significantly reduced the expression of thermal hyperalgesia, mechanical allodynia and cold allodynia in nerve-injured mice. No tolerance to the analgesic effect of S1RA was found after repeated administration. Altogether, these pharmacological results confirm the therapeutic potential of blocking s1 R for the treatment of pain and identify S1RA as a new analgesic compound with a new mechanism of action. 344 PERIPHERAL INJURY REGULATES OPIOID RECEPTOR EXPRESSION IN DORSAL ROOT GANGLIA AND NERVE PAW OF RATS V.O. Zambelli1 *, V.P. Gutierrez1 , C.A. Parada2 , Y. Cury1 . 1 Laboratory of Pathophysiology, Butantan Institute, S˜ ao Paulo, Brazil; 2 Departament of Physiology and Biophysics de Fisiologia e Biof´ısica, UNICAMP, Campinas, Brazil Aims: The efficacy of opioid drugs is enhanced in the presence of tissue injury and inflammation. Previous data of our group demonstrated that, in rats, prostaglandin E2 (PGE2 , intraplantar/i.pl.) and chronic constriction injury (CCI) of the sciatic nerve increase the peripheral antinociceptive efficacy of opioid agonists. The aim of this study is to characterize the effect of PGE2 - induced hyperalgesia and CCI on opioid receptor expression in dorsal root ganglia (DRG) and nerve paw (NP). Methods: The expression of m, k and d-opioid receptors was evaluated by immunoblotting, in DRG or NP (ipsilateral and contralateral to injury) 3 h after i.pl. injection of PGE2 (100 ng/paw) or 14 days after CCI. Results: PGE2 increases the expression of m- and k-opioid receptors in NP (43% and 71%, respectively) and decreases (30%) the expression of d-opioid receptors. m-opioid receptor expression is also increased in the ipsi and contralateral DRG (79 and 27%, respectively), while k-opioid receptor expression is increased only in the ipsilateral DRG (168%). CCI up-regulates m-opioid receptors in NP (27%) and DRG (ipsi and contralaterally, 49 and 20%, respectively) and d-opioid receptors in the ipsilateral DRG. On the other hand, k-opioid receptors are down-regulated by CCI in both NP (51%) and DRG (21%). Conclusion: Peripheral opioid receptor expression is distinct regulated by the presence of acute and chronic tissue injury. The upor down-regulation of opioid receptors can contribute to alterations in the peripheral efficacy of opioids in different pain conditions. Financial Support: FAPESP (07/03404–4, 07/00135–2)
S105
345 LACK OF INTERACTION BETWEEN CUTANEOUS C-NOCICEPTORS AND SYMPATHETIC EFFERENT FIBRES IN PATIENTS WITH COMPLEX REGIONAL PAIN SYNDROME M. Campero1 *, H. Bostock2 , T. Baumann3 , J. Ochoa4 . 1 Departamento de Neurolog´ıa, Facultad de Medicina Cl´ınica Alemana-Universidad del Desarrollo, Santiago, Chile; 2 Institute of Neurology, University College London, Queen Square, London, United Kingdom; 3 Department of Neurological Surgery, Oregon Health & Science University, Portland, United States; 4 Good Samaritan Hospital & Medical Center and Oregon Health & Science University, Portland, United States Background and Aims: Although ‘reflex sympathetic dystrophy’ has been replaced by ‘complex regional pain syndrome’ (CRPS) type I, there remains a widespread presumption that the sympathetic nervous system is actively involved in maintaining chronic neuropathic pain (sympathetically maintained pain, SMP), in absence of detectable nerve damage. Different sites have been entertained for abnormal interaction between sympathetic and somatosensory pathways. Recent data from a patient with SMP has suggested that silent cutaneous nociceptors are activated by catecholamines released from sympathetic efferents in peripheral nerves. Methods: We have used microneurography to evaluate possible electrophysiological sympathetic/nociceptor interactions in 25 patients diagnosed with CRPS I (n = 14) and II (n = 11) by recording from single identified C nociceptor subtypes. Results: Potential effects of sympathetic activity upon 28 polymodal nociceptors and 13 silent nociceptors, recorded in CRPS patients, were assessed but no evidence of activation of nociceptors related to sympathetic discharge was found, even though nociceptors in 6 CRPS II patients exhibited pathological behavior. Conclusions: We conclude that activation of nociceptors by sympathetic efferent discharges is not a common pathogenic event in either CRPS I or CRPS II patients. 346 EVALUATION OF THE SUDOMOTOR C-FIBER FUNCTION WITH TRANSCUTANEOUS ELECTRICAL STIMULATION IN NORMAL SUBJECTS P. Kokotis1 , A. Fyllos1 *, A. Papagianni1 , N. Karandreas1 , M. Schmelz2 . 1 EMG Laboratory, Department of Neurology, Aeginition Hospital, University of Athens, Athens, Greece; 2 Department of Anesthesiology, University of Heidelberg, Mannheim, Germany Aim: Transcutaneous electrical activation of thin efferent sympathetic sudomotor fibers results in sweating. We determined normal values of the quantitive sweating response as an objective functional parameter of the autonomous nervous system. History: Originally the sudomotor responses were chemically induced by acetyl choline – electrical stimulation is suggested to be better controlled. Method: Electrodes and a sweat capsule are fixed on the left medial forearm, with a reference on the right. The skin is stimulated for 30 seconds by constant current stimulus (7.5 mA, 0.5 ms) at 3 frequencies (5, 20, 100 Hz) in random order with an interval of 3 minutes. As possible confounding variables we included in the study: gender, age, height, weight, room and skin temperature. Results: The majority of subjects (70 healthy subjects, 36 men, mean age: 41.67, range: 19–73) responded to electric current of 5 Hz frequency with sweating. Only in 10% a higher threshold (5 Hz10 mA) was found. We evaluated the area under the curve of the responses (AUC), the mean derivative of the single responses, and the slope (b) of the three derivative values of the sweat response increasing with increasing stimulation frequency. Normal values were established and significant correlations were found between age and the log of the maximum area (p = 0.0366) and the log of (b) (p = 0.0038).