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202 SPINAL CORD STIMULATION REDUCES METABOLIC ACTIVITY IN THE SPINAL DORSAL HORN IN RATS WITH NERVE INJURY INDUCED PAIN
Posters / European Journal of Pain Supplements 4 (2010) 47–146
Conclusions: The present study suggests: a) That morphine more potently reduces the emotional than the sensory component of pain and that this differential sensitivity is not confounded by the intrinsic rewarding effects of the drug, and b) That morphine more potently reduces spontaneous pain than evoked pain. 199 PERIPHERAL NERVE INJURY AND ITS EFFECT ON DYNAMIC ALLODYNIA IN A MURINE MODEL OF POSTHERPETIC PAIN A. Sasaki, K. Serizawa, T. Andoh, Y. Kuraishi. Department of Applied Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan Introduction: Postherpetic neuralgia (PHN) is an often painful condition. PHN patients with allodynia are classified into irritable nociceptor and deafferentation subtypes. Percutaneous inoculation of mice with herpes simplex virus type-1 causes zoster-like lesions and prominent dynamic allodynia in the affected dermatome. Almost all of mice showed dynamic allodynia even after the complete cure of the skin lesions. It is important to know whether this murine model is similar to either of PHN subtypes. Objectives: The aim of this study was to determine to which type of human PHN this murine model would be similar. Methods: Peripheral nerve injury was assessed by histological (immunohistochemical and electron microscopy methods) and behavioral examination (capsaicin and thermal nociception tests). Results: Unmyelinated fibers were markedly reduced in the affected skin and ipsilateral lumbar dorsal horn of mice with posthereptic pain (PHP). In the dorsal root ganglia (DRG), the number of peripherin (small DRG neuron marker)-positive neurons was significantly reduced, while no significant difference in the number of NF200 (large DRG neuron marker)-positive neurons. Electron microscopy of the affected sciatic nerve revealed severe damage to unmyelinated fibers and slight changes in myelinated fibers. Capsaicin and thermal sensitivities were impaired in the affected dermatome of mice with PHP. These impairments were positively correlated with the severity of dynamic allodynia. Conclusions: This murine model may be useful for the study of the mechanisms of the deafferented allodynic type of PHN. Small fiber deafferentation is suggested to be responsible for dynamic allodynia of the deafferented allodynic type of PHN. 200 P2X3 RECEPTOR MEDIATES HEAT HYPERALGESIA IN A RAT MODEL OF TRIGEMINAL NEUROPATHIC PAIN M. Shinoda1 , K. Kawashima2 , N. Ozaki3 , H. Asai2 , K. Nagamine2 , Y. Sugiura2 , K. Iwata1 . 1 Department of Physiology, Nihon University School of Dentistry, Tokyo, 2 Department of Functional Anatomy and Neuroscience, Nagoya University Graduate School of Medicine, Nagoya, 3 Department of Anatomy and Neuroembryology, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan Introduction: Trigeminal neuropathic pain is a chronic facial pain caused by trigeminal nerve injury and poorly controlled by drugs. It is very important to evaluate the neuronal mechanisms underlying trigeminal neuropathic pain to develop the appropriate treatments in neuropathic pain patients. Objectives: The present study was undertaken to determine the role of P2X3 receptor (P2X3 R) on heat hyperalgesia in a newly developed rat model of trigeminal neuropathic pain. Methods: The unilateral infraorbital nerve (IoN) was partially ligated by 6–0 silk. To assess heat sensitivity, a vibrissal pad (VP) was placed on a hot plate and the head withdrawal latency was measured. The protein gene product-9.5 (PGP9.5) and calcitonin gene-related peptide (CGRP) positive nerve fibers in the VP, the expression of P2X3 R in the trigeminal ganglion (TG) and phosphorylated extracellular regulated-kinase in the medullary dorsal horn were evaluated immunohistochemically. Results: Heat hyperalgesia was observed at the VP ipsilateral to the IoN ligation. The latency to heat stimuli was prolonged after
59
subcutaneous administration of pyridoxal-phosphate-6-azophenyl2 ,4 -disulfonic acid and 2 ,3 -O-(2,4,6-trinitrophenyl) adenosine 5 triphosphate. The latency was shortened after administration of a,bmethylene ATP. The PGP9.5 and CGRP immunoreactive nerve fibers significantly decreased in the VP of ipsilateral to the IoN ligation. The number of immunoreactive neurons with P2X3 R significantly increased in the ipsilateral TG. Conclusions: We developed an experimental model of trigeminal neuropathic pain by partial IoN ligation, which produced heat hyperalgesia in the VP. Pharmacological and immunohistochemical studies revealed that the P2X3 R plays an important role in the heat hyperalgesia in this model. 201 ANTINOCICEPTIVE EFFECT OF A-LIPOIC ACID IN STZ INDUCED NEUROPATHIC PAIN: INTERVENTIONARY STUDY J. Singh1 , A. Suruchi2 , L. Harbans3 . 1 Pharmacology, Pt. B.D. Sharma University of Health Science, 2 Pharmacology, 3 Biochemistry, PGIMS, Rohtak, India Introduction: The progression of sensory defects in diabetic peripheral neuropathies is enigmatic. Objectives: To evaluate antinociceptive effect of a-lipoic acid (a-LA) in hyperalgesia of diabetic neuropathy. Methods: In albino wistar rats (250–300g) neuropathy was produced by streptozotocin (STZ) 50 mg/kg, intravenously. Hyperalgesia was assessed using tail flick test to thermal stimulation by analgesiometer. A 10 sec cutoff latency was used. Initial reaction time was recorded and animals were divided into 3 groups of 10 each. Group I – control (vehicle), Group II – STZ (50 mg/kg, iv, single injection), Group III – STZ + a-LA (100 mg/kg, po, daily) started 10 weeks after STZ and continued for further 6 weeks. Reaction time was noted every 30 min. for 3 hr (at weeks 2, 4 & 6th ). However, peak effect of a-LA (i.e 1.5 hr after po administration) was considered for comparison purpose. Control (initial) reaction time was compared with STZ (after 10 weeks) and a-LA treated group (at weeks 2, 4 & 6) by using Students’t’ test (paired). Results: STZ diabetic rats exhibited hyperalgesia after 10 weeks. Mean control reaction time was 4.6±0.18 sec, whereas after 10 weeks of STZ, it was 2.5±0.16 sec. Treatment with a-LA (100 mg/kg, po, started after 10 weeks of STZ) increased the tail flick reaction time significantly as observed after 2, 4 & 6 weeks of a-LA administration. In diabetic rats, 6 weeks a-LA treatment almost completely reversed STZ induced hyperalgesia. Conclusions: Interventionary study with a-LA suggests that a-LA is beneficial in ameliorating pain of diabetic neuropathy. 202 SPINAL CORD STIMULATION REDUCES METABOLIC ACTIVITY IN THE SPINAL DORSAL HORN IN RATS WITH NERVE INJURY INDUCED PAIN H. Smits1 , T. Pederzani2,3 , E.A.J. Joosten1 , M. van Kleef1 , F. Huygen4 , J. Jongen2,3,4 . 1 Pain Management and Research Center Dept of Anesthesiology, Maastricht University Medical Centre, Maastricht, 2 Dept. of Neurology, 3 Dept. of Neuroscience, 4 Pain Management Center, Dept. of Anesthesiology, Erasmus MC, Rotterdam, The Netherlands Introduction: Spinal cord stimulation (SCS) is an established treatment for intractable neuropathic pain. The mechanisms of action of SCS are only partially understood and experimental research on this subject is therefore essential. Objectives: In the present study we used Autofluorescent Flavoprotein Imaging (AFI) to study the effect of SCS on spinal dorsal horn metabolic activity in neuropathic rats in vivo. Methods: Mitochondrial oxidized flavoproteins have the ability to absorb blue spectrum photons. This leads to an immediate emission of green spectrum photons, whose intensity (detected by a CCD camera) is a direct measure of neuronal metabolic activity. In a rat model of nerve-injury induced pain, allodynia was quantified
60
Posters / European Journal of Pain Supplements 4 (2010) 47–146
using the hot-plate test and the von Frey test. 14 Days post nerveinjury animals were anesthesized with urethane, a bipolar electrode was placed around the affected proximal sciatic nerve and the spinal cord was exposed by a laminectomy at T13. Subsequently animals were paralysed and mechanically ventilated. Baseline AFI recordings were obtained using 10 seconds electrical stimulation of the sciatic nerve at C-fiber strength. Animals were then treated with 30 minutes of SCS. Directly following SCS, AFI responses were measured every 5 minutes for up to one hour. Results: We found a short-lasting, but strong reduction in AFI intensity relative to baseline in SCS animals (n = 8), which was not observed in animals that received sham SCS (n = 7). The difference between SCS and sham animals was statistically significant. Conclusions: We suggest that our findings reflect a decreased activity of superficial dorsal horn neurons, caused by SCS. 203 STUDY OF THE SITE(S) OF ACTION OF ESLICARBAZEPINE ON ECTOPIC DISCHARGE IN A MOUSE MODEL OF CHRONIC CONSTRICTION NERVE INJURY P. Soares-da-Silva1,2 , F.-Y. Zhao3 , A. Loureiro1 , L. Wright1 , D. Spanswick3 . 1 BIAL – Portela & Co, SA, S. Mamede do Coronado, 2 University of Porto, Porto, Portugal; 3 University of Warwick, Coventry, UK Introduction: Eslicarbazepine is the entity responsible for the pharmacological effect of a novel antiepileptic drug, eslicarbazepine acetate (ESL) (Epilepsia, 50, 454–63, 2009). Objective: Evaluate the effects of eslicarbazepine on ectopic discharge of peripheral nerve filaments and spontaneous activity of dorsal horn neurones in a mouse model of chronic constriction nerve injury (CCI). Methods: The baseline paw withdrawal threshold (PWT) was examined using a series of graduated von Frey hairs on 3 consecutive days before surgery and re-assessed on the 7th and on the 14th days after surgery, before electrophysiological recording. Results: Eslicarbazepine (100 mg/kg, i.p.) significantly inhibited ectopic discharge in peripheral nerves of CCI adult male BL CB F1 mice. The effects of eslicarbazepine were similar on ectopic discharge generated either at the neuroma or dorsal root ganglion (DRG) level. In further experiments, eslicarbazepine (100 mg/kg, i.p.), significantly inhibited spontaneous activity of dorsal horn neurones in CCI mice. The effects of eslicarbazepine were similar in three CCI preparations with or without spinalisation and following dorsal root section. After eslicarbazepine administration (100 mg/kg, i.p.), maximal concentrations in plasma were detected at 30 min and then declined to half-maximal concentrations at 2 hours. Eslicarbazepine maximal concentrations in brain and spinal cord were observed at 30 min after administration and remained stable at 2 hours post administration. Conclusions: Eslicarbazepine acts at the level of the central nervous system, spinal cord level, as well as at the level of the peripheral nervous system. Supported by BIAL-Portela & Co, SA 204 EXCITABILITY OF UNMYELINATED AFFERENT NERVE FIBERS BY PHYSIOLOGICAL STIMULI ALONG THE SURAL NERVE 1 M. Struck1 , A. Teliban1 , F. Bartsch1 , R. Baron2 , W. Janig ¨ . 1 2 Physiologisches Institut, Department of Neurology, Division of Neurological Pain Research and Therapy, Christian Albrechts Universit¨ at zu Kiel, Kiel, Germany Introduction: Recently we have shown that injured cutaneous afferent axons develop ectopic mechano- and thermosensitivity. This ectopic sensitivity may be a peripheral mechanism underlying neuropathic pain. Objectives: We tested the hypothesis if intact unmyelinated axons in a cutaneous nerve are excitable by physiological mechanical or
thermal stimuli and how this excitability is distributed along the axon. Methods: Activity was recorded neurophysiologically from unmyelinated (C-) fibers isolated from the sural nerve in anesthetized Wistar rats. The nerve fibers were characterized by their responses to cold, heat and/or mechanical stimulation of the sural nerve and by their spontaneous activity. Results: 77 C-fibers were tested. 1. Thirty-two fibers (42%) were afferent thermosensitive nerve fibers. They were activated by cold stimuli (N = 17 fibers) or by heat stimuli (N = 15 fibers) applied to the nerve. Only one of these fibers showed spontaneous activity. 2. No C-fiber was activated by mechanical stimulation of the sural nerve. 3. Forty-five C-fibers (58%) were cutaneous postganglionic vasoconstrictor fibers. They showed spontaneous activity which was correlated with the electrocardiogram or inhibited during increase of arterial blood pressure and/or exhibited reflex inhibition to noxious heat stimulation of the sural nerve (see [1]). These fibers were not excited by cold or heat stimuli. Conclusions: Afferent C-fibers show axonal cold or heat sensitivity. Postganglionic vasoconstrictor fibers cannot be excited by cold or heat stimulation of their axons. Reference(s) [1] Habler ¨ HJ, Janig ¨ W, Krummel M, Peters O J Neurophysiol 72, 2222–2236 (1994).
205 PAIN BEHAVIOR AND BLOOD GLUCOSE LEVEL INCREMENT INDUCED BY INTRATHECAL IL-1B: POSSIBLE INVOLVEMENT OF GLUCOCORTICOID, CATECHOAMINE, CRH AND OPIOID SYSTEM Y.B. Sim, S.H. Park, J.K. Lee, H.W. Suh. Pharmacology, Hallym University, Chun-Cheon, Republic of Korea Introduction: The relationship between IL-1b-induced nociception and blood glucose level was studied in ICR mice. Objectives: We found that i.t. injection of IL-1b increased pain behavior. In addition, i.t. IL-1b injection caused an elevation of blood glucose level. Methods: The time-course study showed that maximal blood glucose level was observed 30 and 60 min after i.t. IL-1b administration. Furthermore, i.t. injection of IL-1b enhanced blood glucose level when mice were orally fed with D-glucose. Results: To find the mechanism involved in IL-1b-induced response, opioid and CRH mRNA levels after i.t. IL-1b injection were measured in hypothalamus, pituitary and adrenal glands. I.t. IL1b increased POMC and CRH mRNA levels in hypothalamus. In addition, IL-1b elevated c-fos mRNA level in pituitary and adrenal glands. Injection of IL-1b significantly increased TH mRNA level in adrenal gland and plasma corticosterone level. IL-1binduced elevation of blood glucose level and pain behavior were reduced by RU486 or adrenalectomy. I.p. injection of phentolamine (a1-adrenergic blocker) or yohimbine (a2-adrenergic blocker) significantly inhibited blood glucose level and pain behavior induced by IL-1b. I.c.v. injection of b-endorphin (from 0.1 to 2.0 mg) dose-dependently enhanced blood glucose level when mice were orally fed with D-glucose, without altering the basal blood glucose level. However, both phentolamine and yohimbine attenuated blood glucose level when mice were orally fed with D-glucose. Conclusions: Our results suggest that IL-1b administered i.t. increases blood glucose level via activation of catecolaminergic and glucocorticoid system. Futhermore, IL-1b-induced enhancing glucose upregulation in glucose fed model appears to be mediated by activation of b-endorphinergic system.
Conclusions: The present study suggests: a) That morphine more potently reduces the emotional than the sensory component of pain and that this differential sensitivity is not confounded by the intrinsic rewarding effects of the drug, and b) That morphine more potently reduces spontaneous pain than evoked pain. 199 PERIPHERAL NERVE INJURY AND ITS EFFECT ON DYNAMIC ALLODYNIA IN A MURINE MODEL OF POSTHERPETIC PAIN A. Sasaki, K. Serizawa, T. Andoh, Y. Kuraishi. Department of Applied Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan Introduction: Postherpetic neuralgia (PHN) is an often painful condition. PHN patients with allodynia are classified into irritable nociceptor and deafferentation subtypes. Percutaneous inoculation of mice with herpes simplex virus type-1 causes zoster-like lesions and prominent dynamic allodynia in the affected dermatome. Almost all of mice showed dynamic allodynia even after the complete cure of the skin lesions. It is important to know whether this murine model is similar to either of PHN subtypes. Objectives: The aim of this study was to determine to which type of human PHN this murine model would be similar. Methods: Peripheral nerve injury was assessed by histological (immunohistochemical and electron microscopy methods) and behavioral examination (capsaicin and thermal nociception tests). Results: Unmyelinated fibers were markedly reduced in the affected skin and ipsilateral lumbar dorsal horn of mice with posthereptic pain (PHP). In the dorsal root ganglia (DRG), the number of peripherin (small DRG neuron marker)-positive neurons was significantly reduced, while no significant difference in the number of NF200 (large DRG neuron marker)-positive neurons. Electron microscopy of the affected sciatic nerve revealed severe damage to unmyelinated fibers and slight changes in myelinated fibers. Capsaicin and thermal sensitivities were impaired in the affected dermatome of mice with PHP. These impairments were positively correlated with the severity of dynamic allodynia. Conclusions: This murine model may be useful for the study of the mechanisms of the deafferented allodynic type of PHN. Small fiber deafferentation is suggested to be responsible for dynamic allodynia of the deafferented allodynic type of PHN. 200 P2X3 RECEPTOR MEDIATES HEAT HYPERALGESIA IN A RAT MODEL OF TRIGEMINAL NEUROPATHIC PAIN M. Shinoda1 , K. Kawashima2 , N. Ozaki3 , H. Asai2 , K. Nagamine2 , Y. Sugiura2 , K. Iwata1 . 1 Department of Physiology, Nihon University School of Dentistry, Tokyo, 2 Department of Functional Anatomy and Neuroscience, Nagoya University Graduate School of Medicine, Nagoya, 3 Department of Anatomy and Neuroembryology, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan Introduction: Trigeminal neuropathic pain is a chronic facial pain caused by trigeminal nerve injury and poorly controlled by drugs. It is very important to evaluate the neuronal mechanisms underlying trigeminal neuropathic pain to develop the appropriate treatments in neuropathic pain patients. Objectives: The present study was undertaken to determine the role of P2X3 receptor (P2X3 R) on heat hyperalgesia in a newly developed rat model of trigeminal neuropathic pain. Methods: The unilateral infraorbital nerve (IoN) was partially ligated by 6–0 silk. To assess heat sensitivity, a vibrissal pad (VP) was placed on a hot plate and the head withdrawal latency was measured. The protein gene product-9.5 (PGP9.5) and calcitonin gene-related peptide (CGRP) positive nerve fibers in the VP, the expression of P2X3 R in the trigeminal ganglion (TG) and phosphorylated extracellular regulated-kinase in the medullary dorsal horn were evaluated immunohistochemically. Results: Heat hyperalgesia was observed at the VP ipsilateral to the IoN ligation. The latency to heat stimuli was prolonged after
59
subcutaneous administration of pyridoxal-phosphate-6-azophenyl2 ,4 -disulfonic acid and 2 ,3 -O-(2,4,6-trinitrophenyl) adenosine 5 triphosphate. The latency was shortened after administration of a,bmethylene ATP. The PGP9.5 and CGRP immunoreactive nerve fibers significantly decreased in the VP of ipsilateral to the IoN ligation. The number of immunoreactive neurons with P2X3 R significantly increased in the ipsilateral TG. Conclusions: We developed an experimental model of trigeminal neuropathic pain by partial IoN ligation, which produced heat hyperalgesia in the VP. Pharmacological and immunohistochemical studies revealed that the P2X3 R plays an important role in the heat hyperalgesia in this model. 201 ANTINOCICEPTIVE EFFECT OF A-LIPOIC ACID IN STZ INDUCED NEUROPATHIC PAIN: INTERVENTIONARY STUDY J. Singh1 , A. Suruchi2 , L. Harbans3 . 1 Pharmacology, Pt. B.D. Sharma University of Health Science, 2 Pharmacology, 3 Biochemistry, PGIMS, Rohtak, India Introduction: The progression of sensory defects in diabetic peripheral neuropathies is enigmatic. Objectives: To evaluate antinociceptive effect of a-lipoic acid (a-LA) in hyperalgesia of diabetic neuropathy. Methods: In albino wistar rats (250–300g) neuropathy was produced by streptozotocin (STZ) 50 mg/kg, intravenously. Hyperalgesia was assessed using tail flick test to thermal stimulation by analgesiometer. A 10 sec cutoff latency was used. Initial reaction time was recorded and animals were divided into 3 groups of 10 each. Group I – control (vehicle), Group II – STZ (50 mg/kg, iv, single injection), Group III – STZ + a-LA (100 mg/kg, po, daily) started 10 weeks after STZ and continued for further 6 weeks. Reaction time was noted every 30 min. for 3 hr (at weeks 2, 4 & 6th ). However, peak effect of a-LA (i.e 1.5 hr after po administration) was considered for comparison purpose. Control (initial) reaction time was compared with STZ (after 10 weeks) and a-LA treated group (at weeks 2, 4 & 6) by using Students’t’ test (paired). Results: STZ diabetic rats exhibited hyperalgesia after 10 weeks. Mean control reaction time was 4.6±0.18 sec, whereas after 10 weeks of STZ, it was 2.5±0.16 sec. Treatment with a-LA (100 mg/kg, po, started after 10 weeks of STZ) increased the tail flick reaction time significantly as observed after 2, 4 & 6 weeks of a-LA administration. In diabetic rats, 6 weeks a-LA treatment almost completely reversed STZ induced hyperalgesia. Conclusions: Interventionary study with a-LA suggests that a-LA is beneficial in ameliorating pain of diabetic neuropathy. 202 SPINAL CORD STIMULATION REDUCES METABOLIC ACTIVITY IN THE SPINAL DORSAL HORN IN RATS WITH NERVE INJURY INDUCED PAIN H. Smits1 , T. Pederzani2,3 , E.A.J. Joosten1 , M. van Kleef1 , F. Huygen4 , J. Jongen2,3,4 . 1 Pain Management and Research Center Dept of Anesthesiology, Maastricht University Medical Centre, Maastricht, 2 Dept. of Neurology, 3 Dept. of Neuroscience, 4 Pain Management Center, Dept. of Anesthesiology, Erasmus MC, Rotterdam, The Netherlands Introduction: Spinal cord stimulation (SCS) is an established treatment for intractable neuropathic pain. The mechanisms of action of SCS are only partially understood and experimental research on this subject is therefore essential. Objectives: In the present study we used Autofluorescent Flavoprotein Imaging (AFI) to study the effect of SCS on spinal dorsal horn metabolic activity in neuropathic rats in vivo. Methods: Mitochondrial oxidized flavoproteins have the ability to absorb blue spectrum photons. This leads to an immediate emission of green spectrum photons, whose intensity (detected by a CCD camera) is a direct measure of neuronal metabolic activity. In a rat model of nerve-injury induced pain, allodynia was quantified
60
Posters / European Journal of Pain Supplements 4 (2010) 47–146
using the hot-plate test and the von Frey test. 14 Days post nerveinjury animals were anesthesized with urethane, a bipolar electrode was placed around the affected proximal sciatic nerve and the spinal cord was exposed by a laminectomy at T13. Subsequently animals were paralysed and mechanically ventilated. Baseline AFI recordings were obtained using 10 seconds electrical stimulation of the sciatic nerve at C-fiber strength. Animals were then treated with 30 minutes of SCS. Directly following SCS, AFI responses were measured every 5 minutes for up to one hour. Results: We found a short-lasting, but strong reduction in AFI intensity relative to baseline in SCS animals (n = 8), which was not observed in animals that received sham SCS (n = 7). The difference between SCS and sham animals was statistically significant. Conclusions: We suggest that our findings reflect a decreased activity of superficial dorsal horn neurons, caused by SCS. 203 STUDY OF THE SITE(S) OF ACTION OF ESLICARBAZEPINE ON ECTOPIC DISCHARGE IN A MOUSE MODEL OF CHRONIC CONSTRICTION NERVE INJURY P. Soares-da-Silva1,2 , F.-Y. Zhao3 , A. Loureiro1 , L. Wright1 , D. Spanswick3 . 1 BIAL – Portela & Co, SA, S. Mamede do Coronado, 2 University of Porto, Porto, Portugal; 3 University of Warwick, Coventry, UK Introduction: Eslicarbazepine is the entity responsible for the pharmacological effect of a novel antiepileptic drug, eslicarbazepine acetate (ESL) (Epilepsia, 50, 454–63, 2009). Objective: Evaluate the effects of eslicarbazepine on ectopic discharge of peripheral nerve filaments and spontaneous activity of dorsal horn neurones in a mouse model of chronic constriction nerve injury (CCI). Methods: The baseline paw withdrawal threshold (PWT) was examined using a series of graduated von Frey hairs on 3 consecutive days before surgery and re-assessed on the 7th and on the 14th days after surgery, before electrophysiological recording. Results: Eslicarbazepine (100 mg/kg, i.p.) significantly inhibited ectopic discharge in peripheral nerves of CCI adult male BL CB F1 mice. The effects of eslicarbazepine were similar on ectopic discharge generated either at the neuroma or dorsal root ganglion (DRG) level. In further experiments, eslicarbazepine (100 mg/kg, i.p.), significantly inhibited spontaneous activity of dorsal horn neurones in CCI mice. The effects of eslicarbazepine were similar in three CCI preparations with or without spinalisation and following dorsal root section. After eslicarbazepine administration (100 mg/kg, i.p.), maximal concentrations in plasma were detected at 30 min and then declined to half-maximal concentrations at 2 hours. Eslicarbazepine maximal concentrations in brain and spinal cord were observed at 30 min after administration and remained stable at 2 hours post administration. Conclusions: Eslicarbazepine acts at the level of the central nervous system, spinal cord level, as well as at the level of the peripheral nervous system. Supported by BIAL-Portela & Co, SA 204 EXCITABILITY OF UNMYELINATED AFFERENT NERVE FIBERS BY PHYSIOLOGICAL STIMULI ALONG THE SURAL NERVE 1 M. Struck1 , A. Teliban1 , F. Bartsch1 , R. Baron2 , W. Janig ¨ . 1 2 Physiologisches Institut, Department of Neurology, Division of Neurological Pain Research and Therapy, Christian Albrechts Universit¨ at zu Kiel, Kiel, Germany Introduction: Recently we have shown that injured cutaneous afferent axons develop ectopic mechano- and thermosensitivity. This ectopic sensitivity may be a peripheral mechanism underlying neuropathic pain. Objectives: We tested the hypothesis if intact unmyelinated axons in a cutaneous nerve are excitable by physiological mechanical or
thermal stimuli and how this excitability is distributed along the axon. Methods: Activity was recorded neurophysiologically from unmyelinated (C-) fibers isolated from the sural nerve in anesthetized Wistar rats. The nerve fibers were characterized by their responses to cold, heat and/or mechanical stimulation of the sural nerve and by their spontaneous activity. Results: 77 C-fibers were tested. 1. Thirty-two fibers (42%) were afferent thermosensitive nerve fibers. They were activated by cold stimuli (N = 17 fibers) or by heat stimuli (N = 15 fibers) applied to the nerve. Only one of these fibers showed spontaneous activity. 2. No C-fiber was activated by mechanical stimulation of the sural nerve. 3. Forty-five C-fibers (58%) were cutaneous postganglionic vasoconstrictor fibers. They showed spontaneous activity which was correlated with the electrocardiogram or inhibited during increase of arterial blood pressure and/or exhibited reflex inhibition to noxious heat stimulation of the sural nerve (see [1]). These fibers were not excited by cold or heat stimuli. Conclusions: Afferent C-fibers show axonal cold or heat sensitivity. Postganglionic vasoconstrictor fibers cannot be excited by cold or heat stimulation of their axons. Reference(s) [1] Habler ¨ HJ, Janig ¨ W, Krummel M, Peters O J Neurophysiol 72, 2222–2236 (1994).
205 PAIN BEHAVIOR AND BLOOD GLUCOSE LEVEL INCREMENT INDUCED BY INTRATHECAL IL-1B: POSSIBLE INVOLVEMENT OF GLUCOCORTICOID, CATECHOAMINE, CRH AND OPIOID SYSTEM Y.B. Sim, S.H. Park, J.K. Lee, H.W. Suh. Pharmacology, Hallym University, Chun-Cheon, Republic of Korea Introduction: The relationship between IL-1b-induced nociception and blood glucose level was studied in ICR mice. Objectives: We found that i.t. injection of IL-1b increased pain behavior. In addition, i.t. IL-1b injection caused an elevation of blood glucose level. Methods: The time-course study showed that maximal blood glucose level was observed 30 and 60 min after i.t. IL-1b administration. Furthermore, i.t. injection of IL-1b enhanced blood glucose level when mice were orally fed with D-glucose. Results: To find the mechanism involved in IL-1b-induced response, opioid and CRH mRNA levels after i.t. IL-1b injection were measured in hypothalamus, pituitary and adrenal glands. I.t. IL1b increased POMC and CRH mRNA levels in hypothalamus. In addition, IL-1b elevated c-fos mRNA level in pituitary and adrenal glands. Injection of IL-1b significantly increased TH mRNA level in adrenal gland and plasma corticosterone level. IL-1binduced elevation of blood glucose level and pain behavior were reduced by RU486 or adrenalectomy. I.p. injection of phentolamine (a1-adrenergic blocker) or yohimbine (a2-adrenergic blocker) significantly inhibited blood glucose level and pain behavior induced by IL-1b. I.c.v. injection of b-endorphin (from 0.1 to 2.0 mg) dose-dependently enhanced blood glucose level when mice were orally fed with D-glucose, without altering the basal blood glucose level. However, both phentolamine and yohimbine attenuated blood glucose level when mice were orally fed with D-glucose. Conclusions: Our results suggest that IL-1b administered i.t. increases blood glucose level via activation of catecolaminergic and glucocorticoid system. Futhermore, IL-1b-induced enhancing glucose upregulation in glucose fed model appears to be mediated by activation of b-endorphinergic system.