- Email: [email protected]
205 ENHANCEMENT OF INJURY-EVOKED PAIN-RELATED BEHAVIOR BY INTRAGANGLIONIC INJECTION OF NEUROPEPTIDE Y
Poster Sessions / European Journal of Pain 13 (2009) S55–S285
and an inhibition of ON neuron activity in the RVM. By using double immunofluorescence techniques, we found that TRPV1- and m-opioid receptors are co-expressed in several neurons of the VLPAG. Conclusions: These findings suggest that m-receptors activation not only acts on inhibitory neurons to disinhibit PAG output neurons, but also interacts with TRPV1 activation at increasing glutamate release into the RVM, possibly by acting directly on PAG output neurons projecting to the RVM. 203 ANTINOCICEPTION PRODUCED BY VIRAL-DRIVEN OVEREXPRESSION OF PREPROENKEPHALIN IN THE CAUDAL VENTROLATERAL MEDULLA I. Martins1,3 *, L. Cabral1 , A. Pinto1 , S.P. Wilson2 , D. Lima3 , I. Tavares1 . 1 Institut of Histology and Embriology, Faculty of Medicine of Oporto and IBMC, Porto, Portugal; 2 Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, United States; 3 Laboratory of Molecular Cell Biology, Faculty of Medicine of Oporto and IBMC, Porto, Portugal Background and aims: The success of gene therapy in pain control by peripheral application of viral vectors suggests that the technique could also be effective at supraspinal pain control centers, such as the caudal ventrolateral medulla (VLM). We evaluated the analgesic effects of a recombinant herpes simplex virus (HSV-1) driving the expression of the human preproenkephalin (PPE) cDNA, into the VLM. Methods: Male Wistar rats were stereotaxically injected into the VLM with the HSV-1 vector carrying either PPE or lacZ, under the control of the human cytomegalovirus promoter. Two days after injection, the animals received a subcutaneous injection of 50 ul of formalin at 5% into the hindpaw and the number of flinches was recorded during 5-min periods for 60 min. The animals were then transcardially perfused, the brains serially cut and sections from the control animals were further processed immunocytochemically to detect b-galactosidase in order to study the patterns of neuronal transduction. Results: The HSV-1 vector carrying PPE significantly reduced the number of flinches both in the early and delayed phases of the formalin test. Numerous retrogradely b-galactosidase labelled neurons were observed at the injection site. Few labelled neurons were also found in some VLM brain afferents. Conclusions: Given the high numbers of transduced cells at the VLM, the antinociceptive effects detected in the present study are likely to be mediated by the VLM. The results reinforce the value of gene transfer directed to supraspinal pain control areas in the treatment of pain. 204 RESPONDENT CONDITIONING OF ENDOGENOUS PAIN MODULATION IN HUMANS N. Erpelding, G. Michaux *, F. Anton. University of Luxembourg, Luxembourg, Luxembourg Background and aims: Endogenous pain modulation induced by heterotopic noxious counter-stimulation (HNCS) is put forward to explain therapeutic effects of techniques like transcutaneous electrical nerve stimulation. However, the pain-inhibitory effects observed in experimental investigations employing HNCS are only of short duration (<15 min) and thus might not explain long-term hypoalgesic effects associated with these methods. Respondent conditioning of endogenous pain mechanisms could be a possible explanation for the sustained hypoalgesia over time. The aim of the present study was to investigate whether HNCS-induced hypoalgesia can be conditioned by pairing the heterotopic trigger stimulus with a neutral acoustic stimulus. Methods: We performed a randomized controlled trial in 40 healthy volunteers aged 18–58 (Md = 21) yrs. Iced-water immersion
S67
(0º C for 1 min) was used for HNCS and as unconditioned stimulus (UCS). Test stimuli for hypoalgesia consisted in repeated phasic contact heat stimuli (49ºC for 1 s). We employed a differential conditioning paradigm with one test group (two different conditioning stimuli: CS+ paired, CS− unpaired) and two (no CS and truly random) control groups. In order to analyze physiological reactions accompanying the learning process, cardiovascular, facial muscular and electrodermal activity was recorded. Results: We observed a significant pain suppression in the postacquisition phase exclusively during the CS+ in the test group (p = .05). This was paralleled by a decrease in diastolic blood pressure (p = .04). Conclusions: Our results confirm the conditionability of endogenous pain modulation and demonstrate that it is not attributable to baroreflex hypoalgesia. Supported by grants from the Luxembourg University and the Ministry of Research (AFR TR-PHD BFR06–028). 205 ENHANCEMENT OF INJURY-EVOKED PAIN-RELATED BEHAVIOR BY INTRAGANGLIONIC INJECTION OF NEUROPEPTIDE Y L. Puljak *, K. Vukojevic, ´ D. Sapunar. University of Split School of Medicine, Split, Croatia Background and aims: Neuropeptide Y (NPY) is critically involved in pain processing. However, its mechanism of action in neuropathic pain is incompletely defined and conflicting results have been reported. In neuropathic pain important early and persistent changes occur in peripheral neuron itself. For this, and because of the clinical opportunity for delivery of drugs selectively to peripheral nerves and dorsal root ganglion (DRG) we delivered NPY directly to DRG to study its nociceptive effects on injury-evoked pain-related behavor. To our knowledge this is the first study with targeted delivery of NPY in DRG. Methods: Twenty nine Sprague-Dawley rats were divided into these experimental groups: control, group that had spinal nerve ligation (SNL) and injection of saline into L5 DRG, and group with SNL and direct injection of three different concentrations of NPY into L5 DRG (0.5, 0.1 and 0.01 nM). Behavioral tests were made before the surgery and three times postoperatively (1st, 4th and 8th day). Data were analyzed with repeated measures ANOVA followed by Bonferroni post hoc test. Results: Pin-prick, von Frey and cold tests revealed statistically significant increase of injury-induced pain-related behavior in NPYinjected rats when compared to control and SNL/saline groups. Reduced latency following heat stimulus was not significantly different in SNL/NPY group, when compared to other groups. Conclusions: When NPY is injected into DRG, unlike with other sites of delivery that were studied so far, pain-related behavior is significantly increased. This NPY effect will be investigated further using NPY Y1 and Y2 receptor antagonists. 206 INVOLVEMENT OF OPIOID RECEPTORS AND PARTS OF ANTERIOR PRETECTAL NUCLEUS IN THE STIMULATION-EVOKED ANTINOCICEPTION FROM RETROSPLENIAL CORTEX IN RATS G.M. Reis *, J.W.S. Silveira, A.C. Rossaneis, W.A. Prado. Faculty of Medicine of Ribeir˜ ao Preto, Ribeir˜ ao Preto, Brazil The electrical stimulation (ES) of the retrosplenial cortex (RSC) produces antinociception in rats. Foster et al. (1989) showed afferent inputs from the RSC to the rostral anterior pretectal nucleus (APtN) and Villarreal et al.; (2004) showed that different parts of the APtN may be involved in the spinal control of noxious inputs via activation of descending pathways. We utilized the rat tail flick (TF) test to examine the role of opioid receptors subtypes in the antinociception evoked from the RSC and evaluate whether distinct parts of the APtN participate in this effect. The ES of
and an inhibition of ON neuron activity in the RVM. By using double immunofluorescence techniques, we found that TRPV1- and m-opioid receptors are co-expressed in several neurons of the VLPAG. Conclusions: These findings suggest that m-receptors activation not only acts on inhibitory neurons to disinhibit PAG output neurons, but also interacts with TRPV1 activation at increasing glutamate release into the RVM, possibly by acting directly on PAG output neurons projecting to the RVM. 203 ANTINOCICEPTION PRODUCED BY VIRAL-DRIVEN OVEREXPRESSION OF PREPROENKEPHALIN IN THE CAUDAL VENTROLATERAL MEDULLA I. Martins1,3 *, L. Cabral1 , A. Pinto1 , S.P. Wilson2 , D. Lima3 , I. Tavares1 . 1 Institut of Histology and Embriology, Faculty of Medicine of Oporto and IBMC, Porto, Portugal; 2 Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, United States; 3 Laboratory of Molecular Cell Biology, Faculty of Medicine of Oporto and IBMC, Porto, Portugal Background and aims: The success of gene therapy in pain control by peripheral application of viral vectors suggests that the technique could also be effective at supraspinal pain control centers, such as the caudal ventrolateral medulla (VLM). We evaluated the analgesic effects of a recombinant herpes simplex virus (HSV-1) driving the expression of the human preproenkephalin (PPE) cDNA, into the VLM. Methods: Male Wistar rats were stereotaxically injected into the VLM with the HSV-1 vector carrying either PPE or lacZ, under the control of the human cytomegalovirus promoter. Two days after injection, the animals received a subcutaneous injection of 50 ul of formalin at 5% into the hindpaw and the number of flinches was recorded during 5-min periods for 60 min. The animals were then transcardially perfused, the brains serially cut and sections from the control animals were further processed immunocytochemically to detect b-galactosidase in order to study the patterns of neuronal transduction. Results: The HSV-1 vector carrying PPE significantly reduced the number of flinches both in the early and delayed phases of the formalin test. Numerous retrogradely b-galactosidase labelled neurons were observed at the injection site. Few labelled neurons were also found in some VLM brain afferents. Conclusions: Given the high numbers of transduced cells at the VLM, the antinociceptive effects detected in the present study are likely to be mediated by the VLM. The results reinforce the value of gene transfer directed to supraspinal pain control areas in the treatment of pain. 204 RESPONDENT CONDITIONING OF ENDOGENOUS PAIN MODULATION IN HUMANS N. Erpelding, G. Michaux *, F. Anton. University of Luxembourg, Luxembourg, Luxembourg Background and aims: Endogenous pain modulation induced by heterotopic noxious counter-stimulation (HNCS) is put forward to explain therapeutic effects of techniques like transcutaneous electrical nerve stimulation. However, the pain-inhibitory effects observed in experimental investigations employing HNCS are only of short duration (<15 min) and thus might not explain long-term hypoalgesic effects associated with these methods. Respondent conditioning of endogenous pain mechanisms could be a possible explanation for the sustained hypoalgesia over time. The aim of the present study was to investigate whether HNCS-induced hypoalgesia can be conditioned by pairing the heterotopic trigger stimulus with a neutral acoustic stimulus. Methods: We performed a randomized controlled trial in 40 healthy volunteers aged 18–58 (Md = 21) yrs. Iced-water immersion
S67
(0º C for 1 min) was used for HNCS and as unconditioned stimulus (UCS). Test stimuli for hypoalgesia consisted in repeated phasic contact heat stimuli (49ºC for 1 s). We employed a differential conditioning paradigm with one test group (two different conditioning stimuli: CS+ paired, CS− unpaired) and two (no CS and truly random) control groups. In order to analyze physiological reactions accompanying the learning process, cardiovascular, facial muscular and electrodermal activity was recorded. Results: We observed a significant pain suppression in the postacquisition phase exclusively during the CS+ in the test group (p = .05). This was paralleled by a decrease in diastolic blood pressure (p = .04). Conclusions: Our results confirm the conditionability of endogenous pain modulation and demonstrate that it is not attributable to baroreflex hypoalgesia. Supported by grants from the Luxembourg University and the Ministry of Research (AFR TR-PHD BFR06–028). 205 ENHANCEMENT OF INJURY-EVOKED PAIN-RELATED BEHAVIOR BY INTRAGANGLIONIC INJECTION OF NEUROPEPTIDE Y L. Puljak *, K. Vukojevic, ´ D. Sapunar. University of Split School of Medicine, Split, Croatia Background and aims: Neuropeptide Y (NPY) is critically involved in pain processing. However, its mechanism of action in neuropathic pain is incompletely defined and conflicting results have been reported. In neuropathic pain important early and persistent changes occur in peripheral neuron itself. For this, and because of the clinical opportunity for delivery of drugs selectively to peripheral nerves and dorsal root ganglion (DRG) we delivered NPY directly to DRG to study its nociceptive effects on injury-evoked pain-related behavor. To our knowledge this is the first study with targeted delivery of NPY in DRG. Methods: Twenty nine Sprague-Dawley rats were divided into these experimental groups: control, group that had spinal nerve ligation (SNL) and injection of saline into L5 DRG, and group with SNL and direct injection of three different concentrations of NPY into L5 DRG (0.5, 0.1 and 0.01 nM). Behavioral tests were made before the surgery and three times postoperatively (1st, 4th and 8th day). Data were analyzed with repeated measures ANOVA followed by Bonferroni post hoc test. Results: Pin-prick, von Frey and cold tests revealed statistically significant increase of injury-induced pain-related behavior in NPYinjected rats when compared to control and SNL/saline groups. Reduced latency following heat stimulus was not significantly different in SNL/NPY group, when compared to other groups. Conclusions: When NPY is injected into DRG, unlike with other sites of delivery that were studied so far, pain-related behavior is significantly increased. This NPY effect will be investigated further using NPY Y1 and Y2 receptor antagonists. 206 INVOLVEMENT OF OPIOID RECEPTORS AND PARTS OF ANTERIOR PRETECTAL NUCLEUS IN THE STIMULATION-EVOKED ANTINOCICEPTION FROM RETROSPLENIAL CORTEX IN RATS G.M. Reis *, J.W.S. Silveira, A.C. Rossaneis, W.A. Prado. Faculty of Medicine of Ribeir˜ ao Preto, Ribeir˜ ao Preto, Brazil The electrical stimulation (ES) of the retrosplenial cortex (RSC) produces antinociception in rats. Foster et al. (1989) showed afferent inputs from the RSC to the rostral anterior pretectal nucleus (APtN) and Villarreal et al.; (2004) showed that different parts of the APtN may be involved in the spinal control of noxious inputs via activation of descending pathways. We utilized the rat tail flick (TF) test to examine the role of opioid receptors subtypes in the antinociception evoked from the RSC and evaluate whether distinct parts of the APtN participate in this effect. The ES of