- Email: [email protected]
D5 receptor-mediated mechanisms in the maintenance of pathological pain plasticity
Abstracts
relationship between participant sex and pain outcomes. Results indicated that stoic fortitude and SS were significant mediators of the relationship between sex and heat and cold tolerance. SS, but not stoicism, also mediated the relationship between sex and ischemic and electric pain tolerance. These findings lend support for stoicism and SS as mediators for sex differences in pain, particularly differences in pain tolerance. No evidence was found for mediation of the sex-pain threshold relationship. These findings may have important implications for treatment seeking in males. Because males are more likely to report higher levels of SS, stoicism, and tolerances for pain, they may be less likely to seek treatment. This might inflate sex differences in the precedence rates of chronic pain. This research reported was supported by the National Institute on Minority Health and Health Disparities of the National Institutes of Health under Award Number R01MD007807. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
E19 Inflammation (350) Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) regulates mechanical sensitivity following cutaneous inflammation J Yasko, T Kiprono, B Knight, C Willis, A Nicaise, E Young, S Crocker, and K Baumbauer; University of Connecticut, Storrs, CT Tissue injury and inflammation result in alterations in neuronal function and subsequent development of pain. The development of pain, both normal and pathological, involves activity of neurons and glia in both the peripheral and central nervous systems. Emerging evidence demonstrates activity in nociceptive circuits is coordinated by extracellular matrix (ECM), and that injury and inflammation alter both the ECM and its regulatory proteins, matrix metalloproteinases (MMPs). Under normal conditions MMPs degrade and remodel the ECM, and this process may become dysregulated during the development of pathological pain. This suggests that modulating MMP activity may serve as an important therapeutic target for pain treatment. Endogenous inhibitors, such as tissue inhibitors of metalloproteinases-1 (TIMP-1) maintain the balance of ECM remodeling via reduction of MMP activity. While TIMP-1 is known to have a number of physiological functions in the nervous system, its role in pain processing is largely unknown. To examine the role of TIMP-1 in the development of pain, we exposed global TIMP-1 knockout (KO) and wildtype (WT) mice to cutaneous inflammation. Mechanical and thermal sensitivity were monitored over the course of 7 days following Complete Freud’s Adjuvant (CFA) injection. Strikingly, TIMP-1 KO mice developed rapid onset mechanical sensitivity within 24 hours post injection with no significant change in thermal sensitivity. The development of mechanical hypersensitivity correlated with increased expression of TRPA1, GFRa2, GFR-a3, TrkA, and ASIC1 mRNA in the DRG. Additionally, TIMP1 KO mice showed increased levels of circulating IL-1b, IL-6, and IL10, but not TNF-a. Finally, CFA injections increased cutaneous TIMP-1 protein levels in WT mice. Collectively, our results suggest a role for TIMP-1 in the regulation and development of inflammatory pain.
(351) Neuropeptide regulation of adaptive immune responses after fracture W Kingery, W Li, T Guo, X Shi, and J Clark; Veterans Affairs Palo Alto Health Care System, Palo Alto, CA
Using a murine tibia fracture model of complex regional pain syndrome (CRPS), we previously observed that facilitated substance P (SP) and calcitonin gene-related peptide (CGRP) signaling contributes to the development of chronic nociceptive sensitization after fracture1,2 and that B cells are required for the full expression of post-fracture CRPS-like changes.3 These results support the hypothesis that exaggerated neuropeptide signaling triggers adaptive immune responses contributing to CRPS-like changes after fracture. Immunohistochemical experiments demonstrated close apposition of SP and CGRP containing neurons with Langerhans cells (LCs), the antigen-presenting dendritic cells that critically determine whether autoimmunity or tolerance is generated in the body. Epidermal LC numbers increased ipsilateral but not contralateral to the fracture site in wildtype mice, but not in transgenic fracture
The Journal of Pain
S63
mice lacking either SP or the CGRP receptor RAMP1. After fracture keratinocytes expressed cytokines capable of recruiting monocyte progenitors and stimulating their differentiation into LCs. Epidermal LC numbers were also increased in the painful limb of CRPS patients, compared to the contralateral side. After fracture IgM-antigen complex levels were elevated in the ipsilateral hindpaw skin, sciatic nerve, and lumbar spinal cord of wildtype mice, but not in transgenic fracture mice lacking SP or CGRP receptors. Collectively, these data support the hypothesis that exaggerated neuropeptide signaling in the fracture limb caused keratinocyte activation and cytokine expression, with monocyte recruitment and differentiation into antigen presenting epidermal LCs that migrated to the skin draining lymph nodes where they stimulated B cell antibody production and subsequent IgM-immune complex deposition in ipsilateral hindpaw skin, sciatic nerve, and lumbar spinal cord after fracture. The increased LC numbers observed in CRPS affected skin further supports the hypothesis that neuropeptide dependent adaptive immune responses contribute to CRPS. (1. Guo, Mol Pain, 2012; 2. Wei, Pain, 2009; 3. Li, Pain, 2014.)
E21 Joint and Muscle Pain (352) Differences in psychophysical responses to muscle stimulation in young and old healthy adults M Hoeppli, T Thurston, S Sidhu, T Mangum, J Weavil, T Hureau, W Tang, R Hughen, A Light, M Amann, and P Schweinhardt; University of Utah / McGill University, Salt Lake City / Montreal, UT/ Quebec, United States / Canada
Thin fiber muscle afferents (group III/IV) signal the sensations of muscle ache and fatigue. Aging may influence the sensitivity of these afferents. However, little is known about mechanisms and receptors involved in this age-related impact. Seventeen young (2763 years) and thirteen old (6865 years) matched (sex, BMI, and activity) healthy adults participated in this study. During a first session, participants were familiarized with a two-dimensional (2D) scale adapted from the Gracely Box Scale. In a second session, participants received 3 intramuscular (left abductor pollicis brevis) infusions (each 2 mL over 5 minutes) of combinations of metabolites: 1) pH=7.4, ATP=300nmol, lactate=1mmol - found in resting muscle (neutral concentration mixture), 2) pH=7.0, ATP=1mmol, lactate=15mmol - found during moderate exercise (low concentration mixture), and 3) pH=6.6, ATP=5mmol and lactate=50mmol - found during strenuous exercise (high concentration mixture). ATP activates P2X receptors, hydrogen ions (i.e., lowered pH) activate ASIC and TRPV1 receptors, and lactate enhances ASIC activation. These three metabolites act synergistically to activate group III/IV neurons. During the infusion, participants continuously rated their sensations of fatigue and ache on the 2D scale. Young participants reported significantly more fatigue and ache than the older adults with higher fatigue sensations during the infusion of both the low and high concentration mixture (both p<0.05) and more ache during the infusion of the high concentration mixture (p<0.05). In conclusion, although the combined activation of P2X, ASIC, and TRPV1 receptors causes sensations of muscle ache and fatigue in humans, healthy aging decreases the sensations signaled by these molecular receptors. The current findings cannot distinguish whether aging attenuates the excitability/sensitivity of these molecular receptors or alters the central processing of ache and fatigue. Interestingly, the present data contradict previous findings suggesting that sensitized muscle afferents underlie the higher prevalence of muscle fatigue and ache in older individuals.
(353) Withdrawn
E23 Neuropathic Pain (354) Dopamine D1/D5 receptor-mediated mechanisms in the maintenance of pathological pain plasticity S Megat; University of Texas at Dallas, Richardson, TX Our previous work showed that descending dopaminergic projections, likely originating in the hypothalamic A11 nucleus, play a critical role in maintaining plasticity in hyperalgesic priming. Our findings showed that spinal D1/D5 receptors are the key targets for these descending dopaminergic pathways and that these
S64
Abstracts
The Journal of Pain
receptors play a prominent role in maintenance of plasticity after a transition to a chronic pain state. First, we find that a specific lesion of the dopaminergic neurons arising from the hypothalamic A11 nucleus prevents maintenance of hyperalgesic priming induced by an intrathecal injection of brain derived neurotrophic factor (BDNF). Moreover, intrathecal injection of a D1/D5 agonist, SKF-82958 precipitates priming in mice previously exposed to BDNF recapitulating our previous findings with interleukin 6 and carrageenan injection into the hindpaw. These data suggest that in BDNF-primed mice, dopamine release from A11 neurons would potentially activate post-synaptic D1-like receptors to maintain a primed state. Next we sought to characterize neuronal activation in the spinal dorsal horn of primed and non-primed mice using an indirect marker of neuronal activity, c-fos. Our data show that intrathecal injection of the D1/D5 agonist in BDNF-primed mice activates a specific subset of neurons in the lamina III-IV of the spinal dorsal horn. Most of the neurons in the lamina III-IV are known to be GABAergic provoking us to explore downstream mechanisms of D1/D5 action that could involve the recruitment of the GABAergic system. We find that GABA-A antagonists cause hyperalgesia in na€ıve mice but are antihyperalgesic in mice that have been primed and exposed to either peripheral prostaglandin E2 (PGE2) injection or spinal administration of a D1/D5 agonist. These findings suggest a direct action of D1/D5 receptors on GABAergic circuitry in the spinal dorsal horn in the setting of pathological pain plasticity.
extensively characterized, and like central neurons, the neurons that exist within the DRG do not appear to act in isolation in the peripheral pain circuitry. A resident population of peripheral glial cells, satellite glial cells (SGCs), appears to influence nociceptive activity, but the precise mechanisms by which SGCs alter neuronal function is not well understood because of difficulty in isolating adult cells without their neuronal counterparts. Ultimately, in order to understand the role of SGCs in nociceptive processing we must develop a basal cellular profile by which SGCs can be identified. To accomplish this we used fluorescence activated cell sorting (FACS) to identify neuronal and non-neuronal cell populations in mouse DRG using CD200 and CD45, respectively. Using this broad gating strategy we identified 4 categories of cells that included putative neurons (CD200+ high/CD45-), a non-neuronal cell type (CD200+ intermediate/CD45-), and 2 immune-related cell types (CD45+/CD200-). Using the same gating strategy we also collected and stained sorted cells for glutamine synthetase (GS), a known marker of SGCs. Based on GS immunostaining, we found overlapping populations of SGCs in neuronal (CD200+/CD45-) and non-neuronal (CD45+/CD200-) gated cell populations, suggesting that SGCs may be a heterogeneous population. To further characterize the diversity of these cells we are now developing transcriptional profiles for SGCs harvested from na€ıve and inflamed mice. This profile analysis will provide more detailed information about SGCs as a population and how inflammation changes SGC expression and, ultimately, nociceptive signaling.
(355) Riluzole actions on SK channels in the amygdala in acute arthritic and chronic neuropathic pain J Thompson, G Ji, and V Neugebauer; Texas Tech University Health Sciences Center, Lubbock, TX
Current therapeutic strategies for chronic pain are limited and often have variable efficacy and severe side effects. Complicating treatment further is the association of pain with negative affective states. The amygdala is a limbic structure that plays a key role in mediating emotional-affective aspects of pain. Here we tested effects of riluzole, a clinically available drug for amyotrophic lateral sclerosis, on acute and chronic pain behaviors. Evidence suggests that riluzole effects are mediated through a supraspinal site of action. Among riluzole actions is activation of small-conductance calcium-activated potassium (SK) channels, which have been reported to regulate neuronal firing in the central nucleus of the amygdala (CeA). We hypothesized that riluzole inhibits pain behaviors by activating SK channels in the CeA in rat models of acute arthritis pain (kaolincarrageenan model) and chronic neuropathic pain (spinal nerve ligation [SNL] model). Supraspinally organized audible (nocifensive response) and ultrasonic (emotional-affective response) vocalizations, withdrawal thresholds, and anxiety-like behaviors on the elevated plus maze were measured in normal/sham controls, arthritic rats 5 h after induction, and neuropathic rats 4 weeks after SNL surgery. Arthritic and neuropathic rats showed increased vocalizations and anxiety-like behaviors and decreased withdrawal thresholds. Systemic (i.p.) riluzole administration in arthritic rats inhibited audible and ultrasonic vocalizations and anxiety-like behaviors with no effect on withdrawal thresholds, however in neuropathic rats, inhibitory riluzole effects were weaker and less consistent. Coapplication of systemic riluzole with stereotaxic (into CeA) apamin (selective SK channel blocker) blocked riluzole inhibition of vocalizations, but effects persisted with coapplication (into CeA) of a large-conductance calcium-activated potassium (BK) channel blocker (charybdotoxin) or offsite (into lateral-basolateral amygdala) coapplication of apamin. The data suggest that riluzole has beneficial effects on acute arthritis pain behaviors mediated at least in part by SK channels in the CeA, but benefits on chronic neuropathic pain behaviors are less prominent.
E25 Nociceptive Pathways (356) Identification of a heterogeneous population of satellite glial cells in the mouse dorsal root ganglion
E26 Novel Molecular Entities action (357) Antinociceptive effects of a synthetic tetracycline compound on mechanical and cold allodynia C Sherfey, H Blanton, C Bezboruah, D Curtis, P Marquardt, J Martinez, S Bergeson, and J Guindon; Texas Tech University Health Sciences Center, Lubbock, TX
Synthetic tetracycline compounds have been developed and are able to reduce infection as well as inflammation. They are broadspectrum antibiotics used against different bacterial infectious diseases. However, the effect on mechanical and cold pain sensitivity has not been investigated. The goal of the study is to evaluate the effect of synthetic tetracycline compounds with or without alcohol on mechanical and cold allodynia responses. Mechanical and cold responses will be used to evaluate pain threshold differences between male and female wild-type C57BL/6 mice. First, we have evaluated the effect of a synthetic tetracycline compound on mechanical and cold allodynia. Our data indicate that mechanical and cold allodynia remains unchanged after administration of a synthetic tetracycline compound meaning values are similar to baseline levels. However, synthetic tetracycline compound showed antinociceptive effects to mechanical and cold allodynia following the formalin test (60 minutes after injection of formalin). Moreover, mechanical and cold allodynia responses return to baseline levels 2 hours after the formalin test. Second, we have evaluated the effect of alcohol on mechanical and cold allodynia. Chronic alcohol lowers mechanical and cold allodynia thresholds differently in male and female mice. These results demonstrate potential antinociceptive properties of synthetic tetracycline compound in response to mechanical and cold allodynia. Further studies are needed to investigate the mechanism underlying this antinociceptive effect of synthetic tetracycline compounds and a possible gender specific difference. Antinociceptive properties of synthetic tetracycline compounds could be a great alternative avenue to alleviate pain in patients.
E27 Opioid Action (358) Antinociceptive effects of pluronic lecithin organo (PLO) opioid gels in rats with thermal injury B Cheppudira, R Christy, and J Clifford; United States Army Institute of
B Knight, E Young, S Crocker, and K Baumbauer; University of Connecticut,
Surgical Research, Fort Sam Houston, TX
Storrs, CT
Thermal injuries induce intense pain. Opioids are extensively used as analgesics to control burn pain. However, systemic administration of opioids induces multiple adverse effects that are primarily CNS mediated. Alternately, topical application of low dose of opioids directly
Peripheral inflammation and tissue injury cause alterations in nociceptor activity and contribute to the development of normal and pathological pain states. Primary afferent nociceptors have been
relationship between participant sex and pain outcomes. Results indicated that stoic fortitude and SS were significant mediators of the relationship between sex and heat and cold tolerance. SS, but not stoicism, also mediated the relationship between sex and ischemic and electric pain tolerance. These findings lend support for stoicism and SS as mediators for sex differences in pain, particularly differences in pain tolerance. No evidence was found for mediation of the sex-pain threshold relationship. These findings may have important implications for treatment seeking in males. Because males are more likely to report higher levels of SS, stoicism, and tolerances for pain, they may be less likely to seek treatment. This might inflate sex differences in the precedence rates of chronic pain. This research reported was supported by the National Institute on Minority Health and Health Disparities of the National Institutes of Health under Award Number R01MD007807. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
E19 Inflammation (350) Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) regulates mechanical sensitivity following cutaneous inflammation J Yasko, T Kiprono, B Knight, C Willis, A Nicaise, E Young, S Crocker, and K Baumbauer; University of Connecticut, Storrs, CT Tissue injury and inflammation result in alterations in neuronal function and subsequent development of pain. The development of pain, both normal and pathological, involves activity of neurons and glia in both the peripheral and central nervous systems. Emerging evidence demonstrates activity in nociceptive circuits is coordinated by extracellular matrix (ECM), and that injury and inflammation alter both the ECM and its regulatory proteins, matrix metalloproteinases (MMPs). Under normal conditions MMPs degrade and remodel the ECM, and this process may become dysregulated during the development of pathological pain. This suggests that modulating MMP activity may serve as an important therapeutic target for pain treatment. Endogenous inhibitors, such as tissue inhibitors of metalloproteinases-1 (TIMP-1) maintain the balance of ECM remodeling via reduction of MMP activity. While TIMP-1 is known to have a number of physiological functions in the nervous system, its role in pain processing is largely unknown. To examine the role of TIMP-1 in the development of pain, we exposed global TIMP-1 knockout (KO) and wildtype (WT) mice to cutaneous inflammation. Mechanical and thermal sensitivity were monitored over the course of 7 days following Complete Freud’s Adjuvant (CFA) injection. Strikingly, TIMP-1 KO mice developed rapid onset mechanical sensitivity within 24 hours post injection with no significant change in thermal sensitivity. The development of mechanical hypersensitivity correlated with increased expression of TRPA1, GFRa2, GFR-a3, TrkA, and ASIC1 mRNA in the DRG. Additionally, TIMP1 KO mice showed increased levels of circulating IL-1b, IL-6, and IL10, but not TNF-a. Finally, CFA injections increased cutaneous TIMP-1 protein levels in WT mice. Collectively, our results suggest a role for TIMP-1 in the regulation and development of inflammatory pain.
(351) Neuropeptide regulation of adaptive immune responses after fracture W Kingery, W Li, T Guo, X Shi, and J Clark; Veterans Affairs Palo Alto Health Care System, Palo Alto, CA
Using a murine tibia fracture model of complex regional pain syndrome (CRPS), we previously observed that facilitated substance P (SP) and calcitonin gene-related peptide (CGRP) signaling contributes to the development of chronic nociceptive sensitization after fracture1,2 and that B cells are required for the full expression of post-fracture CRPS-like changes.3 These results support the hypothesis that exaggerated neuropeptide signaling triggers adaptive immune responses contributing to CRPS-like changes after fracture. Immunohistochemical experiments demonstrated close apposition of SP and CGRP containing neurons with Langerhans cells (LCs), the antigen-presenting dendritic cells that critically determine whether autoimmunity or tolerance is generated in the body. Epidermal LC numbers increased ipsilateral but not contralateral to the fracture site in wildtype mice, but not in transgenic fracture
The Journal of Pain
S63
mice lacking either SP or the CGRP receptor RAMP1. After fracture keratinocytes expressed cytokines capable of recruiting monocyte progenitors and stimulating their differentiation into LCs. Epidermal LC numbers were also increased in the painful limb of CRPS patients, compared to the contralateral side. After fracture IgM-antigen complex levels were elevated in the ipsilateral hindpaw skin, sciatic nerve, and lumbar spinal cord of wildtype mice, but not in transgenic fracture mice lacking SP or CGRP receptors. Collectively, these data support the hypothesis that exaggerated neuropeptide signaling in the fracture limb caused keratinocyte activation and cytokine expression, with monocyte recruitment and differentiation into antigen presenting epidermal LCs that migrated to the skin draining lymph nodes where they stimulated B cell antibody production and subsequent IgM-immune complex deposition in ipsilateral hindpaw skin, sciatic nerve, and lumbar spinal cord after fracture. The increased LC numbers observed in CRPS affected skin further supports the hypothesis that neuropeptide dependent adaptive immune responses contribute to CRPS. (1. Guo, Mol Pain, 2012; 2. Wei, Pain, 2009; 3. Li, Pain, 2014.)
E21 Joint and Muscle Pain (352) Differences in psychophysical responses to muscle stimulation in young and old healthy adults M Hoeppli, T Thurston, S Sidhu, T Mangum, J Weavil, T Hureau, W Tang, R Hughen, A Light, M Amann, and P Schweinhardt; University of Utah / McGill University, Salt Lake City / Montreal, UT/ Quebec, United States / Canada
Thin fiber muscle afferents (group III/IV) signal the sensations of muscle ache and fatigue. Aging may influence the sensitivity of these afferents. However, little is known about mechanisms and receptors involved in this age-related impact. Seventeen young (2763 years) and thirteen old (6865 years) matched (sex, BMI, and activity) healthy adults participated in this study. During a first session, participants were familiarized with a two-dimensional (2D) scale adapted from the Gracely Box Scale. In a second session, participants received 3 intramuscular (left abductor pollicis brevis) infusions (each 2 mL over 5 minutes) of combinations of metabolites: 1) pH=7.4, ATP=300nmol, lactate=1mmol - found in resting muscle (neutral concentration mixture), 2) pH=7.0, ATP=1mmol, lactate=15mmol - found during moderate exercise (low concentration mixture), and 3) pH=6.6, ATP=5mmol and lactate=50mmol - found during strenuous exercise (high concentration mixture). ATP activates P2X receptors, hydrogen ions (i.e., lowered pH) activate ASIC and TRPV1 receptors, and lactate enhances ASIC activation. These three metabolites act synergistically to activate group III/IV neurons. During the infusion, participants continuously rated their sensations of fatigue and ache on the 2D scale. Young participants reported significantly more fatigue and ache than the older adults with higher fatigue sensations during the infusion of both the low and high concentration mixture (both p<0.05) and more ache during the infusion of the high concentration mixture (p<0.05). In conclusion, although the combined activation of P2X, ASIC, and TRPV1 receptors causes sensations of muscle ache and fatigue in humans, healthy aging decreases the sensations signaled by these molecular receptors. The current findings cannot distinguish whether aging attenuates the excitability/sensitivity of these molecular receptors or alters the central processing of ache and fatigue. Interestingly, the present data contradict previous findings suggesting that sensitized muscle afferents underlie the higher prevalence of muscle fatigue and ache in older individuals.
(353) Withdrawn
E23 Neuropathic Pain (354) Dopamine D1/D5 receptor-mediated mechanisms in the maintenance of pathological pain plasticity S Megat; University of Texas at Dallas, Richardson, TX Our previous work showed that descending dopaminergic projections, likely originating in the hypothalamic A11 nucleus, play a critical role in maintaining plasticity in hyperalgesic priming. Our findings showed that spinal D1/D5 receptors are the key targets for these descending dopaminergic pathways and that these
S64
Abstracts
The Journal of Pain
receptors play a prominent role in maintenance of plasticity after a transition to a chronic pain state. First, we find that a specific lesion of the dopaminergic neurons arising from the hypothalamic A11 nucleus prevents maintenance of hyperalgesic priming induced by an intrathecal injection of brain derived neurotrophic factor (BDNF). Moreover, intrathecal injection of a D1/D5 agonist, SKF-82958 precipitates priming in mice previously exposed to BDNF recapitulating our previous findings with interleukin 6 and carrageenan injection into the hindpaw. These data suggest that in BDNF-primed mice, dopamine release from A11 neurons would potentially activate post-synaptic D1-like receptors to maintain a primed state. Next we sought to characterize neuronal activation in the spinal dorsal horn of primed and non-primed mice using an indirect marker of neuronal activity, c-fos. Our data show that intrathecal injection of the D1/D5 agonist in BDNF-primed mice activates a specific subset of neurons in the lamina III-IV of the spinal dorsal horn. Most of the neurons in the lamina III-IV are known to be GABAergic provoking us to explore downstream mechanisms of D1/D5 action that could involve the recruitment of the GABAergic system. We find that GABA-A antagonists cause hyperalgesia in na€ıve mice but are antihyperalgesic in mice that have been primed and exposed to either peripheral prostaglandin E2 (PGE2) injection or spinal administration of a D1/D5 agonist. These findings suggest a direct action of D1/D5 receptors on GABAergic circuitry in the spinal dorsal horn in the setting of pathological pain plasticity.
extensively characterized, and like central neurons, the neurons that exist within the DRG do not appear to act in isolation in the peripheral pain circuitry. A resident population of peripheral glial cells, satellite glial cells (SGCs), appears to influence nociceptive activity, but the precise mechanisms by which SGCs alter neuronal function is not well understood because of difficulty in isolating adult cells without their neuronal counterparts. Ultimately, in order to understand the role of SGCs in nociceptive processing we must develop a basal cellular profile by which SGCs can be identified. To accomplish this we used fluorescence activated cell sorting (FACS) to identify neuronal and non-neuronal cell populations in mouse DRG using CD200 and CD45, respectively. Using this broad gating strategy we identified 4 categories of cells that included putative neurons (CD200+ high/CD45-), a non-neuronal cell type (CD200+ intermediate/CD45-), and 2 immune-related cell types (CD45+/CD200-). Using the same gating strategy we also collected and stained sorted cells for glutamine synthetase (GS), a known marker of SGCs. Based on GS immunostaining, we found overlapping populations of SGCs in neuronal (CD200+/CD45-) and non-neuronal (CD45+/CD200-) gated cell populations, suggesting that SGCs may be a heterogeneous population. To further characterize the diversity of these cells we are now developing transcriptional profiles for SGCs harvested from na€ıve and inflamed mice. This profile analysis will provide more detailed information about SGCs as a population and how inflammation changes SGC expression and, ultimately, nociceptive signaling.
(355) Riluzole actions on SK channels in the amygdala in acute arthritic and chronic neuropathic pain J Thompson, G Ji, and V Neugebauer; Texas Tech University Health Sciences Center, Lubbock, TX
Current therapeutic strategies for chronic pain are limited and often have variable efficacy and severe side effects. Complicating treatment further is the association of pain with negative affective states. The amygdala is a limbic structure that plays a key role in mediating emotional-affective aspects of pain. Here we tested effects of riluzole, a clinically available drug for amyotrophic lateral sclerosis, on acute and chronic pain behaviors. Evidence suggests that riluzole effects are mediated through a supraspinal site of action. Among riluzole actions is activation of small-conductance calcium-activated potassium (SK) channels, which have been reported to regulate neuronal firing in the central nucleus of the amygdala (CeA). We hypothesized that riluzole inhibits pain behaviors by activating SK channels in the CeA in rat models of acute arthritis pain (kaolincarrageenan model) and chronic neuropathic pain (spinal nerve ligation [SNL] model). Supraspinally organized audible (nocifensive response) and ultrasonic (emotional-affective response) vocalizations, withdrawal thresholds, and anxiety-like behaviors on the elevated plus maze were measured in normal/sham controls, arthritic rats 5 h after induction, and neuropathic rats 4 weeks after SNL surgery. Arthritic and neuropathic rats showed increased vocalizations and anxiety-like behaviors and decreased withdrawal thresholds. Systemic (i.p.) riluzole administration in arthritic rats inhibited audible and ultrasonic vocalizations and anxiety-like behaviors with no effect on withdrawal thresholds, however in neuropathic rats, inhibitory riluzole effects were weaker and less consistent. Coapplication of systemic riluzole with stereotaxic (into CeA) apamin (selective SK channel blocker) blocked riluzole inhibition of vocalizations, but effects persisted with coapplication (into CeA) of a large-conductance calcium-activated potassium (BK) channel blocker (charybdotoxin) or offsite (into lateral-basolateral amygdala) coapplication of apamin. The data suggest that riluzole has beneficial effects on acute arthritis pain behaviors mediated at least in part by SK channels in the CeA, but benefits on chronic neuropathic pain behaviors are less prominent.
E25 Nociceptive Pathways (356) Identification of a heterogeneous population of satellite glial cells in the mouse dorsal root ganglion
E26 Novel Molecular Entities action (357) Antinociceptive effects of a synthetic tetracycline compound on mechanical and cold allodynia C Sherfey, H Blanton, C Bezboruah, D Curtis, P Marquardt, J Martinez, S Bergeson, and J Guindon; Texas Tech University Health Sciences Center, Lubbock, TX
Synthetic tetracycline compounds have been developed and are able to reduce infection as well as inflammation. They are broadspectrum antibiotics used against different bacterial infectious diseases. However, the effect on mechanical and cold pain sensitivity has not been investigated. The goal of the study is to evaluate the effect of synthetic tetracycline compounds with or without alcohol on mechanical and cold allodynia responses. Mechanical and cold responses will be used to evaluate pain threshold differences between male and female wild-type C57BL/6 mice. First, we have evaluated the effect of a synthetic tetracycline compound on mechanical and cold allodynia. Our data indicate that mechanical and cold allodynia remains unchanged after administration of a synthetic tetracycline compound meaning values are similar to baseline levels. However, synthetic tetracycline compound showed antinociceptive effects to mechanical and cold allodynia following the formalin test (60 minutes after injection of formalin). Moreover, mechanical and cold allodynia responses return to baseline levels 2 hours after the formalin test. Second, we have evaluated the effect of alcohol on mechanical and cold allodynia. Chronic alcohol lowers mechanical and cold allodynia thresholds differently in male and female mice. These results demonstrate potential antinociceptive properties of synthetic tetracycline compound in response to mechanical and cold allodynia. Further studies are needed to investigate the mechanism underlying this antinociceptive effect of synthetic tetracycline compounds and a possible gender specific difference. Antinociceptive properties of synthetic tetracycline compounds could be a great alternative avenue to alleviate pain in patients.
E27 Opioid Action (358) Antinociceptive effects of pluronic lecithin organo (PLO) opioid gels in rats with thermal injury B Cheppudira, R Christy, and J Clifford; United States Army Institute of
B Knight, E Young, S Crocker, and K Baumbauer; University of Connecticut,
Surgical Research, Fort Sam Houston, TX
Storrs, CT
Thermal injuries induce intense pain. Opioids are extensively used as analgesics to control burn pain. However, systemic administration of opioids induces multiple adverse effects that are primarily CNS mediated. Alternately, topical application of low dose of opioids directly
Peripheral inflammation and tissue injury cause alterations in nociceptor activity and contribute to the development of normal and pathological pain states. Primary afferent nociceptors have been