Neurons in the rostroventromedial medulla (RVM) project to spinal loci where the neurons inhibit ... more Neurons in the rostroventromedial medulla (RVM) project to spinal loci where the neurons inhibit or facilitate pain transmission. Abnormal activity of facilitatory processes may thus represent a mechanism of chronic pain. This possibility and the phenotype of RVM cells that might underlie experimental neuropathic pain were investigated. Cells expressing μ-opioid receptors were targeted with a single microinjection of saporin conjugated to the μ-opioid agonist dermorphin; unconjugated saporin and dermorphin were used as controls. RVM dermorphin–saporin, but not dermorphin or saporin, significantly decreased cells expressing μ-opioid receptor transcript. RVM dermorphin, saporin, or dermorphin–saporin did not change baseline hindpaw sensitivity to non-noxious or noxious stimuli. Spinal nerve ligation (SNL) injury in rats pretreated with RVM dermorphin–saporin failed to elicit the expected increase in sensitivity to non-noxious mechanical or noxious thermal stimuli applied to the paw. R...
Many clinical case reports have suggested that sustained opioid exposure can elicit unexpected, p... more Many clinical case reports have suggested that sustained opioid exposure can elicit unexpected, paradoxical pain. Here, we explore the possibility that (1) opioid-induced pain results from tonic activation of descending pain facilitation arising in the rostral ventromedial medulla (RVM) and (2) the presence of such pain manifests behaviorally as antinociceptive tolerance. Rats implanted subcutaneously with pellets or osmotic minipumps delivering morphine displayed time-related tactile allodynia and thermal hyperalgesia (i.e., opioid-induced “pain”); placebo pellets or saline minipumps did not change thresholds. Opioid-induced pain was observed while morphine delivery continued and while the rats were not in withdrawal. RVM lidocaine, or bilateral lesions of the dorsolateral funiculus (DLF), did not change response thresholds in placebo-pelleted rats but blocked opioid-induced pain. The intrathecal morphine antinociceptive dose–response curve (DRC) in morphine-pelleted rats was displ...
Cephalalgia : an international journal of headache, 2017
Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid... more Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid peptide acting preferentially at kappa opioid receptors (KORs), is a key mediator of stress responses. The aim of this study was to use an injury-free rat model of functional cephalic pain with features of migraine and medication overuse headache (MOH) to test the possible preventive benefit of KOR blockade on stress-induced cephalic pain. Methods Following sumatriptan priming to model MOH, rats were hyper-responsive to environmental stress, demonstrating delayed cephalic and extracephalic allodynia and increased levels of CGRP in the jugular blood, consistent with commonly observed clinical outcomes during migraine. Nor-binaltorphimine (nor-BNI), a long-acting KOR antagonist or CYM51317, a novel short-acting KOR antagonist, were given systemically either during sumatriptan priming or immediately before environmental stress challenge. The effects of KOR blockade in the amygdala on stres...
Bv8 is a pronociceptive peptide that binds to two G-protein coupled prokineticin receptors, PK-R1... more Bv8 is a pronociceptive peptide that binds to two G-protein coupled prokineticin receptors, PK-R1 and PK-R2. These receptors are localized in the dorsal horn of the spinal cord and dorsal root ganglia (DRG) of nociceptive neurons in rodents. Systemic administration of Bv8 elicits a biphasic reduction in nociceptive thresholds to thermal and mechanical stimuli. Here, the possibility that Bv8 might directly modulate the expression and release of excitatory transmitters within the early and late phases of hyperalgesia was evaluated. Administration of Bv8 to mouse lumbar spinal cord sections produced a direct, significant and concentration-related release of CGRP. Bv8- or capsaicin-stimulated CGRP release was markedly enhanced in tissues taken from Bv8-pretreated mice during the late, but not the early, phase of hyperalgesia. Pretreatment of rats with protein synthesis inhibitors blocked the expression of the late, but not early, phase of Bv8-induced hyperalgesia. Finally, during the la...
Journal Of Neuropathic Pain & Symptom Palliation, 2005
ABSTRACT This review will focus on our current knowledge of the changes that occur within the cen... more ABSTRACT This review will focus on our current knowledge of the changes that occur within the central nervous system after peripheral nerve injury. Damage to peripheral nerves from either injury or disease often leads to the development of chronic abnormal pain states. Such abnormal pain states include persistent pain, spontaneous paroxysmal pain, allodynia (i.e., normally innocuous stimuli perceived as nociceptive) and hyperalgesia (increased sensitivity to noxious stimuli). Painful neuropathy represents a seriously debilitating syndrome that affects millions of people and their quality of life. Equally important, neuropathic pain is resistant to common protocols for treatment of chronic pain, and is commonly refractory to opioids. It is thus important to understanding the underlying mechanisms of neuronal plasticity that can initiate and maintain neuropathic pain states in order to develop novel and effective treatments. Responses to injury include general cellular and molecular mechanisms for growth of neurons and for strengthening of electrical signaling. In many situations, these cellular responses are advantageous as they can prevent neuronal death or promote the recovery of partially damaged neurons. In peripheral nerve regeneration, for example, denervation supersensitivity and sprouting are beneficial to achieve axonal regrowth and reestab-lishment of the same synapse. However, in some situations, the repair responses do not produce advantageous results. Rather, the plasticity, once triggered, produces unwanted or disadvantageous consequences. Here we will address several issues reported in the literature that have been identified as playing a role in central sensitization including the reduction in sensory threshold, increased responsiveness of the dorsal horn units, recruitment of subthreshold components, increased excitatory neurotransmitter release, enhanced depolarization and temporal summation and descending facilitation.
Opioid-induced hyperalgesia is characterized by hypersensitivity to innocuous or noxious stimuli ... more Opioid-induced hyperalgesia is characterized by hypersensitivity to innocuous or noxious stimuli during sustained opiate administration. Microinjection of lidocaine into the rostral ventromedial medulla (RVM), or dorsolateral funiculus (DLF) lesion, abolishes opioid-induced hyperalgesia, suggesting the importance of descending pain facilitation mechanisms. Here, we investigate the possibility that cholecystokinin (CCK), a pronociceptive peptide, may drive such descending facilitation from the RVM during continuous opioid administration. In opioid-naive rats, CCK in the RVM produced acute tactile and thermal hypersensitivity that was antagonized by the CCK2receptor antagonist L365,260 or by DLF lesion. CCK in the RVM also acutely displaced the spinal morphine antinociceptive dose-response curve to the right. Continuous systemic morphine elicited sustained tactile and thermal hypersensitivity within 3 d. Such hypersensitivity was reversed in a time-dependent manner by L365,260 in the ...
The potential modulation of TRPV1 nociceptive activity by the CB1receptor was investigated here u... more The potential modulation of TRPV1 nociceptive activity by the CB1receptor was investigated here using CB1wild-type (WT) and knock-out (KO) mice as well as selective CB1inverse agonists. No significant differences were detected in baseline thermal thresholds of ICR, CB1WT or CB1KO mice. Intraplantar capsaicin produced dose- and time-related paw flinch responses in ICR and CB1WT mice and induced plasma extravasation yet minimal responses were seen in CB1KO animals with no apparent differences in TRPV1 channel expression. Capsaicin-evoked CGRP release from spinal cord tissue and capsaicin-evoked action potentials on isolated skin-nerve preparation were significantly decreased in CB1KO mice. Pretreatment with intraplantar galanin and bradykinin, compounds known to sensitize TRPV1 receptors, restored capsaicin-induced flinching in CB1KO mice. The possibility that constitutive activity at the CB1receptor is required to maintain the TRPV1 receptor in a “sensitized” state was tested using C...
Proceedings of the National Academy of Sciences, 2012
Relief of pain is rewarding. Using a model of experimental postsurgical pain we show that blockad... more Relief of pain is rewarding. Using a model of experimental postsurgical pain we show that blockade of afferent input from the injury with local anesthetic elicits conditioned place preference, activates ventral tegmental dopaminergic cells, and increases dopamine release in the nucleus accumbens. Importantly, place preference is associated with increased activity in midbrain dopaminergic neurons and blocked by dopamine antagonists injected into the nucleus accumbens. The data directly support the hypothesis that relief of pain produces negative reinforcement through activation of the mesolimbic reward–valuation circuitry.
Recent studies demonstrate the possible existence of tonic modulatory control of nociceptive inpu... more Recent studies demonstrate the possible existence of tonic modulatory control of nociceptive input mediated by spinal cannabinoid receptors (CB1). Accordingly, it is predicted that a reduction in the spinal CB1 receptors may enhance sensitivity to sensory stimuli and a decrease in spinal antinociceptive potency to cannabinoid agonists. An antisense oligodeoxynucleotide (ODN) specific to the CB1 receptor was used to 'knock-down' CB1 receptors in the lumbar spinal cord and dorsal root ganglia by the local, repeated intrathecal (i.th.) administration of the ODN. This treatment resulted in a decrease in lumbar spinal CB1 receptor expression accompanied by a decrease in the response thresholds to both innocuous tactile and noxious thermal stimuli. The antinociceptive action of the CB1 agonist, WIN 55,212-2, by i.th. administration was also significantly attenuated after treatment with the antisense ODN. Similar treatment using a mismatch control ODN had no effect on receptor protein or on sensory thresholds. The effects of the antisense ODN treatment on sensory thresholds were fully reversed after discontinuation of the ODN injection. The antisense ODN treated rats also showed a significant increase in lumbar spinal dynorphin A. Acute i.th. injection of MK-801 or an antidynorphin antiserum blocked the antisense ODN-induced tactile and thermal hypersensitivity. These data support the possibility of endogenous inhibitory cannabinoid tone to limit spinal afferent input of thermal and tactile stimuli. Lifting of this inhibitory tone through a 'knock-down' of spinal CB1 receptors apparently lowers the thresholds for sensory input, as reflected by the actions of MK-801 to block tactile and thermal hypersensitivity. The increased spinal dynorphin may act to further promote afferent outflow and abnormal pain because sequestration of spinal dynorphin with antiserum also reverses the manifestations of abnormal pain following knock-down of CB1 receptors.
Spinal antinociception produced by delta 9-tetrahydro-cannabinol (Delta(9)-THC) and other cannabi... more Spinal antinociception produced by delta 9-tetrahydro-cannabinol (Delta(9)-THC) and other cannabinoid agonists has been suggested to be mediated by the release of dynorphin acting at the kappa opioid receptor. Alternatively, as cannabinoid receptors are distributed appropriately in the pain transmission pathway, cannabinoid agonists might act directly at the spinal level to inhibit nociception, without requiring dynorphin release. Here, these possibilities were explored using mice with a deletion of the gene encoding prodynorphin. Antinociceptive dose-response curves were constructed for spinal Delta(9)-THC and WIN 55,212-2 in prodynorphin knock-out mice and in wild-type littermates. WIN 55,212-2 and Delta(9)-THC were equipotent in the wild-type and prodynorphin knock-out mice. Spinal pretreatment with a kappa opioid receptor antagonist, nor-binaltorphimine (nor-BNI), did not alter the dose-response curves for either WIN 55,212-2 or Delta(9)-THC in prodynorphin knock-out and wild-type mice. However, the same dose of nor-BNI used blocked U50,488H-induced antinociception in both wild-type and prodynorphin knock-out mice, confirming kappa opioid receptor activity. Pretreatment with SR141716A, a cannabinoid receptor antagonist blocked the antinociceptive actions of both WIN 55,212-2 and Delta(9)-THC. These data support the conclusion that antinociception produced by spinal cannabinoids are likely to be mediated directly through activation of cannabinoid receptors without the requirement for dynorphin release or activation of kappa opioid receptors.
Neurons in the rostroventromedial medulla (RVM) project to spinal loci where the neurons inhibit ... more Neurons in the rostroventromedial medulla (RVM) project to spinal loci where the neurons inhibit or facilitate pain transmission. Abnormal activity of facilitatory processes may thus represent a mechanism of chronic pain. This possibility and the phenotype of RVM cells that might underlie experimental neuropathic pain were investigated. Cells expressing μ-opioid receptors were targeted with a single microinjection of saporin conjugated to the μ-opioid agonist dermorphin; unconjugated saporin and dermorphin were used as controls. RVM dermorphin–saporin, but not dermorphin or saporin, significantly decreased cells expressing μ-opioid receptor transcript. RVM dermorphin, saporin, or dermorphin–saporin did not change baseline hindpaw sensitivity to non-noxious or noxious stimuli. Spinal nerve ligation (SNL) injury in rats pretreated with RVM dermorphin–saporin failed to elicit the expected increase in sensitivity to non-noxious mechanical or noxious thermal stimuli applied to the paw. R...
Many clinical case reports have suggested that sustained opioid exposure can elicit unexpected, p... more Many clinical case reports have suggested that sustained opioid exposure can elicit unexpected, paradoxical pain. Here, we explore the possibility that (1) opioid-induced pain results from tonic activation of descending pain facilitation arising in the rostral ventromedial medulla (RVM) and (2) the presence of such pain manifests behaviorally as antinociceptive tolerance. Rats implanted subcutaneously with pellets or osmotic minipumps delivering morphine displayed time-related tactile allodynia and thermal hyperalgesia (i.e., opioid-induced “pain”); placebo pellets or saline minipumps did not change thresholds. Opioid-induced pain was observed while morphine delivery continued and while the rats were not in withdrawal. RVM lidocaine, or bilateral lesions of the dorsolateral funiculus (DLF), did not change response thresholds in placebo-pelleted rats but blocked opioid-induced pain. The intrathecal morphine antinociceptive dose–response curve (DRC) in morphine-pelleted rats was displ...
Cephalalgia : an international journal of headache, 2017
Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid... more Background Stress is the most commonly reported migraine trigger. Dynorphin, an endogenous opioid peptide acting preferentially at kappa opioid receptors (KORs), is a key mediator of stress responses. The aim of this study was to use an injury-free rat model of functional cephalic pain with features of migraine and medication overuse headache (MOH) to test the possible preventive benefit of KOR blockade on stress-induced cephalic pain. Methods Following sumatriptan priming to model MOH, rats were hyper-responsive to environmental stress, demonstrating delayed cephalic and extracephalic allodynia and increased levels of CGRP in the jugular blood, consistent with commonly observed clinical outcomes during migraine. Nor-binaltorphimine (nor-BNI), a long-acting KOR antagonist or CYM51317, a novel short-acting KOR antagonist, were given systemically either during sumatriptan priming or immediately before environmental stress challenge. The effects of KOR blockade in the amygdala on stres...
Bv8 is a pronociceptive peptide that binds to two G-protein coupled prokineticin receptors, PK-R1... more Bv8 is a pronociceptive peptide that binds to two G-protein coupled prokineticin receptors, PK-R1 and PK-R2. These receptors are localized in the dorsal horn of the spinal cord and dorsal root ganglia (DRG) of nociceptive neurons in rodents. Systemic administration of Bv8 elicits a biphasic reduction in nociceptive thresholds to thermal and mechanical stimuli. Here, the possibility that Bv8 might directly modulate the expression and release of excitatory transmitters within the early and late phases of hyperalgesia was evaluated. Administration of Bv8 to mouse lumbar spinal cord sections produced a direct, significant and concentration-related release of CGRP. Bv8- or capsaicin-stimulated CGRP release was markedly enhanced in tissues taken from Bv8-pretreated mice during the late, but not the early, phase of hyperalgesia. Pretreatment of rats with protein synthesis inhibitors blocked the expression of the late, but not early, phase of Bv8-induced hyperalgesia. Finally, during the la...
Journal Of Neuropathic Pain & Symptom Palliation, 2005
ABSTRACT This review will focus on our current knowledge of the changes that occur within the cen... more ABSTRACT This review will focus on our current knowledge of the changes that occur within the central nervous system after peripheral nerve injury. Damage to peripheral nerves from either injury or disease often leads to the development of chronic abnormal pain states. Such abnormal pain states include persistent pain, spontaneous paroxysmal pain, allodynia (i.e., normally innocuous stimuli perceived as nociceptive) and hyperalgesia (increased sensitivity to noxious stimuli). Painful neuropathy represents a seriously debilitating syndrome that affects millions of people and their quality of life. Equally important, neuropathic pain is resistant to common protocols for treatment of chronic pain, and is commonly refractory to opioids. It is thus important to understanding the underlying mechanisms of neuronal plasticity that can initiate and maintain neuropathic pain states in order to develop novel and effective treatments. Responses to injury include general cellular and molecular mechanisms for growth of neurons and for strengthening of electrical signaling. In many situations, these cellular responses are advantageous as they can prevent neuronal death or promote the recovery of partially damaged neurons. In peripheral nerve regeneration, for example, denervation supersensitivity and sprouting are beneficial to achieve axonal regrowth and reestab-lishment of the same synapse. However, in some situations, the repair responses do not produce advantageous results. Rather, the plasticity, once triggered, produces unwanted or disadvantageous consequences. Here we will address several issues reported in the literature that have been identified as playing a role in central sensitization including the reduction in sensory threshold, increased responsiveness of the dorsal horn units, recruitment of subthreshold components, increased excitatory neurotransmitter release, enhanced depolarization and temporal summation and descending facilitation.
Opioid-induced hyperalgesia is characterized by hypersensitivity to innocuous or noxious stimuli ... more Opioid-induced hyperalgesia is characterized by hypersensitivity to innocuous or noxious stimuli during sustained opiate administration. Microinjection of lidocaine into the rostral ventromedial medulla (RVM), or dorsolateral funiculus (DLF) lesion, abolishes opioid-induced hyperalgesia, suggesting the importance of descending pain facilitation mechanisms. Here, we investigate the possibility that cholecystokinin (CCK), a pronociceptive peptide, may drive such descending facilitation from the RVM during continuous opioid administration. In opioid-naive rats, CCK in the RVM produced acute tactile and thermal hypersensitivity that was antagonized by the CCK2receptor antagonist L365,260 or by DLF lesion. CCK in the RVM also acutely displaced the spinal morphine antinociceptive dose-response curve to the right. Continuous systemic morphine elicited sustained tactile and thermal hypersensitivity within 3 d. Such hypersensitivity was reversed in a time-dependent manner by L365,260 in the ...
The potential modulation of TRPV1 nociceptive activity by the CB1receptor was investigated here u... more The potential modulation of TRPV1 nociceptive activity by the CB1receptor was investigated here using CB1wild-type (WT) and knock-out (KO) mice as well as selective CB1inverse agonists. No significant differences were detected in baseline thermal thresholds of ICR, CB1WT or CB1KO mice. Intraplantar capsaicin produced dose- and time-related paw flinch responses in ICR and CB1WT mice and induced plasma extravasation yet minimal responses were seen in CB1KO animals with no apparent differences in TRPV1 channel expression. Capsaicin-evoked CGRP release from spinal cord tissue and capsaicin-evoked action potentials on isolated skin-nerve preparation were significantly decreased in CB1KO mice. Pretreatment with intraplantar galanin and bradykinin, compounds known to sensitize TRPV1 receptors, restored capsaicin-induced flinching in CB1KO mice. The possibility that constitutive activity at the CB1receptor is required to maintain the TRPV1 receptor in a “sensitized” state was tested using C...
Proceedings of the National Academy of Sciences, 2012
Relief of pain is rewarding. Using a model of experimental postsurgical pain we show that blockad... more Relief of pain is rewarding. Using a model of experimental postsurgical pain we show that blockade of afferent input from the injury with local anesthetic elicits conditioned place preference, activates ventral tegmental dopaminergic cells, and increases dopamine release in the nucleus accumbens. Importantly, place preference is associated with increased activity in midbrain dopaminergic neurons and blocked by dopamine antagonists injected into the nucleus accumbens. The data directly support the hypothesis that relief of pain produces negative reinforcement through activation of the mesolimbic reward–valuation circuitry.
Recent studies demonstrate the possible existence of tonic modulatory control of nociceptive inpu... more Recent studies demonstrate the possible existence of tonic modulatory control of nociceptive input mediated by spinal cannabinoid receptors (CB1). Accordingly, it is predicted that a reduction in the spinal CB1 receptors may enhance sensitivity to sensory stimuli and a decrease in spinal antinociceptive potency to cannabinoid agonists. An antisense oligodeoxynucleotide (ODN) specific to the CB1 receptor was used to 'knock-down' CB1 receptors in the lumbar spinal cord and dorsal root ganglia by the local, repeated intrathecal (i.th.) administration of the ODN. This treatment resulted in a decrease in lumbar spinal CB1 receptor expression accompanied by a decrease in the response thresholds to both innocuous tactile and noxious thermal stimuli. The antinociceptive action of the CB1 agonist, WIN 55,212-2, by i.th. administration was also significantly attenuated after treatment with the antisense ODN. Similar treatment using a mismatch control ODN had no effect on receptor protein or on sensory thresholds. The effects of the antisense ODN treatment on sensory thresholds were fully reversed after discontinuation of the ODN injection. The antisense ODN treated rats also showed a significant increase in lumbar spinal dynorphin A. Acute i.th. injection of MK-801 or an antidynorphin antiserum blocked the antisense ODN-induced tactile and thermal hypersensitivity. These data support the possibility of endogenous inhibitory cannabinoid tone to limit spinal afferent input of thermal and tactile stimuli. Lifting of this inhibitory tone through a 'knock-down' of spinal CB1 receptors apparently lowers the thresholds for sensory input, as reflected by the actions of MK-801 to block tactile and thermal hypersensitivity. The increased spinal dynorphin may act to further promote afferent outflow and abnormal pain because sequestration of spinal dynorphin with antiserum also reverses the manifestations of abnormal pain following knock-down of CB1 receptors.
Spinal antinociception produced by delta 9-tetrahydro-cannabinol (Delta(9)-THC) and other cannabi... more Spinal antinociception produced by delta 9-tetrahydro-cannabinol (Delta(9)-THC) and other cannabinoid agonists has been suggested to be mediated by the release of dynorphin acting at the kappa opioid receptor. Alternatively, as cannabinoid receptors are distributed appropriately in the pain transmission pathway, cannabinoid agonists might act directly at the spinal level to inhibit nociception, without requiring dynorphin release. Here, these possibilities were explored using mice with a deletion of the gene encoding prodynorphin. Antinociceptive dose-response curves were constructed for spinal Delta(9)-THC and WIN 55,212-2 in prodynorphin knock-out mice and in wild-type littermates. WIN 55,212-2 and Delta(9)-THC were equipotent in the wild-type and prodynorphin knock-out mice. Spinal pretreatment with a kappa opioid receptor antagonist, nor-binaltorphimine (nor-BNI), did not alter the dose-response curves for either WIN 55,212-2 or Delta(9)-THC in prodynorphin knock-out and wild-type mice. However, the same dose of nor-BNI used blocked U50,488H-induced antinociception in both wild-type and prodynorphin knock-out mice, confirming kappa opioid receptor activity. Pretreatment with SR141716A, a cannabinoid receptor antagonist blocked the antinociceptive actions of both WIN 55,212-2 and Delta(9)-THC. These data support the conclusion that antinociception produced by spinal cannabinoids are likely to be mediated directly through activation of cannabinoid receptors without the requirement for dynorphin release or activation of kappa opioid receptors.
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