Repeated Dosing with Oral Allosteric Modulator of Adenosine A1 Receptor Produces Tolerance in Rats with Neuropathic Pain

2004 ◽  
Vol 100 (4) ◽  
pp. 956-961 ◽  
Author(s):  
Xinhui Li ◽  
Carsten Bantel ◽  
Dawn Conklin ◽  
Steven R. Childers ◽  
James C. Eisenach
Keyword(s):  
Neuropathic Pain ◽  
Radioligand Binding ◽  
Spinal Nerve ◽  
Pain Model ◽  
Withdrawal Threshold ◽  
Receptor Modulator ◽  
A1 Receptor ◽  
Receptor Number ◽  
Repeated Dosing ◽  
Motor Effects

Background The positive allosteric adenosine receptor modulator, T62 (2-amino-3-(4-chlorobenzoyl)-5,6,7,8-tetrahydrobenzothiophene), has been shown to reduce mechanical allodynia in a rat model of neuropathic pain. However, whether chronic oral T62 retains efficacy in this pain model has not been examined. Therefore, the authors studied antiallodynic effects of chronic oral T62 in spinal nerved-ligated rats, as well as motor and sedative behavioral effects. Methods Oral T62, 100 mg/kg, or oral oil was applied daily to spinal nerve-ligated rats for 4 weeks, with rat weights examined daily. Sedation, placing and ambulation scores, and withdrawal threshold were observed for 3 h daily for the first 2 weeks and then once a week. At the end of observation, the animals were killed, and the spinal tissues were collected for radioligand binding. In addition, withdrawal thresholds were also observed in rats with 5 days of treatment with 50 mg/kg oral T62. Furthermore, the effects of intrathecal adenosine on rats with oral T62 or oil treatment were compared. Results Chronic oral T62, at 100 mg/kg, initially returned the withdrawal threshold to mechanical testing to preinjury levels, with minor or no sedative or motor effects. Tolerance was observed, with a 60% loss of most possible effects in antiallodynia within 5 days of daily administration. Similarly, tolerance also occurred with chronic oral T62 at 50 mg/kg but did not alter the effect of intrathecal adenosine. Furthermore, 4 weeks of exposure to 100 mg/kg T62 resulted in a small reduction in spinal cord A1 receptor number. Conclusion The results imply that chronically administered A1 adenosine modulators lose efficacy over time, partly as a result of receptor down-regulation.

scholarly journals Dexmedetomidine versus ketamine in attenuating neuropathic pain through modulating STING/TBK pathway to modulate spinal ER-phagy in neuropathic pain model

2020 ◽  
Author(s):  
Yongda Liu ◽  
Mengmeng Ding ◽  
Zhibin Wang ◽  
Xingyue Li ◽  
Jiao Guo ◽  
...  
Keyword(s):  
Neuropathic Pain ◽  
Er Stress ◽  
Cellular Localization ◽  
Open Field Test ◽  
Spinal Nerve ◽  
Pain Model ◽  
Withdrawal Threshold ◽  
Confocal Immunofluorescence ◽  
Neuropathic Pain Model ◽  
Sting Pathway

Abstract Background: Our previous studies suggested that stimulator of interferon genes (STING) level was altered in medial prefrontal cortex (mPFC) of spinal nerve ligation (SNL) rats.Methods: In this study, we investigated that whether dexmedetomidine and ketamine provide antianxiety and anti-nociceptive effects via modulating spinal STING/TBK pathway to alter ER-phagy in SNL rats. We evaluated the analgesia and antianxiety effects of ketamine and dexmedetomidine in SNL rats. 2’3’-cGAMP (STING pathway agonist) was administrated to investigate whether enhanced spinal STING pathway could reverse dexmedetomidine or ketamine treatment effects in SNL rats respectively. Analgesia effects were measured with mechanical withdrawal threshold (MWT) and antianxiety effect was measured with open field test (OFT). Proteins expression levels were evaluated by Western blotting. Distribution and cellular localization of STING pathway and ER stress were evaluated by confocal immunofluorescence.Results: SNL induced mechanical hypersensitivity and anxiety; STING pathway was involved in the modulation of ER stress and ER-phagy in SNL rats; Dexmedetomidine and ketamine provided analgesia and antianxiety effects in SNL rats; Dexmedetomidine and ketamine alleviated ER stress via inhibiting STING pathway to enhance ER-phagy in SNL rats.Conclusions: In all, both ketamine and dexmedetomidine provided antianxiety and anti-nociceptive effects through alleviating ER stress via inhibiting STING/TBK pathway to modulate spinal ER-phagy in SNL rats.

scholarly journals The activation of galanin receptor 2 plays an antinociceptive effect in nucleus accumbens of rats with neuropathic pain

2021 ◽  
Vol 71 (1) ◽  
Author(s):  
Yan Dong ◽  
Chong-Yang Li ◽  
Xiao-Min Zhang ◽  
Ya-Nan Liu ◽  
Shuang Yang ◽  
...  
Keyword(s):  
Neuropathic Pain ◽  
Nucleus Accumbens ◽  
Pain Threshold ◽  
Antinociceptive Effect ◽  
Galanin Receptor ◽  
Pain Model ◽  
Withdrawal Threshold ◽  
Neuropathic Pain Model ◽  
Galanin Receptors ◽  
Intact Rats

AbstractOur previous research has shown that galanin plays an antinociceptive effect via binding to galanin receptors (GalRs) in nucleus accumbens (NAc). This study focused on the involvement of GalR2 in galanin-induced antinociceptive effect in NAc of neuropathic pain rats. The chronic constriction injury of sciatic nerve (CCI) was used to mimic neuropathic pain model. The hind paw withdrawal latency (HWL) to thermal stimulation and hind paw withdrawal threshold (HWT) to mechanical stimulation were measured as the indicators of pain threshold. The results showed that 14 and 28 days after CCI, the expression of GalR2 was up-regulated in bilateral NAc of rats, and intra-NAc injection of GalR2 antagonist M871 reversed galanin-induced increases in HWL and HWT of CCI rats. Furthermore, intra-NAc injection of GalR2 agonist M1145 induced increases in HWL and HWT at day 14 and day 28 after CCI, which could also be reversed by M871. Finally, we found that M1145-induced antinociceptive effect in NAc of CCI rats was stronger than that in intact rats. These results imply that the GalR2 is activated in the NAc from day 14 to day 28 after CCI and GalR2 is involved in the galanin-induced antinociceptive effect in NAc of CCI rats.

scholarly journals Oral Gabapentin Activates Spinal Cholinergic Circuits to Reduce Hypersensitivity after Peripheral Nerve Injury and Interacts Synergistically with Oral Donepezil

2007 ◽  
Vol 106 (6) ◽  
pp. 1213-1219 ◽  
Author(s):  
Ken-ichiro Hayashida ◽  
Renée Parker ◽  
James C. Eisenach
Keyword(s):  
Neuropathic Pain ◽  
Nerve Injury ◽  
Intrathecal Injection ◽  
Spinal Nerve ◽  
Male Rats ◽  
Additive Interaction ◽  
Alzheimer Dementia ◽  
Routes Of Administration ◽  
Withdrawal Threshold ◽  
The Brain

Background Gabapentin administration into the brain of mice reduces nerve injury-induced hypersensitivity and is blocked by intrathecal atropine and enhanced by intrathecal neostigmine. The authors tested the relevance of these findings to oral therapy by examining the efficacy of oral gabapentin to reduce hypersensitivity after nerve injury in rats and its interaction with the clinically used cholinesterase inhibitor, donepezil. Methods Male rats with hypersensitivity after spinal nerve ligation received gabapentin orally, intrathecally, and intracerebroventricularly with or without intrathecal atropine, and withdrawal threshold to paw pressure was determined. The effects of oral gabapentin and donepezil alone and in combination on withdrawal threshold were determined in an isobolographic design. Results Gabapentin reduced hypersensitivity to paw pressure by all routes of administration, and was more potent and with a quicker onset after intracerebroventricular than intrathecal injection. Intrathecal atropine reversed the effect of intracerebroventricular and oral gabapentin. Oral gabapentin and donepezil interacted in a strongly synergistic manner, with an observed efficacy at one tenth the predicted dose of an additive interaction. The gabapentin-donepezil combination was reversed by intrathecal atropine. Conclusions Although gabapentin may relieve neuropathic pain by actions at many sites, these results suggest that its actions in the brain to cause spinal cholinergic activation predominate after oral administration. Side effects, particularly nausea, cannot be accurately determined on rats. Nevertheless, oral donepezil is well tolerated by patients in the treatment of Alzheimer dementia, and the current study provides the rationale for clinical study of combination of gabapentin and donepezil to treat neuropathic pain.

Increased Expression of Cyclooxygenase and Nitric Oxide Isoforms, and Exaggerated Sensitivity to Prostaglandin E2, in the Rat Lumbar Spinal Cord 3 Days after L5–L6 Spinal Nerve Ligation

2006 ◽  
Vol 104 (2) ◽  
pp. 328-337 ◽  
Author(s):  
Darren D. O’Rielly ◽  
Christopher W. Loomis
Keyword(s):  
Nitric Oxide ◽  
Spinal Cord ◽  
Neuropathic Pain ◽  
Glutamate Release ◽  
Spinal Nerve ◽  
Spinal Nerve Ligation ◽  
Withdrawal Threshold ◽  
Enhanced Sensitivity ◽  
Sham Surgery ◽  
Inducible Nos

Background Spinal prostaglandins seem to be important in the early pathogenesis of experimental neuropathic pain. Here, the authors investigated changes in the expression of cyclooxygenase and nitric oxide synthase (NOS) isoforms in the lumbar, thoracic, and cervical spinal cord and the pharmacologic sensitivity to spinal prostaglandin E2 (PGE2) after L5-L6 spinal nerve ligation (SNL). Methods Male Sprague-Dawley rats, fitted with intrathecal catheters, underwent SNL or sham surgery 3 days before experimentation. Paw withdrawal threshold was monitored for up to 20 days. Immunoblotting, spinal glutamate release, and behavioral testing were examined 3 days after SNL. Results Allodynia (paw withdrawal threshold < or = 4 g) was evident 1 day after SNL and remained stable for 20 days. Paw withdrawal threshold was unchanged (P > 0.05) from baseline (> 15 g) after sham surgery except for a small but significant decrease on day 20. Cyclooxygenase 2, neuronal NOS, and inducible NOS were significantly increased in the ipsilateral lumbar dorsal horn after SNL. Expression in the contralateral dorsal horn and ventral horns (lumbar segments) or bilaterally (thoracic and cervical segments) was unchanged from sham controls. This was accompanied by a significant decrease in both the EC50 of PGE2-evoked glutamate release and the ED50 of PGE2 on brush-evoked allodynia. Enhanced sensitivity to PGE2 was localized to lumbar segments of SNL animals and attenuated by SC-51322 or S(+)-ibuprofen, but not R(-)-ibuprofen (100 mum). Conclusion The increased expression of cyclooxygense-2, neuronal NOS, and inducible NOS and the enhanced sensitivity to PGE2 in spinal segments affected by SNL support the hypothesis that spinal prostanoids play an early pathogenic role in experimental neuropathic pain.

Peripheral Nerve Injury Sensitizes the Response to Visceral Distension but Not Its Inhibition by the Antidepressant Milnacipran

2004 ◽  
Vol 100 (3) ◽  
pp. 671-675 ◽  
Author(s):  
Sang-Wook Shin ◽  
James C. Eisenach
Keyword(s):  
Neuropathic Pain ◽  
Nerve Injury ◽  
Visceral Pain ◽  
Spinal Nerve ◽  
Reflex Response ◽  
Dependent Manner ◽  
Sprague Dawley ◽  
Withdrawal Threshold ◽  
Sprague Dawley Rats ◽  
Lumbar Spinal

Background Manipulations that cause hypersensitivity to visceral stimuli have been shown to also result in hypersensitivity to somatic stimuli coming from convergent dermatomes, but the converse has not been examined. The authors tested whether lumbar spinal nerve ligation in rats, a common model of neuropathic pain that results in hypersensitivity to somatic stimuli, also leads to hypersensitivity to visceral stimuli coming from convergent dermatomes and whether pharmacology of inhibition differed between these two sensory modalities. Methods Female Sprague-Dawley rats were anesthetized, and the left L5 and L6 spinal nerves were ligated. Animals received either intrathecal saline or milnacipran (0.1-3 microg), and withdrawal thresholds to mechanical testing in the left hind paw, using von Frey filaments, and visceral testing, using balloon colorectal distension, were determined. Results Nerve ligation resulted in decreases in threshold to withdrawal to somatic mechanical stimulation (from 13 +/- 1.8 g to 2.7 +/- 0.7 g) and also in decreases in threshold to reflex response to visceral stimulation (from 60 mmHg to 40 mmHg). Intrathecal milnacipran increased withdrawal threshold to somatic stimulation in a dose-dependent manner but failed to alter the response to noxious visceral stimulation. Conclusions Injury of nerves innervating somatic structures enhances nociception from stimulation of viscera with convergent input from nearby dermatomes, suggesting that somatic neuropathic pain could be accompanied by an increased likelihood of visceral pain. Lack of efficacy of the antidepressant milnacipran against visceral stimuli suggests that visceral hypersensitivity may not share the same pharmacology of inhibition as somatic hypersensitivity after nerve injury.

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