Further evidence for the role of the alpha(2)delta subunit of voltage dependent calcium channels in models of neuropathic pain

A Randomized Double-Blinded Study To Compare the Efficacy of Propofol and Thiopentone To Prevent Succinylcholine-Induced Fasciculation and Myalgia in Gabapentin-Premedicated Patients

BACKGROUND

Succinylcholine is the most used short-acting depolarizing muscle relaxant for rapid sequence induction. However, its use is associated with adverse effects, like fasciculations and myalgia. Thus, many pretreatment modalities were used to minimize or prevent these adverse effects. Our aim for this study was to compare the efficacy of propofol and thiopentone in preventing succinylcholine-induced fasciculation and myalgia in gabapentin-premedicated patients.  Methods: Eighty patients with American Society of Anesthesiologists (ASA) physical status I/II, either male or female, in the aged group of 18-60 years, and scheduled to undergo elective abdominal surgery under general anesthesia were randomly allocated into either the propofol (P) or thiopentone (T) group. Anesthesia was induced with IV fentanyl 2 µg/kg, IV succinylcholine 2 mg/kg, and either IV propofol (2 mg/kg) in group P or IV thiopentone (5 mg/kg) in group T. In both groups, oral gabapentin 600 mg was given two hours before the surgery. All patients were observed and graded for intraoperative fasciculations and myalgia during 24 postoperative hours by a blinded observer. Fasciculation grade, myalgia grade, total tramadol consumption, and demographic data were compared using a test of proportion and chi-squared test.

RESULTS

Study results demonstrated that the use of propofol significantly decreases the severity of fasciculation at one, two, and three minutes (P < 0.001) and myalgia at two, six, and 12 hours (P < 0.001) more than thiopentone in gabapentin-premedicated patients. Tramadol consumption in both groups was insignificant (P = 0.658).

CONCLUSIONS

Propofol (2 mg/kg) is more effective than thiopentone (5 mg/kg) in decreasing the severity of fasciculation and myalgia following succinylcholine administration in gabapentin-premedicated patients.

Quantification of stimulus-evoked tactile allodynia in free moving mice by the chainmail sensitivity test

Chronic pain occurs at epidemic levels throughout the population. Hypersensitivity to touch, is a cardinal symptom of chronic pain. Despite dedicated research for over a century, quantifying this hypersensitivity has remained impossible at scale. To address these issues, we developed the Chainmail Sensitivity Test (CST). Our results show that control mice spend significantly more time on the chainmail portion of the device than mice subject to neuropathy. Treatment with gabapentin abolishes this difference. CST-derived data correlate well with von Frey measurements and quantify hypersensitivity due to inflammation. Our study demonstrates the potential of the CST as a standardized tool for assessing mechanical hypersensitivity in mice with minimal operator input.

Pain burden, sensory profile and inflammatory cytokines of dogs with naturally-occurring neuropathic pain treated with gabapentin alone or with meloxicam

Canine neuropathic pain (NeuP) has been poorly investigated. This study aimed to evaluate the pain burden, sensory profile and inflammatory cytokines in dogs with naturally-occurring NeuP. Twenty-nine client-owned dogs with NeuP were included in a prospective, partially masked, randomized crossover clinical trial, and treated with gabapentin/placebo/gabapentin-meloxicam or gabapentin-meloxicam/placebo/gabapentin (each treatment block of 7 days; total 21 days). Pain scores, mechanical (MNT) and electrical (ENT) nociceptive thresholds and descending noxious inhibitory controls (DNIC) were assessed at baseline, days 7, 14, and 21. DNIC was evaluated using ΔMNT (after-before conditioning stimulus). Positive or negative ΔMNT corresponded to inhibitory or facilitatory pain profiles, respectively. Pain scores were recorded using the Client Specific Outcome Measures (CSOM), Canine Brief Pain Inventory (CBPI), and short-form Glasgow Composite Measure Pain Scale (CMPS-SF). Data from baseline were compared to those of sixteen healthy controls. ΔMNT, but not MNT and ENT, was significantly larger in controls (2.3 ± 0.9 N) than in NeuP (-0.2 ± 0.7 N). The percentage of dogs with facilitatory sensory profile was similar at baseline and after placebo (61.5–63%), and between controls and after gabapentin (33.3–34.6%). The CBPI scores were significantly different between gabapentin (CBPI _pain and CBPI _{overall impression}) and/or gabapentin-meloxicam (CBPI _pain and _interference) when compared with baseline, but not placebo. The CBPI scores were not significantly different between placebo and baseline. The concentration of cytokines was not different between groups or treatments. Dogs with NeuP have deficient inhibitory pain mechanisms. Pain burden was reduced after gabapentin and/or gabapentin-meloxicam when compared with baseline using CBPI and CMPS-SF scores. However, these scores were not superior than placebo, nor placebo was superior to baseline evaluations. A caregiver placebo effect may have biased the results.

Gabapentin attenuates intestinal inflammation: Role of PPAR-gamma receptor

Gabapentin is an anticonvulsant drug that is also used for post-herpetic neuralgia and neuropathic pain. Recently, gabapentin showed anti-inflammatory effect. Nuclear factor kappa B (NFκB) is a regulator of the inflammatory process, and Peroxisome Proliferator-activated Receptor gamma (PPAR-gamma) is an important receptor involved in NFκB regulation. The aim of the present work was to study the potential role of PPAR-gamma receptor in gabapentin-mediated anti-inflammatory effects in a colitis experimental model. We induced colitis in rats using trinitrobenzenosulfonic acid and treated them with gabapentin and bisphenol A dicyldidyl ether (PPAR-gamma inhibitor). Macroscopic lesion scores, wet weight, histopathological analysis, mast cell count, myeloperoxidase, malondialdehyde acid, glutathione, nitrate/nitrite, and interleukin levels in the intestinal mucosa were determined. In addition, western blots were performed to determine the expression of Cyclooxygenase-2 (COX-2) and NFκB; Nitric Oxide Inducible Synthase (iNOS) and Interleukin 1 beta (IL-1β) levels were also determined. Gabapentin was able to decrease all inflammatory parameters macroscopic and microscopic in addition to reducing markers of oxidative stress and cytokines such as IL-1β and Tumor Necrosis Factor alpha (TNF-α) as well as enzymes inducible nitric oxide synthase and cyclooxygenase 2 and inflammatory genic regulator (NFκB). These effect attributed to gabapentin was observed to be lost in the presence of the specific inhibitor of PPAR-gamma. Gabapentin inhibits bowel inflammation by regulating mast cell signaling. Furthermore, it activates the PPAR-gamma receptor, which in turn inhibits the activation of NFκB, and consequently results in reduced activation of inflammatory genes involved in inflammatory bowel diseases.

Comparative Evaluation of Dexmedetomidine and Pregabalin as Premedication Agent to Attenuate Adverse Hemodynamic and Stress Response in Patients Undergoing Laparoscopic Cholecystectomy

Background:

Laparoscopic cholecystectomy is the most commonly performed laparoscopic procedure. The goal of anesthetic management is to minimize stress response and early discharge. Dexmedetomidine, and pregabalin have been used successfully to attenuate laryngoscopy and intubation response in various surgical procedures.

Aim:

To compare efficacy of pregablin and dexmedetomidine in attenuating hemodynamic and stress response.

Setting and Design:

A prospective, double blind randomized trial comprising 130 ASA physical status class I and II patients posted for laparsoscopic cholecystectomy.

Materials and Methods:

Patients were randomized in to Group A and Group B. Group A received intravenous dexmedetomidine in a dose of 1 ug.kg^-1, through an infusion pump 20 min prior to induction of anaesthesia. Group B subjects received oral pregabalin 150 mg. Parameters observed were vitals, discharge time, cortisol level, side effects if any.

Results:

Post intervention heart rate got reduced significantly in Group A and it remained low in comparison to baseline during whole peri-operative period. In Group B, immediate post-pneumoperitoneum heart rate, and post exubation heart rate was higher than baseline. Blood pressure (BP) decreased significantly post intervention in Group A which persisted till pneumoperitoneum. In Group B there was statistically significant rise in systolic, diastolic and mean blood pressure postpneumoperitoneum as compared to baseline blood pressure. Post-operative cortisol level was significantly higher than baseline values and the level is more in Group B.

Conclusion:

Intravenous dexmedetomidine is more effective than oral pregabalin in attenuating perioperative stress response.

A Randomized Controlled Trial to Compare Preemptive Analgesic Efficacy and Safety of Pregabalin and Gabapentin for Succinylcholine-Induced Myalgia

Background

Succinylcholine is a drug of choice for rapid induction of anesthesia but produces postoperative myalgia. Preemptive analgesia is intended to decrease perception of pain before exposure to painful stimuli. Pregabalin and gabapentin, analogs of the inhibitory neurotransmitter gamma aminobutyric acid, are effective in several models of neuropathic pain, incisional, inflammatory, and formalin-induced injury. However, the data available on their preemptive analgesic efficacy in succinylcholine myalgia are sparse. This study was designed to compare the preemptive analgesic efficacy and safety of pregabalin and gabapentin.

Materials and Methods

This randomized clinical trial included 120 surgical patients of either sex, between 18 and 70 years, and of American Society of Anesthesiologists-I/II grade. Patients were randomly allocated to control and test groups; received respective treatments 30 min before induction of anesthesia. Myalgia and pain scores were recorded using the myalgia scale and visual analog/facial rating scale at awakening at 6, 12, 18, and 24 h, respectively. Postoperative analgesic requirement over 24 h was recorded. Data were analyzed using OpenEpi (Andrew G. Dean and Kevin M. Sullivan, Atlanta, GA, USA) statistical softwares.

Results

Significantly lower pain scores were observed in the pregabalin group at 6, 12, and 24 h, and in gabapentin group at 24 h as compared to control and placebo (P < 0.05). They were however found to be equianalgesic when compared to each other (P > 0.05). Pregabalin-treated patients were more comfortable throughout with significantly less postoperative myalgia and analgesic requirement (P < 0.05).

Conclusions

Results strongly suggest the preemptive analgesic efficacy of a single oral dose of pregabalin and gabapentin over diclofenac in postoperative myalgia and pain management. However, on the basis of safety profile, pregabalin may be preferred over gabapentin in succinylcholine-induced myalgia.

Systems genetic and pharmacological analysis identifies candidate genes underlying mechanosensation in the von Frey test

Mechanical sensitivity is commonly affected in chronic pain and other neurological disorders. To discover mechanisms of individual differences in punctate mechanosensation, we performed quantitative trait locus (QTL) mapping of the response to von Frey monofilament stimulation in BXD recombinant inbred (BXD) mice. Significant loci were detected on mouse chromosome (Chr) 5 and 15, indicating the location of underlying polymorphisms that cause heritable variation in von Frey response. Convergent evidence from public gene expression data implicates candidate genes within the loci: von Frey thresholds were strongly correlated with baseline expression of Cacna2d1, Ift27 and Csnk1e in multiple brain regions of BXD strains. Systemic gabapentin and PF-670462, which target the protein products of Cacna2d1 and Csnk1e, respectively, significantly increased von Frey thresholds in a genotype-dependent manner in progenitors and BXD strains. Real-time polymerase chain reaction confirmed differential expression of Cacna2d1 and Csnk1e in multiple brain regions in progenitors and showed differential expression of Cacna2d1 and Csnk1e in the dorsal root ganglia of the progenitors and BXD strains grouped by QTL genotype. Thus, linkage mapping, transcript covariance and pharmacological testing suggest that genetic variation affecting Cacna2d1 and Csnk1e may contribute to individual differences in von Frey filament response. This study implicates Cacna2d1 and Ift27 in basal mechanosensation in line with their previously suspected role in mechanical hypersensitivity. Csnk1e is implicated for von Frey response for the first time. Further investigation is warranted to identify the specific polymorphisms involved and assess the relevance of these findings to clinical conditions of disturbed mechanosensation.

A case of gait disturbance caused by low-dose gabapentin

Gabapentin, an anticonvulsant agent, is now often used for the treatment of neuropathic pain all over the world. It is unclear whether the combined use of gabapentin, sodium valproate, and flunitrazepam results in enhancement of the side effect, a gait disturbance. A 60-year-old man was taking oral sodium valproate for symptomatic epilepsy after a brain contusion and flunitrazepam to relieve insomnia. Oral gabapentin therapy was started for suspected neuropathic pain. Although the initial dose of oral gabapentin (200 mg) relieved the pain, the lower extremities became weak, resulting in a gait disturbance. The therapy was restarted with a halved dose, and this resolved the gait disturbance and relieved the pain.

The efficacy of gabapentin/pregabalin in improving pain after tonsillectomy: A meta-analysis

OBJECTIVES/HYPOTHESIS

Gabapentin and pregabalin are useful for treating neuropathic pain because of their antiallodynic and antihyperalgesic properties, which may be beneficial in managing acute postoperative pain. The goal of this meta-analysis was to perform a systematic review of the literature on the effect of gabapentinoids on postoperative pain following tonsillectomy, and its adverse effects in patients.

DATA SOURCES

MEDLINE, SCOPUS, and Cochrane database.

METHODS

Two authors independently searched the databases from their inception of article collection to May 2015. Included in the analysis were studies that compared preoperative gabapentinoid administration (gabapentinoids groups) with a placebo or pain control agent (control group) during a 24-hour postoperative period, the outcomes of interest being postoperative pain intensity; rescue analgesic consumption; or adverse effects such as sedation, nausea and vomiting, dizziness, and headache.

RESULTS

The pain score reported by the physician during the first 8 hours, as well as the need for analgesics during 24 hours postoperatively, were significantly decreased in the gabapentinoids group versus the control group. Additionally, there was no significant difference between gabapentinoids and control groups for adverse effect during 24 hours postoperatively. In the subgroup analyses (gabapentin and pregabalin) regarding pain-related measurements, two subgroups showed the similar effect on reducing the postoperative pain severity.

CONCLUSION

Preoperative administration of gabapentinoids could provide pain relief without side effects in patients undergoing tonsillectomy. However, considering the insufficient evaluation of efficacy of gabapentinoids according to the high heterogeneity in some parameters, further clinical trials with robust research methodology should be conducted in order to confirm the results of this study.

LEVEL OF EVIDENCE

NA.

Gabapentin versus pregabalin in relieving early post-surgical neuropathic pain in patients after lumbar disc herniation surgery: a prospective clinical trial

OBJECTIVES

The roles of gabapentin and pregabalin are well established in the management of chronic neuropathic pain. Here, we investigated the effectiveness of pregabalin and gabapentin for treating acute neuropathic pain following lumbar discectomy.

METHODS

This prospective, non-randomized, and observational study included 54 patients who experienced acute neuropathic pain after lumbar discectomy. The assessments included the Leeds assessment of neuropathic symptoms and signs scale (LANSS), the Oswestry disability index (ODI), and the visual analog scale (VAS) pre-operatively and at 3 days, 6 months, and 1 year after surgery. The LANSS scores ≧12 suggest the presence of neuropathic pain. Those patients who reported neuropathic pain were randomly treated with gabapentin or pregabalin.

RESULTS

In the gabapentin group, the LANSS scores increased to 14 at 3 days after surgery. The patients improved neurologically and on the LANSS, which decreased to 10 points 6 months after surgery and to 4 points at 1 year (P < 0.001). In the pregabalin group, the LANSS scores increased from 12 to 16 points on post-operative day 3 and then decreased to 12 and 5 at the 6-month and 1-year follow-ups, respectively (both P < 0.001). The ODI and VAS scores significantly improved in both groups (P < 0.001).

DISCUSSION

Many patients may suffer from neuropathic pain in the early post-surgical period after lumbar discectomy. Gabapentin and pregabalin are anticonvulsant agents that may decrease perioperative central sensitization and early post-surgical neuropathic pain. Gabapentin and pregabalin effectively relieved neuropathic pain and prevented the conversion of acute pain to chronic pain at the 1-year follow-up after lumbar discectomy.

Evaluating state dependence and subtype selectivity of calcium channel modulators in automated electrophysiology assays

Voltage-gated Ca2+ channels play essential roles in control of neurosecretion and muscle contraction. The pharmacological significance of Cav channels stem from their identification as the molecular targets of calcium blockers used in the treatment of cardiovascular diseases, such as hypertension, angina, and arrhythmia, and neurologic diseases, such as pain and seizure. It has been proposed that state-dependent Cav inhibitors, that is, those that preferentially bind to channels in open or inactivated states, may improve the therapeutic window over relatively state-independent Cav inhibitors. High-throughput fluorescent-based functional assays have been useful in screening chemical libraries to identify Cav inhibitors. However, hit confirmation, mechanism of action, and subtype selectivity are better suited to automated patch clamp assays that have sufficient capacity to handle the volume of compounds identified during screening, even of modest sized libraries (≤500,000 compounds), and the flexible voltage control that allows evaluation of state-dependent drug blocks. IonWorks Barracuda (IWB), the newest generation of IonWorks instruments, provides the opportunity to accelerate the Cav drug discovery studies in an automated patch clamp platform in 384-well format capable of medium throughput screening and profiling studies. We have validated hCav1.2, hCav2.1, hCav2.2, and hCav3.2 channels assays on the IWB platform (population patch clamp mode) and demonstrated that the biophysical characteristics of the channels (activation, inactivation, and steady-state inactivation) obtained with the IWB system are consistent with known subtype-specific characteristics. Using standard reference compounds (nifedipine, BAY K8644, verapamil, mibefradil, and pimozide), we demonstrated subtype-selective and state- and use-dependent characteristics of drug-channel interactions. Here we describe the design and validation of novel robust high-throughput Cav channel assays on the IWB platform. The assays can be used to screen focused compound libraries for state-dependent Cav channel antagonists, to prioritize compounds for potency or to counterscreen for Cav subtype selectivity.

Effects of gabapentin on pain and opioid consumption after abdominal hysterectomy

BACKGROUND

Postoperative pain is an important factor affecting anesthesia and surgery.

OBJECTIVES

The present study assessed the effects of 1200 mg gabapentin, an anticonvulsant drug that acts through voltage-dependent calcium channels, for the control of postoperative pain in patients undergoing abdominal hysterectomy.

METHODS

Fifty patients undergoing hysterectomy were enrolled in the present study. Subjects received either 1200 mg gabapentin or placebo 2 h before surgery. The amount of morphine consumption and level of postoperative pain at 2 h, 6 h, 12 h and 24 h after surgery were measured.

RESULTS

There were no significant differences in age, duration of surgery and anesthesia, or body mass index between the two groups. The mean intensity of pain in the gabapentin group was significantly lower than in the placebo group. The mean amount of morphine used in the placebo group (5.2 ± 2.8 mg) was significantly higher than in gabapentin group (1.2 ± 0.29 mg; P=0.001). Nausea and vomiting in the placebo group was more common than in the gabapentin group (P=0.001). The time interval for initial ambulation after surgery was significantly shorter in the gabapentin group (12.24 ± 2.18 h) compared with the placebo group (15 ± 3.61 h; P=0.002).

CONCLUSION

1200 mg gabapentin reduced postoperative pain and the need for opioids, and enabled earlier ambulation of the patient. Significant side effects were not observed.

Comparison of analgesic effect between gabapentin and diclofenac on post-operative pain in patients undergoing tonsillectomy

Background

Tonsillectomy is a common procedure causing considerable postoperative pain. Postoperative pain intensity of 60 - 70 in the scale of visual analog scale (VAS) has been reported up to 3 - 4 days which could continue until 11 days after the surgery.

Objectives

The current study aimed to compare the analgesic effect of gabapentin and diclofenac on pain after tonsillectomy with the control group.

Patients and Methods

In this double-blind, placebo-controlled clinical trial, 90 patients aged 10-25 years, ASA classes I and II were randomly selected to receive 20 mg/kg oral gabapentin (n = 30), 1.0 mg / kg rectal diclofenac (n = 30) or placebo (n = 30) preoperatively. Pain was evaluated postoperatively on a visual analogue scale at 2, 6, 12 and 24 h. Opioid consumption in the first 24 h after surgery and the side effects were also recorded.

Results

There was no significant difference in terms of age, sex, and time of surgery in the three groups. Patients in the gabapentin and diclofenac groups had significantly lower pain scores at all-time intervals than those in the placebo group. The total meperidine consumed in the gabapentin (14.16 ± 6.97 P = 0.001) and diclofenac (16.66 ± 8.95, P = 0.004) groups was significantly less than that of the placebo (33.4 ± 13.97) group. The frequency of side effects such as vomiting, dizziness, and headache was not significantly different among the groups.

Conclusions

It can be concluded that gabapentin and diclofenac reduced postoperative pain and opioid consumption without obvious side effects.

2-{1-[(2-Nitrobenzenesulfonamido)methyl]cyclohexyl}acetic acid

In the title compound, C₁₅H₂₀N₂O₆S, the C—SO₂—NH—C torsion angle is 64.54 (14)°. In the mol­ecule, there is a bifurcated N—H⋯(O,O) hydrogen bond, forming S(7) rings. In the crystal, inversion dimers are formed via O—H⋯O hydrogen bonds involving the carboxyl group, so forming R₂²(8) rings. These dimers are further linked via pairs of C—H⋯O hydrogen bonds, forming a C(6) chain propagating along the c-axis direction.

Predictive validity of pharmacologic interventions in animal models of neuropathic pain

Introduction

The pathophysiologic and neurochemical characteristics of neuropathic pain must be considered in the search for new treatment targets. Breakthroughs in the understanding of the structural and biochemical changes in neuropathy have opened up possibilities to explore new treatment paradigms. However, long term sequels from the damage are still difficult to treat.

Aim of the study

To examine the validity of pharmacological treatments in humans and animals for neuropathic pain.

Method

An overview from the literature and own experiences of pharmacological treatments employed to interfere in pain behavior in different animal models was performed.

Results

The treatment principles tested in animal models of neuropathic pain may have predictive validity for treatment of human neuropathies. Opioids, neurotransmitter blockers, drugs interfering with the prostaglandin syntheses as well as voltage gated sodium channel blockers and calcium channel blockers are treatment principles having efficacy and similar potency in humans and in animals. Alternative targets have been identified and have shown promising results in the validated animal models. Modulators of the glutamate system with an increased expression of glutamate re-uptake transporters, inhibition of pain promoters as nitric oxide and prostaglandins need further exploration. Modulation of cytokines and neurotrophins in neuropathic pain implies new targets for study. Further, a combination of different analgesic treatments may as well improve management of neuropathic pain, changing the benefit/risk ratio.

Implications

Not surprisingly most pharmacologic principles that are tested in animal models of neuropathic pain are also found to be active in humans. Whereas many candidate drugs that were promising in animal models of neuropathic pain turned out not to be effective or too toxic in humans, animal models for neuropathic pain are still the best tools available to learn more about mechanisms of neuropathic pain. Better understanding of pathogenesis is the most hopeful approach to improve treatment of neuropathic pain.

Pregabalin suppresses spinal neuronal hyperexcitability and visceral hypersensitivity in the absence of peripheral pathophysiology

BACKGROUND

Opioid-induced hyperalgesia is recognized in the laboratory and the clinic, generating central hyperexcitability in the absence of peripheral pathology. We investigated pregabalin, indicated for neuropathic pain, and ondansetron, a drug that disrupts descending serotonergic processing in the central nervous system, on spinal neuronal hyperexcitability and visceral hypersensitivity in a rat model of opioid-induced hyperalgesia.

METHODS

Male Sprague-Dawley rats (180-200 g) were implanted with osmotic mini-pumps filled with morphine (90 μg · μl⁻¹ · h⁻¹) or saline (0.9% w/v). On days 7-10 in isoflurane anesthetized animals, we evaluated the effects of (1) systemic pregabalin on spinal neuronal and visceromotor responses, and (2) spinal ondansetron on dorsal horn neuronal response. Messenger ribonucleic acid concentrations of α2δ-1, 5HT3A, and μ-opioid receptor in the dorsal root ganglia of all animals were analyzed.

RESULTS

In morphine-treated animals, evoked spinal neuronal responses were enhanced to a subset of thermal and mechanical stimuli. This activity was attenuated by pregabalin (by at least 71%) and ondansetron (37%); the visceromotor response to a subset of colorectal distension pressures was attenuated by pregabalin (52.8%; n = 8 for all measures, P < 0.05). Messenger ribonucleic acid concentrations were unchanged.

CONCLUSIONS

The inhibitory action of pregabalin in opioid-induced hyperalgesia animals is neither neuropathy-dependent nor reliant on up-regulation of the α₂δ-1 subunit of voltage-gated calcium channels-mechanisms proposed as being essential for pregabalin's efficacy in neuropathy. In opioid-induced hyperalgesia, which extends to colonic distension, a serotonergic facilitatory system may be up-regulated, creating an environment that is permissive for pregabalin-mediated analgesia without peripheral pathology.

Effects of gabapentin on brain hyperactivity related to pain and sleep disturbance under a neuropathic pain-like state using fMRI and brain wave analysis

Neuropathic pain is the most difficult pain to manage in the pain clinic, and sleep problems are common among patients with chronic pain including neuropathic pain. In the present study, we tried to visualize the intensity of pain by assessing neuronal activity and investigated sleep disturbance under a neuropathic pain-like state in mice using functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG)/electromyogram (EMG), respectively. Furthermore, we investigated the effect of gabapentin (GBP) on these phenomena. In a model of neuropathic pain, sciatic nerve ligation caused a marked decrease in the latency of paw withdrawal in response to a thermal stimulus only on the ipsilateral side. Under this condition, fMRI showed that sciatic nerve ligation produced a significant increase in the blood oxygenation level-dependent (BOLD) signal intensity in the pain matrix, which was significantly decreased 2 h after the i.p. injection of GBP. Based on the results of an EEG/EMG analysis, sciatic nerve-ligated animals showed a statistically significant increase in wakefulness and a decrease in non-rapid eye movement (NREM) sleep during the light phase, and the sleep disturbance was almost completely alleviated by a higher dose of GBP in nerve-ligated mice. These findings suggest that neuropathic pain associated with sleep disturbance can be objectively assessed by fMRI and EEG/EMG analysis in animal models. Furthermore, GBP may improve the quality of sleep as well as control pain in patients with neuropathic pain.

Oral pregabalin reverses cold allodynia in two distinct models of peripheral neuropathic pain

A major symptom of persistent neuropathic pain, which may develop after peripheral nerve injury, is hypersensitivity (allodynia) to normally innocuous cold stimuli. Although the anticonvulsant pregabalin has been demonstrated to relieve neuropathic pain, both in preclinical models and clinically, the analgesic effect of the drug in animals has not been profiled for cold hypersensitivity. Therefore, we examined the effect of pregabalin (single oral dosing: 30, 100, 300 micromol/kg) on cold allodynia in two models of chronic neuropathic pain, the spared nerve injury (SNI) and the spinal nerve ligation (SNL) models. A significant antiallodynic effect was observed with pregabalin at all doses tested with a maximal effect of 71% (SNI) and 60% (SNL), respectively compared to vehicle. For comparison, only the highest dose tested of pregabalin (300 micromol/kg), significantly decreased pain responses in phase 2 of the rat formalin test (approximately 67% pain inhibition). However, pregabalin at this high dose also affected other centrally mediated behavioural functions, such as motor activity and anxiolytic behaviour in naïve animals, which could potentially interfere with the pain readout. The present study demonstrates that oral administration of pregabalin significantly reduces both cold allodynia induced in the SNI and the SNL models of neuropathic pain as well as formalin-induced nociception, albeit with different sensitivity and potency.

Pharmacological characteristics of the hind paw weight bearing difference induced by chronic constriction injury of the sciatic nerve in rats

AIMS

We examined the possible involvement of spontaneous on-going pain in the rat chronic constriction injury (CCI) model of neuropathic pain.

MAIN METHODS

The development of weight bearing deficit, as an index of spontaneous on-going pain, was investigated in comparison to that of mechanical allodynia in CCI rats. We also examined the effects of morphine and a gabapentin analogue (1S, 3R)-3-methyl-gabapentin (3-M-gabapentin) on both the CCI-induced weight bearing deficit and mechanical allodynia.

KEY FINDINGS

Rats with CCI demonstrated a significant reduction in weight bearing of the injured limb with a peak at a week post-operation, which was followed by a gradual recovery for over 7 weeks. The time course of development and recovery of CCI-induced weight bearing deficit appeared to follow that of foot deformation of the affected hind limb. CCI also evoked mechanical allodynia that was fully developed on a week post-operation, but showed no recovery for at least 8 weeks. 3-M-gabapentin significantly inhibited CCI-induced mechanical allodynia, but not weight bearing deficit, at 100 mg/kg p.o. Likewise, morphine was without significant effect on CCI-induced weight bearing deficit at the dose (3 mg/kg, s.c.) that could almost completely inhibit mechanical allodynia, whereas it inhibited both mechanical allodynia and weight bearing deficit at 6 mg/kg, s.c.

SIGNIFICANCE

The present findings suggest that CCI-induced weight bearing deficit is not a consequence of mechanical allodynia, but is attributable to spontaneous on-going pain. The rat CCI model of neuropathic pain thus represents both spontaneous on-going pain and mechanical allodynia.

Protective effects of gabapentin on allodynia and alpha 2 delta 1-subunit of voltage-dependent calcium channel in spinal nerve-ligated rats

This study was designed to determine whether early gabapentin treatment has a protective analgesic effect on neuropathic pain and compared its effect to the late treatment in a rat neuropathic model, and as the potential mechanism of protective action, the alpha(2)delta(1)-subunit of the voltage-dependent calcium channel (alpha(2)delta(1)-subunit) was evaluated in both sides of the L5 dorsal root ganglia (DRG). Neuropathic pain was induced in male Sprague-Dawley rats by a surgical ligation of left L5 nerve. For the early treatment group, rats were injected with gabapentin (100 mg/kg) intraperitoneally 15 min prior to surgery and then every 24 hr during postoperative day (POD) 1-4. For the late treatment group, the same dose of gabapentin was injected every 24 hr during POD 8-12. For the control group, L5 nerve was ligated but no gabapentin was administered. In the early treatment group, the development of allodynia was delayed up to POD 10, whereas allodynia was developed on POD 2 in the control and the late treatment group (p<0.05). The alpha(2)delta(1)-subunit was up-regulated in all groups, however, there was no difference in the level of the alpha(2)delta(1)-subunit among the three groups. These results suggest that early treatment with gabapentin offers some protection against neuropathic pain but it is unlikely that this action is mediated through modulation of the alpha(2)delta(1)-subunit in DRG.

Response of rice advance line PB-95 to potassium application in saline-sodic soil

A field experiment was conducted to evaluate the response of rice crop to potassium fertilization in saline-sodic soil during 2005. Soil samples were collected before transplanting of rice crop and analysed for physical and chemical properties of the soil. In this experiment five rates of K2O (0, 25, 50, 75 and 100 kg ha(-1)) were applied in the presence of basal doses of N and P2O5 i.e., 110 and 90 kg ha(-1), respectively. Whole of P, K and 1/2 of N were applied at the time of rice transplanting. Twelve and halfkg ha(-1) ZnSO4 was also applied 15 days after rice transplanting. The remaining half of N was applied 30 days after rice transplanting. The system of layout was Randomized Complete Block Design with four replications. The net plot size was 6x4 m. Fertilizer sources of NPK were urea, TSP and SOP, respectively. Rice salt tolerant line PB-95 was used as test crops. The data of growth parameters and yield was recorded and samples of paddy and straw were collected treatment-wise and analysed for N, P and K contents. Soil samples after harvesting the crop were also collected, processed and analysed for the changes in the extractable soil K. The results showed that increasing rates of potassium fertilizer increased the number of tillers m(-2), plant height (cm), 1000-paddy weight and paddy as well as straw yield significantly. Maximum paddy (3.24 t ha(-1)) and straw (3.92 t ha(-1)) yields were obtained in T5 (100 kg K2O ha(-1)) which was at par with T4 (75 kg K2O ha(-1)). With increasing rates of potassium fertilizer, concentration of potassium in paddy and straw increased significantly. After harvesting the crop, the extractable potassium contents of soil increased from that of the original soil. It was concluded from the results that there was an increase of 30.65% in paddy over control by applying potassium (100 kg K2O ha(-1)) in saline-sodic soil.

Synergy between a NR2B receptor antagonist DHQ and 3-methyl-gabapentin in mice with neuropathic pain

The synergistic effect of a selective NR2B NMDA receptor antagonist, (-)-(R)-6-{2-[4-(3-Fluorophenyl)-4-hydroxy-1-piperidinyl]-1-hydroxyethyl-3,4-dihydro-2(1H)-quinolinone (DHQ), and a alpha 2 delta ligand, 3-methyl-gabapentin (3M-GBP), was investigated in the mouse partial sciatic nerve model. The interaction was observed after administration of DHQ and 3M-GBP combination at fixed dose ratios of 1:10 and 1:30 and the dose-response curves shifted approximately 13- and 17-fold leftward, respectively, from the theoretical additive values. However, a fixed dose ratio of 1:50 resulted only in an additive effect. These results indicate the synergistic interaction between DHQ and 3M-GBP in this animal model of neuropathic pain.

Gabapentin evoked changes in functional activity in nociceptive regions in the brain of the anaesthetized rat: an fMRI study

BACKGROUND AND PURPOSE

Gabapentin (GBP; 1-(aminomethyl)cyclohexane acetic acid) is used clinically in the treatment of pain. Nevertheless, the sites and mechanisms of action of GBP are poorly defined. Herein, the effects of GBP on brain activation have been studied.

EXPERIMENTAL APPROACH

Changes in blood oxygen level dependent (BOLD) haemodynamic signal following intravenous infusion of GBP (equivalent to 30 mg kg(-1) p.o., followed by 100 mg kg(-1) p.o.), compared to saline control, were studied in isofluorane anaesthetized rats (n=8 per group). Effects of GBP on mean arterial blood pressure (MAP) were also recorded.

RESULTS

Random effect analysis revealed that the lower dose of GBP produced significant (P<0.001) increases in BOLD signal intensity in several brain regions, including the thalamus and periaqueductal grey (PAG), compared to basal. This dose of GBP also produced significant (P<0.001) decreases in BOLD signal intensity in the amygdala and the entorhinal cortex. Increasing the dose of GBP (100 mg kg(-1)) produced significantly greater changes in BOLD signal intensity in several brain regions including the thalamus and PAG. MAP was not significantly altered by GBP, compared to saline.

CONCLUSIONS AND IMPLICATIONS

GBP had marked positive and negative effects on BOLD signal intensity in a number of brain regions in naïve rats. The activation of key areas involved in nociceptive processing indicate a supraspinal site of action of GBP and this may contribute to its well-described analgesic effects in animal models of pain and clinical studies.

Gabapentin for the treatment of neuropathic pain in a pregnant horse

CASE DESCRIPTION

A 24-year-old 732-kg (1,610-lb) pregnant Belgian draft horse mare developed neuropathy and signs of intractable pain following colic surgery.

CLINICAL FINDINGS

Following recovery from colic surgery to treat compression of the small and large intestines because of a large fetus, the mare was noticed to have signs of femoral neuropathy involving the left hind limb. Within 36 hours after recovery, the mare developed signs of severe pain that were unresponsive to conventional treatment. No gastrointestinal tract or muscular abnormalities were found, and the discomfort was attributed to neuropathic pain.

TREATMENT AND OUTCOME

The mare was treated with gabapentin (2.5 mg/kg [1.1 mg/lb], PO, q 12 h). Shortly after this treatment was initiated, the mare appeared comfortable and no longer had signs of pain. Treatment was continued for 6 days, during which the dosage was progressively decreased, and the mare was discharged. The mare subsequently delivered a healthy foal.

CLINICAL RELEVANCE

Gabapentin appeared to be a safe, effective, and economical treatment for neuropathic pain in this horse.

Effects of acetylsalicylic acid on germination, growth and chlorophyll amounts of cucumber (Cucumis sativus L.) seeds

Germination activities, various growth parameters (primary root length, hypocotyl length, primary leaf length, plant length and increase in fresh weight) and chlorophyll (a+b) amounts of cucumber seeds exposed to 0, 10(-5), 10(-4), 10(-3) and 0.5x 10(-2) M aqueous solutions of acetylsalicylic acid (ASA) for 48 h were established. While 0.5x 10(-2) M ASA significantly prevented germination activity of the seeds, other concentrations did not produce any effect, either positive or negative. Meanwhile, 0.5x 10(-2) M ASA inhibited radicle growth of the germinated seeds, while 10(-5) M ASA increased radicle growth. Other concentrations of ASA did not affect radicle growth. The following findings were obtained from the one-week seedlings exposed to ASA for 48 h: 0.5x10(-2) M ASA prevented growth (lengthening) of root, hypocotyl, leaf and plant and increased chlorophyll (a+b) amount with an increase in fresh weight. Contrary to 0.5x 10(-2) M ASA application, these features of the seedlings (except for the leaf length) were encouraged by 10(-5) M ASA. 10(-3)) M ASA only prevented root growth and reduced chlorophyll (a+b) amount. Other concentrations of ASA did not bring about any positive or negative effect on the features studied.

[3H] pregabalin binding is increased in ipsilateral dorsal horn following chronic constriction injury

Pregabalin, a 3-substituted analogue of gamma-amino butyric acid has recently been approved for treatment of neuropathic pain. We have investigated the anatomical binding profile of [(3)H] pregabalin following chronic constriction injury (CCI) and compared this with alpha 2 delta 1 subunit expression using in situ hybridisation. We report here that the intensity and distribution pattern of [(3)H] pregabalin binding is altered in the ipsilateral dorsal horn following CCI and this is associated with a corresponding increase in alpha 2 delta 1 mRNA in the ipsilateral dorsal root ganglion (DRG). It is likely that increased DRG mRNA production leads to increased alpha 2 delta 1 protein production and subsequent transport by primary afferents to the dorsal horn. The increased expression of calcium channel subunits and protein in central terminals is interesting, given that abnormal activity within sensory nerves is likely to significantly contribute to the symptomatology of neuropathic pain. The upregulation of pregabalin binding sites in sensory nerve terminals may occur as part of the response to nerve damage in neuropathic pain patients, and therefore, preferential actions of pregabalin at these sites may contribute to its mechanism of action in man.

Chemotherapy-evoked painful peripheral neuropathy: analgesic effects of gabapentin and effects on expression of the alpha-2-delta type-1 calcium channel subunit

Chemotherapeutics in the taxane and vinca-alkaloid classes sometimes produce a painful peripheral neuropathy for which there is no validated treatment. Experiments with rat models of paclitaxel- and vincristine-evoked pain suggest that these conditions may not respond to all of the analgesics that have efficacy in other models of painful peripheral neuropathy. We tested gabapentin as a potential analgesic for paclitaxel- and vincristine-evoked pain. We used a repeated dosing paradigm because there are precedents showing that repeated drug exposure may be necessary to demonstrate analgesia in neuropathic pain models. Gabapentin is believed to work via binding to voltage-gated calcium channels that contain the alpha-2-delta type-1 (alpha(2)delta-1) subunit, and the expression of this subunit is known to be increased in some painful peripheral neuropathy models. Thus we also examined whether the paclitaxel-evoked pain syndrome was accompanied by an alpha(2)delta-1 increase, and whether gabapentin had any effect on subunit expression. We found that the paclitaxel- and vincristine-evoked mechano-allodynia and mechano-hyperalgesia were significantly reduced by gabapentin, but only with repeated dosing. Paclitaxel-evoked painful peripheral neuropathy was associated with an increased expression of the alpha(2)delta-1 subunit in the spinal dorsal horn, but not in the dorsal root ganglia. The spinal cord increase was normalized by repeated gabapentin injections. Together, these findings suggest that repeated dosing with gabapentin may be beneficial in patients with chemotherapy-evoked painful peripheral neuropathy and that gabapentin's mechanisms of action may include normalization of the nerve injury-evoked increase in calcium channel alpha(2)delta-1 subunit expression.

Identification of the alpha2-delta-1 subunit of voltage-dependent calcium channels as a molecular target for pain mediating the analgesic actions of pregabalin

Neuropathic pain is a debilitating condition affecting millions of people around the world and is defined as pain that follows a lesion or dysfunction of the nervous system. This type of pain is difficult to treat, but the novel compounds pregabalin (Lyrica) and gabapentin (Neurontin) have proven clinical efficacy. Unlike traditional analgesics such as nonsteroidal antiinflammatory drugs or narcotics, these agents have no frank antiinflammatory actions and no effect on physiological pain. Although extensive preclinical studies have led to a number of suggestions, until recently their mechanism of action has not been clearly defined. Here, we describe studies on the analgesic effects of pregabalin in a mutant mouse containing a single-point mutation within the gene encoding a specific auxiliary subunit protein (alpha2-delta-1) of voltage-dependent calcium channels. The mice demonstrate normal pain phenotypes and typical responses to other analgesic drugs. We show that the mutation leads to a significant reduction in the binding affinity of pregabalin in the brain and spinal cord and the loss of its analgesic efficacy. These studies show conclusively that the analgesic actions of pregabalin are mediated through the alpha2-delta-1 subunit of voltage-gated calcium channels and establish this subunit as a therapeutic target for pain control.

α2δ and the mechanism of action of gabapentin in the treatment of pain

Gabapentin is a drug that has been widely used in the treatment of chronic pain states. Despite its widespread usage, it is only recently that light has been shed on the mechanism of action of this agent. In the current review, the authors document the pharmacological, biochemical and molecular information that has led to the identification of the alpha2delta1 auxilliary subunit of voltage gated calcium channels as the target for this drug's actions.

The effect of gabapentin on post-operative pain following tonsillectomy in adults

BACKGROUND

The aim of the present study was to investigate whether a combination of rofecoxib and gabapentin could improve pain relief and reduce opioid requirements, compared with rofecoxib alone, during the first 5 days after tonsillectomy.

METHODS

In a randomized, double-blind, placebo-controlled study, 49 patients received gabapentin 1200 mg pre-operatively, followed by gabapentin 2 x 600 mg on the day of operation and gabapentin 3 x 600 mg for the next 5 days, or placebo. Both groups were given rofecoxib 50 mg daily. In the post-operative care unit, intravenous morphine was administered in doses of 2.5 mg on request. From 4 h to 5 days post-operatively, ketobemidone was offered as escape drug. Pain at rest and during swallowing, and side-effects, were assessed using a four-point verbal rating scale.

RESULTS

As a result of the global withdrawal of rofecoxib, the study had to be terminated prematurely. This report comprises the results from 22 patients in the gabapentin group and 27 patients in the placebo group. Gabapentin reduced ketobemidone requirements during the first 24 h post-operatively [4.5 mg (standard deviation, 3.0 mg) in the placebo group vs. 2.0 mg (standard deviation, 2.0 mg) in the gabapentin group; P < 0.003]. Gabapentin induced more dizziness (P < 0.002), gait disturbance (P < 0.02) and vomiting (P < 0.05) during days 0-5 than placebo. No other statistically significant differences were observed.

CONCLUSION

Gabapentin reduced opioid requirements in the first 24 h after tonsillectomy. The benefits of the reduced opioid intake may be overshadowed by the drawbacks of side-effects.

(L)-Phenylglycine, but not necessarily other alpha2delta subunit voltage-gated calcium channel ligands, attenuates neuropathic pain in rats

Gabapentin and pregabalin have been demonstrated, both in animal pain models and clinically, to be effective analgesics particularly for the treatment of neuropathic pain. The precise mechanism of action for these two drugs is unknown, but they are generally believed to function via initially binding to the alpha2delta subunit of voltage-gated Ca2+ channels. In this study, we used a pharmacological approach to test the hypothesis whether high affinity interactions with the alpha2delta subunit alone could lead to attenuation of neuropathic pain in rats. The anti-allodynic effects of gabapentin and pregabalin, along with three other compounds--(L)-phenylglycine, m-chlorophenylglycine and 3-exo-aminobicyclo[2.2.1]heptane-2-exo-carboxylic acid (ABHCA)--discovered to be potent alpha2delta ligands, were tested in the rat spinal nerve ligation model of neuropathic pain. Gabapentin (Ki = 120 nM), pregabalin (180 nM) and (L)-phenylglycine (180 nM) were shown to be anti-allodynic, with respective ED50 values of 230, 90 and 80 micromol/kg (p.o.). (L)-Phenylglycine was as potent as pregabalin and equi-efficacious in reversing mechanical allodynia. In contrast, two ligands with comparable or superior alpha2delta binding affinities, m-chlorophenylglycine (Ki = 54 nM) and ABHCA (150 nM), exhibited no anti-allodynic effects at doses of 30-300 micromol/kg (p.o.), although these compounds achieved substantial brain levels. The data demonstrate that, at least in the rat spinal nerve ligation model of neuropathic pain, (L)-phenylglycine has an anti-allodynic effect, but two equally potent alpha2delta subunit ligands do not. These results suggest that additional mechanisms, besides alpha2delta interactions, may contribute to the effects of compounds like gabapentin, pregabalin and (L)-phenylglycine in neuropathic pain.

Structure–activity relationships of α-amino acid ligands for the α2δ subunit of voltage-gated calcium channels

A series of alpha-amino acids were identified as ligands which compete with gabapentin for binding to the alpha(2)delta subunit of voltage-dependent Ca(2+) channels. Potent analogs were identified. Their activity in an in vivo pain assay is described.

Mechanisms of the antinociceptive action of gabapentin

Gabapentin, a gamma-aminobutyric acid (GABA) analogue anticonvulsant, is also an effective analgesic agent in neuropathic and inflammatory, but not acute, pain systemically and intrathecally. Other clinical indications such as anxiety, bipolar disorder, and hot flashes have also been proposed. Since gabapentin was developed, several hypotheses had been proposed for its action mechanisms. They include selectively activating the heterodimeric GABA(B) receptors consisting of GABA(B1a) and GABA(B2) subunits, selectively enhancing the NMDA current at GABAergic interneurons, or blocking AMPA-receptor-mediated transmission in the spinal cord, binding to the L-alpha-amino acid transporter, activating ATP-sensitive K(+) channels, activating hyperpolarization-activated cation channels, and modulating Ca(2+) current by selectively binding to the specific binding site of [(3)H]gabapentin, the alpha(2)delta subunit of voltage-dependent Ca(2+) channels. Different mechanisms might be involved in different therapeutic actions of gabapentin. In this review, we summarized the recent progress in the findings proposed for the antinociceptive action mechanisms of gabapentin and suggest that the alpha(2)delta subunit of spinal N-type Ca(2+) channels is very likely the analgesic action target of gabapentin.

Expedited SAR study of high-affinity ligands to the α2δ subunit of voltage-gated calcium channels: Generation of a focused library using a solution-phase Sn2Ar coupling methodology

The SAR of the lead compound 3, a novel ligand for the alpha(2)delta subunit of voltage-gated calcium channels, was rapidly explored. Utilizing a parallel solution-phase Sn2Ar coupling approach, a focused library was obtained. The library was evaluated in vitro and afforded a series of analogues with improved potencies. The SAR trends of the library are also described.

Adverse effects of gabapentin and lack of anti-allodynic efficacy of amitriptyline in the streptozotocin model of painful diabetic neuropathy

Amitriptyline and gabapentin are the primary treatments for painful diabetic neuropathy (PDN), and it is clear that they produce beneficial effects, but there are questions about these treatments that have not been adequately addressed. For example, although there is a growing consensus that the therapeutic effects of amitriptyline in pain patients are independent of its effects on mood, it is not clear that amitriptyline has specific and direct effects on pain. There is also a fairly broad consensus that gabapentin is safe and well tolerated, but the side-effect profile of gabapentin has not been adequately assessed in pain populations. The rat streptozotocin (STZ) model of PDN was used (a) to assess the effects of amitriptyline on objective, quantitative measures of tactile allodynia, a common type of pain in PDN patients, and (b) to assess the side effects of gabapentin using measures of motor/ambulatory and cognitive function. Amitriptyline did not attenuate STZ-induced mechanical allodynia, even after chronic administration of high doses. Gabapentin produced robust anti-allodynic effects but also produced deficits in tests of motor/ambulatory and cognitive functions. The present experiments suggest that the beneficial effects of amitriptyline in PDN may not be a result of anti-allodynic efficacy and that gabapentin produces robust anti-allodynic effects but may also produce significant motor and cognitive deficits even at or near the lowest effective doses. These findings challenge the consensus opinions about these primary treatments for PDN and suggest that their therapeutic and adverse effects should be explored further in pain patients.