Inhibition of neuronal Ca(2+) influx by gabapentin and subsequent reduction of neurotransmitter release from rat neocortical slices

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.

Alcohol Use Disorder Treatment: Problems and Solutions

Alcohol use disorder (AUD) afflicts over 29 million individuals and causes more than 140,000 deaths annually in the United States. A heuristic framework for AUD includes a three-stage cycle-binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation-that provides a starting point for exploring the heterogeneity of AUD with regard to treatment. Effective behavioral health treatments and US Food and Drug Administration-approved medications are available but greatly underutilized, creating a major treatment gap. This review outlines challenges that face the alcohol field in closing this treatment gap and offers solutions, including broadening end points for the approval of medications for the treatment of AUD; increasing the uptake of screening, brief intervention, and referral to treatment; addressing stigma; implementing a heuristic definition of recovery; engaging early treatment; and educating health-care professionals and the public about challenges that are associated with alcohol misuse. Additionally, this review focuses on broadening potential targets for the development of medications for AUD by utilizing the three-stage heuristic model of addiction that outlines domains of dysfunction in AUD and the mediating neurobiology of AUD.

Application of gabapentinoids and novel compounds for the treatment of benzodiazepine dependence: the glutamatergic model

BACKGROUND

Current approaches for managing benzodiazepine (BZD) withdrawal symptoms are daunting for clinicians and patients, warranting novel treatment and management strategies. This review discusses the pharmacodynamic properties of BZDs, gabapentinoids (GBPs), endozepines, and novel GABAergic compounds associated with potential clinical benefits for BZD-dependent patients. The objective of this study was to review the complex neuromolecular changes occurring within the GABAergic and glutamatergic systems during the BZD tolerance and withdrawal periods while also examining the mechanism by which GBPs and alternative pharmacological therapies may attenuate withdrawal symptoms.

METHODS AND RESULTS

An elaborative literature review was conducted using multiple platforms, including the National Center for Biotechnology (NCBI), AccessMedicine, ScienceDirect, pharmacology textbooks, clinical trial data, case reports, and PubChem. Our literature analysis revealed that many distinctive neuroadaptive mechanisms are involved in the GABAergic and glutamatergic systems during BZD tolerance and withdrawal. Based on this data, we hypothesize that GBPs may attenuate the overactive glutamatergic system during the withdrawal phase by an indirect presynaptic glutamatergic mechanism dependent on the α₂δ₁ subunit expression.

CONCLUSIONS

GBPs may benefit individuals undergoing BZD withdrawal, given that the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor current significantly increases during abrupt BZD withdrawal in animal studies. This may be a conceivable explanation for the effectiveness of GBPs in treating both alcohol withdrawal symptoms and BZD withdrawal symptoms in some recent studies. Finally, natural and synthetic GABAergic compounds with unique pharmacodynamic properties were found to exert potential clinical benefits as BZD substitutes in animal studies, though human studies are lacking.

Effects of Gabapentin and Pregabalin on Calcium Homeostasis: Implications for Physical Rehabilitation of Musculoskeletal Tissues

PURPOSE OF REVIEW

In this review, we discuss the mechanism of action of gabapentinoids and the potential consequences of long-term treatment with these drugs on the musculoskeletal system.

RECENT FINDINGS

Gabapentinoids, such as gabapentin (GBP) and pregabalin (PGB) were designed as antiepileptic reagents and are now commonly used as first-line treatment for neuropathic pain and increasingly prescribed off-label for other pain disorders such as migraines and back pain. GBP and PGB exert their analgesic actions by selectively binding the α₂δ₁ auxiliary subunit of voltage-sensitive calcium channels, thereby inhibiting channel function. Numerous tissues express the α₂δ₁ subunit where GBP and PGB can alter calcium-mediated signaling events. In tissues such as bone, muscle, and cartilage, α₂δ₁ has important roles in skeletal formation, mechanosensation, and normal tissue function/repair that may be affected by chronic use of gabapentinoids. Long-term use of gabapentinoids is associated with detrimental musculoskeletal outcomes, including increased fracture risk. Therefore, understanding potential complications is essential for clinicians to guide appropriate treatments.

Comparative Study of the Neurotoxic Effects of Pregabalin Versus Tramadol in Rats

In Egypt, both pregabalin and tramadol misuse increased in the last decade. Although many studies have confirmed the neurotoxic effects of tramadol, those of pregabalin are understudied. The aim of the study is to evaluate the neurotoxic effects of pregabalin compared with tramadol. Thirty male albino rats were included in this experimental study, and they were randomly allocated into three equal groups: group I (normal saline), group II (tramadol misuse), and group III (pregabalin misuse). All rats received the commenced drugs for 1 month. Open field tests were performed on the day of scarification, and after that, cortical samples were taken for immunohistochemical analysis and quantification of dopamine receptors' gene expression. The drug misuse groups showed a significant decrease in weight gain at the end of the study. Open field testing showed the upper hand of controls regarding all of the tested parameters. Tramadol has a more negative impact on the locomotor parameters compared with pregabalin. Both drugs induced relatively low dopamine-1 receptor (D1Rs) expression to dopamine-2 receptors (D2Rs), mimicking the schizophrenia model. Both tramadol and pregabalin were associated with neurotoxic effects in male albino rats. These effects were less noticed with pregabalin. It is suggested that long-term abuse may end in psychosis.

Alterations in Excitatory and Inhibitory Synaptic Development Within the Mesolimbic Dopamine Pathway in a Mouse Model of Prenatal Drug Exposure

The rise in rates of opioid abuse in recent years in the United States has led to a dramatic increase in the incidence of neonatal abstinence syndrome (NAS). Despite improved understanding of NAS and its acute symptoms, there remains a paucity of information regarding the long-term effects of prenatal exposure to drugs of abuse on neurological development. The primary goal of this study was to investigate the effects of prenatal drug exposure on synaptic connectivity within brain regions associated with the mesolimbic dopamine pathway, the primary reward pathway associated with drug abuse and addiction, in a mouse model. Our secondary goal was to examine the role of the Ca+2 channel subunit α2δ-1, known to be involved in key developmental synaptogenic pathways, in mediating these effects. Pregnant mouse dams were treated orally with either the opioid drug buprenorphine (commonly used in medication-assisted treatment for substance use patients), gabapentin (neuropathic pain drug that binds to α2δ-1 and has been increasingly co-abused with opioids), a combination of both drugs, or vehicle daily from gestational day 6 until postnatal day 11. Confocal fluorescence immunohistochemistry (IHC) imaging of the brains of the resulting wild-type (WT) pups at postnatal day 21 revealed a number of significant alterations in excitatory and inhibitory synaptic populations within the anterior cingulate cortex (ACC), nucleus accumbens (NAC), and medial prefrontal cortex (PFC), particularly in the buprenorphine or combinatorial buprenorphine/gabapentin groups. Furthermore, we observed several drug- and region-specific differences in synaptic connectivity between WT and α2δ-1 haploinsufficient mice, indicating that critical α2δ-1-associated synaptogenic pathways are disrupted with early life drug exposure.

Concomitant Antihyperalgesic and Antitumor Effects of Gabapentin in a Murine Cancer Pain Model

Cancer pain may be the consequence of physical nerve compression by a growing tumor. We employed a murine model to study whether gabapentin was able to regulate tumor growth, in addition to controlling hyperalgesic symptoms. A fluorescent melanoma cell line (B16-BL6/Zs green) was inoculated into the proximity of the sciatic nerve in male C57BL/6 mice. The tumor gradually compressed the nerve, causing hypersensitivity. Tumor growth was characterized via in vivo imaging techniques. Every other day, gabapentin (100 mg/Kg) or saline was IP administered to each animal. In the therapeutic protocol, gabapentin was administered once the tumor had induced increased nociception. In the preventive protocol, gabapentin was administered before the appearance of the positive signs. Additionally, in vitro experiments were performed to determine gabapentin's effects on cell-line proliferation, the secretion of the chemokine CCL2, and calcium influx. In the therapeutically treated animals, baseline responses to noxious stimuli were recovered, and tumors were significantly reduced. Similarly, gabapentin reduced tumor growth during the preventive treatment, but a relapse was noticed when the administration stopped. Gabapentin also inhibited cell proliferation, the secretion of CCL2, and calcium influx. These results suggest that gabapentin might represent a multivalent strategy to control cancer-associated events in painful tumors.

Serotonin and beyond-a tribute to Manfred Göthert (1939-2019)

Manfred Göthert, who had served Naunyn-Schmiedeberg's Arch Pharmacol as Managing Editor from 1998 to 2005, deceased in June 2019. His scientific oeuvre encompasses more than 20 types of presynaptic receptors, mostly on serotoninergic and noradrenergic neurones. He was the first to identify presynaptic receptors for somatostatin and ACTH and described many presynaptic receptors, known from animal preparations, also in human tissue. In particular, he elucidated the pharmacology of presynaptic 5-HT receptors. A second field of interest included ligand-gated and voltage-dependent channels. The negative allosteric effect of anesthetics at peripheral nACh receptors is relevant for the peripheral clinical effects of these drugs and modified the Meyer-Overton hypothesis. The negative allosteric effect of ethanol at NMDA receptors in human brain tissue occurred at concentrations found in the range of clinical ethanol intoxication. Moreover, the inhibitory effect of gabapentinoids on P/Q Ca2+ channels and the subsequent decrease in AMPA-induced noradrenaline release may contribute to their clinical effect. Another ligand-gated ion channel, the 5-HT3 receptor, attracted the interest of Manfred Göthert from the whole animal via isolated preparations down to the cellular level. He contributed to that molecular study in which 5-HT3 receptor subtypes were disclosed. Finally, he found altered pharmacological properties of 5-HT receptor variants like the Arg219Leu 5-HT1A receptor (which was also shown to be associated with major depression) and the Phe124Cys 5-HT1B receptor (which may be related to sumatriptan-induced vasospasm). Manfred Göthert was a brilliant scientist and his papers have a major impact on today's pharmacology.

Gabapentin attenuates somatic signs of precipitated THC withdrawal in mice

Cannabis is the most frequently used federally illicit substance in the United States. However, there are currently no FDA-approved pharmacotherapies to mitigate the withdrawal symptoms associated with cessation in heavy users. A promising, readily available, non-cannabinoid therapy are the gabapentinoids. Although currently approved for epilepsy and neuropathic pain, gabapentinoids are increasingly used for their "off-label" efficacy in treating various psychiatric conditions and substance abuse. Gabapentin (GBP) synergizes with cannabinoid agonism in neuropathic pain models, substitutes for Δ⁹-tetrahydrocannabinol (THC) in drug discrimination procedures, and reduced withdrawal symptoms in an outpatient clinical trial. However, there are limited data on the biological plausibility of the therapeutic action of gabapentinoids in cannabinoid withdrawal in preclinical models. The purpose of the current study was to determine the efficacy of GBP on attenuating THC withdrawal in mice, using an array of tests targeting withdrawal-induced and withdrawal-suppressed behaviors. Separate cohorts of male and female mice were administered THC (10 mg/kg, s.c.) or vehicle for 5.5 days, and withdrawal was precipitated by the CB₁ antagonist rimonabant (2 or 3 mg/kg, i.p.) on the sixth day. GBP (≥10 mg/kg) reduced somatic signs of withdrawal (i.e., paw tremors and head twitches), but had no effect in locomotor activity or conditioned place preference. GBP (50 mg/kg) also restored withdrawal-suppressed responding on a progressive ratio reinforcement schedule. However, GBP (50 mg/kg) had no effect in withdrawal-suppressed marble burying or tail suspension struggling and did not normalize the stress response induced by THC withdrawal, as indicated by plasma corticosterone. These data suggest gabapentin may be effective at treating cannabinoid withdrawal symptoms including somatic and affective symptoms but may act independently of endocrine stress activation.

Neurotoxic effects of pregabalin dependence on the brain frontal cortex in adult male albino rats

Pregabalin (PGB) is an analog of the inhibitory neurotransmitter gamma-aminobutyric acid. The currently available evidence favors the misuse and abuse potential of PGB. However, its neurotoxicity remains unclear. Therefore, this study assessed the toxic effects of chronic pregabalin dependence as well as withdrawal on the cortical neurons of the frontal lobe. This study included eighty adult male albino rats which were divided into three groups. Group I (Control) included 40 rats and was further subdivided into two equal subgroups (IA and IB) as negative and positive controls. Group II (PGB-dependent) included 20 rats which received PGB starting with the therapeutic dose (300 mg/day), then the doses were gradually increased until they reached the dependent dose (3400 mg/day) by the end of the first month. Further, the dependent dose was given daily for another 2 months. Group III (PGB withdrawal) included 20 rats which received PGB as described in group II. After that, administration of PGB was stopped and the rats were kept for another one month. By the end of the experiment, all animals were sacrificed by cervical decapitation. The specimens were taken from the frontal cortex for histologic and immunohistochemical staining as well as morphometric analysis. Sections of the frontal cortex of group II showed changes in the form of disturbed architectural pattern of cortical layers, apoptotic cells, weak immunoexpression of Bcl-2 and VEGF as well as moderate-strong immunoexpression of iNOS and nestin. These expressions were significantly different from the control groups, but they were non-significant in comparison with group III. These findings indicate that chronic PGB dependence induces neurotoxic effects mainly in the form of neuronal apoptosis, gliosis, and oxidative stress injury of the frontal cortex. The PGB- induced neurotoxic effects persisted after withdrawal. The influence of these neurotoxic effects and their relevance to the cognitive or neurologic disorders in PGB-dependent individuals warrants further research. Furthermore, it is recommended to quantify the behavioral changes related to PGB dependence as well as withdrawal in future studies.

Appetite-stimulating effect of gabapentin vs mirtazapine in healthy cats post-ovariectomy

OBJECTIVES

The aim of the study was to evaluate the appetite-stimulating effect of gabapentin by comparing it with mirtazapine in healthy cats in the first 8 h after ovariectomy surgery.

METHODS

This double-masked, placebo-controlled, prospective clinical trial included 60 healthy cats presented to the hospital for ovariectomy: 20 received gabapentin, 21 received mirtazapine and 19 received a placebo immediately before and 6 h after surgery. Food was offered at 2, 4, 6 and 8 h post-ovariectomy. After each meal, food intake was measured. Data were analysed using repeated-measure ANOVA and a linear mixed-model analysis. Post-hoc Tukey's honest significant difference test was performed for multiple comparisons.

RESULTS

Food intake increased in both treatment groups vs placebo. No statistically significant difference was found between cats treated with gabapentin or mirtazapine.

CONCLUSIONS AND RELEVANCE

Cats receiving gabapentin ate more than cats in the placebo group. Thirty percent of cats in the gabapentin group covered their resting energy requirements, while none of the cats in the placebo group did. Gabapentin and mirtazapine produced similar effects on food intake.

Management of Neuropathic Pain in Polyneuropathy

PURPOSE OF REVIEW

Many polyneuropathies cause significant neuropathic pain, resulting in substantial morbidity and reduced quality of life. Appropriate management is crucial for maintaining quality of life for patients with painful polyneuropathies. The US Food and Drug Administration (FDA) has only approved one new drug for painful diabetic neuropathy in the past decade, a topical capsaicin patch that was initially approved for the treatment of postherpetic neuralgia in 2009. Gabapentinoids and serotonin norepinephrine reuptake inhibitors (SNRIs) continue to have an advantage in safety profiles and efficacy. Other antiepileptic medications remain second-line agents because of fewer studies documenting efficacy.

RECENT FINDINGS

This article reviews recent literature on complementary and pharmacologic therapies for the management of painful polyneuropathies. Exercise has emerged as an important therapeutic tool and may also improve the underlying polyneuropathy in the setting of obesity, metabolic syndrome, and diabetes.

SUMMARY

The approach to management of painful polyneuropathies is multifactorial, using both pharmacologic and nonpharmacologic measures to improve pain severity and patient quality of life.

Auxiliary α2δ1 and α2δ3 Subunits of Calcium Channels Drive Excitatory and Inhibitory Neuronal Network Development

VGCCs are multisubunit complexes that play a crucial role in neuronal signaling. Auxiliary α2δ subunits of VGCCs modulate trafficking and biophysical properties of the pore-forming α1 subunit and trigger excitatory synaptogenesis. Alterations in the expression level of α2δ subunits were implicated in several syndromes and diseases, including chronic neuropathic pain, autism, and epilepsy. However, the contribution of distinct α2δ subunits to excitatory/inhibitory imbalance and aberrant network connectivity characteristic for these pathologic conditions remains unclear. Here, we show that α2δ1 overexpression enhances spontaneous neuronal network activity in developing and mature cultures of hippocampal neurons. In contrast, overexpression, but not downregulation, of α2δ3 enhances neuronal firing in immature cultures, whereas later in development it suppresses neuronal activity. We found that α2δ1 overexpression increases excitatory synaptic density and selectively enhances presynaptic glutamate release, which is impaired on α2δ1 knockdown. Overexpression of α2δ3 increases the excitatory synaptic density as well but also facilitates spontaneous GABA release and triggers an increase in the density of inhibitory synapses, which is accompanied by enhanced axonaloutgrowth in immature interneurons. Together, our findings demonstrate that α2δ1 and α2δ3 subunits play distinct but complementary roles in driving formation of structural and functional network connectivity during early development. An alteration in α2δ surface expression during critical developmental windows can therefore play a causal role and have a profound impact on the excitatory-to-inhibitory balance and network connectivity.SIGNIFICANCE STATEMENT The computational capacity of neuronal networks is determined by their connectivity. Chemical synapses are the main interface for transfer of information between individual neurons. The initial formation of network connectivity requires spontaneous electrical activity and the calcium channel-mediated signaling. We found that, in early development, auxiliary α2δ3 subunits of calcium channels foster presynaptic release of GABA, trigger formation of inhibitory synapses, and promote axonal outgrowth in inhibitory interneurons. In contrast, later in development, α2δ1 subunits promote the glutamatergic neurotransmission and synaptogenesis, as well as strongly enhance neuronal network activity. We propose that formation of connectivity in neuronal networks is associated with a concerted interplay of α2δ1 and α2δ3 subunits of calcium channels.

Pregabalin as a Pain Therapeutic: Beyond Calcium Channels

Initially developed to generate new treatments for epilepsy, gabapentin, and pregabalin (“gabapentinoids”) were engineered to mimic the action of GABA and to modulate GABA metabolism. Rather than their intended pharmacological action on GABA neurotransmission, instead, they exhibit a high affinity for the α2δ-1 and α2δ-2 subunits of voltage-activated calcium channels, wherein binding of gabapentinoids inhibits cellular calcium influx and attenuates neurotransmission. Despite a lack of activity on GABA levels, gabapentin and pregabalin are effective at suppressing seizures and subsequently approved as a new class of antiepileptic therapy for partial-onset epilepsy. Through the same hypothesized molecular mechanism and by controlling neuronal hyperexcitability, gabapentinoids demonstrate clear efficacy in pain management, which has arguably been their most extensively prescribed application to date. In this review, we focus on pregabalin as a second-generation gabapentinoid widely employed in the treatment of a variety of pain conditions. We also discuss the wider functional roles of α2δ subunits and the contributions that pregabalin might play in affecting physiological and pathophysiological processes.

Comparing the prophylactic effects of oral gabapentin, pregabalin, and celecoxib on postoperative pain management in orthopedic surgery of the lower extremity: A double-blind randomized controlled trial

Background:

Lower extremity pain after orthopedic surgery is so frequent that has led to many treatment modalities. This study aims to compare the prophylactic effects of oral gabapentin, pregabalin, and celecoxib on reducing postsurgical pain of the lower extremity orthopedic surgery.

Materials and Methods:

In a double-blind randomized controlled trial, 120 patients were randomly divided into four groups using block design randomization. 1 h before spinal anesthesia, the studied groups received 300 mg oral gabapentin; 75 mg oral pregabalin; 200 mg oral celecoxib; and starch as placebo. The severity of postoperative pain (using visual analog scale), mean arterial pressure, heart rate, opioid consumption dose, and drug side effects were recorded for six times (each 60 min up to two times and then every 6 h for the next four times). Chi-square, one-way analysis of variance (ANOVA), and ANOVA repeated measure tests were used for statistical analysis.

Results:

Significant reduction of pain severity was observed only at the first time measurement between pregabalin and placebo groups (P: 0.014). Patients in the pregabalin group required lower dose of opioid compared to placebo group during admission in surgical ward. There were no significant differences concerning pain reduction, opioid administration, and side effects between pregabalin, gabapentin, and celecoxib groups.

Conclusion:

Taking 75 mg oral pregabalin before lower extremity orthopedic surgery can attenuate postoperative pain, especially during the 1^st h postoperation as well as less opioid consumption and much more patients' satisfaction.

Gabapentin Reduces Blood Pressure and Heart Rate through the Nucleus Tractus Solitarii

Background

Oral and intravenous gabapentin can markedly attenuate blood pressure (BP) in hypertensive rats. The nucleus tractus solitarii (NTS) is the primary integrative center for cardiovascular control and other autonomic functions in the central nervous system. However, the signaling mechanisms involved in gabapentin-mediated cardiovascular effects in the NTS remain unclear. We investigated whether the nitric oxide synthase (NOS) signaling pathway was involved in gabapentin-mediated BP regulation in the NTS of spontaneously hypertensive (SHR) rats.

Methods

SHR rats were anesthetized with urethane at age 10-12 weeks. Arterial pressure and heart rate (HR) were monitored through a femoral artery catheter. For stereotaxic intra-NTS microinjection, the dorsal surface of the medulla was exposed by limited craniotomy. We observed that unilateral microinjection of gabapentin into the NTS whether to change dose-related BP and HR. Then, unilateral microinjection of gabapentin into the NTS before and after N(ω)-nitro-L-arginine methyl ester (L-NAME) treatment whether to change blood pressure and heart rate.

Results

Unilateral microinjection of gabapentin into the NTS produced prominent dose-related depressor and bradycardic effects in SHR rats. The cardiovascular effects of gabapentin were attenuated by the prior administration of the NOS inhibitor, L-NAME.

Conclusions

Gabapentin modulated central BP and HR control in the NTS of SHR rats in this study through NOS signaling.

Pathological Mechanisms and Therapeutic Targets for Trigeminal Neuropathic Pain

Trigeminal neuropathic pain is a chronic pain condition caused by damage or inflammation of the trigeminal nerve or its branches, with both peripheral and central nervous system dysfunction contributing to the disorder. Trigeminal pain conditions present with diagnostic and therapeutic challenges to healthcare providers and often require multiple therapeutic approaches for pain reduction. This review will provide the overview of pathophysiology in peripheral and central nociceptive circuits that are involved in neuropathic pain conditions involving the trigeminal nerve and the current therapeutics that are used to treat these disorders. Recent advances in treatment of trigeminal pain, including novel therapeutics that target ion channels and receptors, gene therapy and monoclonal antibodies that have shown great promise in preclinical studies and clinical trials will also be described.

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.

Gabapentin-related suicide: Myth or fact?

Background:

The opioid epidemic in America is real and is estimated to be the number one cause of death in adults under 50 years of age. Finding alternative analgesic medications is part of the effort to decrease the prescription of narcotics, with gabapentin being at the top of the list.

Case Description:

In the present case, we discuss the side-effects of gabapentin, used as part of the multimodal treatment approach of painful spinal degenerative disease. The patient stated that he had noticed personality changes after gabapentin was initiated, and that he had become more depressed, frustrated, and aggressive. His uncontrolled pain and acute mood changes led him to attempt suicide by hanging himself. Gabapentin was discontinued and the patient's suicidal ideation completely subsided.

Conclusion:

It is imperative to screen, identify, and appropriately manage patients with underlying psychiatric disorders prior to initiating pain management with gabapentin. Therefore, it is crucial to raise awareness of gabapentin as a potential cause of depression, aggressive behavior, and suicidal ideation.

Gabapentin and NMDA receptor antagonists interacts synergistically to alleviate allodynia in two rat models of neuropathic pain

Background and aims

The clinical management of neuropathic pain remains a challenge. We examined the interaction between gabapentin and NMDA receptor antagonists dextromethrophan and MK-801 in alleviating neuropathic pain-like behaviors in rats after spinal cord or sciatic nerve injury.

Methods

Female and male rats were produced with Ischemic spinal cord injury and sciatic nerve injury. Gabapentin, dextromethorphan, MK-801 or drug combinations were injected with increasing doses. Mechanical response thresholds were tested with von Frey hairs to graded mechanical touch/pressure, and ethyl chloride spray was applied to assess the cold sensitivity before and after injuries.

Results

In spinally injured rats, gabapentin and dextromethorphan did not affect allodynia-like behaviors at doses of 30 and 20 mg/kg, respectively. In contrast, combination of 15 or 30 mg/kg gabapentin with dextromethorphan at 10 mg/kg produced total alleviation of allodynia to mechanical or cold stimulation. Further reducing the dose of gapapentin to 7.5 mg/kg and dextromethorphan to 5 mg/kg still produced significant effect. MK-801, another NMDA receptor antagonist, also enhanced the effect of gabapentin in spinally injured rats. Similar synergistic anti-allodynic effect between dextromethorphan and gabapentin was also observed in a rat model of partial sciatic nerve injury. No increased side effect was seen following the combination between gabapentin and dextromethorphan.

Conclusions

In conclusion, the present study suggested that combining NMDA receptor antagonists with gabapentin could provide synergistic effect to alleviate neuropathic pain and reduced side effects.

Implications

Combining NMDA receptor antagonists with gabapentin may provide a new approach in alleviating neuropathic pain with increased efficacy and reduced side effects.

Remifentanil-induced postoperative hyperalgesia: current perspectives on mechanisms and therapeutic strategies

The use of remifentanil in clinical practice offers several advantages and it is used for a wide range of procedures, ranging from day-surgery anesthesia to more complex procedures. Nonetheless, remifentanil has been consistently linked with development of opioid-induced hyperalgesia (OIH), which is described as a paradoxical increase in sensitivity to painful stimuli that develops after exposure to opioid treatment. The development of OIH may cause several issues, delaying recovery after surgery and preventing timely patient's discharge. Moreover, it causes patient's discomfort with higher pain scores, greater use of analgesics, and associated side effects. Remifentanil is the opioid most convincingly associated with OIH, and hereby we provide a review of remifentanil-induced hyperalgesia, describing both the underlying mechanisms involved and the available studies investigating experimental and clinical pharmacologic approaches aiming at reducing its incidence and degree.

GC-MS/MS detects potential pregabalin abuse in susceptible subjects' hair

Pregabalin, a GABA analogue, binds to the alpha 2 delta subunit of voltage-dependent calcium channels. It is recognised as efficacious in pathologies such as epilepsy, neuropathic pain, and anxiety disorders. Since pregabalin prescriptions have increased worldwide, reports of its abuse have been accumulating, mainly in patients with opioid abuse disorders. The present study investigated potential pregabalin abuse by means of hair analysis, a matrix that provides valuable retrospective information. Half of the pool of 280 susceptible patients had been occasional drug users and were being monitored for driving licence renewals. The other 140 patients had a history of opiate dependency and were monitored to assess compliance with methadone therapy. In view of determining pregabalin in hair samples, it was extracted in methanol, successfully derivatised to give the ethyl chloroformate derivative, and finally pregabalin was analysed by gas chromatography-tandem mass spectrometry. Selectivity, linearity, limit of detection, limit of quantification, recovery, intra- and inter-day precision, and accuracy of the quantification procedure were appraised. Pregabalin limits of detection and quantification were 30 pg/mg and 50 pg/mg, respectively. We found 10.7% of hair samples from methadone patients and 4.29% from occasional drug users were positive to pregabalin without medical prescription. The mean pregabalin concentration in hair was higher than in consumers with medical indications (1.45 ng/mg vs 0.74 ng/mg). These results suggest that pregabalin possesses a significant abuse potential particularly among individuals attending opiate dependence services and that pregabalin abuse is a serious emerging issue, which should be carefully monitored.

Gabapentin for the treatment of alcohol use disorder

INTRODUCTION

Alcohol misuse is the fifth leading risk factor for premature death and disability worldwide. Fewer than 10% of afflicted Americans receive pharmacological treatment for alcohol use disorder. Gabapentin is a calcium channel GABAergic modulator that is widely used for pain. Studies showing reduced drinking and decreased craving and alcohol-related disturbances in sleep and affect in the months following alcohol cessation suggest therapeutic potential for alcohol use disorder. Areas covered: Human laboratory and clinical studies assessing gabapentin for alcohol use disorder are reviewed. Data were obtained by searching for English peer-reviewed articles on PubMed, reference lists of identified articles, and trials registered on clinicaltrials.gov. Additionally, the mechanism of action of gabapentin specific to alcohol use disorder, and studies of gabapentin for alcohol withdrawal and non-alcohol substance use disorders are summarized. Expert opinion: Alcohol use disorder represents a challenge and large, unmet medical need. Evidence from single-site studies lend support to the safety and efficacy of gabapentin as a novel treatment for alcohol use disorder, with unique benefits for alcohol-related insomnia and negative affect, relative to available treatments. Proprietary gabapentin delivery systems may open a path to pivotal trials and registration of gabapentin as a novel treatment for alcohol use disorder.

Should Benzodiazepines and Anticonvulsants Be Used During Electroconvulsive Therapy?: A Case Study and Literature Review

OBJECTIVE

This study aims to investigate the clinical effects of benzodiazepines or anticonvulsant use during a course of electroconvulsive therapy (ECT).

METHOD

A case report study of a patient who received ECT with and without concomitant flurazepam and pregabalin is presented. The literature on the use of benzodiazepines and anticonvulsants during ECT is reviewed.

RESULTS

A woman with treatment resistant depression received a course of ECT while taking flurazepam and pregabalin, but seizures were of short duration and symptomatic improvement was minimal. After discontinuation of flurazepam and pregabalin, a course of right unilateral ultrabrief ECT was associated with adequate seizures and remission of depression and suicidal ideation. Our literature review suggests that benzodiazepines decrease seizure duration, but most evidence shows no association with increased seizure threshold. One prospective RCT and 3 large retrospective studies found that benzodiazepines compromise the efficacy of unilateral but not bilateral ECT. Regarding anticonvulsants, several studies had varied and contradictory results on their effect on seizure duration and seizure threshold. Of the 2 large retrospective studies and 3 RCTs, only 1 retrospective study showed that anticonvulsants decrease the efficacy of ECT.

CONCLUSIONS

Judicious assessment of all medications used in combination with ECT is recommended. Overall, published studies suggest that benzodiazepines and anticonvulsants impact the clinical outcomes of ECT less than what would be expected given their pharmacologic effects. However, there are significant gaps in the literature, including a lack of study on suprathreshold stimulation of right unilateral ECT and the possibility of a greater effect with higher medication doses.

Epilepsy and ion channels

Many mutations of genes for ion channels result in some epilepsies. Their electrophysiological studies reveal pathophysiological mechanisms underlining epilepsy and also mechanism of action of several antiepileptic drugs. In this review, We briefly summarize pathophysiology of epilepsy and the mechanisms of antiepileptic drugs.

The Anti-Allodynic Gabapentinoids: Myths, Paradoxes, and Acute Effects

The gabapentinoids (pregabalin and gabapentin) are first line treatments for neuropathic pain. They exert their actions by binding to the α2δ accessory subunits of voltage-gated Ca²⁺ channels. Because these subunits interact with critical aspects of the neurotransmitter release process, gabapentinoid binding prevents transmission in nociceptive pathways. Gabapentinoids also reduce plasma membrane expression of voltage-gated Ca²⁺ channels but this may have little direct bearing on their therapeutic actions. In animal models of neuropathic pain, gabapentinoids exert an anti-allodynic action within 30 minutes but most of their in vitro effects are 30-fold slower, taking at least 17 hours to develop. This difference may relate to increased levels of α2δ expression in the injured nervous system. Thus, in situations where α2δ is experimentally upregulated in vitro, gabapentinoids act within minutes to interrupt trafficking of α2δ subunits to the plasma membrane within nerve terminals. When α2δ is not up-regulated, gabapentinoids act slowly to interrupt trafficking of α2δ protein from cell bodies to nerve terminals. This improved understanding of the mechanism of gabapentinoid action is related to their slowly developing actions in neuropathic pain patients, to the concept that different processes underlie the onset and maintenance of neuropathic pain and to the use of gabapentinoids in management of postsurgical pain.

Mechanisms of the gabapentinoids and α 2 δ-1 calcium channel subunit in neuropathic pain

The gabapentinoid drugs gabapentin and pregabalin are key front‐line therapies for various neuropathies of peripheral and central origin. Originally designed as analogs of GABA, the gabapentinoids bind to the α₂δ‐1 and α₂δ‐2 auxiliary subunits of calcium channels, though only the former has been implicated in the development of neuropathy in animal models. Transgenic approaches also identify α₂δ‐1 as key in mediating the analgesic effects of gabapentinoids, however the precise molecular mechanisms remain unclear. Here we review the current understanding of the pathophysiological role of the α₂δ‐1 subunit, the mechanisms of analgesic action of gabapentinoid drugs and implications for efficacy in the clinic. Despite widespread use, the number needed to treat for gabapentin and pregabalin averages from 3 to 8 across neuropathies. The failure to treat large numbers of patients adequately necessitates a novel approach to treatment selection. Stratifying patients by sensory profiles may imply common underlying mechanisms, and a greater understanding of these mechanisms could lead to more direct targeting of gabapentinoids.

Gabapentin potentiates sensitivity to the interoceptive effects of alcohol and increases alcohol self-administration in rats

Gabapentin, a drug used in the treatment of epileptic seizures and neuropathic pain, has shown efficacy in the treatment of alcohol dependence. Moreover, given that gabapentin is used in the general population (e.g., non-dependent individuals, social drinkers), we sought to utilize preclinical assessments to examine the effects of gabapentin on sensitivity to moderate alcohol doses and alcohol self-administration in rats with a history of moderate drinking. To this end, we assessed whether gabapentin (0, 10, 30, 120 mg/kg, IG) pretreatment alters sensitivity to experimenter- and self-administered alcohol, and whether gabapentin alone has alcohol-like discriminative stimulus effects in rats trained to discriminate alcohol dose (1 g/kg, IG) vs. water. Second, we assessed whether gabapentin (0, 10, 30, 60 mg/kg, IG) would alter alcohol self-administration. Gabapentin pretreatment potentiated the interoceptive effects of both experimenter-administered and self-administered alcohol in discrimination-trained rats. Additionally, the highest gabapentin doses tested (30 and 120 mg/kg) were found to have partial alcohol-like discriminative stimulus effects when administered alone (e.g., without alcohol). In the self-administration trained rats, gabapentin pretreatment (60 mg/kg) resulted in an escalation in alcohol self-administration. Given the importance of interoceptive drug cues in priming and maintaining self-administration, these data define a specific behavioral mechanism (i.e., potentiation of alcohol effects) by which gabapentin may increase alcohol self-administration in non-dependent populations.

Glutamatergic transmission in drug reward: implications for drug addiction

Individuals addicted to drugs of abuse such as alcohol, nicotine, cocaine, and heroin are a significant burden on healthcare systems all over the world. The positive reinforcing (rewarding) effects of the above mentioned drugs play a major role in the initiation and maintenance of the drug-taking habit. Thus, understanding the neurochemical mechanisms underlying the reinforcing effects of drugs of abuse is critical to reducing the burden of drug addiction in society. Over the last two decades, there has been an increasing focus on the role of the excitatory neurotransmitter glutamate in drug addiction. In this review, pharmacological and genetic evidence supporting the role of glutamate in mediating the rewarding effects of the above described drugs of abuse will be discussed. Further, the review will discuss the role of glutamate transmission in two complex heterogeneous brain regions, namely the nucleus accumbens (NAcc) and the ventral tegmental area (VTA), which mediate the rewarding effects of drugs of abuse. In addition, several medications approved by the Food and Drug Administration that act by blocking glutamate transmission will be discussed in the context of drug reward. Finally, this review will discuss future studies needed to address currently unanswered gaps in knowledge, which will further elucidate the role of glutamate in the rewarding effects of drugs of abuse.

Nerve injury-induced calcium channel alpha-2-delta-1 protein dysregulation leads to increased pre-synaptic excitatory input into deep dorsal horn neurons and neuropathic allodynia

BACKGROUND

Up-regulation of voltage-gated calcium channel α2 δ1 subunit post spinal nerve ligation (SNL) injury or in α2 δ1 -overexpressing transgenic (Tg) mice correlates with tactile allodynia, a pain state mediated mainly by Aβ sensory fibres forming synaptic connections with deep dorsal horn (DDH) neurons. It is not clear, however, whether dysregulated α2 δ1 alters DDH synaptic neurotransmission that underlies tactile allodynia development post nerve injury.

METHODS

Tactile allodynia was tested in the SNL and α2 δ1 Tg models. Miniature excitatory/inhibitory post-synaptic currents were recorded in DDH neurons from these animal models using whole-cell patch clamp slice recording techniques.

RESULTS

There was a significant increase in the frequency, but not amplitude, of miniature excitatory post-synaptic currents (mEPSC) in DDH neurons that correlated with tactile allodynia in SNL and α2 δ1 Tg mice. Gabapentin, an α2 δ1 ligand that is known to block tactile allodynia in these models, also normalized mEPSC frequency dose-dependently in DDH neurons from SNL and α2 δ1 Tg mice. In contrast, neither frequency nor amplitude of miniature inhibitory post-synaptic currents was altered in DDH neurons from SNL and α2 δ1 Tg mice.

CONCLUSION

Our data suggest that α2 δ1 dysregulation is highly likely contributing to tactile allodynia through a pre-synaptic mechanism involving facilitation of excitatory synaptic neurotransmission in DDH of spinal cord.

Analgesic effect of intrathecal gabapentin in a rat model of persistent muscle pain

OBJECTIVE

To evaluate the analgesic effect of intrathecal gabapentin therapy on secondary hyperalgesia in a rat model of persistent muscle pain.

METHODS

Intrathecal catheters were implanted into rats. Mechanical secondary hyperalgesia was induced by repeated intramuscular injections of acidic solution into the gastrocnemius muscle. Gabapentin was administrated intrathecally. Rats were allocated to control and experimental (gabapentin 30, 100, 300, and 1,000 µg) group. After gabapentin administration, mechanical withdrawal threshold was measured every 15 minutes and the motor function was measured 30 minutes later.

RESULTS

Mechanical hyperalgesia was evoked after the second acidic buffer injection. There was a significant improvement on the mechanical threshold after administration of 100, 300, and 1,000 µg gabapentin compared to pre-injection and the control group. The analgesic effect continued for 105, 135, and 210 minutes, respectively. To discern side effects, motor function was measured. Motor function was preserved in both groups after gabapentin administration, except for rats who received 1,000 µg gabapentin.

CONCLUSION

Intrathecal gabapentin administration produces dose-dependent improvements in mechanical hyperalgesia in a persistent muscle pain rat model. This implicates the central nervous system as having a strong influence on the development of persistent mechanical hyperalgesia. These results are helpful in understanding the pathophysiology of secondary hyperalgesia and in the treatment of patients with chronic muscle pain.

Gabapentin in acute postoperative pain management

Gabapentin (1-aminomethyl-cyclohexaneacetic acid) is an amino acid that has the structure of the neurotransmitter γ-aminobutyric acid (GABA). It is a novel drug used for the treatment of postoperative pain with antihyperalgesic properties and a unique mechanism of action. Gabapentin and the related, more potent compound pregabalin have been shown to be beneficial in the treatment of neuropathic pain as well as postoperative pain following spinal surgery and hysterectomy. This study reviews five aspects of gabapentin: (1) chemical and structural characteristics; (2) pharmacokinetics and pharmacodynamics; (3) application in acute pain management; (4) adverse effects; and (5) drug safety. Overall, gabapentin has been reported to be a safe and efficacious drug for the treatment of postoperative pain.

Electrophysiological characterization of spinal neuron sensitization by elevated calcium channel alpha-2-delta-1 subunit protein

BACKGROUND

Voltage-gated calcium channel α2 δ1 subunit is the binding site for gabapentin, an effective drug in controlling neuropathic pain states including thermal hyperalgesia. Hyperalgesia to noxious thermal stimuli in both spinal nerve-ligated (SNL) and voltage-gated calcium channel α2 δ1 overexpressing transgenic (Tg) mice correlates with higher α2 δ1 levels in dorsal root ganglia and dorsal spinal cord. In this study, we investigated whether abnormal synaptic transmission is responsible for thermal hyperalgesia induced by elevated α2 δ1 expression in these models.

METHODS

Behavioural sensitivities to thermal stimuli were test in L4 SNL and sham mice, as well as in α2 δ1 Tg and wild-type mice. Miniature excitatory (mEPSC) and inhibitory (mIPSC) post-synaptic currents were recorded in superficial dorsal spinal cord neurons from these models using whole-cell patch clamp slice recording techniques.

RESULTS

The frequency, but not amplitude, of mEPSC in superficial dorsal horn neurons was increased in SNL and α2 δ1 Tg mice, which could be attenuated by gabapentin dose dependently. Intrathecal α2 δ1 antisense oligodeoxynucleotide treatment diminished increased mEPSC frequency and gabapentin's inhibitory effects in elevated mEPSC frequency in the SNL mice. In contrast, neither the frequency nor the amplitude of mIPSC was altered in superficial dorsal horn neurons from the SNL and α2 δ1 Tg mice.

CONCLUSIONS

Our findings support a role of peripheral nerve injury-induced α2 δ1 in enhancing pre-synaptic excitatory input onto superficial dorsal spinal cord neurons that contributes to nociception development.

Oral gabapentin suppresses pentylenetetrazole-induced seizure-like behavior and cephalic field potential in adult zebrafish

We report the effect of orally administered gabapentin (GBP) on pentylenetetrazole (PTZ)-induced seizure-like activity in adult zebrafish. Zebrafish were pretreated with vehicle or GBP using a novel method of precise oral administration, followed by an intraperitoneal administration of PTZ. Behavioral assessment was carried out using locomotion-based video-tracking analysis and seizure score assignment using visual observation. Cephalic field potential recordings of the zebrafish brain were conducted using an electrical data acquisition system. Orally administered GBP significantly suppressed the seizure-like locomotor activity and strong slow-wave (~3Hz) activity in the cephalic field potential caused by PTZ. This work is the first report of the activity of an orally delivered anticonvulsant in adult zebrafish. Our study provides behavioral and physiological evidence in support of an adult zebrafish model for studying seizures including excitotoxic brain injury and a novel in vivo framework for the evaluation of pharmacological modulators of epilepsy.

The impact of gabapentin administration on brain GABA and glutamate concentrations: a 7T ¹H-MRS study

Gamma-aminobutyric acid (GABA) and glutamate are implicated in numerous neuropsychiatric and substance abuse conditions, but their spectral overlap with other resonances makes them a challenge to quantify in humans. Gabapentin, marketed for the treatment of seizures and neuropathic pain, has been shown to increase in vivo GABA concentration in the brain of both rodents and humans. Gabapentin effects on glutamate are not known. We conducted a gabapentin (900 mg) challenge in healthy human subjects to confirm and explore its effects on GABA and glutamate concentrations, respectively, and to test the ability of single voxel localized proton magnetic resonance spectroscopy (¹H-MRS) to reliably measure GABA and glutamate in the visual cortex at the ultra-high magnetic field of 7 Tesla. Reproducibility of GABA and glutamate measurements was determined in a comparison group without drug twice within day and 2 weeks apart. Although GABA concentration changes were small both within day (average 5.6%) and between day (average 4.8%), gabapentin administration was associated with an average increase in GABA concentration of 55.7% (6.9-91.0%). Importantly, drug-induced change in GABA levels was inversely correlated to the individual's baseline GABA level (R²=0.72). Mean glutamate concentrations did not change significantly with or without drug administration. In conclusion, localized ¹H-MRS at 7 Tesla can be successfully applied to the measurement of GABA concentration and is sensitive to acute drug-induced changes in cortical GABA. Whether baseline GABA concentrations predict clinical efficacy of gabapentin is an area worthy of exploration.

The role of inhibition in oscillatory wave dynamics in the cortex

Cortical oscillations arise during behavioral and mental tasks, and all temporal oscillations have particular spatial patterns. Studying the mechanisms that generate and modulate the spatiotemporal characteristics of oscillations is important for understanding neural information processing and the signs and symptoms of dynamical diseases of the brain. Nevertheless, it remains unclear how GABAergic inhibition modulates these oscillation dynamics. Using voltage-sensitive dye imaging, pharmacological methods, and tangentially cut occipital neocortical brain slices (including layers 3-5) of Sprague-Dawley rat, we found that GABAa disinhibition with bicuculline can progressively simplify oscillation dynamics in the presence of carbachol in a concentration-dependent manner. Additionally, GABAb disinhibition can further simplify oscillation dynamics after GABAa receptors are blocked. Both GABAa and GABAb disinhibition increase the synchronization of the neural network. Theta frequency (5-15-Hz) oscillations are reliably generated by using a combination of GABAa and GABAb antagonists alone. These theta oscillations have basic spatiotemporal patterns similar to those generated by carbachol/bicuculline. These results are illustrative of how GABAergic inhibition increases the complexity of patterns of activity and contributes to the regulation of the cortex.

Adjunctive gabapentin for treatment-resistant insomnia of bipolar disorder: a case report

We report a case with bipolar II disorder having mixed features, in which refractory insomnia persisted. We diagnosed his case as mixed depression with mood fluctuations because increased impulsivity and buying sprees became remarkable, with diminished ability to think or concentrate. Switching to carbamazepine and risperidone improved his mood fluctuations and impulsivity. Nevertheless, his intermittent awakening (fragmentation of the sleep-wake rhythm), related dysfunctional beliefs, anxiety about sleep, and mild impulsivity persisted. The addition of various benzodiazepine sleeping drugs, bromovalerylurea, and antipsychotics did not improve insomnia. His intractable insomnia was markedly responsive to gabapentin, engendering further improvement of mood symptoms. Eventually, its efficacy achieved his reinstatement at work. Results of this case suggest the clinical use of gabapentin for treating bipolar disorder, especially in cases with intractable insomnia, which is a very important point in the symptoms and therapeutics of bipolar disorder.

Elucidating the mechanism of action of pregabalin: α(2)δ as a therapeutic target in anxiety

This review provides a brief summary of what is known about the anxiolytic mechanism of action of pregabalin, a highly selective, high-affinity ligand of the P/Q type of voltage-gated calcium channel (CaV). Evidence from in vivo models of neuronal hyperexcitability suggests that pregabalin reduces synaptic release of neurotransmitters in selected CNS regions including the cortex, olfactory bulb, hypothalamus, amygdala, hippocampus, cerebellum and dorsal horn of the spinal cord. Release of neurotransmitters from the synaptic vesicle, and propagation of neurotransmission, requires the vesicle to fuse with the presynaptic membrane. Pregabalin binding to the α(2)δ type 1 protein of the P/Q type CaV reduces the availability of Ca2+ required for membrane fusion and exocytosis of neurotransmitters. Evidence that the anxiolytic mechanism of action of pregabalin is mediated by binding to the α(2)δ type 1 protein comes from animal models, which have demonstrated a structure-activity relationship between the affinity of ligands for the α(2)δ type 1 protein and their potency in models of anxiety such as the Vogel conflict test. Furthermore, the anxiolytic activity of pregabalin is lost in transgenic mice with specific point mutations in the CaV α(2)δ type 1 protein. Pregabalin-mediated reduction in calcium currents has also been shown to result in a significant inhibition of the release of neurotransmitters implicated in pathological anxiety such as glutamate and monoamine neurotransmitters. However, further research is needed to confirm that these effects contribute to the anxiolytic mechanism of action of pregabalin. Finally, pregabalin may also act by inhibiting synaptogenesis of excitatory neurons formed in response to chronic stress or anxiety, or more acutely inhibit the trafficking of CaV to the plasma membrane.

Gabapentin decreases epileptiform discharges in a chronic model of neocortical trauma

Gabapentin (GBP) is an anticonvulsant that acts at the α2δ-1 submit of the L-type calcium channel. It is recently reported that GBP is a potent inhibitor of thrombospondin (TSP)-induced excitatory synapse formation in vitro and in vivo. Here we studied effects of chronic GBP administration on epileptogenesis in the partial cortical isolation ("undercut") model of posttraumatic epilepsy, in which abnormal axonal sprouting and aberrant synaptogenesis contribute to occurrence of epileptiform discharges. Results showed that 1) the incidence of evoked epileptiform discharges in undercut cortical slices studied 1 day or ~2 weeks after the last GBP dose, was significantly reduced by GBP treatments, beginning on the day of injury; 2) the expression of GFAP and TSP1 protein, as well as the number of FJC stained cells was decreased in GBP treated undercut animals; 3) in vivo GBP treatment of rats with undercuts for 3 or 7 days decreased the density of vGlut1-PSD95 close appositions (presumed synapses) in comparison to saline treated controls with similar lesions;4) the electrophysiological data are compatible with the above anatomical changes, showing decreases in mEPSC and sEPSC frequency in the GBP treated animals. These results indicate that chronic administration of GBP after cortical injury is antiepileptogenic in the undercut model of post-traumatic epilepsy, perhaps by both neuroprotective actions and decreases in excitatory synapse formation. The findings may suggest the potential use of GBP as an antiepileptogenic agent following traumatic brain injury.

Gabapentin inhibits catecholamine release from adrenal chromaffin cells

BACKGROUND

Gabapentin is most commonly prescribed for chronic pain, but acute perioperative effects, including preemptive analgesia and hemodynamic stabilization, have been reported. Adrenal chromaffin cells are a widely used model to investigate neurosecretion, and adrenal catecholamines play important physiologic roles and contribute to the acute stress response. However, the effects of gabapentin on adrenal catecholamine release have never been tested.

METHODS

Primary cultures of bovine adrenal chromaffin cells were treated with gabapentin or vehicle for 18-24 h. The authors quantified catecholamine secretion from dishes of cells using high-performance liquid chromatography and resolved exocytosis of individual secretory vesicles from single cells using carbon fiber amperometry. Voltage-gated calcium channel currents were recorded using patch clamp electrophysiology and intracellular [Ca2+] using fluorescent imaging.

RESULTS

Gabapentin produced statistically significant reductions in catecholamine secretion evoked by cholinergic agonists (24 ± 3%, n = 12) or KCl (16 ± 4%, n = 8) (mean ± SEM) but did not inhibit Ca2+ entry or calcium channel currents. Amperometry (n = 51 cells) revealed that gabapentin inhibited the number of vesicles released upon stimulation, with no change in quantal size or kinetics of these unitary events.

CONCLUSIONS

The authors show Ca2+ entry was not inhibited by gabapentin but was less effective at triggering vesicle fusion. The work also demonstrates that chromaffin cells are a useful model for additional investigation of the cellular mechanism(s) by which gabapentin controls neurosecretion. In addition, it identifies altered adrenal catecholamine release as a potential contributor to some of the beneficial perioperative effects of gabapentin.

Pregabalin reduces alcohol drinking and relapse to alcohol seeking in the rat

RATIONALE

Pregabalin (Lyrica™) is a structural analogue of γ-aminobutyric acid (GABA) approved by FDA for partial epilepsy, neuropathic pain and recently generalized anxiety disorder. While the exact cellular mechanism of action of pregabalin is still unclear, evidence from several studies suggests that it reduces excitatory neurotransmitter release and postsynaptic excitability.

OBJECTIVES

Based on these mechanisms we sought interesting to evaluate the effect of pregabalin on alcohol-abuse-related behaviours.

MATERIALS AND METHODS

For this purpose, using genetically selected alcohol-preferring Marchigian Sardinian (msP) rats, we evaluated the effect of pregabalin on alcohol drinking and relapse to alcohol seeking elicited by environmental conditioning factors or stress.

RESULTS

Our results showed that treatment with pregabalin (0, 10, 30 and 60 mg/kg) given orally selectively reduced home cage alcohol drinking in msP rat. This effect was confirmed in self-administration experiments where pregabalin (0, 10 and 30 mg/kg) significantly reduced operant responding for alcohol but not for food. Using alcohol reinstatement models we also found that pregabalin (0, 10 and 30 mg/kg) abolished seeking behaviour elicited by the pharmacological stressor yohimbine as well as cues predictive of alcohol availability.

CONCLUSIONS

Results demonstrate that pregabalin may have potential in the treatment of alcohol addiction.

Prevention of chronic pain after surgical nerve injury: amputation and thoracotomy

Although techniques for acute pain management have improved in recent years, a dramatic reduction in the incidence and severity of chronic pain following surgery has not occurred. Amputation and thoracotomy, although technically different, share the commonalities of unavoidable nerve injury and the frequent presence of persistent postsurgical neuropathic pain. The authors review the risk factors for the development of chronic pain following these surgeries and the current evidence that supports analgesic interventions. The inconclusive results from many preemptive analgesic studies may require us to reconceptualize the perioperative treatment period as a time of gradual neurologic remodeling.

Levetiracetam: a review of its use in epilepsy

Levetiracetam (Keppra®, E Keppra®) is an established second-generation antiepileptic drug (AED). Worldwide, levetiracetam is most commonly approved as adjunctive treatment of partial onset seizures with or without secondary generalization; other approved indications include monotherapy treatment of partial onset seizures with or without secondary generalization, and adjunctive treatment of myoclonic seizures associated with juvenile myoclonic epilepsy and primary generalized tonic-clonic (GTC) seizures associated with idiopathic generalized epilepsy. Levetiracetam has a novel structure and unique mechanisms of action. Unlike other AEDs, the mechanisms of action of levetiracetam appear to involve neuronal binding to synaptic vesicle protein 2A, inhibiting calcium release from intraneuronal stores, opposing the activity of negative modulators of GABA- and glycin-gated currents and inhibiting excessive synchronized activity between neurons. In addition, levetiracetam inhibits N-type calcium channels. Levetiracetam is associated with rapid and complete absorption, high oral bioavailability, minimal metabolism that consists of hydrolysis of the acetamide group, and primarily renal elimination. It lacks cytochrome P450 isoenzyme-inducing potential and is not associated with clinically significant pharmacokinetic interactions with other drugs, including other AEDs. The efficacy of oral immediate-release levetiracetam in controlling seizures has been established in numerous randomized, double-blind, controlled, multicentre trials in patients with epilepsy. Adjunctive levetiracetam reduced the frequency of seizures in paediatric and adult patients with refractory partial onset seizures to a significantly greater extent than placebo. Monotherapy with levetiracetam was noninferior to that with carbamazepine controlled release in controlling seizures in patients with newly diagnosed partial onset seizures. Levetiracetam also provided seizure control relative to placebo as adjunctive therapy in patients with idiopathic generalized epilepsy with myoclonic seizures or GTC seizures. In addition, patients receiving oral levetiracetam showed improvements in measures of health-related quality of life relative to those receiving placebo. Although treatment-emergent adverse events were commonly reported in the clinical trials of levetiracetam, the overall proportion of patients who experienced at least one treatment-emergent adverse event was broadly similar in the levetiracetam and placebo treatment groups, with most events being mild to moderate in severity. Levetiracetam is not associated with cognitive impairment or drug-induced weight gain, but has been associated with behavioural adverse effects in some patients.