Gabapentin, ineffective in normal rats, markedly reduces C-fibre evoked responses after inflammation

Influence of the descending pain-inhibiting serotonergic pathway on the antihyperalgesic effect of gabapentin in neuropathic pain model rats

Gabapentinoids are used worldwide as first-line agents for the treatment of neuropathic pain. Accumulating evidence indicates that one of the antihyperalgesic mechanisms of gabapentinoids is through activation of the noradrenergic pathway of the descending pain inhibition system. However, the involvement of the serotonin pathway is unclear. We investigated the effects of gabapentin (GBP) on the serotonergic pathway of the descending inhibitory system using the spinal nerve ligation (SNL) rat model. As in previous reports, administration of GBP to SNL rats improved paw withdrawal thresholds (PWT). Intrathecally administered serotonin receptor antagonists abolished GBP's amelioration in PWT. GBP did not ameliorate PWT in noradrenaline-depleted SNL rats by DSP-4. However, GBP ameliorated PWT in serotonin-depleted SNL rats by para-chlorophenylalanine, which was not inhibited by intrathecal administration of a serotonin receptor antagonist. Immunohistochemical analysis of serotonin in the spinal dorsal horn revealed a slight, albeit statistically insignificant, increase in 5-HT levels in SNL rats compared to naive rats. However, no apparent changes were observed before or after GBP administration in naive and SNL rats. In conclusion, the involvement of the serotonergic pathway in the antihyperalgesic effects of GBP on the spinal cord is secondary, although it cooperates with the noradrenergic system to produce analgesia.

Anesthetic considerations for urologic surgeries

Urologic surgeries are widely performed, and the cases have increased owing to the fact that the elderly population is growing. The narrow and limited surgical space is a challenge in performing most urologic surgeries. Additionally, the elderly population is exposed to the risk of perioperative complications; therefore, a comprehensive understanding and approach are required to provide optimized anesthesia during surgery. We have searched the literature on anesthesia for urologic surgeries and summarized the anesthetic considerations for urologic surgeries.

Gabapentin-Associated Urinary Incontinence: A Case Verified by Rechallenge

INTRODUCTION

Gabapentin (GBP) is an analog of γ-aminobutyric acid and was originally designed as an anticonvulsant. Because its mechanism of action is unclear, assumed to have no abuse potential, and apparent lack of toxicity, GBP is used widely off-label to treat an array of disorders, including essential tremor.

CASE REPORT

We present a case of an elderly woman diagnosed with essential tremor, in which GBP was initiated. In the following day, she complained of urinary incontinence with the absence of dysuria and urgency. It was not worse with movement, coughing, sneezing, or laughing. The vaginal parity of the patient was one. Laboratory tests and urinalysis were within normal limits. Assuming that the urinary symptom was an adverse drug reaction, the GBP was withdrawn and the patient's incontinence completely resolved within 2 days. Several weeks later, a rechallenge with GBP was tried. In the day 1 of GBP use, the subject reported intermittent urinary incontinence. Medication was discontinued and her continence returned. One year later, in the follow-up, the subject remained continent.

CONCLUSIONS

Only a few cases with GBP-associated urinary incontinence have been reported in the literature. To the authors' knowledge, these cases described individuals with only 1 attempt of the use of GBP. In this way, the present case was the first to describe a subject with the recurrence of urinary incontinence with the GBP rechallenge. This adverse effect, although not potentially fatal, can be very embarrassing to patients and lead to poor compliance with therapy.

Antiepileptic drugs as analgesics/adjuvants in inflammatory pain: current preclinical evidence

Inflammatory pain is the most common type of pain that is treated clinically. The use of currently available treatments (classic analgesics - NSAIDs, paracetamol and opioids) is limited by insufficient efficacy and/or side effects/tolerance development. Antiepileptic drugs (AEDs) are widely used in neuropathic pain treatment, but there is substantial preclinical evidence on their efficacy against inflammatory pain, too. In this review we focus on gabapentinoids (gabapentin and pregabalin) and dibenzazepine AEDs (carbamazepine, oxcarbazepine, and recently introduced eslicarbazepine acetate) and their potential for relieving inflammatory pain. In models of somatic, visceral and trigeminal inflammatory pain, that have a translational value for inflammatory conditions in locomotor system, viscera and head/face, AEDs have demonstrated analgesic activity. This activity was mostly consistent, dependent on the dose and largely independent on the site of inflammation and method of its induction, nociceptive stimuli, species, specific drug used, its route of administration and dosing schedule. AEDs exerted comparable efficacy with classic analgesics. Effective doses of AEDs are lower than toxic doses in animals and, when expressed as equivalent human doses, they are largely overlapping with AEDs doses already used in humans for treating epilepsy/neuropathic pain. The main mechanism of antinociceptive/antihyperalgesic action of gabapentinoids in inflammatory pain models seems to be α₂δ-dependent suppression of voltage-gated calcium channels in primary sensory neurons that leads to reduced release of neurotransmitters in the spinal/medullar dorsal horn. The suppression of NMDA receptors via co-agonist binding site primarily at spinal sites, activation of various types of K⁺ channels at spinal and peripheral sites, and activation of noradrenergic and serotonergic descending pain modulatory pathways may also contribute. Inhibition of voltage-gated sodium channels along the pain pathway is probably the main mechanism of antinociceptive/antihyperalgesic effects of dibenzazepines. The recruitment of peripheral adrenergic and purinergic mechanisms and central GABAergic mechanisms may also contribute. When co-administered with classic/other alternative analgesics, AEDs exerted synergistic/additive interactions. Reviewed data could serve as a basis for clinical studies on the efficacy/safety of AEDs as analgesics/adjuvants in patients with inflammatory pain, and contribute to the improvement of the treatment of various inflammatory pain states.

Injury-induced maladaptation and dysregulation of calcium channel α2 δ subunit proteins and its contribution to neuropathic pain development

Voltage-gated calcium channels (VGCCs) play important roles in physiological functions including the modulation of neurotransmitter release, neuronal network activities, intracellular signalling pathways and gene expression. Some pathological conditions, including nerve injuries, can cause the dysregulation of VGCCs and their subunits. This in turn can lead to a functional maladaptation of VGCCs and their subunits, which can contribute to the development of disorders such as pain sensations. This review has summarized recent findings related to maladaptive changes in the dysregulated VGCC α2 δ1 subunit (Cav α2 δ1 ) with a focus on exploring the mechanisms underlying the contribution of Cav α2 δ1 to pain signal transduction. At least under neuropathic pain conditions, the dysregulated Cav α2 δ1 can modulate VGCC functions as well as other plasticity changes. The latter includes abnormal excitatory synaptogenesis resulting from its interactions with injury-induced extracellular matrix glycoprotein molecule thrombospondins, which is independent of the VGCC functions. Blocking Cav α2 δ1 with gabapentinoids can reverse neuropathic pain significantly with relatively mild side effects, but only in a small population of neuropathic pain patients due to reasons yet to be explored. There are emerging data suggesting that early preventive treatment with gabapentinoids can prevent aberrant excitatory synapse formation and the development of chronic pain. If these findings are confirmed clinically, this could be an attractive approach for neuropathic pain management.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Central Mechanisms Mediating Thrombospondin-4-induced Pain States

Peripheral nerve injury induces increased expression of thrombospondin-4 (TSP4) in spinal cord and dorsal root ganglia that contributes to neuropathic pain states through unknown mechanisms. Here, we test the hypothesis that TSP4 activates its receptor, the voltage-gated calcium channel Cavα2δ1 subunit (Cavα2δ1), on sensory afferent terminals in dorsal spinal cord to promote excitatory synaptogenesis and central sensitization that contribute to neuropathic pain states. We show that there is a direct molecular interaction between TSP4 and Cavα2δ1 in the spinal cord in vivo and that TSP4/Cavα2δ1-dependent processes lead to increased behavioral sensitivities to stimuli. In dorsal spinal cord, TSP4/Cavα2δ1-dependent processes lead to increased frequency of miniature and amplitude of evoked excitatory post-synaptic currents in second-order neurons as well as increased VGlut2- and PSD95-positive puncta, indicative of increased excitatory synapses. Blockade of TSP4/Cavα2δ1-dependent processes with Cavα2δ1 ligand gabapentin or genetic Cavα2δ1 knockdown blocks TSP4 induced nociception and its pathological correlates. Conversely, TSP4 antibodies or genetic ablation blocks nociception and changes in synaptic transmission in mice overexpressing Cavα2δ1 Importantly, TSP4/Cavα2δ1-dependent processes also lead to similar behavioral and pathological changes in a neuropathic pain model of peripheral nerve injury. Thus, a TSP4/Cavα2δ1-dependent pathway activated by TSP4 or peripheral nerve injury promotes exaggerated presynaptic excitatory input and evoked sensory neuron hyperexcitability and excitatory synaptogenesis, which together lead to central sensitization and pain state development.

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.

Ligands Binding to Cell Surface Ganglioside GD2 Cause Src-Dependent Activation of N-Methyl-D-Aspartate Receptor Signaling and Changes in Cellular Morphology

Ganglioside GD2 is a plasma membrane glycosphinogolipid. In healthy adults it is expressed at low levels, but it is over-expressed in many cancers. For cancer therapy, GD2 is targeted with anti-GD2 monoclonal antibodies (mAbs), and one adverse side effect is severe visceral pain. Pain is not neuropathic, cannot be blocked with morphine, and stops on discontinuation of mAb therapy. Here, we provide evidence that ligand binding to cell surface GD2 induces rapid and transient activation of Src-family kinases, followed by Src-dependent phosphorylation of NMDA-receptor NR2B subunits selectively, activation of Ca++ fluxes, production of cAMP, and changes in cellular morphology. These GD2-ligand activated signals differ in kinetics and in pharmacology from activation of the same signals in the same cells by BDNF, the growth factor agonist of the TrkB receptor, suggesting biological specificity. Hence, cell surface GD2 regulates pathways that can be associated with neoplasia and with morphine-intractable pain; and this can explain why expression of GD2 correlates with these two pathologies.

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.

Neuraxial opioid-induced pruritus: An update

Pruritus is a troublesome side-effect of neuraxial (epidural and intrathecal) opioids. Sometimes it may be more unpleasant than pain itself. The prevention and treatment still remains a challenge. A variety of medications with different mechanisms of action have been used for the prevention and treatment of opioid-induced pruritus, with mixed results. The aim of this article is to review the current body of literature and summarize the current understanding of the mechanisms and the pharmacological therapies available to manage opioid-induced pruritus. The literature source of this review was obtained via PubMed, Medline and Cochrane Database of Systematic Reviews until 2012. The search results were limited to the randomized controlled trials, systemic reviews and non-systemic reviews.

Calcium channel α2δ1 proteins mediate trigeminal neuropathic pain states associated with aberrant excitatory synaptogenesis

To investigate a potential mechanism underlying trigeminal nerve injury-induced orofacial hypersensitivity, we used a rat model of chronic constriction injury to the infraorbital nerve (CCI-ION) to study whether CCI-ION caused calcium channel α2δ1 (Cavα2δ1) protein dysregulation in trigeminal ganglia and associated spinal subnucleus caudalis and C1/C2 cervical dorsal spinal cord (Vc/C2). Furthermore, we studied whether this neuroplasticity contributed to spinal neuron sensitization and neuropathic pain states. CCI-ION caused orofacial hypersensitivity that correlated with Cavα2δ1 up-regulation in trigeminal ganglion neurons and Vc/C2. Blocking Cavα2δ1 with gabapentin, a ligand for the Cavα2δ1 proteins, or Cavα2δ1 antisense oligodeoxynucleotides led to a reversal of orofacial hypersensitivity, supporting an important role of Cavα2δ1 in orofacial pain processing. Importantly, increased Cavα2δ1 in Vc/C2 superficial dorsal horn was associated with increased excitatory synaptogenesis and increased frequency, but not the amplitude, of miniature excitatory postsynaptic currents in dorsal horn neurons that could be blocked by gabapentin. Thus, CCI-ION-induced Cavα2δ1 up-regulation may contribute to orofacial neuropathic pain states through abnormal excitatory synapse formation and enhanced presynaptic excitatory neurotransmitter release in Vc/C2.

Presynaptic inhibitory actions of pregabalin on excitatory transmission in superficial dorsal horn of mouse spinal cord: further characterization of presynaptic mechanisms

Pregabalin is widely used as an analgesic for the treatment of neuropathic pain. In the present experiments using mouse spinal slices, we recorded electrically evoked glutamatergic excitatory postsynaptic currents (eEPSCs) from superficial dorsal horn neurons. Pregabalin reduced the amplitude of eEPSCs, and increased the paired pulse ratio. Pregabalin also inhibited the frequency of spontaneously occurring miniature EPSCs without affecting their amplitude. Partial ligation of the sciatic nerve increased the expression of the calcium channel α2δ-1 subunit, and increased the presynaptic inhibitory action of pregabalin. Intrathecal injection of antisense oligodeoxynucleotide against the α2δ-1 subunit, decreased the expression of α2δ-1 mRNA in the spinal dorsal horn, and decreased pregabalin's action. These results provide further evidence that pregabalin exerts its presynaptic inhibitory action via binding with the α2δ subunit in a state-dependent manner. Furthermore, presynaptic actions of pregabalin were attenuated in knockout mice lacking the protein syntaxin 1A, a component of the synaptic vesicle release machinery, indicating that syntaxin 1A is required for pregabalin to exert its full presynaptic inhibitory action. These observations might suggest that direct and/or indirect interactions with the presynaptic proteins composing the release machinery underlie at least some part of pregabalin's presynaptic actions.

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.

Gabapentin alleviates facet-mediated pain in the rat through reduced neuronal hyperexcitability and astrocytic activation in the spinal cord

Although joint pain is common, its mechanisms remain undefined, with little known about the spinal neuronal responses that contribute to this type of pain. Afferent activity and sustained spinal neuronal hyperexcitability correlate to facet joint loading and the extent of behavioral sensitivity induced after painful facet injury, suggesting that spinal neuronal plasticity is induced in association with facet-mediated pain. This study used a rat model of painful C6-C7 facet joint stretch, together with intrathecal administration of gabapentin, to investigate the effects of one aspect of spinal neuronal function on joint pain. Gabapentin or saline vehicle was given via lumbar puncture prior to and at 1 day after painful joint distraction. Mechanical hyperalgesia was measured in the forepaw for 7 days. Extracellular recordings of neuronal activity and astrocytic and microglial activation in the cervical spinal cord were evaluated at day 7. Gabapentin significantly (P = .0001) attenuated mechanical hyperalgesia, and the frequency of evoked neuronal firing also significantly decreased (P < .047) with gabapentin treatment. Gabapentin also decreased (P < .04) spinal glial fibrillary acidic protein expression. Although spinal Iba1 expression was doubled over sham, gabapentin did not reduce it. Facet joint-mediated pain appears to be sustained through spinal neuronal modifications that are also associated with astrocytic activation.

PERSPECTIVE

Intrathecal gabapentin treatment was used to investigate behavioral, neuronal, and glial response in a rat model of painful C6-C7 facet joint stretch. Gabapentin attenuated mechanical hyperalgesia, reduced evoked neuronal firing, and decreased spinal astrocytic activation. This study supports that facet joint pain is sustained through spinal neuronal and astrocytic activation.

Voltage gated sodium and calcium channel blockers for the treatment of chronic inflammatory pain

The inflammatory response is a natural response of the body that occurs immediately following tissue damage, which may be due to injury, infection or disease. The acute inflammatory response is an essential mechanism that promotes healing and a key aspect is the ensuing pain, which warns the subject to protect the site of injury. Thus, it is common to see a zone of primary sensitization as well as consequential central sensitization that generally, is maintained by a peripheral drive from the zone of tissue injury. Inflammation associated with chronic pain states, such as rheumatoid and osteoarthritis, cancer and migraine etc. is deleterious to health and often debilitating for the patient. Thus there is a large unmet clinical need. The mechanisms underlying both acute and chronic inflammatory pain are extensive and complex, involving a diversity of cell types, receptors and proteins. Among these the contribution of voltage gated sodium and calcium channels on peripheral nociceptors is critical for nociceptive transmission beyond the peripheral transducers and changes in their distribution, accumulation, clustering and functional activities have been linked to both inflammatory and neuropathic pain. The latter has been the main area for trials and use of drugs that modulate ion channels such as carbamazepine and gabapentin, but given the large peripheral drive that follows tissue damage, there is a clear rationale for blocking voltage gated sodium and calcium channels in these pain states. It has been hypothesized that pain of inflammatory origin may evolve into a condition that resembles neuropathic pain, but mixed pains such as low back pain and cancer pain often include elements of both pain states. This review considers the therapeutic potential for sodium and calcium channel blockers for the treatment of chronic inflammatory pain states.

Pregabalin suppresses nociceptive behavior and central sensitization in a rat trigeminal neuropathic pain model

The aim of this study was to determine whether pregabalin affects nociceptive behavior and central sensitization in a trigeminal neuropathic pain model. A partial infraorbital nerve transection (p-IONX) or sham operation was performed in adult male rats. Nociceptive withdrawal thresholds were tested with von Frey filaments applied to the bilateral vibrissal pads pre- and postoperatively. On postoperative day 7, the behavioral assessment was conducted before and at 30, 60, 120, and 180 minutes after and 24 hours after pregabalin (.1, 1, 10, 100 mg/kg intraperitoneally) or saline injection. The effects of pregabalin or saline were also examined on the mechanoreceptive field and response properties of nociceptive neurons recorded in the medullary dorsal horn at postoperative days 7 to 10. Reduced withdrawal thresholds reflecting bilateral mechanical allodynia were observed in p-IONX rats until postoperative day 28, but not in sham-operated rats. At postoperative day 7, pregabalin significantly and dose-dependently reversed the reduced mechanical withdrawal thresholds in p-IONX rats. Pregabalin also attenuated central sensitization of the neurons, as reflected in reversal of their reduced activation threshold, increased responses to pinch/pressure, and enhanced stimulus-response function. This study provides the first documentation that pregabalin attenuates the mechanical allodynia and central sensitization that characterize this trigeminal neuropathic pain model, and supports its clinical use for treating craniofacial neuropathic pain.

PERSPECTIVE

Trigeminal nerve injury in rats produced facial mechanical hypersensitivity and trigeminal central sensitization of medullary dorsal horn neurons that were markedly attenuated by systemically administered pregabalin, suggesting its potential clinical utility for orofacial neuropathic pain.

Gabapentin: a novel drug as add-on therapy in cases of refractory overactive bladder in children

OBJECTIVE

To determine the effectiveness of gabapentin as an add-on therapy in children presenting with overactive bladder (OAB) not responding to conventional anticholinergics.

MATERIALS AND METHODS

Children with refractory OAB were included prospectively from March 2009 to February 2010. The inclusion criterion was persistence of symptoms while on conventional anticholinergics for 6 months. Gabapentin was prescribed as an add-on therapy. The patients were followed 4 weekly with bladder diary and urodynamic study was repeated at 3 months.

RESULTS

There were 31 children, 26 of neurogenic OAB and 5 of non-neurogenic origin. Mean ± SD age was 8.5 ± 5.3 years. Data were analyzed in 30 patients as treatment was terminated in 1 due to adverse effects. Continence improved in 16 (53.3%) patients. Voiding volume improved from 175 ± 90 to 320 ± 110 ml (p<0.03). Objective assessment of OAB symptom relief showed marked improvement (p<0.05). Mean maximum cystometric bladder capacity improved from 210 ± 94 to 360 ± 110 ml (p<0.02). The maximal detrusor contraction decreased from 75 ± 35 to 25 ± 15 cmH(2)O (p<0.02). Fourteen patients (46.7%) failed to respond to gabapentin therapy. These patients had baseline maximum cystometric bladder capacity <60% for age and maximum detrusor contractions >50 cm of water (p<0.03).

CONCLUSIONS

Gabapentin gives moderate results in children with OAB refractory to conventional anticholinergics. In general, the drug is well tolerated with fewer adverse effects.

A novel model of combined neuropathic and inflammatory pain displaying long-lasting allodynia and spontaneous pain-like behaviour

Many clinical cases of chronic pain exhibit both neuropathic and inflammatory components. In contrast, most animal models of chronic pain focus on one type of injury alone. Here we present a novel combined model of both neuropathic and inflammatory pain and characterise its distinctive properties. This combined model of chronic constriction injury (CCI) and intraplantar Complete Freund's Adjuvant (CFA) injection results in enhanced mechanical allodynia, thermal hyperalgesia, a static weight bearing deficit, and notably pronounced spontaneous foot lifting (SFL) behaviour (which under our conditions was not seen in either individual model and may reflect ongoing/spontaneous pain). Dorsal root ganglion (DRG) expression of Activating Transcription Factor-3 (ATF-3), a marker of axonal injury, was no greater in the combined model than CCI alone. Initial pharmacological characterisation of the new model showed that the SFL was reversed by gabapentin or diclofenac, typical analgesics for neuropathic or inflammatory pain respectively, but not by mexiletine, a Na(+) channel blocker effective in both neuropathic and inflammatory pain models. Static weight bearing deficit was moderately reduced by gabapentin, whereas only diclofenac reversed mechanical allodynia. This novel animal model of chronic pain may prove a useful test-bed for further analysing the pharmacological susceptibility of complicated clinical pain states.

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.

Randomised clinical trial: pregabalin attenuates experimental visceral pain through sub-cortical mechanisms in patients with painful chronic pancreatitis

BACKGROUND

Pregabalin has a broad spectrum of analgesic and antihyperalgesic activity in both basic and clinical studies. However, its mechanisms and sites of action have yet to be determined in humans.

AIMS

To assess the antinociceptive effect of pregabalin on experimental gut pain in patients with visceral hyperalgesia due to chronic pancreatitis and to reveal putative changes in corresponding central pain processing as assessed by evoked brain potentials.

METHODS

Thirty-one patients were randomly assigned to receive increasing doses of pregabalin or placebo for three consecutive weeks. Perceptual thresholds to electrical stimulation of the sigmoid with recording of corresponding evoked brain potentials were obtained at baseline and study end. The brain source localisations reflecting direct neuronal activity were fitted by a five-dipole model projected to magnetic resonance imaging of the individuals' brains.

RESULTS

As compared to placebo, pregabalin significantly increased the pain threshold to electrical gut stimulation from baseline (P=0.02). No differences in evoked brain potential characteristics were seen, neither after pregabalin nor placebo treatment (all P>0.05). In agreement with this, brain source locations remained stable during study treatment (all P>0.05).

CONCLUSION

Pregabalin was superior to placebo for attenuation of experimental visceral pain in chronic pancreatitis patients. We suggest its antinociceptive effects to be mediated primarily through sub-cortical mechanisms.

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.

Pregabalin modulation of spinal and brainstem visceral nociceptive processing

Brainstem and spinal mechanisms mediating visceral nociception are investigated here using electrophysiology and immunohistochemistry techniques in a model of acute visceral pain. Colorectal distension (CRD) produced graded visceromotor responses (VMR) in normal rats, and these were facilitated by intracolonic mustard oil (MO) that generated acute visceral hyperalgesia. The neuropathic pain drug pregabalin (PGB) is thought to have state-dependent effects in attenuating neuropathic, but not acute somatic pain, likely by impairing calcium-channel trafficking. We found that systemic PGB produced antinociceptive effects on CRD-evoked VMRs in naïve rats lacking pathophysiology and in MO-pretreated rats. Systemic PGB also significantly reduced Fos labelling in lumbosacral spinal cords of rats given noxious repetitive CRD; however, PGB did not alter this measure of neural activity in the brainstem. Differential brainstem processing of noxious somatic and visceral stimuli may underlie the unique lack of state-dependent actions of PGB in this visceral pain model. Single-unit recordings in the rostral ventromedial medulla (RVM) verify that brainstem processing of somatic and visceral stimuli differs. The effects of CRD on RVM cells classed as ON, OFF, or NEUTRAL were independent of their somatic responses, with surprising changes in RVM cell activity to innocuous visceral stimulation. PGB also markedly reduced the visceral responses of RVM ON-cells to noxious CRD. These results illustrate clear differences in the central processing of visceral and somatic stimuli, yet a common role for descending modulation by brainstem activity in mediating evoked pain measures.

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.

Antagonism of 5-HT(2A) receptors inhibits the expression of pronociceptive mediator and enhances endogenous opioid mechanism in carrageenan-induced inflammation in rats

We have recently reported that treatment with the 5-HT(2A) receptor antagonist ketanserin in the inflamed paw raises the nociceptive threshold above normal level (hypoalgesia) and this response is naloxone-reversible. The present study aimed to investigate neurochemical changes at the site of inflammation and in dorsal root ganglia (DRG) and the spinal cord following the blockade of 5-HT(2A) receptors. Intraplantar injection of ketanserin (20 μg) inhibited carrageenan-induced increase in CGRP immunoreactivity-positive neurons in DRG. On the other hand, administration of ketanserin (20 μg) and 5-HT (10 μg), but not vehicle, enhanced and inhibited recruitment of β-endorphin-expressing immune cells, respectively, in subcutaneous loci of inflamed hindpaw. Moreover, the treatment with ketanserin increased the number of endomorphine-containing cells in the inflamed paw and μ-opioid receptor-expressing neurons in DRG at L4-5 but reduced the expression of endomorphine in superficial layers of the lumbar spinal cord. The present study provided evidence at the cellular level showing that the blockade of 5-HT(2A) receptors inhibited inflammation-associated increase in pronociceptive mediator, and that the pronociceptive property of 5-HT is mediated by the suppression of inflammation-activated opioid mechanism. Therefore, targeting the 5-HT(2A) receptors in the site of inflammation may be a promising approach to inhibit inflammatory pain.

Preclinical and early clinical investigations related to monoaminergic pain modulation

The balance between descending controls, both excitatory and inhibitory, can be altered in various pain states. There is good evidence for a prominent alpha(2)-adrenoceptor-mediated inhibitory system and 5-HT(3) (and likely also 5-HT(2)) serotonin receptor-mediated excitatory controls originating from brainstem and midbrain areas. The ability of cortical controls to influence spinal function allows for top-down processing through these monoamines. The links between pain and the comorbidities of sleep problems, anxiety, and depression may be due to the dual roles of noradrenaline and of 5-HT in these functions and also in pain. These controls appear, in the cases of peripheral neuropathy, spinal injury, and cancer-induced bone pain to be driven by altered peripheral and spinal neuronal processes; in opioid-induced hyperalgesia, however, the same changes occur without any pathophysiological peripheral process. Thus, in generalized pain states in which fatigue, mood changes, and diffuse pain occur, such as fibromyalgia and irritable bowel syndrome, one could suggest an abnormal engagement of descending facilitations with or without reduced inhibitions but with central origins. This would be an endogenous central malfunction of top-down processing, with the altered monoamine systems underlying the observed symptoms. A number of analgesic drugs can either interact with or have their actions modulated by these descending systems, reinforcing their importance in the establishment of pain but also in its control.

Effect of antiepileptic agent, levetiracetam, on urodynamic parameters and neurogenic bladder overactivity in chronically paraplegic rats

OBJECTIVES

To investigate the effects of different levetiracetam (LEV) doses on urodynamic parameters in an animal model of neurogenic detrusor overactivity (NDO).

METHODS

A total of 54 female rats were studied. Of the 54 rats, 6 served as normal controls, and 48 underwent T10 spinal cord transection (SCT). Of the latter 48 rats, 12 were paraplegic controls, and the remaining 36 rats were divided into 3 equal subgroups that received LEV by way of a subcutaneous osmotic minipump at a dose of 17, 54, and 108 mg/kg daily, respectively. The paraplegic control and treatment groups were further subdivided (n = 6), and cystometry was performed at 3 and 4 weeks after SCT, respectively.

RESULTS

All paraplegic controls developed NDO, with spontaneous contractions. At 3 and 4 weeks after SCT, the mean frequency of the contractions was 1.6 +/- 0.3/min and 1.7 +/- 0.2/min. The contraction amplitude and bladder capacity were not significantly different. After 1 week of LEV treatment, these urodynamic parameters improved significantly in a dose-dependent manner, and the changes were more striking at 2 weeks. At a LEV dosage of 17, 54, and 108 mg/kg, respectively, the NDO frequency increased from 1.7 +/- 0.3 to 0.7 +/- 0.2 contractions/min (P = .01), 0.48 +/- 0.16 contractions/min (P = .009), and 0.5 +/- 0.17 contractions/min (P = .01). The bladder capacity increased from 0.51 +/- 0.1 mL to 1.5 +/- 0.2 mL (P = .0001), 2.5 +/- 1.7 mL (P = .006), and 2.6 +/- 0.3 mL (P = .0003), and the micturition pressure improved from 105.8 +/- 6.9 to 73.8 +/- 6.8 cm H(2)O (P = .01), 58.6 +/- 8.9 cm H(2)O (P = .006), and 49.7 +/- 8.9 cm H(2)O (P = .002).

CONCLUSIONS

The results of our study have shown that LEV is an effective treatment of NDO after SCT in rats. It might prove to be a novel, alternative therapeutic approach to NDO. The follow-up of these experimental results with a clinical trial is warranted.

Mechanisms of pain in nonmalignant disease

PURPOSE OF REVIEW

To review key mechanisms underlying the transmission of nociceptive information from the periphery to the central nervous system implicated in different acute pain states.

RECENT FINDINGS

Advances in molecular and transgenic approaches have helped to identify novel therapeutic targets for the treatment of pain from tissue and nerve damage such as acid-sensing ion channels, transient receptor potential and NaV channels. The subsequent development of selective pharmacological ligands has also strengthened the role of other receptors such as hyperpolarization-activated cyclic nucleotide-gated channels and the further development of subunit specific antagonists, such as those available for NR2B, will further advance our understanding of the mechanisms involved in nociceptive transmission.

SUMMARY

Inflammatory and neuropathic pain differ considerably in their peripheral mechanisms but certain central spinal and brain mechanisms are common to both. The mechanisms of pain are not fully established but are thought to be underpinned by changes in the expression of receptors (nociceptive plasticity), central spinal hyperexcitability (central sensitization) and alterations in descending control from the midbrain. This review considers these mechanisms and highlights recent advances in the understanding of pain perception.

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.

The antinociceptive effect of systemic gabapentin is related to the type of sensitization-induced hyperalgesia

Background

Gabapentin is a structural analogue of gamma-aminobutyric acid with strong anticonvulsant and analgesic activities. Important discrepancies are observed on the effectiveness and potency of gabapentin in acute nociception and sensitization due to inflammation and neuropathy. There is also some controversy in the literature on whether gabapentin is only active in central areas of the nervous system or is also effective in the periphery. This is probably due to the use of different experimental models, routes of administration and types of sensitization. The aim of the present study was to investigate the influence of the spinal cord sensitization on the antinociceptive activity of gabapentin in the absence and in the presence of monoarthritis and neuropathy, using the same experimental protocol of stimulation and the same technique of evaluation of antinociception.

Methods

We studied the antinociceptive effects of iv. gabapentin in spinal cord neuronal responses from adult male Wistar rats using the recording of single motor units technique. Gabapentin was studied in the absence and in the presence of sensitization due to arthritis and neuropathy, combining noxious mechanical and repetitive electrical stimulation (wind-up).

Results

The experiments showed that gabapentin was effective in arthritic (max. effect of 41 ± 15% of control and ID50 of 1,145 ± 14 micromol/kg; 200 mg/kg) and neuropathic rats (max. effect of 20 ± 8% of control and ID50 of 414 ± 27 micromol/kg; 73 mg/kg) but not in normal rats. The phenomenon of wind-up was dose-dependently reduced by gabapentin in neuropathy but not in normal and arthritic rats.

Conclusion

We conclude that systemic gabapentin is a potent and effective antinociceptive agent in sensitization caused by arthritis and neuropathy but not in the absence of sensitization. The potency of the antinociception was directly related to the intensity of sensitization in the present experimental conditions. The effect is mainly located in central areas in neuropathy since wind-up was significantly reduced, however, an action on inflammation-induced sensitized nociceptors is also likely.

Pregabalin reduces muscle and cutaneous hyperalgesia in two models of chronic muscle pain in rats

Pregabalin is used for treatment of neuropathic pain conditions. The present study evaluated effects of pregabalin in 2 rat models of muscle-induced hyperalgesia: Inflammatory and noninflammatory. Muscle hyperalgesia (withdrawal threshold to compression of the muscle) and cutaneous hyperalgesia of the paw (withdrawal threshold to von Frey filaments) were measured before and after induction of hyperalgesia and after treatment with pregabalin (saline, 10 to 100 mg/kg i.p.). In the inflammatory model, 3% carrageenan injected into 1 gastrocnemius muscle decreased the mechanical withdrawal threshold of the paw bilaterally and the compression withdrawal threshold of the muscle ipsilaterally 2 weeks later. Pregabalin (10 to 100 mg/kg) increased the compression withdrawal threshold of the inflamed muscle when compared with vehicle controls. Pregabalin also increased the mechanical withdrawal threshold of the paw bilaterally, but only with 100 mg/kg. In the noninflammatory model, 2 unilateral injections of acidic saline into the gastrocnemius muscle produced bilateral cutaneous and muscle hyperalgesia 24 hours after the second injection. Pregabalin (10 to 100 mg/kg i.p.) significantly increased the compression withdrawal thresholds of the muscle and the mechanical withdrawal threshold of the paw bilaterally when compared with vehicle. However, pregabalin also has significant motor effects at the higher doses (60 to 100 mg/kg). Therefore, pregabalin reduces both muscle and cutaneous hyperalgesia that occurs after muscle insult in 2 animal models of muscle pain at doses that do not produce ataxia.

PERSPECTIVE

This study shows that pregabalin reduces both cutaneous and muscle hyperalgesia in inflammatory and noninflammatory models of muscle pain. Thus, pregabalin may be an effective treatment for people with chronic muscle pain.

Premedication with gabapentin: the effect on tourniquet pain and quality of intravenous regional anesthesia

BACKGROUND

Gabapentin, an oral non-opioid analgesic, has been used to decrease pain after a variety of surgical procedures. We hypothesized that premedication with gabapentin would minimize tourniquet-related pain in patients receiving IV regional anesthesia (IVRA).

METHODS

Patients undergoing elective hand surgery with IVRA were randomly assigned to one of two study groups using a double-blind study design. The control group (n = 20) received placebo capsules 1 h before the surgery, and the gabapentin group (n = 20) received gabapentin 1.2 g p.o. before the operation. IVRA was achieved in all patients with lidocaine, 3 mg/kg, diluted with saline to a total volume of 40 mL. Fentanyl, 0.5 microg/kg IV, was administered as a rescue analgesic during surgery. Sensory and motor block onset and recovery times, tourniquet pain, and quality of anesthesia were assessed at specific time intervals during the perioperative period. Visual analog scale pain scores (0-10) were recorded during the 24 h follow-up period, and patients received diclofenac, 75 mg IM, if their pain score was >4.

RESULTS

The onset of the sensory and motor block did not differ between the two study groups. However, tourniquet pain scores at 30, 40, 50, and 60 min after cuff inflation were lower in the gabapentin group (P < 0.05). The time to intraoperative analgesic rescue was prolonged in the gabapentin group (35 +/- 10 min vs 21 +/- 13 min, P < 0.05), and less supplemental fentanyl was required (35 +/- 47 microg vs 83 +/- 73 microg, P < 0.05). The quality of anesthesia, as independently assessed by the anesthesiologist and the surgeon, was significantly better in the gabapentin (versus control) group. In the gabapentin group, the time to requesting a rescue analgesic after surgery was prolonged (135 +/- 25 min vs 85 +/- 19 min, P < 0.05), and postoperative pain scores at 60 min (3.8 +/- 0.9 vs 2.2 +/- 0.5) and 120 min (3.2 +/- 1.4 vs 1.8 +/- 0.8), as well as diclofenac consumption (30 +/- 38 mg vs 60 +/- 63 mg), were reduced after surgery.

CONCLUSIONS

Premedication with oral gabapentin (1.2 g) decreased tourniquet-related pain and improved the quality of anesthesia during hand surgery under IVRA. Gabapentin also reduced pain scores in the early postoperative period.

Calcium channel alpha2delta1 subunit mediates spinal hyperexcitability in pain modulation

Mechanisms of chronic pain, including neuropathic pain, are poorly understood. Upregulation of voltage-gated calcium channel (VGCC) alpha2delta1 subunit (Ca(v)alpha2delta1) in sensory neurons and dorsal spinal cord by peripheral nerve injury has been suggested to contribute to neuropathic pain. To investigate the mechanisms without the influence of other injury factors, we have created transgenic mice that constitutively overexpress Ca(v)alpha2delta1 in neuronal tissues. Ca(v)alpha2delta1 overexpression resulted in enhanced currents, altered kinetics and voltage-dependence of VGCC activation in sensory neurons; exaggerated and prolonged dorsal horn neuronal responses to mechanical and thermal stimulations at the periphery; and pain behaviors. However, the transgenic mice showed normal dorsal horn neuronal responses to windup stimulation, and behavioral responses to tissue-injury/inflammatory stimuli. The pain behaviors in the transgenic mice had a pharmacological profile suggesting a selective contribution of elevated Ca(v)alpha2delta1 to the abnormal sensations, at least at the spinal cord level. In addition, gabapentin blocked VGCC currents concentration-dependently in transgenic, but not wild-type, sensory neurons. Thus, elevated neuronal Ca(v)alpha2delta1 contributes to specific pain states through a mechanism mediated at least partially by enhanced VGCC activity in sensory neurons and hyperexcitability in dorsal horn neurons in response to peripheral stimulation. Modulation of enhanced VGCC activity by gabapentin may underlie at least partially its antihyperalgesic actions.

Gabapentin treatment of neurogenic overactive bladder

OBJECTIVE

Detrusor overactivity is a well-recognized and distressing medical condition affecting both men and women, with a significant prevalence in the population and with a higher incidence rate in people older than 70 years. This pathological condition is characterized by irritative symptoms: urinary urgency, with or without incontinence, and urinary frequency, often seriously compromising the quality of life of the people who have it. The complaint of these symptoms is defined by the International Continence Society (www.continet.org) as "overactive bladder." Many neurological patients experience irritative symptoms of the lower urinary tract related to their disease, and this condition drastically limits their social life. Various drugs have been introduced in therapy protocols to treat neurogenic detrusor overactivity; however, in many cases, the outcomes of these treatments have proven to be unsatisfactory. This fact is probably related to the incomplete understanding of the pathophysiological aspects of detrusor overactivity. Recent studies suggest the possible role in the detrusor overactivity pathogenesis of bladder receptors, afferent pathways, and spinal cord interneurons; consequently, the modulation of bladder receptor and/or spinal cord centers activity has been proposed as a possible approach to control involuntary detrusor contractions, using drugs capable of acting on bladder afferent pathways. The aim of this study was to evaluate the efficacy of gabapentin, an anticonvulsive agent used by neurologists in the treatment of epilepsy and neurogenic pain, in the treatment of detrusor overactivity of neurogenic origin.

METHODS

Sixteen patients affected by neurogenic overactive bladder were enrolled in the study. The clinical outcomes were assessed by symptomatic score evaluations, voiding diary, and urodynamic test before and after 31 days of gabapentin treatment.

RESULTS

The preliminary results showed significant modifications of urodynamic indexes, particularly of the detrusor overactivity, whereas the symptomatic score evaluation and the voiding diary data demonstrated a significant lowering of the irritative symptoms. Furthermore, we did not record significant adverse effects and no patient interrupted the drug treatment.

CONCLUSIONS

These data support the rationale that detrusor overactivity may be controlled by modulating the afferent input from the bladder and the excitability of the sacral reflex center and suggest a novel method to treat overactive bladder patients.