Antidepressants and pain

Antidepressant-like activity of turmerone in behavioral despair tests in mice

Background

The present study was undertaken to evaluate the anti-depressive activity of turmerone after one-week administration by using a mouse forced swimming test (FST) and tail suspension test (TST).

Methods

Animals were divided into four groups (n = 10 /group): control (0.9% saline), the three doses of turmerone (1.25, 2.5, 5.0 mg/kg) for one-week treatment. To assess the effect of turmerone on locomotor activity, mice were evaluated in the open-field paradigm. Forced swimming test (FST) and Tail suspension test (TST) were used to take as a measure of antidepressant activity. The probable mechanisms of action of the anti-depressive effect of turmerone was also investigated by measuring the activity of monoamine oxidase-A and corticosterone levels in the blood and the levels of monoamines in the cortex, striatum, hippocampus and hypothalamus of the mice.

Results

Turmerone (2.5, 5.0 mg/kg, p.o.) significantly reduced the immobility time of mice in both the FST and TST, but it did not significantly affect the ambulatory and total movements of mice. However, hyperactivity might explain the results. In addition, turmerone decreased the corticosterone level in the blood while it increased the levels of 5-HT in cortex, striatum, hippocampus, and hypothalamus, the level of NE in striatum and hippocampus, the levels of MHPG and DOPAC in hypothalamus, the level of 5-HIAA in striatum, and the level of DA in striatum, hippocampus, and hypothalamus. Turmerone (2.5, 5.0 mg/kg) decreased the activity of MAO-A in the frontal cortex and hippocampus of mouse brain.

Conclusions

After one-week administration, turmerone produced antidepressant-like effects. The mechanisms of action of anti-depressive effect of turmerone seemed to involve an increase of the monoamines level decreasing the MAO-A activity and the stress of mice.

The antinociceptive effect of reversible monoamine oxidase-A inhibitors in a mouse neuropathic pain model

Neuropathic pain is a debilitating condition that is often resistant to common analgesics, such as opioids, but is sensitive to some antidepressants, an effect that seems to be mediated by spinal cord 5-HT3 receptors. Because the analgesic potential of monoamine oxidase-A (MAO-A) inhibitors is understudied, we evaluated the potential antinociceptive effect of the reversible MAO-A inhibitors moclobemide and 2-(3,4-dimethoxy-phenyl)-4,5-dihydro-1H-imidazole (2-DMPI) in a mouse neuropathic pain model induced by chronic constriction injury (CCI) of the sciatic nerve. Neuropathic mice showed a decreased mechanical paw withdrawal threshold (PWT) 7 days after lesion compared with the baseline PWT, characterizing the development of hyperalgesia. Moclobemide (100-300 μmol/kg, s.c.) and 2-DMPI (30-300 μmol/kg, s.c.) treatments were able to reverse the CCI-induced hyperalgesia, with 50% inhibitory dose (ID50) values of 39 (18-84) and 11 (4-33) μmol/kg, and maximum inhibition (Imax) values of 88±14 and 98±15%, respectively, at the 300 μmol/kg dose. In addition, we observed a significant increase in the MAO-A activity in the lumbar spinal cord of CCI-submitted mice compared with sham-operated animals. Furthermore, the antihyperalgesic effects of both 2-DMPI and moclobemide were largely reversed by intrathecal injection of the 5-HT3 receptor antagonist ondansetron (10 μg/site). These results suggest a possible involvement of MAO-A in the mechanisms of neuropathic pain and a potential utility of the reversible inhibitors of MAO-A in the development of new therapeutic approaches to treat it.

Undiagnosed mood disorders and sleep disturbances in primary care patients with chronic musculoskeletal pain

OBJECTIVE

The study aims to determine the prevalence of undiagnosed comorbid mood disorders in patients suffering chronic musculoskeletal pain in a primary care setting and to identify sleep disturbances and other associated factors in these patients, and to compare the use of health services by chronic musculoskeletal pain patients with and without comorbid mood disorders.

DESIGN

Cross-sectional study.

SUBJECTS

A total of 1,006 patients with chronic musculoskeletal pain from a representative sample of primary care centers were evaluated.

OUTCOME MEASURES

Pain was measured using a visual analog scale and the Primary Care Evaluation of Mental Disorders questionnaire was used to measure mood disorders.

RESULTS

We observed a high prevalence of undiagnosed mood disorders in chronic musculoskeletal pain patients (74.7%, 95% confidence interval [CI] 71.9-77.4%), with greater comorbidity in women (adjusted odds ratio [OR] = 1.91, 95% CI 1.37-2.66%) and widow(er)s (adjusted OR = 1.87, 95% CI 1.19-2.91%). Both sleep disturbances (adjusted OR = 1.60, 95% CI 1.17-2.19%) and pain intensity (adjusted OR = 1.02, 95% CI 1.01-1.02%) displayed a direct relationship with mood disorders. Moreover, we found that chronic musculoskeletal pain patients with comorbid mood disorders availed of health care services more frequently than those without (P < 0.001).

CONCLUSIONS

The prevalence of undiagnosed mood disorders in patients with chronic musculoskeletal pain is very high in primary care settings. Our findings suggest that greater attention should be paid to this condition in general practice and that sleep disorders should be evaluated in greater detail to achieve accurate diagnoses and select the most appropriate treatment.

Effectiveness of low-dose milnacipran for a patient suffering from pain disorder with delusional disorder (somatic type) in the orofacial region

Glossodynia is chronic pain localized around the tongue, with no perceivable organic abnormalities. In the fields of oral and maxillofacial surgery, it is categorized as an oral psychosomatic disease. In contrast, psychiatric nosology classifies glossodynia as a pain disorder among somatoform disorders, per the DSM-IV. The patient was a 71-year-old woman who developed symptoms of glossodynia, specifically a sore tongue. In the decade before she presented to us, she had had bizarre symptoms of oral cenesthopathy such as the sensation that her teeth had become 'limp and floppy' and that she needles in her mouth. Treatment was attempted using several psychotropic drugs, but no satisfactory response was noted. Because the patient was referred to our outpatient clinic, we tried psychotropic therapy again. Additionally, valproic acid, tandospirone and sertraline were administered (in this order), but the patient still showed no response. However, when sertraline was changed to milnacipran, all symptoms disappeared in a short period. We suggest that a small dose of milnacipran can be effective for controlling oral cenesthopathy as well as glossodynia.

The failure of the antidepressant drug discovery process is systemic

Current antidepressants are crude compared with the ideal and patents on most have expired. There are therefore strong clinical and commercial pressures for new drugs to replace them. The prospects for this are, however, now markedly reduced as several major pharmaceutical companies have abandoned work in this area whilst many others have sharply decreased their research investment. These changes and the lack of progress over such a long period are indicative of a catastrophic systems failure which, it is argued, has been caused in large part by a logical flaw at the animal modelling stage. This tautology has served to lock the current antidepressant drug discovery process into an iterative loop capable only of producing further variations of that which has gone before. Drugs produced by this approach have proved to be only poorly effective in the context of the clinically depressed population as a whole. Hence, the inevitable failure of the current antidepressant drug discovery process has left little behind that can be salvaged. Therefore, it is suggested that this be urgently reformulated on more rational grounds using more appropriate species in new animal models based upon a thorough understanding of the behavioural expressions of depression in the clinic.

Factors associated with chronic pain in patients with bipolar depression: a cross-sectional study

BACKGROUND

While pain is frequently associated with unipolar depression, few studies have investigated the link between pain and bipolar depression. In the present study we estimated the prevalence and characteristics of pain among patients with bipolar depression treated by psychiatrists in their regular clinical practice. The study was designed to identify factors associated with the manifestation of pain in these patients.

METHODS

Patients diagnosed with bipolar disorder (n=121) were selected to participate in a cross-sectional study in which DSM-IV-TR criteria were employed to identify depressive episodes. The patients were asked to describe any pain experienced during the study, and in the 6 weeks beforehand, by means of a Visual Analogical Scale (VAS).

RESULTS

Over half of the bipolar depressed patients (51.2%, 95% CI: 41.9%-60.6%), and 2/3 of the female experienced concomitant pain. The pain was of moderate to severe intensity and prolonged duration, and it occurred at multiple sites, significantly limiting the patient's everyday activities. The most important factors associated with the presence of pain were older age, sleep disorders and delayed diagnosis of bipolar disorder.

CONCLUSIONS

Chronic pain is common in bipolar depressed patients, and it is related to sleep disorders and delayed diagnosis of their disorder. More attention should be paid to study the presence of pain in bipolar depressed patients, in order to achieve more accurate diagnoses and to provide better treatment options.

The atypical antidepressant mianserin exhibits agonist activity at κ-opioid receptors

BACKGROUND AND PURPOSE

Antidepressants are known to interact with the opioid system through mechanisms not completely understood. We previously reported that tricyclic antidepressants act as agonists at distinct opioid receptors. Here, we investigated the effect of the atypical antidepressant mianserin at cloned and native opioid receptors.

EXPERIMENTAL APPROACH

Effects of mianserin were examined in CHO cells transfected with human opioid receptors, C6 glioma cells and rat brain membranes by the use of radioligand binding and functional assays including the stimulation of [(35)S]GTPγS binding and MAPK phosphorylation.

KEY RESULTS

Mianserin displayed 12- and 18-fold higher affinity for κ- than µ- and δ-opioid receptors respectively. In [(35)S]GTPγS assays, mianserin selectively activated κ-opioid receptors. The agonist activity was antagonized by the selective κ-opioid blocker nor-binaltorphimine (nor-BNI). The mianserin analogue mirtazapine also displayed κ-opioid agonist activity. Mianserin and mirtazapine increased ERK1/2 phosphorylation in CHO cells expressing κ-opioid receptors and C6 cells, and these effects were antagonized by nor-BNI. In rat striatum and nucleus accumbens, mianserin stimulated [35S]GTPγS binding in a nor-BNI-sensitive manner with maximal effects lower than those of the full κ-opioid agonists (-)-U50,488 and dynorphin A. When combined, mianserin antagonized the effects of the full κ-opioid receptor agonists in [(35)S]GTPγS assays and reduced the stimulation of p38 MAPK and ERK1/2 phosphorylation by dynorphin A.

CONCLUSIONS AND IMPLICATIONS

In different cell systems, mianserin directly activates κ-opioid receptors, displaying partial agonist activity at brain receptors. Thus, this property appears to be a common feature of different classes of antidepressants.

Milnacipran for fibromyalgia: a useful addition to the treatment armamentarium

INTRODUCTION

Antidepressants are used to treat a variety of chronic pain conditions including peripheral neuropathy, headache, and more recently, fibromyalgia. The antidepressant milnacipran blocks the reuptake of norepinephrine and serotonin and is used for the management of fibromyalgia.

AREAS COVERED

The article contains data primarily obtained from the MEDLINE database using a PubMed search of the keywords including milnacipran, fibromyalgia and depression. Of the available serotonin norepinephrine reuptake inhibitors, milnacipran has greater potency in inhibiting reuptake of norepinephrine relative to serotonin and is proposed to work by attenuating pain signals. Milnacipran is well tolerated and effective for fibromyalgia pain when given in divided doses of 100 - 200 mg daily. Studies show that milnacipran may be effective for fibromyalgia-associated symptoms including depression and fatigue.

EXPERT OPINION

Milnacipran provides modest fibromyalgia pain relief and is best used as part of a multidisciplinary treatment approach. While milnacipran was not studied in fibromyalgia patients with major depression, it may be a wise choice for fibromyalgia patients with depressive symptoms and patients for whom sedation, dizziness, edema or weight gain with gabapentin and pregabalin is a problem. Milnacipran has been found to be beneficial for treating some troublesome fibromyalgia-associated symptoms, including fatigue and cognitive dysfunction.

The plasticity of the association between mu-opioid receptor and glutamate ionotropic receptor N in opioid analgesic tolerance and neuropathic pain

Multiple groups have reported the functional cross-regulation between mu-opioid (MOP) receptor and glutamate ionotropic receptor N (GluN), and the post-synaptic association of these receptors has been implicated in the transmission and modulation of nociceptive signals. Opioids, such as morphine, disrupt the MOP receptor-GluN receptor complex to stimulate the activity of GluN receptors via protein kinase C (PKC)/Src. This increased GluN receptor activity opposes MOP receptor signalling, and via neural nitric oxide synthase (nNOS) and calcium and calmodulin regulated kinase II (CaMKII) induces the phosphorylation and uncoupling of the opioid receptor, which results in the development of morphine analgesic tolerance. Both experimental in vivo activation of GluN receptors and neuropathic pain separate the MOP receptor-GluN receptor complex via protein kinase A (PKA) and reduce the analgesic capacity of morphine. The histidine triad nucleotide-binding protein 1 (HINT1) associates with the MOP receptor C-terminus and connects the activities of MOP receptor and GluN receptor. In HINT1⁻/⁻ mice, morphine promotes enhanced analgesia and produces tolerance that is not related to GluN receptor activity. In these mice, the GluN receptor agonist N-methyl-D-aspartate acid (NMDA) does not antagonise the analgesic effects of morphine. Treatments that rescue morphine from analgesic tolerance, such as GluN receptor antagonism or PKC, nNOS and CaMKII inhibitors, all induce MOP receptor-GluN receptor re-association and reduce GluN receptor/CaMKII activity. In mice treated with NMDA or suffering from neuropathic pain (induced by chronic constriction injury, CCI), GluN receptor antagonists, PKA inhibitors or certain antidepressants also diminish CaMKII activity and restore the MOP receptor-GluN receptor association. Thus, the HINT1 protein stabilises the association between MOP receptor and GluN receptor, necessary for the analgesic efficacy of morphine, and this coupling is reduced following the activation of GluN receptors, similar to what is observed in neuropathic pain.

Myofascial pain syndrome: a treatment review

Myofascial pain syndrome (MPS) is defined as pain that originates from myofascial trigger points in skeletal muscle. It is prevalent in regional musculoskeletal pain syndromes, either alone or in combination with other pain generators. The appropriate evaluation and management of myofascial pain is an important part of musculoskeletal rehabilitation, and regional axial and limb pain syndromes. This article reviews the current hypotheses regarding the treatment modalities for myofascial trigger points and muscle pain. Through a critical evidence-based review of the pharmacologic and nonpharmacologic treatments, the authors aim to provide clinicians with a more comprehensive knowledge of the interventions for myofascial pain.

Effects of monoamine reuptake inhibitors in assays of acute pain-stimulated and pain-depressed behavior in rats

Pain is associated with stimulation of some behaviors (eg, withdrawal reflexes) but depression of many other behaviors (eg, feeding, locomotion, positively reinforced operant behavior). Drugs that block reuptake of serotonin, norepinephrine, and/or dopamine are widely used to treat depression, and they have also emerged as useful drugs for treatment of pain. This study compared effects of selective and mixed-action inhibitors of serotonin, norepinephrine, and/or dopamine reuptake in assays of acute pain-stimulated and pain-depressed behavior. Intraperitoneal injection of dilute acid served as a noxious stimulus to stimulate a writhing response or depress intracranial self-stimulation (ICSS) in Sprague Dawley rats. Selective reuptake inhibitors of serotonin (citalopram, clomipramine) and norepinephrine (nisoxetine, nortriptyline) and a mixed-action reuptake inhibitor of serotonin and norepinephrine (milnacipran) blocked acid-stimulated writhing but failed to block acid-induced depression of ICSS. Selective dopamine reuptake inhibitors (RTI-113 [3ß-(4-chlorophenyl)tropane-2ß-carboxylic acid phenyl ester hydrochloride], bupropion) and a triple reuptake inhibitor of dopamine, serotonin, and norepinephrine (RTI-112 [3ß-(3-methyl-4-chlorophenyl)tropane-2ß-carboxylic acid methyl ester hydrochloride]) blocked both acid-stimulated writhing and acid-induced depression of ICSS, although these drugs also produced an abuse-related facilitation of ICSS in the absence of the noxious stimulus. These results support further consideration of dopamine reuptake inhibitors as candidate analgesics, although abuse liability remains a concern.

PERSPECTIVE

Monoamine reuptake inhibitors are used to treat depression and some forms of pain. This study examined effects of monoamine reuptake inhibitors in a preclinical assay of pain-related behavioral depression. The results support further consideration of dopamine reuptake inhibitors as candidate analgesics under selected circumstances, although abuse liability remains a concern.

Chronic pain leads to concomitant noradrenergic impairment and mood disorders

BACKGROUND

Patients suffering chronic pain are at high risk of suffering long-lasting emotional disturbances characterized by persistent low mood and anxiety. We propose that this might be the result of a functional impairment in noradrenergic circuits associated with locus coeruleus (LC) and prefrontal cortex, where emotional and sensorial pain processes overlap.

METHODS

We used a chronic constriction injury of sciatic nerve as a model of neuropathic pain in male Sprague-Dawley rats to assess the time-dependent changes that might potentially precipitate mood disorders (2, 7, 14, and 28 days after injury). This was measured through a combination of behavioral, electrophysiological, microdialysis, immunohistochemical, and Western blot assays.

RESULTS

As expected, nerve injury produced an early and stable decrease in sensorial pain threshold over the testing period. By contrast, long-term neuropathic pain (28 days after injury) resulted in an inability to cope with stressful situations, provoking depressive and anxiogenic-like behaviors, even more intense than the aversiveness associated with pain perception. The onset of these behavioral changes coincided with irruption of noradrenergic dysfunction, evident as: an increase in LC bursting activity; in tyrosine hydroxylase expression and that of the noradrenaline transporter; and enhanced expression and sensitivity of α2-adrenoceptors in the LC.

CONCLUSIONS

Long-term neuropathic pain leads to anxio-depressive-like behaviors that are more predominant than the aversion of a painful experience. These changes are consistent with the impairment of noradrenergic system described in depressive disorders.

The perception and endogenous modulation of pain

Pain is often perceived an unpleasant experience that includes sensory and emotional/motivational responses. Accordingly, pain serves as a powerful teaching signal enabling an organism to avoid injury, and is critical to survival. However, maladaptive pain, such as neuropathic or idiopathic pain, serves no survival function. Genomic studies of individuals with congenital insensitivity to pain or paroxysmal pain syndromes considerable increased our understanding of the function of peripheral nociceptors, and especially of the roles of voltage-gated sodium channels and of nerve growth factor (NGF)/TrkA receptors in nociceptive transduction and transmission. Brain imaging studies revealed a "pain matrix," consisting of cortical and subcortical regions that respond to noxious inputs and can positively or negatively modulate pain through activation of descending pain modulatory systems. Projections from the periaqueductal grey (PAG) and the rostroventromedial medulla (RVM) to the trigeminal and spinal dorsal horns can inhibit or promote further nociceptive inputs. The "pain matrix" can explain such varied phenomena as stress-induced analgesia, placebo effect and the role of expectation on pain perception. Disruptions in these systems may account for the existence idiopathic pan states such as fibromyalgia. Increased understanding of pain modulatory systems will lead to development of more effective therapeutics for chronic pain.

Transdermal delivery of imipramine and doxepin from newly oil-in-water nanoemulsions for an analgesic and anti-allodynic activity: development, characterization and in vivo evaluation

Antidepressants have been considered by their analgesic activity in numerous studies, and specifically tricyclic antidepressants to possess the greatest efficacy. Imipramine and doxepin have been reported to exhibit local anaesthetic properties. In order to investigate their cutaneous analgesic effect after topical application a nanoemulsion vehicle was developed. This nanoemulsion is composed of propilenglicol, Transcutol, water, Labrasol, Plurol Oleique, isostearyl isostearate, oleic acid, and d-limonene. The final concentration of imipramine or doxepin in the nanoemulsion system was 3% (w/w). The nanoemulsions were characterized by pH, viscosity, droplet size, polydispersity index and finally, a morphological and structural examination was carried out by using transmission electron microscopy. Furthermore, the present work also reports stability studies on the nanoemulsion formulations to evaluate the integrity of the formulation; these indicate that formulations are stable for a period of three months. Moreover ex vivo studies were performed to evaluate permeation behaviour through human skin and predict plasma concentrations concluding that topically applied imipramine and doxepin loaded nanoemulsions were safe for a local effect. Similarly, the in vivo analgesic and anti-allodynic activity in rats was evaluated being stronger for the doxepin loaded nanoemulsion. This study demonstrated that nanoemulsion containing doxepin could be promising as an alternative analgesic therapy with a potential clinical application.

Spinal serotonin 5-HT7 and adenosine A1 receptors, as well as peripheral adenosine A1 receptors, are involved in antinociception by systemically administered amitriptyline

The present study explored a link between spinal 5-HT(7) and adenosine A(1) receptors in antinociception by systemic amitriptyline in normal and adenosine A(1) receptor knock-out mice using the 2% formalin test. In normal mice, antinociception by systemic amitriptyline 3mg/kg was blocked by intrathecal administration of the selective adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) 10 nmol. Blockade was also seen in adenosine A(1) receptor +/+ mice, but not in -/- mice lacking these receptors. In both normal and adenosine A(1) receptor +/+ mice, the selective 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride (SB269970) 3 μg blocked antinociception by systemic amitriptyline, but it did not prevent antinociception in adenosine A(1) receptor -/- mice. In normal mice, flinching was unaltered when the selective 5-HT(7) receptor agonist (2S)-(+)-5-(1,3,5-trimethylpyrazol-4-yl)-2-(dimethylamino)tetralin (AS-19) 20 μg was administered alone, but increased when co-administered intrathecally with DPCPX 10 nmol or SB269970 3 μg. Intrathecal AS-19 decreased flinching in adenosine A(1) receptor +/+ mice compared to -/- mice. Systemic amitriptyline appears to reduce nociception by activating spinal adenosine A(1) receptors secondarily to 5-HT(7) receptors. Spinal actions constitute only one aspect of antinociception by amitriptyline, as intraplantar DPCPX 10 nmol blocked antinociception by systemic amitriptyline in normal and adenosine A(1) receptor +/+, but not -/- mice. Adenosine A(1) receptor interactions are worthy of attention, as chronic oral caffeine (0.1, 0.3g/L, doses considered relevant to human intake levels) blocked antinociception by systemic amitriptyline in normal mice. In conclusion, adenosine A(1) receptors contribute to antinociception by systemic amitriptyline in both spinal and peripheral compartments.

Analgesic antidepressants promote the responsiveness of locus coeruleus neurons to noxious stimulation: implications for neuropathic pain

Antidepressants that block the reuptake of noradrenaline and/or serotonin are among the first-line treatments for neuropathic pain, although the mechanisms underlying this analgesia remain unclear. The noradrenergic locus coeruleus is an essential element of both the ascending and descending pain modulator systems regulated by these antidepressants. Hence, we investigated the effect of analgesic antidepressants on locus coeruleus activity in Sprague-Dawley rats subjected to chronic constriction injury (CCI), a model of neuropathic pain. In vivo extracellular recordings of locus coeruleus revealed that CCI did not modify the basal tonic activity of this nucleus, although its sensory-evoked response to noxious stimuli was significantly altered. Under normal conditions, noxious stimulation evokes an early response, corresponding to the activation of myelinated A fibers, which is followed by an inhibitory period and a subsequent late capsaicin-sensitive response, consistent with the activation of unmyelinated C fibers. CCI provokes an enhanced excitatory early response in the animals and the loss of the late response. Antidepressant administration over 7 days (desipramine, 10mg/kg/day or duloxetine, 5mg/kg/day, delivered by osmotic minipumps) decreased the excitatory firing rate of the early response in the CCI group. Moreover, in all animals, these antidepressants reduced the inhibitory period and augmented the late response. We propose that N-methyl-d-aspartate and alpha-2-adrenoceptors are involved in the analgesic effect of antidepressants. Antidepressant-mediated changes were correlated with behavioral effects indicative of analgesia in healthy and neuropathic rats.

Plasma levels of milnacipran and its effectiveness for the treatment of chronic pain in the orofacial region

OBJECTIVES

This study was performed to assess the relationship between plasma levels of milnacipran and its analgesic/antidepressive effect in patients with chronic orofacial pain treated with this drug.

METHODS

A total of 44 patients took milnacipran for 12 weeks. Patients were assessed for their pain and depressive symptoms using the visual analog scale (VAS) and Hamilton Depression Rating Scale, respectively. The plasma milnacipran level was also assessed at week 12.

RESULTS

Forty patients completed study treatment and were included in the analysis. In these patients, the VAS score at week 12 significantly decreased from the baseline score (t = 5.15, p < 0.0001). The dose of milnacipran was positively correlated in a linear manner with the plasma level of the drug (Y = 44.86 + 0.33X, r = 0.54, R(2)  = 0.29, p = 0.0004). A quadratic regression curve was plotted between the percentage of decrease in the VAS score and plasma milnacipran level (Y = 27.39 + 0.76X - 0.008X(2) , p = 0.048, r = 0.40, R(2)  = 0.16). On the other hand, no significant relationship was noted between the percentage of decrease in the Hamilton Depression Rating Scale score and plasma milnacipran level.

CONCLUSION

The analgesic effect of milnacipran was suppressed in the presence of the plasma level of the drug outside the therapeutic range, whereas its antidepressant effect was not affected by its plasma level.

Drug management of visceral pain: concepts from basic research

Visceral pain is experienced by 40% of the population, and 28% of cancer patients suffer from pain arising from intra- abdominal metastasis or from treatment. Neuroanatomy of visceral nociception and neurotransmitters, receptors, and ion channels that modulate visceral pain are qualitatively or quantitatively different from those that modulate somatic and neuropathic pain. Visceral pain should be recognized as distinct pain phenotype. TRPV1, Na 1.8, and ASIC3 ion channels and peripheral kappa opioid receptors are important mediators of visceral pain. Mu agonists, gabapentinoids, and GABAB agonists reduce pain by binding to central receptors and channels. Combinations of analgesics and adjuvants in animal models have supra-additive antinociception and should be considered in clinical trials. This paper will discuss the neuroanatomy, receptors, ion channels, and neurotransmitters important to visceral pain and provide a basic science rationale for analgesic trials and management.

Brain energy metabolism is increased by chronic administration of bupropion

OBJECTIVES

Based on the hypothesis that energy impairment may be involved in the pathophysiology of depression, we evaluated the activities of citrate synthase, malate dehydrogenase, succinate dehydrogenase (SDH), mitochondrial respiratory chain complexes I, II, II-III, IV and creatine kinase (CK) in the brain of rats submitted to chronic administration of bupropion.

METHODS

Animals received daily administration of bupropion dissolved in saline (10 mg/kg, intraperitoneal) at 1.0 ml/kg body weight. The rats received injections once a day for 14 days; control rats received an equivalent volume of saline. Twelve hours after the last administration, the rats were killed by decapitation and brain was rapidly removed and kept on an ice plate. The activities of the enzymes were measured in different brain areas.

RESULTS

We observed that the activities of citrate synthase and malate dehydrogenase, mithocondrial respiratory chain complexes I, II-III and IV and CK were not altered after chronic administration of bupropion. However, SDH activity was increased in the prefrontal cortex and cerebellum. In the hippocampus, cerebellum and striatum the activity of complex II was increased after chronic administration of bupropion.

CONCLUSIONS

Our results demonstrated that bupropion increased some enzymes of brain energy metabolism. These findings are in accordance with other studies which showed that some antidepressants may improve energy metabolism. The present results reinforce the hypothesis that antidepressants modulate brain energy metabolism.

An increase in spinal cord noradrenaline is a major contributor to the antihyperalgesic effect of antidepressants after peripheral nerve injury in the rat

Antidepressants are often used for the treatment of neuropathic pain. Clinical studies suggest that the efficacy of serotonin (5-HT) and noradrenaline (NA) reuptake inhibitors (SNRIs) for neuropathic pain is greater than that of selective 5-HT reuptake inhibitors (SSRIs). In the present study, we determined the efficacy and mechanisms involved in the antihyperalgesic effects of milnacipran, an SNRI, compared with paroxetine, an SSRI, and maprotiline, a selective NA reuptake inhibitor, using a rat model of neuropathic pain. Male Sprague-Dawley rats underwent spinal nerve ligation (SNL), and the withdrawal threshold to paw pressure was measured. Intraperitoneal injection of milnacipran (3-30mg/kg) produced a dose-dependent antihyperalgesic effect. The effect was reversed by intrathecal injection of the α(2)-adrenoceptor antagonist idazoxan (30μg), but not by various 5-HT receptor antagonists. Paroxetine produced an antihyperalgesic effect only at the highest dose tested (10mg/kg). This effect was reversed by intrathecal injection of both idazoxan and ondansetron (30μg), a 5-HT3 receptor antagonist. Maprotiline produced an antihyperalgesic effect (10 and 30mg/kg), and the effect was reversed by intrathecal idazoxan. In microdialysis studies, NA and 5-HT concentrations in the spinal dorsal horn were increased after injection of either milnacipran or paroxetine, and only NA was increased after maprotiline. Furthermore, the NA content in the spinal cord of SNL rats was greater than that in normal animals. These findings suggest that an increase in NA in the spinal cord plays an important role in the antihyperalgesic effects of not only NA reuptake inhibitors but also SSRIs.

Inhibitory action of antidepressants on mouse Betaine/GABA transporter (BGT1) heterologously expressed in cell cultures

Betaine/γ-aminobutyric acid (GABA) transporter (BGT1, SLC6A12) is a member of the Na⁺- and Cl⁻-dependent neurotransmitter transporter gene family with a homology to the GABA transporters (GATs), GAT1 (SLC6A1), GAT2 (SLC6A13) and GAT3 (SLC6A11) (HUGO nomenclature). Since antidepressants have been reported to inhibit GABA uptake, we examined those effects on mouse BGT1 (mBGT1) in comparison with other mouse GAT (mGAT) subtypes in the heterologously expressed cell cultures. All antidepressants tested here inhibited the [³H]GABA uptake through mBGT1 and mGATs in a rank order of potency with mBGT1 > mGAT1-3. Kinetic analyses for maprotilline, mianserine and trimipramine revealed that they inhibited mBGT1 and mGAT1 noncompetitively, except that mianserine competitively inhibited mBGT1. These results provided a clue to investigate the structure-function relationship of mBGT1 using antidepressants as a tool, leading to the identification of potential candidates for selective and specific inhibitors of mBGT1.

The antinociceptive effects of intravenous tianeptine in colorectal distension-induced visceral pain in rats: the role of 5-HT₃ receptors

Tianeptine is an unusual tricyclic antidepressant drug. In this study, we aimed to investigate the antinociceptive effect of tianeptine on visceral pain in rats and to determine whether possible antinociceptive effect of tianeptine is mediated by serotonergic (5-HT(2,3)) and noradrenergic (α(1,2)) receptor subtypes. Male Sprague Dawley rats (250-300 g) were supplied with a venous catheter, for drug administrations, and enameled nichrome electrodes, for electromyography, at external oblique musculature. Colorectal distension (CRD) was employed as the noxious visceral stimulus and the visceromotor response (VMR) to CRD was quantified electromyographically before and 5, 15, 30, 60, 90 and 120 min after tianeptine administration. Antagonists were administered 10 min before tianeptine for their ability to change tianeptine antinociception. Intravenous administration of tianeptine (2.5-20 mg/kg) produced a dose-dependent reduction in VMR. Administration of 5-HT(3) receptor antagonist ondansetron (0.5, 1 and 2 mg/kg), but not 5-HT(2) receptor antagonist ketanserine (0.5, 1 and 2 mg/kg), reduced the antinociceptive effect of tianeptine (10mg/kg). In addition, administration of α(1)-adrenoceptor antagonist prazosin (1 mg/kg) or α(2)-adrenoceptor antagonist yohimbine (1 mg/kg) did not cause any significant effect on the tianeptine-induced antinociception. Our data indicate that intravenous tianeptine exerts a pronounced antinociception against CRD-induced visceral pain in rats, and suggests that the antinociceptive effect of tianeptine appears to be mediated in part by 5-HT(3) receptors, but does not involve 5-HT(2) receptors or α-adrenoceptors.

Milnacipran dose-effect study in patients with burning mouth syndrome

OBJECTIVE

The object of this study was to evaluate the dose-dependent efficacy and tolerability of milnacipran in patients with burning mouth syndrome (BMS) with inadequate response at low doses.

METHODS

A 12-week open-label dose-escalation study was conducted in 56 female patients (aged 20-83 years, with a mean age of 60.8 years). The initial dosage of milnacipran was 30 mg/d, and the dosage was raised up to 60 mg and 90 mg/d every 4 weeks until an improvement of at least 50% reduction of visual analog scale was achieved.

RESULTS

The mean ± SD effective daily dose of milnacipran was 63.9 ±16.7 mg. The cumulative improvement rate for the daily dose of 30 mg was 28.6%, and this rate rose (50.8%-67.9%) as the daily dose was increased (from 60 to 90 mg, respectively). The cumulative proportion of responders was significantly greater, with maximal daily doses of 60 and 90 mg, compared with that of 30 mg (P < 0.05, χ test). Most adverse events appeared at the low dose, and there was little evidence for dose-dependence of adverse effects. No serious safety issues were observed.

CONCLUSION

From the result of this study, dose escalation of milnacipran for patients with burning mouth syndrome with inadequate response at low doses may be helpful if the 30-mg daily dose has been tolerated well.

Neuropathic pain: a personal case reflection on a critical incident

Neuropathic pain is a distressing symptom for the patient and a difficult symptom for the physician to treat. There is lack of evidence-based clinical guidelines for the management of malignant neuropathic pain. The case reflection is a personal account of what has been learnt from a critical incident in a particular patient in the management of neuropathic pain. Psychological issues are known to increase pain percetion and affect the quality of life. The case reflection explores problem areas, defines lacunae in knowledge, and demonstrates active learning of the management of neuropathic pain through reflective practice.

Evidence for a differential opioidergic involvement in the analgesic effect of antidepressants: prediction for efficacy in animal models of neuropathic pain?

BACKGROUND AND PURPOSE

Antidepressants are one of the recommended treatments for neuropathic pain. However, their analgesic action remains unpredictable, and there are no selection criteria for clinical use. Better knowledge of their mechanism of action could help highlight differences underlying their unequal efficacy.

EXPERIMENTAL APPROACH

We compared the activity of a tricyclic antidepressant (clomipramine) with selective 5-HT and noradrenaline reuptake inhibitors (milnacipran and duloxetine) in streptozocin-induced diabetic and chronic constriction nerve injury-induced neuropathic rats, after repeated injections. We looked for an opioidergic mechanism in their action.

KEY RESULTS

Abolition of mechanical hyperalgesia was observed in mononeuropathic rats after five injections of clomipramine (5 mg·kg(-1) , s.c.) and milnacipran (10 or 20 mg·kg(-1) , i.p.) and in diabetic rats after clomipramine. An additional antinociceptive effect was obtained with five injections of duloxetine (3 mg·kg(-1) , i.p.) in both models and milnacipran (10 mg·kg(-1) , i.p.) in diabetic rats. These effects were observed with plasma antidepressant concentrations similar to those found in patients treated for neuropathic pain. Naloxone (1 mg·kg(-1) , i.v.) only suppressed the anti-hyperalgesic effects of clomipramine in both models of pain and of milnacipran in the traumatic model.

CONCLUSIONS AND IMPLICATIONS

The opioid system appears to be involved in the mechanism of action of antidepressants that only have an anti-hyperalgesic effect but not in those that have a stronger (i.e. antinociceptive) effect. These differences between the antidepressants occurred whatever the aetiology of the neuropathy and, if confirmed in clinical trials, could be used to decide which antidepressant is administered to a patient with neuropathic pain.

Mechanisms of pain transmission and pharmacologic management

BACKGROUND

Pain sensation involves multiple signaling and modulatory pathways, employing a variety of neurotransmitters and other mediators. Inhibitory and facilitatory mechanisms affect the perception of stimuli as painful or non-painful, and in addition may affect the perceived intensity of pain. Endogenous opioids are key mediators in the descending pain suppression pathways. Additionally, monoaminergic neurotransmitters such as norepinephrine, serotonin and dopamine positively or negatively modulate pain signaling, depending on receptor type and location. The various mediators involved in pain signaling provide potential targets for pharmacological interventions. Single analgesic therapies may be limited in their ability to comprehensively target these complex pain signaling pathways. Therapeutic approaches acting on multiple pain transmission pathways through different mechanisms of action provide an opportunity to maximize efficacy and tolerability in the treatment of pain.

SCOPE

This article discusses the various physiologic processes involved in pain signaling and modulation, describes the mechanisms by which various classes of analgesic agents are believed to produce their clinical effects, and explores the potential benefits of a multiple-mechanism approach to analgesia. Published articles describing the physiologic processes involved in pain signaling and modulation and the mechanisms of analgesia for different drug classes were reviewed. MEDLINE searches were conducted to identify relevant studies published through August 2009 that evaluated the efficacy and tolerability of multiple-mechanism analgesic regimens. English language-only randomized controlled trials and meta-analyses of randomized controlled trials were considered.

FINDINGS/CONCLUSION

Multiple neurotransmitters and other mediators are involved in the endogenous modulation of pain signaling, providing numerous opportunities for intervention with different classes of analgesics. Data from numerous clinical trials indicate that multiple-mechanism approaches to analgesia provide comparable or superior analgesic efficacy with lower doses of the individual agents and reduced incidence of side effects. These data support current guidelines which endorse multiple-mechanism strategies for both acute and chronic pain management.

Engagement of descending inhibition from the rostral ventromedial medulla protects against chronic neuropathic pain

A puzzling observation is why peripheral nerve injury results in chronic pain in some, but not all, patients. We explored potential mechanisms that may prevent the expression of chronic pain. Sprague Dawley (SD) or Holtzman (HZ) rats showed no differences in baseline sensory thresholds or responses to inflammatory stimuli. However, spinal nerve ligation (SNL)-induced tactile allodynia occurred in approximately 85% of SD and 50% of HZ rats, respectively. No apparent differences were observed in a survey of dorsal root ganglion or spinal neuropathic markers after SNL regardless of allodynic phenotype. SNL-induced allodynia was reversed by administration of lidocaine within the rostral ventromedial medulla (RVM), a site that integrates descending pain modulation via pain inhibitory (ie, OFF) and excitatory (ie, ON) cells. However, in SD or HZ rats with SNL but without allodynia, RVM lidocaine precipitated allodynia. Additionally, RVM lidocaine produced conditioned place preference in allodynic SD or HZ rats but conditioned place aversion in nonallodynic HZ rats. Similarly, RVM U69,593 (kappa opioid agonist) or blockade of spinal α(2) adrenergic receptors precipitated allodynia in previously nonallodynic HZ rats with SNL. All rats showed an equivalent first-phase formalin responses. However, HZ rats had reduced second-phase formalin behaviors along with fewer RVM OFF cell pauses and RVM ON cell bursts. Thus, expression of nerve injury-induced pain may ultimately depend on descending modulation. Engagement of descending inhibition protects in the transition from acute to chronic pain. These unexpected findings might provide a mechanistic explanation for medications that engage descending inhibition or mimic its consequences.

SLC6 neurotransmitter transporters: structure, function, and regulation

The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.

Pharmacologic therapy for cough

Cough is the commonest symptom for which patients seek medical care and yet effective, well-tolerated cough medicines remain a significant unmet clinical need. The development of anti-tussive agents has probably been restricted by a number of factors; our understanding of the specific mechanisms evoking cough in different diseases and how this differs from the role of cough as a protective reflex is limited. Also well-validated tools for the assessment of cough have been lacking. These issues have not encouraged investment by the pharmaceutical industry and there have been no new licensed treatments for cough in more than 50 years. This article will use a mechanism-based approach to discuss the clinical evidence for the anti-tussive activity of currently available agents.

Pain as a symptom of depression: prevalence and clinical correlates in patients attending psychiatric clinics

BACKGROUND

The need to assess the prevalence and characteristics of painful symptoms among depressed patients attended by psychiatrists in their regular clinical practice.

METHODS

A multi-centre, cross-sectional study was carried out in a large sample (n=3566) of patients attending out-patient psychiatric facilities in Spain. All types of DSM-IV-TR depressive disorders were included. Data on the diagnosis, specific symptoms, intensity of depression and antidepressant and analgesic drug treatments were collected. The presence and characteristics of significant pain (visual analogue scale score>40) at the time of the study were also recorded.

RESULTS

The prevalence of pain in depressed patients was 59.1% (CI 95%: 57.7%; 60.7%). Factors associated independently with the existence of significant pain were: being female, presence of loss of energy and the diagnosis of dysthymia or depression induced by physical disorders. In addition, age and the intensity of depression were two risk factors, where each year of age and each point in the Hamilton scale increased the risk of having pain by 2% and 8% respectively. The presence of anhedonia and the diagnosis of depression induced by illegal drugs were factors inversely related to pain.

LIMITATIONS

The cross-sectional naturalistic characteristics of the study.

CONCLUSION

Our data show a high prevalence of pain among depressive patients attending psychiatric clinics. Painful symptoms are modulated differently depending on the type of depression and the presence of specific symptoms, such as loss of energy or anhedonia. Psychiatrists should ask their depressive patients for the presence of pain on a regular basis.

[Irritable bowel syndrome, levator ani syndrome, proctalgia fugax and chronic pelvic and perineal pain]

OBJECTIVES

To define functional gastrointestinal pain, irritable bowel syndrome (IBS), levator ani syndrome, proctalgia fugax, the pathophysiology of these syndromes and the treatments that can be proposed.

MATERIAL AND METHODS

Review of articles published on the theme based on a Medline (PubMed) search and consensus conferences selected according to their scientific relevance.

RESULTS

IBS is very common. Patients report abdominal pain and/or discomfort, bloating, and abnormal bowel habit (diarrhoea, constipation or both), in the absence of any structural or biochemical abnormalities. IBS has a complex, multifactorial pathophysiology, involving biological and psychosocial interactions resulting in dysregulation of the brain-gut axis associated with disorders of intestinal motility, hyperalgesia, immune disorders and disorders of the intestinal bacterial microflora and autonomic and hormonal dysfunction. Many treatments have been proposed, ranging from diet to pharmacology and psychotherapy.

DISCUSSION

Patients with various types of chronic pelvic and perineal pain, especially those seen in urology departments, very often report associated IBS. This syndrome is also part of a global and integrated concept of pelviperineal dysfunction, avoiding a rigorous distinction between the posterior segment and the midline and anterior segments of the perineum.