Analgesic activity of tricyclic antidepressants

Traditional Aspects of Sciatic Pain Management and Allied Therapies from Persian Medical Reports

Sciatica is a common back pain caused by irritation of the sciatic nerve. Current pharmacologic therapies have proven inadequate for many patients with sciatic pain. On the other hand, there is a globally increasing demand for the use and administration of natural medicaments for this disorder. Traditional Persian Medicine (TPM) is a school of medicine and a medicinal plant-based resource for clinical studies put forward by Persian scholars. The aim of the present study is to gather and study the effectiveness of all medicinal plants from five main Persian pharmacopeias. Furthermore, different databases such as PubMed and Scopus have been checked to derive relevant activities for these plants. In all, 99 medicinal plants related to 42 families have been authenticated. Asteraceae and Apiaceae were the most frequent families and roots and seeds were the most reported botanical parts. The employed routes of administration were oral (54%), topical (33%) and rectal (13%). Anti-inflammatory, analgesic activity and antinociceptive properties of medicines are known as some main mechanisms to manage sciatic pain. These functions are possessed by 30%, 15%, and 15% of the studied plants, respectively. Medicaments that can be introduced as lead agents for further investigation are Zingiber officinale Roscoe, Olea europaea L., Strychnos nux-vomica L and Artemisia vulgaris L which showed all of these properties in previous studies. Hence, conducting adducible clinical trials using these lead agents may lead to novel drugs with lesser undesirable and much more therapeutic effects on controlling sciatic pain.

Relative prevalence of 10 types of pharmacodynamic interactions in psychiatric treatment

OBJECTIVE

To assess the relative prevalence and factors affecting the prescription of medication combinations with a theoretical efficacy limiting pharmacodynamic interaction, defined as two medications with opposing indications and side effects or antagonistic action at the primary receptor of mechanism of action.

METHOD

One hundred sixteen combinations were identified for 10 types of pharmacodynamic interactions. PubMed was searched for each combination to assess the quality of evidence either supporting clinical use or verifying reduced efficacy. Micromedex was searched to determine the presence of warnings to prescribers of reduced efficacy. The prevalence in clinical practice was determined by computer review of the Genoa Healthcare database for all prescribers at 10 participating community mental health centers. The expected prevalence was calculated as the product of the probability of each medication prescribed alone and was compared with the actual prevalence of the combination using the test of proportions.

RESULTS

The frequency of prescription of eight combinations met the Bonferroni corrected level of significance of p < 0.001. Four were combinations of amphetamine and D2 antagonists and each were prescribed less often than chance, p = 0.0001 consistent with epidemiological studies and multiple animal studies verifying an efficacy limiting interaction. Despite epidemiological studies indicating increased risk of accidents, alprazolam and amphetamine were prescribed more often than chance, p = 0.0001. Micromedex generated warnings for efficacy limiting interactions for five other combinations, but with no subsequent change in prescription frequency.

CONCLUSIONS

Neither presence of medical evidence nor warnings from Micromedex consistently affect the prescription of combinations with pharmacodynamic efficacy limiting interactions.

Trazodone and mirtazapine: A possible opioid involvement in their use (at low dose) for sleep?

The efficacy of each antidepressant available has been found equal to that of amitriptyline in double-blind studies. However, a few of them are being prescribed (at under-therapeutic doses) for sleep, in non-depressed persons, when there are relative contraindications for sedative-hypnotics. Following previous studies regarding the antinociceptive mechanisms of various antidepressants, we suggest that the involvement of the opioid system in some of the antidepressants' mechanism of action may contribute to these medications' use for the induction and maintenance of sleep. The mostly prescribed antidepressants for sleep are trazodone (a weak, but specific inhibitor of the synaptosomal uptake of serotonin, that also binds to alpha-1 and alpha-2 adrenoreceptor sites) and mirtazapine (a postsynaptic drug which enhances noradrenergic and 5-HT1A-mediated serotonergic neurotransmission via antagonism of central alpha-2-auto- and hetero-adrenoreceptors). In our previous studies when ICR mice were tested with a hotplate analgesia meter, both trazodone and mirtazapine induced, a naloxone-reversible antinociceptive effect following i.p administration. Summing up the various interactions of trazodone and mirtazapine with opioid, noradrenergic and serotonergic agonists and antagonists, we found that the antinociceptive effect of trazodone is influenced by the opioid receptor subtypes mu and delta (and a clear 5-HT mechanism of antinociception), while the antinociceptive effect of mirtazapine is mainly influenced by kappa and mu opioid receptor subtype (combined with both serotonergic and noradrenergic receptors). This opioid profile of the two drugs may be one of the explanations to their efficacy in the treatment of insomnia, when sedatives (either benzodiazepines or the non-benzodiazepine "Z-compounds") cannot be prescribed.

Fentanyl-related designer drugs W-18 and W-15 lack appreciable opioid activity in vitro and in vivo

W-18 (4-chloro-N-[1-[2-(4-nitrophenyl)ethyl]-2-piperidinylidene]-benzenesulfonamide) and W-15 (4-chloro-N-[1-(2-phenylethyl)-2-piperidinylidene]-benzenesulfonamide) represent two emerging drugs of abuse chemically related to the potent opioid agonist fentanyl (N-(1-(2-phenylethyl)-4-piperidinyl)-N-phenylpropanamide). Here, we describe the comprehensive pharmacological profiles of W-18 and W-15, as examination of their structural features predicted that they might lack opioid activity. We found W-18 and W-15 to be without detectible activity at μ, δ, κ, and nociception opioid receptors in a variety of assays. We also tested W-18 and W-15 for activity as allosteric modulators at opioid receptors and found them devoid of significant positive or negative allosteric modulatory activity. Comprehensive profiling at essentially all the druggable GPCRs in the human genome using the PRESTO-Tango platform revealed no significant activity. Weak activity at the sigma receptors and the peripheral benzodiazepine receptor was found for W-18 (Ki = 271 nM). W-18 showed no activity in either the radiant heat tail-flick or the writhing assays and also did not induce classical opioid behaviors. W-18 is extensively metabolized, but its metabolites also lack opioid activity. Thus, although W-18 and W-15 have been suggested to be potent opioid agonists, our results reveal no significant activity at these or other known targets for psychoactive drugs.

Opioid Receptors Contribute to Antinociceptive Effect of Tianeptine on Colorectal Distension-Induced Visceral Pain in Rats

Tianeptine is a clinically effective atypical antidepressant with distinct neurochemical properties. In this study, we aimed to investigate the contribution of opioid receptors in the antinociceptive effect of tianeptine on visceral pain in awake rats and to differentiate the subtype and the localization (central and/or peripheral) of these opioid receptors involved in this antinociception. Visceromotor response to noxious colorectal distension (CRD) was quantified with electromyographic recordings, obtained from previously implanted electrodes into the external oblique musculature of rats under anesthesia, before and after tianeptine administration. The opioid receptor antagonist naloxone hydrochloride (NLX) and peripherally restricted opioid receptor antagonist naloxone methiodide (NLXM) were administered intravenously 10 min before tianeptine (10 mg/kg, i.v.). The antinociceptive effect of tianeptine was abolished by NLX (1 and 2 mg/kg, i.v.), but was partially reduced by NLXM (1 and 2 mg/kg, i.v.). A µ-opioid receptor-selective dose (0.03 mg/kg, i.v.) of NLX, but not NLXM, significantly inhibited the antinociceptive effect of tianeptine. Our results suggest that antinociceptive effect of tianeptine on CRD-induced visceral nociception in rats involves the activation of both central and peripheral opioid receptors.

Involvement of opioidergic and serotonergic systems in the analgesic activity of Cissus quadrangularis L. stem extract in mice

BACKGROUND

Cissus quadrangularis L. (Vitaceae) is used as a bonesetter and as an analgesic. However, the bioactive fractions and the pharmacological mechanism of analgesic activity are not clearly known. Hence, this study aimed to characterize the analgesic activity profile of successively extracted fractions of C. quadrangularis and the pharmacological mechanism of analgesic activity in mice.

METHODS

Dried C. quadrangularis stem was extracted successively with chloroform and methanol. The dried extracts were separately administered to mice intraperitoneally at the doses of 75, 150 and 300 mg/kg. The mice were tested separately in hot plate and tail flick tests. The mechanism of analgesic activity of chloroform extract was explored in the hot plate test at the dose of 300 mg/kg after pretreatment with naloxone, p-chlorophenylalanine methyl ester (pCPA) and phentolamine. The data were analyzed by one-way analysis of variance followed by Dunnett's test.

RESULTS

Chloroform extract showed significant (p<0.05) analgesic effect at the doses of 75, 150 and 300 mg/kg in hot plate and tail flick tests. Methanol extract showed significant (p<0.05) analgesic effect at the dose of 300 mg/kg in hot plate and tail flick tests. Analgesic activity was not blocked (p<0.05) in the group pretreated with phentolamine but blocked in the groups pretreated with naloxone and pCPA.

CONCLUSIONS

The chloroform extract was found to be more potent than methanol extract in inducing analgesic effect in mice, and the analgesic activity may be mediated through opioidergic and serotonergic pathways.

Mu opioids and their receptors: evolution of a concept

Opiates are among the oldest medications available to manage a number of medical problems. Although pain is the current focus, early use initially focused upon the treatment of dysentery. Opium contains high concentrations of both morphine and codeine, along with thebaine, which is used in the synthesis of a number of semisynthetic opioid analgesics. Thus, it is not surprising that new agents were initially based upon the morphine scaffold. The concept of multiple opioid receptors was first suggested almost 50 years ago (Martin, 1967), opening the possibility of new classes of drugs, but the morphine-like agents have remained the mainstay in the medical management of pain. Termed mu, our understanding of these morphine-like agents and their receptors has undergone an evolution in thinking over the past 35 years. Early pharmacological studies identified three major classes of receptors, helped by the discovery of endogenous opioid peptides and receptor subtypes-primarily through the synthesis of novel agents. These chemical biologic approaches were then eclipsed by the molecular biology revolution, which now reveals a complexity of the morphine-like agents and their receptors that had not been previously appreciated.

The effects of serotonin/norepinephrine reuptake inhibitors and serotonin receptor agonist on morphine analgesia and tolerance in rats

Several studies have demonstrated that serotonergic and noradrenergic systems have important roles in morphine analgesia and tolerance. However, the exact mechanism underlying the development of morphine tolerance is not fully understood. The aim of this study was to investigate the possible role of serotonin/norepinephrine reuptake inhibitors (amitriptyline, venlafaxine) and serotonin receptor (5-HT(1A) and 5-HT(1B/1D)) agonist (dihydroergotamine) in morphine analgesia and tolerance in rats. To constitute morphine tolerance, animals received morphine (50 mg/kg; s.c.) once daily for 3 days. After the last dose of morphine was injected on day 4, morphine tolerance was evaluated. The analgesic effects of amitriptyline (20 mg/kg; i.p.), venlafaxine (20 mg/kg; s.c.), dihydroergotamine (100 μg/kg; i.v.) and morphine (5 mg/kg) were considered at 15- to 30-min intervals (0, 15, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests. In this study, the data obtained suggested that amitriptyline and venlafaxine significantly increased the analgesic effect of morphine and attenuated the expression of morphine tolerance. However, dihydroergotamine significantly increased the analgesic effect of morphine but did not reduce the expression of morphine tolerance. In conclusion, we determined that co-administration of morphine with amitriptyline and venlafaxine increased the analgesic effects of morphine and attenuated the morphine analgesic tolerance.

Review article: palliative care in gynecologic oncology

Patients with advanced gynecologic malignancies have a multitude of symptoms; pain, nausea, and vomiting, constipation, anorexia, diarrhea, dyspnea, as well as symptoms resulting from intestinal obstruction, hypercalcemia, ascites, and/or ureteral obstruction. Pain is best addressed through a multimodal approach. The optimum palliative management of end-stage malignant intestinal obstruction remains controversial, with no clear guidelines governing the choice of surgical versus medical management. Patient selection for palliative surgery, therefore, should be highly individualized because only carefully selected candidates may derive real benefit from such surgeries. There remains a real need for more emphasis on palliative care education in training programs.

A greater role for the norepinephrine transporter than the serotonin transporter in murine nociception

Norepinephrine and serotonin involvement in nociceptive functions is supported by observations of analgesic effects of norepinephrine transporter (NET) and serotonin transporter (SERT) inhibitors such as amitriptyline. However, the relative contribution of NET and SERT to baseline nociception, as well as amitriptyline analgesia, is unclear. Amitriptyline and morphine analgesia in wild-type (WT) mice and littermates with gene knockout (KO) of SERT, NET or both transporters was conducted using the hotplate and tail-flick tests. Hypoalgesia was observed in NET KO mice, and to a lesser extent in SERT KO mice. The magnitude of this hypoalgesia in NET KO mice was so profound that it limited the assessment of drug-induced analgesia. Nonetheless, the necessary exclusion of these subjects because of profound baseline hypoalgesia strongly supports the role of norepinephrine and NET in basal nociceptive behavior while indicating a much smaller role for serotonin and SERT. To further clarify the role of NET and SERT in basal nociceptive sensitivity further experiments were conducted in SERT KO and NET KO mice across a range of temperatures. NET KO mice were again found to have pronounced thermal hypoalgesia compared to WT mice in both the hotplate and tail-flick tests, while only limited effects were observed in SERT KO mice. Furthermore, in the acetic acid writhing test of visceral nociception pronounced hypoalgesia was again found in NET KO mice, but no change in SERT KO mice. As some of these effects may have resulted from developmental consequences of NET KO, the effects of the selective NET blocker nisoxetine and the selective SERT blocker fluoxetine were also examined in WT mice: only nisoxetine produced analgesia in these mice. Collectively these data suggest that NET has a far greater role in determining baseline analgesia, and perhaps other analgesic effects, than SERT in mice.

Preclinical characterization of BRL 44408: antidepressant- and analgesic-like activity through selective alpha2A-adrenoceptor antagonism

Biogenic amines such as norepinephrine, dopamine, and serotonin play a well-described role in the treatment of mood disorders and some types of pain. As alpha2A-adrenoceptors regulate the release of these neurotransmitters, we examined the therapeutic potential of BRL 44408, a potent (Ki=8.5 nM) and selective (>50-fold) alpha2A-adrenoceptor antagonist (K(B)=7.9 nM). In rats, BRL 44408 penetrated the central nervous system resulting in peak brain and plasma concentrations of 586 ng/g and 1124 ng/ml, respectively. In a pharmacodynamic assay, pretreatment with BRL 44408 to rats responding under a fixed-ratio 30 operant response paradigm resulted in a rightward shift of the clonidine dose-response curve, an effect indicative of alpha2-adrenoceptor antagonism in vivo. Consistent with presynaptic autoreceptor antagonism and tonic regulation of neurotransmitter release, acute administration of BRL 44408 elevated extracellular concentrations of norepinephrine and dopamine, but not serotonin, in the medial prefrontal cortex. Additionally, BRL 44408, probably by inhibiting alpha2A heteroceptors, produced a significant increase in cortical levels of acetylcholine. In the forced swim test and schedule-induced polydipsia assay, BRL 44408 produced an antidepressant-like response by dose-dependently decreasing immobility time and adjunctive water intake, respectively, while in a model of visceral pain, BRL 44408 exhibited analgesic activity by decreasing para-phenylquinone (PPQ)-induced abdominal stretching. Finally, BRL 44408 did not produce deficits in overall motor coordination nor alter general locomotor activity. This preclinical characterization of the neurochemical and behavioural profile of BRL 44408 suggests that selective antagonism of alpha2A-adrenoceptors may represent an effective treatment strategy for mood disorders and visceral pain.

Advances in the pathophysiology of tension-type headache: from stress to central sensitization

Tension-type headache (TTH) is the most common and most socioeconomically costly headache. Yet our knowledge regarding TTH pathophysiological mechanisms is still in its early stages. Psychological stress and weak coping mechanisms may initiate and propagate physiological pain via activation of second messengers in downstream substrates involved in pain. It seems that peripheral mechanisms are predominant in the episodic type (ETTH), whereas central mechanisms are involved in the chronic type (CTTH) of tension headache. The conversion from ETTH to CTTH is most relevant to the clinician and the patient, as CTTH is the most debilitating. This paper focuses and summarizes our current understanding of central sensitization, the process by which this conversion occurs in TTH, and proposes an integrated model to explain how ETTH progresses into CTTH in genetically susceptible individuals.

Serotoninergic and non-serotoninergic effects of two tricyclic antidepressants on visceral nociception in a rat model

OBJECTIVE

Tricyclic antidepressants (TCAs) are well established in the treatment of patients with irritable bowel syndrome (IBS). The effects are believed to be linked to serotoninergic antinociceptive properties, but data on the antinociceptive effects of various TCAs with variable serotoninergic and non-serotoninergic properties have not been investigated. The aim of this study was to compare the antinociceptive effects of different TCAs.

MATERIAL AND METHODS

Colorectal distension (CRD) using a barostat device was carried out in rats and the visceromotor response (VMR) to CRD was quantified by abdominal wall electromyography. Prior to CRD, saline (control), amitriptyline (AM), desipramine (DES), reserpine (RES) or a combination of TCAs and RES (AM + RES or DES + RES) was applied intraperitoneally. Serum 5-HT levels were determined using high-performance liquid chromatography (HPLC). RES was used to antagonize the serotoninergic actions of TCAs in order to discriminate between these effects and others.

RESULTS

Both TCAs decreased the VMR compared to placebo. After RES application without TCAs, the VMR was increased compared to controls (6403 microV+/-1772 microV). Co-administration of AM and RES resulted in a modest decrease in VMR (5774 microV+/-1953 microV), while in rats treated with RES and DES the VMR again was significantly lower (3446 microV (+/-1347 microV; p <0.05)). 5-HT levels were higher in TCA pretreated rats than those in controls and significantly lower 5-HT levels were found in all rats pretreated with RES.

CONCLUSIONS

AM and DES have antinociceptive properties while RES is pro-nociceptive. The antinociceptive effects of DES are not abolished by RES pretreatment, while AM only attenuates the pro-nociceptive effects of RES. The non-serotoninergic properties of TCAs substantially contribute to the differences in the antinococeptive effects of various TCAs.

Delta-opioid receptors are critical for tricyclic antidepressant treatment of neuropathic allodynia

BACKGROUND

The therapeutic effect of antidepressant drugs against depression usually necessitates a chronic treatment. A large body of clinical evidence indicates that antidepressant drugs can also be highly effective against chronic neuropathic pain. However, the mechanism by which these drugs alleviate pain is still unclear.

METHODS

We used a murine model of neuropathic pain induced by sciatic nerve constriction to study the antiallodynic properties of a chronic treatment with the tricyclic antidepressants nortriptyline and amitriptyline. Using knockout and pharmacological approaches in mice, we determined the influence of delta-opioid receptors in the therapeutic action of chronic antidepressant treatment.

RESULTS

In our model, a chronic treatment by tricyclic antidepressant drugs totally suppresses the mechanical allodynia in neuropathic C57Bl/6J mice. This therapeutic effect can be acutely reversed by an injection of the delta-opioid receptor antagonist naltrindole. Moreover, the antiallodynic property of antidepressant treatment is absent in mice deficient for the delta-opioid receptor gene.

CONCLUSIONS

The antiallodynic effect of chronic antidepressant treatment is mediated by a recruitment of the endogenous opioid system acting through delta-opioid receptors.

The serotonin reuptake inhibitor citalopram does not affect colonic sensitivity or compliance in rats

Altered serotonin signaling has been implicated in the pathophysiology of irritable bowel syndrome (IBS). Selective serotonin reuptake inhibitors (SSRI) improve IBS symptoms, although the mechanism of action remains unclear. We assessed the effects of the SSRI, citalopram, on colonic sensitivity and compliance in rats after acute and repeated administration. Colorectal distension was performed in conscious rats. Pressure-volume relationships during colorectal distension (2-20 mmHg), fitted using a power exponential model [Vol=V(max)xexp[-(kappaxRelP)(beta)], were used as a measure of colonic compliance. The visceral pain-related visceromotor response during colorectal distension (10-80 mmHg) was used to assess visceral sensitivity. Pressure-volume curves and visceromotor responses were assessed after acute citalopram (3 or 10 mg/kg, ip) or vehicle and after repeated treatment (7 and 14 days; 3 or 10 mg/kg/day). In vehicle-treated animals, pressure-volume curves were similar over time. Citalopram (acute or repeated treatment) did not affect neither the pressure-volume curves nor the visceromotor response to colorectal distension. Thus, citalopram, after acute or repeated administration, had no significant effects on colon compliance or visceral pain during colorectal distension in rats. These results agree with recent observations in humans suggesting that the therapeutic actions of citalopram in IBS are independent of any effects on colonic sensorimotor function.

Differential and synergistic effects of selective norepinephrine and serotonin reuptake inhibitors in rodent models of pain

There is increasing recognition that norepinephrine (NE) and serotonin (5-HT) reuptake inhibitors (NRIs and SRIs) are efficacious in treating some types of pain. To date, studies have not systematically evaluated the relative activity at the NE and/or 5-HT transporter required for maximal efficacy in rodent pain models. Known selective NE and 5-HT reuptake inhibitors reboxetine, desipramine, fluoxetine, and paroxetine were evaluated in both in vitro and in vivo assays. Using the spinal nerve ligation model of neuropathic pain, the compounds differentially reversed tactile allodynia. Evaluation of a broader spectrum of reuptake inhibitors in the para-phenylquinone (PPQ)-induced abdominal constriction model, a model of acute visceral pain, demonstrated that both the SRIs and the NRIs significantly blocked abdominal constrictions. However, the magnitude of this effect was greater following treatment with compounds having greater affinity for NRI compared with SRI affinity. In addition, isobolographic analyses indicated significant synergistic effects for all combinations of desipramine and fluoxetine in the PPQ model of visceral pain. Collectively, the present results support the hypothesis that compounds with greater NRI activity should be more effective for the treatment of pain than compounds having only SRI activity, and this hypothesis is also supported by clinical data. These studies also suggest that the potency and effectiveness of NRIs might be enhanced by the presence of 5-HT activity.

The four-plates test: anxiolytic or analgesic paradigm?

The four-plates test (FPT) is an animal model of anxiety in which the exploration of the novel surroundings is suppressed by the delivery of a mild electric foot shock. The anti-nociceptive system has been reported to be activated by a variety of stressful stimuli such as footshock. The present study was thus designed to compare effects of drugs in the FPT and in the hot-plate test (an animal model of pain), in order to disambiguate the drug-induced anti-punishment effects obtained in the FPT from alterations in pain sensitivity. Various compounds, known to be implicated in anxiety states as well as nociception, have been studied. Although morphine induced a strong anti-nociceptive effect, it did not modify the number of shocks received in the FPT. Alprazolam and diazepam induced an anxiolytic-like effect in the FPT, at doses that did not induce any effect in the hot-plate test. The antidepressants previously reported anxiogenic (desipramine, maprotiline) in the FPT were found to be analgesic at the same doses. Milnacipran, venlafaxine and paroxetine did not modify the pain threshold, whereas they have previously been shown to induce anxiolytic-like effects in the FPT. The dopaminergic antidepressant agent nomifensine was without effect on both tests. Our results suggest that the reported drug-induced anti-punishment effects in the FPT are not related to modifications of pain threshold but to a pure anxiolytic-like effect.

Biopsychosocial pain medicine and mind-brain-body science

This article reviews how emotions, behavior, and psychiatric comorbidity influence the course and outcome of chronic pain disorders and addresses methods of identifying and managing these problems in clinical practice. Successful medical rehabilitation for patients with chronic pain requires (1) appreciating the effects of biopsychosocial factors in the onset, course, and outcomes of pain disorders; (2) understanding neurobiologic mechanisms linking mind, brain, and body in the functions of pain perception and modulation; and (3) being able to review critically and use selectively the plethora of new medications and interventional technologies that are proposed in the literature. Deficits in these skills now are recognized as hazardous to the public health so that medical school education and post residency training in pain medicine is now mandatory in some states.

Surgical treatment of superficial peroneal neuroma

BACKGROUND

Several techniques have been described for the surgical treatment of symptomatic superficial peroneal neuromas, including transection of the nerve with burial in muscle or bone to prevent recurrence.

METHODS

We compared in 27 consecutive patients the results of transection and burial of the proximal peroneal nerve stump into muscle (group A) with results of transection and burial of the proximal stump into bone (group B).

RESULTS

The perceived pain relief and improvement in mean pain score were significantly higher (p < .05) in group B than in group A. In addition, four patients in group A required revision neurotomy compared to none in group B.

CONCLUSION

For symptomatic superficial peroneal neuromas, transection with transposition of the proximal nerve stump into bone provides superior results compared with those of neurotomy with transposition of the proximal stump into muscle.

Evidence-based data from animal and human experimental studies on pain relief with antidepressants: a structured review

OBJECTIVE

It has been hypothesized that serotonin reuptake inhibitor antidepressants (ADs) are only weakly antinociceptive but augment noradrenergic (NA) antinociception. Thus, ADs with combined serotonergic (SN) and NA activity, (i.e., the serotonergic/noradrenergic (SN/NA) ADs) should have greater antinociceptive activity versus the NA ADs, which in turn should have more antinociceptive activity than the SN ADs. The objective of this structured review was to test this hypothesis by reviewing relevant basic science literature on the treatment of experimental pain with the above different types of ADs. DESIGN, SETTING, PARTICIPANTS, OUTCOME, MEASURES: Animal or human experimental AD pain treatment studies were located by the usual search methods. For animal studies only placebo-controlled studies were included for review. For human studies only double blind placebo-controlled studies were selected for review. The animal and human studies were then sorted according to the pain model represented, e.g., neuropathic pain model. Studies were then characterized according to the type of AD utilized, and the antinociceptive outcome of the AD trial.

RESULTS

Twenty-two animal studies and 5 human studies fulfilled the inclusion criteria of this structured review. Within the animal nonspecific pain model there were 10 SN/NA AD trials, 9 NA AD trials and 7 SN AD trials. Of these trials 100%, 88.9%, and 14.3% respectfully demonstrated a positive AD antinociceptive effect. Overall, for all the animal models there were 25 SN/NA, 9 NA, and 8 SN trials. Of these trials 92%, 88.9%, and 25% respectfully demonstrated a positive AD antinociceptive effect. For the human pain models, only the SN/NA ADs had been utilized in 7 trials. Here in 42.8% of the trials there was a reported antinociceptive effect.

CONCLUSIONS

Overall, the results of this structured review support the above hypothesis.

Analgesic effect of amitriptyline in chronic tension-type headache is not directly related to serotonin reuptake inhibition

The tricyclic antidepressant amitriptyline is the only documented and most widely used prophylactic drug for chronic tension-type headache (CTTH). However, it is not fully clarified whether the serotonin (5-HT) reuptake inhibition plays a major role for the analgesic effect of amitriptyline. To explore the importance of 5-HT reuptake inhibition for mechanism of action of the analgesic effect of amitriptyline we investigated platelet 5-HT levels during preventive treatment of CTTH with amitriptyline, the selective serotonin reuptake inhibitor citalopram, and placebo. Thirty-four patients with CTTH were given preventive treatment with amitriptyline 75 mg/day, the selective 5-HT reuptake inhibitor citalopram 20 mg/day, and placebo in a 32-week, double-blind, placebo-controlled, three-way crossover trial. Blood samples were collected in the last week of each treatment period. Platelet 5-HT was used as a measure of 5-HT reuptake inhibition and determined by high performance liquid chromatography. Area under the headache curve was 308 (157-715) (median with quartiles in parentheses) with amitriptyline and significantly lower than 377 (158-1121) with citalopram (P = 0.04) and 441 (178-1408) with placebo (P = 0.002). There was no difference between citalopram and placebo (P = 0.23). Platelet 5-HT was 0.4 (0.3-0.7) x 10(-18)mol/platelet with citalopram, which was significantly lower than 1.7 (1.2-2.4) x 10(-18)mol/platelet with amitriptyline (P < 0.001), and 3.5 (2.8-4.3) x 10(-18)mol/platelet with placebo (P < 0.001). The lower platelet 5-HT during treatment with citalopram than amitriptyline indicates that 5-HT reuptake was most effectively inhibited by citalopram. In contrast, amitriptyline was most effective in reduction of headache. This suggests that the analgesic effect of amitriptyline in CTTH is not solely due to 5-HT reuptake inhibition and that other mechanisms such as norepinephrine reuptake inhibition, NMDA receptor antagonism, blockade of muscarinic receptors and ion channels should be addressed in the future research.

Peripherally administered amitriptyline derivatives have differential anti-allodynic effects in a rat model of neuropathic pain

We assessed if derivatives of amitriptyline could alleviate mechanical allodynia in a rat model of neuropathic pain. N-methyl amitriptyline (NMA), and amitriptyline HCl (AHC) were compared to evaluate the antiallodynic effects produced by systemic and peripheral administration. Under general anesthesia with halothane, neuropathic injury was produced in rats by tightly ligating the left L5 and L6 spinal nerves. All animals developed neuropathic pain behaviors within 7 days after the surgery. For systemic delivery, three groups of rats were injected intraperitoneally with NMA (15 mg/kg), AHC (12.5 mg/kg), or saline. For peripheral routes of injection, rats were divided into 3 x 3 groups and injected with 100, 330, and 1000 nmol/kg doses of each NMA, AHC and 0.9% normal saline. NMA and AHC suppressed mechanical allodynia following peripheral administration but not following intraperitoneal injection. NMA was less potent but showed a longer-acting response than AHC. This study shows that NMA can be used to relieve mechanical allodynia and is a longer-acting agent than AHC.

Antinociceptive effects of tricyclic antidepressants and their noradrenergic metabolites

This study evaluates the antinociceptive effect of several tricyclic antidepressants in four nociceptive tests which employ either thermal (hot plate and tail flick tests) or chemical (formalin and acetic acid tests) stimuli. Forced swimming test was also performed as a model of depression and an activity test was also performed. Mixed antidepressants in current clinical use: amitriptyline, imipramine and clorimipramine and their respective main secondary metabolites which preferentially inhibit noradrenaline reuptake: nortriptyline, desipramine and desmethylclorimipramine, were tested (2.5-20 mg/kg, i.p.) in mice. The results show a stronger antinociceptive effect in chemical tests induced by all the drugs, compared with thermal tests. The doses needed to produce antinociception were lower than those inducing an antidepressive effect, both effects being mutually independent. The overall results show that preferentially noradrenergic tricyclics induced an antinociceptive effect comparable with that of mixed tricyclics, indicating that noradrenaline reuptake plays an important role in tricyclic-induced antinociception.

The antinociceptive effect of mirtazapine in mice is mediated through serotonergic, noradrenergic and opioid mechanisms

The antinociceptive effects of the noradrenergic and specific serotonergic antidepressant (NaSSA) drug mirtazapine and its interaction with various opioid receptor subtypes were evaluated in mice with a hotplate analgesicmeter. Mirtazapine elicited an antinociceptive effect in a dose-dependent manner following doses from 1 to 7.5mg/kg. As the mirtazapine dose increased beyond 10mg/kg latencies returned to baseline, yielding a biphasic dose-response curve. The effect of opioid, adrenergic, and serotonergic receptor antagonists was examined as to their ability to block mirtazapine antinociception. Mirtazapine (at 10mg/kg)-induced antinociception was significantly inhibited by naloxone, nor-BNI, and naltrindole, but neither by beta-FNA nor by naloxonazine, implying the involvement of kappa(1)- and delta-opioid mechanisms. When adrenergic and serotonergic antagonists were used, both metergoline and yohimbine, decreased antinociception elicited by mirtazapine, implying a combined serotonergic and noradrenergic mechanism of antinociception. When mirtazapine was administered together with various agonists of the opioid receptor subtypes, it significantly potentiated antinociception mediated only by kappa(3)-opioid receptor subtypes. Summing up these results we conclude that the antinociceptive effect of mirtazapine is mainly influenced by the kappa(3)-opioid receptor subtype combined with both serotonergic and noradrenergic receptors. These results suggest a potential use of mirtazapine in the management of some pain syndromes, and raise questions regarding a possible indirect opioid-dependence induced by mirtazapine. However, further research is needed in order to establish both the exact clinical indications and the effective doses of mirtazapine when prescribed for pain.

Efficacy of oral doxepin and piroxicam treatment for interstitial cystitis

OBJECTIVE

To establish the efficacy of a multidrug oral treatment with the tricyclic antidepressant agent doxepin and the cyclooxygenase (COX) inhibitor piroxicam in patients with interstitial cystitis (IC), who had failed standard therapy in an open, prospective, nonrandomized study.

METHODS

A total of 37 patients diagnosed with IC received 75 mg doxepin and 40 mg piroxicam daily. The treatment was termed DOXCAM. Effectiveness of therapy was assessed with frequency-volume charts, an IC symptom score and with cystometry prior to treatment, 8 weeks after the start and 4 weeks after termination of drug treatment.

RESULTS

Medication was not tolerated by five patients. Twenty-six of 32 patients have experienced virtual total remission of symptoms (81%) and six patients had significant relief (19%). DOXCAM treatment resulted in a significant percent decrease in pain (65% versus 21%). Daytime frequency decreased from 17.6+/-5.7 to 11.3+/-3.6 voids while nocturia did not improve significantly. Twenty-three of the 26 patients who became symptom free and four of the six patients who showed significant improvement had a return of symptoms after cessation of therapy.

CONCLUSION

It is reasonable to consider oral treatment with DOXCAM in those patients who have failed first-line therapies.

Efficacy of amitriptyline for relief of pain in spinal cord injury: results of a randomized controlled trial

Chronic pain in persons with spinal cord injury (SCI) is a difficult problem for which there is no simple method of treatment. Few randomized controlled trials of medications for pain in persons with SCI have been conducted. This study was designed to determine whether amitriptyline, a tricyclic antidepressant, is efficacious in relieving chronic pain and improving pain-related physical and psychosocial dysfunction in persons with SCI. Eighty-four participants with SCI and chronic pain were randomized to a 6-week trial of amitriptyline or an active placebo, benztropine mesylate. All pre- and post-treatment assessments were conducted by evaluators blind to the allocation. Regression analyses were conducted to examine whether there was a medication group effect on the primary (average pain intensity) and secondary outcome measures. No significant differences were found between the groups in pain intensity or pain-related disability post-treatment, in either intent-to-treat analyses or analyses of study completers. These findings do not support the use of amitriptyline in the treatment of chronic pain in this population, but we cannot rule out the possibility that certain subgroups may benefit.

The psychopharmacologic treatment of depression and anxiety in the context of chronic pain

Chronic pain afflicts millions of people, commonly causing depression and anxiety. These conditions must be treated to achieve a good functional outcome from pain treatment. Selective serotonin reuptake inhibitors, tricyclics, and newer antidepressants effectively treat both depression and selected anxiety disorders. Antidepressants with noradrenergic and serotinergic activity, and anticonvulsants, which may also stabilize mood, are effective in neuropathic pain. Other medications have limited but important pharmacotherapeutic roles.

The antinociceptive effect of moclobemide on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy

The aim of our study was to investigate the antinociceptive activity of moclobemide on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy. The neuropathy was produced by ligation of the sciatic nerve and nociceptive thresholds were determined 15-21 days after surgery by a modification of the Randall-Sellito method. Group 1 (n= 10) received 0.2 ml peroral (p.o.) saline, Group 2 (n= 10) 5 mg x kg(-1), Group 3 (n= 10) 10 mg x kg(-1) and Group 4 (n= 10) 20 mg x kg(-1) p.o. moclobemide. Nociceptive pressure thresholds were then measured every 20 minutes after drug administration. Analysis of variance, Tukey's test and a paired Student's t-test were employed for statistical analysis. The perorally administered moclobemide (5, 10 and 20 mg x kg(-1)) produced an antinociceptive effect on both lesioned and non-lesioned hind paws ( P< 0.05). However, the analgesic effect on the lesioned paw was significantly more potent than the non-lesioned paw. The peak value ( p) remained constant while the maximal increment between the control threshold and the peak value ( I(max)) was significantly more pronounced for the lesioned paw ( P< 0.001). The results of this study may suggest that moclobemide can be a therapeutic alternative to treat some clinical symptoms in peripheral neuropathic conditions.

Chronic administration of amitriptyline and caffeine in a rat model of neuropathic pain: multiple interactions

This study was designed to determine (1) whether chronic amitriptyline administration was effective in alleviating symptoms of neuropathic pain in a rat model of spinal nerve injury, and (2) whether the effect of amitriptyline involved manipulation of endogenous adenosine, by determining the effect of caffeine, a non-selective adenosine A(1) and A(2) receptor antagonist, on its actions. Nerve injury was produced by unilateral spinal nerve ligation of the fifth and sixth lumbar nerves distal to the dorsal root ganglion, and this resulted in stimulus-evoked thermal hyperalgesia and static tactile mechanical allodynia. Animals received pre- and post-surgical intraperitoneal doses of amitriptyline (10 mg/kg) and caffeine (7.5 mg/kg), alone or in combination, and following surgery, were administered amitriptyline (15-18 mg/kg/day) and caffeine (6-8 mg/kg/day), alone or in combination, in the drinking water. Rats were tested for thermal reaction latencies and static tactile thresholds at 7, 14 and 21 days following surgery. In the paw ipsilateral to the nerve ligation, chronic amitriptyline administration consistently decreased the thermal hyperalgesia produced by spinal nerve ligation over a 3-week period, and this effect was blocked by concomitant caffeine administration at all time intervals. In the contralateral paw, thermal withdrawal latencies were more variable, with the most reproducible finding being a reduction in thermal thresholds in the amitriptyline-caffeine combination group. There was no effect by either drug or the drug combination on the static tactile allodynia produced by spinal nerve ligation in the ipsilateral paw. However, chronic amitriptyline administration induced a tactile hyperaesthesia in the contralateral paw at all time intervals, and this effect was exacerbated by concomitant chronic caffeine administration. The results of this study indicate that chronic administration of amitriptyline is effective in alleviating thermal hyperalgesia, but not static tactile allodynia, in the hindpaw ipsilateral to nerve injury, and the block of this effect by caffeine suggests that this effect is partially achieved through manipulation of endogenous adenosine systems. Additionally, chronic amitriptyline administration induces contralateral hyperaesthetic responses that are augmented by caffeine. Both the symptom-specific effect, and adenosine involvement in amitriptyline action may be important considerations governing its use in neuropathic pain.

On the antinociceptive effect of fluoxetine, a selective serotonin reuptake inhibitor

Antidepressant drugs are reported to be used as co-analgesics in clinical management of migraine and neuropathic pain. The mechanism through which they alleviate pain remains unknown. The present study explores the possible mechanism of a selective serotonin reuptake inhibitor (SSRI) fluoxetine-induced antinociception in animals. Acetic acid-induced writhing, hot plate and tail-flick test were used to assess fluoxetine-induced antinociception. Fluoxetine (5-20 mg kg(-1), i.p.) produced a significant and dose-dependent antinociceptive effect against acetic acid-induced writhing in mice. Fluoxetine (20 mg kg(-1)) also exhibited antinociceptive effect in tail flick as well as hot plate assays. Further, i.c.v. administration of fluoxetine showed significant antinociception against writhing test in rats. However, fluoxetine (1 microg/10 microl/rat, i.c.v.) did not exhibit any antinociceptive effect in serotonin-depleted animals. Further, pindolol (10 mg kg(-1), i.p.) enhanced fluoxetine-induced antinociceptive effect. The antinociceptive effect of fluoxetine was sensitive to blockade by naloxone (5 mg kg(-1), i.p.) and naltrexone (5 mg kg(-1), i.p.). These data suggest that fluoxetine-induced antinociception involves both central opioid and the serotoninergic pathways.

Complex salvage procedures for severe lower extremity nerve pain

From 1995 to 1999, the senior author did revision nerve release and vein wrapping (58 limbs in 58 patients) or peripheral nerve stimulation (62 limbs in 62 patients) to relieve intractable lower extremity nerve pain. Vein wrapping was done if the patient had temporary relief after a previous nerve release, if there was evidence of scarring around the nerve, and if nerve pain was triggered by mechanical stimulation. Peripheral nerve stimulation was done when previous nerve operations provided no relief or if the nerve pain was more constant and spontaneous without mechanical provocation. The duration of symptoms preoperatively averaged 52 months, and the number of previous peripheral neurosurgical interventions averaged 2.5. Postoperatively, the average pain improvement was rated as 60% for the patients who had vein wrapping and 41% for the patients who had peripheral nerve stimulation. Of the patients who had vein wrapping, 53% were satisfied, 14% were somewhat satisfied, and 33% were dissatisfied. Of the patients who had peripheral nerve stimulation, 61% were satisfied, 21% were somewhat satisfied, and 18% were dissatisfied. Most patients (78%) stated they would undergo the procedures again.

Neuropharmacology of venlafaxine

Venlafaxine (Effexor) is an effective antidepressant and has also been approved for the treatment of generalized anxiety disorder. Venlafaxine was initially characterized as an inhibitor of both serotonin (5HT) and norepinephrine (NE) uptake and was therefore termed a "dual uptake inhibitor." This chapter reviews data from both in vitro and in vivo studies regarding its effects on 5HT and NE neurotransmission. In addition, the effects of venlafaxine on other systems that may play a role in its therapeutic efficacy effects are described. The data indicate that venlafaxine is a relatively weak inhibitor of NE transport in vitro. In vivo studies indicate that venlafaxine selectively inhibits 5HT uptake at low therapeutic doses and inhibits both 5HT and NE uptake at higher therapeutic doses. This chapter concludes with a discussion of the effects of venlafaxine on various aspects of physiology.

Surgical treatment of chronic lower extremity neuropathic pain

The current authors retrospectively reviewed 147 lower extremity peripheral nerve procedures in 114 patients (average age, 42 years) with chronic lower extremity neuropathic pain to determine whether surgical treatment based on an empirically derived algorithm could reduce pain and improve function. This algorithm assigns crush, stretch, and chronic transection injuries to treatment with transection and containment. Peripheral nerve stimulation was used in conjunction with transection and containment for patients with more chronic presentations for whom previous transections had been unsuccessful. Patients with adhesive neuralgia underwent revision neurolysis with vein wrapping. Patients with repetitive nerve trauma (overuse) underwent primary or revision neurolysis. Duration of symptoms averaged 37 months, and mechanisms of nerve injury included chronic transection, crush, adhesive neuralgia, stretch, repetitive trauma, and idiopathic etiology. Time to followup averaged 38 months. Pain and dysfunction were ranked from 0 points (no pain or dysfunction) to 10 points (pain prompting request for amputation or functional deficit warranting wheelchair use); preoperative and followup work status were documented. Average pain and dysfunction scores improved: 8.8 to 5.6 points and 7.6 to 5.0 points, respectively. Of the 114 patients, 52 (46%) patients improved their work status, including 35 of 87 (40%) involved in workers' compensation. There were no statistically significant differences in outcome based on mechanism of nerve injury or type of procedure. The consistent average improvement suggests this algorithm assigns the appropriate procedure to a given mechanism of injury.

Managing pain and psychological issues in palliative care

The management of psychological issues and pain in dying patients have steadily improved. With currently available drugs and techniques, it should be possible for nearly all women with terminal gynaecological cancer to be pain-free. The World Health Organization (WHO) Analgesic Ladder can be effectively utilized for pharmacological treatment of cancer pain. Most side-effects of opioid therapy can be well controlled. Patients whose pain cannot be adequately relieved by systemic opioid therapy may benefit from invasive anaesthetic or neurosurgical techniques. Terminal sedation should be used only after all other therapy has failed. This chapter describes the assessment and management of opioid analgesics and the treatment of their side-effects. Adjuvant analgesic drugs and therapies are also presented.

Antinociception by tricyclic antidepressants in the rat formalin test: differential effects on different behaviours following systemic and spinal administration

The present study (1) examined analgesic effects of systemically and spinally administered antidepressants (ADs) on phase 2 flinching and biting/licking behaviours in the rat formalin test, a model considered to be of greater relevance to clinical pain than acute threshold tests, and (2) determined whether motor or anti-inflammatory effects contributed to such actions. Systemic administration of amitriptyline (3-20 mg/kg) produced a dose-related enhancement of flinching behaviours, while at the same time suppressing biting/licking behaviours. Imipramine (except for 20 mg/kg), nortriptyline, desipramine and fluoxetine had no significant effect on flinching behaviours, while producing a dose-related suppression of biting/licking behaviours. When administered spinally, either by acute lumbar puncture or via chronically implanted intrathecal cannulas, amitriptyline similarly augmented flinching behaviours. When given by lumbar puncture, amitriptyline suppressed biting/licking behaviours, but when intrathecal cannulas were used, this behaviour was not expressed in the formalin group. Other ADs also suppressed biting/licking behaviours without affecting flinching when given by lumbar puncture. Effects on paw volume were determined at the end of behavioural testing. Systemic administration of all ADs produced a dose-related reduction in paw volume. Spinal administration of nortriptyline by lumbar puncture also reduced paw volume, but for other agents, the reduction was not significant. Motor effects were noted qualitatively throughout these experiments, and considered in relation to nociceptive behaviours. These results indicate (a) a marked dissociation between the effects of systemic ADs on flinching and biting/licking behaviours in the formalin test, (b) spinal efficacy of ADs that essentially reproduces effects seen with systemic administration when given by lumbar puncture, (c) a lack of causality between anti-inflammatory effects of ADs and their analgesic properties in the formalin test, and (d) a contribution of motor effects to analgesic actions at higher doses affecting biting/licking but not flinching behaviours.

Nonoperative treatment for lumbar spinal stenosis

The natural history of degenerative lumbar spinal stenosis is documented poorly. Little is known about the efficacy of nonoperative treatments. An aggressive nonoperative treatment consisting of therapeutic exercise, analgesics, and epidural steroid injections is proposed. The clinical evaluation of the patients is reviewed and the relevance to the selection of the nonoperative treatment plans is emphasized. Efficacy of nonoperative treatment may depend greatly on the nature and severity of the patient's symptomatic and radiographic presentation. Several studies on nonoperative treatment of patients with between 1 and 5 years of followup suggest that variably 15% to 43% of patients will have continued improvement after nonoperative treatment.

Effect of chronic and acute administration of fluoxetine and its additive effect with morphine on the behavioural response in the formalin test in rats

Serotonergic systems are involved in the central regulation of nociceptive sensitivity. Fluoxetine, a selective inhibitor of the reuptake of serotonin (5-hydroxytryptamine, 5-HT), was administered orally (0.16, 0.32, 0.8 mg kg(-1) daily for 7 days), intraperitoneally (0.04, 0.08, 0.16 mg kg(-1) day(-1) for 7 days and a single dose of 0.32 mg kg(-1)) and intracerebroventricularly (10 microg/rat) to rats and nociceptive sensitivity was evaluated using the formalin test (50 microL of 2.5% formalin injected subcutaneously). The effect of fluoxetine was also studied in the presence of 5,7-dihydroxytryptamine creatinine sulfate (5,7-DHT) and after co-administration with morphine. Oral (0.8 mg kg(-1)), intraperitoneal (0.16 and 0.32 mg kg(-1)) and intracerebroventricular (10 microg/rat) fluoxetine induced antinociception in the late phase of the formalin test. Furthermore, intrathecal administration of 5-HT (100 microg/rat) induced an analgesic effect. The analgesic effect of fluoxetine (0.16 and 0.32 mg kg(-1), i.p.) and 5-HT (100 microg/rat, i.t.) was abolished by pre-treatment with 5,7-DHT (100 microg/rat, i.t.). In addition, the analgesic effect of 5-HT (100 microg/rat, i.t.) was decreased by pre-treatment with naloxone (2 mg kg(-1), i.p.). Morphine (5 mg kg(-1), i.p.) induced analgesia that was increased by fluoxetine (0.32 mg kg(-1), i.p.). These results suggest that fluoxetine has an antinociceptive effect in tonic inflammatory pain through functional alteration of the serotonergic system and also potentiates the analgesic effect of morphine.

Neurophysiology of Cancer Pain: From the Laboratory to the Clinic

Pain is one of the most distressing symptoms associated with cancer. Basic science research has provided much insight into the mechanisms of peripheral and central pain and the actions of new drugs. Despite these advances, pain accompanying malignancy can be difficult to treat. Pain most commonly presents when the tumor has invaded somatic,visceral, or neural structures. An understanding of pain mechanisms is essential when deciding on the appropriate treatment. New therapeutic options have been developed and will hopefully provide clinicians with tools to successfully alleviate cancer pain.

The antinociceptive effect of trazodone in mice is mediated through both mu-opioid and serotonergic mechanisms

The antinociceptive effects of trazodone (a triazolopyridine derivative with antidepressant activity) and its interaction with various opioid, noradrenaline and serotonin receptor subtypes were evaluated. Mice were tested with a hotplate analgesia meter. Trazodone induced a dose-dependent antinociceptive effect following i.p. administration. The ED(50) for mice in the hotplate assay for trazodone was 24.8 mg/kg (9.8; 67.4; 95% CL). The effect of opioid, adrenergic and serotonergic receptor antagonists was examined as to their ability to block trazodone antinociception. Trazodone-induced antinociception was significantly inhibited by naloxone, beta-FNA and naloxonazine, but not by nor-BNI or naltrindole, implying involvement of mu1- and mu2-opioid mechanisms. When adrenergic and serotonergic antagonists were used, metergoline (p<0.05) but not phentolamine or yohimbine, decreased antinociception elicited by trazodone, implying a clear 5-HT mechanism of antinociception. When trazodone was administered together with various agonists of the opioid receptor subtypes, it significantly potentiated antinociception mediated by mu1- and mu2- opioid receptor subtypes. Summing up these results, we conclude that the antinociceptive effect of trazodone is mainly influenced by the mu1- +mu2-opioid receptor subtype combined with the serotonergic receptor. These results explain the diffuse clinical use of trazodone in the management of some pain syndromes, and in opioid- and alcohol-detoxification programs, but raise questions regarding a possible 'indirect' opioid-dependence induced by trazodone itself.

Amitriptyline reduces myofascial tenderness in patients with chronic tension-type headache

The tricyclic anti-depressant amitriptyline is widely used in the treatment of chronic tension-type headache. The aim of the present study was to investigate whether the analgesic effect is caused by a reduction of muscle pain or by a general reduction of pain sensitivity. Thirty-three non-depressed patients with chronic tension-type headache were treated with amitriptyline 75 mg/day and with the highly selective serotonin reuptake inhibitor citalopram 20 mg/day in a 32-week, double-blind, placebo-controlled, three-way crossover study. At the end of each treatment period, actual headache intensity and pericranial myofascial tenderness were recorded, pressure pain detection and tolerance thresholds were measured in the finger and in the temporal region and the electrical pain threshold was measured at the labial commissure. Amitriptyline reduced tenderness and headache intensity significantly more than placebo (P=0.01 and P=0.04, respectively). The reduction in tenderness could be ascribed solely to the group of patients who responded to amitriptyline treatment by at least 30% reduction in headache while tenderness was unchanged in non-responders. Amitriptyline did not affect pressure or electrical pain thresholds at any of the examined locations. Citalopram had no significant effect on any of the examined parameters. These findings indicate that amitriptyline elicits its analgesic effect in chronic myofascial pain by reducing the transmission of painful stimuli from myofascial tissues rather than by reducing overall pain sensitivity. We suggest that this effect is caused by a segmental reduction of central sensitization in combination with a peripheral anti-nociceptive action.

Peripheral nerve vein wrapping for intractable lower extremity pain

HYPOTHESIS/PURPOSE

The purpose of this study was to determine the effectiveness of lower extremity peripheral nerve vein wrapping procedures in the management of patients with intractable lower extremity pain. The hypothesis was that nerve insulation through vein wrapping is effective in treating symptoms related to adhesive neuralgia, but not those secondary to intraneural damage.

METHODS

We retrospectively reviewed 25 consecutive patients whose intractable chronic lower extremity peripheral neuralgia had been treated with revision neurolysis and vein wrapping. The 14 women and 11 men had an average age of 39 years (range, 21 to 53 years). Vein wrapping was performed using a saphenous vein autograft in 19 patients and a fetal umbilical vein in six patients. The average length of follow-up after vein wrapping was 24 months (range, 12 to 63 months). Assessment of pain and dysfunction was on a scale of 0 (no pain/dysfunction) to 10 (severe enough to prompt request for amputation and required use of a wheelchair).

RESULTS

Pain scores improved from a preoperative average of 8.7 points (range, 6 to 10 points) to a postoperative average of 4.6 points (range, 0 to 10 points); dysfunction improved from a preoperative average of 7.3 points (range, 3 to 10 points) to a postoperative average of 4.4 points (range, 0 to 9 points). Although 17/25 patients were satisfied with the procedure, only 14/25 stated they would undergo the surgery again. All eight patients who exhibited no improvement had preoperative and intraoperative evidence of an idiopathic etiology and/or intraneural damage. Preoperatively, 18/25 patients could not work; postoperatively, that number improved to 8/25.

CONCLUSIONS

Vein wrapping of lower extremity peripheral nerves is most effective in relieving symptoms related to adhesive neuralgia and less beneficial in the presence of intraneural damage. Although symptoms are rarely relieved completely, vein wrapping typically results in a substantial improvement in symptoms related to scar entrapment of peripheral nerves.

Antinociception induced by amitriptyline and imipramine is mediated by alpha2A-adrenoceptors

The involvement of alpha2-adrenoceptors in the antinociception induced by the tricyclic antidepressants amitriptyline and imipramine was investigated in mice by using the hot-plate and abdominal constriction tests. The antinociception produced by amitriptyline (15 mg/kg, i.p.) and imipramine (15 mg/kg, i.p.) was prevented by reserpine (2 mg/kg, i.p.) and yohimbine (3-10 mg/kg, i.p.) but not by naloxone (1 mg/kg, i.p.), atropine (5 mg/kg, i.p.), CGP 35348 (100 mg/kg, i.p.) and prazosin (1 mg/kg, i.p.). On the basis of the above data, it can be postulated that amitriptyline and imipramine exerted their antinociceptive effect by activation of alpha2-adrenoceptors. Administration of the alpha2A-adrenoceptor antagonist BRL 44408 (1 mg/kg, i.p.) prevented amitriptyline and imipramine antinociception, whereas the alpha2B/C-adrenoceptor antagonist ARC 239 (10 mg/kg, i.p.) was ineffective. These data indicate that the enhancement of the pain threshold produced by amitriptyline and imipramine is mediated by activation of alpha2A-adrenoceptors. Neither tricyclic antidepressants nor the antagonists used impaired mouse performance evaluated by the rota-rod and hole-board tests.

Adhesive capsulitis of the glenohumeral joint with an unusual neuropathic presentation: a case report

A 37-yr-old woman presented with a 7-mo history of unilateral shoulder girdle stiffness, pain, and weakness and had already been diagnosed with frozen shoulder. Physical examination revealed scapular winging and suspicious focal paralysis of shoulder girdle muscles. Subsequently, electrodiagnostic studies reported denervation of deltoid, infraspinatus, serratus anterior, and lower cervical paraspinal muscles, in addition to a prolonged long thoracic nerve latency. The history, physical examination, and cervical magnetic resonance imaging scan seemed most consistent with neuralgic amyotrophy, although the electrodiagnostic examination could be interpreted as cervical radiculopathy. Some of the difficulties in identifying neuralgic amyotrophy and distinguishing it from cervical radiculopathy are discussed herein. Historically, frozen shoulder has seemed to develop as a complication of the neuropathic process. Both neuralgic amyotrophy and frozen shoulder have a poorly understood pathogenesis, and their combined presence is presumed to be rare. Because of difficulties inherent in the physical examination of frozen shoulder, a coexistent neuropathic process may go undetected.

Effects of noradrenergic and serotonergic antidepressants on chronic low back pain intensity

To understand the relative efficacy of noradrenergic and serotonergic antidepressants as analgesics in chronic back pain without depression, we conducted a randomized, double-blind, placebo-control head-to-head comparison of maprotiline (a norepinephrine reuptake blocker) and paroxetine (a serotonin reuptake blocker) in 103 patients with chronic low back pain. Of these 74 completed the trial; of the 29 who did not complete, 19 were withdrawn because of adverse effects. The intervention consisted of an 8-week course of maprotiline (up to 150 mg daily) or paroxetine (up to 30 mg daily) or an active placebo, diphenhydramine hydrochloride (up to 37.5 mg daily). Patients were excluded for current major depression. Reduction in pain intensity (Descriptor Differential Scale scores) was significantly greater for study completers randomized to maprotiline compared to placebo (P=0.023), and to paroxetine (P=0.013), with a reduction of pain by 45% compared to 27% on placebo and 26% on paroxetine. These results suggest that at standard dosages noradrenergic agents may provide more effective analgesia in back pain than do selective serotonergic reuptake inhibitors.

The antinociceptive effect of venlafaxine in mice is mediated through opioid and adrenergic mechanisms

The antinociceptive effects of the novel phentylethylamine antidepressant drug venlafaxine and its interaction with various opioid, noradrenaline and serotonin receptor subtypes were evaluated. When mice were tested with a hotplate analgesia meter, venlafaxine induced a dose-dependent antinociceptive effect following i.p. administration with an ED50 of 46.7 mg/kg (20.5; 146.5; 95% CL). Opioid, adrenergic and serotoninergic receptor antagonists were tested for their ability to block venlafaxine antinociception. Venlafaxine-induced antinociception was significantly inhibited by naloxone, nor-BNI and naltrindole but not by beta-FNA or naloxonazine, implying involvement of kappa1- and delta-opioid mechanisms. When adrenergic and serotoninergic antagonists were used, yohimbine (P < 0.005) but not phentolamine or metergoline, decreased antinociception elicited by venlafaxine, implying a clear alpha2- and a minor alpha1-adrenergic mechanism of antinociception. When venlafaxine was administered together with various agonists of the opioid and alpha2- receptor subtypes, it significantly potentiated antinociception mediated by kappa1- kappa3- and delta-opioid receptor subtypes. The alpha2-adrenergic agonist clonidine significantly potentiated venlafaxine-mediated antinociception. Summing up these results, we conclude that the antinociceptive effect of venlafaxine is mainly influenced by the kappa- and delta-opioid receptor subtypes combined with the alpha2-adrenergic receptor. These results suggest a potential use of venlafaxine in the management of some pain syndromes. However, further research is needed in order to establish both the exact clinical indications and the effective doses of venlafaxine when prescribed for pain.

Peripheral antinociceptive actions of desipramine and fluoxetine in an inflammatory and neuropathic pain test in the rat

Amitriptyline, a non-selective noradrenaline (NA) and 5-hydroxytryptamine (5-HT) reuptake inhibitor, has recently been demonstrated to produce a peripheral antinociceptive action in an inflammatory (formalin test) and a neuropathic pain model (spinal nerve ligation). In the present study, we determined whether desipramine, a selective NA reuptake inhibitor, and fluoxetine, a selective 5-HT reuptake inhibitor, could produce peripheral antinociceptive actions in these same tests. Effects on paw volume also were determined. In the 2.5% formalin test, desipramine and fluoxetine 10-300 nmol produced a dose-related reduction in phase 2 (16-60 min) flinching and biting/licking behaviours when coadministered with the formalin. Phase 1 flinch behaviours (0-12 min) were significantly reduced at the highest dose. These actions are peripherally mediated, as they were not seen when desipramine or fluoxetine (100, 300 nmol) were injected into the contralateral hindpaw. The peripheral action of desipramine and fluoxetine was not altered by coadministration of caffeine 1500 nmol. In the spinal nerve ligation model, desipramine 100 nmol, but not fluoxetine 100 nmol, produced a peripheral anti-hyperalgesic action in the hindpaw corresponding to the ligated side when thresholds were determined using a thermal paw stimulator. In paw volume experiments, desipramine, at doses which are maximally effective in behavioural tests, produced only a slight increase in paw volume, but fluoxetine (10-300 nmol) produced a robust and sustained dose-related increase in paw volume. Amitriptyline also produced minimal effects on paw volume. When coinjected with formalin, no agent significantly altered the degree of paw swelling produced by formalin. The increase in paw volume produced by fluoxetine was inhibited by ketanserin (5-HT2 receptor antagonist), mepyramine (histamine H1 receptor antagonist) and phentolamine (alpha-adrenergic receptor antagonist), but not by the other selective 5-HT receptor antagonists tested or caffeine. The pronounced peripheral pain alleviating actions in the absence of marked changes in paw volume produced by desipramine and amitriptyline, but not fluoxetine, in the formalin test and the spinal nerve ligation model suggest that these agents could be developed as cream or gel formulations to recruit a peripheral antinociceptive action in inflammatory and neuropathic pain states. Such a formulation might permit the attainment of higher and more efficacious concentrations in the region of the sensory nerve terminal, with limited systemic side effects.