Antinociceptive effect of the agonist of 5-HT1A receptors buspirone in the model of abdominal pain in dogs

Opposing effects of 5-HT1A receptor agonist buspirone on supraspinal abdominal pain transmission in normal and visceral hypersensitive rats

The serotonergic 5-HT1A receptors are implicated in the central mechanisms of visceral pain, but their role in these processes is controversial. Considering existing evidences for organic inflammation-triggered neuroplastic changes in the brain serotonergic circuitry, the ambiguous contribution of 5-HT1A receptors to supraspinal control of visceral pain in normal and post-inflammatory conditions can be assumed. In this study performed on male Wistar rats, we used microelectrode recording of the caudal ventrolateral medulla (CVLM) neuron responses to colorectal distension (CRD) and electromyography recording of CRD-evoked visceromotor reactions (VMRs) to evaluate post-colitis changes in the effects of 5-HT1A agonist buspirone on supraspinal visceral nociceptive transmission. In rats recovered from trinitrobenzene sulfonic acid colitis, the CRD-induced CVLM neuronal excitation and VMRs were increased compared with those in healthy animals, revealing post-inflammatory intestinal hypersensitivity. Intravenous buspirone (2 and 4 mg/kg) under urethane anesthesia dose-dependently suppressed CVLM excitatory neuron responses to noxious CRD in healthy rats, but caused dose-independent increase in the already enhanced nociceptive activation of CVLM neurons in post-colitis animals, losing also its normally occurring faciliatory effect on CRD-evoked inhibitory medullary neurotransmission and suppressive action on hemodynamic reactions to CRD. In line with this, subcutaneous injection of buspirone (2 mg/kg) in conscious rats, which attenuated CRD-induced VMRs in controls, further increased VMRs in hypersensitive animals. The data obtained indicate a shift from anti- to pronociceptive contribution of 5-HT1A-dependent mechanisms to supraspinal transmission of visceral nociception in intestinal hypersensitivity conditions, arguing for the disutility of buspirone and possibly other 5-HT1A agonists for relieving post-inflammatory abdominal pain.

Antihyperalgesic and Antiallodynic Effects of Amarisolide A and Salvia amarissima Ortega in Experimental Fibromyalgia-Type Pain

Salvia amarissima Ortega is an endemic species of Mexico used in folk medicine to alleviate pain and as a nervous tranquilizer. The S. amarissima extract and one of its abundant metabolites, identified and isolated through chromatographic techniques, were investigated to obtain scientific evidence of its potential effects to relieve nociplastic pain such as fibromyalgia. Then, the extract and amarisolide A (3-300 mg/kg, i.p.) were pharmacologically evaluated in reserpine-induced fibromyalgia-type chronic pain and in depressive-like behavior (as a common comorbidity) by using the forced swimming test in rats. The 5-HT_1A serotonin receptor (selective antagonist WAY100635, 1 mg/kg, i.p.) was explored after the prediction of a chemical interaction using in silico analysis to look for a possible mechanism of action of amarisolide A. Both the extract and amarisolide A produced significant and dose-dependent antihyperalgesic and antiallodynic effects in rats, as well as significant antidepressive behavior without sedative effects when the antinociceptive dosages were used. The 5-HT_1A serotonin receptor participation was predicted by the in silico descriptors and was corroborated in the presence of WAY100635. In conclusion, S. amarissima possesses antihyperalgesic, antiallodynic, and anti-depressive activities, partially due to the presence of amarisolide A, which involves the 5-HT_1A serotonin receptor. This pharmacological evidence suggests that S. amarissima and amarisolide A are both potential alternatives to relieve pain-like fibromyalgia.

Are Psychotropic Medications Effective in Chronic Pain Management in Children and Adolescents? A Meta-Analysis of Randomized Control Trials

Objective

Data defining and subsequently guiding the use of psychotropic medications in children and adolescents is sparse. We conducted a meta-analysis of randomized control trials to examine the effectiveness of psychotropic medications in children and adolescents with chronic pain.

Methods

We conducted a comprehensive literature search from published studies, and annual scientific sessions of psychiatry conferences. We identified double-blind, randomized control trials (RCTs) in which psychotropic medications were compared to placebo. Data was collected for the total number of patients, baseline characteristics, and changes in pain score. Meta-analysis was performed using a random effect model evaluating average change in pain score and the number of patients with a reduction in pain score for both groups. Pooled data are expressed as standardized mean differences (SMD) and odds ratios (OR) with 95% confidence intervals (CI).

Results

We found 5 studies that included amitriptyline (n=2), citalopram (n=1), buspirone (n=1) and duloxetine (n=1). In the pooled analysis for the difference in the average change in pain score, 4 RCTs with 395 patients were included. After 12–13 weeks of therapy, reductions in pain score were significantly greater in the psychotropic drug group as compared to placebo (SMD: −0.77, 95% CI −1.54, 0.0001, p= 0.05). For the analysis on the number of patients with a reduction in pain, data were available for 445 patients (224-medication group, 221-placebo group). More patients in the psychotropic drug group experienced a meaningful reduction in pain score at 12–13 weeks of therapy compared to placebo (OR 1.66, 95% CI 1.08–2.54, p= 0.02).

Conclusion

The results of this meta-analysis demonstrate significant analgesic efficacy of psychotropic medications in the management of children with chronic pain. This review is limited by the small number of studies included for analysis. There is a pressing need for more robust clinical trials to further investigate these promising findings.

The Buspirone-dependent Abdominal Pain Transmission Within the Nucleus Tractus Solitarius in the Rat

Buspirone, a partial agonist of the 5-HT_1aR, due to potential antinociceptive properties can be useful for abdominal pain treatment in IBS patients. Pain-related effects of buspirone can be mediated by the 5-HT_1aRs, located within the nucleus tractus solitarius. The 5-HT_1aR involvement in pain transmission within the NTS is unclear. The objective of our study was to evaluate the involvement of the 5-HT_1aR in abdominal pain transmission within the NTS. Using a model of abdominal pain on urethane-anesthetized rats, two types of NTS pain-related neurons responding to the noxious colorectal distension (CRD) with excitatory and inhibitory sustained patterns of evoked activity were revealed. Buspirone (1.0-4.0 mg kg^-1, iv) has complex time- and dose-depended action on the CRD-induced NTS neuron responses. Buspirone inhibits the responses of the excitatory neurons and inverts the responses of the inhibitory pain-related neurons but at a dose of 4.0 buspirone, the effect on NTS pain-related neurons attenuates. The inhibitory effect of buspirone on the CRD-evoked responses of the excitatory NTS neurons is completely blocked by an intra-cerebroventricular administration of buspirone agonist WAY100,635. The inhibitory responses do not change by this agonist. The inhibitory action of buspirone is mediated by supraspinal 5-HT_1a receptors however, its excitatory effect on inhibitory neurons does not dependents on these receptors. We proposed that the NTS pain-related neurons could be involved in anti- or pronociceptive effects of buspirone on abdominal pain.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Comparison of the Efficacy of Buspirone and Placebo in Childhood Functional Abdominal Pain: A Randomized Clinical Trial

INTRODUCTION

Pharmacological interventions have not been successful in the treatment of childhood functional abdominal pain (FAP) hitherto. Buspirone is suggested to be efficacious in some of the abdominal pain-related functional gastrointestinal disorders based on evidences from the studies on adults. We aim to investigate the efficacy of buspirone on childhood FAP.

METHODS

This randomized clinical trial was conducted on 117 patients with childhood FAP aged 6-18 years. We randomly assigned patients to receive buspirone or placebo for 4 weeks, with the adjusted dosage for age. Participants completed the questionnaires assessing pain, depression, anxiety, somatization, and sleep disturbances at baseline, at the end of the 4-week therapy (first follow-up), and at 8 weeks after medication discontinuation (second follow-up). The primary outcome was treatment response rate, defined as reduced pain score of ≥2 or reporting no pain at the follow-up assessments.

RESULTS

Ninety-five patients completed the 4-week therapy (48 and 47 in buspirone and placebo groups, respectively). Both buspirone and placebo reduced pain after 4 weeks of treatment, and these effects were persistent 8 weeks after medication discontinuation (P < 0.001 for both groups at weeks 4 and 12). Treatment response rates for buspirone and placebo were 58.3% and 59.6% at week 4 (P = 0.902) and 68.1% and 71.1% at week 12 (P = 0.753), respectively.

DISCUSSION

Buspirone effectively improves pain and associated psychological symptoms including depressive symptoms, anxiety, somatization, and sleep disturbances in childhood FAP but has no superiority over placebo. Further studies, with the higher doses of buspirone and longer follow-ups are recommended.

The Role of Descending Pain Modulation in Chronic Primary Pain: Potential Application of Drugs Targeting Serotonergic System

Chronic primary pain (CPP) is a group of diseases with long-term pain and functional disorders but without structural or specific tissue pathologies. CPP is becoming a serious health problem in clinical practice due to the unknown cause of intractable pain and high cost of health care yet has not been satisfactorily addressed. During the past decades, a significant role for the descending pain modulation and alterations due to specific diseases of CPP has been emphasized. It has been widely established that central sensitization and alterations in neuroplasticity induced by the enhancement of descending pain facilitation and/or the impairment of descending pain inhibition can explain many chronic pain states including CPP. The descending serotonergic neurons in the raphe nuclei target receptors along the descending pain circuits and exert either pro- or antinociceptive effects in different pain conditions. In this review, we summarize the possible underlying descending pain regulation mechanisms in CPP and the role of serotonin, thus providing evidence for potential application of analgesic medications based on the serotonergic system in CPP patients.

The central effects of buspirone on abdominal pain in rats

BACKGROUND

Buspirone, a partial agonist of the 5-HT_1a receptor (5-HT_1a R), owing to potential antinociceptive properties may be useful in treatment of abdominal pain in IBS patients. The pain-related effects of buspirone are mediated via the 5-HT_1a Rs, specifically located within the ventrolateral medulla (VLM). The most animal studies of the 5-HT_1a R involvement in pain control have been carried out with somatic behavioral tests. The 5-HT_1a R contribution in visceral pain transmission within the VLM is unclear. The objective of our study was to evaluate the 5-HT_1a R contribution in abdominal pain transmission within the VLM.

METHODS

Using animal model of abdominal pain (urethane-anaesthetized rats), based on the noxious colorectal distension (CRD) as pain stimulus we studied effects of buspirone (1.0-4.0 mg kg^-1 , iv) on the CRD-induced VLM neuron and blood pressure responses as markers of abdominal pain before and after the 5-HT_1a R blockade by antagonist, WAY 100,635.

RESULTS

The CRD induced a significant increase in VLM neuron activity up to 201.5 ± 18.0% and depressor reactions up to 68 ± 1.8% of baseline. Buspirone (1.0-4.0 mg kg^-1 , iv) resulted in an inhibition of the CRD-induced neuron responses which were changed inversely with dose increase and decreased depressor reactions directly with dose increase. These effects were antagonized by intracerebroventricular WAY 100,635.

CONCLUSION

Buspirone exerts complex biphasic action on the pain-related VLM neuron activity inversely depending on dose. The final effect of buspirone depends on the functional balance between of activation the pre- and postsynaptic 5-HT_1a Rs in mediating pain control networks.