Does a single intravenous injection of the 5HT3 receptor antagonist ondansetron have an analgesic effect in neuropathic pain? A double-blinded, placebo-controlled cross-over study

Efficacy of azasetron on postoperative chronic pain after pulmonary surgery: a randomized triple-blind controlled trial

BACKGROUND

Inhibition of 5-HT3 (5-Hydroxyl Tryptamine) receptors is known to enhance morphine analgesia in animal models. We tested the efficacy of azasetron, a 5-HT3 receptor antagonist, on postoperative chronic pain after pulmonary surgery in a randomized triple-blind controlled study.

METHODS

A total of 250 patients who were scheduled to receive pulmonary surgery were randomized to patient-controlled analgesia (PCA) using 200 µg sufentanil with normal saline or 200 µg sufentanil with 20 mg azasetron. The numerical rating scale of pain (NRS) was recorded at baseline, postoperative day (POD) 1, 2, 3, 90, and 180. Negative binomial regression was used to identify associated factors for postoperative NRS six months after surgery.

RESULTS

The results showed that azasetron did not affect the primary outcomes: the incidence of postoperative chronic pain on POD90 and 180. However, azasetron decreased postoperative NRS at rest and activity on POD1, 2, and 3. Furthermore, azasetron decreased postoperative nausea and vomiting on POD1 and 2. Univariate and multivariate negative binomial regression analysis identified preoperative pain, smoking, drinking and open surgery are risk factors of chronic pain six months after surgery.

CONCLUSIONS

Azasetron did not affect the incidence of chronic pain after pulmonary surgery. The presence of preoperative pain, smoking, drinking, and open surgery were found to be associated with chronic pain six months after surgery.

CLINICAL TRIAL REGISTRATION

The trial was registered prior to patient enrollment at the Chinese Clinical Trial Registry (ChiCTR2200060139), 20/05/2022; the site url is https://www.chictr.org.cn/ .

Pharmacokinetic Modeling of the Effect of Tariquidar on Ondansetron Disposition into the Central Nervous System

PURPOSE

Serotonin (5-HT3) receptor antagonists are promising agents for treatment of neuropathic pain. However, insufficient drug exposure at the central nervous system (CNS) might result in lack of efficacy. The goal of this study was to evaluate the impact of administration of a Pgp inhibitor (tariquidar) on ondansetron exposure in the brain, spinal cord, and cerebrospinal fluid in a wild-type rat model.

METHODS

Ondansetron (10 mg/kg) and tariquidar (7.5 mg/kg) were administered intravenously, plasma and tissue samples were collected and analyzed by HPLC. A mathematical model with brain, spinal cord, cerebrospinal fluid and two systemic disposition compartments was developed to describe the data.

RESULTS

The results demonstrate that tariquidar at 7.5 mg/kg resulted in a complete inhibition of Pgp efflux of ondansetron in the brain and spinal cord. The compartmental model successfully captured pharmacokinetics of ondansetron in wild type and Pgp knockout (KO) animals receiving the drug alone or in wild type animals receiving the ondansetron and tariquidar combination.

CONCLUSIONS

The study provided important quantitative information on enhancement of CNS exposure to ondansetron using co-administration of Pgp Inhibitor in a rat model, which will be further utilized in conducting a clinical study. Tariquidar co-administration resulted in ondansetron CNS exposure comparable to observed in Pgp KO rats. Results also highlighted the effect of tariquidar on plasma disposition of ondansetron, which may not be dependent on Pgp inhibition, and should be evaluated in future studies.

Phytoconstituents Targeting the Serotonin 5-HT3 Receptor: Promising Therapeutic Strategies for Neurological Disorders

The 5-hydroxytryptamine-3 receptor (5-HT3R), a subtype of serotonin receptor, is a ligand-gated ion channel crucial in mediating fast synaptic transmission in the central and peripheral nervous systems. This receptor significantly influences various neurological activities, encompassing neurotransmission, mood regulation, and cognitive processing; hence, it may serve as an innovative target for neurological disorders. Multiple studies have revealed promising results regarding the beneficial effects of these phytoconstituents and extracts on conditions such as nausea, vomiting, neuropathic pain depression, anxiety, Alzheimer's disease, cognition, epilepsy, sleep, and dyskinesia via modulation of 5-HT3R in the pathophysiology of neurological disorder. The review delves into a detailed exploration of in silico, in vitro, and in vivo studies and clinical studies that discussed phytoconstituents acting on 5-HT3R and attenuates difficulties in neurological diseases. The diverse mechanisms by which plant-derived phytoconstituents influence 5-HT3R activity offer exciting avenues for developing innovative therapeutic interventions. Besides producing an agonistic or antagonistic effect, some phytoconstituents exert modulatory effects on 5-HT3R activity through multifaceted mechanisms. These include γ-aminobutyric acid and cholinergic neuronal pathways, interactions with neurokinin (NK)-1, NK2, serotonergic, and γ-aminobutyric acid(GABA)ergic systems, dopaminergic influences, and mediation of calcium ions release and inflammatory cascades. Notably, the phytoconstituent's capacity to reduce oxidative stress has also emerged as a significant factor contributing to their modulatory role. Despite the promising implications, there is currently a dearth of exploration needed to understand the effect of phytochemicals on the 5-HT3R. Comprehensive preclinical and clinical research is of the utmost importance to broaden our knowledge of the potential therapeutic benefits associated with these substances.

Effects on ondansetron of postdural puncture headache after cesarean section under spinal anesthesia

Background

Spinal anesthesia is commonly performed for cesarean section, however, postdural puncture headache (PDPH) is one of its most common adverse effects. Ondansetron is an antiemetic for cancer treatment and analgesia-induced nausea and vomiting. In this study, the authors aim to evaluate the effect of postoperative ondansetron on PDPH.

Methods

In this randomized controlled clinical trial study, 120 pregnant patients are ASA ll, undergoing elective cesarean section, were randomized into two groups (placebo or study). The patients in the study group, immediately after the birth of a baby and 24 h after the operation, received ondansetron 4 mg IV while the placebo group received a placebo. The severity and incidence of headache, postoperative nausea and vomiting, dizziness, neck and lower back pain, and the use of analgesia was assessed in the two groups.

Results

The significant meaning of the time effect (P<0.001) indicated that regardless of the group, for each unit increase in time, the chance of developing a headache increased by 23%, which was statistically significant. Also, the significant meaning of the group effect indicated that regardless of time, patients who did not take indomethacin had ~4.11 times higher chances of developing a headache compared to those who received the medication, which was statistically significant (P=0.004).

Conclusion

The administration of ondansetron significantly reduces the occurrence of postspinal anesthesia headaches and neck pain. There was no significant difference in headache severity between the two study groups.

Analgesic effects of oral Yokukansan on acute postoperative pain and involvement of the serotonin nervous system: a mouse model study

BACKGROUND

Yokukansan, a traditional Japanese medicine (Kampo), has been widely used to treat neurosis, dementia, and chronic pain. Previous in vitro studies have suggested that Yokukansan acts as a partial agonist of the 5-HT1A receptor, resulting in amelioration of chronic pain through inhibition of nociceptive neuronal activity. However, its effectiveness for treating postoperative pain remains unknown, although its analgesic mechanism of action has been suggested to involve serotonin and glutamatergic neurotransmission. This study aimed to investigate the effect of Yokukansan on postoperative pain in an animal model.

METHODS

A mouse model of postoperative pain was created by plantar incision, and Yokukansan was administered orally the day after paw incision. Pain thresholds for mechanical and heat stimuli were examined in a behavioral experiment. In addition, to clarify the involvement of the serotonergic nervous system, we examined the analgesic effects of Yokukansan in mice that were serotonin-depleted by para-chlorophenylalanine (PCPA) treatment and intrathecal administration of NAN-190, 5-HT1A receptor antagonist.

RESULTS

Orally administered Yokukansan increased the pain threshold dose-dependent in postoperative pain model mice. Pretreatment of para-chlorophenylalanine dramatically suppressed serotonin immunoreactivity in the spinal dorsal horn without changing the pain threshold after the paw incision. The analgesic effect of Yokukansan tended to be attenuated by para-chlorophenylalanine pretreatment and significantly attenuated by intrathecal administration of 2.5 µg of NAN-190 compared to that in postoperative pain model mice without para-chlorophenylalanine treatment and NAN-190 administration.

CONCLUSION

This study demonstrated that oral administration of Yokukansan has acute analgesic effects in postoperative pain model mice. Behavioral experiments using serotonin-depleted mice and mice intrathecally administered with a 5-HT1A receptor antagonist suggested that Yokukansan acts as an agonist at the 5-HT1A receptor, one of the serotonin receptors, to produce analgesia.

An LC-ESI-MS/MS method for determination of ondansetron in low-volume plasma and cerebrospinal fluid: Method development, validation, and clinical application

Ondansetron is used in clinical settings as an antiemetic drug. Although the animal studies showed its potential effectiveness also in treating neuropathic pain, the results from humans are inconclusive. The lack of efficacy of ondansetron in a subset of patients might be due to the overexpression of P-glycoprotein, which could result in low concentrations of ondansetron in the central nervous system (CNS). A surrogate of the CNS exposure might be drug concentration in the cerebrospinal fluid (CSF), especially in humans, as assessing the drug disposition directly in the patient's brain would be challenging. The study aimed to develop a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to determine concentrations of ondansetron in human K3EDTA plasma and CSF. Ondansetron was extracted from biological matrices by liquid-liquid extraction. The quantification was performed on a Sciex QTRAP 6500+ mass spectrometer with labeled ondansetron as an internal standard. The calibration range was 0.25-350 ng/mL in plasma and 0.025-100 ng/mL in CSF; for both matrices, 25 µL of samples was required for the assays. The method was validated according to the FDA and EMA guidelines and showed acceptable results. A pilot study confirmed its suitability for clinical samples: after 4-16 mg of intravenous ondansetron, the determined concentrations in plasma were 1.22-235.90 ng/mL, while in CSF - 0.018-11.93 ng/mL. In conclusion, the developed method fulfilled all validation requirements and can be applied to pharmacokinetic studies assessing the CNS ondansetron exposure in humans. The method's advantages, such as a low volume of matrix and a wide calibration range, support its use in a study in which rich sampling and various drug doses are expected.

Evaluation of Peripheral Versus Central Route of Ondansetron as Pretreatment to Prevent Pain on the Injection of Propofol: A Randomized Controlled Study

Objective

We evaluated whether systemic ondansetron was also useful in the attenuation of propofol injection pain similar to ondansetron pretreatment.

Methods

Eighty patients were enrolled. Patients in group S received ondansetron 4 mg in saline in the right hand followed 30 min later by 5 mL saline in the left hand along with venous occlusion. Group L patients received 4 mL of saline in the right hand followed by 5 mL 4 mg ondansetron in the left hand after 30 min. Two minutes later the occlusion was released. Patients received one-fourth of the calculated total dose of propofol, and their level of pain was graded on a scale of 0 to 3, with 0 denoting no discomfort. Mean blood pressure and heart rates were also recorded. Continuous variables were checked for normality using Shapiro-Wilks test. Normal continuous variables were expressed as mean standard deviation and non-normal continuous variables were expressed as median interquartile range. T-test for the difference in the mean and paired test were used for normally distributed continuous variable whereas Mann-Whitney U test-Wilcoxon test and sign test were used for non-normally distributed variables. Repeated measure analysis of variance was used for a variable measured over different periods of time to control for the baseline effect on subsequent measures.

Results

Our results demonstrated that both systemic administration 30 min before and local venous pretreatment with ondansetron were equally beneficial in reducing pain during propofol injection.

Conclusion

A systemic administration of ondansetron may play a role in the attenuation of propofol injection pain.

Evaluation of the Effect of Intravenous Dexamethasone on the Duration of Spinal Anaesthesia in Parturients Undergoing Lower Segment Caesarean Section

Introduction Dexamethasone is shown to prolong the duration of nerve blocks when administered perineurally as well as intravenously. The effect of intravenous dexamethasone on the duration of hyperbaric bupivacaine spinal anesthesia is lesser known. We conducted a randomized control trial to determine the effect of intravenous dexamethasone on the duration of spinal anesthesia in parturients undergoing lower-segment cesarean section (LSCS). Methods Eighty parturients planned for LSCS under spinal anesthesia were randomly allocated to two groups. Patients in group A were administered dexamethasone intravenously, and group B received normal saline intravenously before spinal anesthesia. The primary objective was to determine the effect of intravenous dexamethasone on the duration of sensory and motor block after spinal anesthesia. The secondary objective was to determine the duration of analgesia and complications in both groups. Result The total duration of the sensory and motor blocks in group A was 118.38 ± 19.88 minutes and 95.63 ± 19.91 minutes, respectively. The entire sensory and motor blockade duration in group B was 116.88 ± 13.48 minutes and 97.63 ± 15.15 minutes, respectively. The difference between the groups was found to be statistically insignificant. Conclusion Intravenous 8 mg dexamethasone in patients planned for LSCS under hyperbaric spinal anesthesia does not prolong the sensory or motor block duration compared to placebo.

Targeted Therapy for Orofacial Pain: A Novel Perspective for Precision Medicine

Orofacial pain (OFP) is a dental specialty that includes the diagnosis, management and treatment of disorders of the jaw, mouth, face, head and neck. Evidence-based understanding is critical in effectively treating OFPs as the pathophysiology of these conditions is multifactorial. Since OFP impacts the quality of life of the affected individuals, treating patients successfully is of the utmost significance. Despite the therapeutic choices available, treating OFP is still quite challenging, owing to inter-patient variations. The emerging trends in precision medicine could probably lead us to a paradigm shift in effectively managing the untreatable long-standing pain conditions. Precision medicine is designed based on the patient's genetic profile to meet their needs. Several significant relationships have been discovered based on the genetics and genomics of pain in the past, and some of the notable targets are discussed in this review. The scope of this review is to discuss preclinical and clinical trials that include approaches used in targeted therapy for orofacial pain. Future developments in pain medicine should benefit from current trends in research into novel therapeutic approaches.

Randomised, placebo-controlled trial and meta-analysis show benefit of ondansetron for irritable bowel syndrome with diarrhoea: The TRITON trial

BACKGROUND

Ondansetron may be beneficial in irritable bowel syndrome with diarrhoea (IBS-D).

AIM

To conduct a 12-week parallel group, randomised, double-blind, placebo-controlled trial of ondansetron 4 mg o.d. (titrated up to 8 mg t.d.s.) in 400 IBS-D patients.

PRIMARY ENDPOINT

% responders using the Food and Drug Administration (FDA) composite endpoint. Secondary and mechanistic endpoints included stool consistency (Bristol Stool Form Scale) and whole gut transit time (WGTT). After literature review, results were pooled with other placebo-controlled trials in a meta-analysis to estimate relative risks (RR), 95% confidence intervals (CIs) and number needed to treat (NNT).

RESULTS

Eighty patients were randomised. On intention-to-treat analysis, 15/37 (40.5%; 95% CI 24.7%-56.4%) met the primary endpoint on ondansetron versus 12/43 (27.9%; 95% CI 14.5%-41.3%) on placebo (p = 0.19). Ondansetron improved stool consistency compared with placebo (adjusted mean difference - 0.7; 95% CI -1.0 to-0.3, p < 0.001). Ondansetron increased WGTT between baseline and week 12 (mean (SD) difference 3.8 (9.1) hours, versus placebo -2.2 (10.3) hours, p = 0.01). Meta-analysis of 327 patients from this, and two similar trials, demonstrated ondansetron was superior to placebo for the FDA composite endpoint (RR of symptoms not responding = 0.86; 95% CI 0.75-0.98, NNT = 9) and stool response (RR = 0.65; 95% CI 0.52-0.82, NNT = 5), but not abdominal pain response (RR = 0.95; 95% CI 0.74-1.20).

CONCLUSIONS

Although small numbers meant the primary endpoint was not met in this trial, when pooled with other similar trials meta-analysis suggests ondansetron improves stool consistency and reduces days with loose stool and urgency. Trial registration - http://www.isrctn.com/ISRCTN17508514.

Involvement of the NO/cGMP/K ATP pathway in the antinociceptive effect of rosemary ( Rosmarinus officinalis ) essential oil in mice

Rosemary essential oil (REO) has been used for several medical purposes. Previous studies have shown the antinociceptive effect of the oil. This study aimed to investigate the role of some well-known receptors in the antinociceptive effect of REO. Male Swiss mice (25-30 g) were used. To assess the antinociceptive activity, the formalin test was used. At first, the antinociceptive effect of three doses of rosemary oil (150, 300 and 450 µL/kg) was tested, and then a dose of 300 µL/kg was selected for the mechanistic study. Animals were pretreated with several antagonists and enzyme inhibitors to evaluate the role of adrenergic, cholinergic, serotoninergic, dopaminergic and opioid receptors as well as the NO/cGMP/K ATP pathway in the antinociceptive effect of rosemary essential oil. Yohimbine (5 mg/kg), prazocin (2 mg/kg), propranolol (2 mg/kg), atropine (2.5 mg/kg) naloxone (5 mg/kg), cyproheptadine (2 mg/kg), ondansetron (2 mg/kg) and haloperidol (1 mg/kg) could not reverse the antinociceptive effect. Sulpiride (20 mg/kg) only showed preventive activity in the early phase of formalin test while methylene blue (5 mg/kg), L-NAME (20 mg/kg) and glibenclamide (10 mg/kg) significantly attenuated the antinociceptive effect of REO in both phases. Tadalafil (2 mg/kg) potentiated the antinociceptive effect of REO in the late phase of formalin test and arginine (100 mg/kg) had no effect on both phases. Therefore the NO/cGMP/K ATP pathway might have an important role in the antinociceptive effect of REO.

Spinal γ-Aminobutyric Acid Interneuron Plasticity Is Involved in the Reduced Analgesic Effects of Morphine on Neuropathic Pain

Systemic administration of morphine increases serotonin (5-HT) in the spinal dorsal horn (SDH), which attenuates the analgesic effects of morphine on neuropathic pain through spinal 5-HT3 receptors. We hypothesized that dysfunction of the descending serotonergic system, including the periaqueductal gray (PAG), contributes to attenuate the efficacy of morphine on neuropathic pain through spinal 5-HT3 receptors and GABA neurons. Morphine (100 ng) injected into the PAG produced analgesic effects in normal rats, but not in spinal nerve ligation (SNL) rats. In vivo microdialysis showed that PAG morphine increased the SDH 5-HT concentration in both groups. Intrathecal injection of the 5-HT3 receptor antagonist ondansetron and the GABA_A receptor antagonist bicuculline attenuated the analgesic effects of PAG morphine in normal rats, but increased the effects in SNL rats. The increased analgesic effect of PAG morphine induced by bicuculline was reversed by pretreatment with the tropomyosin receptor kinase B (TrkB) antagonist K252a. Activation of spinal 5-HT3 receptors by 2-methyl-5-HT increased the GABA concentration in both groups. Morphine activates GABAergic interneurons in the SDH by activating descending serotonergic neurons. Functional changes in GABA_A receptors from inhibitory to facilitatory through the activation of TrkB receptors may contribute to the attenuated efficacy of morphine against neuropathic pain. PERSPECTIVE: Although morphine provides strong analgesia against acute pain, it has limited efficacy against neuropathic pain. This article demonstrates that functional changes in GABA_A receptors in the spinal dorsal horn after nerve injury might strongly contribute to the attenuation of opioid-induced analgesia for neuropathic pain.

Impact of Palonosetron on Cough Suppression in Females Undergoing Sevoflurane-Remifentanil Anesthesia for Laparoscopic Cholecystectomy: A Randomized Trial

Remifentanil has been used to suppress peri-extubation cough. Palonosetron, a 5-HT₃ receptor antagonist, is an effective antiemetic, and 5-HT receptors mediate the cough reflex. We assessed the impact of palonosetron on effect-site concentration (Ce) of remifentanil for preventing emergence cough in females. Forty-five female patients undergoing laparoscopic cholecystectomy randomly received 0.075 mg of palonosetron (n = 21) or normal saline (n = 24) intravenously at the end of surgery. The remifentanil Ce for 50% (EC₅₀) and for 95% (EC₉₅) of patients were estimated via Dixon’s up-and-down method or isotonic regression. Using Dixon’s method, EC₅₀ in the control group (1.33 ± 0.38 ng/mL) was comparable to that of the palonosetron group (1.42 ± 0.75 ng/mL) (p = 0.813). Using isotonic regression, EC₅₀ (83% CIs) and EC₉₅ (95% CIs) did not reveal significant differences between the control and the palonosetron groups (1.17 (0.86–1.43) and 1.90 (1.45–1.96) ng/mL and 0.88 (0.78–1.23) and 2.43 (1.94–2.47) ng/mL, respectively). No difference was found in the remifentanil Ce to suppress emergence cough in the palonosetron group compared with the control group. It may indicate no effect of palonosetron on antitussive activity of remifentanil.

Involvement of Serotonergic System in Oxaliplatin-Induced Neuropathic Pain

Oxaliplatin is a chemotherapeutic agent widely used against colorectal and breast cancers; however, it can also induce peripheral neuropathy that can rapidly occur even after a single infusion in up to 80-90% of treated patients. Numerous efforts have been made to understand the underlying mechanism and find an effective therapeutic agent that could diminish pain without damaging its anti-tumor effect. However, its mechanism is not yet clearly understood. The serotonergic system, as part of the descending pain inhibitory system, has been reported to be involved in different types of pain. The malfunction of serotonin (5-hydroxytryptamine; 5-HT) or its receptors has been associated with the development and maintenance of pain. However, its role in oxaliplatin-induced neuropathy has not been clearly elucidated. In this review, 16 in vivo studies focused on the role of the serotonergic system in oxaliplatin-induced neuropathic pain were analyzed. Five studies analyzed the involvement of 5-HT, while fourteen studies observed the role of its receptors in oxaliplatin-induced allodynia. The results show that 5-HT is not involved in the development of oxaliplatin-induced allodynia, but increasing the activity of the 5-HT1A, 5-HT2A, and 5-HT3 receptors and decreasing the action of 5-HT2C and 5-HT6 receptors may help inhibit pain.

Plasma and cerebrospinal fluid pharmacokinetics of ondansetron in humans

AIMS

Changes in serotonergic sensory modulation associated with overexpression of 5-HT3 receptors in the central nervous system (CNS) have been implicated in the pathophysiology of neuropathic pain after peripheral nerve damage. 5-HT3 receptor antagonists such as ondansetron can potentially alleviate neuropathic pain, but have limited effectiveness, due potentially to limited CNS access. However, there is currently limited information on CNS disposition of systemically-administered 5-HT3 receptor antagonists. This study evaluated the cerebrospinal fluid (CSF) disposition of ondansetron, as a surrogate of CNS penetration.

METHODS

Fifteen patients were given a single 16 mg intravenous 15 minute infusion of ondansetron, followed by serial blood and a single CSF sampling. Population pharmacokinetic (PK) modelling was implemented to describe the average and individual plasma and CSF profiles of ondansetron. A two-compartmental model was used to capture ondansetron plasma PK with a single CSF compartment to describe distribution to the CNS.

RESULTS

The individual model-estimated CSF to plasma partition coefficients of ondansetron were between 0.09 and 0.20. These values were mirrored in the calculated CSF penetration ratios, ranging from 0.08 to 0.26.

CONCLUSIONS

After intravenous administration, CSF concentrations of ondansetron were approximately 7-fold lower than those observed in the plasma. A model could be developed to describe individual CSF concentration-time profiles of ondansetron based on a single CSF data point. The low CSF penetration of ondansetron may explain its limited analgesic effectiveness, and affords an opportunity to explore enhancing its CNS penetration for targeting conditions such as neuropathic pain.

Pharmacokinetic Modeling of the Impact of P-glycoprotein on Ondansetron Disposition in the Central Nervous System

PURPOSE

Modulation of 5-HT3 receptor in the central nervous system (CNS) is a promising approach for treatment of neuropathic pain. The goal was to evaluate the role of P-glycoprotein (Pgp) in limiting exposure of different parts of the CNS to ondansetron (5-HT3 receptor antagonist) using wild-type and genetic knockout rat model.

METHODS

Plasma pharmacokinetics and CNS (brain, spinal cord, and cerebrospinal fluid) disposition was studied after single 10 mg/kg intravenous dose.

RESULTS

Pgp knockout resulted in significantly higher concentrations of ondansetron in all tested regions of the CNS at most of the time points. The mean ratio of the concentrations between KO and WT animals was 2.39-5.48, depending on the region of the CNS. Male and female animals demonstrated some difference in ondansetron plasma pharmacokinetics and CNS disposition. Mechanistic pharmacokinetic model that included two systemic disposition and three CNS compartments (with intercompartmental exchange) was developed. Pgp transport was incorporated as an efflux from the brain and spinal cord to the central compartment. The model provided good simultaneous description of all data sets, and all parameters were estimated with sufficient precision.

CONCLUSIONS

The study provides important quantitative information on the role of Pgp in limiting ondansetron exposure in various regions of the CNS using data from wild-type and Pgp knockout rats. CSF drug concentrations, as a surrogate to CNS exposure, are likely to underestimate the effect of Pgp on drug penetration to the brain and the spinal cord.

Pharmacokinetic profile of the selective 5-HT3 receptor antagonist ondansetron in the rat: an original study and a minireview of the behavioural pharmacological literature in the rat

The availability of agonists and antagonists to modulate the activity of the 5-hydroxytryptamine (5-HT) type 3 (5-HT3) receptor has renewed interest in its role as a therapeutic target. Ondansetron is a highly selective 5-HT3 receptor antagonist that is well tolerated as an anti-emetic for patients undergoing chemotherapy. Preclinical studies in rat have shown the effects of small doses of ondansetron on cognition, behavioural sensitisation, and epilepsy. However, the pharmacokinetic (PK) profile of ondansetron in rat has not been described, which limits the translational relevance of these findings. Here, we aim to determine, in the rat, the PK profile of ondansetron in the plasma and to determine associated brain levels. The plasma PK profile was determined following acute subcutaneous administration of ondansetron (0.1, 1, and 10 μg/kg). Brain levels were measured following subcutaneous administration of ondansetron at 1 μg/kg. Plasma and brain levels of ondansetron were determined using high-performance liquid chromatography – tandem mass spectrometry. Following administration of all three doses, measured ondansetron plasma levels (≈30–3000 pg/mL) were below levels achieved with doses usually administered in the clinic, with a rapid absorption phase and a short half-life (≈30–40 min). We also found that brain levels of ondansetron at 1 μg/kg were significantly lower than plasma levels, with brain to plasma ratios of 0.45 and 0.46 in the motor and pre-frontal cortices. We discuss our findings in the context of a minireview of the literature. We hope that our study will be helpful to the design of preclinical studies with therapeutic end-points.

Role of 5-HT receptors in neuropathic pain: potential therapeutic implications

5-HT plays a crucial role in the progress and adjustment of pain both centrally and peripherally. The therapeutic action of the 5-HT receptors` agonist and antagonist in neuropathic pain have been widely reported in many studies. However, the specific roles of 5-HT subtype receptors have not been reviewed comprehensively. Therefore, we summarized the recent findings on multiple subtypes of 5-HT receptors in both central and peripheral nervous system in neuropathic pain, particularly, 5-HT1, 5-HT2, 5-HT3 and 5-HT7 receptors. In addition, 5-HT4, 5-HT5 and 5-HT6 receptors were also reviewed. Most of studies focused on the function of 5-HT subtype receptors in spinal level compared to brain areas. Based on these evidences, the pain process can be facilitated or inhibited that depending on the specific subtypes and the distribution of 5-HT receptors. Therefore, this review may provide potential therapeutic implications in treatment of neuropathic pain.

What goes up must come down: insights from studies on descending controls acting on spinal pain processing

Descending controls link higher processing of noxious signals to modulation of spinal cord responses to their noxious inputs. It has become possible to study one key inhibitory system in animals and humans using one painful stimulus to attenuate another distant response and so eliciting diffuse noxious inhibitory controls (DNIC) or the human counterpart, conditioned pain modulation (CPM). Here, we discuss the neuronal pathways in both species, their pharmacology and examine changes in descending controls with a focus on osteoarthritis. We will also discuss the opposing descending facilitatory system. Strong parallels between DNIC and CPM emphasize the possibility of forward and reverse translation.

Translational issues in precision medicine in neuropathic pain

Neuropathic pain remains poorly treated, with most new drugs falling through the translational gap. The traditional model of bench-to-bedside research has relied on identifying new mechanisms/targets in animal models and then developing clinical applications. Several have advocated bridging the translational gap by beginning with clinical observations and back-translating to animal models for further investigation of mechanisms. There is good evidence that phenotyping of patients through quantitative sensory testing can lead to improved treatment selection and hence improved patient outcomes. This practice has been widely adopted in clinical investigations, but its application in preclinical research is not mainstream. In this review, we retrospectively examine our historical rodent data sets with the aim of reconsidering drug effects on sensory neuronal endpoints, their alignment with clinical observations, and how these might guide future clinical studies.

Serotonin discovery and stepwise disclosure of 5-HT receptor complexity over four decades. Part II. Some contributions of Manfred Göthert

About 40% of the papers within the scientific oeuvre of Manfred Göthert (1939-2019) were dedicated to serotonin (5-hydroxytryptamine, 5-HT). He was not only the witness of the gradual definition of the fourteen 5-HT receptor subtypes but also was involved directly by identifying 5-HT_1B, 5-HT_1D and 5-HT₃ receptors. Moreover, he identified presynaptic 5-HT receptors on central and/or peripheral serotoninergic, noradrenergic and/or cholinergic neurones. Two inhibitory (5-HT_1B, 5-HT_1D) and two facilitatory (5-HT₃, 5-HT₄) receptors were found, the 5-HT_1B receptor representing a possible target for antidepressant drugs. Ten years earlier than electrophysiologists, he identified ligand-gated receptors like the 5-HT₃ and the nicotinic acetylcholine (nACh) receptor as targets of halothane. Simultaneously with, but independent of, other authors he found that ethanol allosterically inhibits N-methyl-D-aspartate (NMDA) receptors, which are affected at an even lower concentration than 5-HT₃ and nACh receptors. The latter two receptors were shown to be subject to allosteric inhibition also by cannabinoids via a mechanism unrelated to cannabinoid CB₁ or CB₂ receptors; cannabinoid inhibition of 5-HT₃ receptors may represent a new target for the treatment of neuropathic pain.

Comparative transcriptome profiling of the human and mouse dorsal root ganglia: an RNA-seq-based resource for pain and sensory neuroscience research

Molecular neurobiological insight into human nervous tissues is needed to generate next-generation therapeutics for neurological disorders such as chronic pain. We obtained human dorsal root ganglia (hDRG) samples from organ donors and performed RNA-sequencing (RNA-seq) to study the hDRG transcriptional landscape, systematically comparing it with publicly available data from a variety of human and orthologous mouse tissues, including mouse DRG (mDRG). We characterized the hDRG transcriptional profile in terms of tissue-restricted gene coexpression patterns and putative transcriptional regulators, and formulated an information-theoretic framework to quantify DRG enrichment. Relevant gene families and pathways were also analyzed, including transcription factors, G-protein-coupled receptors, and ion channels. Our analyses reveal an hDRG-enriched protein-coding gene set (∼140), some of which have not been described in the context of DRG or pain signaling. Most of these show conserved enrichment in mDRG and were mined for known drug-gene product interactions. Conserved enrichment of the vast majority of transcription factors suggests that the mDRG is a faithful model system for studying hDRG, because of evolutionarily conserved regulatory programs. Comparison of hDRG and tibial nerve transcriptomes suggests trafficking of neuronal mRNA to axons in adult hDRG, and are consistent with studies of axonal transport in rodent sensory neurons. We present our work as an online, searchable repository (https://www.utdallas.edu/bbs/painneurosciencelab/sensoryomics/drgtxome), creating a valuable resource for the community. Our analyses provide insight into DRG biology for guiding development of novel therapeutics and a blueprint for cross-species transcriptomic analyses.

High-dose ondansetron reduces activation of interoceptive and sensorimotor brain regions

Several psychiatric disorders involve abnormalities of interoception and associated neural circuitry centered on the insula. The development of interventions modulating interoceptive circuits could lead to novel treatment approaches for these disorders. The 5-HT3 receptor antagonist ondansetron is a good candidate for the modulation of interoceptive circuits, as 5-HT3 receptors are located abundantly on sensory pathways and ondansetron has shown some clinical utility in disorders characterized by sensory and interoceptive abnormalities. The present study tested the ability of three different doses of ondansetron to engage neural regions involved in interoception to determine the drug's utility as a therapeutic agent to target circuit abnormalities in patients. Fifty-three healthy subjects were randomized to receive a single 8-mg (n = 18), 16-mg (n = 17), or 24-mg (n = 18) dose of ondansetron and placebo before MRI scanning on separate days. Subjects performed an fMRI task previously shown to engage interoceptive circuitry in which they viewed videos depicting body movements/sensation and control videos. The results revealed a highly significant relationship between dosage and activation in bilateral insula, somatosensory and premotor regions, cingulate cortex, and temporal cortex for control but not body-focused videos. These effects were driven by a robust reduction in activation for ondansetron compared to placebo for the 24-mg group, with weaker effects for the 16-mg and 8-mg groups. In conclusion, high-dose ondansetron reduces activation of several areas important for interoception, including insula and sensorimotor cortical regions. This study reveals the potential utility of this drug in modulating hyperactivity in these regions in patients.

Monoamines as Drug Targets in Chronic Pain: Focusing on Neuropathic Pain

Monoamines are involved in regulating the endogenous pain system and indeed, peripheral and central monoaminergic dysfunction has been demonstrated in certain types of pain, particularly in neuropathic pain. Accordingly, drugs that modulate the monaminergic system and that were originally designed to treat depression are now considered to be first line treatments for certain types of neuropathic pain (e.g., serotonin and noradrenaline (and also dopamine) reuptake inhibitors). The analgesia induced by these drugs seems to be mediated by inhibiting the reuptake of these monoamines, thereby reinforcing the descending inhibitory pain pathways. Hence, it is of particular interest to study the monoaminergic mechanisms involved in the development and maintenance of chronic pain. Other analgesic drugs may also be used in combination with monoamines to facilitate descending pain inhibition (e.g., gabapentinoids and opioids) and such combinations are often also used to alleviate certain types of chronic pain. By contrast, while NSAIDs are thought to influence the monoaminergic system, they just produce consistent analgesia in inflammatory pain. Thus, in this review we will provide preclinical and clinical evidence of the role of monoamines in the modulation of chronic pain, reviewing how this system is implicated in the analgesic mechanism of action of antidepressants, gabapentinoids, atypical opioids, NSAIDs and histaminergic drugs.

Anti-inflammatory effects of alosetron mediated through 5-HT3 receptors on experimental colitis

Development of new medicine with fewer deleterious effects and more efficacies for treatment of inflammatory bowel disease is needed. 5-Hydroxytryptamine 3 receptor (5-HT₃R) antagonists have exhibited analgesic and anti-inflammatory features in vitro and in vivo. The present study was designed to evaluate the anti-inflammatory effect of alosetron, a 5-HT₃R antagonist, on trinitrobenzenesulfonic acid (TNBS)-induced ulcerative colitis in rats. Two h subsequent to induce colitis (intracolonic instillation of TNBS, 50 mg/kg) in male Wistar rats, alosetron (1 mg/kg), dexamethasone (1 mg/kg), meta-chlorophenylbiguanide (mCPBG, a 5-HT₃R agonist, 5 mg/kg), or alosetron + mCPBG were administrated intraperitoneally for 6 days. Animals were thereafter sacrificed and the efficacy of drugs was evaluated macroscopically, histologically, and biochemically (myeloperoxidase, tumor necrosis factor-alpha, interleukin-6, and interleukin-1 beta) on distal colon samples. Treatment with alosetron and dexamethasone improved macroscopic and microscopic colonic damages significantly and decreased myeloperoxidase activity and colonic levels of inflammatory cytokines. The profitable effects of alosetron were antagonized by concurrent administration of mCPBG. Our data provided evidence that the protective effects of alosetron on TNBS-induced colitis can be mediated by 5- HT3R.

Modality selective roles of pro-nociceptive spinal 5-HT2A and 5-HT3 receptors in normal and neuropathic states

Descending brainstem control of spinal nociceptive processing permits a dynamic and adaptive modulation of ascending sensory information. Chronic pain states are frequently associated with enhanced descending excitatory drive mediated predominantly through serotonergic neurones in the rostral ventromedial medulla. In this study, we examine the roles of spinal 5-HT_2A and 5-HT₃ receptors in modulating ascending sensory output in normal and neuropathic states. In vivo electrophysiology was performed in anaesthetised spinal nerve ligated (SNL) and sham-operated rats to record from wide dynamic range neurones in the ventral posterolateral thalamus. In sham rats, block of spinal 5-HT₃Rs with ondansetron revealed tonic facilitation of noxious punctate mechanical stimulation, whereas blocking 5-HT_2ARs with ketanserin had minimal effect on neuronal responses to evoked stimuli. The inhibitory profiles of both drugs were altered in SNL rats; ondansetron additionally inhibited neuronal responses to lower intensity punctate mechanical stimuli and noxious heat evoked responses, whereas ketanserin inhibited innocuous and noxious evaporative cooling evoked responses. Neither drug had any effect on dynamic brush evoked responses nor on spontaneous firing rates in both sham and SNL rats. These data identify novel modality and intensity selective facilitatory roles of spinal 5-HT_2A and 5-HT₃ receptors on sensory neuronal processing within the spinothalamic-somatosensory cortical pathway.

Comparison of Ondansetron versus Clonidine efficacy for prevention of postoperative pain, nausea and vomiting after orthognathic surgeries: A triple blind randomized controlled trial

Background

The aim of this randomized controlled triple blind trial was to compare the efficacy of clonidine with dexamethasone versus ondansetron with dexamethasone for postoperative pain, nausea and vomiting prevention in orthognathic surgery patients.

Material and Methods

In this clinical trial study, 30 consecutive patients with skeletal class III deformities were candidates for orthognathic surgery in Qaem hospital, Mashhad University of medical sciences, Mashhad, Iran from March to November 2017. These subjects were randomly assigned to two equal number groups, ondansetron or clonidine. Patients received either oral ondansetron 8mg or oral clonidine 150μg as premedication, 1 hour before the surgery (both dissolved in 20 cc of water). Also both groups received intravenous dexamethasone 8mg (1 hour preoperatively and every 4 hours intraoperatively).

Results

In this study, a total of 30 patients (14 males and 16 females) with a mean age of 23.9 ± 3.9 were investigated. The incidence of postoperative nausea in women was more than men (p=0.003), also the correlation between the incidence of PON and the surgery duration ≥ 3 hours was statistically significant (p = 0.050). The frequency of postoperative nausea (PON) in the ondansetron group was less than clonidine (53.3% vs 73.3% respectively). There was no postoperative vomiting (POV) in the ondansetron group, but 6.7% of cases in clonidine group suffered POV. Post-operative nausea in ondansetron group occurred significantly later than clonidine (525.0±233.2 vs 100.0±34.0 min; p<0.001). On the other hand, the incidence time of post-operative severe pain or in other word the analgesia time in clonidine group was significantly more than ondansetron one (875/0±68/5 vs 614.3±159.1 min; p<0.001).

Conclusions

Ondansetron with dexamethasone premedication was more effective in controlling PONV after orthognathic surgery compared to clonidine with dexamethasone group.

Key words:Postoperative nausea and vomiting, ondansetron, clonidine.

The effect of ondansetron on analgesic efficacy of acetaminophen after hysterectomy: A randomized double blinded placebo controlled trial

OBJECTIVES

To determine that perioperative ondansetron reduces the analgesic efficacy of acetaminophen.

DESIGN

Randomized, double-blinded study.

PATIENTS

120 patients ASA I-II who underwent abdominal hysterectomy.

INTERVENTIONS

All the patients were given 1g acetaminophen at skin closure. Patients were divided into two groups; ondansetron HCl (8mg, 2ml IV) (Group I, N=60) and saline (2ml IV) (Group II, N=60) at the skin closure.

MEASUREMENT

Postoperative pain scores (VAS) while resting in bed and sitting, total opioid consumption were noted.

MAIN RESULTS

Patients randomized to ondansetron had significantly worse pain scores upon arrival to the recovery unit [by 1.7 (99.7% CI: 0.75, 2.59) cm] and at 1h [by 1.3 (0.5, 2.1) cm] while resting in bed. Pain scores while sitting were also significantly greater in ondansetron group at arrival in PACU by 0.6 (99.7% CI: 0.1, 1.0) cm. Thereafter, pain scores did not differ significantly. Median total opioid (tramadol) consumption was 441 [Q1, Q3: 280, 578] mg in the ondansetron group and 412 [309, 574] mg in the placebo group, P=0.95.

CONCLUSIONS

Ondansetron significantly decreased the analgesic effect of acetaminophen during the initial postoperative period. Our results thus confirm that acetaminophen analgesia is partially mediated by serotonin receptors. However, the reduction was of marginal clinical importance and short-lived.

[Comparison of granisetron and lidocaine on reducing injection pain of etomidate: a controlled randomized study]

BACKGROUND AND OBJECTIVES

Reducing pain on injection of anesthetic drugs is of importance to every anesthesiologist. In this study we pursued to define if pretreatment by granisetron reduces the pain on injection of etomidate similar to lidocaine.

METHODS

Thirty patients aged between 18 and 50 years of American Society of Anesthesiologists physical status class I or II, whom were candidates for elective laparoscopic cholecystectomy surgery were enrolled in this study. Two 20 gauge cannulas were inserted into the veins on the dorsum of both hands and 100mL of normal saline was administered during a 10min period from each cannula. Using an elastic band as a tourniquet, venous drainage of both hands was occluded. 2mL of granisetron was administered into one hand and 2mL of lidocaine 2% at the same time into the other hand. One minute later the elastic band was opened and 2mL of etomidate was administered to each hand with equal rates. The patients were asked to give a score from 0 to 10 (0=no pain, 10=severe pain) to each the pain sensed in each hand.

RESULTS

Two patients were deeply sedated after injection of etomidate and unable to answer any questions. The mean numerical rating score for injection pain of intravenously administered etomidate after intravenous granisetron was 2.3±1.7, which was lower when compared with pain sensed due to intravenously administered etomidate after administration of lidocaine 2% (4.6±1.8), p<0.05.

CONCLUSION

The result of this study demonstrated that, granisetron reduces pain on injection of etomidate more efficiently than lidocaine.

The electroacupuncture-induced analgesic effect mediated by 5-HT1, 5-HT3 receptor and muscarinic cholinergic receptors in rat model of collagenase-induced osteoarthritis

BACKGROUND

Osteoarthritis (OA) is an degenerative disease characterized by chronic joint pain. Complementary and alternative treatment such as acupuncture have been utilized to alleviate pain. The objective of this study was to investigate the analgesic mechanisms of electroacupuncture (EA) in the collagenase-induced osteoarthritis (CIOA) rat model.

METHODS

Four weeks after inducing CIOA by injecting collagenase solution into the left knee of 5-week-old male Sprague-Dawley rats, 2 Hz and 100 Hz EA on Zusanli (ST 36) was performed. The analgesic effect of EA was evaluated by the tail flick latency (TFL) and paw pressure threshold (PPT) tests. To investigate the analgesic mechanism, serotonergic and muscarinic cholinergic receptor agonists and antagonists were injected 20 min prior to EA and the resultant changes were evaluated by the TFL and PPT tests.

RESULTS

EA on Zusanli (ST 36) demonstrated an analgesic effect in the CIOA rat model. The 2 Hz EA treatment showed a significantly greater analgesic effect than the 100 Hz treatment. The analgesic effect of 2 Hz EA was not strengthened by 5-HT1, 5-HT2, 5-HT3, and muscarinic cholinergic receptor agonist pretreatment, was blocked by 5-HT1, 5-HT3, and muscarinic cholinergic receptor antagonist pretreatment, but not blocked by 5-HT2 receptor antagonist pretreatment.

CONCLUSIONS

In the CIOA rat model, EA on Zusanli (ST 36) exhibited analgesic effects, and 2 Hz EA resulted in a significantly greater analgesic effect than 100 Hz EA. The analgesic effect of 2 Hz EA was reduced by pretreatment of 5-HT1 receptor, 5-HT3 receptor and muscarinic cholinergic receptor antagonists.

Implications of palonosetron in elderly patients undergoing laparoscopic cholecystectomy with respect to its anti-shivering effect

BACKGROUND

The elderly are vulnerable to hypothermia and have a higher risk of cardiovascular events induced by marked increases in oxygen consumption due to shivering. Five-hydroxytryptamine-3 (5-HT3) receptor antagonists have been previously reported to reduce post-anesthesia shivering.

AIM

In the present study, the authors investigated the effects of palonosetron, a new-generation 5-HT3 antagonist, on core hypothermia and the incidence of shivering after laparoscopic cholecystectomy in elderly patients.

METHODS

Forty-eight patients (65-80 years) were randomly assigned to one of two groups and administered palonosetron 0.075 mg (palonosetron group, n = 24) or the same volume of normal saline (control group, n = 24) before anesthesia induction. Core body temperatures and hemodynamic variables were monitored during and after operation. Post-anesthetic shivering (PAS) and pain scores were obtained in a post-anesthetic care unit.

RESULTS

Intraoperative esophageal temperature changed significantly over time (P = 0.010), but significant intergroup difference in change was not observed (P = 0.706). Furthermore, shivering frequencies were similar in the two groups (P = 0.610). However, postoperative pain scores at 30 min after entering the post-anesthesia care unit were significantly lower in the palonosetron group (P = 0.002).

DISCUSSION

Regardless of the previously reported anti-shivering effect of 5-HT3 receptor antagonists, pre-operative palonosetron 0.075 mg did not influence perioperative hypothermia or PAS in this study. This discrepancy might be due to the dose responsiveness of palonosetron to PAS and relatively low incidence of PAS in the elderly.

CONCLUSIONS

Pre-operative administration of palonosetron 0.075 mg did not influence perioperative hypothermia or post-anesthesia shivering in elderly patients undergoing laparoscopic cholecystectomy. However, palonosetron might be beneficial for reducing early postoperative pain in elderly patients with opioid-based patient-controlled analgesia.

Spinal 5-HT3 receptor mediates nociceptive effect on central neuropathic pain; possible therapeutic role for tropisetron

OBJECTIVES

To test the analgesic effect of 5-HT-3 receptor antagonist, tropisetron, in a clip compression injury model of spinal cord pain in rats.

METHODS

Four weeks post compression of the spinal cord at lumbar level, tropisetron was administered intrathecally at 100 μg and 150 μg dosages. Behavioral tests were assessed before administration. Fifteen minutes after injection, behavioral tests were repeated. Randall-Sellitto and plantar test was used for mechanical and thermal hyperalgesia, respectively. Mechanical and cold allodynia were evaluated by Von Frey filament and acetone droplets, respectively. The analgesic effect of tropisetron was compared with intrathecal administration of salicylate. Locomotor score was evaluated by Basso, Beattie and Bresnahan (BBB) test every week after spinal cord injury.

RESULTS

Intrathecal administration of tropisetron, decreased hyperalgesia and mechanical allodynia, but not cold allodynia were observed after compression of the spinal cord.

CONCLUSION

Blockade of 5-HT-3 receptors by tropisetron at the spinal level induces an antinociceptive effect on chronic central neuropathic pain and suggests that this compound may have potential clinical utility for the management of central neuropathic pain, particularly in patients with hyperalgesia and tactile allodynia.

Galanin-Mediated Behavioural Hyperalgesia from the Dorsomedial Nucleus of the Hypothalamus Involves Two Independent Descending Pronociceptive Pathways

Activation of the dorsomedial nucleus of the hypothalamus (DMH) by galanin (GAL) induces behavioural hyperalgesia. Since DMH neurones do not project directly to the spinal cord, we hypothesized that the medullary dorsal reticular nucleus (DRt), a pronociceptive region projecting to the spinal dorsal horn (SDH) and/or the serotoninergic raphe-spinal pathway acting on the spinal 5-HT3 receptor (5HT3R) could relay descending nociceptive facilitation induced by GAL in the DMH. Heat-evoked paw-withdrawal latency (PWL) and activity of SDH neurones were assessed in monoarthritic (ARTH) and control (SHAM) animals after pharmacological manipulations of the DMH, DRt and spinal cord. The results showed that GAL in the DMH and glutamate in the DRt lead to behavioural hyperalgesia in both SHAM and ARTH animals, which is accompanied particularly by an increase in heat-evoked responses of wide-dynamic range neurons, a group of nociceptive SDH neurones. Facilitation of pain behaviour induced by GAL in the DMH was reversed by lidocaine in the DRt and by ondansetron, a 5HT3R antagonist, in the spinal cord. However, the hyperalgesia induced by glutamate in the DRt was not blocked by spinal ondansetron. In addition, in ARTH but not SHAM animals PWL was increased after lidocaine in the DRt and ondansetron in the spinal cord. Our data demonstrate that GAL in the DMH activates two independent descending facilitatory pathways: (i) one relays in the DRt and (ii) the other one involves 5-HT neurones acting on spinal 5HT3Rs. In experimental ARTH, the tonic pain-facilitatory action is increased in both of these descending pathways.

Inhibition of spinal 5-HT3R reverted diabetes-induced mechanical hypersensitivity in a GABAAR-mediated neurotransmission-dependent manner

Spinal 5-HT3 receptor (5-HT3R) has been implicated in chronic pain development. The extent to which 5-HT3R contributes to spinal sensitization and diabetic neuropathic pain (DNP) remains elusive and the mechanisms subserving the effects of 5-HT3R activation on spinal pain processing during chronic pain are still unclear. In this study, we evaluated the contribution of spinal 5-HT3R to pain facilitation and spinal sensitization during DNP, exploiting the role of GABAAR-mediated neurotransmission and glial activation in the effects elicited by intrathecal administration of a 5-HT3R antagonist. Mechanical nociception was evaluated by paw pressure test in streptozotocin (STZ)-diabetic and control rats after intrathecal (i.t.) administration of a 5-HT3R antagonist (Y25130). The spinal activation of extracellular signal-regulated kinases (ERKs) pathway and the expression of 5-HT3R, glial fibrillary acidic protein (GFAP; marker of astroglia activation) and ionized calcium binding adaptor molecule 1 (IBA-1; marker of microglia activation) were evaluated at the peak maximum effect of Y25130. The involvement of GABAAR-mediated neurotransmission in the behavioral pain effect of Y25130, was assessed in STZ-diabetic animals receiving i.t. administrations of muscimol (GABAAR agonist). Intrathecal administration of Y25130 reverted mechanical hyperalgesia and decreased the activation of ERKs in STZ-diabetic rats, while no effects were observed in control animals. The spinal activation of GABAAR by i.t. administration of muscimol abolished Y25130-driven antinociception. The expression of IBA-1, GFAP and 5-HT3R was unaltered by treatment. These findings point to a GABA-mediated pronociceptive role of spinal 5-HT3R during DNP.

Effects of pretreatment with intravenous palonosetron for propofol-remifentanil-based anesthesia in breast and thyroid cancer surgery: a double-blind, randomized, controlled study

Background

We postulated that palonosetron, a novel antiemetic agent, might have the effect of alleviating injection pain from propofol and rocuronium. A double-blind, controlled study was undertaken to evaluate the effect of palonosetron on injection pain during total intravenous anesthesia and postoperative nausea and vomiting (PONV) using propofol-remifentanil in breast and thyroid cancer surgery.

Methods

Sixty patients were randomly allocated to one of two groups. Before injection of propofol and rocuronium, patients in group S (n = 30) received 4 ml of saline and patients in group P (n = 30) received 75 µg (1.5 ml) of palonosetron mixed with 2.5 ml of saline (n = 30). Patients were evaluated by a blinded anesthesiologist with regard to the scoring of injection pain of propofol, withdrawal response by rocuronium, PONV, shivering, postoperative pain, recall of pain, and overall satisfaction.

Results

The differences between groups in the incidence of injection pain due to propofol and rocuronium were insignificant. However, in group P, the severity of propofol-induced injection pain (3% vs. 33%, P = 0.003) and postoperative pain (P = 0.038) was significantly lower during the first 12 h after surgery. No differences were observed between the groups with respect to PONV, shivering, recall of pain, and overall satisfaction.

Conclusions

We concluded that pretreatment of palonosetron was effective to reduce the severity of propofol-induced injection pain and early postoperative pain, although it did not reduce the incidence of injection pain from propofol and rocuronium.

Central terminal sensitization of TRPV1 by descending serotonergic facilitation modulates chronic pain

The peripheral terminals of primary nociceptive neurons play an essential role in pain detection mediated by membrane receptors like TRPV1, a molecular sensor of heat and capsaicin. However, the contribution of central terminal TRPV1 in the dorsal horn to chronic pain has not been investigated directly. Combining primary sensory neuron-specific GCaMP3 imaging with a trigeminal neuropathic pain model, we detected robust neuronal hyperactivity in injured and uninjured nerves in the skin, soma in trigeminal ganglion, and central terminals in the spinal trigeminal nucleus. Extensive TRPV1 hyperactivity was observed in central terminals innervating all dorsal horn laminae. The central terminal TRPV1 sensitization was maintained by descending serotonergic (5-HT) input from the brainstem. Central blockade of TRPV1 or 5-HT/5-HT3A receptors attenuated central terminal sensitization, excitatory primary afferent inputs, and mechanical hyperalgesia in the territories of injured and uninjured nerves. Our results reveal central mechanisms facilitating central terminal sensitization underlying chronic pain.

Spinal cord transection-induced allodynia in rats--behavioral, physiopathological and pharmacological characterization

In humans, spinal cord lesions induce not only major motor and neurovegetative deficits but also severe neuropathic pain which is mostly resistant to classical analgesics. Better treatments can be expected from precise characterization of underlying physiopathological mechanisms. This led us to thoroughly investigate (i) mechanical and thermal sensory alterations, (ii) responses to acute treatments with drugs having patent or potential anti-allodynic properties and (iii) the spinal/ganglion expression of transcripts encoding markers of neuronal injury, microglia and astrocyte activation in rats that underwent complete spinal cord transection (SCT). SCT was performed at thoracic T8-T9 level under deep isoflurane anaesthesia, and SCT rats were examined for up to two months post surgery. SCT induced a marked hyper-reflexia at hindpaws and strong mechanical and cold allodynia in a limited (6 cm2) cutaneous territory just rostral to the lesion site. At this level, pressure threshold value to trigger nocifensive reactions to locally applied von Frey filaments was 100-fold lower in SCT- versus sham-operated rats. A marked up-regulation of mRNAs encoding ATF3 (neuronal injury) and glial activation markers (OX-42, GFAP, P2×4, P2×7, TLR4) was observed in spinal cord and/or dorsal root ganglia at T6-T11 levels from day 2 up to day 60 post surgery. Transcripts encoding the proinflammatory cytokines IL-1β, IL-6 and TNF-α were also markedly but differentially up-regulated at T6-T11 levels in SCT rats. Acute treatment with ketamine (50 mg/kg i.p.), morphine (3-10 mg/kg s.c.) and tapentadol (10-20 mg/kg i.p.) significantly increased pressure threshold to trigger nocifensive reaction in the von Frey filaments test, whereas amitriptyline, pregabalin, gabapentin and clonazepam were ineffective. Because all SCT rats developed long lasting, reproducible and stable allodynia, which could be alleviated by drugs effective in humans, thoracic cord transection might be a reliable model for testing innovative therapies aimed at reducing spinal cord lesion-induced central neuropathic pain.

Ondansetron reducing pain on injection of etomidate: a controlled randomized study

INTRODUCTION

Etomidate causes pain when injected intravenously. In this study we sought to determine if pretreatment by ondansetron reduces the pain on injection of etomidate.

METHODS

In this randomized, double blinded, placebo-controlled clinical trial, 20 patients of both sexes aged between 18 and 50 years of American Society of Anesthesiologists (ASA) physical status class I or II, whom were candidates for various elective surgical procedures and need more than one intravenous access were enrolled in the study. On arrival to the operating room two 22 gauge cannulas were inserted into veins on the dorsum of both hands. Following the infusion of 100mL normal saline into both intravenous lines, using an elastic band, venous drainage of hands was occluded at midarm. The patients were administered 8 mg (2 mL) of ondansetron into one hand and 2 mL of 0.9% saline into the other hand at the same time. The elastic band was removed after 1 min and 2mg (1 mL) of etomidate was administered at the same rate simultaneously into intravenous lines. The patients were asked to give a score of pain based on a verbal analog scale (VAS) to each hand.

RESULTS

A total number of 20 patients were studied (male = 55%, female = 45%). The mean age of the participants was 37.5 ± 13.1 years old and the mean weight was 67.7 ± 7.3 kg. The mean VAS for injection pain of etomidate after pre-administration of intravenous ondansetron was 1.5 ± 1.2 which was lower compared to pre-administration of placebo (3.2 ± 2.8, p < 0.05).

CONCLUSION

This study illustrates that pre-treatment with intravenous ondansetron significantly reduces the pain on injection of etomidate.

Effects of Palonosetron, a 5-HT3 Receptor Antagonist, on Mechanical Allodynia in a Rat Model of Postoperative Pain

Background

5-hydroxytryptamine 3 (5-HT3) receptors have been known to be associated with the modulation of nociceptive transmission. However, it is uncertain whether 5-HT3 plays a role in the antinociceptive or pronociceptive pathway for incisional pain. In this study, we evaluated the effects of palonosetron, a 5-HT3 receptor antagonist, on incisional pain in rats when administered intrathecally or intraplantarly.

Methods

An intrathecal catheter was implanted through the cisterna magna and placed in the intrathecal space of rats. An incision in the plantaris muscle of the right hind paw was done under anesthesia with sevoflurane. Withdrawal thresholds were evaluated with the von Frey filament after 2 hours. Palonosetron (0.5 and 0.1 µg intrathecally; 0.5 µg intraplantarly) was administered and the thresholds were observed for 4 hours.

Results

Mechanical hypersensitivity developed after the incision. Intrathecal palonosetron (0.5 µg and 0.1 µg) did not alter the paw withdrawal threshold. Intraplantar palonosetron (0.5 µg) also did not change the paw withdrawal threshold.

Conclusions

Intrathecal and intraplantar palonosetron (0.5 µg) had no effect on modulating the mechanical hypersensitivity in the incisional pain model of rats.

Spinal 5-HT3 receptors facilitate behavioural hypersensitivity induced by elevated calcium channel alpha-2-delta-1 protein

BACKGROUND

Peripheral nerve injury induces up-regulation of the calcium channel alpha-2-delta-1 proteins in the dorsal root ganglia and dorsal spinal cord that correlates with neuropathic pain development. Similar behavioural hypersensitivity was also observed in injury-free transgenic (TG) mice over-expressing the alpha-2-delta-1 proteins in neuronal tissues. To investigate pathways regulating alpha-2-delta-1 protein-mediated behavioural hypersensitivity, we examined whether spinal serotonergic 5-HT3 receptors are involved similarly in the modulation of behavioural hypersensitivity induced by either peripheral nerve injury in a nerve injury model or neuronal alpha-2-delta-1 over-expression in the TG model.

METHODS

The effects of blocking behavioural hypersensitivity in these two models by intrathecal or systemic injections of 5-HT3 receptor antagonist, ondansetron, were compared.

RESULTS

Our data indicated that the TG mice displayed similar behavioural hypersensitivities to non-painful mechanical stimulation (tactile allodynia) and painful thermal stimulation (thermal hyperalgesia) as that observed in the nerve injury model. Interestingly, tactile allodynia and thermal hyperalgesia in both models can be blocked similarly by intrathecal, but not systemic, injection of ondansetron.

CONCLUSIONS

Our data suggest that spinal 5-HT3 receptors are likely to play a role in alpha-2-delta-1-mediated behavioural hypersensitivities through a descending serotonergic facilitation.

Transition to persistent orofacial pain after nerve injury involves supraspinal serotonin mechanisms

The orofacial region is a major focus of chronic neuropathic pain conditions characterized by primary hyperalgesia at the site of injury and secondary hyperalgesia outside the injured zone. We have used a rat model of injury to the maxillary branch (V2) of the trigeminal nerve to produce constant and long-lasting primary hyperalgesia in the V2 territory and secondary hyperalgesia in territories innervated by the mandibular branch (V3). Our findings indicate that the induction of primary and secondary hyperalgesia depended on peripheral input from the injured nerve. In contrast, the maintenance of secondary hyperalgesia depended on central mechanisms. The centralization of the secondary hyperalgesia involved descending 5-HT drive from the rostral ventromedial medulla and the contribution of 5-HT3 receptors in the trigeminal nucleus caudalis (Vc), the homolog of the spinal dorsal horn. Electrophysiological studies further indicate that after nerve injury spontaneous responses and enhanced poststimulus discharges in Vc nociresponsive neurons were time-dependent on descending 5-HT drive and peripheral input. The induction phase of secondary hyperalgesia involved central sensitization mechanisms in Vc neurons that were dependent on peripheral input, whereas the maintenance phase of secondary hyperalgesia involved central sensitization in Vc neurons conducted by a delayed descending 5-HT drive and a persistence of peripheral inputs. Our results are the first to show that the maintenance of secondary hyperalgesia and underlying central sensitization associated with persistent pain depend on a transition to supraspinal mechanisms involving the serotonin system in rostral ventromedial medulla-dorsal horn circuits.

Multiple roles of serotonin in pain control mechanisms--implications of 5-HT₇ and other 5-HT receptor types

Among monoamine neurotransmitters, serotonin (5-HT) is known to play complex modulatory roles in pain signaling mechanisms since the first reports, about forty years ago, on its essentially pro-nociceptive effects at the periphery and anti-nociceptive effects when injected directly at the spinal cord level. The discovery of multiple 5-HT receptor subtypes allowed possible explanations to this dual action at the periphery versus the central nervous system (CNS) since both excitatory and inhibitory effects can be exerted through 5-HT activation of different 5-HT receptors. However, it also appeared that activation of the same receptor subtype at CNS level might induce variable effects depending on the physiological or pathophysiological status of the animal administered with agonists. In particular, the marked neuroplastic changes induced by nerve lesion, which account for sensitization of pain signaling mechanisms, can contribute to dramatic changes in the effects of a given 5-HT receptor agonist in neuropathic rats versus intact healthy rats. This has notably been observed with 5-HT₇ receptor agonists which exert a pronociceptive action in healthy rats but alleviate hyperalgesia consecutive to nerve lesion in neuropathic animals. Analysis of cellular mechanisms underlying such dual 5-HT actions mediated by a single receptor subtype indicates that the neuronal phenotype which expresses this receptor also plays a key role in determining which modulatory action 5-HT would finally exert on pain signaling mechanisms.

Effect of adding 8 milligrams ondansetron to lidocaine for Bier's block on post-operative pain

BACKGROUND

Ondansetron has analgesic properties. The aim of the present study was to assess the analgesic effect of 8 mg ondansetron when added to lidocaine for intravenous regional anesthesia (IVRA).

MATERIALS AND METHODS

Ninety patients undergoing hand surgery were randomly allocated to the three groups to receive 3 mg/kg 2% lidocaine diluted with saline to a total dose of 40 mL (Group L, n = 30) or 8 mg ondansetron plus 3 mg/kg 2% lidocaine diluted with saline to a total dose of 40 mL (group LO, n = 30) or 3 mg/kg 2% lidocaine diluted with saline to a total dose of 40 mL plus 8 mg ondansetron intravenously (Group IO, n = 30). Tourniquet pain and analgesic use were recorded before and after the tourniquet application.

RESULTS

The sensory and motor block onset times were significantly shorter in Group LO compared with Group L and Group IO (4.2 ± 1.7 vs. 5.2 ± 0.8 and 5.1 ± 1.2 respectively, P < 0.05; 4.5 ± 1.4 vs. 5.8 ± 1.5 and 5.7 ± 1.4 respectively, P < 0.05). The sensory and motor block recovery times were significantly longer in Group LO compared with Group L and Group IO (6.1 ± 1.1 vs. 4.1 ± 1.3 and 4.5 ± 0.9 respectively, P < 0.05; 6.7 ± 1.4 vs. 4.4 ± 0.9 and 4.7 ± 0.7 respectively, P < 0.05). Post-operative VAS scores were significantly less in Group LO compared with Group L and Group IO till 24 h after tourniquet deflation (P < 0.05).

CONCLUSION

The addition of 8 mg ondansetron to lidocaine for IVRA reduced intraoperative and post-operative analgesic use till 24 h.

Analgesic mechanisms of Fagopyrum cymosum extracts in rats with irritable bowel syndrome

AIM: To observe the effect of Fagopyrum cymosum extracts (Fag) on visceral hypersensitivity in rats with irritable bowel syndrome (IBS)-like colon irritation (CI) and to explore the possible mechanisms involved.

METHODS: IBS-like models were created using neonatal CI method. CI adult rats were given Fag intragastrically for 2 wk, and visceral sensitivity was then evaluated using abdominal withdrawal reflex (AWR) score. The expression of 5-hydroxytryptamine (5-HT) in the spinal cord was detected by immunohistochemistry and that of 5-HT1A receptor (5-HT1AR) and 5-HT3A receptor (5-HT3AR) was detected by Western blot.

RESULTS: Compared to control rats, AWR scores in CI rats were significantly increased (20 mmHg: 0.625 ± 0.518 vs 1.333 ± 0.778; 30 mmHg: 0.750 ± 0.463 vs 1.667 ± 0.888; 40 mmHg: 1.125 ± 0.641 vs 2.000 ± 0.739; 50 mmHg: 1.500 ± 0.926 vs 2.583 ± 0.793; 60 mmHg: 2.125 ± 0.991 vs 3.083 ± 0.669; all P < 0.05). In the spinal cord, the expression of 5-HT and 5-HT3AR was enhanced and that of 5-HT1AR expression was reduced in CI rats compared to control rats (all P < 0.01). Fag at a high dose could markedly reduce AWR scores (20 mmHg: 0.250 ± 0.002; 30 mmHg: 0.875 ± 0.044; 40 mmHg: 1.250 ± 0.036; 50 mmHg: 1.875 ± 0.050; 60 mmHg: 2.625 ± 0.037; all P < 0.05), down-regulate the expression of 5-HT and 5-HT3AR, and up-regulate the expression of 5-HT1AR (all P < 0.05) in spinal cord (P < 0.05) in CI rats. Fag at a low dose had no significant effect on CI rats.

CONCLUSION: Fag can exert an analgesic role in IBS-like CI rats by regulating 5-HT and its receptors in the spinal cord.