Pharmacological mechanisms involved in the antinociceptive effects of dexmedetomidine in mice

Antinociceptive effects of Raphanus sativus sprouts involve the opioid and 5-HT1A serotonin receptors, cAMP/cGMP pathways, and the central activity of sulforaphane

Raphanus sativus L. cv. Sango, commonly known as red radish, is widely consumed around the world as a vegetable, but its benefit in pain relief is not sufficiently investigated. This study aimed to evaluate the antinociceptive effects of R. sativus and a possible mechanism of action. An aqueous extract of R. sativus sprouts (AERSS) was investigated by parenteral (10, 30, and 100 mg kg-1, i.p.) and enteral (500 mg kg-1, p.o.) administration in the neurogenic and inflammatory phases of the formalin test, where gastric damage was also evaluated as a possible adverse effect. Ketorolac (5 mg kg-1, i.p.) was used as the reference drug. Endogenous opioid and 5-HT1A serotonin receptors, as well as the cAMP/NO-cGMP pathways, were explored in the study of a possible mechanism of action by using their corresponding antagonists: naloxone, 1 mg kg-1, i.p., WAY100635, 1 mg kg-1, i.p., and enzymatic activators or inhibitors, respectively. Sulforaphane (SFN), a known bioactive metabolite, was analyzed using electroencephalography (EEG) to evidence its central involvement. A significant and dose-dependent antinociceptive activity was observed with the AERSS resembling the antinociceptive effect of the reference drug, with an equivalent significant response with a dose of 500 mg kg-1, p.o. without causing gastric damage. The participation of the endogenous opioid and 5-HT1A serotonin receptors at central and peripheral levels was also observed, with a differential participation of cAMP/NO-cGMP. SFN as one metabolite produced significant changes in the EEG analysis, reinforcing its effects on the CNS. Our preclinical evidence supports the benefits of consuming Raphanus sativus cv. Sango sprouts for pain relief.

Dexmedetomidine relieves inflammatory pain by enhancing GABAergic synaptic activity in pyramidal neurons of the anterior cingulate cortex

Pyramidal neuron (Pyn) hyperactivity in the anterior cingulate cortex (ACC) is involved in the modulation of pain. Previous studies indicate that the activation of α2 adrenoceptors (α2-ARs) by dexmedetomidine (DEX) is a safe and effective means of alleviating multiple types of pain. Here, we showed that systemically administered DEX can ameliorate the inflammatory pain induced by hindpaw injection of formalin (FA) and further examined the molecular and synaptic mechanisms of this DEX-elicited antinociceptive effect. We found that FA caused an increase in c-Fos expression in contralateral layer 2/3 (L2/3) ACC, and that intra-ACC infusion of DEX could also relieve phase 2 inflammatory pain behavior. DEX elicited an increase in the amplitude and frequency of miniature inhibitory post-synaptic currents (mIPSCs) and evoked IPSC amplitude, as well as a reduction in the hyperexcitability and both paired-pulse and excitation/inhibition ratios in contralateral L2/3 ACC Pyns of FA mice. These electrophysiological effects were associated with the upregulation of GABA A receptor (GABAAR) subunits. The interaction of phosphorylated Akt (p-Akt) with GABAAR subunits increased in the ACC following administration of DEX. These results suggest that DEX treatment reduces hyperactivity and enhances GABAergic inhibitory synaptic transmission in ACC Pyns, which produces analgesic effects by increasing GABAAR levels and activating the Akt signaling pathway.

Combination of ion-pair strategy and chemical enhancers for design of dexmedetomidine long-acting patches: Dual action mechanism induced longer controlled release and better delivery efficiency

The purpose of this study was to prepare a dexmedetomidine (Dex) 72 h long-acting patch by the combined use of ion-pair strategy and chemical enhancers (CEs), and to investigate molecular mechanisms of drug-loading enhancement and controlled release. The formulation of patch was optimized by single-factor investigation and Box-Behnken design. The pharmacokinetics, analgesic pharmacodynamics and irritation of the formulation were evaluated, respectively. Moreover, the effects of ion-pairs and CEs on the patch were characterized by DSC, rheology study, FTIR, and molecular docking, and the effects on the skin were evaluated by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), Raman study, and molecular dynamics, respectively. The optimized formulation was 17.00 % (w/w) Dex-NA (Naphthoic acid), 7.20 % Polyglyceryl-3 dioleate (POCC), 25-AAOH as pressure sensitive adhesives (PSA) and 66.50 μm in thickness. Compared with the control group (C_max = 62.02 ± 16.55 ng/mL, MRT_0-t = 26.74 ± 1.27 h), the pharmacokinetics behavior of the optimization group was more stable and durable (C_max = 31.22 ± 13.26 ng/mL, MRT_0-t = 33.62 ± 1.62 h). Besides, it also showed good analgesic effect and no obvious irritation. The results indicated that Dex-NA both increased the drug-PSA interactions and inhibited the penetration of the drug into the skin. POCC increased the molecular mobility of the PSA and disrupted skin lipids thereby improving the drug penetration rate. In summary, the Dex long-acting patch was developed, which provided a reference for the combined application of ion-pair strategy and CEs in other long-acting transdermal delivery.

Safety Assessment and Pain Relief Properties of Saffron from Taliouine Region (Morocco)

Saffron is the most expensive spice in the world. In addition to its culinary utilization, this spice is used for medicinal purposes such as in pain management. In this study, the analgesic activity of Crocus sativus stigma extract (CSSE) was evaluated in rodents and its possible physiological mechanism was elucidated. The anti-nociceptive effect of CSSE was evaluated using three animal models (hot plate, writhing, and formalin tests). The analgesic pathways involved were assessed using various analgesia-mediating receptors antagonists. The oral administration of CSSE, up to 2000 mg/kg, caused no death or changes in the behavior or in the hematological and biochemical blood parameters of treated animals nor in the histological architecture of the animals’ livers and kidneys. CSSE showed a central, dose-dependent, anti-nociceptive effect in response to thermal stimuli; and a peripheral analgesic effect in the test of contortions induced by acetic acid. The dual (central and peripheral) analgesic effect was confirmed by the formalin test. The anti-nociceptive activity of CSSE was totally or partially reversed by the co-administration of receptor antagonists, naloxone, atropine, haloperidol, yohimbine, and glibenclamide. CSSE influenced signal processing, by the modulation of the opioidergic, adrenergic, and muscarinic systems at the peripheral and central levels; and by regulation of the dopaminergic system and control of the opening of the ATP-sensitive K⁺ channels at the spinal level. The obtained data point to a multimodal mechanism of action for CSSE: An anti-inflammatory effect and a modulation, through different physiological pathways, of the electrical signal generated by the nociceptors. Further clinical trials are required to endorse the potential utilization of Moroccan saffron as a natural painkiller.

Dexmedetomidine Co-Administered with Lidocaine Decreases Nociceptive Responses and Trigeminal Fos Expression without Motor Dysfunction and Hypotension in a Murine Orofacial Formalin Model

Administration of dexmedetomidine significantly induces sedation and anti-nociception in several nociceptive models, but clinical trials are restricted due to adverse side effects, including lethargy, hypotension, and bradycardia. Herein, we investigated whether intraperitoneal inoculation of dexmedetomidine reduced the orofacial nociceptive response and affected motor coordination and blood pressure and examined whether a lower dose of dexmedetomidine in combination with 0.5% lidocaine produced an antinociceptive effect without any adverse side events in a murine model. To perform the experiment, 5% formalin (10 µL) was subcutaneously inoculated into the right upper lip, and the rubbing responses were counted for 45 min. Different doses of dexmedetomidine combined with 0.5% lidocaine were administered 10 and 30 min before formalin injection, respectively. Dexmedetomidine (10 μg/kg) significantly reduced orofacial nociceptive responses during the second phase of the formalin test and decreased the expression of Fos in trigeminal nucleus caudalis (TNC). Besides, a high dose of dexmedetomidine (30 μg/kg) induced lessening physical ability and significantly reduced systolic pressure and heart rate. When 0.5% lidocaine was injected subcutaneously, nociceptive responses were reduced only in the first phase. Interestingly, although a low dose of dexmedetomidine (3 μg/kg) alone did not show an antinociceptive effect, its co-administration with lidocaine significantly reduced the nociceptive response in both phases and decreased TNC Fos expression without motor dysfunction and hypotension. This finding suggests that the combination of a low-dose of systemic dexmedetomidine with lidocaine may be a safe medicinal approach for acute inflammatory pain management in the orofacial region, particularly mucogingival pain.

Bombax costatum enhances piroxicam's efficacy: Possible involvement of alpha-2 adrenergic receptor, opioidergic and arachidonic pathways

BACKGROUND

With increasing drug-herb combination and widespread use of Bombax costatum as analgesic in Africa, this research studies effects of Bombax costatum on piroxicam's efficacy and possible mechanisms of antinociception.

MATERIALS AND METHODS

In efficacy studies, four groups of mice were respectively treated with 1mL/kg distilled water, 400mg/kg Bombax costatum, 20mg/kg piroxicam and a combination of both. Acetic acid and hot plate were used to induce pain in mice while prostaglandin-E₂ and formalin were used to induce inflammation in rats. For mechanistic studies, different groups of mice were treated intraperitoneally with 2mg/kg naloxone, 1mg/kg yohimbine, 20mg/kg propranolol, 5mg/kg glibenclamide and 1mg/kg prazosin respectively. Two other groups were treated orally with 1mL/kg of the vehicle and 400mg/kg Bombax costatum respectively. 60minutes later, 10mL/kg of 0.6% acetic acid was administered via the intraperitoneal route and number of writhes were observed for 10minutes.

RESULTS

Concurrent administration of Bombax costatum and piroxicam decreased the number of writhes significantly (P≤0.001), increased reaction time with decreased paw diameter in comparison to control. Additionally, this drug-herb combination showed enhanced anti-nocipective efficacy than when administered singly. Also, pre-treatment with yohimbine and naloxone significantly (P≤0.01) inhibited the antinociceptive activities of Bombax costatum.

CONCLUSION

Bombax costatum posses antinociceptive and anti-inflammatory activities and may involve α-₂ adrenergic receptor, opioidergic and arachidonic pathways. In addition, Bombax costaum augments the efficacy of piroxicam and could be of clinical benefits if studied on man.

Possible Participation of Ionotropic Glutamate Receptors and l-Arginine-Nitric Oxide-Cyclic Guanosine Monophosphate-ATP-Sensitive K+ Channel Pathway in the Antinociceptive Activity of Cardamonin in Acute Pain Animal Models

The perception of pain caused by inflammation serves as a warning sign to avoid further injury. The generation and transmission of pain impulses involves various pathways and receptors. Cardamonin isolated from Boesenbergia rotunda (L.) Mansf. has been reported to exert antinociceptive effects in thermal and mechanical pain models; however, the precise mechanism has yet to be examined. The present study investigated the possible mechanisms involved in the antinociceptive activity of cardamonin on protein kinase C, N-methyl-d-aspartate (NMDA) and non-NMDA glutamate receptors, l-arginine/cyclic guanosine monophosphate (cGMP) mechanism, as well as the ATP-sensitive potassium (K⁺) channel. Cardamonin was administered to the animals intra-peritoneally. Present findings showed that cardamonin significantly inhibited pain elicited by intraplantar injection of phorbol 12-myristate 13-acetate (PMA, a protein kinase C activator) with calculated mean ED₅₀ of 2.0 mg/kg (0.9–4.5 mg/kg). The study presented that pre-treatment with MK-801 (NMDA receptor antagonist) and NBQX (non-NMDA receptor antagonist) significantly modulates the antinociceptive activity of cardamonin at 3 mg/kg when tested with glutamate-induced paw licking test. Pre-treatment with l-arginine (a nitric oxide precursor), ODQ (selective inhibitor of soluble guanylyl cyclase) and glibenclamide (ATP-sensitive K⁺ channel inhibitor) significantly enhanced the antinociception produced by cardamonin. In conclusion, the present findings showed that the antinociceptive activity of cardamonin might involve the modulation of PKC activity, NMDA and non-NMDA glutamate receptors, l-arginine/nitric oxide/cGMP pathway and ATP-sensitive K⁺ channel.

Anti-inflammatory and antinociceptive activity profile of a new lead compound - LQFM219

LQFM219 is a molecule designed from celecoxibe (COX-2 inhibitor) and darbufelone (inhibitor of COX-2 and 5-LOX) lead compounds through a molecular hybridisation strategy. Therefore, this work aimed to investigate the antinociceptive and anti-inflammatory activities of this new hybrid compound. The acute oral systemic toxicity of LQFM219 was evaluated via the neutral red uptake assay. Acetic acid-induced abdominal writhing and CFA-induced mechanical hyperalgesia were performed to evaluate the antinociceptive activity, and the anti-oedematogenic activity was studied by CFA-induced paw oedema and croton oil-induced ear oedema. Moreover, the acute anti-inflammatory activity was determined by carrageenan-induced pleurisy. In addition, cell migration, myeloperoxidase enzyme activity, and TNF-α and IL-1β levels were determined in pleural exudate. Moreover, a redox assay was conducted using electroanalytical and DPPH methods. The results demonstrated that LQFM219 was classified as GHS category 4, and it showed better free radical scavenger activity compared to BHT. Besides, LQFM219 decreased the number of writhings induced by acetic acid and the response to the mechanical stimulus in the CFA-induced mechanical hyperalgesia test. Furthermore, LQFM219 reduced oedema formation, cell migration, and IL-1β and TNF-α levels in the pleural cavity and inhibited myeloperoxidase enzyme activity. Thus, our study provides that the new pyrazole derivative, LQFM219, demonstrated low toxicity, antinociceptive and anti-inflammatory potential in vitro and in vivo.

Locomotor mal-performance and gait adaptability deficits in sickle cell mice are associated with vascular and white matter abnormalities and oxidative stress in cerebellum

Patients with sickle cell disease (SCD) can develop strokes and as a result, present neurologic and neurocognitive deficits. However, recent studies show that even without detectable cerebral parenchymal abnormalities on imaging studies, SCD patients can have significant cognitive and motor dysfunction, which can present as early as during infancy. As the cerebellum plays a pivotal role in motor and non-motor functions including sensorimotor processing and learning, we examined cerebellar behavior in humanized SCD mice using the Erasmus ladder. Homozygous (sickling) mice had significant locomotor malperformance characterized by miscoordination and impaired locomotor gait/stepping pattern adaptability. Conversely, Townes homozygous mice had no overall deficits in motor learning, as they were able to associate a conditioning stimulus (high-pitch warning tone) with the presentation of an obstacle and learned to decrease steptimes thereby increasing speed to avoid it. While these animals had no cerebellar strokes, these locomotor and adaptive gait/stepping patterns deficits were associated with oxidative stress, as well as cerebellar vascular endothelial and white matter abnormalities and blood brain barrier disruption, suggestive of ischemic injury. Taken together, these observations suggest that motor and adaptive locomotor deficits in SCD mice mirror some of those described in SCD patients and that ischemic changes in white matter and vascular endothelium and oxidative stress are biologic correlates of those deficits. These findings point to the cerebellum as an area of the central nervous system that is vulnerable to vascular and white matter injury and support the use of SCD mice for studies of the underlying mechanisms of cerebellar dysfunction in SCD.

Elucidation of the possible mechanism of analgesic action of methanol stem bark extract of Uapaca togoensis pax in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Uapaca togoensis is a medicinal plant used traditionally in Africa for the treatment of rheumatism, epilepsy, cough, pneumonia, vomitting and fever. Previously, the analgesic activity of its methanol stem bark extract has been scientifically demonstrated. However, the mechanism responsible for this activity remains to be investigated.

AIM OF THE STUDY

To elucidate the possible mechanism(s) through which the methanol stem bark extract of Uapaca togoensis (MEUT) exhibits analgesic activity in mice.

MATERIALS AND METHODS

Analgesic activity of MEUT was evaluated using acetic acid-induced abdominal writhing test in mice at doses of 250, 500 and 1000 mg/kg orally. For the mechanistic studies, mice were pre-treated with Naloxone (2 mg/kg), Atropine (1 mg/kg), Yohimbine (1 mg/kg), Glibenclamide (10 mg/kg), Prazosin (1 mg/kg) and Yohimbine (1 mg/kg) 15 min prior to MEUT (1000 mg/kg) administration, then assessed using AAWT 1 h later. Data was analysed using One way Anova followed by Bonferroni post hoc test.

RESULTS

The extract (at the doses of 250, 500 and 1000 mg/kg) and morphine (10 mg/kg) significantly (p < 0.05) decreased the number of abdominal writhes. Naloxone (opioid receptor antagonist), Atropine (muscarinic receptor antagonist) and Glibenclamide (ATP-sensitive K+ channel blocker) significantly (p < 0.05) reversed the analgesic effect of MEUT. On the other hand, Prazosin and Yohimbine (α₁ and α₂ receptor antagonists respectively) had no effect on the analgesic action of MEUT.

CONCLUSION

The results obtained from this study suggests the possible involvement of opioidergic, cholinergic and sensitive potassium ATP channel pathways in the analgesic activity of the methanol stem bark extract of Uapaca togoensis.

Molecular determinants of behavioral changes induced by neonatal ketamine and dexmedetomidine application

Ketamine (KET), an anesthetic, analgesic, and a sedative N-methyl-D-aspartate (NMDA) receptor antagonist agent, exposure during neonatal period may lead to learning impairment, behavioral abnormalities, and cognitive decline in the later years of life. In recent studies, it has been reported that sedative-acting α2 agonist dexmedetomidine (DEX), which is commonly used in clinical practice with KET, has neuroprotective effects and prevents the undesirable effects of anesthesia. To elucidate the underlying mechanisms of these actions, we investigated the interaction between NMDA receptors α₂ adrenoceptor and adulthood behaviors in neonatally KET and/or DEX administrated mice. Balb/c male mice were administrated with saline, KET (75 mg/kg), DEX (10 µg/kg), or KET + DEX (75 mg/kg + 10 µg/kg) on postnatal day 7. During adulthood (8-10 weeks old) mice were subjected to elevated plus maze, open field, and Morris water maze tests. After behavioral tests, hippocampus samples were extracted for mRNA expression studies of NMDAR subunits (GluN1, GluN2A, and GluN2B) and α₂ adrenoceptor subunits (α_2A, α_2B, and α_2C) by real-time PCR. Ketamine increased horizontal and vertical locomotor activity (p < 0.01) and impaired spatial learning-memory (p < 0.05). DEX increased anxiety-like behavior (p < 0.01), but did not affect spatial learning-memory and locomotor activity. KET + DEX impaired spatial learning-memory (p < 0.01), increased horizontal locomotor activity (p < 0.01), and anxiety-like behavior (p < 0.05). Our study implies that DEX cannot prevent the adverse effects of KET, on spatial learning-memory, and locomotor activity. In addition to this, it can be thought that during brain development, there is an interaction between NMDAR and α₂ adrenoceptor systems.

Antinociceptive activity of methanol extract of Chlorophytum alismifolium tubers in murine model of pain: Possible involvement of α2-adrenergic receptor and KATP channels

The tubers of Chlorophytum alismifolium are used in Nigerian Herbal Medicine for the management of diabetes mellitus, painful and inflammatory conditions. The antinociceptive activity has been validated but the mechanism of this activity is yet to be explored. This study therefore, aimed to investigate the probable mechanism(s) of the antinociceptive activity of C. alismifolium tubers using experimental animal model of pain. HPLC and GC-MS analyses were carried out on the extract. Antinociceptive activity was investigated using acetic acid-induced writhing response test in mice. Three groups of mice were orally administered distilled water (10 ml/kg), C. alismifolium (400 mg/kg) and morphine (10 mg/kg) 60 min before administration of acetic acid and the resulting writhing were counted for 10 min. To establish the probable mechanism(s) of action of C. alismifolium, separate groups of animals were pretreated intraperitoneally with naloxone (2 mg/kg), prazosin (1 mg/kg), yohimbine (1 mg/kg), propranolol (20 mg/kg) and glibenclamide (5 mg/kg) 15 min before C. alismifolium administration. HPLC chromatogram of the extract revealed seventeen characteristic peaks with retention times ranging between 2.1 and 7.4 min. Administration of C. alismifolium significantly (p < 0.01) reduced the mean number of writhes compared to control group. Pretreatment with yohimbine and glibenclamide significantly (p < 0.05 and p < 0.01 respectively) reduced the antinociceptive activity of extract-alone treated group. However, pretreatment with prazosin, naloxone and propranolol showed no effect on its analgesic activity. The findings from this research revealed the possible involvement of α₂-adrenergic receptor and K_ATP channels in the antinociceptive activity of Chlorophytum alismifolium tuber extract.

Impact of local administration of various doses of dexmedetomidine on ropivacaine-induced lumbar plexus-sciatic nerve block

The present study aimed to investigate the impact of various doses of dexmedetomidine (DEX) on ropivacaine (ROP)-induced lumbar plexus-sciatic nerve block (LSB). A total of 80 patients who underwent ankle surgery under LSB were divided into group R (applied with 30 ml 5% ROP), Dex1 (30 ml 0.5% ROP + 1 µg/kg DEX), Dex2 (30 ml 0.5% ROP + 1.5 µg/kg DEX) and Dex3 (30 ml 0.5% ROP + 2 µg/kg DEX), with 20 cases in each group. The onset time and duration of sensory and motor block, mean arterial pressure (MAP), heart rate (HR), oxygen saturation, Ramsay score, serum vascular endothelial growth factor (VEGF) level and adverse reactions in the four groups were observed. Results demonstrated that the durations of sensory and motor block in group R were shorter than those in groups Dex1-3 (P<0.01), followed by the sequence of group Dex1<Dex2<Dex3 (P<0.05). MAP and HR in groups Dex1-3 at T2-T5 were significantly lower than those in group R (P<0.01), and HR in group Dex3 at T3 and T4 was significantly lower than that in groups Dex1 and Dex2 (P<0.05). Ramsay scores in groups Dex1-3 at T2-T4 were significantly higher than those in group R (P<0.05). Serum VEGF levels in groups Dex2 and Dex3 at T2-T5 were significantly higher than those in group R (P<0.01). The incidences of over-sedation, bradycardia and dry mouth in group Dex3 were notably higher than those in the other groups. In conclusion, 1.5 µg/kg DEX exhibits a superior effect in improving ROP-induced LSB.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Alfaxalone versus alfaxalone-dexmedetomidine anaesthesia by immersion in oriental fire-bellied toads (Bombina orientalis)

OBJECTIVE

To determine a dexmedetomidine concentration, to be added to an alfaxalone-based bath solution, that will enhance the anaesthetic and analgesic effects of alfaxalone; and to compare the quality of anaesthesia and analgesia provided by immersion with either alfaxalone alone or alfaxalone with dexmedetomidine in oriental fire-bellied toads (Bombina orientalis).

STUDY DESIGN

Pilot study followed by a prospective, randomized, experimental trial.

ANIMALS

Fourteen oriental fire-bellied toads.

METHODS

The pilot study aimed to identify a useful dexmedetomidine concentration to be added to an anaesthetic bath containing 20 mg 100 mL(-1) alfaxalone. Thereafter, the toads were assigned to one of two groups, each comprising eight animals, to be administered either alfaxalone (group A) or alfaxalone-dexmedetomidine (group AD). After immersion for 20 minutes, the toads were removed from the anaesthetic bath and the righting, myotactic and nociceptive reflexes, cardiopulmonary variables and von Frey filaments threshold were measured at 5 minute intervals and compared statistically between groups. Side effects and complications were noted and recorded.

RESULTS

In the pilot study, a dexmedetomidine concentration of 0.3 mg 100 mL(-1) added to the alfaxalone-based solution resulted in surgical anaesthesia. The toads in group AD showed higher von Frey thresholds and lower nociceptive withdrawal reflex scores than those in group A. However, in group AD, surgical anaesthesia was observed in two out of eight toads only, and induction of anaesthesia was achieved in only 50% of the animals, as compared with 100% of the toads in group A.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of dexmedetomidine to an alfaxalone-based solution for immersion anaesthesia provided some analgesia in oriental fire-bellied toads, but failed to potentiate the level of unconsciousness and appeared to lighten the depth of anaesthesia. This limitation renders the combination unsuitable for anaesthetizing oriental fire-bellied toads for invasive procedures.

Dexmedetomidine as an Adjuvant to Analgesic Strategy During Vaso-Occlusive Episodes in Adolescents with Sickle-Cell Disease

Patients with sickle-cell disease (SCD) can experience recurrent vaso-occlusive episodes (VOEs), which are associated with severe pain. While opioids are the mainstay of analgesic therapy, in some patients with SCD, increasing opioid use is associated with continued and increasing pain. Dexmedetomidine, an α2 -adrenoreceptor agonist with sedative and analgesic properties, has been increasingly used in the perioperative and intensive care settings and has been shown to reduce opioid requirement and to facilitate opioid weaning. Therefore, there might be a role for dexmedetomidine in pain management during VOEs in patients with SCD. Here, we present the hospital course of 3 patients who during the course of VOEs had severe pain unresponsive to opioids and ketamine and were treated with dexmedetomidine. Dexmedetomidine infusions that lasted for 3 to 6 days were associated with marked reduction in daily oral morphine-equivalent intake and decreases in pain scores (numeric rating scale). There were no hemodynamic changes that required treatment with vasoactive or anticholinergic agents. These preliminary findings of possible beneficial effects of dexmedetomidine in decreasing opioid requirements support the hypothesis that dexmedetomidine may have a role as a possible analgesic adjuvant to mitigate VOE-associated pain in patients with SCD.

Dexmedetomidine ameliorates nocifensive behavior in humanized sickle cell mice

Patients with sickle cell disease (SCD) can have recurrent episodes of vaso-occlusive crises, which are associated with severe pain. While opioids are the mainstay of analgesic therapy, in some patients, increasing opioid use results in continued and increasing pain. Many believe that this phenomenon results from opioid-induced tolerance or hyperalgesia or that SCD pain involves non-opioid-responsive mechanisms. Dexmedetomidine, a specific α2-adrenoreceptor agonist, which has sedative and analgesic properties, reduces opioid requirements, and can facilitate opioid withdrawal in clinical settings. We hypothesized that dexmedetomidine would ameliorate the nociception phenotype of SCD mice. Townes and BERK SCD mice, strains known to have altered nociception phenotypes, were used in a crossover preclinical trial that measured nocifensive behavior before and after treatment with dexmedetomidine or vehicle. In a linear dose-effect relationship, over 60-min, dexmedetomidine, compared with vehicle, significantly increased hot plate latency in Townes and BERK mice (P≤0.006). In sickle, but not control mice, dexmedetomidine improved grip force, an indicator of muscle pain (P=0.002). As expected, dexmedetomidine had a sedative effect in sickle and control mice as it decreased wakefulness scores compared with vehicle (all P<0.001). Interestingly, the effects of dexmedetomidine on hot plate latency and wakefulness scores were different in sickle and control mice, i.e., dexmedetomidine-related increases in hotplate latency and decreases in wakefulness scores were significantly smaller in Townes sickle compared to control mice. In conclusion, these findings of beneficial effects of dexmedetomidine on the nociception phenotype in SCD mice might support the conduct of studies of dexmedetomidine in SCD patients.