Increase In Tail-flick Latency Research Articles

S-nitroso-L-cysteine stereoselectively blunts the adverse effects of morphine on breathing and arterial blood gas chemistry while promoting analgesia

S-nitrosothiols exert multiple effects on neural processes in the central and peripheral nervous system. This study shows that intravenous infusion of S-nitroso-L-cysteine (SNO-L-CYS, 1 μmol/kg/min) in anesthetized male Sprague Dawley rats elicits (a) sustained increases in minute ventilation, via increases in frequency of breathing and tidal volume, (b) a decrease in Alveolar-arterial (A-a) gradient, thus improving alveolar gas-exchange, (c) concomitant changes in arterial blood-gas chemistry, such as an increase in pO2 and a decrease in pCO2, (d) a decrease in mean arterial blood pressure (MAP), and (e) an increase in tail-flick (TF) latency (antinociception). Infusion of S-nitroso-D-cysteine (SNO-D-CYS, 1 μmol/kg/min, IV), did not elicit similar responses, except for a sustained decrease in MAP equivalent to that elicited by SNO-L-CYS. A bolus injection of morphine (2 mg/kg, IV) in rats receiving an infusion of vehicle elicited (a) sustained decreases in frequency of breathing tidal volume, and therefore minute ventilation, (b) a sustained decrease in MAP, (c) sustained decreases in pH, pO2 and maximal sO2 with sustained increases in pCO2 and A-a gradient, and (d) a sustained increase in TF latency. In rats receiving SNO-L-CYS infusion, morphine elicited markedly smaller changes in minute ventilation, arterial blood gas chemistry, A-a gradient and MAP. In contrast, the antinociceptive effects of morphine were enhanced in rats receiving the infusion of SNO-L-CYS. The morphine-induced responses in rats receiving SNO-D-CYS infusion were similar to vehicle-infused rats. These data are the first to demonstrate that infusion of an S-nitrosothiol, such as SNO-L-CYS, can stereoselectively ameliorate the adverse effects of morphine on breathing and alveolar gas exchange while promoting antinociception.

Effect of oxytocin pretreatment on the development of morphine tolerance and dependence in rats

Increased opioid synthesis and release, and enhanced alpha-2 adrenoceptor signaling have been suggested to mediate repeated oxytocin-induced long-lasting effects including elevated pain threshold in rats. This study evaluated whether oxytocin pretreatment would influence development of dependence and tolerance to the nociceptive and body temperature responses to morphine and enhance effects of alpha-2 adrenergic agonist clonidine on nociceptive threshold, body temperature and morphine withdrawal signs. Rats injected subcutaneously with saline or 1 mg/kg oxytocin for 5 days were implanted with placebo or morphine pellets 24 h after the treatment period. Body temperature and nociception were assessed, with nociception determined via by hot plate and tail immersion tests, before and 4, 24 and 48 h after pellet implantation, and following a challenge dose of morphine. Withdrawal signs were determined after naloxone administration. Oxytocin produced analgesia, as evidenced by increased paw withdrawal latency in the hot plate test. Morphine increased body temperature and nociceptive threshold which declined over time. Morphine challenge could not demonstrate tolerance to the body temperature response. Analgesic tolerance was observed in the hot plate test in saline and in both tests in oxytocin pretreated rats. Naloxone-precipitated withdrawal appeared to be less severe in oxytocin pretreatment. Clonidine was ineffective on the withdrawal signs but decreased body temperature and increased tail flick latency in the tail immersion test in oxytocin pretreated animals. These results, while producing evidence for a hyperresponsiveness in alpha-2 adrenoceptors, provide contrasting effects on morphine tolerance and dependence, and their partial mediation by opioidergic and adrenergic activation in repeated oxytocin treatment.

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague–Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO2 and sO2 and increases in pCO2 (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.

Synthesis and Assessment of Fused β-Carboline Derivatives as Kappa Opioid Receptor Agonists.

The synthesis of 5-formyl-6-aryl-6H-indolo[3,2,1-de][1,5] naphthyridine-2-carboxylates by reaction between 1-formyl-9H-β-carbolines and cinnamaldehydes in the presence of pyrrolidine in water with microwave irradiation is described. Pharmacophoric modification of the formyl group offered several new fused β-carboline derivatives, which were investigated for their κ-opioid receptor (KOR) agonistic activity. Two compounds 4 a and 4 c produced appreciable agonist activity on KOR with EC50 values of 46±19 and 134±9 nM, respectively. Moreover, compound-induced KOR signaling studies suggested both compounds to be extremely G-protein-biased agonists. The analgesic effect of 4 a was validated by the increase in tail flick latency in mice in a time-dependent manner, which was completely blocked by the KOR-selective antagonist norBNI. Moreover, unlike U50488, an unbiased full KOR agonist, 4 a did not induce sedation. The docking of 4 a with the human KOR was studied to rationalize the result.

Pharmacological evaluation of processed Cannabis leaves as a non sedative analgesic: The novel approach

Background: Ayurvedic pharmacopoeia records vivid indications of Cannabis (Bhanga) including its analgesic, sedative and intoxicant actions. For inhibition of intoxication, Ayurveda recommends certain processing (Shodhana) techniques for Cannabis. The present study is planned to evaluate the analgesic potential and sedative effects of water washed (Jalaprakshalana)–processed Cannabis sativa leaves through pharmacological experimentation. Methods: Wistar strain albino rats weighing 200 ± 20 g and Swiss albino mice (25–35 g) of either sex were used in the study. Pharmacologically validated models were used to evaluate the analgesic effects (by formalin test and tail flick method) and neuromuscular coordination by rotarod experiment. water-washed–processed Cannabis leaves powder (test drug [TD]) was administered at dose of 22.5 and 45 mg/kg for rat and mouse, respectively, against reference standard morphine sulfate (MS) 5 mg/kg and the results were evaluated statistically. Results: TD at 22.5 and 45 mg/kg showed significant decrease in paw licking response at early phase in formalin test. TD at 22.5 mg/kg showed significant increase in tail flick latency after 3 h, and in 45 mg/kg dose, it was significant up to 4 h. In rotarod experiment, TD did not show any decrease in latency of fall-off time after 1 and 3 h. Conclusion: Water-washed processed Cannabis leaves powder possesses significant analgesic effect at 22.5 mg/kg (250 mg human dose) and 45 mg/kg (500 mg human dose) comparable to MS 5 mg while nonsignificant effect in neuromuscular in-coordination, thus devoid of sedative effect.

Influence of forced treadmill and voluntary wheel running on the sensitivity of gastric mucosa to ulcerogenic stimuli in male rats.

Physical activity is crucial for maintaining health. Here we investigated the preconditioning effects of exercise on the vulnerability of gastric mucosa to ulcerogenic action of indomethacin (IM, 35 mg/kg, s.c.) or cold-restraint stressor (CR, 3 h, 10°C) in male rats. Single or repeated (5 days) training was used either voluntarily (2 h/day, wheel running) or in a forced way (treadmill). The intensity of the later was either "moderate" (9 m/min, 15 min) or "intensive" (15 m/min, 30 min). All protocols were confirmed by elevated plasma corticosterone and increased tail flick latencies (analgesia). IM-induced ulceration was attenuated by single intensive forced exercise, repeated voluntary and moderate forced exercise. On the contrary, single 2 h voluntary session aggravated the IM-induced ulceration. The ulcerogenic effect of CR was aggravated by single and repeated voluntary and single intensive forced exercise, while repeated moderate forced running was gastroprotective. Single moderate forced running did not influence the ulcerogenic effect of both agents. The results suggest that physical training might have both beneficial and harmful effects on the vulnerability of gastric mucosa to ulcerogenic stimuli depending on the nature of ulcerogenic stimulus as well as the intensity of running and its duration.

N-(7-(1H-Imidazol-1-yl)-2,3-dioxo-6-(trifluoromethyl)-3,4-dihydroquinoxalin-1(2H)-yl)benzamide, a New Kainate Receptor Selective Antagonist and Analgesic: Synthesis, X-ray Crystallography, Structure-Affinity Relationships, and in Vitro and in Vivo Pharmacology.

Selective pharmacological tool compounds are invaluable for understanding the functions of the various ionotropic glutamate receptor subtypes. For the kainate receptors, these compounds are few. Here we have synthesized nine novel quinoxaline-2,3-diones with substitutions in the 7-position to investigate the structure-activity relationship at kainate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Compound 11 exhibited the highest binding affinity across GluK1-3 while having selectivity toward kainate vs AMPA receptors. Compound 11 potently inhibited glutamate evoked currents at homomeric GluK1 and GluK3 receptors in HEK293 cells with Kb values of 65 and 39 nM, respectively. The binding mode of 11 in the ligand binding domain of GluK1 was investigated by X-ray crystallography, revealing that 11 stabilizes the receptor in an open conformation, consistent with its demonstrated antagonism. Furthermore, 11 was tested for analgesic effects in the mouse tail flick test where it significantly increased tail flick latency at doses where 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]-quinoxaline-7-sulfonamide (NBQX) was ineffective.

Association between intravenous ketamine-induced stress hormone levels and long-term fear memory renewal in Sprague-Dawley rats

Ketamine is a multimodal dissociative anesthetic and analgesic that is widely used after traumatic injury. We previously reported that an analgesic dose of intravenous (IV) ketamine infusion (10 mg/kg, 2-h) after fear conditioning enhanced short-term fear memory in rats. Here, we investigated the effects of the same dose of an IV ketamine infusion on plasma stress hormone levels and long-term fear memory in rats. Adult male Sprague-Dawley rats (9-week-old with an average weight of 308 g upon arrival) received a ketamine infusion (0 or 10 mg/kg, 2-h) immediately after auditory fear conditioning (three auditory tone and footshock [0.6 mA, 1-s] pairings) on Day 0. After the infusion, a blood sample was collected from a jugular vein catheter for corticosterone and progesterone assays, and each animal was tested on tail flick to measure thermal antinociception. One week later, animals were tested on fear extinction acquisition (Day 7), fear extinction retrieval (Day 8), and fear renewal (Day 9). The IV ketamine infusion, compared to the saline infusion, reduced locomotor activity (sedation), increased tail flick latency (antinociception), and elevated plasma corticosterone and progesterone levels. The ketamine infusion did not alter long-term fear memory extinction or fear renewal. However, elevated corticosterone and progesterone levels resulting from the ketamine infusion were correlated with sedation, antinociception, and long-term fear memory renewal. These results suggest that individual differences in sensitivity to acute ketamine may predict vulnerability to develop fear-related disorders.

Vulnerability of gastric and small intestinal mucosa to ulcerogenic action of indomethacin in C57/BL6/J mice and transient receptor potential channel vanilloid type 1 knockout mice.

Capsaicin-sensitive sensory nerves are densely distributed in the gastrointestinal system and involved in maintenance of gastrointestinal mucosal integrity. capsaicin selectively stimulates nociceptive neurons and its action is mediated through the transient receptor potential channel vanilloid type 1 (TRPV1) receptor. Activation TRPV1 receptors that play a fundamental role in pain signaling, may also exert protective effects against gastrointestinal injury. The present study was performed to investigate and compare the vulnerability of gastric as well as small intestinal mucosa to ulcerogenic action of indomethacin (IM) in mice with genetically deleted TRPV1 receptor (TRPV1 KO) and in C57/BL6/J mice. IM-induced injury was assessed macroscopically as well as histologically; the somatic pain sensitivity was estimated by tail flick latency (tail flick test); plasma corticosterone levels and body weight were also monitored. A single IM administration (35 mg/kg, subcutaneously) into pre-starving (24 h) mice caused the formation of gastric erosions 4 h later and, then, after refeeding, induced formation of the small intestinal injury which was visible 24, 48, 72 h after IM administration. Although IM-induced gastrointestinal injury was detectable in both C57/BL6/J and TRPV1 KO mice, area of gastric damage was greater in C57/BL6/J than in TRPV1 KO mice, whereas the small intestinal injury (48 and 72 h after IM injection), on the contrary, prevailed in TRPV1 KO mice compared to C57/BL6/J mice. In 24 h after IM injection, the total area of intestinal injury did not differ in C57BL6/J and TRPV1 KO mice, however histological score was higher in TRPV1 KO mice than C57BL6/J mice. TRPV1 KO mice showed the increased tail flick latencies and the lacking IM-induced corticosterone rise. The data suggest that in TRPV1 KO mice the gastric mucosa is less vulnerable to ulcerogenic action of IM compared to C57/BL6/J mice, however, their small intestinal mucosa, on the contrary, is more vulnerable to the ulcerogenic action than in C57/BL6/J mice.

Long‐term Somatic Hypoalgesia as a Marker of Pathological Conditions in Gastrointestinal Tract

Pain is traditionally considered as an evolutionarily developed defensive response to noxious stimulus. Short‐term pain suppression in response to stressful factors (stress‐induced analgesia) is an important adaptive reaction that is required for survival if further injury or death were threatened. In contrast, long‐term pain suppression may be considered as a sign of pain abnormality induced by disturbance of endogenous pain mechanisms under circumstances of pathology. Indomethacin (IM) is commonly used in clinic; however, it has a side ulcerogenic effect on the gastrointestinal tract. Previously we have shown that the formation IM‐induced injury in gastrointestinal tract is accompanied by a decrease in somatic pain sensitivity lasting, a least, for 72 h after IM injection (long‐term somatic hypoalgesia). Here we tested hypothesis that suppression of pathological process in gastrointestinal tract may prevent somatic hypoalgesia and normalize pain regulation in conscious rats. For this we studied effects of “stress preconditioning” on the gastrointestinal tract and somatic pain sensitivity under circumstances of ulcerogenic action of IM (35 mg/kg, sc). Preliminary (24 h) fasted rats were subjected one of four exposures (“stress preconditioning”) before IM administration: a) cold restraint (30 min, t=10 degree C, 1 h before IM); b) CRF (1.25 mkg/kg, ip, 30 min before IM) administration; c) capsaicin (0.5/kg, sc, 1 h before IM) administration, d) forced treadmill running (30 min, 1 h before IM). Pain sensitivity was assessed by tail flick latencies (tail flick test) or number of pain responses induced by acetic acid (“writhing test”). IM administration caused the formation of gastric erosion (2–4 h after injection) and small intestine injury (24, 48, 72 h after injection) that was accompanied by an increase in tail flick latencies (long‐term somatic hypoalgesia). Somatic hypoalgesia 48 h after IM injection was also supported by a decrease in number of pain responses induced by acetic acid. IM‐induced pathological process in the gastrointestinal tract was followed by changes in plasma corticosterone levels, cardiovascular (heart rate, blood pressure) and somatic (weights of thymus and adrenals, body weight) parameters. Each preconditioning exposure attenuated IM‐induced gastric mucosa injury and prevented somatic hypoalgesia. The results obtained suggest that long‐term somatic hypoalgesia may be one of characteristics of pathological process in the gastrointestinal tract induced by ulcerogenic action of IM.Support or Funding InformationThe study was supported by grant of Russian Science Foundation (RSF) №14‐15‐00790.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Is 2-Hydroxypropyl-β-cyclodextrin a Suitable Carrier for Central Administration of Δ9 -Tetrahydrocannabinol? Preclinical Evidence.

Preclinical Research Δ9 -Tetrahydrocannabinol (THC) is a hydrophobic compound that has a potent antinociceptive effect in animals after intrathecal (IT) or intracerebroventricular (ICV) administration. The lack of a suitable solvent precludes its IT administration in humans. 2-Hydroxypropyl-β-cyclodextrin (HPβCD) increases the water solubility of hydrophobic drugs and is approved for IT administration in humans. To investigate whether HPβCD might be a suitable carrier for ICV administration of THC in rats, two formulations containing THC complexed with HPβCD (30 and 135 μg of THC per animal) and vehicle were administered to Wistar rats. The antinociceptive effect (using the tail flick test), locomotor activity, and body temperature were evaluated. ICV injection of 135 μg of THC/HPβCD complex increased tail flick latency, reduced locomotor activity, and had a dual effect on body temperature. The 30 μg THC/HPβCD formulation only produced a hyperthermic effect. All animals appeared healthy, with no difference between the groups. These results were similar to those obtained in other preclinical studies in which THC was administered centrally using solvents that are unsuitable for IT administration in humans because of their toxicity. Our findings suggest that HPβCD may be a useful carrier for IT administration of THC in humans. Drug Dev Res 78 : 411-419, 2017. © 2017 Wiley Periodicals, Inc.

Pharmacological mechanisms involved in the analgesia induced by ethanol extract of Hybanthus enneaspermus leaves.

BackgroundHybanthus enneaspermus (HE) leaves are being used traditionally to relieve pain, and scientific studies have demonstrated their analgesic potential. This study attempted to elucidate the pharmacological mechanism(s) involved in the analgesic action of ethanol extract of H. enneaspermus leaves (EEHE).Materials and methodsForty-two male Wistar rats were separately randomized into seven groups (n=6 rats in each group) for tail immersion and formalin tests. Group I (control) received distilled water (10 mL/kg) while groups II and III received acetaminophen (the reference drug, 100 mg/kg ip) and EEHE (1000 mg/kg po), respectively. Groups IV–VII were pretreated with cimetidine (50 mg/kg ip), naloxone (5 mg/kg ip), propranolol (0.15 mg/kg ip), and prazosin (0.15 mg/kg ip), respectively, 1 hour before EEHE (1000 mg/kg po) treatment.ResultsThe EEHE-induced increase in tail-flick latency was reduced by blockade of histamine and adrenergic receptors but prevented by blockade of opiate receptor in the tail-flick test. However, the EEHE-induced decrease in paw licking time was prevented only by blockade of opiate receptor but unaffected by histamine and adrenergic receptors blockers.ConclusionThese findings suggest that the analgesic effect of EEHE in different pain types may involve different neural mechanisms and that the opioidergic pathway contributes more to EEHE-induced analgesia than the other pathways.

The analgesic effect of orexin-A in a murine model of chemotherapy-induced neuropathic pain

Orexins are neuropeptides that are localized to neurons in the lateral and dorsal hypothalamus but its receptors are distributed to many different regions of the central nervous system. Orexins are implicated in a variety of physiological functions including sleep regulation, energy homeostats, and stress reactions. Furthermore, orexins administered exogenously have been shown to have analgesic effects in animal models. A type of intractable pain in patients is pain due to chemotherapy-induced peripheral neuropathy (CIPN). Several chemotherapeutic agents used for the treatment of malignant diseases induce dose-limiting neuropathic pain that compromises patients' quality of life. Here, we examined the analgesic effect of orexin-A in a murine model of CIPN, and compared it with the effect of duloxetine, the only drug recommended for the treatment of CIPN pain in patients. CIPN was induced in male BALB/c mice by repeated intraperitoneal injection of oxaliplatin, a platinum chemotherapeutic agent used for the treatment of advanced colorectal cancer. Neuropathic mechanical allodynia was assessed by the von Frey test, and the effect on acute thermal pain was assessed by the tail flick test. Intracerebroventricularly administered orexin-A dose-dependently attenuated oxaliplatin-induced mechanical allodynia and increased tail flick latencies. Oxaliplatin-induced mechanical allodynia was completely reversed by orexin-A at a low dose that did not increase tail flick latency. Duloxetine only partially reversed mechanical allodynia and had no effect on tail flick latency. The analgesic effect of orexin-A on oxaliplatin-induced mechanical allodynia was completely antagonized by prior intraperitoneal injection of SB-408124 (orexin type-1 receptor antagonist), but not by prior intraperitoneal injection of TCS-OX2-29 (orexin type-2 receptor antagonist). Our findings suggest that orexin-A is more potent than duloxetine in relieving pain CIPN pain and its analgesic effect is mediated by orexin type-1 receptors. Orexin type-1 receptor agonists may have potential therapeutic roles in the treatment of CIPN pain in patients.

Effects of Corticotropin-Releasing Factor (CRF) on Somatic Pain Sensitivity in Conscious Rats: Involvement of Types 1 and 2 CRF Receptors

Corticotropin-releasing factor (CRF) is involved in the regulation of pain sensitivity and can cause an analgesic effect in animals and humans. The aim of the study was to investigate the involvement of CRF1 and CRF2 receptors in CRF-induced analgesic effect (after intraperitoneal injection) on somatic pain sensitivity in conscious rats. Somatic pain sensitivity was tested by tail flick latency (tail flick test). The involvement of CRF1 and CRF2 receptors was studied by their selective antagonists NBI 27914 and astressin 2B, respectively. Systemic administration of CRF caused an increase in tail flick latency (analgesic effect). Pretreatment with NBI 27914 or astressin 2B eliminated CRF-induced analgesic effect. Besides, NBI 27914, but not astressin 2B, increased basal tail flick latency. The data obtained indicate that the analgesic effect can be mediated by both CRF1 and CRF2 receptors. CRF-1 receptor, in contrast to the CRF2 receptors, may be involved in the regulation of the basal level of pain sensitivity.

MiRNAs are involved in chronic electroacupuncture tolerance in the rat hypothalamus.

Acupuncture tolerance is the gradual decrease in analgesic effect due to its prolonged application. However, its mechanism in terms of miRNA is still unknown. To explore the role of miRNAs in electroacupuncture (EA) tolerance of rats using deep sequencing, rats with more than a 50% increase in tail flick latency (TFL) in response to EA were selected for this experiment. EA tolerance was induced by EA once daily for eight consecutive days. The hypothalami were harvested for deep sequencing. As a result, 49 differentially expressed miRNAs were identified and validated by real-time PCR. Of them, let-7b-5p, miR-148a-3p, miR-124-3p, miR-107-3p, and miR-370-3p were further confirmed to be related to EA tolerance by an intracerebroventricular injection of agomirs or antagomirs of these miRNAs. Potential targets of the 49 miRNAs were enriched in 9 pathways and 282 gene ontology (GO) terms. Five miRNAs were confirmed to participate in EA tolerance probably through the functional categories related to nerve impulse transmission, receptor signal pathways, and gene expression regulation, as well as pathways related to MAPK, neurotrophin, fatty acid metabolism, lysosome, and the degradation of valine, leucine, and isoleucine. Our findings reveal a characterized panel of the differentially expressed miRNAs in the hypothalamus in response to EA and thus provide a solid experimental framework for future analysis of the mechanisms underlying EA-induced tolerance.

Involvement of opioid and GABA systems in the ventrolateral periaqueductal gray on analgesia associated with tonic immobility

Ventrolateral periaqueductal gray (VL-PAG) contains key neuronal circuits related to the analgesic effect involved in integrated defensive behaviors such as immobility response (IR). The latter is characterized by a reversible state of motor inhibition that can be elicited in rats under several conditions including restriction of movements (tonic immobility: TI). It is known that IR-induced analgesia can be elicited by manipulations or drugs acting on the central nervous system (CNS) at different levels. The aim of this study was to assess the role of the opioid and the GABA systems in TI-elicited analgesia. After inducing TI in naïve rats by neck clamping, the analgesic effect was evaluated by the tail-flick (TF) test. Compared to the control group, rats with TI had increased TF latency evidencing an analgesic effect. An opioid receptor agonist and antagonist were injected systemically, as well as microinjected locally in VL-PAG, as well as GABAA receptor agonist and antagonist were microinjected into VL-PAG. Under both injection schemes, morphine increased TF latency and TI duration, while naloxone blocked TI-induced analgesia. Muscimol reduced TF latency and TI duration while bicuculline increased TF latency but not TI duration. This suggests that TI-elicited analgesia was mediated by opioids at different levels of the CNS especially in the VL-PAG by inhibition of intrinsic tonic GABAergic activity. There were no additive analgesic effects of morphine or bicuculline with tonic immobility, which probably means reach a certain upper limit under such conditions.

GABAA Receptors in the Central Nucleus of the Amygdala Are Involved in Pain- and Itch-Related Responses

Itch and pain are unpleasant sensations that distress many patients with disease. However, most studies have focused on the neural mechanisms of pain, and much less effort has been devoted to itch. It has been reported that itch and pain might share a common pathway, and γ-aminobutyric acid type A (GABAA) receptors in the central nucleus of the amygdala (CeA) are involved in pain modulation. However, the contribution of GABAA receptors in the CeA to the modulation of itch remains poorly understood. Herein, we report that bilateral intra-CeA microinjection of a selective GABAA receptor agonist muscimol hydrochloride (Mus; 50 ng per side), but not a selective GABAA receptor antagonist bicuculline (Bic; 20 ng per side) or vehicle, showed significant analgesic effects, reflected by an increase in tail-flick latency and a decrease in allyl isothiocyanate (mustard oil)–evoked ipsilateral forelimb wipes. More importantly, rats subjected to intra-CeA infusion of Bic showed a significantly greater number of scratching bouts and time in acute and chronic pruritus animal models than control rats. Conversely, intra-CeA infusion of Mus in animal models dramatically decreased the number of scratching bouts and time compared with control rats. In addition, intra-CeA infusion of Bic or Mus at the current dose had no obvious effects on other behaviors including locomotor activity and spontaneous facial grooming in rats subjected to cheek microinjection of 5-hydroxytryptamine. Taken together, these results indicate that the GABAA receptor–mediated inhibitory system in the CeA is involved in itch modulation as well as is known in pain control. PerspectiveItch, especially chronic itch, remains a challenge in clinic. Results of this study showed that the GABAA receptors in the CeA play an important role in itch modulation, which might help us to better understand the mechanisms of itch and subsequently develop novel mechanisms-based strategies to treat chronic itch in clinic.

Regulation of Somatic Pain Sensitivity under the Circumstances of Indometacin‐InducedGastric Injury: Participation of Cortricotropin‐Releasing Factor

In the present study we investigated the somatic pain sensitivity under the circumstances of indometacin (IM)‐induced gastric ulceration and effect of cortricotropin‐releasing factor (CRF) on the somatic pain sensitivity under the circumstances in conscious rats. IM (35 mg/kg) was administered subcutaneously to preliminary (24h) fasted as well as fed rats. CRF was injected 30 min before IM administration. The somatic pain sensitivity was estimated by tail flick latencies. A single IM administration caused the gastric erosion formation 4 h after the injection only in fasted but not fed rats. IM‐induced gastric injury was accompanied by an increase in tail flick latency in fasted rats. Pretreatment with CRF prevented this increase. CRF by itself did not influence the somatic pain sensitivity. Since we did not observe any changes in tail flick latency in fed IM‐treated rats without gastric mucosal lesions, it was reasonable to assume that an increase in tail flick latency in preliminary fasted IM‐treated rats was associated with the pathological changes in the gastric mucosa, but not with IM‐caused analgesic action by itself. Thus, IM‐induced gastric injury resulted in the suppression of the somatic pain sensitivity and CRF might be involved in regulation of the somatic pain sensitivity under the circumstances in conscious rats. Supported by the Russian Scientific Foundation (grant N 14‐15‐00790).

Membrane stabilizing, thrombolytic, analgesic, anti-diarrheal and CNS activities of Polyalthia longifolia (Sonn.)

Different fractions of Polialthia longifolia (Sonn.) bark were evaluated for membrane stabilizing, thrombolytic, analgesic, anti-diarrheal and CNS de-pressant activities upon oral administration at 200 and 400 mg/kg body weight. The membrane stabilizing activity was assessed by heat and hypo-tonic solution. Carbon tetrachloride fraction of methanol extract of P. longi-folia bark demonstrated strong membrane stabilizing activity, while the crude methanol extract demonstrated mild to moderate thrombolytic activi-ty in human blood specimen. The analgesic activity was assessed by tail im-mersion and formalin-induced pain method in Swiss-albino mice. The crude methanol extract of P. longifolia bark exhibited significant peripheral and central analgesic activity, since inhibited chemical induced writhing at 200 mg/kg and increased tail flick latency time both at 200 and 400 mg/kg. The anti-diarrheal activity of the bark extract was assessed by using castor oil induced diarrhea in mice however significant anti-diarrheal activity was not revealed. The CNS inhibitory activity of the methanol extract was assessed in Swiss albino mice where it reduced phenobarbitone sodium induced sleep-ing time at 400 mg/kg.

Anti-inflammatory activities of melatonin derivatives in lipopolysaccharide-stimulated RAW 264.7 cells and antinociceptive effects in mice.

Preclinical Research This study describes the anti-inflammatory activities of two semisynthesized melatonin (MT) derivatives, benzoyl-melatonin (BMT) and acetyl-melatonin (AMT), on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated macrophage cells (RAW 264.7) and their antinociceptive effects in mice. The MT derivatives inhibited production of nitric oxide NO and prostaglandin E2 in LPS-stimulated RAW264.7 cells in a dose-dependent manner with IC50 values lower than those of MT. BMT produced increased tail flick latency time, decreased number of writhes, and reduced nociceptive response in mice when compared with AMT and MT. BMT and AMT had enhanced anti-inflammatory effects in LPS-stimulated RAW264.7 compared with MT. However, in mouse studies BMT exhibited the highest potency as an anti-inflammatory agent and was longer-acting as an antinociceptive compound compared with AMT or MT, suggesting that BMT has potential as an anti-inflammatory and analgesic compound.