The involvement of TRPA1 channel activation in the inflammatory response evoked by topical application of cinnamaldehyde to mice

AimsIn the present work, we characterize the inflammatory process induced by the topical application of cinnamaldehyde on the skin of mice and verify the participation of transient receptor potential A1 TRPA1 receptors in this process.Main methodsWe measured mouse ear edema and sensitization/desensitization after topical application of cinnamaldehyde or/and capsaicin. We also quantified cellular infiltration through myeloperoxidase (MPO) activity and histological and immunohistochemical analyses and evaluated the expression of TRPV1 and TRPA1 by western blot.Key findingsCinnamaldehyde induced ear edema in mice (1–6 μg/ear) with a maximum effect of 4 μg/ear. Cinnamaldehyde promoted leukocyte infiltration as detected by increasing MPO activity and confirmed by histological analyses. The edema and cellular infiltration evoked by the application of 4 μg/ear of cinnamaldehyde were prevented by topical application of ruthenium red, a non-selective TRP antagonist as well as camphor and HC030031, two TRPA1 receptor antagonists. Cinnamaldehyde-induced edema, but not cellular infiltration, was prevented by topical application of the tachykinin NK1 antagonist, aprepitant, indicating a neuropeptide release phenomenon in this process. Additionally, we observed that repeated topical applications of cinnamaldehyde did not induce changes in sensitization or desensitization with respect to the edema response. Interestingly, repeated treatment with the TRPV1 agonist, capsaicin, abrogated it edematogenic response, confirming the desensitization process and partially decreasing the cinnamaldehyde-induced edema, suggesting the involvement of capsaicin-sensitive fibers.SignificanceOur data demonstrate that the topical application of cinnamaldehyde produces an inflammatory response that is dependent on TRPA1 receptor stimulation.     

Synergistic interactions between the antinociceptive effect of Rhodiola rosea extract and B vitamins in the mouse formalin test

AimIn this study, the pharmacological interactions between a Rhodiola rosea ethanol extract and B-vitamins such as thiamine (B₁), riboflavine (B₂), pyridoxine (B₆), cyanocobalamin (B₁₂) and a mixture of vitamins B₁ + B₆ + B₁₂ was investigated in the mouse formalin test.MethodsIndividual dose response curves of the Rhodiola rosea ethanol extract, as well as B-vitamins alone or in a mixture were evaluated in mice in which nociception was induced with 2% formalin intraplantarly. The antinociceptive mechanisms of the Rhodiola rosea were investigated by exploring the role of the opioid and serotonin receptors and the nitric oxide pathway. Isobolographic analysis was used to evaluate the pharmacological interactions between the Rhodiola rosea ethanol extract and each B-vitamin individually or the mixture of vitamins B₁ + B₆ +B₁₂ by using the ED₃₀ and a fixed 1:1 ratio combination.ResultsAdministration of the Rhodiola rosea extract alone or in combination with all of the vitamins produced a significant and dose-dependent antinociceptive response. The antinociceptive effect of the Rhodiola rosea extract (ED₅₀ = 81 mg/kg, p.o.) was significant and reverted in the presence of antagonists of the 5-HT_1A, GABA/BDZs and opioid receptors and by blocking mediators of the nitric oxide/cGMP/K⁺ channels pathway. Isobolograms demonstrate that all of the combinations investigated in this study produced a synergistic interaction experimental ED₃₀ values were significantly smaller than those calculated theoretically.ConclusionsThese results provide evidence that a Rhodiola rosea ethanol extract in combination with B-vitamins produces a significant diminution in the nociceptive response in a synergistic manner, which is controlled by various mechanisms. These findings could aid in the design of clinical studies and suggest that these combinations could be applied for pain therapy.     

Discovery of potent transient receptor potential vanilloid 1 antagonists: Design and synthesis of phenoxyacetamide derivatives

We aimed to discover a novel type of transient receptor potential vanilloid 1 (TRPV1) antagonist because such antagonists are possible drug candidates for treating various disorders. We modified the structure of hit compound 7 (human TRPV1 IC₅₀ = 411 nM) and converted its pyrrolidino group to a (hydroxyethyl)methylamino group, which substantially improved inhibitory activity (15d; human TRPV1 IC₅₀ = 33 nM). In addition, 15d ameliorated bladder overactivity in rats in vivo.     

Xenon reduces activation of transient receptor potential vanilloid type 1 (TRPV1) in rat dorsal root ganglion cells and in human TRPV1-expressing HEK293 cells

AimsXenon provides effective analgesia in several pain states at sub-anaesthetic doses. Our aim was to examine whether xenon may mediate its analgesic effect, in part, through reducing the activity of transient receptor potential vanilloid type 1 (TRPV1), a receptor known to be involved in certain inflammatory pain conditions.Main methodsWe studied the effect of xenon on capsaicin-evoked cobalt uptake in rat cultured primary sensory neurons and in human TRPV1 (hTRPV1)-expressing human embryonic kidney 293 (HEK293) cells. We also examined xenon's effect on the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in the rat spinal dorsal horn evoked by hind-paw injection of capsaicin.Key findingsXenon (75%) reduced the number of primary sensory neurons responding to the TRPV1 agonist, capsaicin (100 nM–1 μM) by ~ 25% to ~ 50%. Xenon reduced the number of heterologously-expressed hTRPV1 activated by 300 nM capsaicin by ~ 50%. Xenon (80%) reduced by ~ 40% the number of phosporylated ERK1/2-expressing neurons in rat spinal dorsal horn resulting from hind-paw capsaicin injection.SignificanceXenon substantially reduces the activity of TRPV1 in response to noxious stimulation by the specific TRPV1 agonist, capsaicin, suggesting a possible role for xenon as an adjunct analgesic where hTRPV1 is an active contributor to the excitation of primary afferents which initiates the pain sensation.     

Endogenous cannabinoid receptor agonist anandamide induces peripheral antinociception by activation of ATP-sensitive K+ channels

AimsThe effects of several potassium (K⁺) channel blockers were studied to determine which K⁺ channels are involved in peripheral antinociception induced by the cannabinoid receptor agonist, anandamide.Main methodsHyperalgesia was induced by subcutaneous injection of 250 μg carrageenan into the plantar surface of the hind paw of rats. The extent of hyperalgesia was measured using a paw pressure test 3 h following carrageenan injection. The weight in grams (g) that elicited a nociceptive response, paw flexion, during the paw pressure test was used as the nociceptive response threshold.Key findingsDoses of 50, 75, and 100 ng of anandamide elicited a dose-dependent antinociceptive effect. Following a 100 ng dose of anandamide no antinociception was observed in the paw that was contralateral to the anandamide injection site, which shows that anandamide has a peripheral site of action. Pretreatment with 20, 40 and 80 μg AM251, a CB₁ receptor antagonist, caused a dose-dependent decrease in anandamide-induced antinociception, suggesting that the CB₁ receptor is directly involved in anandamide effect. Treatment with 40, 80 and 160 μg glibenclamide, an ATP-sensitive K⁺ channel blocker, caused a dose-dependent reversal of anandamide-induced peripheral antinociception. Treatment with other K⁺ channel antagonists, tetraethylammonium (30 μg), paxilline (10 μg) and dequalinium (50 μg), had no effect on the induction of peripheral antinociception by anandamide.SignificanceThis study provides evidence that the peripheral antinociceptive effect of the cannabinoid receptor agonist, anandamide, is primarily caused by activation of ATP-sensitive K⁺ channels and does not involve other potassium channels.     

The putative somatostatin antagonist cyclo-somatostatin has opioid agonist effects in gastrointestinal preparations

AimsSpecificity of receptor antagonists used is crucial for clarifying physiological/pathophysiological roles of the respective endogenous agonist. We studied the effects (somatostatin antagonist and possibly other actions) of cyclo-somatostatin (CSST), a putative somatostatin receptor antagonist on the guinea-pig small intestine, a preparation where somatostatin causes inhibition of nerve-mediated contractions.Main methodsIn isolated organ experiments, half-maximal cholinergic “twitch” contractions of the guinea-pig small intestine were evoked or tonic contractions of the rat stomach fundus strip (in the presence of physostigmine) were elicited by electrical field stimulation. The effects of somatostatin (somatostatin-14), CSST, naloxone, as well as of direct smooth muscle stimulants were examined.Key findingsSomatostatin (10 nM–1 μM) caused transient inhibition of the twitch contraction, in a naloxone-insensitive manner. Surprisingly, CSST (0.3–1 μM) also inhibited twitch contractions (more than 50% reduction at 1 μM). This effect was prevented by the opioid receptor antagonist naloxone. Responses to acetylcholine or histamine were not or only minimally inhibited by CSST (up to 3 μM). CSST (0.3 μM in the absence or 1–10 μM in the presence of naloxone) failed to inhibit the effect of somatostatin. The SST₂ receptor antagonist CYN-154806 (3 μM) attenuated the effect of somatostatin and failed to evoke naloxone-sensitive inhibition of the twitch response. The naloxone-sensitive inhibitory effect of CSST on cholinergic contractions was also confirmed in the rat stomach fundus preparation.SignificanceCyclo-somatostatin exerts opioid agonist activity in the two preparations tested, while it does not behave as a somatostatin-receptor antagonist in the guinea-pig intestine.     

Desflurane but not sevoflurane augments laryngeal C-fiber inputs to nucleus tractus solitarii neurons by activating transient receptor potential-A1

AimsVolatile anesthetics have distinct odors and some are irritating to the upper airway and may cause cough and laryngospasm, which may result, in part, from stimulation of C-fiber reflex. Local exposure of such anesthetics increases the sensitivity of capsaicin-sensitive laryngeal C-fiber endings compatible with airway irritability presumably by activation of transient receptor potential (TRP) ion channels, but the physiological relevance of this sensitization transmitted to the higher-order neurons in the central reflex pathway and output is unknown.Main methodsIn anesthetized young guinea pigs, baseline and left atrial capsaicin evoked changes in the extracellular unit activity of laryngeal C-fiber-activated neurons in the nucleus tractus solitarii (NTS) and phrenic nerve activity were compared between irritant (desflurane) and non-irritant (sevoflurane) anesthetic gas exposure to the isolated larynx.Key findingsDesflurane significantly augmented the peak and duration (p < 0.01) of the NTS neuronal responses and the prolongation of expiratory time (p = 0.017). The effect was enhanced by iontophoretic application of the TRPA1 agonist allyl-isothiocyanate (p < 0.05), inhibited by TRPA1 antagonist HC-030031 (p < 0.01), but not by TRPV1 antagonist BCTC. Sevoflurane did not affect the central pathway.SignificanceThus, the sensitization of the laryngeal C-fiber endings by irritant volatile anesthetics is transmitted to the NTS via activation of the TRPA1 and is associated with a prolonged reflexively evoked expiratory apnea. The findings may help to explain local deleterious effects of irritant volatile general anesthetics on the airways during inhaled induction or bronchodilator therapy for status asthmatics.     

Up-regulation of TRPV1 in mononuclear cells of end-stage kidney disease patients increases susceptibility to N-arachidonoyl-dopamine (NADA)-induced cell death

Transient receptor potential vanilloid (TRPV) 1 channels function as sensors for a variety of noxious and inflammatory signals, including capsaicin, heat and protons, and are up-regulated under inflammatory conditions. As end-stage kidney disease (ESKD) is associated with chronic inflammation, impaired immunity and depressed lymphocyte numbers, we sought to determine whether altered TRPV1 (and related TRPV2) expression in immune cells might be a contributing factor. TRPV1 and TRPV2 mRNA expression in peripheral blood mononuclear cells (PBMC) was similar in controls and ESKD patients by quantitative real-time RT-PCR. However, using immunocytochemistry, TRPV1-immunoreactivity was significantly higher and TRPV2-immunoreactivity was significantly lower in PBMC from ESKD patients compared to controls. The plant-derived TRPV1 agonists, capsaicin and resiniferatoxin (RTX) and the putative endovanilloid/endocannabinoids, N-arachidonoyl-dopamine (NADA) and N-oleoyl-dopamine (OLDA), induced concentration-dependent death of PBMC from healthy donors with a rank order of potency of RTX > NADA > OLDA >> capsaicin. TRPV1 (5′-iodoresiniferatoxin) and cannabinoid (CB₂; AM630) receptor antagonists blocked the cytotoxic effect of NADA. In subsequent experiments, PBMC from ESKD patients exhibited significantly increased susceptibility to NADA-induced death compared to PBMC from controls. The apparent up-regulation of TRPV1 may be a response to the inflammatory milieu in which PBMC exist in ESKD and may be responsible for the increased susceptibility of these cells to NADA-induced death, providing a possible explanation as to why ESKD patients have reduced lymphocyte counts and impaired immune function. Thus, TRPV1 (and possibly CB₂) antagonists may have potential for the treatment of immune dysfunction in ESKD.     

Oxytocin induces penile erection and yawning when injected into the bed nucleus of the stria terminalis: Involvement of glutamic acid,dopamine, and nitric oxide

Oxytocin (5–100 ng), but not Arg⁸-vasopressin (100 ng), injected unilaterally into the bed nucleus of the stria terminalis (BNST) induces penile erection and yawning in a dose-dependent manner in male rats. The minimal effective dose was 20 ng for penile erection and 5 ng for yawning. Oxytocin responses were abolished not only by the oxytocin receptor antagonist d(CH₂)₅Tyr(Me)²-Orn⁸-vasotocin (1 μg), but also by (+) MK-801 (1 μg), an excitatory amino acid receptor antagonist of the N-methyl-d-aspartic acid (NMDA) subtype, SCH 23390 (1 μg), a D1 receptor antagonist, but not haloperidol (1 μg), a D2 receptor antagonist, and SMTC (40 μg), an inhibitor of neuronal nitric oxide synthase, injected into the BNST 15 min before oxytocin. Oxytocin-induced penile erection, but not yawning, was also abolished by CNQX (1 μg), an excitatory amino acid receptor antagonist of the AMPA subtype. In contrast, oxytocin responses were not reduced by bicuculline (20 ng), a GABA_A receptor antagonist, phaclofen (5 μg), a GABA_B receptor antagonist, CP 376395, a CRF receptor-1 antagonist (5 μg), or astressin 2B, a CRF receptor-2 antagonist (150 ng). Considering the ability of NMDA (100 ng) to induce penile erection and yawning when injected into the BNST and the available evidence showing possible interaction among oxytocin, glutamic acid, and dopamine in the BNST, oxytocin possibly activates glutamatergic neurotransmission in the BNST. This in turn leads to the activation of neural pathways projecting back to the paraventricular nucleus, medial preoptic area, ventral tegmental area, and/or ventral subiculum/amygdala, thereby inducing penile erection and yawning.     

Probable involvement of Ca2 +-activated Cl− channels (CaCCs) in the activation of CB1 cannabinoid receptors

AimsRecently, we demonstrated that peripheral antinociception induced by δ opioid receptor is dependent of Ca^2 +-activated Cl^? channels (CaCCs). Because opioid and cannabinoid receptors share some common mechanisms of action, our objective was to identify a possible relationship between CaCCs and the endocannabinoid system.Main methodsTo induce hyperalgesia, rat paws were treated with intraplantar prostaglandin E₂ (PGE₂, 2 μg). Nociceptive thresholds to pressure (grams) were measured using an algesimetric apparatus 3 h following injection. Probabilities were calculated using ANOVA/Bonferroni's test, and values that were less than 5% were considered to be statistically significant.Key findingsAdministration of the cannabinoid agonist CB₁ anandamide (12.5, 25 and 50 μg/paw) and the cannabinoid agonist CB₂ PEA (5, 10 and 20 μg/paw) decreased the PGE₂-induced hyperalgesia in a dose-dependent manner. The possibility of the higher doses of anandamide (50 μg) and PEA (20 μg) having a central or systemic effect was excluded because the administration of the drug into the contralateral paw did not elicit antinociception in the right paw. As expected, the antinociceptive effects induced by anandamide and PEA were blocked by the CB₁ and CB₂ receptor antagonists AM251 and AM630, respectively. The peripheral antinociception was induced by anandamide but not PEA and was dose-dependently inhibited by the CaCC blocker niflumic acid (8, 16 and 32 μg).SignificanceThese results provide the first evidence for the involvement of CaCCs in the peripheral antinociception induced by activation of the CB₁ cannabinoid receptor.     

Involvement of NO-guanylyl cyclase pathway for the depression of spinal monosynaptic reflex by Mesobuthus tamulus venom in neonatal rat in vitro

AimsThe present study was undertaken to evaluate the role of nitric oxide (NO) in Mesobuthus tamulus (MBT) venom-induced depression of spinal reflexes.Main methodsExperiments were performed on isolated hemisected spinal cords from 4 to 6 day old rats. Stimulation of a dorsal root with supramaximal strength evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root.Key findingsSuperfusion of MBT venom (0.3 μg/ml) depressed the spinal reflexes in a time-dependent manner and the maximum depression was seen at 10 min (MSR by 63%; PSR by 79%). The time to produce 50% depression (T-50) of MSR and PSR was 7.7 ± 1.3 and 5.7 ± 0.5 min, respectively. Pretreatment with bicuculline (1 μM; GABA_A receptor antagonist) or strychnine (1 μM; glycine_A receptor antagonist) did not block the venom-induced depression of spinal reflexes. However, Nω-nitro-L-arginine methyl ester (L-NAME, 100 or 300 μM; NO synthase inhibitor) or hemoglobin (Hb, 100 μM; NO scavenger) antagonized the venom-induced depression of MSR. Further, soluble guanylyl cylase inhibitors (1 H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one, ODQ; 1 μM or methylene blue, 100 μM) also antagonized the venom-induced depression of MSR but not PSR. Nitrite concentration (indicator of NO activity) of the cords exposed to venom (0.3 μg/ml) was not different from the control group.SignificanceThe results indicate that venom-induced depression of MSR is mediated via NO-guanylyl cyclase pathway without involving GABAergic or glycinergic system.     

The CCKB antagonist CI988 reduces food intake in fasted rats via a dopamine mediated pathway

Studies have shown a reduction of food intake following peripheral and brain injection of CCK. However, it remains to be established whether endogenous central CCK is involved in the regulation of food intake. We investigated the role of central CCK in the regulation of food intake by pharmacological manipulation of the CCK_B (CCK₂) receptor system. Intracerebroventricularly (ICV) cannulated male Sprague Dawley rats were fasted for 24 h and received an ICV injection of the CCK_B receptor antagonist CI988 at a dose of 10 nmol or 49 nmol or vehicle. Another group received two consecutive ICV injections consisting of the corticotropin-releasing factor (CRF) receptor-1 (CRF₁) antagonist, CP376395 (3 nmol) or the CRF₂ receptor antagonist, K41498 (2 nmol) alone, or followed by CI988 (49 nmol). Lastly, another group of rats received an intraperitoneal (IP) injection of the dopamine antagonist, flupentixol (∼197 and ∼493 nmol/kg) alone, or followed by CI988 (49 nmol, ICV). Cumulative food intake was assessed for 11 h. Vehicle injected rats showed a robust feeding response. CI988 at 49 nmol reduced food intake by 30% starting at 2 h post injection. CP376395 and K41498 had no effect on food intake. Flupentixol injected IP at a dose of 197 and 493 nmol/kg alone did not modulate food intake whereas the higher dose blocked the CI988-induced reduction of feeding. During the dark phase, CI988 had no effect on food intake in unfasted rats. In summary, CCK_B signaling is involved in the regulation of food intake after a fast likely by downstream dopamine signaling.     

Inhibition by capsaicin and its related vanilloids of compound action potentials in frog sciatic nerves

AimsAlthough capsaicin not only activates transient receptor potential vanilloid-1 (TRPV1) channels but also inhibits nerve conduction, the latter action has not yet been fully examined. The purpose of the present study was to know whether various vanilloids have an inhibitory action similar to that of capsaicin and further to compare their actions with that of local anesthetic procaine.Main methodsFast-conducting compound action potentials (CAPs) were recorded from frog sciatic nerve fibers by using the air-gap method.Key findingsCapsaicin reversibly and concentration-dependently reduced the peak amplitude of the CAP. TRPV1 antagonist capsazepine did not affect the capsaicin activity, and powerful TRPV1 agonist resiniferatoxin had no effect on CAPs, indicating no involvement of TRPV1 channels. Capsaicin analogs and other various vanilloids also inhibited CAPs in a concentration-dependent manner. An efficacy sequence of these inhibitions was capsaicin = dihydrocapsaicin > capsiate > eugenol > guaiacol ≥ zingerone ≥ vanillin > vanillylamine. Vanillic acid had almost no effect on CAPs; olvanil and curcumin appeared to be effective less than capsaicin. Capsaicin and eugenol were, respectively, ten- and two-fold effective more than procaine in CAP inhibition, while each of guaiacol, zingerone and vanillin was five-fold effective less than procaine.SignificanceVarious vanilloids exhibit CAP inhibition, the extent of which is determined by the property of the side chain bound to the vanillyl group, and some of them are more effective than procaine. These results may serve to unveil molecular mechanisms for capsaicin-induced conduction block and to develop antinociceptive drugs related to capsaicin.     

Withania somnifera root extract prolongs analgesia and suppresses hyperalgesia in mice treated with morphine

Previous studies demonstrated that Withania somnifera Dunal (WS), a safe medicinal plant, prevents the development of tolerance to the analgesic effect of morphine.In the present study, we investigated whether WS extract (WSE) (100 mg/kg, i.p.) may also modulate the analgesic effect induced by acute morphine administration (2.5, 5, 10 mg/kg, s.c.) in the tail-flick and in the hot plate tests, and if it may prevent the development of 2.5 mg/kg morphine-induced rebound hyperalgesia in the low intensity tail-flick test. Further, to characterize the receptor(s) involved in these effects, we studied, by receptor-binding assay, the affinity of WSE for opioid (μ, δ, k), cannabinoid (CB₁, CB₂), glutamatergic (NMDA), GABAergic (GABA_A, GABA_B), serotoninergic (5HT_2A) and adrenergic (α₂) receptors.The results demonstrated that (i) WSE alone failed to alter basal nociceptive threshold in both tests, (ii) WSE pre-treatment significantly protracted the antinociceptive effect induced by 5 and 10 mg/kg of morphine only in tail-flick test, (iii) WSE pre-treatment prevented morphine-induced hyperalgesia in the low intensity tail-flick test, and (iv) WSE exhibited a high affinity for the GABA_A and moderate affinity for GABA_B, NMDA and δ opioid receptors.WSE prolongs morphine-induced analgesia and suppresses the development of morphine-induced rebound hyperalgesia probably through involvement of GABA_A, GABA_B, NMDA and δ opioid receptors. This study suggests the therapeutic potential of WSE as a valuable adjuvant agent in opioid-sparing therapies.     

Specific functioning of Cav3.2 T-type calcium and TRPV1 channels under different types of STZ-diabetic neuropathy

Streptozotocin (STZ)-induced type 1 diabetes in rats leads to the development of peripheral diabetic neuropathy (PDN) manifested as thermal hyperalgesia at early stages (4th week) followed by hypoalgesia after 8 weeks of diabetes development. Here we found that 6–7 week STZ-diabetic rats developed either thermal hyper- (18%), hypo- (25%) or normalgesic (57%) types of PDN. These developmentally similar diabetic rats were studied in order to analyze mechanisms potentially underlying different thermal nociception. The proportion of IB4-positive capsaicin-sensitive small DRG neurons, strongly involved in thermal nociception, was not altered under different types of PDN implying differential changes at cellular and molecular level. We further focused on properties of T-type calcium and TRPV1 channels, which are known to be involved in Ca^2 + signaling and pathological nociception. Indeed, TRPV1-mediated signaling in these neurons was downregulated under hypo- and normalgesia and upregulated under hyperalgesia. A complex interplay between diabetes-induced changes in functional expression of Cav3.2 T-type calcium channels and depolarizing shift of their steady-state inactivation resulted in upregulation of these channels under hyper- and normalgesia and their downregulation under hypoalgesia. As a result, T-type window current was increased by several times under hyperalgesia partially underlying the increased resting [Ca^2 +]_i observed in the hyperalgesic rats. At the same time Cav3.2-dependent Ca^2 + signaling was upregulated in all types of PDN. These findings indicate that alterations in functioning of Cav3.2 T-type and TRPV1 channels, specific for each type of PDN, may underlie the variety of pain syndromes induced by type 1 diabetes.     

μ1- and 5-HT1-dependent mechanisms in the anterior pretectal nucleus mediate the antinociceptive effects of retrosplenial cortex stimulation in rats

AimThis study examines if injection of cobalt chloride (CoCl₂) or antagonists of muscarinic cholinergic (atropine), μ₁-opioid (naloxonazine) or 5-HT₁ serotonergic (methiothepin) receptors into the dorsal or ventral portions of the anterior pretectal nucleus (APtN) alters the antinociceptive effects of stimulating the retrosplenial cortex (RSC) in rats.Main methodChanges in the nociceptive threshold were evaluated using the tail flick or incision pain tests in rats that were electrically stimulated at the RSC after the injection of saline, CoCl₂ (1 mM, 0.10 μL) or antagonists into the dorsal or ventral APtN.Key findingsThe injection of CoCl₂, naloxonazine (5 μg/0.10 μL) or methiothepin (3 μg/0.10 μL) into the dorsal APtN reduced the stimulation-produced antinociception from the RSC in the rat tail flick test. Reduction of incision pain was observed following stimulation of the RSC after the injection of the same substances into the ventral APtN. The injection of atropine (10 ng/0.10 μL) or ketanserine (5 μg/0.10 μL) into the dorsal or ventral APtN was ineffective against the antinociception resulting from RSC stimulation.Significanceμ₁-opioid- and 5-HT₁-expressing neurons and cell processes in dorsal and ventral APtN are both implicated in the mediation of stimulation-produced antinociception from the RSC in the rat tail flick and incision pain tests, respectively.     

Identification and synthesis of 2,7-diamino-thiazolo[5,4-d]pyrimidine derivatives as TRPV1 antagonists

We have identified and synthesized a series of 2,7-diamino-thiazolo[5,4-d]pyrimidines as TRPV1 antagonists. An exploration of the structure–activity relationships at the 2-, 5-, and 7-positions of the thiazolo[5,4-d]pyrimidine led to the identification of several potent TRPV1 antagonists, including 3, 29, 51, and 57. Compound 3 was orally bioavailable and afforded a significant reversal of carrageenan-induced thermal hyperalgesia with an ED₅₀ = 0.5 mg/kg in rats.     

Aryl sulfonamides containing tetralin allylic amines as potent and selective bradykinin B1 receptor antagonists

The bradykinin B1 receptor has been shown to mediate pain response and is rapidly induced upon injury. Blocking this receptor may provide a promising treatment for inflammation and pain. We previously reported tetralin benzyl amines as potent B1 antagonists. Here we describe the synthesis and SAR of B1 receptor antagonists with homobenzylic amines. The SAR of different linkers led to the discovery of tetralin allylic amines as potent and selective B1 receptor antagonists (hB1 IC₅₀ = 1.3 nM for compound 16). Some of these compounds showed modest oral bioavailability in rats.     

Supplemental intermittent-day heat training and the lactate threshold

Heat acclimation over consecutive days has been shown to improve aerobic-based performance. Recently, it has been suggested that heat training can improve performance in a temperate environment. However, due to the multifactorial training demands of athletes, consecutive-day heat training may not be suitable. The current study aimed to investigate the effect of brief (8×30 min) intermittent (every 3–4 days) supplemental heat training on the second lactate threshold point (LT₂) in temperate and hot conditions. 21 participants undertook eight intermittent-day mixed-intensity treadmill exercise training sessions in hot (30 °C; 50% relative humidity [RH]) or temperate (18 °C; 30% RH) conditions. A pre- and post-incremental exercise test occurred in temperate (18 °C; 30% RH) and hot conditions (30 °C; 50% RH) to determine the change in LT₂. The heat training protocol did not improve LT₂ in temperate (Effect Size [ES]±90 confidence interval=0.10±0.16) or hot (ES=0.26±0.26) conditions. The primary finding was that although the intervention group had a change greater than the SWC, no statistically significant improvements were observed following an intermittent eight day supplemental heat training protocol comparable to a control group training only in temperate conditions. This is likely due to the brief length of each heat training session and/or the long duration between each heat exposure.