SR 141716A Research Articles

The pyramidal neurons in the medial prefrontal cortex show decreased response to 5-hydroxytryptamine-3 receptor stimulation in a rodent model of Parkinson's disease

In the present study, effect of SR 57227A, a selective 5-hydroxytryptamine-3 (5-HT3) receptor agonist, on the firing activity of pyramidal neurons in the medial prefrontal cortex (mPFC) was studied in normal rats and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta by using extracellular recording. Systemic administration of SR 57227A (40–640μg/kg, i.v.) decreased the mean firing rate of pyramidal neurons in normal and the lesioned rats. This inhibition was significant only at doses higher than 320μg/kg and 640μg/kg in normal and the lesioned rats, respectively, and was reversed by i.v. administration of 5-HT3 receptor antagonist tropisetron or GABAA receptor antagonist bicuculline. Furthermore, local application of SR 57227A (0.01μg) in the mPFC inhibited the firing rate of pyramidal neurons in normal rats while having no effect on firing rate in the lesioned rats. The i.v. administration of bicuculline excited the pyramidal neurons in normal rats, and then local application of SR 57227A did not alter the mean firing rate of these neurons. However, these two drugs did not affect the activity of the pyramidal neurons in the lesioned rats. We conclude that activation of 5-HT3 receptors inhibited pyramidal neurons in the mPFC of normal rats via GABAergic interneurons, and degeneration of the nigrostriatal pathway decreased response of the pyramidal neurons to SR 57227A, suggesting the dysfunction of 5-HT3 receptors and/or down-regulation of the expression on GABAergic interneurons in the lesioned rats.

Acetaminophen inhibits status epilepticus in cultured hippocampal neurons

Status epilepticus (SE) is a major neurological disorder and SE survivors often develop acquired epilepsy and cognitive deficits. Thus, it is important to stop SE and limit brain damage. However, rapid pharmacoresistance develops to anticonvulsants as seizure duration lengthens. Recently, acetaminophen was reported to increase endocannabinoid levels by its conversion to AM 404. Further, cannabinoids are potent anticonvulsants. Here we investigated whether acetaminophen would block SE-like activity in hippocampal neurons. Exposure of cultured hippocampal neurons to a low Mg2+ medium elicits high-frequency epileptiform discharges that exceed 3 Hz (in-vitro SE). Acetaminophen (500 μM) blocks the SE-like activity. CB1 receptor antagonist SR 141716A (1 μM) blocked this inhibitory effect of acetaminophen on SE, indicating that acetaminophen was mediating its anticonvulsant effects through CB1 receptors.

The β3‐adrenoceptor mediates the inhibitory effects of β‐adrenoceptor agonists via the urothelium in pig bladder dome

Relaxation of detrusor muscle via β-adrenoceptors may contribute to urine storage during bladder filling. Thus there is increasing interest in β-adrenoceptor agonists as a potential treatment for detrusor overactivity. The role of the urothelium in bladder responses to β-adrenoceptor agonists is not yet clear, although we have shown that these agonists have a greater inhibitory effect on detrusor contraction when the urothelium is intact. The aim was to determine which β-adrenoceptor subtype is involved in this effect. Paired strips of pig bladder dome mucosa-intact and mucosa-denuded, were mounted in tissue baths. Relaxation responses were obtained to β-adrenoceptor agonists (isoprenaline, dobutamine, salbutamol or BRL37344) in carbachol pre-contracted tissues. Inhibitory effects were studied by obtaining concentration-response curves (CRCs) to carbachol in the presence and absence of β-adrenoceptor agonists. The inhibitory effects of isoprenaline were also studied following incubation with β-adrenoceptor antagonists (propranolol, CGP20712, ICI-118, 551 or SR 59230A; non selected, β(1), β(2) and β(3) selective respectively). isoprenaline, dobutamine, salbutamol and BRL37344 all relaxed carbachol pre-contracted tissues and responses were similar in intact and denuded strips. In inhibition experiments, β-adrenoceptor agonists caused rightward shifts of carbachol CRCs. In intact strips the shift was greater with isoprenaline and BRL37344, but not with dobutamine or salbutamol. This increased shift was still observed in tissues pre-incubated with propranolo, CGP20712 and ICI-118, 551, but not with SR 59230A. β(3)-adrenoceptors are involved in mediating inhibitory effects of β-adrenoceptor agonists on detrusor contractions via the urothelium in pig bladder dome.

Revisiting the complex influences of cannabinoids on motor functions unravels pharmacodynamic differences between cannabinoid agonists

While numerous cannabinoid ligands were historically characterized using the tetrad test (hypomobility, catalepsy, hypothermia, analgesia), only few studies have extensively compared HU 210 and CP 55,940 which are nowadays classically used as reference agonists. Therefore, we herein re-examined the acute and the sustained changes in motor activities mediated by these two agonists in adult rats. As expected for cannabinoid agonists, exposure to either HU 210 or CP 55,940 induced a marked reduction in spontaneous locomotion. This reduction observed as early as 15 min after injection was correlated with the typical rearing and cataleptic responses, and was reversed by co-administration of the CB 1 cannabinoid receptor antagonist SR 141716A. Nevertheless, HU 210, but not CP 55,940, was found to induce persistent responses, lasting for at least 24 h. Also suggesting the involvement of additional targets for HU 210, 10 mg/kg SR 141716A failed to reverse the persistent HU 210-mediated decline in locomotion and rearing, while 1 mg/kg was sufficient to completely abolish the behavioural responses measured 6 h after the injection. Beside pharmacokinetic differences, these data therefore denote distinct pharmacodynamic profiles for HU 210 and CP 55,940. Together, these results suggest that HU 210 displays multicomponent responses that should be taken into account when interpreting data from in vivo/ex vivo studies.

Quantification of Rimonabant (SR 141716A) in Monkey Plasma Using HPLC with UV Detection

Using an isocratic high-performance liquid chromatography (HPLC) system and UV detection, a simple and precise analytical procedure was developed to quantify levels of the CB(1) receptor antagonist rimonabant in the plasma of rhesus monkeys. Rimonabant was extracted from plasma samples into 5% isopropanol in hexane. After separation, the isopropanol-hexane fractions were dried to residue, redissolved in mobile phase, and then injected into the HPLC. The HPLC system included an acetonitrile-phosphate buffer (62:38, v/v) mobile phase (pH 6.7), flow rate of 1.5 mL/min, C(18) column (4.6 mm i.d. x 150 mm length, 5 microm), and UV detection at 280 nm. Retention times for rimonabant and doxepin (internal standard) were 9.9 and 2.4 min, respectively. The regression of the spiked calibrator curve was linear from 60 to 4000 ng/mL (r(2) = 0.996). The lower limit of quantification was 60 ng/mL, and recovery was 83.6%. Rimonabant was stable in stock solutions and monkey plasma across a range of temperatures and concentrations. To demonstrate utility, plasma rimonabant was measured in six rhesus monkeys at 60 and 240 min after intramuscular administration of 1 mg/kg rimonabant. Rimonabant levels ranged from 175 to 1290 ng/mL. The analytical assay described here provides a simple and accurate procedure for multiple within-subject measurements of the CB(1) antagonist rimonabant.

Evaluation of the role of superoxide anions in endotoxin-induced impairment of β-adrenoceptor-mediated vasodilation in equine digital veins

To investigate the role of superoxide anions in the lipopolysaccharide (LPS)-induced impairment of beta-adrenoceptor-mediated equine digital vein (EDV) vasodilation. EDVs isolated from forelimbs of 24 healthy adult horses. Endothelium-intact or endothelium-denuded EDV rings were incubated with or without LPS (10 microg/mL) of Escherichia coli (O55:B5) for 4 hours. Cumulative concentration-relaxation curves resulting from administration of isoprenaline, a nonselective beta-adrenoceptor agonist, or from administration of SR 58611A, a selective beta(3)-adrenoceptor agonist, were recorded in phenylephrine-preconstricted EDVs in the absence or the presence of superoxide dismutase (200 U/mL). Isoprenaline-induced relaxation was also evaluated with or without the cyclooxygenase inhibitors indomethacin (10 microM) and NS-398 (10 microM). Isoprenaline and SR 58611A induced concentration-dependent relaxation of EDV rings, which was inhibited by LPS exposure. Superoxide dismutase abolished the inhibitory effect of LPS on the isoprenaline- and SR 58611A-mediated relaxation. Pretreatment of the LPS-treated EDVs with indomethacin or NS-398 restored the isoprenaline-mediated relaxation and abolished the LPS-induced impairment to a similar extent as superoxide dismutase. Results supported a role of superoxide anions in the LPS-induced impairment of beta-adrenoceptor-mediated EDV vasodilation. The LPS-induced oxidative stress in EDVs may contribute to vascular dysfunctions associated with laminitis in horses.

PRECLINICAL STUDY: FULL ARTICLE: Altered architecture and functional consequences of the mesolimbic dopamine system in cannabis dependence

Cannabinoid withdrawal produces a hypofunction of mesencephalic dopamine neurons that impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment with two structurally different cannabinoid agonists, Delta(9)-tetrahydrocannabinol and CP55 940 (CP) rats were withdrawn spontaneously and pharmacologically with the CB1 antagonist SR141716A (SR). In these two conditions, evaluation of tyrosine hydroxylase (TH)-positive neurons revealed significant morphometrical reductions in the ventrotegmental area but not substantia nigra pars compacta of withdrawn rats. Similarly, confocal analysis of Golgi-Cox-stained sections of the nucleus accumbens revealed a decrease in the shell, but not the core, of the spines' density of withdrawn rats. Administration of the CB1 antagonist SR to control rats, provoked structural abnormalities reminiscent of those observed in withdrawal conditions and support the regulatory role of cannabinoids in neurogenesis, axonal growth and synaptogenesis by acting as eu-proliferative signals through the CB1 receptors. Further, these measures were incorporated into a realistic computational model that predicts a strong reduction in the excitability of morphologically altered MSN, yielding a significant reduction in action potential output. These pieces of evidence support the tenet that withdrawal from addictive compounds alters functioning of the mesolimbic system and provide direct morphological evidence for functional abnormalities associated with cannabinoid dependence at the level of dopaminergic neurons and their postsynaptic counterpart and are coherent with recent hypothesis underscoring a hypodopaminergic state as a distinctive feature of the 'addicted brain'.

In vivo modulation of the firing activity of putative slow- and fast-spiking interneurons in the medial prefrontal cortex by 5-HT3 receptors in 6-hydroxydopamine-induced Parkinsonian rats

In the present study, we examined changes in the firing rate and firing pattern of putative slow-spiking (SS) and fast-spiking (FS) interneurons in medial prefrontal cortex (mPFC) and the effect of 5-hydroxytryptamine-3 (5-HT3) receptor agonist SR 57227A on the neuronal firing in rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc) by using extracellular recording. The lesion of the SNc in rats decreased the firing rate of FS interneurons and the firing pattern of both SS and FS interneurons changed towards a more burst-firing. Systemic administration of SR 57227A (40–640 μg/kg, i.v.) increased the firing rate of SS interneurons, and decreased FS interneurons in sham-operated and the lesioned rats, respectively. The doses producing excitation or inhibition in the lesioned rats were higher than sham-operated rats. The local application of SR 57227A (0.01 μg) in mPFC excited SS interneurons, and inhibited FS interneurons in sham-operated rats, while having no effects on firing rate in the lesioned rats. Systemic administration of GABAA receptor antagonist bicuculline (2 mg/kg, i.v.) excited FS interneurons in sham-operated rats, whereas bicuculline did not change the activity of FS interneurons in the lesioned rats. Our findings indicate that the putative SS and FS interneurons activity is modulated through activation of 5-HT3 receptor by direct or indirect action, and the lesion of the SNc leads to changes in firing activity of the SS and FS interneurons and decreased response of these interneurons to SR 57227A, suggesting dysfunction and/or down-regulation of 5-HT3 receptor on interneurons in the 6-hydroxydopamine-lesioned rats.

Chronic constriction injury reduces cannabinoid receptor 1 activity in the rostral anterior cingulate cortex of mice

The present studies examined the effect of chronic neuropathic pain on cannabinoid receptor density and receptor-mediated G-protein activity within supraspinal brain areas involved in pain processing and modulation in mice. Chronic constriction injury (CCI) produced a significant decrease in WIN 55,212-2-stimulated [ 35S]GTPγS binding in membranes prepared from the rostral anterior cingulate cortex (rACC) of CCI mice when compared to sham-operated controls. Saturation binding with [ 3H]SR 141716A in membranes of the rACC showed no significant differences in binding between CCI and sham mice. Analysis of levels of the endocannabinoids anandamide (AEA) or 2-arachidonoylglycerol (2-AG) in the rACC following CCI showed no significant differences between CCI and sham mice. These data suggest that CCI produced desensitization of the cannabinoid 1 receptor in the rACC in the absence of an overall decrease in cannabinoid 1 receptor density or change in levels of AEA or 2-AG. These data are the first to show alterations in cannabinoid receptor function in the rostral anterior cingulate cortex in response to a model of neuropathic pain.

Vasorelaxant activities of the putative endocannabinoid virodhamine in rat isolated small mesenteric artery.

Virodhamine is a recently identified novel endocannabinoid. Cannabinoids may evoke vasorelaxation through novel receptors in the vasculature and/or through release of vasodilator peptides from sensory nerve endings. Virodhamine induced endothelium-dependent relaxation in the rat isolated small mesenteric artery mounted in a myograph and precontracted with methoxamine. Desensitization of vanilloid receptors by capsaicin did not affect relaxation responses to virodhamine. The CB(1) receptor antagonist SR 141716A (3 microM), but not the more CB(1)-selective blocker AM 251 (1 microM), attenuated the response, while two CB(2) receptor antagonists, SR 144528 (1 microM) and AM 630 (10 microM), had no effect. The novel antagonist for the putative endothelial 'abnormal-cannabidiol receptor', O-1918 (30 microM), inhibited virodhamine relaxations. Hence virodhamine may activate this novel receptor, which might also recognize SR 141716A. Inhibition of nitric oxide synthase (L-NAME 300 microM) did not affect relaxation to virodhamine but the responses were markedly reduced when tone was induced with 60 mM KCl, suggesting a role for the activation of K(+) channels. The Ca(2+)-activated K(+) channel (K(Ca)) blockers, apamin (50 nM) and charybdotoxin (50 nM), inhibited virodhamine vasorelaxation. Combination of these blockers with SR 141716A (3 microM) caused no further inhibition. It was concluded that virodhamine relaxes the rat small mesenteric artery by endothelium-dependent activation of K(Ca), perhaps via the putative abnormal-cannabidiol receptor.

Cannabinoid 1 receptors modulate intestinal sensory and motor function in rat

Cannabinoid receptors are involved in visceral pain perception and control of intestinal motility in vivo. The underlying mechanisms are not well characterized. We aimed to determine whether the cannabinoid-1 (CB(1)) receptor modulates intestinal afferent nerve discharge and the peristaltic reflex. Rats were anesthetized and intestinal segments were removed. Afferent nerve discharge from a mesenteric nerve was investigated in vitro in the presence of the CB(1) antagonist SR 141716A or the CB(1) agonist WIN 55212-2. The myenteric peristaltic reflex was induced by electrical field stimulation and influence of SR 141716A or WIN 55212-2 was recorded. Afferent nerve discharge to the algesic mediator bradykinin was reduced to 11 +/- 5.1 imp s(-1) following pretreatment with SR 141716A and unchanged after WIN 55212-2 compared to 63 +/- 15.4 imp s(-1) in controls. At maximum distension pressure (80 cmH(2)O) during ramp distension, 92 +/- 12.4 imp s(-1) were reached following SR 141716A compared to 260 +/- 13.2 in vehicle controls and 227 +/- 15.4 in WIN 55212-2 pretreated animals. In contrast, afferent discharge to 5-HT (500 micromol L(-1)) was increased to 75 +/- 24.6 imp s(-1) following WIN 55212-2 compared to 18 +/- 5.9 imp s(-1) in controls, whereas SR 141716A had no effect. Ascending neuronal contractions were dose-dependently attenuated in the presence of SR 141716A and latency of these contractions was reduced. WIN 55212-2 had opposite effects that were abolished by SR 141716A. Activation of the CB(1) receptor differentially alters afferent intestinal nerve sensitivity to bradykinin, 5-HT, and noxious mechanical distension, while it strengthens ascending neuronal contractions. Further studies are needed to determine the physiological relevance of these observations.

.BETA.3-adrenoceptor-mediated increased circulating transaminase levels in mice treated with its agonist BRL 37344

Treatment with the selective β(3)-adrenoceptor agonist BRL 37344 increased circulating levels of alanine transaminase (ALT) and aspartate transaminase (AST) in mice without causing hepatocellular injury. To clarify whether this was a β(3)-adrenoceptor-mediated effect, the inhibitory effect of the selective β(3)-adrenoceptor antagonist SR 59230A on the increase in circulating transaminase levels induced by BRL 37344 was examined. A single intraperitoneal dose of BRL 37344 alone initially increased insulin and non-esterified fatty acid (NEFA) dose-proportionally at 0.5 hr post-dose, findings considered attributable to β(3)-adrenoceptor-stimulating effects. Levels of the gluconeogenic precursors pyruvate (PA) and lactate (LA) were increased corresponding to the change in insulin. Thereafter, glucose (GLU) level was decreased at 4 and 8 hr post-dose, suggesting disruption of glucose homeostasis. In association with these changes in glucose metabolism, transaminase levels were increased maximally at 4 hr post-dose. The transaminase changes were not accompanied by increases in circulating levels of other hepatocellular enzymes, including guanine deaminase (GUA), glutamate dehydrogenase (GLDH), and lactate dehydrogenase (LDH), or any morphological hepatocellular injury. Intraperitoneal pre-treatment with SR 59230A partly inhibited the effects of BRL 37344 alone, indicating that the increase in levels of circulating ALT by BRL 37344 was attributable to a β(3)-adrenoceptor-stimulating effect. In conclusion, the β(3)-adrenoceptor agonist BRL 37344 was shown to increase circulating transaminase levels in mice accompanied with dynamic changes in glucose metabolism. These findings suggest the possibility that circulating transaminase levels are increased as pharmacological effects of drugs disrupting glucose metabolism, and that hepatotoxic markers should be selected considering these effects to distinguish between acceptable pharmacology and toxicity.

Agmatine enhances cannabinoid action in the hot-plate assay of thermal nociception

Agmatine–cannabinoid interactions are supported by the close association between cannabinoid CB 1 receptors and agmatine immunoreactive neurons and evidence that shared brain mechanisms underlie the pharmacological effects of agmatine and cannabinoid agonists. In the present study, we used the hot-plate assay of thermal nociception to determine if agmatine alters cannabinoid action through activation of imidazoline sites and/or alpha 2-adrenoceptors. WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) administration increased hot-plate response latency. Agmatine (50 or 100 mg/kg, i.p.) was ineffective. Administration of agmatine (50 mg/kg, i.p.) with WIN 55212-2 (1, 2 or 3 mg/kg, i.p.) or CP55,940 (1, 2 or 3 mg/kg, i.p.) produced response-latency enhancement. Regression analysis indicated that agmatine increased the potency of WIN 55212-2 and CP55,940 by 3- and 4.4-fold, respectively, indicating synergy for both drug interactions. Idazoxan, a mixed imidazoline site/alpha 2-adrenoceptor antagonist, but not yohimbine (5 mg/kg, i.p.), a selective alphia 2-adrenoceptor antagonist, blocked response-latency enhancement produced by a combination of WIN 55212-2 (2 mg/kg) and agmatine. Response-latency enhancement produced by WIN 55212-2 (2 mg/kg) was blocked by SR 141716A (5 mg/kg, i.p.), a cannabinoid CB 1 receptor antagonist; attenuated by idazoxan (2 and 5 mg/kg); and not affected by yohimbine (5 mg/kg). These results demonstrate a synergistic interaction between agmatine and cannabinoid agonists and suggest that agmatine administration enhances cannabinoid action in vivo.

NO production and eNOS phosphorylation induced by epinephrine through the activation of β-adrenoceptors

Epinephrine plays a key role in the control of vasomotor tone; however, the participation of the NO/cGMP pathway in response to beta-adrenoceptor activation remains controversial. To evaluate the involvement of the endothelium in the vascular response to epinephrine, we assessed NO production, endothelial NO synthase phosphorylation, and tissue accumulation of cGMP in the perfused arterial mesenteric bed of rat. Epinephrine elicited a concentration-dependent increase in NO (EC(50) of 45.7 pM), which was coupled to cGMP tissue accumulation. Both NO and cGMP production were blocked by either endothelium removal (saponin) or NO synthase inhibition (N(omega)-nitro-L-arginine). Blockade of beta(1)- and beta(2)-adrenoceptors with 1 microM propranolol or beta(3)-adrenoceptor with 10 nM SR 59230A displaced rightward the concentration-NO production curve evoked by epinephrine. Selective stimulation of beta(1)-, beta(2)-, or beta(3)-adrenoceptors also resulted in NO and cGMP production. Propranolol (1 microM) inhibited the rise in NO induced by isoproterenol or the beta(2)-adrenoceptor agonists salbutamol, terbutaline, or fenoterol. Likewise, 10 nM SR 59230A reduced the effects of the beta(3)-adrenoceptor agonists BRL 37344, CGP 12177, SR 595611A, or pindolol. The NO production induced by epinephrine and BRL 37344 was associated with the activation of the phosphatidylinositol 3-kinase/Akt pathway and phosphorylation of eNOS in serine 1177. In addition, in anaesthetized rats, bolus administration of isoproterenol, salbutamol, or BRL 37344 produced NO-dependent reductions in systolic blood pressure. These findings indicate that beta(1)-, beta(2)-, and beta(3)-adrenoceptors are coupled to the NO/cGMP pathway, highlighting the role of the endothelium in the vasomotor action elicited by epinephrine and related beta-adrenoceptor agonists.

Effects of Chronic Exposure to the CB1 Agonist AM 411 in Squirrel Monkeys

Cannabinoid CB1 agonists produce tolerance that may be associated with dependence and increased sensitivity to the behavioral effects of the CB1 antagonist SR141716A, perhaps indicative of antagonist‐precipitated withdrawal. In the present studies, the effects of the long‐acting CB1 agonist AM 411 and the CB1 antagonist SR141716A on operant responding were examined in squirrel monkeys before and during chronic AM 411 treatment (1.0 mg/kg/day, im). Prechronically, AM 411 (0.01‐1 mg/kg) produced dose‐related decreases in responding; the highest dose decreased behavior to approximately 20% of control values. In contrast, SR 141716A (1‐10 mg/kg) had little effect on behavior; the highest dose decreased responding only to >80% of control values. Re‐determination of drug effects during the chronic regimen revealed a >10‐fold rightward shift in the dose‐response function for AM 411, indicative of tolerance. On the other hand, SR 141716A (0.32‐3.2 mg/kg) produced dose‐related decreases in behavior; the highest dose decreased responding to <50% of control values. These data are consistent with the view that chronic CB1 receptor activation produces tolerance to the effects of CB1 agonists and enhances sensitivity to the behaviorally disruptive effects of CB1 antagonists. The increased sensitivity to the effects of SR 141716A may be indicative of antagonist‐precipitated withdrawal (supported by DA19205).

Cannabinoid Receptor Interacting Protein (CRIP1a) attenuates CB1 signalling

A recently discovered protein, Cannabinoid Receptor Interacting Protein (CRIP1a) interacts with the C‐terminal tail of the CB1 receptor (aa 418‐473). Initial studies found that CRIP1a decreased the effects of the inverse agonist SR141716A (SR1) on Ca2+ currents in superior cervical ganglion neuronal expression system, while leaving the effects of the full agonist WIN 55,212‐2 unchanged, suggesting a decrease in constitutive activity (Niehaus et. al. Molecular Pharmacology (2007) 72:1557‐1566). To examine CRIP1a, previous studies in this laboratory have characterized HEK cells transfected with CB1, with and without CRIP1a co‐transfection. Stable co‐transfection of CRIP1a had no effect on CB1 expression levels in HEK cells stably expressing CB1 receptor (hCB1‐HEK) or CB1 receptor and CRIP1a (hCB1‐HEK CRIP1a). CRIP1a protein expression was verified using immunoblot analysis. The effect of CRIP1a on G‐protein activity was examined in the presence of Na+ concentrations, a negative allosteric modulator of G‐protein‐coupled receptor activity. [35S]GTPγS binding in hCB1‐HEK cells ± CRIP1a showed that CRIP1a significantly reduced WIN‐stimulated G‐protein activity at all NaCl concentrations. CRIP1a significantly decreased basal, THC‐stimulated and SR1‐inhbited G‐protein activity at low NaCl concentrations (0‐25 mM NaCl). In conclusion, CRIP1a attenuates G‐protein activation by agonists and inhibition by inverse agonists when spontaneous receptor activity is high, suggesting a decrease in constitutive activity. Funded by F31‐DA023747 from NIDA (TAH) and a Jeffress Memorial Trust Research Award (DES).

Rabbit, a relevant model for the study of cardiac β3‐adrenoceptors

The beta(3)-adrenoceptors (beta(3)-ARs) have been identified and characterized in the human heart. Specific beta(3)-AR stimulation, unlike beta(1)-AR or beta(2)-AR stimulation, decreases cardiac contractility, partly via the G(i)-NO pathway. However, the precise role of cardiac beta(3)-ARs is not yet completely understood. Indeed, under normal conditions, the beta(3)-AR response is present only to a very low degree in rats and mice. Therefore, we evaluated whether beta(3)-ARs were present and functional in rabbit ventricular cardiomyocytes, and whether the rabbit could serve as a relevant model for the study of cardiac beta(3)-ARs. We used RT-PCR and Western blot to measure the beta(3)-AR transcripts and protein levels in rabbit ventricular cardiomyocytes. We also analysed the effect of beta(3)-AR stimulation using isoproterenol in combination with nadolol or SR 58611A on cardiomyocyte shortening, Ca(2+) transient, L-type Ca(2+) current (I(Ca,L)), delayed rectifier potassium current (I(Ks)) and action potential duration (APD). For the first time, we show that beta(3)-ARs are expressed in rabbit ventricular cardiomyocytes. The mRNA and protein sequences present a high homology to those of rat and human beta(3)-ARs. Furthermore, beta(3)-AR stimulation decreases cardiomyocyte shortening, Ca(2+) transient and I(Ca,L) amplitudes, via a G(i)-NO pathway. Importantly, beta(3)-AR stimulation enhances I(Ks) amplitude and shortens the APD. Taken together, our results indicate that the rabbit provides a relevant model, easily used in laboratories, to study the roles of cardiac beta(3)-ARs in physiological conditions.

β2‐adrenoceptors are critical for antidepressant treatment of neuropathic pain

Tricyclic antidepressants (TCAs) are one of the first-line pharmacological treatments against neuropathic pain. TCAs increase the extracellular concentrations of noradrenaline and serotonin by blocking the reuptake transporters of these amines. However, the precise downstream mechanism leading to the therapeutic action remains identified. In this work, we evaluated the role of adrenergic receptors (ARs) in the action of TCAs. We used pharmacological and genetic approaches in mice to study the role of ARs in the antiallodynic action of the TCA nortriptyline. Peripheral neuropathy was induced by the insertion of a polyethylene cuff around the main branch of the sciatic nerve. The specific role of beta(2)-AR was evaluated by studying beta(2)-AR(-/-) mice. We used von Frey filaments to assess mechanical allodynia. The antiallodynic action of nortriptyline was not affected by cotreatment with the alpha(2)-AR antagonist yohimbine, the beta(1)-AR antagonists atenolol or metoprolol, or the beta(3)-AR antagonist SR 59230A. On the contrary, the beta-AR antagonists propranolol or sotalol, the beta(1)/beta(2)-AR antagonists alprenolol or pindolol, or the specific beta(2)-AR antagonist ICI 118,551 blocked the action of nortriptyline. The effect of nortriptyline was also totally absent in beta(2)-AR-deficient mice. Stimulation of beta(2)-AR is necessary for nortriptyline to exert its antiallodynic action against neuropathic pain. These findings provide new insight into the mechanism by which antidepressants alleviate neuropathic pain. Our results also raise the question of a potential incompatibility between beta-blockers that affect beta(2)-AR and antidepressant drugs in patients treated for neuropathic pain.

Opioid, cannabinoid CB 1 and NOP receptors do not mediate APAP-induced hypothermia in rats

Acetaminophen (APAP) produces antinociception and hypothermia. Because the antinociceptive effect in rats is partially dependent on opioid and cannabinoid CB 1 receptor activation, we determined if activation of these receptors also contributes to the hypothermic effect of APAP. Rats injected with APAP (100, 250, 375 or 500 mg/kg, i.p.) displayed dose-related hypothermia. For combined administration, the hypothermic effect of APAP (400 mg/kg, i.p.) was not altered by pretreatment with: naltrexone (10 mg/kg, s.c.), a non-selective opioid antagonist; naltrindole (1 mg/kg, s.c.), a delta opioid antagonist; nor-binaltorphimine (10 mg/kg, i.p.), a kappa opioid antagonist; SR 141716A (3 mg/kg, i.m.), a cannabinoid CB 1 receptor antagonist; or JTC-801(1 mg/kg, i.p.), a nociceptin/orphanin FQ peptide (NOP) receptor antagonist. The demonstration that APAP produces hypothermia independent of opioid, cannabinoid CB 1 or NOP receptor activation is contrary to its antinociceptive effect, which requires opioid and cannabinoid CB 1 receptor activation.

Cannabinoid CB1 receptor can mediate gastric mucosal protection in the rat

Event Abstract Back to Event Cannabinoid CB1 receptor can mediate gastric mucosal protection in the rat Nashwan Shujaa1*, Zoltan S. Zadori1 and Klara Gyires1 1 Department of Pharmacology and Pharmacotherapy, Semmelweis University, Hungary Cannabinoid CB1 receptor agonists can modulate several functions of the gastrointestinal tract: they inhibit the gastrointestinal motor function, the stimulated gastric acid secretion and the formation of gastric mucosal ulcerations in acid dependent ulcer models. We aimed to investigate the role of CB1 receptor agonists in an acid independent (ethanol-induced) ulcer model in the rat and to explore any possible interaction between the opioid and cannabinoid systems in this field. Our results showed that the endocannabinoid anandamide (5.75 µmol/kg i.v., 2.8-28.7 nmol/rat i.c.v.), its synthetic analogue methanandamide (1.38-5.53 µmol/kg i.v., 2.27-69 nmol/rat i.c.v.) and the synthetic cannabinoid agonist WIN 55,212-2 (0.047-0.19 µmol/kg i.v., 18.8-75.24 nmol/rat i.c.v.) inhibited the ethanol-induced gastric mucosal damage after both peripheral and central administration. The selective CB1 receptor antagonist SR 141716A (21.6 nmol/rat i.c.v.) reversed the effect of centrally administered anandamide and methanandamide. Moroever, the non-selective opioid receptor antagonist naloxone (27.5 nmol/rat i.c.v.) antagonized the gastroprotective effect of intravenously administered anandamide, methanandamide and WIN 55,212-2. The gastroprotective effect of WIN 55,212-2 (0.19 µmol/kg i.v.) was also reversed by the δ-opioid receptor selective antagonist naltrindole (4.88 nmol/rat i.c.v.) but not by the κ-opioid receptor selective antagonist norBNI (13.6 nmol/rat i.c.v.). In conclusion, the cannabinoid CB1 receptors are likely to be involved in the gastric mucosal defense, this effect seems to be central and correlation between the cannabinoid and opioid system in gastric mucosal protection may be raised. Acknowledgements: Funded by ETT grant 389. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Pathophysiology and neurology - non-degenerative disorders Citation: Shujaa N, Zadori ZS and Gyires K (2009). Cannabinoid CB1 receptor can mediate gastric mucosal protection in the rat. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.041 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Mar 2009; Published Online: 02 Mar 2009. * Correspondence: Nashwan Shujaa, Department of Pharmacology and Pharmacotherapy, Semmelweis University, Budapest, Hungary, Nashwan@freemail.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Nashwan Shujaa Zoltan S Zadori Klara Gyires Google Nashwan Shujaa Zoltan S Zadori Klara Gyires Google Scholar Nashwan Shujaa Zoltan S Zadori Klara Gyires PubMed Nashwan Shujaa Zoltan S Zadori Klara Gyires Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.