Analgesic, respiratory and heart rate effects of cannabinoid and opioid agonists in rhesus monkeys: antagonist effects of SR 141716A

This study characterized the antinociceptive, respiratory and heart rate effects of the cannabinoid receptor agonists Delta-9-tetrahydrocannabinol (Delta-9-THC) and WIN 55212 ((R)-(+)-2, 3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol-[1,2,3-de]-1, 4-benzoxazin-6-yl)(1-naphtalenyl)methanone monomethanesulfonate), N-arachidonyl ethanolamide (anandamide) and the mu and kappa opioid receptor agonists heroin and U69593, alone and in conjunction with a cannabinoid receptor antagonist, SR 141716A [N-(piperidin-1-1-yl)-5-(4-chlorophenyl)-1(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride] and an opioid receptor antagonist, quadazocine, in rhesus monkeys (Macaca mulatta). Using 12 adult rhesus monkeys, latencies to remove the tail from a 50 degrees C water bath, respiration in 5% CO2 and heart rate were measured. When administered alone, SR 141716A (1.8, 5.6 mg/kg i.m.) did not alter nociception, respiration or heart rate. Delta-9-THC (0.1-10 mg/kg i.m.) and WIN 55212 (0.1-10 mg/kg i.m.) dose-dependently increased antinociception and dose-dependently decreased respiratory minute and tidal volumes and heart rate. These antinociceptive, respiratory and heart rate effects were reversed by SR 141716A but not by the opioid antagonist quadazocine (1 mg/kg i.m.). Anandamide (10 mg/kg i.m.) also produced antinociception. Heroin (0.01-10 mg/kg i.m.) and U69593 (0.01-3.2 mg/kg i.m.) also dose-dependently increased antinociception and decreased respiratory and heart rate measures; these effects were antagonized by quadazocine but not by SR 141716A. These results demonstrate selective and reversible antagonism of cannabinoid behavioral effects by SR 141716A in rhesus monkeys.     

Comparison of cannabinoid binding sites in guinea-pig forebrain and small intestine

We have investigated the nature of cannabinoid receptors in guinea-pig small intestine by establishing whether this tissue contains cannabinoid receptors with similar binding properties to those of brain CB1 receptors. The cannabinoids used were the CB1-selective antagonist SR141716A, the CB2-selective antagonist SR144528, the novel cannabinoid receptor ligand, 6'-azidohex-2'-yne-delta8-tetrahydrocannabinol (O-1184), and the agonists CP55940, which binds equally well to CB1 and CB2 receptors, and WIN55212-2, which shows marginal CB2 selectivity. [3H]-CP55940 (1 nM) underwent extensive specific binding both to forebrain membranes (76.3%) and to membranes obtained by sucrose density gradient fractionation of homogenates of myenteric plexus-longitudinal muscle of guinea-pig small intestine (65.2%). Its binding capacity (Bmax) was higher in forebrain (4281 fmol mg(-1)) than in intestinal membranes (2092 fmol mg(-1)). However, the corresponding KD values were not significantly different from each other (2.29 and 1.75 nM respectively). Nor did the Ki values for its displacement by CP55940, WIN55212-2, O-1184, SR141716A and SR144528 from forebrain membranes (0.87, 4.15, 2.85, 5.32 and 371.9 respectively) differ significantly from the corresponding Ki values determined in experiments with intestinal membranes (0.99, 5.03, 3.16, 4.95 and 361.5 nM respectively). The Bmax values of [3H]-CP55940 and [3H]-SR141716A in forebrain membranes did not differ significantly from each other (4281 and 5658 fmol mg(-1)) but were both greater than the Bmax of [3H]-WIN55212-2 (2032 fmol mg(-1)). O-1184 (10 or 100 nM) produced parallel dextral shifts in the log concentration-response curves of WIN55212-2 and CP55940 for inhibition of electrically-evoked contractions of the myenteric plexus-longitudinal muscle preparation, its KD values being 0.20 nM (against WIN55212-2) and 0.89 nM (against CP55940). We conclude that cannabinoid binding sites in guinea-pig small intestine closely resemble CB1 binding sites of guinea-pig brain and that 0-1184 behaves as a cannabinoid receptor antagonist in the guinea-pig myenteric plexus-longitudinal muscle preparation.     

Systemic candidiasis with acute Epstein-Barr virus infection

The binding of a classical cannabinoid agonist, [3H]R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol[1,2 ,3-de]-1,4-benzoxazin-6-yl)(1-napthalenyl)methanone monomethanesulfonate ([3H] WIN55212-2), and a selective cannabinoid receptor (CB1) antagonist, N-(piperidin-1-yl)-5-(4-chlorophenyl)1-(2,4-dichlorophenyl)-4-meth yl-1H-pyrazole-3-carboxamide hydrochloride ([3H]SR141716A), to rat cannabinoid receptors was evaluated using rat cerebellar membranes. Guanine nucleotides inhibited [3H]WIN55212-2 binding by approximately 50% at 10 microM and enhanced [3H]SR141716A binding very slightly. In the same tissue, the binding of guanosine 5'-O-[gamma-[35S]thio]triphosphate ([35S]GTP-gamma-S) was characterized and the influence of cannabinomimetics evaluated on this binding. Cannabinoid receptor agonists enhanced [35S]GTP-gamma-S binding, whereas SR141716A was devoid of action by itself but antagonized the action of cannabinoid receptor agonists. The good correlation obtained between the half maximum efficient concentration (EC50) values in [35S]GTP-gamma-S binding and the IC50 values [3H]WIN55212-2 binding shows that [35S]GTP-gamma-S binding could be a good functional assay for brain cannabinoid receptors.     

Characterization and distribution of binding sites for [3H]-SR 141716A, a selective brain (CB1) cannabinoid receptor antagonist, in rodent brain

SR 141716A belongs to a new class of compounds (diarylpyrazole) that inhibits brain cannabinoid receptors (CB1) in vitro and in vivo. The present study showed that [3H]-SR 141716A binds with high affinity (Kd=0.61 +/- 0.06 nM) to a homogenous population of binding sites (Bmax=0.72 +/- 0.05 pmol/mg of protein) in rate whole brain (minus cerebellum) synaptosomes. This specific binding was displaced by known cannabinoid receptor ligands with the following rank order of potency SR 141716A > CP 55,940 > WIN 55212-2 = delta9-THC > anandamide. Apart from anandamide, all these compounds were found to interact competitively with the binding sites labeled by [3H]-SR 141716A. On the other hand, agents lacking affinity for cannabinoid receptors were unable to displace [3H]-SR 141716A from its binding sites (IC50 > 10 microM). In addition, the binding of [3H]-SR 141716A was insensitive to guanyl nucleotides. Regional rat brain distribution of CB1 cannabinoid receptors detected by [3H]-SR 141716A saturation binding and autoradiographic studies, showed that this distribution was very similar to that found for [3H]-CP 55,940. In vivo, the [3H]-SR 141716A binding was displaced by SR 141716A with ED50 values of 0.39 +/- 0.07 and 1.43 +/- 0.29 mg/kg following intraperitoneal and oral administration, respectively. Finally, the [3H]-SR 141716A binding sites remained significantly occupied for at least 12 hr following oral administration of 3 mg/kg SR 141716A. Taken together, these results suggest that SR 141716A in its tritiated form is a useful research tool for labeling brain cannabinoid receptors (CB1) in vitro and in vivo.     

Electrically evoked acetylcholine release from hippocampal slices is inhibited by the cannabinoid receptor agonist, WIN 55212-2, and is potentiated by the cannabinoid antagonist, SR 141716A

This study examined the effect of the cannabinoid receptor agonist, WIN 55212-2, on the electrically evoked release of [14C]acetylcholine (ACh) from superfused brain slices from the hippocampus, a region with a high density of cannabinoid receptors. A comparison was also made with [14C]ACh release from the nucleus accumbens, which has relatively fewer cannabinoid receptors. In the hippocampal slices, WIN 55212-2 produced a dose-dependent inhibition of [14C]ACh release, with an EC50 of 0.03 microM and a maximal inhibition of 81% at 1 microM. In the nucleus accumbens slices, WIN 55212-2 produced a weak inhibition of [14C]ACh release, which did not quite reach statistical significance. The inhibition of electrically evoked hippocampal [14C]ACh release by WIN 55212-2 could be prevented by the cannabinoid receptor antagonist, SR 141716A (EC50, 0.3-1.0 microM). In addition to antagonizing the effects of WIN 55212-2, SR 141716A alone produced a 2-fold potentiation of the electrically stimulated [14C]ACh release in this region (EC50, 0.1-0.3 microM). By contrast, in nucleus accumbens slices, no potentiation of the stimulated release of [14C]ACh release by SR 141716A was observed. Basal [14C]ACh release was unaffected by WIN 55212-2 or SR 141716A in either area. These results suggest that cannabinoid receptor activation can produce a strong inhibition of ACh release in the hippocampus. Furthermore, the potentiation of ACh release in the hippocampus by SR 141716A alone suggests either that this compound is an inverse agonist at cannabinoid receptors or it is antagonizing the actions of an endogenous ligand acting on these receptors.     

In vitro functional evidence of neuronal cannabinoid CB1 receptors in human ileum

We investigated the effect of the cannabinoid agonist (+)WIN-55212-2 on human ileum longitudinal smooth muscle preparations, either electrically stimulated or contracted by carbachol. Electrical field stimulation mostly activated cholinergic neurons, since atropine and tetrodotoxin (TTX), alone or coincubated, reduced twitch responses to a similar degree (85%). (+)WIN-55212-2 concentration-dependently inhibited twitch responses (IC50 73 nM), but had no additive effect with atropine or TTX. The cannabinoid CB1 receptor antagonist SR 141716 (pA2 8.2), but not the CB2 receptor antagonist, SR 144528, competitively antagonized twitch inhibition by (+)WIN-55212-2. Atropine but not (+)WIN-55212-2 or TTX prevented carbachol-induced tonic contraction. These results provide functional evidence of the existence of prejunctional cannabinoid CB1-receptors in the human ileum longitudinal smooth muscle. Agonist activation of these receptors prevents responses to electrical field stimulation, presumably by inhibiting acetylcholine release. SR 141716 is a potent and competitive antagonist of cannabinoid CB1 receptors naturally expressed in the human gut.     

Appetite suppression and weight loss after the cannabinoid antagonist SR 141716

The effect of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight was assessed in adult, non-obese Wistar rats. The daily administration of SR 141716 (2.5 and 10 mg/kg; i.p.) reduced dose-dependently both food intake and body weight. Tolerance to the anorectic effect developed within 5 days; in contrast, body weight in SR 141716-treated rats remained markedly below that of vehicle-treated rats throughout the entire treatment period (14 days). The results suggest that brain cannabinoid receptors are involved in the regulation of appetite and body weight.     

Cannabinoid-induced hypotension and bradycardia in rats mediated by CB1-like cannabinoid receptors

Previous studies indicate that the CB1 cannabinoid receptor antagonist, N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-met hyl-1H-pyrazole-3-carboxamide HCl (SR141716A), inhibits the anandamide- and delta9-tetrahydrocannabinol- (THC) induced hypotension and bradycardia in anesthetized rats with a potency similar to that observed for SR141716A antagonism of THC-induced neurobehavioral effects. To further test the role of CB1 receptors in the cardiovascular effects of cannabinoids, we examined two additional criteria for receptor-specific interactions: the rank order of potency of agonists and stereoselectivity. A series of cannabinoid analogs including the enantiomeric pair (-)-11-OH-delta9-THC dimethylheptyl (+)-11-OH-delta9-THC dimethylheptyl were evaluated for their effects on arterial blood pressure and heart rate in urethane anesthetized rats. Six analogs elicited pronounced and long lasting hypotension and bradycardia that were blocked by 3 mg/kg of SR141716A. The rank order of potency was (-)-11-OH-delta9-THC dimethylheptyl > or = (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol > (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol > THC > anandamide > or = (-)-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-4-[3-hydroxy-propyl]c yclohexan-1-ol, which correlated well with CB1 receptor affinity or analgesic potency (r = 0.96-0.99). There was no hypotension or bradycardia after palmitoylethanolamine or (+)-11-OH-delta9-THC dimethylheptyl. An initial pressor response was also observed with THC and anandamide, which was not antagonized by SR141716A. We conclude that the similar rank orders of potency, stereoselectivity and sensitivity to blockade by SR141716A indicate the involvement of CB1-like receptors in the hypotensive and bradycardic actions of cannabinoids, whereas the mechanism of the pressor effect of THC and anandamide remains unclear.     

Differential blockade of the antinociceptive effects of centrally administered cannabinoids by SR141716A

We evaluated delta-9 tetrahydrocannabinol (Delta9-THC), delta-8 tetrahydrocannabinol (Delta8-THC), CP55,940 (CP55), 1-deoxy-11-hydroxy-Delta8-THC-dimethylheptyl (deoxy-HU210, a CB2-selective cannabinoid that also binds the CB1 receptor) and the endogenous cannabinoid anandamide (ANA) via i.c.v. and/or intrathecal (i.t.) routes of administration, alone and in combination with SR141716A (SR), a CB1 antagonist, using the tail-flick test. Our studies were performed in order better to characterize potential diversity in interactions of the cannabinoids with the cannabinoid (CB1) receptor. When SR was administered i.c.v. or i.p. before Delta9-THC, Delta8-THC or CP55 (i.c.v. or i.t.), SR was a potent antagonist and the blockade was complete (AD50 相似文献   

Glutamate dehydrogenase, the marker protein of Plasmodium falciparum--cloning, expression and characterization of the malarial enzyme

To characterize the time course of the behavioral and biochemical aspects of the cannabinoid withdrawal syndrome, we injected the cannabinoid antagonist SR141716A (5 mg/kg i.p.) in rats made tolerant to CP-55,940 (0.4 mg/kg i.p., twice daily for 6.5 days), 1, 24 and 96 h after the last CP-55,940 injection. Because the CB1 receptor and G protein alpha subunit are involved in cannabinoid tolerance, we observed their changes throughout the brain during the withdrawal syndrome by use of in situ hybridization. In vehicle-pretreated rats SR141716A per se induced abnormal behavior significantly different from the vehicle group: wet dog shakes, forepaw fluttering and scratching. These signs remained significantly elevated even after the second and third antagonist doses. SR141716A significantly modified the mRNA levels of G alpha s and G alpha i subunits in some brain areas without affecting CB1 receptor and G alpha o expression. These findings led us to conclude that SR141716A may have intrinsic activity. Concerning cannabinoid withdrawal, the first SR141716A injection in tolerant rats resulted in behavioral signs different from those observed with the antagonist alone; this moderate withdrawal syndrome was characterized by turning, chewing and digging. Additional SR141716A doses 24 and 96 h later did not induce a significant abstinence syndrome. In situ hybridization after the first SR141716A injection showed that CB1 receptor and G protein alpha subunits, whose levels were low in tolerance, recovered their basal level of expression. Thus, the general desensitization of the cannabinoid receptor and of the transduction system in tolerance are recovered in abstinent rats and might be part of the molecular mechanisms underlying cannabinoid dependence.     

Release of somatostatin and its role in the mediation of the anti-inflammatory effect induced by antidromic stimulation of sensory fibres of rat sciatic nerve

1. The effect of antidromic stimulation of the sensory fibres of the sciatic nerve on inflammatory plasma extravasation in various tissues and on cutaneous vasodilatation elicited in distant parts of the body was investigated in rats pretreated with guanethidine (8 mg kg(-1), i.p.) and pipecuronium (200 microg kg(-1), i.v.). 2. Antidromic sciatic nerve stimulation with C-fibre strength (20 V, 0.5 ms) at 5 Hz for 5 min elicited neurogenic inflammation in the innervated area and inhibited by 50.3 +/- 4.67% the development of a subsequent plasma extravasation in response to similar stimulation of the contralateral sciatic nerve. Stimulation at 0.5 Hz for 1 h also evoked local plasma extravasation and inhibited the carrageenin-induced (1%, 100 microl s.c.) cutaneous inflammation by 38.5 +/- 10.0% in the contralateral paw. Excitation at 0.1 Hz for 4 h elicited no local plasma extravasation in the stimulated hindleg but still reduced the carrageenin-induced oedema by 52.1 +/- 9.7% in the paw on the contralateral side. 3. Plasma extravasation in the knee joint in response to carrageenin (2%, 200 microl intra-articular injection) was diminished by 46.1 +/- 12.69% and 40.9 +/- 4.93% when the sciatic nerve was stimulated in the contralateral leg at 0.5 Hz for 1 h or 0.1 Hz for 4 h, respectively. 4. Stimulation of the peripheral stump of the left vagal nerve (20 V, 1 ms, 8 Hz, 10 min) elicited plasma extravasation in the trachea, oesophagus and mediastinal connective tissue in rats pretreated with atropine (2 mg kg(-1), i.v.), guanethidine (8 mg kg(-1), i.p.) and pipecuronium (200 microg kg(-1), i.v.). These responses were inhibited by 37.8 +/- 5.1%, 49.7 +/- 9.9% and 37.6 +/- 4.2%, respectively by antidromic sciatic nerve excitation (5 Hz, 5 min) applied 5 min earlier. 5. Pretreatment with polyclonal somatostatin antiserum (0.5 ml/rat, i.v.) or the selective somatostatin depleting agent cysteamine (280 mg kg(-1), s.c.) prevented the anti-inflammatory effect of sciatic nerve stimulation (5 Hz, 5 min) on a subsequent neurogenic plasma extravasation of the contralateral paw skin. The inhibitory effect of antidromic sciatic nerve excitation on plasma extravasation in response to vagal nerve stimulation was also prevented by somatostatin antiserum pretreatment. 6. Cutaneous blood flow assessment by laser Doppler flowmetry indicated that antidromic vasodilatation induced by sciatic nerve stimulation was not inhibited by excitation of the sciatic nerve of the contralateral leg (1 Hz, 30 min) or by somatostatin (10 microg/rat, i.v.) injection. 7. Plasma levels of somatostatin increased more than 4 fold after stimulation of both sciatic nerves (5 Hz, 5 min) but the stimulus-evoked increase was not observed in cysteamine (280 mg kg(-1), s.c.) pretreated rats. 8. These results suggest that somatostatin released from the activated sensory nerve terminals mediates the systemic anti-inflammatory effect evoked by stimulating the peripheral stump of the sciatic nerve.     

Classifying extraintestinal non-typhoid Salmonella infections

The cannabinoid receptors expressed in the mouse neuroblastoma X rat glioma NG108-15 cell and the rat pituitary tumor GH4C1 cell were determined by polymerase chain reaction, dideoxysequencing and pharmacologically. The CB1 but not the CB2 or CB1A cannabinoid receptor was found in both cell lines. The cDNA identified in GH4C1 cells corresponds to the rat CB1 receptor. Interestingly, NG108-15 cells express two distinct cDNAs, one corresponds to the rat and the other to the mouse CB1 receptor. The newly developed CB1 receptor selective antagonist SR141716A was found to reverse cannabinoid agonist (WIN55212-2 or CP55940)-induced adenylyl cyclase inhibition. These results provide more direct evidence that the CB1 receptor is mediating the pharmacological actions of cannabinoids in NG108-15 and GH4C1 cells.     

SR 141716A acts as an inverse agonist to increase neuronal voltage-dependent Ca2+ currents by reversal of tonic CB1 cannabinoid receptor activity

The CB1 cannabinoid receptor antagonist SR 141716A abolished the inhibition of Ca2+ currents by the agonist WIN 55,212-2. However, SR 141716A alone increased Ca2+ currents, with an EC50 of 32 nM, in neurons that had been microinjected with CB1 cRNA. For an antagonist to elicit an effect, some receptors must be tonically active. Evidence for tonically active CB1 receptors was seen as enhanced tonic inhibition of Ca2+ currents. Preincubation with anandamide failed to enhance the effect of SR 141716A, indicating that anandamide did not cause receptor activity. Under Ca2+-free conditions designed to block the Ca2+-dependent formation of anandamide and sn-2-arachidonylglycerol, SR 141716A again increased the Ca2+ current. The Ca2+ current was tonically inhibited in neurons expressing the mutant K192A receptor, which has no affinity for anandamide, demonstrating that this receptor is also tonically active. SR 141716A had no effect on the Ca2+ current in these neurons, but SR 141716A could still antagonize the effect of WIN 55, 212-2. Thus, the K192 site is critical for the inverse agonist activity of SR 141716A. SR 141716A appeared to become a neutral antagonist at the K192A mutant receptor. Native cannabinoid receptors were studied in male rat major pelvic ganglion neurons, where it was found that WIN 55,212-2 inhibited and SR 141716A increased Ca2+ currents. Taken together, our results demonstrate that a population of native and cloned CB1 cannabinoid receptors can exist in a tonically active state that can be reversed by SR 141716A, which acts as an inverse agonist.     

Excitatory transmission to the circular muscle of the guinea-pig ileum: evidence for the involvement of cannabinoid CB1 receptors

1. The effect of cannabinoid drugs has been investigated on cholinergic and non-adrenergic non-cholinergic (NANC) contractile responses to the circular smooth muscle of guinea-pig ileum elicited by electrical field stimulation (EFS). 2. The cannabinoid receptor agonist WIN 55,212-2 (1-1000 nM) and the putative endogenous ligand anandamide (0.1-100 microM) both produced a concentration-dependent inhibition of the cholinergic (9-57% and 1-51% inhibition) and NANC (9 55% and 2-57% inhibition) contractile responses. WIN 55,212-2 and anandamide did not modify the contractions produced by exogenous acetylcholine or substance P. 3. Apamin (30 nM), a blocker of Ca2+-activated K+ channels, reduced the inhibitory effect of WIN 55,212-2 on cholinergic, but not NANC, contractile response. NG-nitro-L-arginine methyl ester (100 microM), an inhibitor of nitric oxide synthase, or naloxone (1 microM), an opioid receptors antagonist, did not modify the inhibitory effect of WIN 55,212-2 on both cholinergic and NANC contractions. 4. The inhibitory effects of WIN 55,212-2 and anandamide on both cholinergic and NANC contractile response was competitively antagonized by the cannabinoid CB1 receptor antagonist SR 141716A (10-1000 nM). 5. In absence of other drugs, SR 141716A (1-1000 nM) enhanced cholinergic (1-45% increase) and NANC (2-38% increase) contractile responses elicited by electrical stimulation, but did not modify the contractions produced by acetylcholine or substance P. 6. It is concluded that activation of prejunctional cannabinoid CB1 receptors produces inhibition of cholinergic and NANC excitatory responses in the guinea-pig circular muscle. The inhibition of cholinergic (but not NANC) transmission involves activation of apamin-sensitive K+ channels. In addition, an endogenous cannabinoid ligand could inhibit cholinergic and NANC transmission in the guinea-pig ileal circular muscle.     

Inhibition of intestinal motility by anandamide, an endogenous cannabinoid

The endogenous cannabinoid ligand anandamide (arachidonylethanolamide) inhibited the intestinal passage of a charcoal meal when administered s.c. in mice at doses ranging from 0.1 to 50 mg/kg. This effect was prevented by the cannabinoid CB1 receptor antagonist SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide x HCl] (1 mg/kg s.c.), but it was not affected by the anandamide transport inhibitor, N-(4-hydroxyphenyl) arachidonylethanolamide (AM404) (50 mg/kg, s.c.). The results indicate that anandamide modulates intestinal motility in mice by activating cannabinoid CB1 receptors. They also suggest that anandamide transport, which was previously shown to participate in terminating neural and vascular responses to anandamide, does not contribute to anandamide inactivation in intestinal tissue.     

Increase in meso-prefrontal dopaminergic activity after stimulation of CB1 receptors by cannabinoids

The intravenous administration of the psychoactive constituent of marijuana, delta9-tetrahydrocannabinol (delta9-THC) (62.5-1000 microg/kg), and the synthetic cannabinoid agonist WIN 55212,2 (WIN) (62.5-500 microg/kg), produced a dose-related increase in the firing rate and burst firing in the majority of antidromically identified meso-prefrontal dopaminergic neurons. In a restricted number of neurons (n=4), WIN administration did not increase firing rate but produced an increment of bursting activity. These effects of the cannabinoids were reversed by the intravenous administration of SR 141716 A, a selective cannabinoid antagonist (1 mg/kg), per se ineffective to modify the electrical activity of dopaminergic neurons. The results indicate that stimulation of cannabinoid CB1 receptors produces an activation of meso-prefrontal dopaminergic transmission. Considering that supranormal stimulation of D1 dopamine receptors in the prefrontal cortex has been shown to impair working memory, the present results suggest that the negative effects of cannabinoids on cognitive processes might be related to the activation of dopaminergic transmission in the prefrontal cortex.     

Systemic anti-inflammatory effect induced by counter-irritation through a local release of somatostatin from nociceptors

1. Neurogenic plasma extravasation evoked by topical application of 1% vv(-1) mustard oil on the skin of the acutely denervated rat hindleg (primary reaction) inhibited the development of a subsequent oil-induced plasma extravasation induced in the skin of the contralateral hindleg by 49.3+/-7.06% (n=9) and in the conjunctival mucosa due to 0.1% wv(-1) capsaicin instillation by 33.5+/-10.05% (n=6). The primary reaction also inhibited the non-neurogenic hindpaw oedema evoked by s.c. injection of 5% wv(-1) dextran into the chronically denervated hindpaw by 48.0+/-4.6% (n= 5). 2. Capsaicin injection (100 microg ml(-1) in 50 microl, s.c.) into the acutely denervated hindleg caused 56.5+/-4.0% (n=5) inhibition in the intensity of plasma extravasation elicited by 1% vv(-1) mustard oil smearing on the contralateral side. After chronic denervation, subplantar injection of 5% wv(-1) dextran elicited a non-neurogenic inflammatory response with intensive tissue oedema without causing any systemic anti-inflammatory effect. Bilateral adrenalectomy did not inhibit the mustard oil-induced anti-inflammatory effect in the contralateral hindleg. 3. Pretreating the rats with polyclonal somatostatin antiserum (0.5 ml rat(-1), i.v.) or with the somatostatin depleting agent cysteamine (280 mg kg(-1), s.c.) prevented the inhibitory action of mustard oil-induced inflammation on subsequent neurogenic plasma extravasation and strongly diminished the inhibition of non-neurogenic oedema formation evoked by dextran. 4. Exogenous somatostatin (10 microg kg(-1), i.p.) caused a 30.3+/-8.3% (n=6) inhibition of plasma extravasation caused by mustard oil smearing on the acutely denervated hindleg and this inhibitory effect was abolished by somatostatin antiserum (0.5 ml rat(-1), i.v.). The plasma level of somatostatin-like immunoreactivity (SST-LI) increased by 40.03+/-6.8% (n= 6) 10 min after topical application of 1% vv(-1) mustard oil on the acutely denervated hindpaws compared to the paraffin oil treated control group. Chronic denervation of the hindlegs or cysteamine (280 mg kg(-1), s.c.) pretreatment prevented the mustard oil-induced elevation of SST-LI in plasma. 5. It is concluded that chemical excitation of the capsaicin-sensitive sensory receptors not only induces local neurogenic plasma extravasation but also inhibits the development of a subsequent inflammatory reaction at remote sites of the body in the rat. A role for somatostatin in this systemic anti-inflammatory effect is suggested.     

Differences in the sensitivity to purinergic stimulation of myelinating and non-myelinating Schwann cells in peripheral human and rat nerve

The administration of the 5-hydroxytryptamine (5-HT) precursor 5-hydroxytryptophan (5-HTP) (25 mg/kg i.p.), in combination with an inhibitor of peripheral 5-HTP decarboxylase, produced a dose-dependent increase in the ejaculation latency of male rats, and this effect was enhanced by additional treatment with the 5-HT1 receptor antagonist (-)-pindolol (2 mg/kg s.c.). The 5-HT2A/C receptor agonist (+/-) 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.125-0.5 mg/kg s.c.) did not by itself affect male ejaculatory behavior, but additional treatment with (-)-pindolol (2 mg/kg s.c.) produced a dose-dependent decrease in number of ejaculating animals. The increased ejaculation latency produced by 5-HTP was fully antagonized by treatment with the 5-HT1B receptor antagonist isamoltane (4 mg/kg s.c.), but not by ritanserin (2 mg/kg s.c.) treatment. The selective 5-HT1A receptor antagonist WAY-100635 (0.15 mg/kg s.c.) enhanced the inhibitory actions of 5-HTP on the male rat ejaculatory behavior, and this dose of WAY-100635 fully antagonized 8-OH-DPAT-induced facilitation (0.25 mg/kg s.c.) of the ejaculatory behavior. WAY-100635 (0.04-0.60 mg/kg s.c.) did not, by itself, significantly affect male rat sexual behavior. Taken together, the results suggest an inhibitory role for postsynaptic 5-HT1B receptors in the effects produced by 5-HTP on male rat ejaculatory behavior. Furthermore, 5-HTP-induced inhibition of male rat ejaculatory behavior is partially controlled by stimulation of inhibitory 5-HT1A autoreceptors, since the effects of 5-HTP were accentuated by treatment with (-)-pindolol, as well as by the more selective 5-HT1A receptor antagonist WAY-100635.     

Discriminative Stimulus Effects of the Cannabinoid Antagonist, SR 141716A, in Δ?-Tetrahydrocannabinol-Treated Rhesus Monkeys.

This study examined whether the cannabinoid antagonist, SR 141716A, could be established as a discriminative stimulus in rhesus monkeys treated with Δ?-tetrahydrocannabinol (Δ?-THC). Stimulus control was established with SR 141716A (1.0 mg/kg) in 3 Δ?-THC-treated monkeys (1.12 mg/kg/day) in 113-124 sessions. The SR 141716A discriminative stimulus was dose related, attenuated by an acute injection of Δ?-THC, and not mimicked by cocaine or ketamine. SR 141716A-appropriate responding occasioned by temporary discontinuation of Δ?-THC treatment was attenuated by Δ?-THC and not ketamine. The SR 141716A discriminative stimulus in Δ?-THC-treated monkeys appears to be mediated by cannabinoid receptors and could be related to Δ?-THC withdrawal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Histamine-induced biphasic macromolecular leakage in the microcirculation of the conscious hamster: evidence for a delayed nitric oxide-dependent leakage

1. Late effects (up to 3 h) of intravenously-injected histamine on FITC-dextran extravasation were investigated in the conscious hamster, by use of computer-assisted image analysis of fluorescence distribution in a microscopic window of dorsal skin fold preparations. This analysis allowed measurement of local (skin) and general (all organs) extravasations caused by a bolus injection of histamine (1 mg kg(-1), i.v.) 2. Histamine doses higher than 0.01 mg kg(-1) caused biphasic local and general extravasations. Initial phases developed fully within 15 min (for local) and 60 min (for general) and were followed by late phases beginning 90 min after histamine injection. Although the initial and late phases of histamine-induced extravasations had differential apparent reactivities to the autacoid, all the effects of histamine on the microcirculation (1 mg kg[-1]) were inhibited by pyrilamine (1 mg kg(-1), i.v.) but not by cimetidine (1 mg kg(-1), i.v.). 3. Pretreatment with N(G)-monomethyl-L-arginine (L-NMMA, 30 mg kg(-1), i.v.) or N(G)-nitro-L-arginine methyl ester (L-NAME, 100 mg kg(-1), i.v.) did not affect the initial phases but did prevent the late phases of local and general extravasations triggered by 1 mg kg(-1) histamine. The inhibitory effects of L-NAME were reversed by L-arginine (30 mg kg[-1]) but not by D-arginine (30 mg kg[-1]) according to the enantioselectivity of nitric oxide synthase (NOS). A late NO-mediated venular dilatation occurred in response to plasma histamine. 4. A low dose of aminoguanidine (1 mg kg(-1), i.v.), a selective inhibitor of the inducible isoform of NOS (iNOS), mimicked the inhibitory effects of L-NAME on the late phases of histamine-induced macromolecular extravasations and venular dilatation. 5. Pretreatment with dexamethasone (1 mg kg(-1), i.v.) prevented both the initial and late phases of histamine-induced extravasations. Fucoidan (1 or 25 mg kg(-1), i.v.) prevented the late phases without affecting initial phases, consistent with a role for leukocytes adhesion in the development of the late NO-mediated effects of histamine. 6. We conclude that intravenous injection of histamine triggers a biphasic inflammatory cascade via initial activation of H1 receptors which induces a late NO-mediated PMN-dependent extravasation process.