Dextrorotatory opioids induce stereotyped behavior in Sprague-Dawley and Dark Agouti rats.

Dextromethorphan and dextrorphan elicited a stereotyped behavioral syndrome in rats indistinguishable from that produced by PCP and other non-competitive NMDA antagonists. The rank order of potency for the induction of stereotyped behavior in male Sprague-Dawley rats was: MK-801>PCP>(+/-)cyclazocine>dextrorphan>(+/-)ketamine>dextromethorphan. These behavioral potencies were significantly correlated (0.91; P<0.05) with their respective affinities for high affinity [3H]dextrorphan-labelled NMDA receptors in rat forebrain membranes. To address the propensity of dextromethorphan to induce stereotyped behavior, dextrorotatory-opioid induced stereotypies were investigated in female Dark Agouti and female Sprague-Dawley rats. The female Dark Agouti lacks CYP2D1, the cytochrome P450 enzyme which catalyses the oxidative O-demethylation of dextromethorphan to dextrorphan. No differences were observed in either potency or time to peak effect for dextromethorphan to induce stereotyped behavior in the rat strains, suggesting that the affinity of dextromethorphan for NMDA receptors adequately accounts for its ability to induce stereotyped behavior. Female Dark Agouti rats were, however, more sensitive to the effects of dextrorphan, which may reflect differences in the ability of this strain to metabolize dextrorphan. We find no evidence to suggest that dextromethorphan produces a behavioral syndrome in rats that is distinct from that induced by dextrorphan. The commonality between the pharmacologic profiles of these compounds suggests that the abuse potential of dextromethorphan containing antitussive preparations is related to the non-competitive NMDA antagonist activity of dextromethorphan and its metabolites.

Platelet activation in patients with sickle cell disease.

Vascular occlusion and vasculopathy underlie much of the morbidity in patients with sickle cell anaemia. Platelets may play a role in this vasculopathy. Samples from 43 patients with sickle cell disease (SCD) were examined for evidence of platelet activation using fluorescent-labelled monoclonal antibodies and flow cytometry. There was increased expression of activation-dependent antigens on the platelets from patients with SCD compared to those from both Caucasian and African-American controls. In addition, SCD patients had increased levels of platelet microparticles. Platelets are activated in patients with sickle cell disease. The contribution of platelet activation to sickle cell pathophysiology is under active investigation in our laboratories.

High level expression of the NMDAR1 glutamate receptor subunit in electroporated COS cells.

The rat N-methyl-D-aspartate (NMDA) glutamate receptor subunit NR1-1a was transiently expressed in COS cells using the technique of electroporation, which was fivefold more efficient than the calcium phosphate precipitation method of transfection. The glycine site antagonist 5,7-[3H]dichlorokynurenic acid labeled a single high-affinity site (KD = 29.6 +/- 6 nM; Bmax = 19.4 +/- 1.6 pmol/mg of protein) in membranes derived from COS cells electroporated with NR1-1a. In contrast to previous reports using transiently transfected human embryonic kidney 293 cells, binding of the noncompetitive antagonist (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine ([3H]MK-801) was not detected in NR1-1a-transfected COS cells. Although immunofluorescent labeling of electroporated COS cells demonstrated that the NR1-1a protein appears to be associated with the cell membrane, neither NMDA nor glutamate effected an increase in intracellular calcium concentration in fura-2-loaded cells, suggesting that homomeric NR1-1a receptors do not act as functional ligand-gated ion channels. Therefore, COS cells appear to differ from Xenopus oocytes with respect to the transient expression of functional homomeric NR1 receptors. Although expression of NR1-1a is sufficient to reconstitute a glycine binding site with wild-type affinity for antagonists in COS cells, recombinant homomeric NR1-1a receptors do not display properties that are characteristic of native NMDA receptors, such as permeability to Ca2+ and channel occupancy by MK-801, when expressed in this mammalian cell line.

Regional distribution and characterization of [3H]dextrorphan binding sites in rat brain determined by quantitative autoradiography.

The pharmacologic specificity and anatomic distribution of [3H]dextrorphan recognition sites in the rat brain was characterized by quantitative autoradiography. Equilibrium saturation analysis indicated that [3H]dextrorphan labeled a single population of high affinity binding sites. These sites are heterogeneously distributed throughout rat forebrain with the following order of binding densities: hippocampal formation > cerebral cortex > thalamic nuclei > striatum. The association rate of [3H]dextrorphan with its binding site in area stratum radiatum of CA1 is accelerated by the addition of glycine and glutamate. [3H]Dextrorphan binding is, however, relatively insensitive to glycine and glutamate under equilibrium conditions, despite extensive prewashing procedures to deplete endogenous levels of these substances. The competitive N-methyl-D-aspartate (NMDA) antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) and the glycine site antagonist 7-chlorokynurenic acid completely inhibit specific [3H]dextrorphan binding. D-AP5 suppresses [3H]dextrorphan binding in a regionally distinctive manner; a population of binding sites is weakly inhibited by D-AP5 in the lateral thalamic regions, whereas D-AP5 potently inhibits [3H]dextrorphan binding in the cerebral cortex. The rank order of potencies of an array of noncompetitive antagonists to inhibit [3H]dextrorphan binding unambiguously displays the pharmacologic profile of the noncompetitive antagonist domain of the NMDA receptor-channel complex. Furthermore, the distribution of [3H]dextrorphan binding sites in slide-mounted tissue appears qualitatively similar to the distribution of NMDA receptors previously reported using NMDA-displacement of [3H]glutamate, [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) and [3H]1-[1-(2-thienyl)cyclohexyl]-piperidine (TCP) in most brain areas examined except the cerebellum. The molecular layer of the cerebellum displays a particularly high density of [3H]dextrorphan binding sites. The regional distribution of [3H]dextrorphan binding sites in rat brain does not correspond to the reported distributions of [3H]dextromethorphan or sigma binding sites.

Activation of adenosine A1 receptors underlies anticonvulsant effect of CGS21680.

Focal injection of the adenosine A2A receptor agonist CGS21680 (2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethyl-carboxamidoaden osine) in the rat prepiriform cortex produced a reduction in the severity of bicuculline methiodide-induced motor seizures. The anticonvulsant effect of CGS21680 exhibited dose-dependency and modest potency (ED50 = 605 +/- 47 pmol/rat). Pharmacological characterization of the anticonvulsant response in the prepiriform cortex revealed a significant correlation between the potency of adenosine analogs as anticonvulsants and their respective affinities for adenosine A1 receptors in vitro. These results indicate that the low affinity of CGS21680 for adenosine A1 receptors is sufficient to account for the anticonvulsant activity of this compound in the rat prepiriform cortex.

The sigma receptor ligand 1,3-di(2-tolyl)guanidine is anticonvulsant in the rat prepiriform cortex.

Unilateral focal injection of 1,3-di(2-tolyl)guanidine (DTG) caused a dose-dependent and potent (ED50 = 5.25 nmol, 95% confidence limits 1.1 to 25.0 nmol) suppression of generalized motor seizures induced by (-)-bicuculline methiodide in the rat prepiriform cortex. These findings indicate that DTG is equipotent to the noncompetitive NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate) as an anticonvulsant. This potent pharmacological effect of DTG distinguishes it from two other prototypic sigma ligands, haloperidol and (+)-pentazocine, which are ineffective as anticonvulsants. Pretreatment of animals with haloperidol failed to block the anticonvulsant effects of DTG. These data therefore document a novel anticonvulsant action of DTG in vivo by a mechanism that does not involve sigma receptors.

Manipulation of endogenous adenosine in the rat prepiriform cortex modulates seizure susceptibility.

A1 adenosine receptors in the rat prepiriform cortex play an important role in the inhibition of bicuculline methiodide-induced convulsions. In the present study we evaluated manipulation of endogenous adenosine in this brain area as a strategy to effect seizure suppression. All compounds evaluated were unilaterally microinjected into the rat prepiriform cortex. Administration of exogenous adenosine afforded a dose-dependent protection (ED50 = 48.1 +/- 8.4 nmol) against bicuculline methiodide-induced seizures, and these anticonvulsant effects were significantly potentiated by treatment with an adenosine kinase inhibitor, 5'-amino-5'-deoxyadenosine; by the adenosine transport blockers, dilazep or nitrobenzylthioinosine 5'-monophosphate; and by an adenosine deaminase inhibitor, 2'-deoxycoformycin. When administered alone, 5'-amino-5'-deoxyadenosine, 5'-iodotubercidin and dilazep were found to be highly efficacious as anticonvulsants with respective ED50 values of 2.6 +/- 0.8, 4.0 +/- 2.7 and 5.6 +/- 1.5 nmol. In contrast, 2'-deoxycoformycin was both less potent and less efficacious. These results suggest that accumulation of endogenous adenosine may contribute to seizure suppression, and that adenosine kinase and adenosine transport may play a pivotal role in the regulation of extracellular levels of adenosine in the central nervous system. The adenosine antagonist, 8-(p-sulfophenyl)theophylline, increased markedly the severity of bicuculline methiodide-induced seizures. Moreover, reduction of extracellular adenosine formation by a focal injection of an ecto-5'-nucleotidase inhibitor, alpha, beta-methyleneadenosine diphosphate, produced generalized seizures (ED50 = 37.3 +/- 22.7 nmol). Together the proconvulsant effect of an adenosine receptor antagonist and the convulsant action of an ecto-5'-nucleotidase inhibitor further support the role of endogenous adenosine as a tonically active antiepileptogenic substance in the rat prepiriform cortex.

Guanyl nucleotides modulate binding to steroid receptors in neuronal membranes.

The recently characterized corticosteroid receptor on amphibian neuronal membranes appears to mediate rapid, stress-induced changes in male reproductive behaviors. Because the transduction mechanisms associated with this receptor are unknown, we performed radioligand binding studies to determine whether this steroid receptor is negatively modulated by guanyl nucleotides. The binding of [3H]corticosterone to neuronal membranes was inhibited by nonhydrolyzable guanyl nucleotides in both equilibrium saturation binding and titration studies. The addition of guanyl nucleotide plus unlabeled corticosterone induced a rapid phase of [3H]corticosterone dissociation from membranes that was not induced by addition of unlabeled ligand alone. Furthermore, the equilibrium binding of [3H]corticosterone and the sensitivity of the receptor to modulation by guanyl nucleotides were both enhanced by Mg2+. These results are consistent with the formation of a ternary complex of steroid, receptor, and guanine nucleotide-binding protein that is subject to regulation by guanyl nucleotides. Therefore, rapid signal transduction through corticosteroid receptors on neuronal membranes appears to be mediated by guanine nucleotide-binding proteins.

Dextrorotatory opioids and phencyclidine exert anticonvulsant action in prepiriform cortex.

We have investigated the ability of an array of putative noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists to suppress convulsions induced by a unilateral, focal injection of (-)-bicuculline methiodide (118 pmol) into the rat prepiriform cortex. The anticonvulsant potency of these compounds, (+)-5-methyl-10,11- dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) greater than dextrorphan greater than or equal to 1-(1-phenylcyclohexyl)piperidine hydrochloride (PCP) greater than dextromethorphan greater than (+)-pentazocine, upon microinjection into the prepiriform cortex, was highly correlated (r = 0.971; P less than 0.01) with their respective affinities for the [3H]dextrorphan-labelled NMDA receptors in rat forebrain membranes. These results suggest that noncompetitive antagonism of NMDA receptors underlies the anticonvulsant action of these compounds.

High affinity [3H]dextrorphan binding in rat brain is localized to a noncompetitive antagonist site of the activated N-methyl-D-aspartate receptor-cation channel.

[3H]Dextrorphan recognition sites were characterized in rat brain membranes. The pharmacological profile and regional distribution of [3H]dextrorphan binding sites appear to distinguish these sites from those labeled either by [3H]dextromethorphan or by putative sigma receptor radioligands. Data from thoroughly washed forebrain membranes suggest that [3H]dextrorphan predominantly labels a high affinity site defined by the activated state of the N-methyl-D-aspartate (NMDA) receptor-channel complex. Regulation of [3H]dextrorphan binding by specific modulators of NMDA receptor function suggests that [3H]dextrorphan binding is predominantly localized to a domain of the receptor-channel complex also recognized by the prototypical noncompetitive antagonist radioligands (+)-[3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) and [3H]1-[1-(2-thienyl)cyclohexyl]piperidine (TCP). The critical relationship between [3H]dextrorphan binding and activation of the NMDA receptor-complex is suggested by the profound dependence of [3H]dextrorphan binding on glutamate in well washed membranes. Basal specific [3H]dextrorphan binding is nearly totally suppressed by the specific competitive NMDA antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5), in a glutamate- but not glycine-surmountable manner. Glutamate and glycine each stimulate [3H]dextrorphan binding in a concentration-dependent manner, effecting maximal increases from control of up to 30- and 14-fold, respectively. The NMDA receptor specificity of the modulation of [3H]dextrorphan binding by glutamate and glycine is indicated by the sensitivity of their effects to competitive antagonism by D-AP5 and 3-amino-1-hydroxy-2-pyrrolidone (HA-966), respectively, and by the accordant rank orders of potency of glycine analogs as modulators of [3H]dextrorphan binding and as ligands at the strychnine-insensitive glycine site. The divalent cations Mg2+ and Zn2+ and the polyamines spermine and spermidine regulate [3H]dextrorphan binding in a manner consistent with radioligand interaction at the noncompetitive NMDA antagonist domain. Mg2+ and spermidine regulate [3H]dextrorphan binding biphasically in well washed forebrain membranes, whereas Zn2+ monotonically inhibits [3H]dextrorphan binding. Mg2+ and spermidine regulate [3H]dextrorphan binding with qualitative similarity and in a contrasting fashion to their regulation of [3H]MK-801 and [3H]TCP binding. First, spermidine and Mg2+ are significantly more potent modulators of [3H]dextrorphan binding than of [3H]MK-801 and [3H]TCP binding in well washed membranes; second, whereas the potencies of spermidine and Mg2+ as modulators of [3H]MK-801 and [3H]TCP binding are significantly increased by glutamate and glycine in well washed membranes, their potencies as regulators of [3H]dextrorphan binding appear to be unaffected by glutamate and glycine.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and initial characterization of high-affinity [3H]dextrorphan binding sites in rat brain.

We have identified specific high-affinity [3H]dextrorphan binding sites in rat forebrain. [3H]Dextrorphan binds saturably and reversibly to an apparently homogenous class of sites characterized by a Bmax of 2.62 +/- 0.06 pmol/mg protein and KD of 60 +/- 4 nM. Glycine and glutamate independently increase [3H]dextrorphan binding in a concentration-dependent manner. The pharmacological profiles of [3H]dextrorphan binding characterized by equilibrium competition experiments together with these data suggest that [3H]dextrorphan labels a site at or near the N-methyl-D-aspartate receptor.

Anticonvulsant effect of N-ethylcarboxamidoadenosine against kainic acid-induced behavioral seizures in the rat prepiriform cortex.

Kainic acid (KA), microinjected unilaterally into the rat prepiriform cortex (PC), produces generalized motor seizures in a dose-dependent manner. The adenosine agonist N-ethylcarboxamidoadenosine (NECA), when co-injected with KA, protects against seizures in a dose-dependent and highly potent manner: ED50 = 25.6 +/- 2.1 pmol/rat. The seizure-suppressing effects of NECA are completely abolished by co-administration of the adenosine receptor antagonist 8-(p-sulfophenyl)theophylline (8-pSPT), suggesting that adenosine receptor activation underlies the efficacy of NECA against KA seizures. Moreover, dilazep, an effective blocker of adenosine uptake, when co-administered with KA, provides significant protection against seizures. Together, these findings suggest that adenosine receptors may play an important role in the regulation of the inhibitory neuronal circuitry of this paleocortical brain area.

Adenosine A1 receptor activation mediates suppression of (-) bicuculline methiodide-induced seizures in rat prepiriform cortex.

The protective effects of a series of stable adenosine analogs against generalized seizures initiated by focal injection of bicuculline methiodide into the rat prepiriform cortex (PPC) were studied by microinjection of these compounds into this brain area. The adenosine agonists, 5'-N-(ethyl)carboxamido-adenosine (NECA), cyclohexyladenosine, cyclopentyadenosine, 2-chloroadenosine and R- and S-phenylisopropyladenosine (R- and S-PIA), protected animals against seizures in a dose-dependent, and extremely potent manner. NECA, the most potent compound evaluated, completely prevented seizures at doses greater than or equal to 6.8 pmol. In contrast, heroic doses of the A2 selective ligand, 2-phenylaminoadenosine, afforded no protection against seizures. The rank order of potency of these compounds in suppressing seizures is as follows: NECA greater than cyclohexyladenosine greater than cyclopentyladenosine greater than or equal to R-PIA greater than 2-chloroadenosine greater than S-PIA much greater than 2-phenylaminoadenosine. These data suggest that the antiseizure activity of these compounds in the PPC results from activation of A1 adenosine receptors. Quantitative autoradiographic analysis of the distribution of tritiated adenosine agonists 30 min after microinjection in the PPC reveals that [3H]NECA diffuses to a significantly greater extent than R-[3H]PIA, which may contribute to the relatively greater potency of the former compound in suppressing bicuculline methiodide-induced seizures. These results suggest that adenosine A1 receptors may participate in the normal inhibitory regulation of the PPC, a forebrain area which may play a significant role in the pathobiology of epilepsy.

Characterization of low Km GTPase activity in rat brain: comparison of opioid and muscarinic receptor stimulation.

Guanosine 5'-triphosphate (GTP)-binding proteins (G-proteins) have an essential role in mediating the actions of drugs on neurotransmitter receptors by coupling them to their effectors with the attendant hydrolysis of GTP. The resulting GTPase activity was characterized in rat brain with a view toward selecting conditions under which specific hormone-stimulated activity could be monitored. Kinetic analysis with washed membranes suggested the presence of two distinct GTPases, a low Km GTPase with an apparent Km value of 0.35 +/- 0.04 microM and apparent Vmax of 108 pmol min-1 mg protein-1, together with a much higher Km component. Low Km (but not high Km) GTPase activity is stimulated by muscarinic and opioid agonists and inhibited by a nonhydrolyzable analogue of GTP, providing further evidence that the low Km component is a distinct enzyme. The activity of the low Km component is a linear function of protein concentration (20-100 micrograms/mL), time (2-10 min), and temperature (25-37 degrees C). The specific activity of the low Km component is selectively increased by approximately 50% in purified synaptic membranes compared with the washed membrane preparation. Both carbamylcholine-stimulated and basal low Km GTPase activities, but not the high Km component, are inhibited by a nonhydrolyzable analogue of GTP but not by the comparable analogue of ATP, demonstrating the specificity of low Km GTPase for guanine nucleotides. Opioid- and muscarinic-stimulated GTPase activities are additive in brain, suggesting that the two receptor systems are associated with different domains of G-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Labeling of A1 adenosine receptors in porcine atria with the antagonist radioligand 8-cyclopentyl-1,3-[3H]dipropylxanthine.

We have used the antagonist radioligand 8-cyclopentyl-1,3-[3H]dipropylxanthine to label adenosine recognition sites in porcine atrial membranes. 8-Cyclopentyl-1,3-[3H]dipropylxanthine bound saturably, reversibly and with high affinity to an apparently homogeneous population of recognition sites with a Bmax of 32.0 +/- 0.9 fmol/mg protein and a KD of 0.394 +/- 0.049 nM. Prototypic adenosine receptor agonists inhibited the specific binding of 8-cyclopentyl-1,3-[3H]dipropylxanthine in a manner consistent with the labeling of an A1 adenosine receptor. 8-Cyclopentyl-1,3-[3H]dipropylxanthine appears to be a valuable antagonist radioligand for the characterization of cardiac adenosine receptors.