The acoustical behavior of a bass guitar bridge with no saddles

The acoustics of a bass guitar bridge without saddles was tested experimentally and the results contextualised. Conclusions were obtained demonstrating that the bridge without saddles (where knot around the ball end of the string forms part of the sounding length) produced no measurable reduction in sustain and may increase the sustain for lower pitched strings, in comparison to a conventional bridge featuring saddles. The bridge without saddles showed a reduction in string inharmonicity, and produced a splitting of the frequency peaks associated within the resonances of the string. This peak splitting is explained as being due to differences in the frequency of vibrations parallel to and perpendicular to the body. Since the loop of core wire strongly resists vibration perpendicular to the body but vibrates freely as part of the sounding length for vibration parallel to the body, the relative length of the loop of core wire with respect to the sounding length of the string determines the fractional difference in frequency. The perceptual quality of the sound is similar to the beating due to multiple strings per note (as in piano) and to electronic chorus effects.

Can resveratrol supplementation reduce uremic toxins plasma levels from the gut microbiota in non-dialyzed chronic kidney disease patients?

BACKGROUND

Uremic toxins such as indoxyl sulfate (IS), p-cresyl sulfate (pCS), and indole-3-acetic acid (IAA) produced by the gut microbiota are recognized as risk factors for many comorbidities, including cardiovascular diseases. Chronic kidney disease (CKD) patients have an accumulation of these toxins and nutritional strategies have been proposed to mitigate gut dysbiosis and, consequently, reduce these toxins. This study aimed to evaluate the effects of resveratrol supplementation on the plasma levels of IS, pCS, and IAA in non-dialyzed CKD patients.

METHODS

In this placebo-controlled crossover study, twenty non-dialyzed patients were randomly divided into two groups: they received either one capsule/day containing 500 mg of trans-resveratrol (63 ± 7.5 years, glomerular filtration ratio (GFR): 34 ± 14 mL/min, body mass index (BMI): 26.8 ± 5.6 kg/m²) or a placebo containing 500 mg wheat flour (62 ± 8.4 years, GFR: 34 ± 13 mL/min, BMI: 28.6 ± 4.4 kg/m²) during four weeks. After eight weeks of washout (no supplementation), another four weeks of supplementation with crossover was initiated. IS, IAA, and pCS plasma levels were quantified by the Reverse Phase High-Efficiency Liquid Chromatography method with fluorescent detection. The mRNA expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor kappa B (NF-κB) in peripheral blood mononuclear cells was evaluated by polymerase chain reaction. C-reactive protein (CRP) plasma levels were also evaluated.

RESULTS

As expected, the uremic toxins levels were negatively correlated with GFR, but no effect of trans-resveratrol supplementation was found on levels of IS, IAA, and pCS. There was a positive correlation between IS and Nrf2 (r = 0.24, p = 0.03) and also between IS and CRP (r = 0.21, p = 0.05).

CONCLUSION

Supplementation with trans-resveratrol did not reduce the plasma levels of IS, pCS, and IAA in non-dialyzed CKD patients. The interactions among uremic toxins and anti- and pro-inflammatory pathways deserve more studies.

The physics of unwound and wound strings on the electric guitar applied to the pitch intervals produced by tremolo/vibrato arm systems

The physics of wound and unwound strings on the electric guitar are presented here, and the pitch intervals produced by the movements of a Fender Stratocaster tremolo unit are explained. Predicted changes in pitch sensitivity of different strings are given, and experimentally verified, for changes in saddle height, the distance of string free to move behind the nut and ratio of diameters/masses of the core and windings of wound strings. Also, it is shown that changes to the gauge of strings (assuming the string tension is sufficient for linear behaviour and in absence of changes to other construction details) don’t alter the pitch intervals produced by a given angle of tremolo arm use assuming the instrument is set up with the same sounding pitches and starting bridge angle. It is demonstrated that it not possible to equalise the relative sensitivity of unwound steel stings on a Fender Stratocaster type tremolo unit through string construction techniques. The ratio of core to winding mass in the string, on the other hand, was found to be a very powerful design parameter for choosing the sensitivity of the string to tremolo arm use and standard pitch bends. For instance, the pitch intervals produced by operation of tremolo arm for wound strings may be made to approximately match that for one of the unwound strings if they share very similar core gauges (assuming the winding masses are chosen to give approximately the same tension at their sounding pitches). Such a design, only available currently by custom order, also delivers the optimum equalisation in sensitivity of strings for standard string bends (due to these also being produced by altering the length of the string to generate changes in tension and therefore pitch).

Wave separation in the trumpet under playing conditions and comparison with time domain finite difference simulation

Wave separation within a trumpet is presented using three high pressure microphones to measure pressure waves within the curved, constant cross-section tuning slide of the instrument while the instrument was being played by a virtuoso trumpet player. A closer inter-microphone spacing was possible in comparison to previous work through the use of time domain windowing on non-causal transfer functions and performing wave separation in the frequency domain. Time domain plots of the experimental wave separation were then compared to simulations using a physical model based on a time domain finite difference simulation of the trumpet bore coupled to a one mass, two degree of freedom lip model. The time domain and frequency spectra of the measured and synthesized sounds showed a similar profile, with the sound produced by the player showing broader spectral peaks in experimental data. Using a quality factor of 5 for the lip model was found to give greater agreement between the simulated and experimental starting transients in comparison to the values in the range 1-3 often assumed. Deviations in the spectral content and wave shape provide insights into the areas where future research may be directed in improving the accuracy of physical modeling synthesis.

Time domain wave separation using multiple microphones

Methods of measuring the acoustic behavior of tubular systems can be broadly characterized as steady state measurements, where the measured signals are analyzed in terms of infinite duration sinusoids, and reflectometry measurements which exploit causality to separate the forward and backward going waves in a duct. This paper sets out a multiple microphone reflectometry technique which performs wave separation by using time domain convolution to track the forward and backward going waves in a cylindrical source tube. The current work uses two calibration runs (one for forward going waves and one for backward going waves) to measure the time domain transfer functions for each pair of microphones. These time domain transfer functions encode the time delay, frequency dependent losses and microphone gain ratios for travel between microphones. This approach is applied to the measurement of wave separation, bore profile and input impedance. The work differs from existing frequency domain methods in that it combines the information of multiple microphones within a time domain algorithm, and differs from existing time domain methods in its inclusion of the effect of losses and gain ratios in intermicrophone transfer functions.

Controlled trial of interventions to increase testing and treatment for Helicobacter pylori and reduce medication use in patients with chronic acid-related symptoms

BACKGROUND

Many symptomatic patients take proton pump inhibitors or histamine-2 blockers for years and those without gastro-oesophageal reflux disease might benefit from Helicobacter pylori eradication.

AIM

To increase testing and treatment of H. pylori and reduce chronic use of proton pump inhibitors and histamine-2 blockers.

METHODS

We conducted a three-armed controlled trial in 14 managed care practices. We included adults who used proton pump inhibitors or histamine-2 blockers for >1 year and excluded those with gastro-oesophageal reflux disease or previous endoscopy. We compared usual care (n = 312 patients from 6 practices) to low-intensity (n = 147 from 3 practices) and high-intensity (n = 122 from 5 practices) interventions. Low-intensity intervention consisted of guidelines, patient-lists, and a "toolkit"; high-intensity intervention added academic group detailing by a gastroenterologist with reinforcement by pharmacists.

RESULTS

Compared with usual care, the high-intensity intervention increased H. pylori test-ordering (29% versus 9% at 12 months, P = 0.02). About half (23 of 58) of patients tested positive and 22 received eradication treatments. The high-intensity intervention decreased proton pump inhibitor use by 9% per year (P = 0.028), but did not alter histamine-2 blocker use. The low intensity intervention was ineffective.

CONCLUSIONS

Providing guidelines, patient-lists, and toolkits was no better than usual care. Adding group detailing and pharmacist reinforcements led to improvements in H. pylori management and decreases in proton pump inhibitor use.

Evaluation of the NR2B-selective NMDA receptor antagonist Ro 63-1908 on rodent behaviour: evidence for an involvement of NR2B NMDA receptors in response inhibition

We have characterised the effects of the recently described NMDA NR2B subtype selective antagonist, Ro 63-1908, on spontaneous behaviour and in tasks sensitive to non-selective NMDA antagonists. In both rats and wild type mice, Ro 63-1908 (1-30mg/kg sc) produced a mild increase in motor activity of lesser magnitude than that elicited by dizocilpine. No signs of overt PCP-like stereotypy were seen in either species at equivalent doses. PPI was also unaffected. However, in mice lacking the NR2A subunit, Ro 63-1908 (3-30mg/kg) produced a profound hyperactivity of similar magnitude to dizocilpine but few other 'PCP-like' behaviours. In rats, Ro 63-1908 (1-10mg/kg) did not affect Morris water maze or delayed matching performance. In a 5-choice serial reaction time task, requiring rats to respond to a visual stimulus presented after a fixed time interval, Ro 63-1908 (0.3-3mg/kg) produced a dramatic increase in premature responses - accuracy was relatively unaffected. Finally in a DRL24 task, Ro 63-1908 (0.3-3mg/kg) reduced inter-response time, increased response rate, and consequently reduced efficiency. We conclude that the improved profile of Ro 63-1908 compared to NMDA channel blockers is due to both its selectivity for the NR2B vs. NR2A subunit containing receptors and its activity-dependent mechanism of action. However, in the 5-CSRT and DRL24 tasks, Ro 63-1908 produced behaviours suggestive of impaired response inhibition, implicating a critical role of NMDA NR2B transmission in this process.

Pharmacological characterization of Ro 63-1908 (1-[2-(4-hydroxy-phenoxy)-ethyl]-4-(4-methyl-benzyl)-piperidin-4-ol), a novel subtype-selective N-methyl-D-aspartate antagonist

Ro 63-1908, 1-[2-(4-hydroxy-phenoxy)-ethyl]-4-(4-methyl-benzyl)-piperidin-4-ol, is a novel subtype-selective N-methyl-D-aspartate (NMDA) antagonist that has been characterized in vitro and in vivo. Ro 63-1908 inhibited [(3)H]dizocilpine ((3)H-MK-801) binding in a biphasic manner with IC(50) values of 0.002 and 97 microM for the high- and low-affinity sites, respectively. Ro 63-1908 selectively blocked recombinant receptors expressed in Xenopus oocytes containing NR1C + NR2B subunits with an IC(50) of 0.003 microM and those containing NR1C + NR2A subunits with an IC(50) of >100 microM, thus demonstrating greater than 20,000-fold selectivity for the recombinant receptors expressing NR1C + NR2B. Ro 63-1908 blocked these NMDA NR2B-subtype receptors in an activity-dependent manner. Ro 63-1908 was neuroprotective against glutamate-induced toxicity and against oxygen/glucose deprivation-induced toxicity in vitro with IC(50) values of 0.68 and 0.06 microM, respectively. Thus, the in vitro pharmacological characterization demonstrated that Ro 63-1908 was a potent and highly selective antagonist of the NR2B subtype of NMDA receptors. Ro 63-1908 was active against sound-induced seizures (ED(50) = 4.5 mg/kg i.p. when administered 30 min beforehand) in DBA/2 mice. The dose required to give a full anticonvulsant effect did not produce a deficit in the Rotarod test. NMDA-induced seizures were also inhibited by Ro 63-1908 with an ED(50) of 2.31 mg/kg i.v. when administered 15 min before testing. Ro 63-1908 gave a dose-related neuroprotective effect against cortical damage in a model of permanent focal ischemia. Maximum protection of 39% was seen at a plasma concentration of 450 ng/ml. There were, however, no adverse cardiovascular or CNS side-effects seen at this dosing level.

Donepezil reverses a mnemonic deficit produced by scopolamine but not by perforant path lesion or transient cerebral ischaemia

The purpose of these studies were threefold. Firstly, to further characterize the effect of perforant path transection on a test of short-term memory: delayed matching (or nonmatching)-to-position [D(N)MTP]. Secondly, to evaluate the effect of a transient cerebral ischaemia in the same task. Both surgical procedures were chosen as they produce a CNS lesion similar to that described in Alzheimer's Disease (AD). Thirdly, the effect of the acetylcholinesterase inhibitor, donepezil (Aricept(R), E2020), on the resulting cognitive impairment was studied. Perforant path transection produced a robust, delay-dependent impairment of choice accuracy in rats performing either a delayed matching- or nonmatching-to-position task. Sample latency was also reduced following lesion, yet the lesion-induced impairment was not affected by increasing the response requirement at the sample stage. An 11-min period of transient ischaemia (two-vessel occlusion model) resulted in almost complete loss of hippocampal CA1 pyramidal cells and a delay-dependent impairment in DMTP performance. However, unlike perforant path lesions, this deficit was unstable and declined in magnitude over the experimental period. Increasing the delay interval restored this deficit. Donepezil, at doses that robustly attenuated a scopolamine (0.06 mg/kg s.c.)-induced DMTP accuracy impairment in naïve, unoperated rats, had no effect against either lesion-induced impairment. The results are considered in terms of the effectiveness of acetylcholinesterase inhibitors in noncholinergic-based preclinical cognitive models.

Targeted pharmacological depletion of serum amyloid P component for treatment of human amyloidosis

The normal plasma protein serum amyloid P component (SAP) binds to fibrils in all types of amyloid deposits, and contributes to the pathogenesis of amyloidosis. In order to intervene in this process we have developed a drug, R-1-[6-[R-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid, that is a competitive inhibitor of SAP binding to amyloid fibrils. This palindromic compound also crosslinks and dimerizes SAP molecules, leading to their very rapid clearance by the liver, and thus produces a marked depletion of circulating human SAP. This mechanism of drug action potently removes SAP from human amyloid deposits in the tissues and may provide a new therapeutic approach to both systemic amyloidosis and diseases associated with local amyloid, including Alzheimer's disease and type 2 diabetes.

A combined pharmacological and genetic approach to investigate the role of orphanin FQ in learning and memory

Using a combination of the selective opioid receptor-like1 (ORL1) receptor agonist, Ro 64-6198, and orphanin FQ/nociceptin (OFQ/N) peptide knockout (KO) mice, the influence of OFQ/N on cognition has been studied in the rodent. In wild type, C57BL/6J mice, Ro 64-6198 (0.3-1 mg/kg i.p.) impaired the acquisition of spatial learning in the Morris water maze, although a mild neurological impairment was evident which complicated precise interpretation. In Lister hooded rats, Ro 64-6198 (6 mg/kg i.p.) produced delay dependent impairments in rats performing either a delayed matching or a delayed nonmatching to position task with only a modest (< 20%) effect on omissions - an effect consistent with a short-term memory impairment. Electrophysiological studies demonstrated an inhibitory effect of OFQ/N on LTP recorded from the CA1 region of wild type mice, but not in ORL1 receptor knockout mice. In contrast to the ORL1 agonist, mice deficient in the OFQ/N peptide showed some evidence of improved spatial learning, fear conditioning and passive avoidance retention. However, CA1 LTP was similar between OFQ/N peptide KO mice and wild type controls. Subsequent receptor radioautography studies demonstrated the presence of ORL1 receptors within various regions of the medial temporal lobe system: i.e. CA1, dentate gyrus molecular layer, subiculum, perirhinal cortex. Taken together, these results suggest a bi-directional effect of OFQ/N containing systems on aspects of cognitive behaviour, particularly those elements associated with hippocampal function. This is consistent with a likely modulatory role of OFQ/N on hippocampal and associated cortical circuitry.

Analysis of photoreceptor function and inner retinal activity in juvenile X-linked retinoschisis

Thirteen retinoschisis males with genotyped XLRS1 gene mutations were examined by electroretinogram (ERG) techniques to determine photoreceptor involvement and ON-pathway and OFF-pathway sites of dysfunction. Parameters R(max) and logS determined by fitting the mathematical model of the activation phase of phototransduction to the scotopic and photopic a-wave responses, were not significantly different from normal. However, the XLRS photopic a-wave amplitudes were significantly lower than normal across all intensities, consistent with defective signaling in the OFF pathway. Long flash (150 ms) ON-OFF photopic responses showed reduced b-wave amplitude but normal d-wave amplitude, giving a reduced b/d ratio of <1.32 Hz photopic flicker ERG fundamental frequency responses showed reduced amplitude and delayed phase, consistent with abnormal signaling by both the ON- and OFF-pathway components. These results indicate that the XLRS1 protein appears not to affect photoreceptor function directly for most XLRS males, and that ERG signaling abnormalities occur in both the ON- and OFF-pathway components that originate in the proximal retina.

Positive allosteric modulators of metabotropic glutamate 1 receptor: characterization, mechanism of action, and binding site

We have identified two chemical series of compounds acting as selective positive allosteric modulators (enhancers) of native and recombinant metabotropic glutamate 1 (mGlu1) receptors. These compounds did not directly activate mGlu1 receptors but markedly potentiated agonist-stimulated responses, increasing potency and maximum efficacy. Binding of these compounds increased the affinity of a radiolabeled glutamate-site agonist at its extracellular N-terminal binding site. Chimeric and mutated receptors were used to localize amino acids in the receptor transmembrane region critical for these enhancing properties. Finally, the compounds potentiated synaptically evoked mGlu1 receptor responses in rat brain slices. The discovery of selective positive allosteric modulators of mGlu1 receptors opens up the possibility to develop a similar class of compounds for other family 3 G protein-coupled receptors.

Identification of essential residues involved in the glutamate binding pocket of the group II metabotropic glutamate receptor

Metabotropic glutamate (mGlu) receptors are a family of G-protein-coupled receptors that play central roles as modulators of both glutamatergic and other major neurotransmitter systems in CNS. Using molecular modeling, site-directed mutagenesis, [(3)H]LY354740 binding, [(35)S]GTPgammaS binding, and activation of GIRK current, we have been able to identify residues crucial for the binding of LY354740 and glutamate to rat mGlu2 receptors. Several of the crucial residues located in the binding site (Arg-57, Tyr-144, Tyr-216, Asp-295) have not been identified previously. We propose that the gamma-carboxyl group of LY354740 forms H-bonds to Arg-57, whereas the alpha-carboxyl group forms an H-bond with the hydroxyl group of Ser-145. The alpha-amino group of LY354740 forms H-bonds to Asp-295 and to the side-chain hydroxyl group of Thr-168. In addition, Tyr-144 may establish a hydrophobic (C-H/pi)-interaction with the bicyclo-hexane ring of LY354740. Furthermore, the mutation of residues Ser-148 and Arg-183, which are too remote for a direct interaction, affected the ligand affinity dramatically. These results suggest that Ser-148 and Arg-183 may be important for the 3D structure and/or are involved in closure of the domain. Finally, Asp-146, which is also remote from the binding site, was shown to be involved in the differential binding affinity of [(3)H]LY354740 for mGlu2 versus mGlu3 receptors. All the mGlu receptors except mGlu2 are activated by Ca(2+) and have serine instead of aspartic acid at this position, which suggests a critical role of this aspartic acid residue in the binding properties of this unique receptor.

Management of asthma in children

The prevalence of asthma in children has increased 160 percent since 1980, and the disease currently affects nearly 5 million children in the United States. The National Asthma Education and Prevention Program provides guidelines for improved asthma care. The goals of this program are to limit the frequency, severity and costliness of asthma exacerbations through extensive education of physicians, children and caregivers. The four components of asthma management include regular assessment and monitoring, control of factors that contribute to or aggravate symptoms, pharmacologic therapy and education of children and their caregivers. The guidelines recommend a stepwise approach to pharmacologic treatment, starting with aggressive therapy to achieve control and followed by a "step down" to the minimal therapy that will maintain control. Quick relief of symptoms can be achieved preferentially by the use of short-acting beta2 agonists. Medications for long-term control should be considered for use in children with persistent symptoms. Inhaled corticosteroids are the most potent long-term anti-inflammatory medications. Other options include long-acting beta2 agonists, cromolyn sodium and nedocromil, antileukotriene agents and theophylline. All have advantages and disadvantages in individual situations.

Pharmacological properties of native metabotropic glutamate receptors in freshly dissociated Golgi cells of the rat cerebellum

We have examined the pharmacological properties of native metabotropic glutamate (mGlu) receptors in freshly isolated rat cerebellar Golgi cells using the whole-cell configuration of the patch-clamp technique. Group II mGlu receptor agonists inhibited voltage-gated Ca(2+) channels (VGCC) currents in a reversible and concentration-dependent manner with a rank order of potency being LY354740> DCG-IV > L-CCG-I > glutamate >>1S,3R-ACPD > NAAG. The maximum degree of inhibition obtained was similar for all drugs tested, saturating at about 33-41%, except for NAAG that had a non saturating effect of 50% at 1mM. Two novel group II mGlu receptor antagonists, LY341495 and Ro 65-3479, reversed VGCC current inhibition by LY354740 with pK(B) values of 7.0 and 6.3, respectively. In a subpopulation of Golgi cells, the antagonistic effect of LY341495 was only partial, suggesting a remaining effect of group I mGlu receptors. This was confirmed by experiments with S-DHPG, a selective group I mGlu receptor agonist. These experiments suggest that Golgi cells of the cerebellum express group II mGlu receptors that couple to the inhibition of VGCCs. Therefore, inhibition of VGCCs in cerebellar Golgi cells is a useful model system to evaluate novel group II mGlu receptor ligands.

Activity-dependent presynaptic autoinhibition by group II metabotropic glutamate receptors at the perforant path inputs to the dentate gyrus and CA1

Pharmacological activation of metabotropic glutamate receptors (mGluRs) can inhibit synaptic transmission; however, relatively little evidence exists regarding the physiological conditions under which such autoreceptors are activated by synaptically released glutamate. Bath application of selective group II mGluR agonists profoundly inhibited field excitatory postsynaptic potentials (fEPSPs) evoked by stimulation of the perforant path inputs to both the mid-molecular layer of the dentate gyrus and the stratum lacunosum moleculare of the CA1. Application of the group II selective mGluR antagonist LY341495 resulted in an increase in the relative amplitude of a test fEPSP evoked 200 ms after a conditioning burst, but not after a single conditioning stimulus, in both pathways. Antagonist application also resulted in a marked increase in the relative amplitude of test population spikes evoked in the dentate gyrus following a conditioning burst. These observations are consistent with a presynaptic autoinhibitory action of group II metabotropic receptors that is revealed following burst stimulation of the pathway, consistent with their localisation in the preterminal zone. Activation of group II mGluRs during theta-gamma pattern discharge of projection neurones in the entorhinal cortex is likely to play an important role in the regulation of synaptic transmission and plasticity in the perforant pathway.

Functional consequences of reduction in NMDA receptor glycine affinity in mice carrying targeted point mutations in the glycine binding site

We have used site-directed mutagenesis in conjunction with homologous recombination to generate two mouse lines carrying point mutations in the glycine binding site of the NMDAR1 subunit (Grin1). Glycine concentration-response curves from acutely dissociated hippocampal neurons revealed a 5- and 86-fold reduction in receptor glycine affinity in mice carrying Grin1(D481N) and Grin1(K483Q) mutations, respectively, whereas receptor glutamate affinity remained unaffected. Homozygous mutant Grin1(D481N) animals are viable and fertile and appear to develop normally. However, homozygous mutant Grin1(K483Q) animals are significantly lighter at birth, do not feed, and die within a few days. No gross abnormalities in CNS anatomy were detected in either Grin1(D481N) or Grin1(K483Q) mice. Interestingly, in situ hybridization and Western blot analysis revealed changes in the expression levels of NMDA receptor subunits in Grin1(D481N) mice relative to wild type that may represent a compensatory response to the reduction in receptor glycine affinity. Grin1(D481N) mice exhibited deficits in hippocampal theta burst-induced long-term potentiation (LTP) and spatial learning and also a reduction in sensitivity to NMDA-induced seizures relative to wild-type controls, consistent with a reduced activation of NMDA receptors. Mutant mice exhibited normal prepulse inhibition but showed increased startle reactivity. Preliminary analysis indicated that the mice exhibit a decreased natural aversion to an exposed environment. The lethal phenotype of Grin1(K483Q) animals confirms the critical role of NMDA receptor activation in neonatal survival. A milder reduction in receptor glycine affinity results in an impairment of LTP and spatial learning and alterations in anxiety-related behavior, providing further evidence for the role of NMDA receptor activation in these processes.

Controlling polymerization of beta-amyloid and prion-derived peptides with synthetic small molecule ligands

The Alzheimer beta-amyloid peptide (Abeta) and a fragment of the prion protein have the capacity of forming amyloid-like fibrils when incubated under physiological conditions in vitro. Here we show that a small amyloid ligand, RO-47-1816/001, enhances this process severalfold by binding to amyloid molecules and apparently promote formation of the peptide-to-peptide bonds that join the monomers of the amyloid fibrils. This effect could be antagonized by other ligands, including analogues of RO-47-1816/001, as well as the structurally unrelated ligand Congo red. Analogues of RO-47-1816/001 with low affinity for amyloid did not display any antagonistic effect. In conclusion, these data suggest that synthetic molecules, and possibly also small natural substances present in the brain, may act in a chaperone-like fashion, promoting Abeta polymerization and growth of amyloid fibrils in vitro and possibly also in vivo. Furthermore, we demonstrate that small organic molecules can be used to inhibit the action of amyloid-enhancing compounds.

A randomized controlled trial of an enhanced patient compliance program for Helicobacter pylori therapy

OBJECTIVES

To determine whether an enhanced compliance program (ECP) improves patient compliance with bismuth subsalicylate, metronidazole, and tetracycline hydrochloride (BMT) triple therapy for the treatment of Helicobacter pylori infection and to identify factors that affect compliance with therapy.

DESIGN

A randomized controlled trial conducted in 4 staff-model health centers of a health maintenance organization in Massachusetts.

PATIENTS AND METHODS

A total of 125 patients 18 years of age or older with peptic ulcer disease or dyspepsia whose clinicians prescribed BMT triple therapy for 14 days were randomized to a control group or to the ECP group. The ECP group received medication counseling (written and oral) from a pharmacist, along with a medication calendar and a minipillbox, as well as a follow-up telephone call after initiation of therapy. Compliance was assessed by a pill count, and factors affecting adherence to the regimen were identified by patients' reports.

RESULTS

There was no statistically significant difference between the 2 groups in the number of patients taking more than 60% of the medications (89% of the control group vs 95% of the ECP group; P>.30). However, there was a statistically significant difference in the number of patients taking more than 90% of the medications (67% of the control group vs 89% of the ECP group; P<.01). An intention-to-treat analysis confirmed these results. The most frequently reported adverse effect was gastrointestinal intolerance. Other factors reported to affect compliance included the frequency of dosing and the number of pills.

CONCLUSIONS

These findings suggest that although adverse effects were common, most patients were able to complete 60% or more of the 2-week regimen. An ECP further improved the percentage of medications taken.

Screening for colorectal cancer with flexible sigmoidoscopy by nonphysician endoscopists

PURPOSE

Screening with sigmoidoscopy reduces the risk of death from colorectal cancer. Only 30% of eligible patients have undergone sigmoidoscopy, in part because of a limited supply of endoscopists. We evaluated the performance and safety of screening sigmoidoscopic examinations by trained nonphysician endoscopists in comparison with board-certified gastroenterologists.

SUBJECTS AND METHODS

Asymptomatic patients 50 years or older without evidence of fecal occult blood and no personal history or family history of a first-degree relative with colorectal cancer under age 55 years were offered sigmoidoscopy. All examinations were performed either by a gastroenterologist or a trained nonphysician endoscopist at a staff model health maintenance organization. Outcomes included the depth of examination, number and histology of polyps, and complications.

RESULTS

Nonphysicians performed 2,323 sigmoidoscopic examinations, and physicians performed 1,378 examinations. The mean (+/-SD) depth of sigmoidoscopy examinations performed by nonphysicians was 52 +/- 10 cm compared with 55 +/- 9 cm (P <0.001) in physicians. Nonphysicians detected neoplastic polyps in a greater proportion of patients (7.8%) than physicians (5.8%), but this difference was not significant after adjusting for differences in the age, sex, and family history of the patients (P = 0.35). No major complications occurred. The cost per examination, including the nonphysician training cost, was lower for nonphysicians ($186 per examination) than for physicians ($283 per examination).

CONCLUSIONS

Appropriately trained nonphysicians may be capable of performing safe and effective screening for colorectal cancer with flexible sigmoidoscopy. An increased use of nonphysicians to perform sigmoidoscopy may increase the availability and reduce the cost of the procedure.

Methotrexate in Crohn's disease: results of a randomized, double-blind, placebo-controlled trial

BACKGROUND/AIMS

Immunosuppression with methotrexate may be useful in the treatment of Crohn's disease. We tested the efficacy of methotrexate in refractory Crohn's disease in a randomized, controlled trial.

METHODOLOGY

Randomized, double-blind placebo-controlled trial of methotrexate in 33 patients with steroid-dependent Crohn's disease, 33% of whom had previously failed therapy with 6-mercaptopurine. Patients were given placebo or oral methotrexate 15 mg/week, or adjusted up to 22.5 mg/week, for up to 1 year or until treatment failure. Outcome was assessed by reduction in prednisone dosage, Crohn's Disease Activity Index, hospital admission, and laboratory parameters.

RESULTS

Four patients were dropped from the study for non-compliance and one because of intercurrent illness, and 28 patients could be evaluated. Fewer methotrexate-treated patients (6/13 or 46%) had flares of Crohn's disease as compared to placebo-treated patients (12/15 or 80%), but this did not achieve statistical significance (p<0.1). There was a non-significant trend toward an increased number of significant side effects in the methotrexate-treated patients (3/13 or 23%) as compared to the placebo-treated patients (0/15 or 0%) (p<0.2). Laboratory indices of inflammation did not differ between the two groups.

CONCLUSIONS

The methotrexate-treated group showed a trend toward fewer Crohn's disease flares, balanced by an increased number of significant side effects.

Characterization of (2S,2'R,3'R)-2-(2',3'-[3H]-dicarboxycyclopropyl)glycine binding in rat brain

[(2S,2'R,3'R)-2-(2',3'-[3H]Dicarboxycyclopropyl)glycine ([3H]DCG IV) binding was characterized in vitro in rat brain cortex homogenates and rat brain sections. In cortex homogenates, the binding was saturable and the saturation isotherm indicated the presence of a single binding site with a K(D) value of 180 +/- 33 nM and a Bmax of 780 +/- 70 fmol/mg of protein. The nonspecific binding, measured using 100 microM LY354740, was <30%. NMDA, AMPA, kainate, L(-)-threo-3-hydroxyaspartic acid, and (S)-3,5-dihydroxyphenylglycine were all inactive in [3H]DCG IV binding up to 1 mM. However, several compounds inhibited [3H]DCG IV binding in a concentration-dependent manner with the following rank order of potency: LY341495 = LY354740 > DCG IV = (2S,1'S,2'S)-2-(2-carboxycyclopropyl)glycine > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid > (2S,1'S,2'S)-2-methyl-2-(2-carboxycyclopropyl)glycine > L-glutamate = ibotenate > quisqualate > (RS)-alpha-methyl-4-phosphonophenylglycine = L(+)-2-amino-3-phosphonopropionic acid > (S)-alpha-methyl-4-carboxyphenylglycine > (2S)-alpha-ethylglutamic acid > L(+)-2-amino-4-phosphonobutyric acid. N-Acetyl-L-aspartyl-L-glutamic acid inhibited the binding in a biphasic manner with an IC50 of 0.2 microM for the high-affinity component. The binding was also affected by GTPgammaS, reducing agents, and CdCl2. In parasagittal sections of rat brain, a high density of specific binding was observed in the accessory olfactory bulb, cortical regions (layers 1, 3, and 4 > 2, 5, and 6), caudate putamen, molecular layers of the hippocampus and dentate gyrus, subiculum, presubiculum, retrosplenial cortex, anteroventral thalamic nuclei, and cerebellar granular layer, reflecting its preferential (perhaps not exclusive) affinity for pre- and postsynaptic metabotropic glutamate mGlu2 receptors. Thus, the pharmacology, tissue distribution, and sensitivity to GTPgammaS show that [3H]DCG IV binding is probably to group II metabotropic glutamate receptors in rat brain.

An allosteric interaction between the NMDA receptor polyamine and ifenprodil sites in rat cultured cortical neurones

1. The atypical NR2B subunit-selective NMDA receptor antagonist ifenprodil was originally believed to act as a competitive antagonist at the polyamine binding site of the NMDA receptor. However, a number of studies have suggested that ifenprodil might bind to a distinct site. 2. Using whole-cell voltage clamp recordings, we have studied the interaction of spermine with both ifenprodil and the related NR2B selective antagonist Ro 8-4304 at the NMDA receptor in rat cultured cortical neurones in the presence of saturating concentrations of glycine. 3. Ifenprodil and Ro 8-4304 inhibited steady-state currents evoked by 100 microM NMDA in the absence of spermine with IC50 values of 0.3 and 0.6 microM, respectively. In the presence of 1 and 3 mM spermine, IC50 values for ifenprodil were 1.4 and 1.8 microM and for Ro 8-4304 they were 3. 0 and 7.5 microM, respectively. 4. In the presence of spermine, the on-time constant of receptor blockade by both antagonists was significantly slower than control and the off-time constant of recovery from receptor blockade following removal of Ro 8-4304 was significantly faster. 5. Fast application of spermine during an NMDA steady-state current in the continuous presence of a subsaturating concentration of either antagonist resulted in a biphasic increase in the current, consistent with a fast increase upon spermine binding and a slow increase resultant from dissociation of antagonist due to spermine binding-induced allosteric reduction in receptor antagonist affinity. In agreement with this, at higher, saturating concentrations of antagonist, the slow increase in current amplitude was markedly reduced or absent. 6. These observations are consistent with a non-competitive, allosteric interaction between spermine and the antagonists, such that spermine binding to the NMDA receptor results in a reduction in receptor affinity for the antagonists and vice versa. 7. The effects of Mg2+ on the NMDA-evoked currents and its interaction with ifenprodil were similar to those of spermine, supporting the suggestion that Mg2+ might be the physiological ligand acting at the spermine site mediating glycine-independent stimulation.

Is colonoscopy indicated for small adenomas found by screening flexible sigmoidoscopy?

BACKGROUND

There is controversy over whether patients who have a small tubular adenoma on screening flexible sigmoidoscopy should undergo colonoscopic examination of the proximal colon.

OBJECTIVE

To prospectively determine the prevalence of advanced polyps in the proximal colon among patients who have small adenomas on screening sigmoidoscopy.

DESIGN

Prospective cohort study.

SETTING

A health maintenance organization and a Veterans Affairs medical center.

PATIENTS

Asymptomatic patients older than 50 years of age who had no risk factors for colon cancer and underwent sigmoidoscopy.

INTERVENTION

At the time of sigmoidoscopy, all polyps were biopsied and characterized. All patients with distal adenomas were offered colonoscopy.

MEASUREMENTS

The size and histology of polyps identified by sigmoidoscopy and colonoscopy were noted. Polyps were considered advanced if they were larger than 10 mm or were tubulovillous, villous, or malignant. The prevalence of advanced proximal polyps was determined, and patients were stratified by the size and number of distal polyps found by sigmoidoscopy.

RESULTS

Among 4490 patients who underwent sigmoidoscopy, a neoplastic lesion was detected in 401 (8.9%) and colonoscopy was done in 301 (75%). Of 90 patients with a single tubular adenoma 1 to 5 mm in diameter in the distal colon, 0% (95% CI, 0.0% to 4.0%) had an advanced proximal polyp compared with 5.4% (CI, 2.4% to 10.4%) of those who had multiple distal polyps 1 to 5 mm or 6 to 10 mm in diameter and 7.9% (CI, 2.6% to 17.6%) of those who had advanced distal polyps (P = 0.013 for trend). The low-risk group with a single tubular adenoma 1 to 5 mm in diameter represented 44% of all patients with distal adenomas or cancers found at flexible sigmoidoscopy.

CONCLUSIONS

Among patients undergoing screening sigmoidoscopy, those with single tubular adenomas of 5 mm or less had a low prevalence of advanced proximal polyps. These patients may not benefit from colonoscopy.

L-687,414, a low efficacy NMDA receptor glycine site partial agonist in vitro, does not prevent hippocampal LTP in vivo at plasma levels known to be neuroprotective

N-methyl-D-aspartic acid (NMDA) receptors are known to play a key role in the induction phase of long-term potentiation (LTP) at certain hippocampal synapses and to represent some component of spatial learning in animals. The ability of NMDA receptor antagonists (or gene knockout) to impair LTP has led to the suggestion that the therapeutic use of such antagonists may impair cognitive function in humans. The present study compares the effects on LTP of NMDA receptor ion channel block by MK-801 and glycine-site antagonism by 3R(+)cis-4-methyl-pyrrollid-2-one (L-687,414). In vitro experiments using rat cortical slices revealed L-687,414 to be approximately 3.6 fold more potent than its parent analogue, R(+)HA-966 at antagonizing NMDA-evoked population depolarizations (apparent Kbs: 15 microM and 55 microM, respectively). Whole-cell voltage-clamp experiments using rat cultured cortical neurones revealed L-687,414 to shift to the right the concentration-response relationship for NMDA-evoked inward current responses (pKb=6.2+/-0.12). L-687,414 affinity for the glycine site on the NMDA receptor complex was also determined from concentration-inhibition curves, pKi=6.1+/-0.09. In the latter experiments, L-687,414 and R(+)HA-966 were unable to completely abolish inward current responses suggesting each compound to be a low efficacy partial agonist (estimated intrinsic activity = approximately 10 and 20% of glycine, respectively). L-687,414 and MK-801 were compared for their effects on NMDA receptor-dependent LTP in the dentate gyrus of anaethestized rats following high frequency stimulation of the medial perforant path (mPP) afferents. Control rats, administered saline (0.4 ml kg(-1) followed by 0.0298 ml min(-1)), showed a robust augmentation of the population e.p.s.p. risetime (LTP) recorded in the dentate hilus following tetanic stimulation of the mPP. LTP was effectively abolished in a separate group of rats treated with an MK-801 dosing regimen (0.12 mg kg(-1) i.v. followed by 1.8 microg kg(-1) h(-1)) known to produce maximal neuroprotection in a rat stroke model but, by contrast, remained largely intact in a third group of animals given a similarly neuroprotective L-687,414 treatment (28 mg kg(-1) i.v. followed by 28 mg kg(-1) h(-1)). These experiments suggest that a low level of intrinsic activity at the glycine site may be sufficient to support NMDA receptor-dependent LTP but in circumstances where there is likely to be an excessive NMDA receptor activation the agonism associated with a low efficacy partial agonist, such as L-687,414, is dominated by the antagonist properties. Thus, an NMDA receptor partial agonist profile may offer a therapeutic advantage over neutral antagonists by permitting an acceptable level of 'normal' synaptic transmission whilst curtailing excessive receptor activation.

Metabotropic glutamate group II receptors activate a G protein-coupled inwardly rectifying K+ current in neurones of the rat cerebellum

1. The effects of the group II metabotropic glutamate receptor (mGluR) agonists DCG-IV and LY354740 were examined in neurones freshly dissociated from the rat cerebellum and olfactory bulb, using the whole-cell configuration of the patch-clamp technique. 2. Under experimental conditions in which K+ currents would be inward, rapid application of DCG-IV and LY354740 to interneurones expressing the group II mGluRs induced an inward current in a subpopulation of interneurones of the cerebellum, the unipolar brush cells. 3. The currents induced by DCG-IV and LY354740 had the major characteristics of a G protein-coupled inwardly rectifying K+ channel (GIRK) current; namely, rapid activation and deactivation upon agonist application and removal, G protein dependence, strong inward rectification, Cs+ and Ba2+ sensitivity, and K+ selectivity. 4. In Golgi cells of the cerebellum and interneurones of the accessory olfactory bulb, which also express group II mGluRs, LY354740 did not induce GIRK activation but inhibited voltage-gated Ca2+ channel currents. 5. These results demonstrate that, in unipolar brush cells, native group II mGluRs can functionally couple to activation of GIRKs. Thus, the absence of coupling in the majority of CNS neurones examined to date may be due to restricted cellular co-localization or co-expression of the appropriate proteins.

In vitro binding properties in rat brain of [3H]Ro 25-6981, a potent and selective antagonist of NMDA receptors containing NR2B subunits

The in vitro binding of a new subtype-selective NMDA receptor antagonist, [3H]Ro 25-6981, to rat brain membranes and sections was characterized. The compound bound to a single site on the membranes with a K(D) of 3 nM and a Bmax of 1.6 pmol/mg of protein. Specific binding, defined with a new NR2B-specific antagonist, Ro 04-5595 [1-(4-chlorophenyl)-2-methyl-6-methoxy-7-hydroxy-1,2,3,4-tetrahydroisoqu inoline], at 10 microM, was fully inhibited by several compounds with the following rank order of affinities--Ro 25-6981 > CP-101,606 > Ro 04-5595 = ifenprodil >> eliprodil > haloperidol > spermine > spermidine > MgCl2 > CaCl2--and partially inhibited by competitive glutamate recognition site antagonists. A high density of binding sites was detected, radioautographically, in several layers of the cerebral cortex, in the hippocampus, dentate gyrus, tuberculum olfactorium, caudate putamen, medium densities in the globus pallidus, thalamus, spinal cord dorsal horn, and motoneurons, whereas the cerebellum, pons, and medulla were, with a few exceptions, e.g., locus coeruleus, poorly labeled. Overall, the distribution of [3H]Ro 25-6981 binding sites correlated well with that of NR2B (but not NR2A) transcripts, revealed by in situ hybridization histochemistry. The high affinity of [3H]Ro 25-6981 for NR2B-containing receptors renders this compound the ligand of choice to study the regulation of NR2B-containing receptor expression.

Effect of metabotropic glutamate receptor activation on receptor-mediated cyclic AMP responses in primary cultures of rat striatal neurones

Co-activation of group I metabotropic glutamate (mGlu) receptors and adenosine receptors resulted in an augmented cyclic AMP response in primary cultures of rat striatal neurones. L-glutamate and the selective group I agonist, (S)-dihydroxyphenylglycine (S-DHPG) evoked concentration-dependent potentiations of cyclic AMP accumulation stimulated by the adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA), with EC50 values of 3.41+/-0. 39 and 5.69+/-1.64 microM, respectively, and maximal augmentations of approximately 350% at concentrations of 100 microM. The S-DHPG potentiation was inhibited by group I mGlu receptor antagonists and a protein kinase C inhibitor, Ro 31-8220, implicating products of PI hydrolysis in this effect. Furthermore, L-glutamate and S-DHPG stimulated PI hydrolysis in striatal neuronal cultures with similar EC50 values to those observed for the augmentation of NECA cyclic AMP responses (5.19+/-1.18 and 3.78+/-1.42 microM, respectively). In situ hybridization and immunofluorescence techniques indicate that group I mGlu receptor-evoked potentiations are likely to be mediated via mGlu5 receptors, which are expressed at high levels in these cultures. In contrast to cross-chopped slices of neonatal rat striatum, of equivalent age, the group II mGlu receptor agonist, (2S, 2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) was without effect on NECA- or forskolin-stimulated cyclic AMP responses in primary striatal neuronal cultures. This lack of effect might be due to a low level of expression of group II mGlu receptors in cultured striatal neurones.

Developmental changes in NMDA receptor glycine affinity and ifenprodil sensitivity reveal three distinct populations of NMDA receptors in individual rat cortical neurons

Previous work with recombinant receptors has shown that the identity of the NMDA NR2 subunit influences receptor affinity for both glutamate and glycine. We have investigated the developmental change in NMDA receptor affinity for both glutamate and glycine in acutely dissociated parietal cortex neurons of the rat, together with the expression during ontogeny of NR2A and NR2B mRNA and protein. Whereas there is little change in NMDA receptor glutamate affinity with age, a population of NMDA receptors emerges in 14- and 28-d-old animals with a markedly reduced affinity for glycine (mKD = approximately 800 nM) and a reduced sensitivity to the NR2B subunit-selective NMDA antagonist ifenprodil. These changes are paralleled by a developmental increase in the expression of NR2A. Thus, in mature animals a population of NMDA receptors appears with a lower affinity for glycine that might not be saturated under normal physiological conditions. Ifenprodil (10 microM) inhibits virtually all of the NMDA receptor-evoked current in very young neurons that contain a single population of receptors exhibiting a high affinity for glycine (mKD = approximately 20 nM). In older neurons, which contain NMDA receptors with both high and low affinities for glycine, ifenprodil (10 microM) inhibits both the high-affinity population and a significant proportion of the low-affinity component, thus revealing three pharmacologically distinct populations of NMDA receptors in single neurons. Moreover, these observations suggest that ifenprodil might bind with high affinity to NMDA receptors containing both NR2A and NR2B subunits as well as those containing only NR2B.

Characterization of [3H]-(2S,2'R,3'R)-2-(2',3'-dicarboxy-cyclopropyl)glycine ([3H]-DCG IV) binding to metabotropic mGlu2 receptor-transfected cell membranes

1. The binding of the new selective group II metabotropic glutamate receptor radioligand, [3H]-(2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine ([3H]-DCG IV), was characterized in rat mGlu2 receptor-transfected CHO cell membranes. 2. [3H]-DCG IV binding was pH-dependent, but was not sensitive to temperature. Saturation analysis showed the presence of a single binding site, with a Kd value of 160 nM and a Bmax value of 10 pmol mg(-1) protein. Binding was not sensitive to Na+-dependent glutamate uptake blockers or Cl-dependent glutamate binding inhibitors. Furthermore, up to concentrations of 1 mM, the glutamate ionotropic receptor agonists, N-methyl-D-aspartic acid (NMDA), (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate, did not affect [3H]-DCG IV binding. 3. Of the compounds observed to inhibit [3H]-DCG IV binding, the most potent were the recently described selective group II agonist, (+)-2-aminobicyclo-[3.1.0]hexane-2,6-dicarboxylate (LY 354740; Ki value 16 nM) and antagonist, 2-amino-2-(2-carboxycyclopropan-1-yl)-3-(dibenzopyran-4-yl) propanoic acid (LY 341495; Ki value 19 nM). As expected, for a G-protein-coupled receptor, guanosine-5'-O-(3-thiotriphosphate) (GTPgammaS) inhibited [3H]-DCG IV binding in a concentration-dependent manner, with an IC50 value of 12 nNM. 4. A highly significant correlation was observed between the potencies of compounds able to inhibit [3H]-DCG IV binding and potencies obtained for agonist activity in a GTPgamma35S binding functional assay. In addition, these studies identified a number of compounds with previously unknown activity at mGlu2 receptors, including L(+)-2-amino-3-phosphonopropionic acid (L-AP3), L(+)-2-amino-5-phosphonopentanoic acid (L-AP5), 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (R-CPP), N-acetyl-L-aspartyl-L-glutamic acid (NAAG) and (RS)-alpha-methylserine-O-phosphate (MSOP).

In vitro binding characteristics of a new selective group II metabotropic glutamate receptor radioligand, [3H]LY354740, in rat brain

The in vitro binding of [3H]LY354740, the first high affinity group II-selective metabotropic glutamate (mGlu) receptor radioligand, was characterized in rat cortical, hippocampal, and thalamic membranes as well as in rat brain sections. [3H]LY354740 binding was saturable in all regions investigated. Nonspecific binding (in the presence of 10 microM DCG-IV) was approximately 8% of the total. Ionotropic glutamate receptor agonists, N-methyl-D-aspartate, (R,S)-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid/kainate, a Na+-dependent glutamate uptake blocker as well as a group I-selective mGlu receptor agonist (all up to 1 mM) did not inhibit [3H]LY354740 binding to cortical membranes. However, several known metabotropic receptor ligands inhibited the binding with the following rank order of potency: LY354740 = LY341495 > (2S,2'R, 3'R)-2-(2',3'-dicarboxycyclopropyl)glycine = (2S,1'S, 2'S)-2-(2-carboxycyclopropyl)glycine > glutamate = (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid > (2S,1'S, 2'S)-2-methyl-2-(2-carboxycyclopropyl)-glycine > quisqualate > ibotenate > L-2-amino-3-phosphonopropionic acid = (S)-alpha-methyl-4-carboxyphenylglycine > L-(+)-2-amino-4-phosphonobutyric acid. N-Acetyl-aspartyl-glutamate, (2S)-alpha-ethylglutamic acid, and (R, S)-alpha-methyl-4-phosphonophenylglycine inhibited [3H]LY354740 binding in a biphasic manner. Guanosine-5'-O-(3-thiotriphosphate concentration-dependently and almost completely inhibited the binding. Finally, in parasagittal sections of rat brain, a high density of specific binding was observed in the accessory olfactory bulb, cortical regions (layers 1-3 > 4-6), caudate putamen, molecular layers of the hippocampus and dentate gyrus, presubiculum, retrosplenial cortex, anteroventral thalamic nuclei, and cerebellar granular layer, reflecting its preferential (perhaps not exclusive) affinity for presynaptic and postsynaptic mGlu2 receptors. Thus, the pharmacology, tissue distribution, and sensitivity to guanosine-5'-O-(3-thiotriphosphate show that [3H]LY354740 binding probably occurs to group II mGlu receptors in rat brain.

State-dependent NMDA receptor antagonism by Ro 8-4304, a novel NR2B selective, non-competitive, voltage-independent antagonist

1. Subunit-selective blockade of N-methyl-D-aspartate (NMDA) receptors provides a potentially attractive strategy for neuroprotection in the absence of undesirable side effects. Here, we describe a novel NR2B-selective NMDA antagonist, 4-¿3-[4-(4-fluoro-phenyl)-3,6-dihydro-2H-pyridin-1-yl]-2-hydroxy-propoxy ¿-benzamide (Ro 8-4304), which exhibits >100 fold higher affinity for recombinant NR1(001)/NR2B than NR1(001)/NR2A receptors. 2. Ro 8-4304 is a voltage-independent, non-competitive antagonist of NMDA receptors in rat cultured cortical neurones and exhibits a state-dependent mode of action similar to that described for ifenprodil. 3. The apparent affinity of Ro 8-4304 for the NMDA receptor increased in an NMDA concentration-dependent manner so that Ro 8-4304 inhibited 10 and 100 microM NMDA responses with IC50s of 2.3 and 0.36 microM, respectively. Currents elicited by 1 microM NMDA were slightly potentiated in the presence of 10 microM Ro 8-4304, and Ro 8-4304 binding slowed the rate of glutamate dissociation from NMDA receptors. 4. These results were predicted by a reaction scheme in which Ro 8-4304 exhibits a 14 and 23 fold higher affinity for the activated and desensitized states of the NMDA receptor, respectively, relative to the agonist-unbound resting state. Additionally, Ro 8-4304 binding resulted in a 3 4 fold increase in receptor affinity for glutamate site agonists. 5. Surprisingly, whilst exhibiting a similar affinity for NR2B-containing NMDA receptors as ifenprodil, Ro 8-4304 exhibited markedly faster kinetics of binding and unbinding to the NMDA receptor. This spectrum of kinetic behaviour reveals a further important feature of this emerging class of NR2B-selective compounds.

Multiple pathways for regulation of the KCl-induced [3H]-GABA release by metabotropic glutamate receptors, in primary rat cortical cultures

In rat cortical primary cultures, group II- and III-metabotropic glutamate receptor-selective agonists concentration-dependently reduced KCl-induced [3H]GABA release, with IC50 values of 11 nM for LY354740, 80 nM for L(+)-2-amino-4-phosphonobutyric acid (L-AP4), 180 nM for DCG-IV, and 330 nM for L-SOP. The group II antagonists, LY341495 and EGLU, reversed the effect of LY354740, and the group III antagonist MTPG reversed the effect of L-AP4. In the presence of omega-conotoxin GVIA, LY354740 inhibited the remaining [3H]GABA release, whereas L-AP4 was inactive. In contrast, in the presence of nifedipine, L-AP4 inhibited the remaining [3H]GABA release, but LY354740 was no longer active. The PKA inhibitor, H89, blocked the effects of both L-AP4 and LY354740, whereas the PKC inhibitor Ro 31-8220 blocked only the effect of LY354740. Both Ro 31-8220 and H89 reduced the [3H]GABA release to 60% of control. In whole-cell, voltage-clamp experiments, LY354740 and L-AP4 inhibited voltage-gated calcium channel currents with IC50 values of 28 nM and 22 microM, respectively. The results suggest that, in these cells, KCl-induced [3H]GABA release is modulated by two different mechanisms, one involving group II receptors and a direct control of the Ca2+ channel activity, and the other mediated by group III receptors and possibly involving a regulation located downstream of the Ca2+ channel activation.

Effect of plasma protein binding on in vivo activity and brain penetration of glycine/NMDA receptor antagonists

A major issue in designing drugs as antagonists at the glycine site of the NMDA receptor has been to achieve good in vivo activity. A series of 4-hydroxyquinolone glycine antagonists was found to be active in the DBA/2 mouse anticonvulsant assay, but improvements in in vitro affinity were not mirrored by corresponding increases in anticonvulsant activity. Here we show that binding of the compounds to plasma protein limits their brain penetration. Relative binding to the major plasma protein, albumin, was measured in two different ways: by a radioligand binding experiment or using an HPLC assay, for a wide structural range of glycine/NMDA site ligands. These measures of plasma protein binding correlate well (r = 0.84), and the HPLC assay has been used extensively to quantify plasma protein binding. For the 4-hydroxyquinolone series, binding to plasma protein correlates (r = 0.92) with log P (octanol/pH 7.4 buffer) over a range of log P values from 0 to 5. The anticonvulsant activity increases with in vitro affinity, but the slope of a plot of pED50 versus pIC50 is low (0.40); taking plasma protein binding into account in this plot increases the slope to 0.60. This shows that binding to albumin in plasma reduces the amount of compound free to diffuse across the blood-brain barrier. Further evidence comes from three other experiments: (a) Direct measurements of brain/blood ratios for three compounds (2, 16, 26) show the ratio decreases with increasing log R. (b) Warfarin, which competes for albumin binding sites dose-dependently, decreased the ED50 of 26 for protection against seizures induced by NMDLA. (c) Direct measurements of brain penetration using an in situ brain perfusion model in rat to measure the amount of drug crossing the blood-brain barrier showed that compounds 2, 26, and 32 penetrate the brain well in the absence of plasma protein, but this is greatly reduced when the drug is delivered in plasma. In the 4-hydroxyquinolones glycine site binding affinity increases with lipophilicity of the 3-substituent up to a maximum at a log P around 3, then does not improve further. When combined with increasing protein binding, this gives a parabolic relationship between predicted in vivo activity and log P, with a maximum log P value of 2.39. Finally, the plasma protein binding studies have been extended to other series of glycine site antagonists, and its is shown that for a given log P these have similar protein binding to the 4-hydroxyquinolones, except for compounds that are not acidic. The results have implications for the design of novel glycine site antagonists, and it is suggested that it is necessary to either keep log P low or pKa high to obtain good central nervous system activity.

Ro 25-6981, a highly potent and selective blocker of N-methyl-D-aspartate receptors containing the NR2B subunit. Characterization in vitro

The interaction of Ro 25-6981 with N-methyl-D-aspartate (NMDA) receptors was characterized by a variety of different tests in vitro. Ro 25-6981 inhibited 3H-MK-801 binding to rat forebrain membranes in a biphasic manner with IC50 values of 0.003 microM and 149 microM for high- (about 60%) and low-affinity sites, respectively. NMDA receptor subtypes expressed in Xenopus oocytes were blocked with IC50 values of 0.009 microM and 52 microM for the subunit combinations NR1C & NR2B and NR1C & NR2A, respectively, which indicated a >5000-fold selectivity. Like ifenprodil, Ro 25-6981 blocked NMDA receptor subtypes in an activity-dependent manner. Ro 25-6981 protected cultured cortical neurons against glutamate toxicity (16 h exposure to 300 microM glutamate) and combined oxygen and glucose deprivation (60 min followed by 20 h recovery) with IC50 values of 0.4 microM and 0.04 microM, respectively. Ro 25-6981 was more potent than ifenprodil in all of these tests. It showed no protection against kainate toxicity (exposure to 500 microM for 20 h) and only weak activity in blocking Na+ and Ca++ channels, activated by exposure of cortical neurons to veratridine (10 microM) and potassium (50 mM), respectively. These findings demonstrate that Ro 25-6981 is a highly selective, activity-dependent blocker of NMDA receptors that contain the NR2B subunit.

Inhibition of the electrostatic interaction between beta-amyloid peptide and membranes prevents beta-amyloid-induced toxicity

The accumulation of beta-amyloid peptides (Abeta) into senile plaques is one of the hallmarks of Alzheimer disease. Aggregated Abeta is toxic to cells in culture and this has been considered to be the cause of neurodegeneration that occurs in the Alzheimer disease brain. The discovery of compounds that prevent Abeta toxicity may lead to a better understanding of the processes involved and ultimately to possible therapeutic drugs. Low nanomolar concentrations of Abeta1-42 and the toxic fragment Abeta25-35 have been demonstrated to render cells more sensitive to subsequent insults as manifested by an increased sensitivity to formazan crystals following MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) reduction. Formation of the toxic beta-sheet conformation by Abeta peptides is increased by negatively charged membranes. Here we demonstrate that phloretin and exifone, dipolar compounds that decrease the effective negative charge of membranes, prevent association of Abeta1-40 and Abeta25-35 to negatively charged lipid vesicles and Abeta induced cell toxicity. These results suggest that Abeta toxicity is mediated through a nonspecific physicochemical interaction with cell membranes.

L-AP4 inhibition of depolarization-evoked cGMP formation in rat cerebellum

The effects of the group III mGluR agonist, L-2-amino-4-phosphonobutyrate (L-AP4), on depolarization-stimulated cGMP levels in adult rat cerebellar slices were determined. L-AP4 elicited a concentration-dependent, complete inhibition of cGMP formation stimulated by 4-aminopyridine (4-AP; 1 mM), yielding an IC50 value of 4.2 +/- 1.6 microM (n = 3). The 4-AP response was also reduced by the P-type Ca2+ channel toxins omega-conotoxin MVIIC (3 microM; 39 +/- 7% inhibition) and omega-Agatoxin IVA (30 nM; 53 +/- 4%), and was abolished in the absence of Ca2+ or in the presence of Co2+. The inhibitions of the 4-AP cGMP response by 10 microM L-AP4 and 30 nM omega-Agatoxin IVA were not additive, indicating that part of the actions of L-AP4 in the cerebellum involves the modulation of P-type Ca2+ channels.

4-substituted-3-phenylquinolin-2(1H)-ones: acidic and nonacidic glycine site N-methyl-D-aspartate antagonists with in vivo activity

4-Substituted-3-phenylquinolin-2(1H)-ones have been synthesized and evaluated in vitro for antagonist activity at the glycine site on the NMDA (N-methyl-D-aspartate) receptor and in vivo for anticonvulsant activity in the DBA/2 strain of mouse in an audiogenic seizure model. 4-Amino-3-phenylquinolin-2(1H)-one (3) is 40-fold lower in binding affinity but only 4-fold weaker as an anticonvulsant than the acidic 4-hydroxy compound 1. Methylsulfonylation at the 4-position of 3 gives an acidic compound (6, pKa = 6.0) where affinity is fully restored but in vivo potency is significantly reduced (Table 1). Methylation at the 4-position of 1 to give 18 results in the abolition of measurable affinity, but the attachment of neutral hydrogen bond-accepting groups to the methyl group of 18 produces compounds with comparable in vitro and in vivo activity to 1 (e.g., 23 and 28, Table 2). Replacement of the 4-hydroxy group of 1 with an ethyl group abolishes activity (42), but again, incorporation of neutral hydrogen bond acceptors to the terminal carbon atom restores affinity (e.g., 36, 39, and 40, Table 3). Replacement of the 4-hydroxy group of the high-affinity compound 2 with an amino group produces a compound with 200-fold reduced affinity (43; IC50 = 0.42 microM, Table 4) which is nevertheless still 10-fold higher in affinity than 3. The results in this paper indicate that anionic functionality is not an absolute requirement for good affinity at the glycine/NMDA site and provide compelling evidence for the existence of a ligand/receptor hydrogen bond interaction between an acceptor attached to the 4-position of the ligand and a hydrogen bond donor attached to the receptor.

In vitro propagation and inducible differentiation of multipotential progenitor cells from human fetal brain

Central nervous system neurons and glia arise from undifferentiated embryonic neuroepithelial cells. Such progenitor cells from the human fetal forebrain can be propagated in vitro for extended periods, when grown on non-adhesive substrates in medium containing epidermal growth factor and insulin-like growth factor-1. These actively-dividing cells can be induced to differentiate into a variety of histochemically-characterized neurons and glia consistent with their forebrain origin. Electrophysiological recording indicates that differentiated neurons derived from these progenitors mature slowly, and display a range of glutamate- and GABA-mediated conductances characteristic of normal mammalian forebrain neurons. Our observations support a role for these trophic factors in normal development of the human brain. The methods described here may provide abundant normal, untransformed human forebrain neurons and glia for research and therapeutic applications.

A novel mechanism of activity-dependent NMDA receptor antagonism describes the effect of ifenprodil in rat cultured cortical neurones

1. Ifenprodil is a selective, atypical non-competitive antagonist of NMDA receptors that contain the NR2B subunit with an undefined mechanism of action. Ifenprodil is neuroprotective in in vivo models of cerebral ischaemia but lacks many of the undesirable side-effects associated with NMDA antagonist. 2. Using whole-cell voltage-clamp recordings, we have studied the mechanism of inhibition of NMDA-evoked currents by ifenprodil in rat cultured cortical neurones in the presence of saturating concentrations of glycine. 3. Ifenprodil antagonized NMDA receptors in an activity-dependent manner, whilst also increasing the receptor affinity for glutamate recognition-site agonists. Ifenprodil inhibition curves against 10 and 100 microM NMDA-evoked currents yielded IC50 values of 0.88 and 0.17 microM, respectively. Thus, the apparent affinity of ifenprodil for the NMDA receptor is increased in an NMDA concentration-dependent manner. 4. Currents evoked by 0.3 and 1 microM NMDA were potentiated to approximately 200% of control levels in the presence of 3 microM ifenprodil. Thus, with increasing concentration of NMDA the effect of ifenprodil on NMDA-evoked currents changed from one of potentiation to one of increasing inhibition. 5. These results are predicted by a reaction scheme in which ifenprodil exhibits a 39- and 50-fold higher affinity for the agonist-bound activated and desensitized states of the NMDA receptor, respectively, relative to the resting, agonist-unbound state. Furthermore, ifenprodil binding to the NMDA receptor results in a 6-fold higher affinity for glutamate site agonists. 6. This represents a novel mechanism of NMDA receptor antagonism that, together with the subunit selectivity, probably contributes to the attractive neuropharmacological profile of this and related compounds.

Modulation of voltage-gated calcium channels by orphanin FQ in freshly dissociated hippocampal neurons

Orphanin FQ (OFQ) has recently been reported to be an endogenous ligand for the opioid-like LC132 receptor. The effect of OFQ on high voltage-gated calcium channels (VGCCs) was examined in freshly dissociated rat pyramidal neurons using the whole-cell configuration of the patch-clamp technique. High-threshold Ba2+ currents were reversibly inhibited by OFQ. The depression of the currents was associated with a slowed rate of activation and a change in the activation I-V relationship at step potentials higher than +30 mV. In concentration-response experiments, a mean (+/-SEM) pEC50 value of 7.0 +/- 0.07 and a Hill coefficient of 1.5 +/- 0.08 (n = 5) were obtained. The near-maximum inhibition of the Ba2+ currents by OFQ (1 microM) amounted to 31 +/- 2.2% of control (n = 15). Opioid receptors could not account for the effects of OFQ on VGCCs, because naloxone, a broad spectrum mu-, delta-, and kappa-receptor antagonist, did not reduce the effectiveness of OFQ. When GTP-gamma-S was included in the pipette, the depression of the currents by OFQ was irreversible, whereas currents from neurons preincubated with pertussis toxin were not inhibited by OFQ, consistent with the involvement of a PTX-sensitive G-protein. When selective blockers of VGCCs were used, it was demonstrated that all subtypes of VGCCs were affected by OFQ. In conclusion, the effect of OFQ on VGCCs expressed in hippocampal CA3 and CA1 neurons may play an important role in the regulation of hippocampal cell excitability and neurotransmitter release.

Beta-amyloid-induced cell toxicity: enhancement of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-dependent cell death

In an attempt to understand the cause of neurodegeneration in Alzheimer's disease, the toxic effects of beta-amyloid (Abeta) peptides have been widely studied. At high micromolar concentrations Abeta peptides have been demonstrated to be acutely toxic to various cell types. At submicromolar concentrations, Abeta peptides have been suggested to inhibit cellular metabolic activity, due to their inhibition of the ability of cells to metabolize the oxidoreductase substrate 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Here we show, first, that MTT reduction surprisingly leads to a breakdown in PC12 cell membrane integrity and cell death, presumably through the formation of a crystalline formazan product, and, second, that pretreatment of PC12 cells with nanomolar concentrations of Abeta peptide, rather than inhibiting their metabolic activity, increases the susceptibility of these cells to the secondary toxic effect of formazan crystal formation. These results suggest that low nanomolar concentrations of Abeta render membranes more susceptible to damage by a secondary insult, in this case, MTT reduction. It is plausible that such an effect, when combined with additional risk factors, could contribute to the neurodegeneration that occurs in Alzheimer's disease.

Electrophysiological characterisation of the antagonist properties of two novel NMDA receptor glycine site antagonists, L-695,902 and L-701,324

The pharmacological effects of two novel N-methyl-D-aspartate (NMDA) receptor glycine site antagonists, L-701,324 and L-695,902 were examined on whole-cell voltage-clamped cells and compared to a prototypic antagonist, 7-chlorokynurenic acid. Both L-701,324 and L-695,902 non-competitively antagonised NMDA responses elicited in rat cultured cortical neurones, this was shown to be due to a competitive interaction at the glycine co-agonist site on the receptor complex (Kb values: 19 nM and 2.6 microM, respectively). Inhibition curves for the antagonism of responses to combined applications of NMDA and glycine showed that both antagonists were devoid of any intrinsic activity i.e. "full" antagonists and were, therefore, capable of completely abolishing inward currents. Despite this fact, both of these novel antagonists apparently modulated glutamate affinity for its recognition site-a property hitherto associated only with glycine site partial agonists. Human recombinant NMDA receptors comprising NR1a/NR2A and NR1a/NR2B subunits expressed in mouse fibroblast cells were also used to determine whether L-701,324 and L-695,902 were capable of discriminating between subtypes of NMDA receptor. Inhibition curves to each antagonist showed no difference in affinity for either of these subunit assemblies (mK1 values L-701,324 = 0.005 microM on both assemblies; L-695,902 = 4.37 and 3.7 microM on NR1a/NR2A and NR1a/NR2B, respectively). Kinetic analysis of the off-rates of antagonism with L-701,324 revealed that the high affinity of this compound compared to 7-chlorokynurenic acid were attributable to an exceptionally slow dissociation of the antagonist from the receptor.

The neuroprotective effect of the glycine site antagonist 3R-(+)-cis-4-methyl-HA966 (L-687,414) in a rat model of focal ischaemia

3R-(+)-cis-4-Methyl-HA966 (L-687,414) is a novel and selective, low intrinsic activity, partial agonist at the glycine site of the N-methyl-D-aspartate (NMDA) receptor. Thus, while it acts primarily to block NMDA receptor function in the presence of glycine, it fails to produce a complete block of NMDA receptor activation. In this study, we have investigated its neuroprotective effects in a rat model of focal ischaemia, involving permanent occlusion of the left middle cerebral artery. L-687,414 was administered as a bolus dose of 17.6 mg/kg i.v. straight after the occlusion or as a bolus dose + infusion for 4 h. The doses of L-687,414 used for the infusion studies were 7 mg/kg i.v. + 7 mg/kg/h, 14 mg/kg + 14 mg/kg/h, or 30 mg/kg + 30 mg/kg/h. The 17.6-mg/kg dose gave an estimated peak plasma level of 24 micrograms/ml, which decayed with a t1/2 of 56 min. The three infusion dosing regimens gave mean plasma levels over the 4 h of 11, 25 and 61 micrograms/ml plasma, respectively. The 17.6-mg/kg dose of L-687,414 gave no significant protection against the volume of hemispheric, cortical, or caudate damage when compared with the control group of animals. The lowest infusion dosing regimen of L-687,414 which gave a plasma level of 11 micrograms/ml over the 4 h was also ineffective against the volume of infarction measured in the different brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of amino acids in the N-methyl-D-aspartate receptor NR1 subunit that contribute to the glycine binding site

The mammalian N-methyl-D-aspartate (NMDA) receptor complex is though to consist of an NR1 subunit in combination with one or more of the four NR2 subunits (A, B, C, and D). When corresponding cDNAs are expressed in Xenopus oocytes, ion channels with the characteristic profile of NMDA receptors are formed. The receptor is unique in requiring two coagonists, glutamate and glycine, for activation of the channel. We have used site-directed mutagenesis to study amino acids in the human NR1 subunit that contribute to the glycine binding site of the NMDA receptor without affecting the agonist site for glutamate. Mutations to D481 and K483 produced receptors with up to 160-fold lower affinities for glycine, as well as other agonists and partial agonists, without affecting maximum current size or the degree of agonist efficacy. The D481A mutation also led to 40-50-fold lower affinities for two structurally diverse glycine site antagonists. From these data we propose that the carboxyl group of this aspartate interacts with the amino moiety of glycine and the equivalent group contained in other agonists and antagonists.