ODP350 Safety and Efficacy of Tesomet over 48 Weeks of Treatment: Results From a 24-Week Phase 2, Randomized, Double-Blind Study With 24 Week Open-Label Extension in Adults With Hypothalamic Obesity

Objective

To assess the safety and efficacy of Tesomet (tesofensine plus metoprolol) in adults with hypothalamic obesity, a rare disease with no approved therapy.

Research Design and Methods

Twenty-one adults with hypothalamic obesity (16 females, 5 males) were randomized to Tesomet (0.5 mg tesofensine/50 mg metoprolol) (n=14) or placebo (n=8) during a 24-week double-blind period. On completion of the double-blind period, 17 (81%) subjects (11 Tesomet; 6 placebo) entered in to a 24-week open-label extension period and were treated with Tesomet. The primary endpoint was safety while secondary endpoints included measures of body weight, waist circumference, and body composition. Trial NCT03845075.

Results

The most common adverse events following the 24-week double-blind period and the 24-week open-label extension period were sleep disorder, dizziness, dry mouth, and headache; the majority of these adverse events were mild to moderate in severity. No significant nor clinically meaningful changes in heart rate or blood pressure were observed during the study. On completion of the double-blind period mean change in body weight (kg) was -7.84 for the Tesomet group versus -0.34 kg for the placebo group (P=0. 03). At the end of the open-label extension period mean change in body weight (kg) from baseline was -6.34 for the Tesomet-Tesomet group and -6. 03 for the placebo-Tesomet group. On completion of the double-blind period mean change in waist circumference (cm) was -7. 09 cm for the Tesomet group versus -1.16 for the placebo group (P=NS). At the end of the open-label extension period mean change in waist circumference (cm) from baseline was -5.73 for the Tesomet-Tesomet group and -3. 04 for the placebo-Tesomet group. On completion of the double-blind period mean change in fat mass (kg) was -5.28 for the Tesomet group versus -1.11 for the placebo group (P=NS). At the end of the open-label extension period mean change in fat mass (kg) from baseline was -4.84 for the Tesomet-Tesomet group and -3.85 for the placebo-Tesomet group. On completion of the double-blind period mean change in lean tissue mass (kg) was -2.76 for the Tesomet group versus 0.36 for the placebo group (P<0. 01). At the end of the open-label extension period mean change in lean mass (kg) from baseline was -1.64 for the Tesomet-Tesomet group and -2.22 for the placebo-Tesomet group.

Discussion

Tesomet was generally well tolerated after 48 weeks treatment and resulted in clinically meaningful improvements in body weight and body composition measures in adults with hypothalamic obesity. In contrast to previous studies of tesofensine monotherapy in general obesity, no significant nor clinically meaningful changes in cardiovascular measures were observed during the study.

Conclusion

Tesomet is a promising new experimental treatment for hypothalamic obesity. A randomized, placebo controlled, multi-center, dose-finding, Phase 2b study has now been initiated.

Presentation: No date and time listed

Randomized controlled trial of Tesomet for weight loss in hypothalamic obesity

CONTEXT

Hypothalamic injury often leads to rapid, intractable weight gain causing hypothalamic obesity, which is associated with increased risk of cardiovascular and metabolic morbidity and mortality. There are no approved or effective pharmacological treatments for hypothalamic obesity, and conventional lifestyle management remains ineffective.

OBJECTIVE

To investigate the safety and efficacy of Tesomet (0.5 mg tesofensine/50 mg metoprolol) in adults with hypothalamic obesity.

METHODS

Twenty-one adults with hypothalamic obesity (16 females) were randomized to Tesomet (0.5 mg/50 mg) or placebo for 24 weeks. Patients also received diet/lifestyle counselling. The primary endpoint was safety; secondary endpoints included measures of body weight, appetite scores, quality of life, and metabolic profile.

RESULTS

Eighteen patients completed 24 weeks. Consent withdrawal, eligibility, and serious adverse events (SAE) unrelated to treatment resulted in dropouts. One patient experienced a Tesomet-related SAE of exacerbated pre-existing anxiety leading to treatment discontinuation. Tesomet-related adverse events were otherwise mostly mild and included sleep disturbances (Tesomet 50%, placebo 13%), dry mouth (Tesomet 43%, placebo 0%), and headache (Tesomet 36%, placebo 0%). No significant differences in heart rate or blood pressure were observed between groups. Compared to placebo, Tesomet resulted in additional mean (95% CI) weight change of -6.3% ((-11.3; -1.3); P = 0.017), increased the number of patients achieving ≥5% weight loss (Tesomet 8/13, placebo 1/8; P = 0.046), and tended to augment the reduction in waist circumference by 5.7 cm ((-0.1; 11.5); P = 0.054).

CONCLUSION

Tesomet was welltolerated, did not affect heart rate or blood pressure, and resulted in significant reductions in body weight compared to placebo in adults with hypothalamic obesity.

Ontogenetic development of glutamate and GABA metabolizing enzymes in cultured cerebral cortex interneurons and in cerebral cortex in vivo

The development of the enzymes phosphate activated glutaminase (PAG), glutamate dehydrogenase (GLDH), glutamic-oxaloacetic-transaminase (GOT), glutamine synthetase (GS), GABA-transaminase (GABA-T) and ornithine-δ-aminotransferase (Orn-T) was followed in mouse cerebral cortex in vivo and in cultured mouse cerebral cortex interneurons. It was found that GLDH, GOT and Orn-T exhibited an enhanced developmental pattern in the cultured neurons compared to cerebral cortex. The activities of PAG and GABA-T developed in parallel in vivo and in culture but the activity of GS remained low in the cultured neurons compared to the increasing activity of this enzyme found in vivo. Compared to cerebral cortex the cultured neurons exhibited higher activities of PAG, GLDH and Orn-T, whereas the activities of GABA-T and GOT were lower in the cultured cells. The activity of GS in the cultured neurons was only 5-10% of the activity in cerebral cortex in vivo. It is concluded that neurons from cerebral cortex represent a reliable model system by which the metabolism and function of GABAergic neurons can be conveniently studied in a physiologically meaningful way.

Postnatal development of glutamate metabolizing enzymes in hippocampus from mice

The specific activity profiles of the glutamate synthesizing enzymes, phosphate activated glutaminase (EC 3.5.1.2), aspartate aminotransferase (EC 2.6.1.1), glutamate dehydrogenase (EC 1.4.1.2) and ornithine aminotransferase (EC 2.6.1.13) have been followed postnatally for 28 days in mouse hippocampus and compared to corresponding profiles in cerebellum and cerebral cortex (cf. refs 10 and 18). Phosphate activated glutaminase and glutamate dehydrogenase showed activity patterns similar to those found for cerebellum and glutamatergic granula cells cultured from cerebellum, whereas the aspartate aminotransferase activity pattern was found to be more similar to that previously observed for cerebral cortex as well as cultured cerebral interneurons which are likely to be GABAergic. The specific activity of ornithine aminotransferase was essentially unaltered during postnatal development, which is similar to what has been found for cerebellum and cerebral cortex.

Adenosine inhibits glutamate stimulated [(3)H]d-aspartate release from cerebellar granule cells

The release of [(3)H]d-aspartate from cultured cerebellar granule cells (a glutamatergic neuron) was studied. It was found that the l-glutamate induced stimulation of [(3)H]d-aspartate release from the neurons could be decreased 30-40% by adenosine, cyclohexyladenosine and (?)N(6)-(2-phenylisopropyl)-adenosine all in the dose range 1-10 ?M. The effects of adenosine agonists could be blocked and even reversed by the adenosine antagonist theophyllin indicating a possible endogenous adenosine tonus on the neurons. The results add further evidence to the notion that adenosine A(1) receptors present on parallel fiber terminals in the cerebellar cortex are involved in the regulation of glutamate transmitter release from the nerve terminals.

NS 1231, a novel compound with neurotrophic-like effects in vitro and in vivo

NS 1231 [5-(4-chlorophenyl)-6,7,8,9-tetrahydro-1H-pyrrolo-[3.2-h]naphthalene-2,3-dione-3-oxime] belongs to a chemical series of compounds, which exhibit neurotrophic-like activities. In vitro, NS 1231 rescued nerve growth factor (NGF)-differentiated PC12 cells from death induced by withdrawal of trophic factors. In addition, NS 1231 stimulated NGF-induced neurite outgrowth of undifferentiated PC12 cells. At the molecular level, NS 1231 enhanced NGF-induced signalling events, such as TrkA phosphorylation at the Shc-binding site Tyr490 as well as ERK activation in PC12 cells. Moreover, NS 1231 reduced NMDA-induced excitotoxicity in organotypic hippocampal slice cultures. In a gerbil model of transient global ischaemia, treatment with NS 1231 reduced the delayed loss of neurons in the hippocampal CA1 layer. Furthermore, NS 1231 treatment resulted in a 43% reduction in total infarct volume in the mouse middle cerebral artery occlusion (MCAO) model. The present data thus implicate a therapeutic potential of NS 1231 or structural analogues in treatment of cerebral ischaemia.

NS-417, a novel compound with neurotrophic-like effects

NS-417 (5-(4-Chlorophenyl)-8-methyl-6-7-8-9-tetrahydro-1-H-pyrrolo[3.2-h]isoquinoline-2,3-dione-3-oxim hydrochloric acid salt) belongs to a new chemical series of compounds. NS-417 rescued differentiated PC12 cells from death induced by withdrawal of serum and nerve growth factor. Furthermore, NS-417 stimulated neurotrophic factor-induced neurite outgrowth in undifferentiated PC12 cells. In accordance with this observation, NS-417 potentiated NGF-induced signaling, such as activation of the extracellular signal-regulated kinases ERK1 and ERK2 and the Akt kinase. NS-417 also enhanced ERK activation induced by 10 minutes stimulation with NGF, bFGF or EGF in PC12 cells. In addition to the effect in PC12 cells, NS-417 increased the number of tyrosine hydroxylase (TH) positive cells in cultures established from dissociated E14 rat ventral mesencephali.

Neuroprotection by a novel compound, NS521

NS521 (1-(1-butyl)-4-(2-oxo-1-benzimidazolinyl)piperidine) belongs to a group of novel benzimidazolones, which exhibit neurotrophic-like activities. In vitro, NS521 rescued neuronal PC12 cells from death induced by serum and nerve growth factor deprivation. The survival effect of NS521 appeared to reflect a delay of the apoptotic process, because the extent of DNA fragmentation was attenuated transiently by NS521. NS521 did not preserve the neurites of the rescued cells, which, otherwise, appeared to be healthy and were able to regenerate when serum and nerve growth factor were added back to the culture. In vivo, NS521 provided significant protection against the delayed loss of hippocampal CA1 neurons in a gerbil model of transient global ischemia. A neuroprotective effect of NS521 in the peripheral nervous system also was observed in rats after transection of the sciatic nerve, where daily treatment with NS521 was found to inhibit retrograde degeneration of the transected nerve. The neuroprotective effect of NS521 is unlikely to be mediated through neurotrophin receptors, such as TrkA, because NS521 did not induce phosphorylation of the 44- and 42-kDa isoforms of mitogen-activated protein kinases (ERK1/2) in PC12 cells.

SPD 502: a water-soluble and in vivo long-lasting AMPA antagonist with neuroprotective activity

Accumulating preclinical data suggest that compounds that block the excitatory effect of glutamate on excitatory amino acid receptors may have neuroprotective effects and utility for the treatment of neurodegeneration after brain ischemia. In the present study, the in vitro and in vivo pharmacological properties of the novel glutamate antagonist SPD 502 [8-methyl-5(4-(N,N-dimethylsulfamoyl)phenyl)-6,7, 8,9,-tetrahydro-1H-pyrrolo[3,2-h]-isoquinoline-2, 3-dione-3-O-(4-hydroxybutyric acid-2-yl)oxime] are described. In binding studies, SPD 502 was shown to display selectivity for the [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-binding site (IC50 = 0.043 microM) compared with the [3H]kainate- (IC50 = 81 microM), [3H]cis-4-phosphonomethyl-2-piperidine carboxylic acid-(CGS 19755), and [3H]glycine-binding sites (IC50 > 30 microM) in rat cortical membranes. In an in vitro functional assay, SPD 502 blocked the AMPA-induced release of [3H]gamma-aminobutyric acid from cultured mouse cortical neurons in a competitive manner with an IC50 value of 0.23 microM. Furthermore, SPD 502 potently and selectively inhibited AMPA-induced currents in cortical neurons with an IC50 value of 0.15 microM. In in vivo electrophysiology, SPD 502 blocked AMPA-evoked spike activity in rat hippocampus after i.v. administration with an ED50 value of 6.1 mg/kg and with a duration of action of more than 1 h. Furthermore, SPD 502 increased the seizure threshold for electroshock-induced tonic seizures in mice at i.v doses of 40 mg/kg and higher. In the two-vessel occlusion model of transient forebrain ischemia in gerbils, SPD 502 (10 mg/kg bolus injection followed by a 10 mg/kg/h infusion for 2 h) resulted in a highly significant protection against the ischemia-induced damage in the hippocampal CA1 pyramidal neurons.

Characterization of NS 2028 as a specific inhibitor of soluble guanylyl cyclase

1 The haeme-containing soluble guanylyl cyclase (alpha1beta1-heterodimer) is a major intracellular receptor and effector for nitric oxide (NO) and carbon monoxide (CO) and mediates many of their biological actions by increasing cyclic GMP. We have synthesized new oxadiazolo-benz-oxazins and have assessed their inhibitory actions on guanylyl cyclase activity in vitro, on the formation of cyclic GMP in cultured cells and on the NO-dependent relaxation of vascular and non-vascular smooth muscle. 2 Soluble guanylyl cyclase, purified to homogeneity from bovine lung, was inhibited by 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028) in a concentration-dependent and irreversible manner (IC50 30 nM for basal and 200 nM for NO-stimulated enzyme activity). Evaluation of the inhibition kinetics according to Kitz & Wilson yielded a value of 8 nM for Ki, the equilibrium constant describing the initial reversible reaction between inhibitor and enzyme, and 0.2 min(-1) for the rate constant k3 of the subsequent irreversible inhibition. Inhibition was accompanied by a shift in the soret absorption maximum of the enzyme's haem cofactor from 430 to 390 nm. 3 S-nitroso-glutathione-enhanced soluble guanylyl cyclase activity in homogenates of mouse cerebellum was inhibited by NS 2028 (IC50 17 nM) and by 17 structural analogues in a similar manner, albeit with different potency, depending on the type of substitution at positions 1, 7 and 8 of the benzoxazin structure. Small electronegative ligands such as Br and Cl at position 7 or 8 increased and substitution of the oxygen at position 1 by -S-,- NH- or -CH2- decreased the inhibition. 4 In tissue slices prepared from mouse cerebellum, neuronal NO synthase-dependent activation of soluble guanylyl cyclase by the glutamate receptor agonist N-methyl-D-aspartate was inhibited by NS 2028 (IC50 20 nM) and by two of its analogues. Similarly, 3-morpholino-sydnonimine (SIN-1)-elicited formation of cyclic GMP in human cultured umbilical vein endothelial cells was inhibited by NS 2028 (IC50 30 nM). 5 In prostaglandin F2alpha-constricted, endothelium-intact porcine coronary arteries NS 2028 elicited a concentration-dependent increase (65%) in contractile tone (EC50 170 nM), which was abolished by removal of the endothelium. NS 2028 (1 microM) suppressed the relaxant response to nitroglycerin from 88.3+/-2.1 to 26.8+/-6.4% and induced a 9 fold rightward shift (EC50 15 microM) of the concentration-relaxation response curve to nitroglycerin. It abolished the relaxation to sodium nitroprusside (1 microM), but did not affect the vasorelaxation to the KATP channel opener cromakalim. Approximately 50% of the relaxant response to sodium nitroprusside was recovered after 2 h washout of NS 2028. 6 In phenylephrine-preconstricted, endothelium-denuded aorta of the rabbit NS 2028 (1 microM) did not affect relaxant responses to atrial natriuretic factor, an activator of particulate guanylyl cyclase, or forskolin, an activator of adenylyl cyclase. 7 NO-dependent relaxant responses in non-vascular smooth muscle were also inhibited by NS 2028. The nitroglycerin-induced relaxation of guinea-pig trachea preconstricted by histamine was fully inhibited by NS 2028 (1 microM), whereas the relaxations to terbutaline, theophylline and vasoactive intestinal polypeptide (VIP) were not affected. The relaxant responses to electrical field stimulation of non-adrenergic, non-cholinergic nerves in the same tissue were attenuated by 50% in the presence of NS 2028 (1 microM). 8 NS 2028 and its analogues, one of which is the previously characterized 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), appear to be potent and specific inhibitors of soluble guanylyl cyclase present in various cell types. Oxidation and/or a change in the coordination of the haeme-iron of guanylyl cyclase is a likely inhibitory mechanism.

Pharmacological characterisation of voltage-sensitive calcium channels and neurotransmitter release from mouse cerebellar granule cells in culture

Using subtype-specific Ca-channel blockers, we have characterised the voltage-sensitive Ca2+ currents as well as neurotransmitter release from cultured mouse cerebellar granule cells. The whole cell version of the patch clamp technique was adapted to monitor the isolated Ca-channel currents. The currents were activated at potentials more positive than -40 mV and were composed of at least four pharmacological distinct components being sensitive to nifedipine (35%), omega-conotoxin GVIA (10%), and omega-agatoxin IVA (42%) corresponding to L-, N-, and P-channel-mediated currents. The insensitive fraction (13%) possibly represented R channels. High potassium-evoked release of 3H-D-aspartate was used as a model of synaptic release. These studies were performed at relatively mild stimulation conditions (30 mM K+, 0.4 mM Ca2+), and 85% of the evoked release was Ca2+ dependent as well as tetrodotoxin and Cd2+ sensitive. Nifedipine and omega-agatoxin IVA dose dependently (IC50 values of 10 nM and 0.7 nM, respectively) blocked most of the release, whereas omega-conotoxin MVIIA (IC50 = 5 nM) caused partial blockage. The results indicate that several subtypes of voltage-sensitive Ca channels are present in mouse cerebellar granule cells. Furthermore, the data suggest that L, N, and P channels act in concert in the neurotransmitter release process.

Selective reduction in domoic acid toxicity in vivo by a novel non-N-methyl-D-aspartate receptor antagonist

Our objective was to characterize the neurotoxic actions of systemically administered domoic acid on different excitatory amino acid receptors, and to compare the receptor selectivity of domoate with the related compound kainic acid. Groups of mice were injected with various ligands selective for N-methyl-D-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid-kainate (AMPA/kainate) receptors prior to injection of equitoxic doses of domoic acid or kainic acid. Domoic acid toxicity was not significantly altered by pretreatment with any NMDA receptor selective antagonists, with the exception of 3-(2-carboxypiperazine-4-yl)propyl-1 -phosphonic acid. Consistent with its characterization as an AMPA/kainate agonist, domoate toxicity was significantly antagonized by all non-NMDA receptor antagonists tested. Non-NMDA receptor antagonists that do not distinguish between high- and low-affinity [3H]kainic acid binding (i.e., quinoxalinediones) were equally effective at reducing domoic acid and kainic acid toxicity. However, the novel isatinoxime NS-102, which has been shown to interact selectively with low-affinity [3H]kainic acid binding sites, produced a selective dose-related antagonism of domoic acid toxicity relative to kainic acid. NS-102 produced significant reductions in overall toxicity, onset of motor seizures, and hippocampal CA3 cell damage induced by domoic acid at NS-102 doses that did not antagonize kainic acid induced toxicity. We conclude that domoic acid toxicity in vivo is mediated largely by a subclass of non-NMDA receptors that are selectively antagonized by NS-102.

Evaluation of the importance of transamination versus deamination in astrocytic metabolism of [U-13C]glutamate

Glutamate metabolism was studied in primary cultures of cerebral cortical astrocytes to determine the significance of transamination for the oxidative metabolism of glutamate. Cultures were incubated with [U-13C]glutamate (0.5 mM) in the presence and absence of the transaminase inhibitor aminooxyacetic acid (AOAA) and in some cases with methionine sulfoximine, an inhibitor of glutamine synthetase. Perchloric acid extracts of the cells as well as redissolved lyophilized incubation media were subjected to nuclear magnetic resonance spectroscopy to identify 13C-labeled metabolites. Additionally, biochemical analyses were performed to quantify amino acids, lactate, citrate, and ammonia. Glutamine released into the medium and intracellular glutamate were labeled uniformly to a large extent, but the C-3 position showed not only the expected apparent triplet but also a doublet due to 12C incorporation into the C-4 and C-5 positions. Incorporation of 12C into the C-4 and C-5 positions of glutamate and glutamine as well as labeling of lactate, citrate, malate, and aspartate could only arise via metabolism of [U-13C]glutamate through the tricarboxylic acid (TCA) cycle. Entry of the carbon skeleton of glutamate into the TCA cycle must proceed via 2-oxoglutarate. This conversion can occur as a transamination or an oxidative deamination. After blocking transamination with AOAA, metabolism of glutamate through the TCA cycle was still taking place since lactate labeling was only slightly reduced. Glutamate and glutamine synthesis from 2-oxoglutarate could, however, not be detected under this condition. It therefore appears that while glutamate dehydrogenase is important for glutamate degradation, glutamate biosynthesis occurs mainly as a transamination.

Characterization of a chemical anoxia model in cerebellar granule neurons using sodium azide: protection by nifedipine and MK-801

Induction of chemical anoxia, using sodium azide in cerebellar granule cells maintained in primary culture, was evaluated as an in vitro assay for screening of potential neuroprotective compounds. The purpose of this study was to evaluate sodium azide as an alternative to cyanide salts, compounds which, despite their unfavorable characteristics, are often used in assays for chemical anoxia. The viability of neuronal cultures after treatment with azide, with or without preincubation with calcium channel blockers, tetrodotoxin (TTX), or glutamate receptor antagonists, was monitored by subsequent incubation with the tetrazolium dye MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), followed by isopropanol extraction and spectrophotometric quantification of cellularly reduced MTT. The azide-induced degeneration of neurons was shown to be dependent on the concentration as well as on the duration of incubation with submaximal concentrations of azide. Incubation of the neurons with nifedipine, a blocker of L-type voltage-sensitive calcium channels (L-VSCC), or with the noncompetitive N-methyl-D-aspartate (NMDA) subtype glutamate receptor antagonist MK-801, prior to addition of submaximal concentrations of azide, significantly attenuated azide-induced neuronal death. Blockers of N-type and Q-type VSCC (omega-conotoxin MVIIA and MVIIC, respectively) and the P-type VSCC blocker omega-agatoxin IVA had no effect in this assay. The sodium channel blocker TTX was without effect when added to neurons under depolarizing conditions, but potently and effectively protected cells when experiments were performed in a nondepolarizing buffer. The results show that chemical anoxia induced by incubation of cultured neurons with azide leads to detrimental effects, which may be quantitatively monitored by the capability of the cells to reduce MTT. This procedure is a suitable method for screening of compounds for possible protective effects against neuronal death induced by energy depletion. In addition, the results suggest involvement of L-type VSCC as well as of glutamate receptors in the pathways leading to neuronal degradation induced by energy depletion in cerebellar granule neurons. This would further support the notion that these pathways might be important in neurodegeneration induced by cerebral ischemia or anoxia.

Pharmacological profile and anti-ischemic properties of the Ca(2+)-channel blocker NS-638

Included in the sequence of events leading to neuronal death in ischemic tissue following stroke is an excessive and toxic rise in the intracellular Ca(2+)-concentration, predominantly due to an influx of Ca2+ through nonselective cation-channels as well as Ca(2+)-channels. In the present study we have characterized the pharmacological profile and anti-ischemic effects of 2-amino-1-(4-chlorobenzyl)-5-trifluoromethylbenzimidazole (NS-638), a small nonpeptide molecule with Ca(2+)-channel blocking properties. NS-638 dose dependently inhibited K(+)-stimulated [45Ca2+]-uptake in chick cortical synaptosomes and 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA)-stimulated [3H]GABA-release from cultured cortical neurons with IC50 values of 2.3 and 4.3 microM, respectively. K(+)-stimulated intracellular Ca(2+)-elevation in cultured cerebellar granule cells was equipotently blocked with an IC50 value of 3.4 microM. At this concentration no effect on Ca(2+)-induced contractions in K(+)-depolarized guinea pig taenia coli was observed. The effect of NS-638 on neuronal Ca(2+)-channels was evaluated using whole cell patch clamp techniques. The compound reversibly blocked N- and L-type Ca(2+)-channels in cultured chick dorsal root ganglion cells in the concentration range of 1-30 microM. In the mouse middle cerebral artery occlusion (MCAO) model, NS-638 administered i.p. (50 mg kg-1) at 1 h and 6 h post-ischemia, and once a day for the next two days, resulted in a 48% reduction in total infarct volume. The compound did not show protection against ischemic neuronal damage in the gerbil model of bilateral carotid artery occlusion (BCAO). This data suggests, that neuronal Ca(2+)-channel blockers may have potential in ameliorating the pathological damage after focal ischemia.

Characterization of the binding of [3H]NS 257, a novel competitive AMPA receptor antagonist, to rat brain membranes and brain sections

The binding of [3H]NS 257 (1,2,3,6,7,8-hexahydro-3-(hydroxyimino)-N,N-[3H]dimethyl-7-methyl- 2- oxobenzo[2,1-b:3,4-c']dipyrrole-5-sulfonamide) to rat cortical membranes was characterized in the absence and presence of thiocyanate. Specific [3H]NS 257 binding was saturable and reversible, and the stimulating effect of thiocyanate on binding was optimal at 100 mM. In the presence of thiocyanate [3H]NS 257 bound to a single population of binding sites with an affinity of 225 +/- 8 nM and a binding site density of 0.61 +/- 0.04 pmol/mg of original tissue. Thiocyanate increased the affinity of the binding site labeled by [3H]NS 257 for both alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and L-glutamate by a factor of 20 and 5, respectively. However, the affinity of the agonist domoate and the antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline (NBQX) was decreased in the presence of thiocyanate. Apparently, the affinities of antagonists as well as agonists for the AMPA receptor can be either increased or decreased by thiocyanate. The rank order of potency of the putative agonists quisqualate > AMPA > L-glutamate > domoate > kainate and of the antagonists NBQX > CNQX is consistent with the labeling of AMPA receptors. Autoradiographic studies showed that the distribution of [3H]NS 257 binding sites in rat brain was similar to that of [3H]AMPA binding sites. NS 257 is the first AMPA antagonist to be described showing an increased affinity for the AMPA receptor in the presence of thiocyanate.

Low-field MR imaging of the spine. A comparative study of a traditional and a new, completely balanced gradient-echo sequence

PURPOSE

To evaluate a new steady-state sequence in the delineation of the various structures in the spine at low-field MR imaging with a very high homogeneity of the main field.

METHODS

49 patients underwent 53 examinations with both a traditional T1-weighted gradient-echo (PS) sequence and a new completely balanced steady-state 3-D (CBASS3D) sequence; 20 examinations included the cervical spine, 8 the thoracic spine and 25 the lumbar spine. All 106 examinations were reviewed twice regarding visibility of selected structures in the spinal region and diagnostic usefulness.

RESULTS

The CBASS3D sequence delineated the medulla, nerve roots, CSF, the intervertebral discs and the posterior longitudinal ligament significantly better than the PS sequence. Disc hernia was also better visualised (p < 0.01). There were significantly more artefacts on images obtained with the CBASS3D sequence, but they were usually outside the region of interest and occurred less frequently over time due to increased experience of the staff. Both reviewers found the diagnostic usefulness of CBASS3D to be superior compared to that of PS and excellent for diagnostic purposes.

CONCLUSION

The CBASS3D sequence is a considerable improvement in the visualisation of degenerative changes of the spine at low-field MR imaging.

Selective block of recombinant glur6 receptors by NS-102, a novel non-NMDA receptor antagonist

The diversity of neuronal glutamate receptors continues to increase with the discovery of multiple subunits and subunit families. The significance of this potential receptor heterogeneity is unknown because pharmacological tools that could clearly distinguish between different structural isoforms have not yet been identified. A novel glutamate receptor antagonist, 5-nitro-6,7,8,9-tetrahydrobenzo[g]indole-2,3-dione-3-oxime (NS-102), has been shown previously to selectively block the low affinity [3H]kainate binding site in rat brain. We have examined the effect of NS-102 on receptors expressed in fibroblasts from either glur6 subunits or a combination of glurB and glurD (glurB/D receptors). NS-102 (3 microM) reduced currents mediated by glur6 receptors and had very little effect on currents mediated by glurB/D receptors. The binding of [3H]kainate to glur6 receptors showed properties similar to those of the brain low affinity [3H]kainate binding site, and NS-102 inhibited specific binding to glur6 receptors with a potency nearly identical to those sites in brain membranes. Our findings suggest that NS-102 will be useful in identifying the functional role of native receptors containing a glur6 subunit.

NS 004--an activator of Ca(2+)-dependent K+ channels in cerebellar granule cells

The large-conductance Ca(2+)-dependent K+ channels or BK channels in cerebellar granule cells were studied by patch-clamp technique, and the effects on channel activity of the molecule NS 004 (1-(2-hydroxy-5-chlorophenyl)-5-trifluoromethyl-2- benzimidazolone) were investigated. The channels had a unit conductance of 187 pS, were blocked by charybdotoxin and activated by internal Ca2+. NS 004 (10-30 microM) significantly increased the single channel opening frequency as well as the mean open time. In whole-cell recordings the compound shifted the BK current-voltage relationship by up to 40 mV towards negative membrane potentials. NS 004 is an efficient BK channel opener, which may represent a novel approach to relaxation of neuronal cells expressing this type of K+ channel.

Selective activation of Ca(2+)-dependent K+ channels by novel benzimidazolone

Activators and blockers of specific ion channels are important pharmacological tools for characterizing ion channels and their influence on cell function. The large-conductance Ca(2+)-dependent K+ channel (BK channel) is blocked by peptides such as charybdotoxin and iberiotoxin, but no selective activator of the channel has been described. Here we report single-channel and whole-cell patch-clamp experiments on the specific activation of BK channels in aortic smooth muscle cells with a new heterocyclic molecule, NS 1619 (1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl- 2(3H)benzimidazolone). The effect of NS 1619 on the BK channel was dose-dependent, resulting in a shift of the activation curve by up to -50 mV towards negative membrane potentials. The effect was fully reversible and was antagonized by charybdotoxin as well as by tetraethylammonium ions. The compound hyperpolarized the smooth muscle cells. NS 1619 is a selective and new type of K+ channel activator, which may significantly modulate cell excitability.

A novel non-NMDA receptor antagonist shows selective displacement of low-affinity [3H]kainate binding

5-Nitro-6,7,8,9-tetrahydrobenzo[G]indole-2,3-dione-3-oxime (NS-102), a new competitive glutamate receptor antagonist displaced binding to non-N-methyl-D-aspartate (non-NMDA) binding sites with no activity at the NMDA and strychnine-insensitive glycine binding sites. Under experimental conditions in which both high- and low-affinity sites were labelled, NS-102 only partially inhibited the binding of [3H]kainate. Studies of NS-102 displacement of high-affinity versus low-affinity [3H]kainate binding showed a high selectivity of NS-102 for the low-affinity [3H]kainate binding site (Ki = 0.6 microM) compared to the high-affinity [3H]kainate binding site (Ki > 10 microM). NS-102 was a relatively weak inhibitor of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) binding (IC50 = 7.2 microM). NS-102 and related compounds with similar pharmacological profiles may become valuable tools in the characterization of the functional importance of the low-affinity [3H]kainate binding site.

Development of binding sites for excitatory amino acids in cultured cerebral cortex neurons

Binding of [3H]glutamate, [3H]AMPA (RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazolo-propionate) and [3H]kainate was investigated in membranes prepared from cerebral cortex of 4-day-old and adult mice and from cerebral cortex neurons cultured for different periods of time (2, 4, 8 and 14 days). For all ligands, the number of binding sites increased as a function of development both in vivo and in culture. A significant number of binding sites for the ligands could be demonstrated on the cultured neurons already after 2 days in culture. Scatchard analysis of the binding data showed a single population of binding sites for glutamate (KD approximately 200 nM) and kainate (approximately 6 nM) regardless of the developmental stage in vivo or in culture. In case of [3H] AMPA binding two binding sites with KD values of approximately 6 nM and 100-200 nM could be demonstrated both in vivo and in culture. Binding of [3H]glutamate to cultured neurons could be displaced by N-methyl-D-aspartate (100 microM) and quisqualate (3 microM) in an additive manner but D,L-4-aminophosphonobutyrate (100 microM) had no effect. AMPA binding to cultured neurons was much more (40-fold) sensitive than kainate binding to the newly developed AMPA selective antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline) indicating that kainate and AMPA bind to independent binding sites. Monitoring membrane potentials in the cultured neurons using the lipophilic cation TPP+ (tetraphenylphosphonium) it was demonstrated that potassium (55 mM) as well as glutamate, AMPA and kainate (100 microM) could depolarize the neurons both at early (2 days) and late (9 days) developmental stages in culture. The demonstration of functionally active receptors for the 3 excitatory amino acids in both immature (2 days in culture) and mature (8-9 days in culture) neurons is discussed in the light of previous studies of the development as a function of the culture period of effects of excitatory amino acids in neurons. It is concluded that no simple correlation exists between expression of binding sites for the excitatory amino acids and their ability to induce cytotoxicity and neurotransmitter release.

Autoradiographic characterization and localization of quisqualate binding sites in rat brain using the antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione: comparison with (R,S)-[3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites

Using quantitative autoradiography, we have investigated the binding sites for the potent competitive non-N-methyl-D-aspartate (non-NMDA) glutamate receptor antagonist [3H]6-cyano-7-nitro-quinoxaline-2,3-dione ([3H]-CNQX) in rat brain sections. [3H]CNQX binding was regionally distributed, with the highest levels of binding present in hippocampus in the stratum radiatum of CA1, stratum lucidum of CA3, and molecular layer of dentate gyrus. Scatchard analysis of [3H]CNQX binding in the cerebellar molecular layer revealed an apparent single binding site with a KD = 67 +/- 9.0 nM and Bmax = 3.56 +/- 0.34 pmol/mg protein. In displacement studies, quisqualate, L-glutamate, and kainate also appeared to bind to a single class of sites. However, (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) displacement of [3H]CNQX binding revealed two binding sites in the cerebellar molecular layer. Binding of [3H]AMPA to quisqualate receptors in the presence of potassium thiocyanate produced curvilinear Scatchard plots. The curves could be resolved into two binding sites with KD1 = 9.0 +/- 3.5 nM, Bmax = 0.15 +/- 0.05 pmol/mg protein, KD2 = 278 +/- 50 nM, and Bmax = 1.54 +/- 0.20 pmol/mg protein. The heterogeneous anatomical distribution of [3H]CNQX binding sites correlated to the binding of L-[3H]glutamate to quisqualate receptors and to sites labeled with [3H]AMPA. These results suggest that the non-NMDA glutamate receptor antagonist [3H]CNQX binds with equal affinity to two states of quisqualate receptors which have different affinities for the agonist [3H]AMPA.

A potent antagonist of the strychnine insensitive glycine receptor has anticonvulsant properties

5.7-Dinitro-quinoxaline-2.3-dione (MNQX) displaced [3H]glycine binding to cortical membranes but had no effect n [3H]3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid ([3H]CPP) binding. MNQX potently antagonized N-methyl-D-aspartate (NMDA)-evoked release of [3H]GABA from cultured cortical neurones, NMDA evoked spreading depression and NMDA depolarizations in the rat neo-cortex. All of these responses were reversed by addition of glycine to the perfusion media. These results suggested that MNQX is an antagonist at the strychnine-insensitive glycine receptor associated with the NMDA receptor/ionophore complex. Furthermore the compound was found to antagonise audiogenic seizures in DBA-2 mice indicating the potential of glycine antagonists of this type in anticonvulsant therapy.

Glutamate-induced 45Ca2+ uptake into immature cerebral cortex neurons shows a distinct pharmacological profile

Glutamate-induced 45Ca2+ uptake was studied in cerebral cortex neurons cultured for 4 days, i.e., at a developmental stage where the neurons are sensitive to the mixed agonist glutamate but not to the actions of N-methyl-D-aspartate or other excitatory amino acids. Using this experimental approach, allowing the investigation of effects elicited only by glutamate, it was demonstrated that the glutamate-stimulated Ca2+ influx could be completely antagonized by MK-801, phencyclidine, and cyclazocine in the nanomolar range, and by 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate and D-2-amino-5-phosphonopentanoate (APV) in the low micromolar range. However, the glutamate response was unaffected by variations in the Mg2+ concentration in the exposure media. In addition, the two quinoxalinediones 6-cyano-7-nitroquinoxaline-2,3-dione and 6,7-dinitroquinoxaline-2,3-dione were equipotent with APV in blocking the glutamate-stimulated Ca2+ uptake. PK 26124 blocked the response in the high micromolar concentration range. Ketamine and gamma-glutamylaminomethylsulfonate were essentially without effect at concentrations up to 10 microM and 300 microM, respectively. These results may suggest the existence of a glutamate receptor with a pharmacological profile not compatible with the existent classification of glutamate receptor subtypes.

Glutamate-induced increase in intracellular Ca2+ in cerebral cortex neurons is transient in immature cells but permanent in mature cells

The free cytosolic Ca2+ concentration ([Ca2+]i) of cultured cerebral cortex neurons was determined using a fluorescent Ca2+ chelator (Fluo-3) after exposure of the neurons to glutamate. Mature neurons (8 days in culture) responded within 45 s to 100 microM glutamate by an increase in [Ca2+]i from 75 to 340 nM, an increase that during the following 6 min of exposure reached 400 nM. This increase in [Ca2+]i could not be reversed by removal of glutamate. In the absence of extracellular CaCl2, only part of the initial, rapid, glutamate-induced increase in [Ca2+]i was observed in these neurons. In contrast to these findings, neurons cultured for only 2 days (immature neurons) exhibited only a small (from 75 to 173 nM) increase in [Ca2+]i after exposure to 100 microM glutamate, and this rapid increase in [Ca2+]i tended to decline on prolonged exposure to glutamate. Moreover, after removal of glutamate, the increase in [Ca2+]i was fully reversible. Pharmacological characterization of the response to glutamate in mature neurons showed that the N-methyl-D-aspartate (NMDA) receptor antagonists phencyclidine and D-2-amino-5-phosphonovalerate phosphonovalerate blocked 75 and 90%, respectively, of the response, whereas the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione had little effect.

Evidence for evoked release of adenosine and glutamate from cultured cerebellar granule cells

Evoked release of [3H]-D-aspartate which labels the neurotransmitter glutamate pool in cultured cerebellar granule cells was compared with evoked release of adenosine from similar cultures. It was found that both adenosine and [3H]-D-aspartate could be released from the neurons in a calcium dependent manner after depolarization of the cells with either 10-100 microM glutamate or 50 mM KCl. Cultures of cerebellar granule cells treated with 50 microM kainate to eliminate GABAergic neurons behaved in the same way. This together with the observation that cultured astrocytes did not exhibit a calcium dependent, potassium stimulated adenosine release strongly suggest that cerebellar granule cells release adenosine in a neurotransmitter-like fashion together with glutamate which is the classical neurotransmitter of these neurons. Studies of the metabolism of adenosine showed that in the granule cells adenosine is rapidly metabolized to ATP, ADP, and AMP, but in spite of this, adenosine was found to be released preferential to ATP.

Molecular target size analyses of the NMDA-receptor complex in rat cortex

The molecular weights of different subunits of the NMDA-receptor complex were determined by high-energy radiation inactivation analyses of the binding of [3H]L-glutamate, [3H](3-(+/-)-2-(carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), [3H]N-(1-[2-thienyl]cyclohexyl)3,4-piperidine (TCP) and [3H]glycine to rat cortical membranes. The molecular target sizes of [3H]L-glutamate binding (the recognition site), [3H]TCP binding (the ionophore) and [3H]glycine (a modulatory unit) were similar: 121,000, 118,000 and 115,000 Da, respectively. These results suggest that the three subunits are on the same protein. The molecular weight of [3H]CPP binding was 209,000 Da. This suggests that in order to bind [3H]CPP (a competitive antagonist) with high affinity an additional macromolecule may be associated to the agonist site.

Selection of a pure cerebellar granule cell culture by kainate treatment

Chronic exposure of dissociated cerebellar cultures to 50 microM kainate results in a complete loss of [3H]-GABA release which is a marker of GABAergic interneurons. No loss of granule cells was found and the glutamatergic nature of the granule cells appeared unaltered by the kainate treatment, since evoked release of [3H]-D-aspartate was maintained after kainate exposure. Glial cells in such cultures are virtually eliminated by treatment with an antimitotic such as cytarabine. In consequence a pure culture of cerebellar granule cells virtually free of stellate, basket and glial cells may be obtained by a combined chronic treatment of the cultures with kainate and cytarabine.

Glutamate receptor activation in cultured cerebellar granule cells increases cytosolic free Ca2+ by mobilization of cellular Ca2+ and activation of Ca2+ influx

The Ca2+ sensitive fluorescent probe, fura-2 has been used to monitor cytosolic free calcium levels in mature primary cultures of cerebellar granule cells during exposure to L-glutamate and other excitatory amino acids: quisqualate (QA) kainate (KA) and N-methyl-D-aspartate (NMDA). Glutamate at micromolar concentrations produced a prompt and dose-related increase in the intracellular concentration of free Ca2+, ([Ca2+]i), whereas QA, KA and NMDA had no effect. This increase was also seen in the absence of extracellular Ca2+, suggesting that L-glutamate promotes mobilization of Ca2+ from intracellular stores. In the presence of extracellular calcium, the elevation of [Ca2+]i was, in part, mediated by an increase in the plasma membrane permeability to Ca2+. This Ca2+ influx was not affected by the Ca2+-channel antagonist l-Verapamil. However, L-Verapamil did block the increase in [Ca2+]i seen after depolarization of the cells with potassium. The Ca2+ response elicited by glutamate was partially blocked by the excitatory amino acid antagonist glutamate diethyl ester (GDEE). Furthermore, glutamate stimulated the formation of inositol mono-, bis-, tris- and tetrakisphosphates (IP1, IP2, IP3, and IP4) suggesting a role for these compounds for the increase in [Ca2+]i.

Direct evidence that excitotoxicity in cultured neurons is mediated via N-methyl-D-aspartate (NMDA) as well as non-NMDA receptors

Cultured GABAergic cerebral cortex neurons were exposed to the excitatory amino acid (EAA) L-glutamate, kainate (KA), N-methyl-D-aspartate (NMDA), or RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionate (AMPA). To ensure a constant glutamate concentration in the culture media during the exposure periods, the glutamate uptake inhibitor L-aspartic acid beta-hydroxamate was added at 500 microM to the cultures that were exposed to glutamate. Each of these EAAs was able to induce neurotoxicity. It was not possible to reduce or prevent glutamate-induced cytotoxicity by blocking only one of the glutamate receptor subtypes with either the NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoate (APV) or with one of the specific non-NMDA antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX). However, if the cultures were exposed simultaneously to glutamate and the antagonists in combination, i.e., APV plus CNQX or APV plus DNQX, the toxicity was completely prevented. Furthermore, CNQX and DNQX were shown to be selective blockers of cytotoxic phenomena induced by non-NMDA glutamate agonists with no effect on NMDA-induced cell death. Likewise, APV prevented NMDA-induced cell death without affecting the KA- or AMPA-induced neurotoxicity. It is concluded that EAA-dependent neurotoxicity is induced by NMDA as well as non-NMDA receptors.

Glycine reverses the effect of HA-966 on NMDA responses in cultured rat cortical neurons and in chick retina

The effects of glycine on NMDA antagonism by a series of excitatory amino acid antagonists were tested in two functional in vitro models: NMDA induced [3H]GABA release from cultured mouse cortical neurons and NMDA evoked spreading depression in chick retina. In both models glycine reversed the NMDA antagonism by HA-966. Also NMDA block by kynurenic acid and by DNQX were partly reversed by glycine. However, CNQX, D-APV, ketamine and MK 801 showed the same NMDA antagonism in the absence and presence of glycine.

Quinoxalinediones: potent competitive non-NMDA glutamate receptor antagonists

The N-methyl-D-aspartate (NMDA)-subtype of glutamate receptors has been well described as a result of the early appearance of NMDA antagonists, but no potent antagonist for the "non-NMDA" glutamate receptors has been available. Quinoxalinediones have now been found to be potent and competitive antagonists at non-NMDA glutamate receptors. These compounds will be useful in the determination of the structure-activity relations of quisqualate and kainate receptors and the role of such receptors in synaptic transmission in the mammalian brain.

Chaotropic ions affect the conformation of quisqualate receptors in rat cortical membranes

Binding of [3H](R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]AMPA) to quisqualate receptors in the presence of SCN- ions produced curvilinear Scatchard plots. Kinetic investigations of [3H]AMPA binding showed that the curvilinearity cannot be explained by assuming binding to two separate binding sites or by considering it due to cooperative interaction. A more likely explanation is that the quisqualate receptors exist in two states, one with high and one with low affinity for [3H]AMPA. Chaotropic ions change the relaxation constant between the two states.

Energy metabolism in glutamatergic neurons, GABAergic neurons and astrocytes in primary cultures

Several aspects of energy metabolism (glucose utilization, lactate production, 14CO2 production from labeled glucose, glutamate or pyruvate, oxygen consumption and contents of ATP and phosphocreatine) were measured in cerebellar granule cells (glutamatergic) in primary cultures and compared with corresponding data for cerebral cortical neurons (mainly GABA-ergic) and astrocytes. Cerebellar granule cells and astrocytes were metabolically more active than cerebral cortical neurons. Glutamate which is utilized as a major metabolic fuel as astrocytes and, to a lesser extent, in cerebral cortical neurons, was virtually not oxidized in cerebellar granule cells.

New quinoxalinediones show potent antagonism of quisqualate responses in cultured mouse cortical neurons

Two new quinoxalines, DNQX (6,7-dinitro-quinoxaline-2,3-dion = FG 9041) and CNQX (6-nitro-7-cyano-quinoxaline-2,3-dion = FG 9065), were tested as antagonists of excitatory amino acid responses in cultured neurons and brain slices. DNQX and CNQX showed potent competitive antagonism of quisqualate and kainate induced [3H]GABA release from cultured mouse cortical neurons with weaker effects on NMDA responses (Schild values for DNQX were 6.2, 5.9 and 5.4, respectively). Also in a model of excitatory amino acid induced 22Na efflux from striatal slices DNQX blocked responses to quisqualate and kainate more effectively than responses to NMDA.

Phencyclidine analogues inhibit NMDA-stimulated [3H]GABA release from cultured cortex neurons

The inhibition of [3H]TCP binding to rat cortical membranes by substances of the PCP/sigma-opiate type was compared with effects of the same compounds on N-methyl-D-aspartate (NMDA) responses in cultured mouse cortex neurons. A new technique of excitatory amino acid-induced [3H]GABA (gamma-amino-butyric acid) release in a continuous superfusion model was used for the purpose. A similar rank order of potencies was found for the substances whether as inhibitors of [3H]TCP binding (MK 801 greater than PCP greater than ketamine-cyclazocine) or as antagonists of NMDA (20 microM)-stimulated [3H]GABA release in the cultured neurons (phencyclidine = MK 801 greater than ketamine greater than cyclazocine).

Regional cerebral glucose phosphorylation and blood flow after insertion of a microdialysis fiber through the dorsal hippocampus in the rat

Local cerebral glucose metabolism (LCMRglc) and local cerebral blood flow (LCBF) were studied following implantation of a microdialysis fiber in rat dorsal hippocampus. Recovery time after implantation varied from 0 to 24 h. All rats showed pronounced disturbances in LCMRglc and LCBF during the first 2 h of implantation. The changes consisted of (a) a general decrease in blood flow and glucose phosphorylation and (b) small areas (spots) around the fiber with increased glucose phosphorylation and decreased blood flow. Animals allowed to recover for 24 h demonstrated a near normalization of LCMRglu and LCBF, and the focal disturbances (spots) of glucose phosphorylation and blood flow disappeared. The slight reduction in blood flow and glucose metabolism at this time must be accepted, because extension of the recovery period beyond 24 h may give interpretation problems due to the developing gliosis.

Excitatory amino acid-induced release of 3H-GABA from cultured mouse cerebral cortex interneurons

A newly developed continuous superfusion model was used for studies of 3H-GABA release from cultured mouse cerebral cortex neurons. It was found that a series of excitatory amino acids (EAAs) representing all receptor subtypes evoked Ca2+- dependent release of 3H-GABA from the neurons. Quisqualate was the most potent agonist tested, with an EC50 value of 75 nM. L-Glutamate, N-methyl-D-aspartate (NMDA), and kainate showed EC50 values of 12, 16 and 29 microM, respectively. The EAA-evoked 3H-GABA release could be blocked by a series of EAA antagonists. The highly selective NMDA antagonist D-2-amino-5-phosphonovaleric acid (D-APV) was found to block NMDA responses, whereas the nonselective antagonists cis-2,3-piperidine dicarboxylic acid (PDA) and gamma-D-glutamyl-aminomethyl sulphonic acid (GAMS) blocked responses to all agonists. NMDA responses were found to be sensitive to Mg+ blockade. EAA- as well as potassium-induced 3H-GABA release from the neurons could be detected as early as day 5 in culture. However, during the culture period up to 12 d, the responses to K+, quisqualate, and NMDA were increased. The ontogenetic development of binding sites for quisqualate, kainate, and NMDA in mouse cortex was studied using the radioligands 3H-alpha-amino-3-hydroxy-5-methyl-4-isoxasole propionate (3H-AMPA), 3H-kainate, and 3H-L-glutamate, respectively. The development of binding sites for the different EAA-receptor subtypes showed a good correlation with the development of neuronal 3H-GABA release evoked by the excitatory amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Different target sizes of the voltage-dependent Ca2+ channel and the [3H]nitrendipine binding site in rat brain

High energy irradiation of frozen rat frontal cortex was used to determine the molecular target sizes of the [3H]nitrendipine binding site (93,500 +/- 9,700 daltons and of the voltage-dependent Ca2+ channel (340,500 +/- 34,000 daltons) determined as the K+-induced 45Ca2+ uptake into synaptosomes. The conclusion that could be drawn from the target size analysis was that 45Ca2+ flux occurs via a structure of molecular weight very different from that of the dihydropyridine binding site. Furthermore, it was found that [3H]nitrendipine binding to synaptosomes was not influenced by depolarization with K+.

Pharmacologically distinct glutamate receptors on cerebellar granule cells

Cultured cerebellar granule cells were found to exhibit calcium-dependent release of 3H-D-aspartate when stimulated with excitatory amino acids. L-glutamate and L-aspartate were found to be potent stimulators of 3H-D-aspartate release, D-aspartate was weaker and only minor effects were seen with D-glutamate, quisqualate, kainate, N-methyl-D-aspartate (NMDA) and L-alpha-aminoadipate (L-alpha AA). It was also found that only L-glutamate and L-aspartate showed high affinity for the 3H-L-glutamate binding sites on granule cell membranes. Stimulation by L-glutamate of 3H-D-aspartate release could be blocked by various excitatory amino acid antagonists. From the relative potencies of agonists and antagonists on D-aspartate release it is suggested that cerebellar granule cells express functionally active glutamate receptors with pharmacological characteristics different from all known excitatory amino acid receptors.

Differentiation of Cl-/Ca2+-dependent and sodium dependent 3H-glutamate binding to cortical membranes from rat brain by high energy radiation inactivation analysis

The molecular weights of 3H-L-glutamate binding in the presence of chloride and calcium ions and in the presence of sodium ions were determined by the high energy irradiation technique. The molecular weight of sodium dependent 3H-L-glutamate binding, which has pharmacological specificities similar to the high-affinity uptake system for L-glutamate, was 670,000 daltons. The high-energy radiation inactivation study of chloride and calcium dependent and sodium independent 3H-L-glutamate binding is consonant with the idea that, this binding represent glutamate transport into resealed plasma membrane vesicles.

Calcium discriminates two [3H]kainate binding sites with different molecular target sizes in rat cortex

Binding of [3H]kainate to the kainate subtype of excitatory amino acid receptors revealed two binding sites. The high-affinity site (Kd = 3.5 nM) was sensitive to calcium ions and has a molecular target size as determined by high-energy radiation inactivation analysis of 76,600 daltons. The low-affinity site (Kd = 65 nM) was insensitive to calcium ions and has a molecular target size similar to the quisqualate-subtype of excitatory amino acid receptors. The change in binding parameters of the two sites with radiation dose strongly suggests that low affinity, calcium-insensitive [3H]kainate binding sites are equivalent to quisqualate sites.

Phenobarbitone enhances [35S]TBPS binding to extensively washed rat cortical membranes

Pentobarbitone and phenobarbitone enhance [35S]TBPS binding to extensively washed rat cortical membranes with ED50 values of 15 and 120 microM, respectively, indicative of an interaction with the chloride ionophore part of the GABA-receptor different from the TBPS binding site, but allosterically coupled to this site.