Affinity of 1-aminoadamantanes for the sigma binding site in post-mortem human frontal cortex

Characterisation of [3H]MK-801 binding and its cooperative modulation by pig brain membranes

Cooperative modulation of [3H]MK-801 binding to extensively washed pig cortical brain membranes in the presence of various concentrations of L-glutamate, glycine, spermine, CPP and DCKA was evaluated in association experiments. In saturation experiments [3H]MK-801 labelled a homogeneous population of binding sites with a Kd-value of 1.26 +/- 0.18 nmol 1(-1) and a Bmax-value of 2130 +/- 200 fmol/mg protein. The pharmacological profile of this site was further evaluated in competition experiments with known NMDA receptor channel blockers. In nonequilibrium binding experiments EC50-values of reference compounds acting at the L-glutamate, at the glycine, and at the polyamine site, were determined by increasing or decreasing [3H]MK-801 binding. Ifenprodil reduced [3H]MK-801 binding in a biphasic manner. All the data obtained are in agreement with results from [3H]MK-801 binding to rodent as well as human brain membranes. This study therefore strongly suggests, that pig cortical membranes are a suitable alternative to rodent brain membranes, and an acceptable substitute for human brain membranes in [3H]MK-801 binding experiments.

Characterization of [3H]pentazocine binding sites in post-mortem human frontal cortex

We investigated binding characteristics of [3H](+)-pentazocine in homogenates of post-mortem human frontal cortex. At equilibrium, specific binding was linear with protein concentration, was saturable, reversible, stereoselective, heat-labile and was nearly absent in the white matter. Saturation experiments revealed a KD of 3.68 +/- 0.46nM and a B(max) of 0.636 +/- 0.107 pmol/mg protein. The rank order of Ki values of competing substances was: haloperidol < N,N'-di(o-tolyl)guanidine (DTG) < (+)-SKF 10,047 < (-)-SKF 10,047. We also examined the influence of age, gender, hemisphere, post-mortem time and storage time of brain tissue at -80 degrees C on [3H](+)-pentazocine binding sites. Of these variables, only age was significantly related to [3H](+)-pentazocine binding (diminished binding with increasing age). Together, our results demonstrate the presence of specific [3H](+)-pentazocine binding sites in post-mortem human brain tissue. Furthermore, the binding sites decrease with increasing age and are apparently independent of gender, hemisphere, post-mortem time and storage time of brain tissue.

Therapeutic brain concentration of the NMDA receptor antagonist amantadine

Amantadine (1-amino-adamantane) is clinically used for the management of Parkinson's disease and drug-induced extrapyramidal symptoms. It has previously been shown that amantadine is a low-affinity uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist with rapid blocking and unblocking channel kinetics (Ki-value at the PCP binding site = 10 microM). The aim of the present studies was to estimate concentrations of amantadine in the central nervous system under therapeutic conditions. In homogenates of postmortem human brain tissue the amantadine concentration appeared to be homogeneously distributed over a wide range of brain areas. Amantadine concentration increased with duration of treatment and decreased wit drug-free time. When the duration of treatment was > or = 10 days and drug-free time < or = 3 days, mean amantadine concentrations in postmortem brain tissue ranged from 48.2 to 386 microM. In contrast to brain tissue, amantadine concentration in cerebrospinal fluid (CSF) and serum was in the low micromolar range ( < 17 microM). CSF and serum total values were highly correlated to each other and were always lower in CSF. The mean CSF/serum ratio for total amantadine was 0.76. To further estimate the extracellular concentration, amantadine was determined in microdialysates in the rat striatum. At behaviorally active doses, amantadine concentration in striatal microdialysates ranged between 6 and 21 microM. These results indicate that extracellular concentrations of amantadine (CSF and serum values in patients, striatal microdialysates in the rat) are in the range of its Ki-value at the PCP binding site. Amantadine concentrations in brain tissue are much higher, probably due to intralysosomal accumulation.

Novel assay for the influenza virus M2 channel activity

The influenza A M2 ion channel was expressed and activity characterized in Xenopus oocytes. Based on the activation properties of the channels, a high throughput, non-electrophysiological screening assay was developed in order to identify novel inhibitors of the channel. This will facilitate discovery of novel agents to treat influenza viral infections.

Are NMDA antagonistic properties relevant for antiparkinsonian-like activity in rats?--case of amantadine and memantine

Amantadine (25, 50, 100 mg/kg), memantine (5, 10, 20 mg/kg) and MK-801 (0.05, 0.1, 0.2 mg/kg), all having NMDA channel blocking properties, were compared in three tests used for screening of antiparkinsonian agents in rats, namely: haloperidol-induced catalepsy, locomotor activity in monoamine depleted rats and rotation in rats with a unilateral substantia nigra lesion. Additionally, plasma levels of amantadine and memantine were assessed to gain an insight into the concentration ranges achieved at behaviorally active doses. Amantadine and (+)-MK-801 produced dose-dependent inhibition of haloperidol-induced catalepsy while memantine was less efficacious producing clear-cut anticataleptic action at a dose of 10 mg/kg only but failing at 20 mg/kg due to myorelaxant activity. All agents attenuated sedation in monoamine depleted rats with amantadine being the least and MK-801 being the most effective. The same rank order of efficacy was seen in inducing ipsilateral rotations in rats after a substantia nigra lesion. On the basis of the present study and published data, it can be assumed that the doses of amantadine, memantine and MK-801 showing antiparkinsonian-like activity in animals result in plasma levels leading to NMDA antagonism. However, in the haloperidol-induced catalepsy test the efficacy of amantadine was higher than memantine, while the opposite was true for rotation and reserpine-induced sedation indicating pharmacodynamic differences between both agents.