Possible hazards in serotonin binding assays in human and rat brain: effects of ascorbate, pargyline, and buffer concentration.
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Animals↗
Biomedical subjects
W Wesemann
Publications and source records attributed to W Wesemann.
Regulation of cerebral serotonin binding and metabolism in sleep-deprived rats.
Two different binding sites are found for serotonin binding to crude membrane fractions isolated from rat brain. After 12 h sleep deprivation (SD) the dissociation constant of the high affinity binding KD1 = 1.4 mM, remains unchanged whereas the dissociation constant, KD2, of the low affinity binding increased from 26 to 42 nM. The number of binding sites are only moderately affected. The dissociation constant of the low affinity binding, KD2, is decreased towards control values if SD is followed by 1 or 4 h sleep. As indicated by serotonin and 5-hydroxyindoleacetic acid analyses, a statistically significant increase in serotonin metabolism is found only, if SD is followed by 1 h recovery sleep.
Animals↗
[The Effect of memantine on spinal alpha-motoneurons and on the content of dopamine, noradrenaline and serotonin in the striatum and lumbar spinal cord].
In the present paper the pharmacological effect of 1,3-dimethyl-5-aminoadamantane (DMAA, D-145, memantine, Memantine was investigated on the reflex activity of spinal alpha-motoneurones of the cat and on spontaneous hyperactivity of alpha-motoneurones of spastic Han-Wist rats. The activity of both systems is reduced by the drug. Furthermore the content of dopamine, noradrenaline, and serotonin of striatum and lumbar spinal cord of normals and mutants is dose dependently decreased. It is assumed that memantine depresses the activation of central nervous membranes and reduces repetitive discharges of axons and in addition acts by release of neurotransmitters.
Amantadine↗
Effect of 1-aminoadamantanes on the MAO activity in brain, liver, and kidney of the rat.
In order to elucidate the possible interference of the antiparkinson drug 1-aminoadamantane (D-1, PK Merz) and the antispastic compound 1,3-dimethyl-5-aminoadamantane (DMAA, D-145, memantine, Memantine) on neurotransmitter metabolism, the effect of D-1 and its C-alkyl derivatives memantine, 1-amino-3,5,7-trimethyladamantane (D-191), and 1-amino-3-(n)-butyladamantane (D-178) on MAO activity in brain, liver, and kidney of the rat was investigated. A radioisotope method using [14C]5-hydroxytryptamine as substrate was used. The highest MAO activity was found in liver followed by brain and kidney (Vmax: 137, 64, and 26 nmol/mg protein X h, respectively). The Km values did not differ significantly for the three tissues (liver: 107 mumol/l; brain: 96 mumol/l; kidney: 86 mumol/l). The MAO activity in liver, brain and kidney was noncompetitively inhibited by all 1-aminoadamantanes studied, each derivative, respectively, showing in all three tissues about the same percentage inhibition. The inhibitory activity was found to be increased with the degree of C-alkylation: D-1 (Ki approximately 1 mmol/l) less than D-145 (Ki approximately 0.1 mmol/l) less than D-191 (Ki approximately 0.07 mmol/l) less than D 178 (Ki approximately 0.02 mmol/l).
Amantadine↗
Distribution of memantine in brain, liver, and blood of the rat.
The distribution of 1,3-dimethyl-5-aminoadamantane (DMAA, D-145, memantine, Memantine), a compound used in the treatment of CNS disorders, is investigated in liver, brain, and blood of the rat. The tissue concentration of memantine is analyzed by gaschromatography after i.p. and p.o. administration. After i.p. application the blood levels are only about 1/10-1/20 of the concentrations found in liver and brain. The highest drug concentration in blood is obtained within the first 15 min, followed by liver and brain, 30 and 60 min after i.p. administration, respectively. The memantine concentration per g brain tissue is almost identical to the dose applied per g body weight. Lower brain levels are obtained if memantine is given p.o. However, in contrast to the rapid decrease after i.p. treatment, the plateau reached 1 h after p.o. administration does not level off within the next 3 h.
Amantadine↗
Transitional states of central serotonin receptors in Parkinson's disease.
Crude membrane preparations from the frontal cortex of controls and parkinsonian patients were used to demonstrate affinity changes of the specific 3H-5-hydroxytryptamine (5-HT) binding sites. Two such sites were notable in controls, a finding consistent with earlier observations. In Parkinson's disease, both high- and low-affinity sites are significantly decreased. Additional experiments either with prolonged incubation times or pre-incubation with N-ethylmaleimide change the two affinities to a single high-affinity or low-affinity constant. The concept of transitional states of 5-HT receptors is discussed and seems to have important implications in the treatment of parkinsonism.
Aged↗
Effect of 1-aminoadamantanes on adenine nucleotide and serotonin storage in blood platelets.
The platelet release reaction, the liberation of adenine nucleotides and serotonin (5-HT) from osmiophilic dense granules, can be induced in human platelets by C-alkyl-derivatives of the antiviral and anti-Parkinson drug 1-aminoadamantane (D 1). The release-inducing activity is enhanced with increasing chain length and with the number of C-alkylsubstituents, respectively. The parent compound, D 1, liberates only 5-HT. Analyses of LDH activity in the incubation medium of the platelets and electron micrographs of platelets treated with 1-aminoadamantanes support the assumption that ATP, ADP, and 5-HT are released from the organelles by an exocytosis-like process rather than by destruction of the plasma and organelle membranes. The number of osmiophilic dense granules in platelets isolated from human and rabbit blood is decreased by the action of the drugs. This is in contrast to other subcellular structures where no morphological changes can be observed. The ADP-stimulated platelet aggregation is inhibited by preincubation with 1-aminoadamantanes. The inhibitory activity of the drugs on platelet aggregation parallels the effects observed after induction of the release reaction: the inhibition of platelet aggregation is enhanced with increasing C-alkylation. Hence, the inhibition of ADP-induced platelet aggregation can be used to screen for the releasing activity of 1-aminoadamantanes which have, as far as tested, similar effects on 5-HT storage in blood platelets and in the CNS. The time-, temperature, and concentration-dependent 5-HT uptake by platelets (K = 0.75 micro M; V max = 0.22 nmoles/min X 10 9 cells) is noncompetitively inhibited by the drugs with K1-values varying from 10 to 100 micro M depending on the degree of C-alkylation.
Adenosine Diphosphate↗
Distribution of metabolism of the potential anti-parkinson drug memantine in the human.
GC-MS of tissue extracts obtained from a parkinsonian patient who died from secondary causes during memantine (1-amino-3.5-dimethyladamantane) treatment showed the drug to be largely unmetabolized. In the kidney and liver a second peak corresponded to less than 1% of the main temporal lobe, hypothalamus and pons. Thus treatment with 2 X 10 mg memantine/day reveals an accumulation of the drug in microM concentrations in the brain. This is probably high enough to explain the ameliorating effect of memantine treatment in patients suffering from Parkinson's disease.
Aged↗
Studies on megakaryocytes: isolation from rat and guinea pig and incorporation of 5-hydroxytryptamine.
A new, two step method is described for the isolation of megakaryocytes from bone marrow. By means of centrifugation in a PercollR density gradient megakaryocytes can be enriched by factor 68 or 24 starting from rat or guinea pig bone marrow, respectively. The purity of the megakaryocytes can be improved ca. 4 fold if gradient centrifugation is followed by separation in an Elutriator rotor.-The isolated megakaryocytes take up exogenous 5-hydroxytryptamine with a time and concentration dependent transport mechanism, K11=30 micrometer, K12=1.5 micrometer. As shown by electron microscopy the number and density of storage granules within the megakaryocytes is enhanced after incubation with 5-hydroxytryptamine. This finding suggests that 5-hydroxytryptamine is incorporated into the organelles.
Animals↗
Intracellular distribution of adenine and 5-hydroxytryptamine in megakaryocytes isolated by density gradient and velocity sedimentation from bone marrow.
Megakaryocytes were isolated from rat and guinea pig bone marrow by Percoll density and/or elutriator centrifugation. As compared with the suspension of bone marrow an enrichment of factor 530 with a recovery of 34% can be achieved if a combination of both methods is applied.--The pattern of DNA percentage distribution in isolated cells paralleled the polyploidy found in megakaryocytes of the bone marrow. As determined by scanning cytophotometry and impulse cytophotometry the percentage distribution was maximal for the 16 C cells.--Exogenous [3H]adenine was incorporated by isolated megakaryocytes via a time and concentration dependent process showing two different affinities, Kt1 = 11 nM, V1 = 0.07 pmol/min per 10(5) cells; Kt2 = nM, V2 = 0.21 pmol/min per 10(5) cells.--Autoradiographic studies quantificated by means of the "probability circle" and "percent density" analysis showed that [3H]5-hydroxytryptamine (5-HT) accumulated in the osmiophilic dense bodies in contrast to [3H]adenine (metabolite) which was found mainly in the cytoplasm.
Adenine↗
The role of sialic acid in 5-HT binding to synaptic membranes.
The high affinity binding of [14C]5-HT to nerve ending membranes isolated from rat brain is not affected by neuraminidase treatment. The specificity of ligand receptor interaction was demonstrated by displacement studies with tryptamine derivatives, noradrenaline, and acetylcholine.
Animals↗
In vitro studies on the possible effects of 1-aminoadamantanes on the serotonergic system in M. Parkinson.
Synaptosomes, synaptic vesicles, and membranes were isolated from rat brain homogenates by differential and density gradient centrifugation in sucrose. Synaptosomes incorporated serotonin (5-HT) with two different uptake mechanisms, high affinity: Kt1 = 47 nM and low affinity: Kt2 = 660 nM. Both uptake mechanisms are non-competitively inhibited by the potential antiparkinson drugs 1-aminoadamantane (amantadine, D 1: Ki1 = 57 microM, Ki2 = 96 microM) and 1-amino-3,5-dimethyladamantane (memantine, D 145: Ki1 = 97 microM, Ki2 = 150 microM). The incorporated 5-HT is released from synaptosomes on incubation with high concentrations (0.5--5 mM) of the drugs or on electrical stimulation with rectangular pulses of alternating polarity. Subthreshold concentrations of these drugs (5--50 microM) which are too low to liberate 5-HT increase the electrically stimulated release of 5-HT.--The effect of D 1, D 145, and electrical stimulation on DA release parallels the results observed with 5-HT. The uptake of 5-HT into isolated synaptic vesicles and the binding to isolated nerve ending membranes is non-competitively inhibited by 1-aminoadamantanes. D 145 inhibits the binding of 5-HT to membranes more effectively (Ki = 0.95 mM) than its uptake into vesicles (Ki = 1.2 mM) contrasting with D 1 which is a weaker inhibitor affecting vesicular uptake (Ki = 2.5 mM) slightly more than membrane binding (Ki = 3.1 mM). The results obtained suggest that, in addition to other mechanisms like receptor stimulation, 1-aminoadamantanes may act in parkinsonian patients by enriching the transmitter content in the synaptic cleft.
Adamantane↗
Effects of post-mortem storage on synaptic 5-HT binding and uptake in mammalian brain.
Synaptosomes and synaptic membranes were isolated from rat brain after various storage times and temperatures of the tissue. Synaptosomal 5-HT uptake was diminished by about 20% within the first hour after decapitation. No significant change in the incorporation rate was observed for the seven proceeding hours if the brains were stored at room temperature. After an initial decrease of about 15%, 5-HT incorporation remained constant for at least 24 hours if the tissue was stored at 4 degrees C. Electron micrographs showed that nerve endings were highly disrupted by freezing and thawing of the brains.--The capacity of high affinity 5-HT binding to the microsomal synaptic membrane fraction decreased with the first hour by about 13% to 120--130 fmoles 5-HT/mg protein and remained almost constant for the next eight hours. Freezing at --80 degrees C of whole brain or of isolated membranes did not affect 5-HT receptor interaction.--The capacity of specific 5-HT binding to membranes isolated from human post-mortem brain was comparable to that found with synaptic membranes from rat brain. In contrast to the control values, a significant decrease in 5-HT binding was observed in membrane fractions isolated from brain after cerebral insult.
Animals↗
Release-induced changes in adenine nucleotide metabolism of human blood platelets.
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Adenine↗
The influence of hypothalamic lesions on metabolism and peripheral organization [proceedings].
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Humans↗
[Optical properties and clinical performance of the Topcon retinal camera TRC-FET 3 (author's transl)].
A Topcon Retinal Camera TRC-FET 3 was tested for several weeks under laboratory and clinical routine conditions. The optical properties turned out as good and meet the requirements for retinal cameras in all details. Remarkable is the high speed of the imaging system, which allows working with low flash energies and with high flash frequency. The resolving power is high (8 microns at the center) and decreases slowly to the periphery. The illumination of the fundus is fairly homogeneous. Many filters of good performance are provided. There was no problem in handling the camera, and the test photographs as well as the clinical routine photographs were of high quality.
Clinical Trials as Topic↗
On the significance of sialic acid in high affinity 5-hydroxytryptamine uptake by synaptosomes.
Synaptosomes isolated from rat brain cortex incorporated [14C]5-hydroxytryptamine at 37 degrees C with high affinity. An apparent transport constant of Kt = 50nM was found. The high affinity uptake was decreased by treatment of synaptosomes with neuraminidase from Vibrio cholerae or Clostridium perfringens prior to incubation with [14C]5-hydroxytryptamine. The inhibition was related to the amount of sialic acid released, with a Ki value of 3.5 micrometer. A non-competitive type of inhibition was observed after treatment with neuraminidase. The inhibition caused by ouabain could not be enhanced by simultaneous treatment with neuraminidase. Neuraminidase did not lower the activity of (Na + K)-ATPase or Mg2-ATPase. These results suggest that sialic acid is involved in the 5-hydroxytryptamine uptake mechanism without functional linkage to the energy pump of the membrane, which maintains the sodium gradient necessary for 5-hydroxytryptamine transport.
Animals↗
On the possible mode of action of serotonin in neurotransmission and brain dysfunction.
Criteria necessary to classify a substance as neurotransmitter are used to determine whether disturbances in neurotransmitter function are involved in brain disorders. Six rather stringent criteria for a neurotransmitter are satisfied by the biogenic amine 5-hydroxytryptamine (5-HT): 1. the availability of 5-HT within the CNS is proved by its synthesis and transport, 2. it is stored within the presynaptic bouton, 3. presynaptic stimulation releases 5-HT, 4. it reacts with receptors of the synaptic membranes. 5. a functional equivalence of presynaptic stimulation and subsynaptic 5-HT action can be demonstrated, 6. the transmission is terminated by a retrieval mechanism.--On the basis of this transmitter concept brain dysfunctions as described in the literature are discussed in the light of results obtained using in vitro techniques with isolated synaptic structures. In renal and hepatic insufficiency the transport of the 5-HT precursor tryptophan is affected at the site of the blood-brain barrier. Tryptophan-5-hydroxylase, the rate-limiting enzyme in 5-HT synthesis, is inhibited in hypoxia. The antiparkinson drug 1-aminoadamantane and its 3.5-dimethyl derivative, D 145, inhibit 5-HT catabolism as well as 5-HT storage in synaptic vesicles and reuptake into isolated nerve endings. Since 1-aminoadamantanes enhance the electrically stimulated 5-HT and DA release from nerve endings spatial shifts of transmitter substances within the synaptic area as well as direct receptor stimulation by the drugs may be the cause for the ameliorating effect.
Adenosine Triphosphate↗