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A Adem

Publications and source records attributed to A Adem.

At least 91 records · Page 5Linked to original sources
PubMed1989

Multiple actions of THA on cholinergic neurotransmission in Alzheimer brains.

1,2,3,4-tetrahydro-9-aminoacridine (THA) is a cholinesterase inhibitor presently under investigation in clinical trials for treatment of Alzheimer's disease, senile dementia of Alzheimer type (AD/SDAT). To further analyse the underlying mechanisms for its effect in human brain, an in vitro model which allows measurement of acetylcholine (ACh) release from human postmortem brain slices has been used. In control cortical tissue THA induces a decreased release of ACh probably due to negative feedback mechanisms mediated via presynaptic muscarinic autoreceptors. In AD/SDAT cortex THA enhances the release of ACh to control level. This effect is prevented by nicotinic or muscarinic receptor antagonists, which suggest receptor mechanisms involving both nicotinic and muscarinic receptors. Subchronic treatment of rats with THA (10 mg/kg sc twice daily) or physostigmine (0.9 mg/kg sc five times daily) causes a significant increase in the number of high affinity nicotinic receptors in the cortex of THA treated rats whereas no change is found in the physostigmine treated rats. The number of muscarinic receptors are decreased following both THA and physostigmine treatment.

Alzheimer Disease↗
PubMed1988

Change in nicotinic receptor subtypes in temporal cortex of Alzheimer brains.

Competition experiments using (-)-[3H]nicotine and unlabelled nicotine revealed both high and low affinity nicotinic binding sites in temporal cortex of control and Alzheimer (AD/SDAT) brains. A significant reduction in the proportion of high affinity nicotinic binding sites (-20%) and a parallel increase in the proportion of low affinity nicotinic binding sites was obtained in AD/SDAT brain cortex compared to control brain. Moreover, a marked decrease was observed in the affinity of the low affinity nicotinic binding sites in AD/SDAT.

Aged↗
PubMed1988

Subchronic treatment of rats with nicotine: interconversion of nicotinic receptor subtypes in brain.

A significant increase in the number of cortical high-affinity (-)-[3H]nicotine binding sites was measured in rats treated with nicotine (0.45 mg/kg) twice daily for 18 days. Competition experiments with (-)-[3H]nicotine and various concentrations of unlabelled (-)-nicotine revealed that the proportion of high-affinity nicotine binding sites was significantly increased in the nicotine-treated group while the proportion of low-affinity nicotinic binding sites was similarly significantly reduced compared to the controls. In addition there was a significant decrease in the affinity of both subtypes of nicotinic binding sites.

Animals↗
PubMed1988

Toxins from the venom of the green mamba Dendroaspis angusticeps that inhibit the binding of quinuclidinyl benzilate to muscarinic acetylcholine receptors.

Two protein toxins that displace the muscarinic antagonist quinuclidinyl benzilate from rat cortex synaptosomal membranes have been isolated from the green mamba (Dendroaspis angusticeps) venom by gel filtration on sephadex G-50, chromatography on the ion-exchangers Bio-Rex 70 and Sulphopropyl-Sephadex C-25 and reversed-phase HPLC. Toxin 1 has 64 amino acids and four disulfides and a formula weight of 7200 and the corresponding values for toxin 2 are 63, 4 and 6840, respectively. Ultracentrifugation gave a molecular weight of 6900 for toxin 1 and 6700 for toxin 2, Quinuclidinyl benzilate that binds to all types of muscarinic cholinergic receptor was displaced to about 50% by both toxins. This partial displacement indicates that the toxins might be specific for one subtype of receptor.

Amino Acids↗
PubMed1988

Distribution of nicotinic receptors in human thalamus as visualized by 3H-nicotine and 3H-acetylcholine receptor autoradiography.

Nicotinic cholinergic receptors in human thalamus were measured using (-)3H-nicotine (20 nM) and 3H-acetylcholine (3H-ACh) (20 nM) as radioligands. The specific binding for 3H-nicotine to homogenates of thalamus was 51.6 +/- 8.3 pmol/g protein and for 3H-ACh 18.6 +/- 1.9 pmol/g protein. Receptor autoradiography indicated a high labelling of both 3H-Nicotine and 3H-ACh in the antero-ventral nucleus of thalamus and dorso-medial nucleus of thalamus, while the labelling was lower in the postero-lateral nucleus of thalamus and in the postero-lateral ventral nucleus of thalamus. Quantitative measurement of the 3H-nicotine autoradiograms showed highest labelling in the anteroventral nucleus of thalamus (17.34 +/- 0.76 pmol/g tissue). This study indicates a heterogeneous distribution of high-affinity nicotinic receptors in the human thalamus.

Acetylcholine↗
PubMed1988

Characterization of agonist and antagonist binding to muscarinic cholinergic receptors solubilized from rat cerebral cortex.

The muscarinic acetylcholine receptor was solubilized from rat brain cortex by the zwitter-ionic detergent, 3-[3-cholamidopropyl)dimethylamino)-1-propane sulfonate (CHAPS). The supernatant, after centrifugation at 100,000 x g, was shown to contain molecules with binding sites for both 3H-pirenzepine (3H-PZ) and 3H-(-) quinuclidinyl benzilate (3H-QNB). Maximum binding values for 3H-PZ and 3H-QNB binding to solubilized receptors were approximately 176 +/- 24 pmol/g and 370 +/- 53 pmol/g of protein, respectively. The Kd values for 3H-PZ and 3H-QNB binding to solubilized receptors were 27 +/- 6.3 nM and 0.17 +/- 0.03 nM, respectively. The rank order of potencies of muscarinic drugs, in terms of their ability to inhibit binding of either 3H-PZ or 3H-QNB, was atropine greater than pirenzepine greater than oxotremorine greater than carabachol. Pirenzepine inhibited 3H-QNB binding with a Hill coefficient of 0.77, but inhibited 3H-PZ with a Hill coefficient of 0.94. Hill coefficients for agonists were less than 1. These findings indicate that muscarinic receptors solubilized from rat brain cortex retain their abilities to interact selectively with muscarinic receptor agonists and antagonists.

Animals↗
PubMed1988

Distribution of nicotinic cholinergic receptors in the rat tel- and diencephalon: a quantitative receptor autoradiographical study using [3H]-acetylcholine, [alpha-125I]bungarotoxin and [3H]nicotine.

The topographical distribution of [alpha-125I]bungarotoxin [125I]BTX, [3H]nicotine ([3H]Nic), [3H]acetylcholine ([3H]ACh) (in the presence of atropine) binding in rat tel- and diencephalon was investigated using a quantitative receptor autoradiographical technique. With the [3H]ACh and [3H]Nic radioligands, a strong labelling was observed in various thalamic nuclei, including the medial habenula, a moderate labelling in different areas of the cortex cerebri, the nucleus caudatus putamen, the nucleus accumbens and tuberculum olfactorium and a uniform weak labelling in the hypothalamus. When the binding data for [3H]Nic were plotted against binding data for [3H]ACh in various brain nuclei, a significant correlation was obtained. Considering [125I]BTX, the strongest labelling was observed in the lateral mammillary nucleus and the hilus gyrus dentatus of the hippocampal formation. A weak labelling occurred in areas such as the nucleus causatus putamen, the thalamus and the cerebral cortex. No significant correlation was therefore obtained between the degree of [125I]BTX binding in various brain nuclei and the degree of binding observed with [3H]Nic or [3H]ACh. The present results underline the view that the high-affinity [3H]Nic and [3H]ACh binding sites label the same cholinergic nicotinic receptor binding site, while [125I]BTX labels another subpopulation of nicotinic cholinergic receptors, predominantly found in discrete areas of the hypothalamus and the limbic cortex.

Acetylcholine↗
PubMed1987

[3H]acetylcholine nicotinic recognition sites in human brain: characterization of agonist binding.

In the presence of a cholinesterase inhibitor to prevent hydrolysis and atropine to block muscarinic cholinergic receptors, [3H]acetylcholine ([3H]ACh) binding to human brain membranes showed highest levels of nicotinic binding sites in the thalamus. [3H]ACh, in the presence of atropine, binds to heterogeneous high-affinity binding sites in human thalamus. Scatchard analysis of the binding gave a Kd of 0.58 nM and a Bmax of 3.3 pmol/g protein for the 'super high-affinity' site and a Kd of 27 nM and a Bmax of 70 pmol/g protein for the 'high-affinity' site. Moreover, in competition studies nicotinic agonists such (-)-nicotine and carbachol displaceable [3H]ACh-specific binding sites consist of both a high- and a low-affinity population of sites. These results indicate that highest levels of [3H]ACh binding in human brain were found in the thalamus. Moreover, the human thalamus was found to have multiple high-affinity nicotinic agonist sites.

Acetylcholine↗
PubMed1987

In vitro binding of 3H-acetylcholine to nicotinic receptors in rodent and human brain.

The binding of 3H-acetylcholine (3H-ACh) to nicotinic receptors in rodent and human brain was measured in the presence of atropine to prevent binding to muscarinic binding sites. 3H-ACh binds specifically and saturably to rodent brain. From saturation binding Kd was 30 nM in rat cerebral cortex, which is close to that calculated from kinetic experiments. The binding was temperature-dependent, being highest at low temperatures and decreasing at higher temperatures. The regional distribution of binding in mouse brain was not uniform. The binding was highest in the midbrain, intermediate in the cerebral cortex and striatum, and lowest in the cerebellum, hippocampus, hypothalamus and medulla oblongata. No significant correlation was found between the regional 3H-ACh binding and the regional binding of 3H-alpha-bungarotoxin (3H-BTX), 3H-nicotine (3H-NIC), 3H-tubocurarine and the endogenous acetylcholine content, although the correlation value for 3H-ACh/3H-NIC was at the limit for significance. 3H-ACh also bound specifically to human cerebral cortical tissue and this binding was approximately three times lower than in rodent brain, when a low 3H-ACh concentration was used. In contrast to rat brain there appears to exist multiple binding sites for 3H-ACh in human cerebral cortex as suggested by the curvelinear nature of the Scatchard plot. It was calculated that 3H-ACh bound with Kd 4 nM and Bmax 8 pmol/g protein and Kd 112 nM and Bmax 67 pmol/g protein. The Hill number of 1.5 for the binding of low concentration and 2.5 for high concentration of 3H-ACh also suggest that the 3H-ACh-binding sites interaction exhibit positive cooperativity.

Acetylcholine↗
PubMed1987

Do tetrahydroaminoacridine (THA) and physostigmine restore acetylcholine release in Alzheimer brains via nicotinic receptors?

In the presence of 9-amino-1,2,3,4-tetrahydroacridine (THA) 10(-4) M or physostigmine 10(-4) M, the in vitro 3H-Acetylcholine (3H-ACh) release from control cortical slices was significantly reduced. In contrast, THA 10(-4) M and physostigmine 10(-4) M significantly increased the release of 3H-ACh in AD/SDAT brain tissue. This facilitating effect on 3H-ACh release was partially blocked (50%) in the presence of the nicotinic antagonist d-tubocurarine 10(-6) M indicating a possible interaction via nicotinic receptors. The muscarinic antagonist atropine 10(-5) M significantly increased the 3H-ACh release both in control and AD/SDAT brains, thus indicating preservation of muscarinic autoreceptors in the AD/SDAT cortical tissue. In receptor competition studies with 3H-nicotine, 3H-ACh and 3H-quinuclidinyl benzilate (3H-QNB) as receptor ligands, THA interfered with both nicotinic and muscarinic receptor ligand binding, while physostigmine had much less effect.

Acetylcholine↗
PubMed1987

Muscarinic receptors in human SH-SY5Y neuroblastoma cell line: regulation by phorbol ester and retinoic acid-induced differentiation.

The specific binding of the muscarinic ligand [3H](-)quinuclidinyl benzilate [( 3H]QNB) to cell membranes of human SH-SY5Y neuroblastoma cells was studied. Saturation isotherms yielded a Kd = 0.28 +/- 0.06 nM and a Bmax of 337 +/- 47 pmol/g protein. Pirenzepine inhibited [3H]QNB binding; inhibition data showed best fit to a 2-site binding model revealing both a high affinity pirenzepine site (34%, KH = 10 nM) and a low affinity site (66%, KL = 1 microM). These results indicate that muscarinic receptors on SH-SY5Y cells may be subclassified as M1/M2 subtypes. Morphological and biochemical differentiation of these cells after treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or retinoic acid (RA) resulted in a decrease and an increase in the number of muscarinic binding sites, respectively. Furthermore, TPA- and RA-treated cells showed a significant increase in acetylcholinesterase activity compared with non-treated cells. However, only RA-treated cells showed significant increase in choline acetyltransferase activity compared to non-treated cells. These findings demonstrate that TPA and RA can regulate both the number of muscarinic receptors and the acetylcholinesterase activity in human SH-SY5Y neuroblastoma cells.

Acetylcholinesterase↗
PubMed1986

A muscarinic receptor type in human lymphocytes: a comparison of 3H-QNB binding to intact lymphocytes and lysed lymphocyte membranes.

Human blood lymphocytes from normal blood donors exhibited specific binding of the muscarinic antagonist 3H-quinuclidinyl benzilate (3H-QNB). The 3H-QNB binding to intact viable lymphocytes as well as to lysed lymphocyte membranes "P2" was saturable and displaceable by both muscarinic agonists and antagonists. For the lysed lymphocyte membranes "P2" a single binding site with a Bmax of 109 pmol/g protein and a Kd of 15 nM was obtained. Intact viable lymphocytes also showed one binding site with a Kd of 24 nM and a Bmax of 1556 pmol/g protein. The higher Bmax value might be explained in terms of uptake of the ligand when using intact cells or through loss of binding sites when using lysed lymphocyte membranes "P2". IC50 values were lower by a factor of 10(2) for atropine and scopolamine and by 10(4) for pirenzepine when lysed lymphocyte membranes "P2" were used instead of intact viable lymphocytes.

Adult↗
PubMed1986

Extraneural cholinergic markers in Alzheimer's and Parkinson's disease.

Muscarinic and nicotinic binding sites were analysed in lymphocytes from patients with Alzheimer's disease, Multi-infarct dementia, Parkinson's disease and age- matched controls. A significant decrease in the number of both muscarinic and nicotinic binding sites was obtained in lymphocytes from Alzheimer patients while in Parkinson patients a significant decrease was found only in the nicotinic binding sites. Using butyrylthiocholine as substrate, no change was observed in cholinesterase activity in plasma from Alzheimer patients, whereas a significant decrease in plasma cholinesterase activity was found in Parkinson patients.

Aged↗
PubMedDate not supplied

Growth factor receptors in amyotrophic lateral sclerosis.

The regional distribution of nerve growth factor (NGF) and insulin-like growth factor-1 (IGF-1) receptors in human spinal cords from controls and amyotrophic lateral sclerosis (ALS) patients was studied by quantitative autoradiography. High-affinity nerve growth factor receptors were found to be distributed to a similar extent within the various segments of the human spinal cord and predominantly within the substantia gelatinosa of the dorsal horn, whereas no significant binding could be detected in the motor-neuron areas. A similar pattern of binding was obtained in the ALS spinal cords. Moreover, no reexpression of NGF receptors could be demonstrated in the motor-neuron areas of ALS spinal cords. When comparing 125I-IGF-1 binding in the different spinal levels of normal spinal cord, the same distribution pattern was found in which the binding was highest in the central canal > dorsal horn > ventral horn > white matter. In the ALS cases, although a general upregulation of IGF-1 receptors was observed throughout the spinal cord, significant increases were observed in the cervical and sacral segments compared to controls. The cartography of IGF-1 receptors in the normal spinal cord as well as the change of these receptors in diseased spinal cord may be of importance in future treatment strategies of ALS.

Aged↗
PubMedDate not supplied

Snake toxins with high selectivity for subtypes of muscarinic acetylcholine receptors.

There are five subtypes of muscarinic acetylcholine receptors (M(1) to M(5)) which control a large number of physiological processes, such as the function of heart and smooth muscles, glandular secretion, release of neurotransmitters, gene expression and cognitive functions as learning and memory. A selective ligand is very useful for studying the function of a subtype in presence of other subtypes, which is the most common situation, since a cell or an organ usually has several subtypes. There are many non-selective muscarinic ligands, but only few selective ones. Mambas, African snakes of genus Dendroaspis have toxins, muscarinic toxins, that are selective for M(1), M(2) and M(4) receptors. They consist of 63-66 amino acids and four disulfides which form four loops. They are members of a large group of snake toxins, three-finger toxins; three loops are extended like the middle fingers of a hand and the disulfides and the shortest loop are in the palm of the hand. Some of the toxins target the allosteric site which is located in a cleft of the receptor molecule close to its extracellular part. A possible explanation to the good selectivity is that the toxins bind to the allosteric site, but because of their size they probably also bind to extracellular parts of the receptors which are rather different in the various subtypes. Some other allosteric ligands also have good selectivity, the alkaloid brucine and derivatives are selective for M(1), M(3) and M(4) receptors. Muscarinic toxins have been used in several types of experiments. For instance radioactively labeled M(1) and M(4) selective toxins were used in autoradiography of hippocampus from Alzheimer patients. One significant change in the receptor content was detected in one region of the hippocampus, dentate gyrus, where M(4) receptors were reduced by 50% in patients as compared to age-matched controls. Hippocampus is essential for memory consolidation. M(4) receptors in dentate gyrus may play a role, since they decreased in Alzheimers disease which destroys the memory. Another indication of the role of M(4) receptors for memory is that injection of the M(4) selective antagonist muscarinic toxin 3 (M(4)-toxin 1) into rat hippocampus produced amnesia.

Amino Acid Sequence↗