Biomedical subjects

R N Kalaria

Publications and source records attributed to R N Kalaria.

At least 109 records · Page 6Linked to original sources

PubMed1989

Ouabain binding in the human brain. Effects of Alzheimer's disease and aging.

We studied Na+,K+-adenosine triphosphatase by assaying specific tritiated ouabain binding in the frontal cortex, temporal cortex, hippocampus, putamen, cerebellum, and cerebral microvessels in subjects with Alzheimer's disease and control subjects. Ouabain binds specifically, in a saturable manner, and with a high affinity to a single class of binding sites in all the tissues studied. The density of ouabain binding sites was highest in cerebellum and frontal cortex (approximately 40 pmol/mg of protein); intermediate in temporal cortex, hippocampus, and putamen; and lowest in brain microvessels (approximately 8 pmol/mg of protein). The dissociation constant of binding was about 30 nmol/L in all tissues. In control subjects, there were no age-related alterations in ouabain binding, nor was there any correlation between ouabain binding and postmortem delay. However, there was a marked decrease in brain ouabain binding in subjects with Alzheimer's disease when compared with age-matched controls, especially in the cerebral cortex. Ouabain binding was also significantly decreased in the cerebellum and putamen of subjects with Alzheimer's disease even though these brain regions are not particularly affected in this disease. Ouabain binding to brain microvessels, which constitute the blood-brain barrier, was not significantly decreased in subjects with Alzheimer's disease. The decreased specific ouabain binding in the brain of subjects with Alzheimer's disease probably reflects the loss of neuronal membranes.

Adult↗

PubMed1989

Reduced glucose transporter at the blood-brain barrier and in cerebral cortex in Alzheimer disease.

We studied the hexose transporter protein of the frontal and temporal neocortex, hippocampus, putamen, cerebellum, and cerebral microvessels (which constitute the blood-brain barrier) in Alzheimer disease and control subjects by reversible and covalent binding with [3H]cytochalasin B and by immunological reactivity. In Alzheimer disease subjects, we found a marked decrease in the hexose transporter in brain microvessels and in the cerebral neocortex and hippocampus, regions that are most affected in Alzheimer disease, but there were no abnormalities in the putamen or cerebellum. Hexose transporter reduction in cerebral microvessels of Alzheimer subjects is relatively specific because other enzyme markers of brain endothelium were not significantly altered. The low density of the hexose transporter at the blood-brain barrier and in the cerebral cortex in Alzheimer disease may be related to decreased in vivo measurements of cerebral oxidative metabolism.

Adult↗

PubMed1989

Adrenergic receptors in aging and Alzheimer's disease: increased beta 2-receptors in prefrontal cortex and hippocampus.

Loss of pigmented noradrenergic locus ceruleus neurons occurs in Alzheimer's disease (AD) and, to a lesser extent, in aging. We studied beta-adrenergic receptors and their subtypes, beta 1 and beta 2, by the specific binding of 125I-pindolol to particulate membrane preparations from prefrontal cortex, hippocampus, putamen, and cerebellum and to sections from frontal cortex by in vitro autoradiography. In prefrontal cortex from controls, numbers of total beta- and beta 2-adrenoceptors did not significantly correlate with age, but number of beta 1-adrenoceptors showed a weak but significant negative correlation. Binding in tissue particulate preparations to total beta-receptors did not reveal significant differences in samples from prefrontal cortex between AD subjects and age-matched controls. However, beta 1-adrenoceptors were decreased and beta 2-adrenoceptors were increased in number by approximately 30-50% in AD subjects. Thus, the relative ratio of beta 1-/beta 2-receptors was decreased in AD. Binding by in vitro receptor autoradiography performed in a subset of samples of frontal cortex also showed beta 2-adrenoceptors, and less consistently total beta- and beta 1-receptors, to be increased significantly in number in cortical laminae II, III, IV, and V of tissue sections from AD subjects. In these subjects, number of locus ceruleus cells and norepinephrine concentrations in putamen and frontal cortex were markedly reduced compared with values in controls. In the hippocampus, total beta- and both beta 2- and beta 1-adrenoceptors were increased in number in AD. In contrast, in the putamen, where beta 1-receptors predominate, total beta- and beta 1-receptors were significantly decreased in number with no consistent change in content of beta 2-receptors in AD. There were no significant changes in the cerebellum. Specific pindolol binding was not affected by interval between death and sampling of tissue at autopsy. Our results indicate selective changes in number of beta-receptors in AD. These changes in the cortex and hippocampus suggest receptor upregulation in response to noradrenergic deafferentation from the locus ceruleus or may simply reflect glial proliferation in AD.

Aged↗

PubMed1989

Alterations in adrenergic receptors of frontal cortex and cerebral microvessels in Alzheimer's disease and aging.

Biochemical and pathological abnormalities are evident in the noradrenergic innervation of the cerebral cortex in Alzheimer's Disease (AD), and there is also a decline in aging, which may lead to changes in adrenergic receptors. To assess this question, we analyzed adrenergic receptor subtypes by ligand binding methods in prefrontal cortex and brain microvessels from subjects with AD and aging controls. Ligand binding to adrenoceptors and their subtypes did not change with postmortem delay in obtaining tissues. alpha 1-adrenergic receptors of the frontal cortex did not correlate with age but there was a small (approximately 25%), though significant, reduction in AD subjects. In cerebral microvessels, there were no changes in these receptors. alpha 2-receptors of the cortex significantly declined with age in controls and were also significantly reduced by approximately 50% in AD subjects. However, in cerebral microvessels alpha 2-adrenergic receptors were significantly increased by approximately 60% in AD. We suggest that presynaptic alpha 2-adrenoceptors on noradrenergic synapses may be those that are selectively decreased in the prefrontal cortex in AD. Total beta-receptors in cortex did not correlate with age, nor were they altered in AD. However, beta 1-receptors were decreased but beta 2-receptors were significantly increased in AD, indicating a change in the relative ratio of beta 1/beta 2-receptors. Similarly, beta 2-receptors of cerebral microvessels were significantly increased in AD. These changes suggest receptor "up-regulation" in response to noradrenergic denervation in AD and may reflect functional changes at the blood-brain barrier.

Adult↗

PubMed1989

Neurochemistry of dementia: establishing the links.

Neurochemical research in dementia needs to move beyond descriptive inventories of neurotransmitter systems affected in the specific disorders and to link to molecular studies of mechanism and clinical studies of cognition. New advances in Alzheimer's Disease (AD), Huntington's Disease (HD), and Parkinson's Disease (PD) are being guided by models of how nerve cells die in these disorders. Theories of pathophysiology which address the cellular level need to explain the selective vulnerability of neuronal populations in the different diseases. Clinically, the importance of neurochemical studies will be increased by understanding the bridges between neural and cognitive processes. Clinicians are concerned about the nosology of dementias, diagnostic tests, and more effective therapies. The value of neurochemical studies will be enhanced to the extent that they can contribute to understanding and modifying the clinical phenomenology of these disorders. In this paper, we will briefly review what is known about the neurochemistry of dementia but focus most of our attention on establishing the linkage between this level of description and the levels of description which are either "downstream" (molecular biology) or "upstream" (cognition) in terms of a reductionistic conception of understanding the disease process. We will explore how understanding neurochemistry relates to our understanding of disease mechanism and what constraints neurochemical studies place on understanding clinical aspects of disease. We will conclude by briefly discussing some of the problems with our current understanding of the neurochemistry of dementia and how we can address those problems in the future.

Alzheimer Disease↗

PubMed1989

The hexose transporter of human erythrocytes in aging and Alzheimer dementia.

The hexose transporter protein of human erythrocyte membranes was investigated in aging and in demented patients with Alzheimer disease (AD) and Parkinson disease (PD) by assessing the D-glucose-displaceable binding of the ligand cytochalasin-B. We found no alteration in the hexose transporter of erythrocyte membranes in aging or in dementia of AD and PD. These findings indicate that the marked decrease in the density of hexose transporter that we previously reported in the cerebral cortex and brain microvessels in AD do not occur in erythrocyte membranes that have the highest density of the hexose transporter protein.

Adult↗

PubMed1989

Abnormalities of the glucose transporter at the blood-brain barrier and in brain in Alzheimer's disease.

We have previously demonstrated the glucose transporter (GT) by [3H]cytochalasin B binding and immunocytochemistry in brain and in cerebral microvessels which form the blood-brain barrier. In this study, we assessed the GT protein in the frontal cortex, hippocampus, cerebellum, and cerebral microvessels in subjects with Alzheimer's disease (AD) and controls. In AD, we found a marked decrease in the GT in brain microvessels and in the frontal cortex and hippocampus, regions that are classically affected in AD, but there were no significant changes in the cerebellum. The binding of [3H]cytochalasin B to frontal cortex was not correlated with age or with the interval between death and autopsy. The impairment of GT in cerebral microvessels and cortex in AD subjects is relatively specific and appears to be disease-related. Our findings may be associated with the decreased in vivo measurements of cerebral oxidative metabolism in AD.

Aged↗

PubMed1988

The glucose transporter of the human brain and blood-brain barrier.

We identified and characterized the glucose transporter in the human cerebral cortex, cerebral microvessels, and choroid plexus by specific D-glucose-displaceable [3H]cytochalasin B binding. The binding was saturable, with a dissociation constant less than 1 microM. Maximal binding capacity was approximately 7 pmol/mg protein in the cerebral cortex, approximately 42 pmol/mg protein in brain microvessels, and approximately 27 pmol/mg protein in the choroid plexus. Several hexoses displaced specific [3H]cytochalasin B binding to microvessels in a rank-order that correlated well with their known ability to cross the blood-brain barrier; the only exception was 2-deoxy-D-glucose, which had much higher affinity for the glucose transporter than the natural substrate, D-glucose. Irreversible photoaffinity labeling of the glucose transporter of microvessels with [3H]cytochalasin B, followed by solubilization and polyacrylamide gel electrophoresis, labeled a protein band with an average molecular weight of approximately 55,000. Monoclonal and polyclonal antibodies specific to the human erythrocyte glucose transporter immunocytochemically stained brain blood vessels and the few trapped erythrocytes in situ, with minimal staining of the neuropil. In the choroid plexus, blood vessels did not stain, but the epithelium reacted positively. We conclude that human brain microvessels are richly endowed with a glucose transport moiety similar in molecular weight and antigenic characteristics to that of human erythrocytes and brain microvessels of other mammalian species.

Adult↗

PubMed1988

Neurochemical development of the striatum in a precocial (guinea pig) and an altricial (rat) species.

In this study, the developmental patterns of key neurotransmitter marker enzymes, namely choline acetyltransferase (ChAT), glutamate decarboxylase (GAD), and tyrosine hydroxylase (TH) in the corpus striatum were compared between the guinea pig and rat. In an attempt to assess cell acquisition and differentiation, striatal DNA and protein content were also determined during development in the two species. The most outstanding feature apparent from these investigations was a sequential maturation of the three neurotransmitter-synthesizing enzymes: TH and GAD first, followed by ChAT in striata of both species. The developmental increase in DNA content suggests that cell acquisition in the rat striatum is approximately 50% at birth, whereas in the guinea pig, the total population is present before birth, and thereafter cell numbers decline. The accretion of protein, reflecting the increase in region size, continued into adulthood in both species. With emphasis on cholinergic neurons, the neurochemical findings are assessed in relation to the morphological descriptions of cellular changes during pre- and postnatal development of the striatum.

Animals↗

PubMed1988

Adenosine receptors and the nucleoside transporter in human brain vasculature.

Evidence suggests that adenosine modulates neuronal and cerebral vascular functions by interacting with specific receptors on brain cells and blood vessels. Adenosine and other nucleosides are also transported across the blood-brain barrier via a saturable, carrier-mediated mechanism. Using direct ligand binding methods, we studied the two adenosine receptor subtypes, A1 and A2 and the nucleoside transporter moiety in human brain microvessels, pial vessels, choroid plexus, and cerebral cortex membranes. The following specific tritiated ligands were used: cyclohexyladenosine (CHA) for A1 receptors; 5'-N-ethylcarboxamide adenosine (NECA) for A2 receptors; nitrobenzylthioinosine (NBMPR) and dipyridamole (DPY) for nucleoside transporters. We find that cerebral microvessels, pial vessels, and choroid plexus have few, if any, A1 receptors, in contradistinction to cerebral membranes, which have a 10-20-fold higher density of A1 receptor sites. Specific high-affinity NECA binding to A2 receptors in cerebral microvessels, pial vessels, and choroid plexus was saturable and was equivalent to that of cerebral cortical membranes. The Bmax and Kd of the high-affinity NECA binding to vessel preparations were approximately 1.3 pmol/mg protein and approximately 250 nM, respectively, which is similar to our previous findings in the rat and pig. NBMPR and DPY binding were also saturable and were consistent with a single class of high-affinity binding sites. The density of nucleoside transporters was approximately four-fold higher in cerebral microvessels than in cerebral cortex, pial vessels, and choroid plexus. These results suggest that human cerebral microvessels have A2, but not A1, receptors and are particularly enriched with the adenosine transporter moiety.

Adenosine↗

PubMed1988

Monoamine oxidases of the human brain and liver.

The two molecular forms of monoamine oxidase (MAO), MAO-A and MAO-B, were determined quantitatively in discrete regions of the human brain at autopsy, and in cerebral microvessels, choroid plexus and liver samples from the same subjects. MAO was assessed by specific[3H] pargyline binding, which is stoichiometric and irreversible, and by measuring the rate of oxidation of several MAO substrates. Basal ganglia structures (caudate, putamen, globus pallidus and substantia nigra) and hippocampus had about twice the levels of MAO that were present in the cerebral cortex and cerebellum. Cerebral microvessels, which constitute the blood-brain barrier, had minimal MAO, while the choroid plexus, which constitutes the blood-cerebrospinal fluid barrier, and the liver had higher MAO levels than any brain region. The vast majority of MAO (80-95%) in these tissues was of the B type, except in microvessels, where total MAO activity was low. Specific [3H]pargyline binding correlated well with the oxidation rates for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and benzylamine in all tissues. Both specific [3H]pargyline binding and the rate of oxidation of MAO substrates increased with age.

Adult↗

PubMed1988

Glucose transporter of the blood-brain barrier and brain in chronic hyperglycemia.

The effect of chronic hyperglycemia on the glucose transporter moiety of the blood-brain barrier and cerebral cortex was studied in rats 3 weeks after the administration of a single intravenous dose of streptozotocin (60 mg/kg), using specific [3H]cytochalasin B binding methods. Streptozotocin-treated rats developed hyperglycemia, as well as polydipsia and polyuria, and failed to gain weight. The density of D-glucose-displaceable cytochalasin B binding sites in the brain microvessels of streptozotocin-treated hyperglycemic rats was increased by about 30% compared with those of control rats, without change in the affinity of binding. Chronic hyperglycemia had no effect on the density or affinity of specific binding of cytochalasin B to cerebral cortical membranes. These findings do not support the hypothesis that glucose transporters in brain microvessels comprising the blood-brain barrier are "down-regulated" in chronic hyperglycemia.

Animals↗

PubMed1988

On the mechanisms underlying 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity. II. Susceptibility among mammalian species correlates with the toxin's metabolic patterns in brain microvessels and liver.

Systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes parkinsonism in humans and other primates, but not in rats; mice are intermediate in their susceptibility which varies among strains. We hypothesized previously that the rat's resistance to systemic MPTP toxicity is likely due to the unique enrichment of its blood-brain barrier with enzymes that metabolize MPTP. MPTP metabolites, such as 1-methyl-4-phenylpyridinium (MPP+) and 1-methyl-4-phenyl-2,3-dihydropyridinium, may have difficulty in traversing biological membranes and reaching the brain sites of toxicity. We tested this hypothesis by studying MPTP metabolism: 1) in vitro, by human, rat and mouse brain microvessels and 2) in vivo, in the brain and liver of Wistar rats and two strains of mice known to react differently to systemic MPTP. We found that rat brain microvessels were very efficient at converting MPTP to MPP+ and that this conversion was abolished by pargyline. Microvessels from C57 black mice, which are more sensitive to MPTP toxicity than CF1 white mice, were less capable of metabolizing MPTP to MPP+. Human microvessels were least capable of producing MPP+. In vivo metabolism of MPTP in Wistar rats and the two strains of mice showed that the clearance of MPTP and its metabolites from the brains was most rapid in rats, intermediate in white mice and slowest in black mice. On the other hand, liver metabolism of MPTP by the three groups of animals showed a high rate of MPTP metabolism to a compound(s) other than MPP+ in rats, and a lower rate in mice.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1987

Correlation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity with blood-brain barrier monoamine oxidase activity.

Systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes parkinsonism in humans and subhuman primates, but not in rats and many other laboratory animals; mice are intermediate in their susceptibility. Since MPTP causes selective dopaminergic neurotoxicity when infused directly into rat substantia nigra, we hypothesized that systemic MPTP may be metabolized by monoamine oxidase and/or other enzymes in rat brain capillaries and possibly other peripheral organs and thus prevented from reaching its neuronal sites of toxicity. We tested this hypothesis by assessing monoamine oxidase in isolated cerebral microvessels of humans, rats, and mice by measuring the specific binding of [3H]pargyline, an irreversible monoamine oxidase inhibitor, and by estimating the rates of MPTP and benzylamine oxidation. [3H]Pargyline binding to rat cerebral microvessels was about 10-fold higher than to human or mouse microvessels. Also, MPTP oxidation by rat brain microvessels was about 30-fold greater than by human microvessels; mouse microvessels yielded intermediate values. These results may explain, at least in part, the marked species differences in susceptibility to systemic MPTP. They also suggest the potential importance of "enzyme barriers" at the blood-brain interface that can metabolize toxins not excluded by structural barriers, and may provide biological bases for developing therapeutic strategies for the prevention of MPTP-induced neurotoxicity and other neurotoxic conditions including, possibly, Parkinson disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1987

Blood-brain barrier monoamine oxidase: enzyme characterization in cerebral microvessels and other tissues from six mammalian species, including human.

We studied the enzyme monoamine oxidase (MAO) in isolated cerebral microvessels, and in mitochondria-enriched brain and liver preparations from six mammalian species, including human. We also studied MAO distribution in various tissues and in discrete brain regions of the rat. MAO was assessed by measuring the specific binding of [3H]pargyline, an irreversible MAO inhibitor, and the rates of oxidation of known MAO substrates: benzylamine, tyramine, tryptamine, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Molecular forms of MAO were examined by using specific MAO inhibitors, and by polyacrylamide gel electrophoresis after [3H]pargyline binding. In general, the liver from all species had higher MAO levels than the brain, with minor variation among species in their brain and liver MAO content. However, there were remarkable species differences in brain microvessel MAO, with rat microvessels having one of the highest MAO activity among all tissues, whereas MAO activities in brain microvessels from humans, mice, and guinea pigs were very low. In most rat tissues, including the brain, there was a preponderance of MAO-B over MAO-A. The only exceptions were the heart and skeletal muscle. Estimates of MAO half-life in rat brain microvessels, rat brain, and rat liver indicated that microvessel MAO had a higher turnover rate. The reasons underlying the remarkable enrichment of rat cerebral microvessels with MAO-B are unknown, but it is evident that there are marked species differences in brain capillary endothelium MAO activity. The biological significance of these findings vis a vis the role of MAO as a "biochemical blood-brain barrier" that protects the brain from circulating neurotoxins and biogenic amines should be investigated.

Adult↗

PubMed1987

Differential postnatal development of monoamine oxidases A and B in the blood-brain barrier of the rat.

We studied the monoamine metabolizing mitochondrial enzyme, monoamine oxidase (MAO), in cerebral microvessels obtained from postnatally developing rats by measuring the specific binding of [3H]pargyline, an irreversible inhibitor of MAO, and the rate of oxidation of three known MAO substrates: benzylamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and tryptamine. MAO activity increased postnatally, with the greatest increase occurring in the second week and reaching a peak at 3 weeks of age. A concomitant increase in MAO of the cerebral cortex also occurred, but was several-fold less than that of cerebral microvessels. Using clorgyline and deprenyl, relatively specific inhibitors of MAO-A and MAO-B, we showed that cerebral microvessels contain both forms of MAO at all ages, but there was a major preponderance in the postnatal development of MAO-B. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of rat microvessels after [3H]pargyline binding also showed two distinct bands of radioactivity at all ages. These two bands corresponded to molecular weights of approximately 65,000 for MAO-A and approximately 60,000 for MAO-B. SDS-PAGE results of brain microvessels obtained from 1-, 14-, and 42-day-old rats confirm the differential postnatal development of MAO-B in rat brain microvessels.

Aging↗

PubMed1986

Decreased neurotransmitter receptor binding in striatum and cortex from adult hypothyroid rats.

The consequences of propylthiouracil-induced thyroid deficiency on pre- and postsynaptic biochemical markers in the corpus striatum and the visual cortex were investigated in adult rats. Hypothyroidism in adult rats significantly impaired (by 30%) striatal [3H]spiroperidol binding capacity. In the visual cortex, small but significant reductions in [3H]WB.4101 and in [3H]muscimol binding were evident, whereas glutamate decarboxylase activity was increased by 18% in the thyroid-deficient rats. Compatible with previous morphological evidence (Ruiz-Marcos et al.), the present observations may imply alterations in dendritic morphology of neurones in the striatum and cortex during long-term hypothyroidism in adult rats. However, the molecular changes observed suggest a differential sensitivity of transmitter-specific neurones in the central nervous system to thyroid hormone.

Animals↗

PubMed1986

Adenosine receptors of cerebral microvessels and choroid plexus.

We studied, by ligand binding methods, the two adenosine receptors, A1 and A2, in rat and pig cerebral microvessels and pig choroid plexus. Ligand binding to cerebral microvessels was compared with that to membranes of the cerebral cortex. [3H]Cyclohexyladenosine and [3H]L-phenylisopropyladenosine were the ligands used for A1-receptors, and [3H]5'-N-ethylcarboxamide adenosine ([3H]NECA) was used to assess A2-receptors. We report that cerebral microvessels and choroid plexus exhibit specific [3H]NECA binding, but have no appreciable A1-receptor ligand binding sites. Specific binding of [3H]NECA to cerebral microvessels, choroid plexus, and cerebral cortex was saturable and suggested the existence of two classes of A2-receptor sites: high-affinity (Kd approximately 250 nM) and low-affinity (Kd approximately 1-2 microM) sites. The Kd and Bmax of NECA binding to cerebral microvessels and cerebral cortex were similar within each species. Our results, indicating the existence of A2-receptors in cerebral microvessels, are consistent with results of increased adenylate cyclase activity by adenosine and some of its analogues in these micro-vessels.

Adenosine↗