Sites In Human Brain Research Articles

Parametric in vivo imaging of benzodiazepine receptor distribution in human brain.

Emission computed tomographic methods for the in vivo quantification of radioligand-binding sites in human brain have previously been limited either by a lack of correction for possible effects of altered ligand transport or by highly complicated physiological models that preclude display of binding data in a detailed anatomical format. We investigated the application of a simplified compartmental model to the kinetic analysis of in vivo ligand binding to central benzodiazepine receptors. The human brain distribution of [11C]flumazenil, as determined by dynamic positron emission tomography, combined with metabolite-corrected arterial blood samples, permitted estimations of local cerebral ligand transport and of receptor binding. This approach allows calculation of transport and binding "maps" on a pixel-by-pixel basis, resulting in the display of binding data in a familiar tomographic format while maintaining much of the physiological accuracy inherent in more complex methods. The results obtained in a study of 6 normal volunteers revealed good interindividual precision, with coefficients of variation between 10 and 15% of mean regional values, suggesting the utility of this approach in future clinical studies of benzodiazepine receptor binding.

Distribution of catecholamine uptake sites in human brain as determined by quantitative [3H] mazindol autoradiography

Because of the importance of the catecholamine system in Parkinson's disease and its relevance to a variety of clinical movement disorders, catecholamine uptake sites were mapped in the human brain using [3H] mazindol autoradiography. Displacement studies with known dopamine (DA) and noradrenaline (NA) uptake blockers showed that binding in the striatum was to dopamine uptake sites; binding in the locus coeruleus was to noradrenergic uptake sites. By using the selective noradrenergic uptake blocker desmethylimipramine (DMI), a comprehensive map of both DA and NA uptake sites was generated. In general, catecholamine uptake sites were better seen in terminals than in cells of origin or axonal projections. In some areas, such as the locus coeruleus, punctate binding could be seen over individual pigmented cells. A variegated pattern of binding was seen in caudate nucleus and putamen and some correspondence of patches of low binding with striosomes was observed in the caudate. The highest levels of binding to DA uptake sites was observed in the striatum, where regional differences in binding occurred. The most dense binding was seen in the ventral striatum, and a rostral-to-caudal decrement in binding levels in caudate nucleus and putamen was evident. Binding was more intense in the putamen compared to the caudate and within the caudate lower values were seen laterally. The highest levels of binding to noradrenergic uptake sites were in the locus coeruleus and dorsal raphé, although these sites may be on terminals from other projections. Whereas uptake sites were more often evident in known catecholamine pathways, [3H] mazindol binding was seen in some areas where catecholamine neurons or terminals had not been identified previously. These maps of the catecholamine uptake system add further information concerning the nature of the distribution of catecholamines in human brain and provide an important baseline for the study of disease and ageing processes.

Characterization and quantification of 125I-bolton hunter substance P binding sites in human brain

(125)I-Bolton Hunter substance P (BHSP) specific binding sites in human brain synaptosomal membrane preparations were studied with respect to binding characteristics and regional distribution. Specific binding of (125)I-BHSP, which constituted 75% of total binding, and 7% of the total radioactivity added to the incubation medium, was saturable and stable at 20 degrees C. Scatchard analysis of data from equilibrium studies revealed the existence of a single class of binding sites (K(D) = 0.37 nM, B(MAX) = 47.3 fmol/mg tissue protein) in human nucleus caudatus. Competitive studies of (125)I-BHSP binding in human nucleus caudatus gave the following rank order of potencies among tachykinins: substance P > physalaemin > neurokinin A ? neurokinin B ? kassinin ? eledoisin. Measurements of (125)I-BHSP receptor binding densities in different regions of autopsy human brain revealed highest densities in the corpus of nucleus caudatus and the putamen. Moderately high binding densities were detected in the amygdala, hypothalamus, caput of nucleus caudatus and certain parts of the frontal lobe, whereas other regions showed only low levels of binding.

3H]Nipecotic Acid Binding to γ‐Aminobutyric Acid Uptake Sites in Postmortem Human Brain

Binding of [3H]nipecotic acid, a proposed marker for GABAergic neurons, was investigated in postmortem human brain by use of a centrifugation assay. Binding was displaceable, apparently saturable, and to a single site, with typical KD and Bmax values of 1.85 microM and 124.2 pmol/mg of protein in the hippocampus. Regional distribution studies indicated a heterogeneous population of [3H]nipecotic acid binding sites with highest concentrations in the lateral globus pallidus. Putamen tissue from four cases of Huntington's disease showed a marked reduction in [3H]nipecotic acid binding. Binding correlated with both age and postmortem delay in the hippocampus. There was an effect of agonal state in which prolonged illness before death apparently caused a reduction in binding. Our results indicate that [3H]nipecotic acid may be used successfully as a marker for neuronal GABAergic uptake sites in human brain, but that the effects of variables such as age, postmortem delay, and agonal state must always be taken into account.

Prolactin binding sites in human brain and choroid plexus

Prolactin binding sites in human brain and choroid plexus

Neuropeptide Y receptor binding sites in human brain. Possible alteration in Alzheimer's disease

Neuropeptide Y (NPY) and peptide YY (PYY) receptor sites were studied in human brain using saturation binding experiments and receptor autoradiography. Additionally, the affinities and densities of [ 3H]NPY binding sites were compared in the temporal cortex, hippocampus and putamen of patients dying from Alzheimer's disease (AD) and aged matched controls. High densities of [ 3H]NPY binding sites were found in the putamen ( 192 ± 32fmol/mg protein), followed by the hippocampus ( 165 ± 42fmol/mg protein) and temporal cortex ( 118 ± 19fmol/mg protein). Receptor autoradiography revealed that these sites were especially concentrated in certain layers of the hippocampus, laminae I and IV–V of the temporal cortex and the amygdalo-hippocampal area. No significant changes in [ 3H]NPY binding affinities were seen between the AD and aged-matched groups ( K d ranges: 2.5–6.8 nM). However significant decreases in [ 3H]NPY receptor densities ( B max ) were found in temporal cortex (−43%) and hippocampus (−49%) in AD brains. No significant change in [ 3H]NPY B max values was found in the putamen. It is therefore possible that decreases in [ 3H]NPY receptor densities may be associated to the degenerative process taking place in certain brain regions in AD, although further work will be necessary to confirm this hypothesis. Part of this work was presented at the 17th Annual Meeting of the Society for Neuroscience 35.

Lack of asymmetry in serotonin uptake sites in human brain : Bruce Parsons, M.D., Ph.D., Yung-Yu Huang, M.S., Narendra Budhakar, M.D., Shaoning Wang, M.D., Michael Stanley, Ph.D. New York State Psychiatric Institute, New York, NY 10032

Lack of asymmetry in serotonin uptake sites in human brain : Bruce Parsons, M.D., Ph.D., Yung-Yu Huang, M.S., Narendra Budhakar, M.D., Shaoning Wang, M.D., Michael Stanley, Ph.D. New York State Psychiatric Institute, New York, NY 10032

Characterization of [3H]Hemicholinium‐3 Binding Sites in Human Brain Membranes: A Marker for Presynaptic Cholinergic Nerve Terminals

We report here on the binding properties of [3H]hemicholinium-3, a selective inhibitor of the high-affinity choline uptake process, to human brain membranes. Under the assay conditions described, the binding of [3H]hemicholinium-3 exhibited a dependency of physiological conditions on pH, temperature, and NaCl concentrations. Striatal binding proved to be specific, to a single site, saturable, and reversible, with an apparent KD of 10 nM and a Bmax of 82 fmol/mg of protein. [3H]Hemicholinium-3 specific binding exhibited a pharmacological profile and an ionic dependency suggestive of physiologically relevant interactions and comparable with those reported for the high-affinity choline uptake. Moreover, specific [3H]hemicholinium-3 binding exhibited an uneven regional distribution: striatum much greater than nucleus basalis greater than spinal cord much greater than midbrain = cerebellum greater than or equal to hippocampus greater than neocortex = anterior thalamus greater than posterior thalamus much much greater than white matter. This distribution closely corresponds to the reported activity of both enzymatic cholinergic presynaptic markers and high-affinity choline uptake in mammalian brain. There are no significant differences between these results and those previously found in the rat brain using this radioligand. Our results demonstrate, for the first time, the presence of [3H]hemicholinium-3 binding sites in human brain and strongly support the proposal that this radioligand binds to the carrier site mediating the high-affinity choline uptake process on cholinergic neurons. Thus, [3H]hemicholinium-3 binding may be used in postmortem human brain as a selective and quantifiable marker of the presynaptic cholinergic terminals.

Autoradiographic distribution of [ 3H]hemicholinium-3 binding sites in human brain

Since previous radioligand binding studies support the evidence that [ 3H]hemicholinium-3 ([ 3H]HC-3) selectively labels the high-affinity choline uptake (HACU) process, we have studied the autoradiographic characteristics and regional distribution of [ 3H]HC-3 binding to post mortem human brain tissue. [ 3H]HC-3 specific binding was saturable, of high affinity and exhibited an uneven distribution. High densities were observed in caudate-putamen, nucleus basalis accesorius of the amygdala, hippocampal gyrus dentatus and CA3 field, locus niger, nucleus interpeduncularis and motor trigeminal and facial nuclei. Low densities were found in areas such as neocortex, thalamus, hypothalamus or cerebellum. Our results agree with those obtained in human brain membranes and are comparable to previous autoradiographic data from rat brain. Remarkably, the distribution of [ 3H]HC-3 binding sites closely corresponds with that of cholinergic enzymatic presynaptic markers and HACU. These findings, together with previous data from membrane studies, allow the use of [ 3H]HC-3 as a selective anatomical marker of cholinergic presynaptic terminals.

High affinity serotonin binding sites in human brain: a comparison of cerebral cortex and basal ganglia

The high-affinity binding of 3H-serotonin and 3H-DPAT was studied in membrane preparations and tissue sections of cerebral cortex and basal ganglia of human brain. In tissue sections, 3H-serotonin bound to sites present at high density in the cerebral cortex, hippocampus and basal ganglia. 3H-DPAT bound predominantly to the outer layers of the cerebral cortex and the hippocampus, no significant binding was observed in the basal ganglia. In cortical membranes 3H-serotonin bound to a heterogeneous population of sites, one of which was similar to a binding site labelled by 3H-DPAT (the putative 5HT-1A receptor). 3H-serotonin binding to membranes prepared from the putamen displayed low affinity for DPAT, mesulergine and spiperone, RU24969 was considerably less potent than serotonin itself. This 3H-serotonin binding site does not have the properties of those sites described in rodent brain (5HT-1A, 5HT-1B, and 5HT-1C), and may represent a novel serotoninergic binding site.

Phorbol ester binding sites in human brain: characterization, regional distribution, age-correlation, and alterations in Parkinson's disease.

We have characterized and localized phorbol ester binding sites in human autopsied brains, using [3H]phorbol 12,13-dibutyrate ([3H]PDBu). When the tissue was homogenized in the absence of Ca2+ chelator (10 mM EGTA/2 mM EDTA), Scatchard analysis of the specific [3H]PDBu bindings to both particulate and soluble fractions yielded a single class of high-affinity binding site (Kd = 7.1 and 7.4 nM: Bmax = 45.4 and 3.1 pmol/mg protein, respectively). The particulate fraction retained the majority of [3H]PDBu binding (98% of total binding activity), while the soluble fraction was almost devoid of binding activity (2%). In the presence of Ca2+ chelator, more of the activity was found in the soluble fraction (30%). The binding of [3H]PDBu was potently inhibited by active phorbol esters and related diterpenes with Ki of nanomolar concentration but not by inactive ones. Diolein (OAG), a synthetic diacylglycerol, and polymixin B, an inhibitor of protein kinase C (PKC), inhibited the binding moderately (Ki = 5.8 and 1.3 microM, respectively). H-7, an inhibitor of PKC and cyclic nucleotides-dependent kinase, did not compete with [3H]PDBu for the binding sites (Ki greater than 100,000 nM). The regional distribution of specific [3H]PDBu binding in the human brain was rather uneven and resembled that of [3H]PDBu autoradiograms and PKC-like immunoreactivities in the rat brain. The binding capacities were generally in the order: rhinencephalon greater than basal ganglia greater than cerebral cortex greater than diencephalon greater than cerebellum greater than mesencephalon. Age-related loss of binding sites was observed in the prefrontal cortex of the subjects 33-81 years of age. In Parkinson's disease, the phorbol ester binding showed a significant reduction in the substantia nigra, caudate putamen, and pallidum, whereas it was unchanged in the prefrontal cortex and caudate nucleus of schizophrenics, when compared with the relevant controls.

1-( m-Chlorophenyl)piperazine (mCPP) interactions with neurotransmitter receptors in the human brain

The affinity of 1-(m-chlorophenyl)piperazine (mCPP) for 11 neurotransmitter receptor binding sites was determined in human brain membranes. mCPP is essentially equipotent at all 5-hydroxytryptamine (5-HT) receptor subtypes (IC 50 values ranging from 360 to 1300 nM). The drug displays similar affinity ( IC 50 = 570 nM for alpha 2-adrenergic receptors labeled for 3H-rauwolscine. mCPP is less potent at alpha 1 and beta-adrenergic, dopamine, and muscarinic cholinergic receptors (IC 50 values 2500-24,000 nM). mCPP is inactive at both benzodiazepine receptors and the 5-HT uptake sites at concentrations below 100,000 nM. These data demonstrate that mCPP displays similar potency for multiple neurotransmitter receptor binding sites in human brain.

P-034 - Characterization of [3H]inositol 1,4,5-trisphosphate binding sites in human brain

P-034 - Characterization of [3H]inositol 1,4,5-trisphosphate binding sites in human brain

3H]inositol 1,4,5-trisphosphate binding sites in human brain: Binding characteristics and changes in the brain of patients with Parkinson's disease : Takeshi Hashimoto, Noboru Kitamura, Takashi Nakai, Yasuo Kajimoto, Osamu Komure, Naoki Nishino, Chikako Tanaka, Department of Pharmacology, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650, Japan

3H]inositol 1,4,5-trisphosphate binding sites in human brain: Binding characteristics and changes in the brain of patients with Parkinson's disease : Takeshi Hashimoto, Noboru Kitamura, Takashi Nakai, Yasuo Kajimoto, Osamu Komure, Naoki Nishino, Chikako Tanaka, Department of Pharmacology, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650, Japan

Calcium Channel Binding Sites in Human Braina

Calcium Channel Binding Sites in Human Brain^a

Specific [ 3H]UK14,304 binding in human cortex occurs at multiple high affinity states with alpha 2-adrenergic selectivity and differing affinities for GTP

[ 3H]UK14,034 is a full agonist at α2-adrenergic receptors. Although the characteristics of the binding of the partial α2-adrenergic agonists in postmortem human brain were known, the binding of [ 3H]UK14,304 had not been studied in this issue. Multi-site binding of this radiolabel had been reported in other tissues and guanosine triphosphate (GTP) had been shown to reduce [ 3H]UK14,304 binding. We now report that [ 3H]UK14,304 labels at least 2 specific binding sites in human brain that both have the characteristics of an α2-adrenergic binding site. GTP decreases agonist binding at both of these sites, but with different potencies at each site.

3H]Neurotensin(8–13) Binds in Human Brain to the Same Sites as Does [3H]Neurotensin but with Higher Affinity

The binding of [3H]neurotensin(8-13) to membranes from human frontal cortex at 0 degree C was time dependent, specific, saturable, and reversible. Saturation isotherms provided an equilibrium dissociation constant (KD) of 0.52 nM, and the maximal number of binding sites (Bmax) was 3.5 pmol/g original wet weight of tissue. Scatchard analysis yielded a straight line, and the Hill coefficient was equal to 1, a result indicating that [3H]neurotensin(8-13) bound to single, noncoopertive sites. The KD values of several analogs of neurotensin determined in competition with [3H]neurotensin(8-13) were similar to those previously determined in competition with [3H]neurotensin. The regional distribution of binding sites for [3H]neurotensin(8-13) was also similar to that for [3H]neurotensin. These results suggest that [3H]neurotensin(8-13) binds to the same sites as [3H]neurotensin and that [3H]neurotensin(8-13) has a higher affinity than [3H]neurotensin for these sites in human brain.

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 heterogenous high-affinity binding sites in human thalamus. Scatchard analysis of the binding gave a K d of 0.58 nM and a B max of 3.3 pmol/g protein for the ‘super high-affinity’ site and a K d of 27 nM and a B max 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.

Relationships between CSF drug concentrations, receptor binding characteristics, and pharmacokinetic and pharmacodynamic properties of selected 1,4-substituted benzodiazepines.

Pharmacokinetic profiles of the 1,4-substituted benzodiazepines are defined by their absorption, distribution, metabolism, and excretion characteristics. An ability to cross the blood-brain barrier and the onset of pharmacological activity have been associated with the physiochemical properties of the benzodiazepines. In addition, drug concentrations in the CSF correlate with the unbound drug concentrations in blood or plasma. Duration of pharmacological activity of the benzodiazepines in humans is associated with the affinity of these compounds for the benzodiazepine receptors in human brain. Therefore, benzodiazepines with high affinity for the benzodiazepine receptor sites in human brain tend to exhibit prolonged half-lives of elimination from the CSF which correlate with the prolonged duration of clinical and pharmacological effects and lower therapeutic doses of these drugs in vivo.

Divergent changes in D-1 and D-2 dopamine binding sites in human brain during aging

The density of D-1 and D-2 dopamine receptors in human caudate nucleus and putamen, obtained postmortem, were studied throughout the adult lifespan using [ 3H]fluphenazine as the dopamine receptor ligand. The D-1 subtype increased progressively with age in both regions, while the D-2 subtype declined in caudate nucleus. The ratio of D-1/D-2 B max in both regions increased from approximately 1 at age 20 to 2 by age 75. The dopamine content in putamen declined with age and was inversely correlated with D-1 receptor density. We suggest that D-1 receptor density is up-regulated by loss of dopamine during aging. The D-2 receptor density in caudate nucleus was positively correlated with choline acetyltransferase activity, suggesting that loss of intrastriatal neurons with age may contribute to the decrease in D-2 sites. These divergent changes in dopamine receptor subtypes with age result in an altered complement of dopamine receptors in older humans and may provide a basis for selective pharmacotherapy in disorders of the basal ganglia.