摘要:

Remarkable advances during the past few years have sparked new interest in the molecular identification of receptor types and in the spatiotemporal regulation of their expression. Because dopamine (DA) receptors have been implicated in major neuropsychiatric illnesses, such as schizophrenia and affective disorders, both of which have significant heritable components, new research is now aimed at testing hypotheses which deal with the genetic regulation of DA receptor expression and with linkage of such expression to behavioral disorders. The purpose of this article, which is not intended to be an exhaustive review, is to examine the findings of two decades of genetic studies on DA receptor expression in terms of radioligand binding and inbred mouse and rat strains, as well as to discuss some of the pitfalls in past research and new strategies in current work.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08317.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:In brain synaptic membranes not extensively washed, (+)‐5‐[3H]methyl‐10,1 l‐dihydro‐5H‐dibenzo[a, d]‐cyclohepten‐5,10‐imine ([3H]MK‐801) binding was markedly inhibited in a concentration‐dependent manner (at concentrations above 1μM) by several compounds having antagonistic activity at the Ca2+‐binding protein calmodulin. Scatchard analysis revealed thatN‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulfonamide (W‐7) inhibited the binding through a significant decrease in the density of binding sites without affecting the affinity at 10μM. In membranes extensively washed and treated with a low concentration of Triton X‐100, L‐glutamic acid (Glu) drastically accelerated the initial association rate of [3H]MK‐801 binding with glycine (Gly), almost doubling the initial association rate found in the presence of Glu alone. The addition of W‐7 invariably reduced the initial association rate observed in the presence of either Glu alone or both Glu and Gly, without significantly altering the dissociation rate of bound [3H]‐MK‐801, irrespective of the presence of the two stimulatory amino acids. The maximal potencies of Glu, Gly, and spermidine in potentiating the binding were all attenuated by W‐7. These results suggest that calmodulin antagonists may interfere with opening processes of an ion channel associated with anN‐methyl‐D‐aspartate‐sensi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08318.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:Three major subtypes of glutamate receptors that are coupled to cation channels—N‐methyl‐d‐aspartate (NMDA), kainate, and α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA) receptors—are known as ionotropic receptors in the mammalian CNS. Recently, an additional subtype that is coupled to GTP binding proteins and stimulates (or inhibits) metabolism of phosphoinositides has been proposed as a metabotropic receptor. Incubation of dispersed hippocampal cells from adult rats with glutamate or NMDA decreased forskolin‐stimulated cyclic AMP (cAMP) accumulation; half‐maximal effects were obtained with 5.6 ± 2.2 and 6.4 ± 2.3 μM, respectively. Kainate and quisqualate were less potent. The effect of glutamate was antagonized by 2,3‐diaminopropionate and 2‐amino‐5‐phosphonovalerate, NMDA/glutamate receptor antagonists, but not by 0.5 μMJoro spider toxin, a specific blocker of the AMPA receptor. The inhibitory effect of glutamate on cAMP formation was not blocked by 2 μMtetrodotoxin or by the absence of Ca2+. In hippocampal membranes, glutamate, similar to carbachol, inhibited adenylate cyclase activity in a GTP‐dependent manner. These findings suggest that the glutamate inhibition of adenylate cyclase is direct and is not due to a result of the release of other neurotransmitters. The effect of glutamate on cAMP accumulation was observed in an assay medium containing 0.7 mMMgCl2, which is known to inhibit both ionotropic NMDA receptor/channels in the hippocampus and metabotropic NMDA receptors in the cerebellum. The inhibitory effect of glutamate was abolished by pertussis toxin treatment. In conclusion, the rat hippocampus appears to contain a novel class of metabotropic receptors that prefer glutamate and NMDA and is coupled with adenylate cyclase in an inhibitory manner via per

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08319.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The binding of α‐[3H]amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid ([3H]AMPA), a selective ligand for the ion channel‐linked quisqualate receptor, was evaluated in Triton X‐100‐treated membranes of human cerebral cortex. The presence of chaotropic ions produced divergent effects on specific [3H]AMPA binding: A twofold increase in the binding was observed with thiocyanide at 100 mM, although iodide (100 mM) and perchlorate (100 mM) reduced the binding. Chemical modifications of the sulfhydryl group withp‐chloromercuriphenylsulfonic acid (PCMBS) produced threefold increases in specific [3H]‐AMPA binding in the absence of KSCN as well as in the presence of KSCN. Treatment with dithiothreitol restored the enhanced specific [3H]AMPA binding by PCMBS to the basal level. Although specific [3H]AMPA binding in the absence of KSCN showed a single site (KD=220 nM, Bmax= 235 fmol/mg of protein), curvilinear Scatchard plots of, specific [3H]AMPA binding in the presence of 100 mMKSCN can be resolved into two binding sites with the following parameters:KDI= 5.82 nM, Bmaxx= 247 fmol/mg of protein;KD2= 214 nM, Bmax2= 424 fmol/mg of protein. Quisqualate and AMPA were the most potent inhibitors of the [3H]AMPA binding in the presence of KSCN. Potent inhibitors of the binding included β‐N‐oxalylamino‐l‐alanine (l‐BOAA), cysteine‐S‐sulfate, l‐glutamate, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione, and 6,7‐dinitroquinoxaline‐2,3‐dione. Kainate, l‐homocysteine sulfinic acid, and l‐homocysteic acid were active with an IC50value of a micromolar concentration, whereas l‐cysteic acid and l‐cysteine sulfinic acid were weakly active.N‐Methyl‐d‐aspartate, l‐aspartate,N‐acetylaspartylglutamate, quinolinate, and 1‐naphthylacetyl spermine, an analogue of Joro spider toxin, were inactive at 1 mM. These results suggest that l‐glutamate has an important effect on AMPA receptors in the human cerebral cortex and that l‐BOAA and cysteine‐S‐sulfate exhibit their neurotoxicity through AMPA receptors. Specific [3H]AMPA binding, using the ligand at 6 nM, in the presence of 100 mMKSCN exhibited a heterogeneous distribution pattern in the human cerebral cortex: [3H]AMPA binding values were high in the frontal and occipital cortex, whereas they were low in the parietotemporal cortex. However, no statistically significant changes in [3H]AMPA binding were observed in 22 brain areas of the cerebral cortex of chronic schizophrenics, compared with controls, suggesting that AMPA receptors in the cerebral cortex are minimally involved in an

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08320.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The polypeptide composition and glycosylation of soluble isoforms of neural cell adhesion molecule (NCAM) in developing rat brain, CSF, and plasma were characterized. Soluble NCAM in rat brain consisted of several glycosylated isoforms. The degree of glycosylation was developmentally regulated. After desialylation, four polypeptides of Mrvalues of ∼ 190,000 (sl), 135,000 (s2), 115,000 (s3), and 110,000 (s4) were observed. Polypeptides si, s2, and s3 were also present in CSF, whereas only s3 and s4 were observed in plasma. Treatment of soluble brain NCAM withN‐glycosidase F, which removesN‐linked carbohydrates, produced polypeptides of Mrvalues of ∼ 190,000, 125,000, and 108,000–97,000. The monoclonal antibody OB11, which recognizes an epitope on the cytoplasmic part of transmembrane forms of NCAM, did not react with any of the soluble isoforms. Purified soluble NCAM, consisting mainly of s3, contained anN‐terminal sequence identical to that of membrane‐associated NCAM. Gel nitration of s3 indicated that it was present as a dimer under the chosen conditions. NCAM‐expressing glioma cells adhered specifically to immobilized soluble NCAM. This implies that functionally significant soluble forms of NCAM are present in the extr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08321.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:This study establishes that presynaptic nicotinic receptors modulate dopamine release in the mouse striatum. Nicotinic agonists elicit a dose‐dependent increase in the release of [3H]dopamine from synaptosomes prepared from mouse striatum. At low concentrations, this release is Ca2+dependent, whereas at higher concentrations Ca2+‐independent, mecamylamine‐insensitive release was also observed. The Ca2+‐dependent nicotine‐evoked release was not blocked by α‐bungarotoxin but was effectively blocked by neuronal bungarotoxin as well as several other nicotinic receptor antagonists. The relationship between potency for stimulation of release for agonists and potency for inhibition of release for antagonists was compared to the affinity of these compounds for the [3H]nicotine binding site. The overall correlation between release and binding potency was not high, but the drugs may be classified into separate groups, each of which has a high correlation with binding. This finding suggests either that more than one nicotinic receptor regulates dopamine release or that not all agonists interact with the same receptor in an ident

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08322.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:Synaptosomes from rat forebrain were analyzed for the presence of phosphotyrosine‐containing proteins by immunoblotting with antiphosphotyrosine antibodies. Using this technique, 10–11 phosphotyrosine‐containing proteins were detected. Depolarization of synaptosomes by transfer to a high (41mM) K+medium resulted in increases in the phosphotyrosine content of several synaptosomal proteins, the most pronounced increase being associated with a membrane protein of Mr117,000 (ptp 117). Additional proteins exhibiting depolarization‐dependent increases in phosphotyrosine content had molecular weights of 39,000, 104,000, 135,000, and 160,000. The depolarization‐dependent increase in the phosphotyrosine content of ptp117 was apparent within 30 s of the onset of depolarization, reached a maximum between 3 and 5 min, and then decreased to near control values by 30 min. The increase in tyrosine phosphorylation of ptp117 was dependent on the concentration of K+in the depolarizing medium and was maximal with [K+] in excess of 50 mM. It was also calcium dependent and did not occur in the absence of extracellular calcium. The addition of veratridine to the incubation medium also resulted in an increase in the tyrosine phosphorylation of ptpl 17. The results suggest that the phosphorylation of synaptic proteins on tyrosine residues may be involved in the regulation or modulation of synaptic

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08323.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The quantitative autoradiographic L‐[1–14C]leucine method for the determination of regional rates of cerebral protein synthesis in vivo takes into account recycling of unlabeled leucine derived from protein degradation into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the apparent steady‐state leucine specific activity in the precursor amino acid pool (tRNA‐bound leucine) to that in the arterial plasma. In the whole brain of the conscious rat this ratio (λWB) equals 0.58. The equivalent ratio for leucine in the acid‐soluble pool in whole brain (ΨWB) is 0.49. A first‐degree polynomial equation for λWBas a function of ΨWBwas fitted from paired determinations. To determine the degree of recycling in local regions of the brain, we have measured in individual brain regions (i) Ψiand calculated λiassuming that the fitted equation also applies to these localized regions. Our results indicate that the degree of recycling into the precursor pool does vary regionally; λiin the individual regions varies from 0.62 in the hypoglossal nucleus to 0.50 in the globus pallidus. Local rates of protein synthesis were then determined by the autoradiographic technique with regional corrections for recycling of unlabeled leucine. Rates of leucine incorporation into protein averaged 6.1 nmol/g of tissue/min in the brain as a whole, with the rates in gray matter about twice tho

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08324.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The high‐molecular‐weight dendritic cytoskeletal protein known as microtubule‐associated protein (MAP)‐2 displays the capacity to stimulate tubulin polymerization and to associate with microtubules. Serine proteases cleave MAP‐2 into a C‐terminal Mr28,000–35,000 microtubule‐binding fragment and a larger N‐terminal Mr240,000 projection‐arm region. We now show that human immunodeficiency virus (HIV) proteinase also progressively degrades purified MAP‐2 in vitro. This proteolysis reaction is characterized by transient accumulation of at least six intermediates, and most abundant of these is an Mr72,000 species that retains the ability to associate with taxol‐stabilized microtubules. Treatment of this Mr72,000 species with thrombin releases the same Mr28,000 component as that derived from thrombin action on intact high‐molecular‐weight MAP‐2, indicating that the viral aspartoproteinase action preferentially occurs further toward the N‐terminus. The association of the Mr72,000 component with microtubules can be disrupted by the presence of a 21 ‐amino acid peptide analogue of the second repeated sequence in the MAP‐2 microtubule‐binding region. We also studied HIV proteinase action on MAP‐2 in the presence of tubulin and other MAPs that recycle with tubulin, and contrary to other published studies we found no effect of such treatment on microtubule self‐assembly behavior. Cleavage of isolated MAP‐2 by the HIV enzyme at high salt concentrations, followed by desalting and addition of tubulin, also resulted in microtubule assemb

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08325.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The presence and release of endogenous catechol‐amines in rat and guinea pig hippocampal nerve terminals was studied by fluorimetric HPLC analysis. In isolated nerve terminals (synaptosomes) the levels and breakdown of endogenous catecholamines were determined and the release process was characterized with respect to its kinetics and Ca2+and ATP dependence. Endogenous noradrenaline and dopamine, but not adrenaline, were detected in isolated hippocampal nerve terminals. For dopamine both the levels and the amounts released were more than 100‐fold lower than those for noradrenaline. In suspension, released endogenous catecholamines were rapidly broken down. This could effectively be blocked by monoamine oxidase inhibitors, Ca2+‐free conditions, and gluthatione. The release of both noradrenaline and dopamine was highly Ca2+and ATP dependent. Marked differences were observed in the kinetics of release between the two catecholamines. Noradrenaline showed an initial burst of release within 10 s after K+depolarization. The release of noradrenaline was terminated after approximately 3 min of K+depolarization. In contrast, dopamine release was more gradual, without an initial burst and without clear termination of release within 5 min. It is concluded that both catecholamines are present in nerve terminals in the rat hippocampus and that their release from (isolated) nerve terminals is exocytotic. The characteristics of noradrenaline release show several similarities with those of other classical transmitters, whereas dopamine release characteristics resemble those of neuropeptide release in the hippocampus but not those of dopamine release in other brain areas. It is hypothesized that in the hippocampus dopamine is released from large, dense‐cored vesicles, probably colocalized with neurop

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1992.tb08326.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY