摘要:

Abstract:TheN‐methyl‐D‐aspartate (NMDA) receptor‐mediated regulation of the release of newly synthesized [3H]dopamine ([3H]DA) was studied in vitro, both on rat striatal slices using a new microsuperfusion device and on rat striatal synaptosomes. Under Mg2+‐free medium conditions, the NMDA (5 × 10−5M)‐evoked release of [3H]DA from slices was found to be partly insensitive to tetrodotoxin (TTX). This TTX‐resistant stimulatory effect of NMDA was blocked by either Mg2+(10−3M) or the noncompetitive antagonist MK‐801 (10−6M). In addition, the TTX‐resistant NMDA‐evoked response could be potentiated by glycine (10−6M) in the presence of strychnine (10−6M). The coapplication of NMDA (5 × 10−5M) and glycine (10−6M) stimulated the release of [3H]DA from striatal synaptosomes. This effect was blocked by Mg2+(10−3M) or MK‐801 (10−5M). These results indicate that some of the NMDA receptors involved in the facilitation of DA release are located on DA nerve terminals. These presynaptic receptors exhibit pharmacological properties similar to those described in electro‐physiologi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02565.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:The kinetics of Ca2+‐dependent release of glutamate from guinea‐pig cerebrocortical synaptosomes evoked by KCl or 4‐aminopyridine are investigated using a continuous flu‐orimetric assay. Release by both agents is biphasic, with a rapid phase complete within 2 s followed by a more extensive slow phase with a half‐maximal release in 52 s for KCl‐evoked release and>120 s for 4‐aminopyridine‐evoked release. The two phases ofglutamate release may reflect a dual localization of releasable vesicles at the active zone and in the bulk cytoplasm. Decreasing depolarization depresses the extent rather than increasing the time for half‐maximal Ca2+‐dependent release. Both the fast and the slow phases of glutamate release require external Ca2+and cytoplasmic ATP. KCl depolarization produces a transient “spike”of cytoplasmic free Ca2+([Ca2+]c), which recovers to a plateau; the major component of glutamate release occurs during this plateau. Predepolarization in the absence of added external Ca2+, to inhibit transient Ca2+channels, does not affect the subsequent glutamate release evoked by Ca2+readdition. Thus, release involves primarily noninactivating Ca2+channels. For a given increase in [Ca2+]c, KCl and 4‐aminopyridine cause equal release of glutamate, while ionomycin releases much less glutamate. This lowered efficiency is not due to ATP depletion. It is concluded that glutamate exocytosis is evoked by localized Ca2+entering through noninactivating voltage‐dependent Ca2+channels and that nonlocalized Ca2+entry wi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02566.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Treatment of three neuroblastoma cell types in culture with neuraminidase resulted in enhanced neurite outgrowth. These included the mouse Neuro‐2A and rat B104 and B50 lines. The morphological changes depended on the presence of exogenous Ca2+and were accompanied by modest but statistically significant increases in45Ca2+influx. Neur‐aminidase‐stimulated neuritogenesis was blocked by the B subunit of cholera toxin (cholera B) and anti‐GM1 antibody, a finding suggesting the effect was due to an increased amount of GM1 on the cell surface. Cholera B also blocked the increase in45Ca2+influx. The mouse N1A‐103 line, previously characterized as “neurite minus,” did not respond to neuraminidase with either neurite outgrowth or enhanced Ca2+influx. These results point to an influence of GM1 on neuritogenesis in cells with differentiation potential and suggest a mechanism involving modulatio

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02567.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:C6 rat glioma cells incubated in serum‐free medium with D‐[14C]glucosamine secrete, on stimulation with nerve growth factor (NGF) or monosialogangliosides (MSGs), several glycoproteins (Gps), the most prominent of which are a 270‐, 220‐, and 69‐kDa Gp. Several growth factors, hormones, phorbol ester, and disialo‐ and trisialogangliosides did not stimulate secretion. Western blot analysis of the conditioned medium from C6 cells stimulated with NGF or MSG identified one distinct band of ∼220 kDa for fibronectin and J1/tenascin, which comigrated. Antiserum to NGF prevented NGF‐stimulated release and also blocked MSG‐evoked release. The 220‐kDa band was labeled after pulse labeling with [35S]methionine in the presence of NGF, and by a 15‐min chase period radioactively labeled J1/tenascin could be immunoprecipitated. Tunicamycin drastically inhibited almost completely release of the 220‐kDa Gp labeled by D‐[14C]glucosamine or [35S]methionine. These results extend the range of neurotrophic properties attributed to NGF to cells of glial origin and suggest that NGF regulates secretion of extracellular matrix proteins. MSG stimulation of fibronectin and J1/tenascin secretion may be mediated by NGF or an NGF‐like molecule also secr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02568.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:In this report, two changes that occur in the presynaptic terminal following induction of long‐term potentiation in the dentate gyrus are examined, and the results demonstrate that the same changes are stimulated by the putative retrograde messenger arachidonic acid. First, there is an increase in the concentration of intracellular calcium in synaptosomes prepared from potentiated tissue compared with control tissue. This effect on intracellular calcium concentration was mimicked in control tissue by treatment of synaptosomes with either arachidonic acid or inositol 1,4,5‐trisphosphate in a dose‐dependent but nonadditive manner. Second, there is an increase in phosphoinositide turnover in synaptosomes prepared from potentiated tissue compared with control tissue, and this change can also be mimicked in control tissue by exposure of synaptosomes to arachidonic acid. These findings are consistent with the hypothesis that the increase in glutamate release associated with long‐term potentiation may be stimulated by arachidonic acid, as a result of an increase in intrasynaptosomal calcium concentration, perhaps occurring as a result of arachidonate‐stimulated phosphoinositide m

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02569.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Sex differences were investigated in cholinergic neurons of the septal‐diagonal band region of adult rats subjected to neonatal treatment with 3,3′,5‐triiodo‐L‐thyronine (T3). Neonatal hyperthyroidism resulted in a 44% increase in specific activity of choline acetyltransferase (ChAT; EC 2.3.1.6) in adult male rat septal‐diagonal band region, whereas no change in ChAT activity could be detected in either dorsal or ventral hippocampus. An increase in muscarinic cholinergic receptors, as measured by [3H]quinu‐clidinyl benzilate ([3H]QNB) binding, was discovered in both septum‐diagonal band and dorsal hippocampus of the T3‐treated male rats. Immunohistochemistry in the septal‐diagonal band region indicated a more intense staining in the neonatally T3‐treated adult male rats than in controls, with larger and more abundant ChAT‐positive and nerve growth factor receptor (NGF‐R)‐positive varicosities. ChAT immunocytochemistry showed a substantial decrease in cell body area in the medial septum and in the vertical limb of the diagonal band of T3‐treated male rats, while cell density increased twofold. Female littermates subjected to the same treatment showed no changes in any of the biochemical or immunohistochemical cholinergic markers. Only in the medial septum was morphology significantly altered in the female T3‐treated rats in that ChAT‐positive cell body area increased. These results indicate a marked sexual variation in the septal‐diagonal band region with respect to the sensitivity of postnatally developing cholinergic neurons to th

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02570.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Canavan disease, an autosomal recessive disorder, is characterized biochemically byN‐acetylaspartic aciduria and aspartoacylase (N‐acyl‐L‐aspartate amidohydrolase; EC 3.5.1.15) deficiency. However, the role of aspartoacylase andN‐acetylaspartic acid in brain metabolism is unknown. Aspartoacylase has been purified to apparent homogeneity with a specific activity of ∼ 19,000–20,000 nmol of aspartate released/mg of protein. The native enzyme is a 58‐kDa monomer. The purified aspartoacylase activity is enhanced by divalent cations, nonionic detergents, and dithiothreitol. Low levels of dithiothreitol or β‐mercaptoethanol are required for enzyme stability. Aspartoacylase has aKmof 8.5 × 10−4Mand aVmaxof 43,000 nmol/min/mg of protein. Inhibition of aspartoacylase by glycyl‐L‐aspartate and amino derivatives of D‐aspartic acid suggests that the carbon backbone of the substrate is primarily involved in its interaction with the active site and that a blocked amino group is essential for the catalytic activity of aspartoacylase. Biochemical and immunocytochemical studies revealed that aspartoacylase is localized to white matter, whereas theN‐acetylaspartic acid concentration is threefold higher in gray matter than in white matter. Our studies so far indicate that aspartoacylase is conserved across species during evolution and suggest a significant role for aspartoacylase andN‐acetylaspart

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02571.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:The effects of dopamine on [32P]ATP‐labelled phosphatidylinositol 4‐phosphate, phosphatidylinositol 4,5‐bisphosphate, and phosphatidic acid were analyzed by TLC in synaptosomal membranes of the rat neostriatum. The incorporation of32P into these compounds was found to be stable within 1 min and was maintained during the 30 min of incubation. Dopamine (0.1–10μM) was found to attenuate the levels of phosphatidylinositol 4,5‐bisphosphate without affecting the levels of phosphatidylinositol 4‐phosphate or phosphatidic acid. The maximal decrease (−35 ± 4%) was reached at 10 μMof dopamine after 30 min of incubation. The dopamine (0.1 μM)‐induced decrease was blocked by the D2selective antagonist raclopride (1 μM), but not by the D1selective antagonist SCH 23390 (1 μM). These findings indicate the existence of an intramembrane coupling of dopamine D2receptors to phosphoinositide turnover and may underlie some of the physiological effects of D

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02572.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:5′‐Nucleotidase activity was assayed in 105,000‐g supernatants from rat brain by following conversion of [3H]AMP into adenosine. The effect of ATP on this process was complex and suggested the presence of at least two soluble 5′‐nucleotidase activities: one inhibited by ATP and another activated by ATP. The relative proportions of these activities differed considerably among brain regions. Activity changes induced by hypothyroidism also suggested that these activities may be regulated independently. These findings may have consequences for the regional regulation of adenosine formation in

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02573.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Recent studies have identified protein tyrosine phosphorylation as a major intracellular signaling pathway. However, little is known about regulation of this signaling pathway in neuronal systems. To help identify changes in levels of protein tyrosine phosphorylation in brain, we have utilized specific anti‐phosphotyrosine antibodies to detect phosphotyrosine‐containing proteins by immunoblotting techniques. We have found that electroconvulsive treatment induces a selective increase in tyrosine phosphorylation of a soluble 40‐kDa protein. The rise is rapid and transient, reaching maximal levels at 1–2 min and returning to basal levels by 8 min. The phosphotyrosine‐containing 40‐kDa protein is most prominent in hippocampus, smaller in neocortex, and not detected in brainstem or cerebellum. A phosphotyrosine‐containing 42‐kDa protein present in several cell types has recently been identified as a serine/threonine phosphotransferase, referred to as microtubule‐associated protein 2 kinase. Comparison of the levels of tyrosine phosphorylation of the 40‐kDa protein and microtubule‐associated protein 2 kinase activity during column chromatography of hippocampal extracts demonstrates that the phosphotyrosine‐containing 40‐kDa protein and microtubule‐associated protein 2 co‐purify. Moreover, the tyrosine phosphorylation of the 40‐kDa protein and microtubule‐associated protein 2 kinase activity are increased to a similar extent following electroconvulsive treatment. These findings suggest that the phosphotyrosine‐containing 40‐kDa protein identified in brain is closely related to mi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb02574.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY