摘要:

Abstract:Amyloid A4 protein (ß‐protein) is deposited in the brain of a patient with Alzheimer's disease (AD) as one of the main components of extracellular cerebrovascular amyloid, as well as neurofibrillary tangles. It is derived from a precursor protein, and its formation has been considered to be a rate‐limiting step for brain degeneration in AD. In this article, proteolytic cleavage events that can degrade amyloid precursor protein are reviewed with respect to how the topographical distribution of the proteinase and its substrates disturbs normal processing steps in AD b

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08160.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:The molecular species of 1,2‐diacyl‐sn‐glycerol (DAG), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylinositol 4‐phosphate (PIP), and phosphatidylinositol 4,5‐bisphosphate (PIP2) from brains of adult rats (weighing 150 g) were determined. The DAG, isolated from brain lipid extracts by TLC, was benzoylated, and the molecular species of the purified benzoylated derivatives were separated from each other by reverse‐phase HPLC. The total amount and the concentration of each species were quantified by using 1,2‐distearoyl‐sn‐glycerol (18:0–18:0) as an internal standard. About 30 different molecular species containing different fatty acids at thesn‐1 andsn‐2 positions of DAG were identified in rat brains (1 min postmortem), and the predominant ones were 18:0–20:4 (35%), 16:0–18:1 (15%), 16:0–16:0 (9%), and 16:0–20:4 (8%). The molecular species of PC, PE, PS, and PI were determined by hydrolyzing the lipids with phospholipase C to DAG, which was then benzoylated and subjected to reverse‐phase HPLC, PIP and PIP2were first dephosphorylated to PI with alkaline phosphatase before hydrolysis by phospholipase C. The molecular species composition of phosphoinositides showed predominantly the 18:0–20:4 species (50% in PI and ∼65% in PIP and PIP2). PS contained mainly the 18:0–22:6 (42%) and 18:0–18:1 (24%) species. PE was mainly composed of the 18:0–20:4 (22%), 18:0–22:6 (18%), 16:0–18:1 (15%), and 18:0–18:1 (15%) species. In PC the main molecular species were 16:0–18:1 (36%), 16:0–16:0 (19%), and 18:0–18:1 (14%). Studies on postmortem brains (30 s to 30 min) showed a rapid increase in the total amount (from 40–50 nmol/g in 0 min to 210–290 nmol/g in 30 min) and in all the molecular species of DAG. Comparatively larger increases (seven‐ to 10‐fold) were found for the 18:0–20:4 and 16:0–20:4 species. Comparison of DAG species with the molecular species of different glycerolipids indicated that the rapid postmortem increase in content of DAG was mainly due to the breakdown of phosphoinositides. Howe

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08161.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:In a previous work we have shown that histidine decarboxylase (HD) activity is found in a soluble and a membrane‐bound form. A major part (82%) of the membrane‐bound HD activity in the crude mitochondrial fraction (P2) was present in the synaptic plasma membrane‐containing subfraction. Physiological concentrations of Ca2+had no direct effect on HD activity but caused a solubilization of ∼50% of membrane‐bound HD in the P2fraction. Mg2+had similar but lower effects (20% solubilization) than Ca2+. Incubation with depolarizing concentrations of K+in the presence of 1 mMCaCl2caused a significant (30%) solubilizat

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08162.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:A cDNA probe specific to microtubule‐associated protein 2 (MAP2) was used to study the expression of the mRNAs encoding the high‐ and low‐molecular‐weight MAP2 variants in cultured neurons and astrocytes. The timing and relative abundance of these MAP2 transcripts and of their encoded proteins were also studied in the developing cerebral hemispheres and cerebellum of the mouse. A 9‐kb mRNA, known to encode high‐molecular‐weight MAP2, was expressed in cultured astrocytes, albeit at a lower level than in neurons. The 6‐kb transcript, recently shown to encode low‐molecular‐weight MAP2 (MAP2c), was expressed in neurons and was the predominant MAP2 transcript of the astrocytes. The level of the 9‐ and 6‐kb transcripts decreased at late stages of astroglial and neuronal cell culture. The 9‐kb mRNA was detected in the cerebellum and cerebral hemispheres at every developmental stage. Although the levels of this mRNA varied slightly in the cerebral hemispheres, its expression was biphasic in the cerebellum. This might be explained by the differences in timing of development of the various neuronal cell types formed in these two brain areas. The 6‐kb transcript was detected only at early developmental stages in the two brain areas. Correlating the temporal expression of the 9‐kb mRNA to that of high‐molecular‐weight MAP2 indicates that the accumulation of this protein is in part

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08163.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:We have measured [3H]dopamine ([3H]DA) uptake and tyrosine hydroxylase‐immunopositive immunostaining in cells acutely dissociated from the embryonic ventral mesencephalon (MSC). DA and its metabolites as well as catechol‐O‐methyltransferase (COMT) and monoamine oxidase (MAO) activities were determined in homogenates taken from the MSC and striatum (STR). In the embryonic ventral MSC measurable DA and tyrosine hydroxylase (TH) immunostaining were present as early as embryonic day (E) 12.5. At E14 the number of TH+neurons was about 50% of the values at E18. In the MSC, DA concentration increased sharply at E16 and reached a plateau before birth that was 10‐fold lower than adult values. In the STR, DA was first detected at E16, suggesting that DA fibers reach the STR at this embryonic stage. High‐affinity DA uptake appeared in the MSC only at E16, concomitantly with the arrival of DA fibers in the STR, increased sharply between E16 and E18, and reached a plateau before birth. This uptake mechanism was not selective for catecholamine uptake inhibitors. Thus, DA synthesis in the MSC preceded the onset of high‐affinity uptake mechanism, which could be correlated to the beginning of striatal DA innervation. Measurable MAO and COMT activities were detected as early as E13 (MSC) and E15 (STR), but not DA metabolites, which appeared later. We conclude that the high‐affinity DA uptake mechanism in MSC DA neurons develops coincident with the arrival of DA fibers to the STR. The sharp increase of DA uptake between E16 and E18 is due only in part to an increase in the number of TH+cells. These results support the hypothesis that in vivo the target STR neurons regulate the maturation of

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08164.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Previous studies have shown that certain peptides of the secretin‐glucagon family stimulate tyrosine hydroxylase activity in sympathetic neurons of the superior cervical ganglion and three of its end organs, i.e., the iris, pineal gland, and submaxillary gland. To determine whether a similar regulation occurs in other sympathetic neurons, the effects of two of these peptides, secretin and vasoactive intestinal peptide, were examined in the right cardiac ventricle of the rat, a tissue innervated primarily by the middle and inferior cervical ganglia. Both peptides stimulated tyrosine hydroxylase activity, measured in situ, in this tissue. In addition, several second messenger systems were investigated as possible mediators of this peptidergic stimulation of tyrosine hydroxylase activity in autonomic end organs. 8‐Bromoadenosine 3′,5′‐cyclic monophosphate and forskolin elevated tyrosine hydroxylase activity in slices of both the right ventricle and the submaxillary gland. 8‐Bromoguanosine 3′,5′‐cyclic monophosphate also stimulated tyrosine hydroxylase activity in both tissues, whereas nitroprusside stimulated activity only in the submaxillary slices. Furthermore, the phosphodiesterase inhibitors 3‐isobutyl‐1‐methylxanthine and/or Ro 20–1724 potentiated the stimulation by secretin, as well as the stimulations by forskolin and nitroprusside. Phorbol 12,13‐dibutyrate also stimulated tyrosine hydroxylase activity in cardiac and submaxillary slices; however, no potentiation of these effects was seen following addition of either phosphodiesterase inhibitor. These data, taken together with those of previous studies, suggest a role for a cyclic nucleotide, probably adenosine 3′,5′‐cyclic monophosphate, in the peptidergic stimulation of tyrosine hydroxylase activi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08165.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Being a catechol, dopamine (DA) is easily autoxidized in solution to a semiquinone and then further to a quinone. These quinones and by‐products, as reduced forms of oxygen, are all cytotoxic. By quantifying quinone metabolites, such as 5‐S‐cysteinyl adducts of DA, 3,4‐dihydroxy‐phenylalanine (DOPA), and 3,4‐dihydroxyphenylacetic acid (DOPAC), an indirect measure of catechol autoxidation is available. Ascorbic acid (AA) has an important role as an antioxidant in the organism. A group of guinea pigs (Dunkin‐Hartley) received an AA‐free diet for 37 days, whereas a control group was fed an AA‐containing diet (1,400 mg/kg of pellets). To one group of AA‐deprived animals a single dose of AA (500 mg/kg, i.p.) was administered 2 h before death, whereas another group received two doses 9 and 24 h before death. The striatal levels of 5‐S‐cysteinyl adducts, DA, noradrenaline, and DOPAC and the cerebellar and the limbic levels of AA were determined. A significant increase in 5‐S‐cysteinyl‐DA content was found in the striatum of AA‐deficient animals (143 ± 12% of control values). A further increase was found 2 h after an AA injection (177 ± 16% of control values), which was significant compared with both controls and AA‐deficient animals. An elevation in 5‐S‐cysteinyl‐DA content was still observed following two AA injections during a 24‐h period (153 ± 7% of control values). The 5‐S‐cysteinyl‐DOPAC content increased significantly (134 ± 14% of control values) in the AA‐deficient animals given AA acutely (2 h), both compared with controls and with the AA‐deficient group. DA levels increased nonsignificantly to 113% 2 h following an AA injection and significantly to 117% following two doses of AA within 24 h of AA injection. No other changes compared with normal animals were detected for any catechol examined. In guinea pigs given a scorbutogenic diet the AA levels decreased to 11–12% in the cerebellum and in the limbic system. Following a single dose of AA the brain levels increased to 19–23%, and in animals given AA 9 and 24 h before death AA levels reached 61–72% of control values in the cerebellum and in the limbic system. Thus, the present study indicates an increased autoxidation rate of DA in the striatum of AA‐depleted guinea pigs and

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08166.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:Subcellular fractionation of rabbit optic nerve resolves three populations of membranes that are rapidly labelled in the axon. The lightest membranes are>200 nm and are relatively immobile. The intermediate density membranes consist of 84 nm vesicles which disappear from the nerve with kinetics identical to those of the rapid component. A third population of membranes, displaying a distinct protein profile, is present in the most dense region of the gradient. Immunological characterization of these membranes suggests the following. (1) The lightest peak contains rapidly transported glucose transporter and most of the total glucose transporters present in the nerve; this peak is therefore enriched in axolemma. (2) The intermediate peak contains rapidly transported glucose transporters and synaptophysin, an integral synaptic vesicle protein, and about half of the total synaptophysin; this peak therefore contains transport vesicles bound for both the axolemma and the nerve terminal, and these subpopulations can be separated by immunoadsorption with specific antibodies against the aforementioned proteins. (3) The heaviest peak contains rapidly transported synaptophysin and tachykinin neuromodulators and about half of the total synaptophysin, and 80% of the total tachykinins present in the nerve; this peak appears to represent a class of synaptic vesicle precursor bound for the nerve terminal exclusively. (4) Synaptophysin is present in the membranes of vesicles carrying tachykinins. (5) Both the intermediate and the heaviest peaks are enriched in kinesin heavy chain, suggesting that both vesicle classes may be transported by the same mechanism.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08167.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:The levels of mRNA encoding glutamic acid decarboxylase (GAD) and preproenkephalin (PPE) were measured by Northern blot analysis, in the dorsal and the ventral part of the striatum, following long‐term treatments with drugs acting selectively on D1or D2dopaminergic receptors. Chronic injection of the selective D1antagonist SCH 23390 elicited a significant decrease in level of both GAD and PPE mRNA (−30%) in the dorsal striatum, whereas no significant change was observed in the ventral striatum. Chronic administration of both SCH 23390 and RU 24926, a D2agonist, decreased the GAD and PPE mRNA levels in the dorsal (−38 and −57%, respectively) as well as in the ventral (−70 and −60%, respectively) striatum. In the ventral striatum the marked reduction of GAD mRNA levels was paralleled by a significant decrease ofVmaxvalues of GAD enzymatic activity (−41%). These results suggest that the decrease in content of both GAD and PPE mRNA, promoted by the chronic blockade of D1receptors, is mainly due to the action of dopamine acting on unaffected D2receptors. Indeed, this decrease is further amplified when the D2agonist and the D1antagonist are administered together. Our results substantiate further the molecular mechanisms by which dopamine acts on different populations of GABAergic and enkephalinergic neurons in the two striatal reg

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08168.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract:The myelin‐deficient (mld) mutation is an autosomal recessive mutation in the murine CNS exhibiting severe hypomyelination. The primary defect results in a drastic reduction of myelin basic protein synthesis caused by a duplication of the myelin basic protein gene with partial inversion of the upstream gene copy. The severe deficit of myelin basic protein is responsible for the absence of the major dense line but cannot explain the heterogeneity of myelin compaction found inmid. We have tested the hypothesis that the endogenous cerebellar soluble lectin (CSL) and/or its endogenous glycoprotein ligands could be involved in myelin abnormalities in the dysmyelinating mutant,mld. Immunocytochemical and immunoblotting techniques showed that the CSL level was not reduced significantly in themldmutant. Furthermore, two ligands of CSL, the myelin‐associated glycoprotein and an axonal glycoprotein, with a relative molecular mass of 31 kDa, were not decreased in level in the purified myelin fraction isolated frommldmice. In contrast, three minor glycoprotein ligands of CSL of relative molecular mass of 23, 18, and 16 kDa were greatly reduced in content. The reduced concentration of these low‐molecular‐mass glycoproteins inmldmyelin suggests that they are constituents of compact myelin. Furthermore, the observation that CSL is specifically localized in vivo in regions wheremldmyelin is more compact and absent from regions devoid of myelin compaction may suggest that the endogenous CSL lectin, as well as its minor glycoprotein ligands, plays a role in the stabilization of the myelin

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb08169.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY