首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 250 毫秒
1.
Abstract: The development and regional distribution of thymidylate synthetase (TS) (EC 2.1.1.45) in rabbit brain were determined. After optimization of the assay for brain, TS activity in brain was measured by a nonspecific (3H2O release) and specific method. The specific method involved the conversion of [6-3H]deoxyuridine monophosphate (dUMP) to [3H]thymidine phosphate and the subsequent identification of [3H]thymidine. The specific activity of the enzyme in whole brain of newborn rabbits declined from 10.35 ± 1.17 units/mg protein to 0.71 ± 0.09 units/mg protein at 10–12 weeks of age. Two-year-old rabbits had 0.81 ± 0.04 units/mg protein. The decline in specific activity with age was not due to an inhibitor of TS activity or a change in the Km for dUMP. The Km for dUMP of the unpurified enzyme in the brains of both 10-day-old and young adult rabbits was 0.8 μ m . In young adult rabbits (3 months) the specific activity of TS was similar in the various regions of the brain tested except for the cerebellum, which had 40% higher specific activity than the whole brain. The results show that TS is widely distributed in adult rabbit brain, and, although the activity declines with age, it stabilizes at adult levels at 3 months of age.  相似文献   

2.
Abstract: Effects of thyroxine (T4) on nerve growth factor (NGF) level and choline acetyltransferase (ChAT) activity of rat brains were investigated. Repetitive intraperitoneal administration of T4 caused increases in both NGF level and ChAT activity in the frontal cortex, septum, hippocampus, and striatum and decreases in the cerebellum in 2-day-old rats. Only ChAT activity was elevated in the olfactory bulb, and the NGF level remained unchanged there. No changes were observed in the midbrain and pons/medulla. Furthermore, T4 was effective on the post-natal rats only up to day 11. These results suggest that T4 plays a role in the developmental regulation of NGF level and ChAT activity in rat brain in a region- and/or stage-specific manner. That (1) changes in NGF level and ChAT activity occurred in regions nearly identical to those that contained NGF-responding neurons, and (2) the change in NGF level in the hippocampus and frontal cortex was followed by the change of ChAT activity after a single injection of T4 suggest that the effects of T4 on cholinergic differentiation are, at least in part, mediated via NGF, which itself is quantitatively regulated by T4.  相似文献   

3.
Abstract: We have carried out assays for glutamic acid decarboxylase (GAD) in homogenates of brain and spinal cord from larval and adult sea lamprey ( Petromyzon marinus ). The enzyme had similar characteristics in both stages. Optimal pH was 6.8; optimal temperature was 27–30° C; K m at 27°C was 5 mM. GAD activity was distributed uniformly along the length of the spinal cord. Specific activities for the larval cord and brain were 26 and 63 nm CO2/mg protein/h. respectively. The specific activities for the adult cord and brain were 29 and 236 nm CO2/mg protein/h, respectively. Thus, the activity of cord homogenates did not change significantly between larval and adult stages, but that of the brain increased about fourfold.  相似文献   

4.
Abstract: Histamine H1- receptors labeled with [3H]mepyramine in rat brain show an age-dependent development. [3H]Mepyramine receptor density and histidine decarboxylase activity in whole rat brain reach adult levels at 25–30 days after birth and they attain 50% of adult level at day 10 and 17, respectively. The apparently later development of histidine decarboxylase activity in whole rat brain is partly accounted for by a biphasic developmental increase of this enzymatic activity in cerebral cortex. For all other brain regions examined, the development of histamine H1- receptors parallels that of histidine decarboxylase. The increase in [3H]mepyramine binding can be accounted for by an absolute increase in the numbers of the receptor sites, with no change in affinity. Subcellular fractionation studies indicate that histamine H1- receptors are predominantly associated with synaptosomal fractions derived from both newborn and adult rat.  相似文献   

5.
Abstract: Telencephalic membranes from rats of different embryonic (E16, E19) and postnatal (P2, P7, P14, adult) ages were assessed for α-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA) binding and for immunoreactivity levels of AMPA receptor subunits (GluR1, GluR2/3, and GluR4). In addition, the synaptic markers synaptophysin and NCAM140 (a neural cell adhesion molecule isoform) were examined by immunoblot. The density of [3H]AMPA binding sites increased steadily with advancing age. This increase was due mainly to the development of the large low-affinity component ( K D = 400 n M ) that dominates the [3H]AMPA binding profile of adult rat brain membranes. As resolved by two-site regression analysis, the high-affinity component ( K D = 15 n M ) of the [3H]AMPA binding increased by approximately twofold from E16 to adult, whereas the low-affinity component increased by 25-fold. Staining for GluR1 and GluR2/3 increased steadily with increasing age at all time points examined; synaptophysin and NCAM140 exhibited similar ontogenic immunostaining profiles. GluR4 immunoreactivity was first evident at P14 and increased by adulthood. These results indicate that AMPA receptor density increases steadily during development and that this increase is coincident with the ontogenic expression of other synaptic components. Furthermore, there is a shift toward a preponderance of low-affinity [3H]AMPA binding, which occurs during the period when AMPA receptors are being sorted into postsynaptic regions, suggesting that some element of the postsynaptic membrane environment modulates AMPA receptor properties.  相似文献   

6.
Abstract: The development of the thymidine phosphorylating systems was studied in various regions of brain. Brain slices from cerebellum, brain stem, and forebrain of rabbits 2, 7, 14, 30, 90, 500, and 2500 days of age were incubated for various times in artificial CSF containing 3 nM-[3H]thymidine at 37°C under 95% O2-5% CO2. When slices from all brain regions of 2-day-old rabbits were incubated in [3H]thymidine for 30 min, tissue-to-medium ratios of 3H were between 2 and 4 and declined with age, and the percentages of the total 3H in perchloric acid homogenates of brain slices as [3H]DNA were 26–29%, declining to low levels with age. However, at all ages and in all regions studied, 41 -88% of the 3H within the slices was phosphorylated. After homogenization and subcellular fractionation of the brain slices incubated in [3H]thymidine for 30 min, the highest percentage of [3H]thymidine phosphates plus [3H]DNA was present in the nuclear (crude and purified) and mitochondrial fractions of all brain regions. The [3H]DNA content in the nuclear and mitochondrial fractions declined with age, but the percentage of [3H]thymidine phosphates did not. Thymidine phosphates were synthesized from thymidine in all brain regions tested throughout the entire life span.  相似文献   

7.
Abstract: The neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+) in the brain striatum has recently been shown to bind at a putatively vesicular site labeled by [3H]tyramine ([3H]TY). Whereas in the rat and mouse striatum MPP+ antagonized TY binding competitively, in the cerebellum there was a mixed-type antagonism, which suggests the simultaneous occupancy of two different sites. K i values from displacement curves revealed a fourfold difference in the affinity of MPP+ for TY sites in the two brain regions. The degeneration of central noradrenergic terminals induced by an intraperitoneal injection of the toxin N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine in rats decreased by 80% the maximal number of cerebellar TY binding sites, while not affecting striatal binding. Furthermore, guanethidine, a marker for noradrenaline (NA) vesicles, potently inhibited TY binding in NA-innervated regions, such as the cerebellum and the parietal cortex, and poorly in the striatum. It is concluded (a) that both MPP+ and TY may also label NA vesicles and (b) that the vesicular carriers for dopamine and NA have different characteristics, which may underlie a regional specificity in the rate of endovesicular sequestration of MPP+, with either neurodegenerative or neuroprotective consequences, depending on the brain area involved.  相似文献   

8.
Abstract— The effects of 10−5 m -noradrenaline (NA), 5-hydroxytryptamine (5-HT) and dopamine (DA) on the activities of Na+-K+ ATPase (EC 3.6.1.3) were studied in synaptic membranes from 6 regions of the rabbit brain. NA and 5-HT stimulated the synaptic membrane Na+-K+ ATPase from the cerebrum, but none of the amines influenced the activity of this enzyme in the other brain regions. The Na+-K+ ATPase activity of the cerebral synaptic membrane isolated at the 0.8/0.9 m & 0.9/1.0 m interphase of a sucrose density gradient was increased two-fold by 10−5 m -NA and 5-HT. The Na+-K + ATPase recovered at the 1.0/1.2 m interphase was not influenced by NA, DA or 5-HT. NA, DA and 5-HT did not activate the Mg ATPase of synaptic membranes from any of the 6 brain regions or whole brain synaptic vesicles. The cortex synaptic membrane (Na+-K+) ATPase is postulated to have a direct role in the uptake of the biogenic amines. An indirect role is proposed for this enzyme in amine uptake into brain stem.  相似文献   

9.
Polypeptide Elongation Factors of the Developing Chick Brain   总被引:2,自引:1,他引:1  
Abstract: The polypeptide elongation factors (EF-1L, EF-1H, and EF-2) of the developing chick brain were separated and purified by means of a combination of gel chromatographic methods. The molecular weight of EF-1H of the chick brain ranged from 5 to 10 × 105, and was different from that of the chick liver (about 7 × 105). The molecular weight of other purified factors was about 5 × 104 for EF-1L. and 9.4 × 104 for EF-2. High activities of polyphenylalanine (poly-Phe) synthesis per mg protein in the developing chick brain were observed between the 3rd embryonic week and the 1st post-hatch week and declined afterwards. On the other hand, the levels of both EF-1 and EF-2 per mg protein in the brain were observed to be high in an early embryonic stage, gradually declining afterwards to the adult level. The brain EF-1L was a major component of EF-1 in an early embryonic stage, while EF-1H became recognizable in the 3rd embryonic week. Moreover, the EF-1H activities were found to be more than double with regard to the binding reaction and to be more than 10-fold as active in respect to poly-Phe synthesis in comparison with the activities of EF-1L. It is proposed that the brain EF-1H could be due to aggregates consisting of EF-1L, a stimulatory factor, and other components.  相似文献   

10.
Increases (>2.5-fold) in GABA levels in rat brain lead to a large decrease in the level of the 67-kDa form of glutamate decarboxylase (GAD67) through a mechanism involving either a change in GAD67 protein stability or a change in GAD67 mRNA translation. In the present study, brain levels of GABA were manipulated by treating rats with various doses of γ-vinyl-γ-aminobutyric acid (GVG), and the dependence of total GAD activity and levels of GAD67 and GAD65 protein on the levels of GABA was analyzed. Initial studies showed that both GABA and GAD67protein levels reached new steady-state levels after two to four daily injections; GABA increased 1.5- (30 mg of GVG/kg) and fourfold (150 mg of GVG/kg), and GAD67 protein content decreased by 30 and 70%. To assess the sensitivity of GAD67 to GABA, rats were injected with eight different doses of GVG (15-150 mg/kg) for 5 days. With increasing doses of GVG, we observed a gradual increase in both whole-tissue and synaptosomal GABA levels and a gradual decrease in GAD67 protein and GAD activity. The levels of GAD67 remained constant at all GVG doses. GAD67 was remarkably sensitive to GABA. The synaptosomal GAD67 level decreased ∼12% and the whole-neuron GAD67 level decreased ∼3% for each 1 % increase in nerve terminal GABA content when it was close to its physiological level. Our results clearly demonstrate that GAD67 is tightly controlled by intraneuronal GABA, and we suggest that this regulatory mechanism has important implications for the physiological regulation of GABAergic function in the mammalian brain.  相似文献   

11.
12.
13.
Abstract: The ex vivo tissue concentration of nitrite and nitrate (NOx) was found to correlate closely with the activity of nitric oxide synthase (NOS; EC 1.14.13.39) in various brain regions. Systemic administration of the nonselective NOS inhibitor N ω-nitro- l -arginine ( l -NA) at doses that completely inhibited both central and peripheral NOS, depleted whole-brain and CSF NOx by up to 75% but had no effect on plasma NOx. Selective inhibition of central NOS by intracerebroventricular administration of l -NA methyl ester produced similar decreases in levels of whole-brain NOx. A residual concentration of NOx of 10–15 µ M remained in all brain regions even after complete inhibition of brain NOS. Brain NOx content decreased rapidly and in parallel with the inhibition of brain NOS. The ex vivo measurement of levels of brain NOx was found to reflect the in vivo efficacy of several different types of NOS inhibitor: l -NA, N ω-monomethyl- l -arginine, and 7-nitroindazole. Intraperitoneal administration of the NOS substrate l -arginine increased brain NOx concentrations by up to 150% of control values. These results demonstrate that the ex vivo measurement of levels of brain tissue NOx is a rapid, reliable, and straightforward technique to determine NOS activity in vivo. This method can be used to assess both the regional distribution and the degree of inhibition of NOS activity in vivo.  相似文献   

14.
Abstract: The role of dopaminergic innervation on the postnatal developmental expression of D1 dopamine receptors was investigated. Bilateral destruction of dopa-mine-containing neurons was achieved by treating rats intracisternally with 6-hydroxydopamine (6-OHDA) on postnatal day 3, and rats were killed on day 21. To ensure effective reduction of D1 receptor activation by residual dopamine, a group of 6-OHDA-lesioned rats was given twice daily injections of the D1 receptor antagonist SCH-23390, from day 4 to 20. D1 dopamine receptor binding was assessed in the caudate—putamen, nucleus accumbens, and olfactory tubercle by quantitative autoradiographic analysis of [3H]SCH-23390 binding. In addition, the relative amount of D1A receptor mRNA was assessed by in situ hybridization of a 35S-labeled riboprobe. In the developing rats, neither the amount of [3H]SCH-23390 binding nor the amount of D1A receptor mRNA was altered by 6-OHDA lesioning followed by chronic treatment with SCH-23390. Thus, bilateral destruction of dopamine-containing neurons and treatment with SCH-23390 in neonatal rats did not interfere with the developmental expression of D1 receptors or alter the levels of mRNA that code for this receptor protein. Treatment of intact rats with SCH-23390 from postnatal day 4 to 20 also did not alter [3H]SCH-23390 binding or levels of D1 receptor mRNA. However, adult rats treated chronically with SCH-23390 exhibited increased [3H]SCH-23390 binding but did not show a significant change in D1 receptor mRNA levels.  相似文献   

15.
ABSTRACT The central nervous system of Agrius convolvuli is composed of brain, followed by subesophageal ganglion, three thoracic ganglia, and eight abdominal ganglia in late larval stage. After metamorphic transition from larva to pupa, thoracic (T1 and T2) and abdominal ganglia (A1 and A2) are moved toward T3 and fused together to construct composite ganglion, pterothoracic ganglion. The formation of composite ganglion is completed about 90% at 4 day and 100% at 7 day after pupation. Neuronal cell death was occurred significantly around 3 or 4 day after pupation and just after adult ecdysis. Although 170 neurons were detected 3 day before adult ecdysis, 24 cells were counted 5 day after adult ecdysis. Data of scanning and tandem electron microscope showed the symptom of cell death. In order to identify the mechanism of cell death in A. convolvuli , 1,200 ventral nerve cords were homogenized. Extracts were boiled for 3 minutes at 100°C and collected below 30,000 dalton of molecular mass. Each fraction from reverse phase column chromatography by HPLC system was tested in ventral nerve cord culture system, and fractions having killing activity in culture were isolated. By the addition of 20 hydroxyecdysone, actinomycin D, or cycloheximide into the culture medium, cell death was delayed significantly when compared to control group.  相似文献   

16.
Abstract: We describe the molecular cloning of a cDNA encoding a human brain Na+-dependent inorganic phosphate (Pi) cotransporter (hBNPI). The nucleotide and deduced amino acid sequences of hBNPI reveal a protein of 560 amino acids with six to eight putative transmembrane segments. hBNPI shares a high degree of homology with other Na+-dependent inorganic Pi cotransporters, including those found in rat brain and human and rabbit kidney. Expression of hBNPI in COS-1 cells results in Na+-dependent Pi uptake. Northern blot analysis demonstrates that hBNPI mRNA is expressed predominantly in brain and most abundantly in neuron-enriched regions such as the amygdala and hippocampus. Moderate levels of expression are also observed in glia-enriched areas such as the corpus callosum, and low levels are observed in the substantia nigra, subthalamic nuclei, and thalamus. In situ hybridization histochemistry reveals relatively high levels of hBNPI mRNA in pyramidal neurons of the cerebral cortex and hippocampus and in granule neurons of dentate gyrus. The level of hBNPI mRNA is quite low in fetal compared with adult human brain, suggesting developmental regulation of hBNPI gene expression. Southern analyses of nine eukaryotic genomic DNAs probed under stringent conditions with hBNPI cDNA revealed that the hBNPI gene is highly conserved during vertebrate evolution and that each gene is most likely present as a single copy. Using fluorescent in situ hybridization, we localized hBNPI to the long arm of chromosome 19 (19q13) in close proximity to the late-onset familial Alzheimer's disease locus.  相似文献   

17.
Abstract: Ethanol dependence and tolerance involve perturbation of GABAergic neurotransmission. Previous studies have demonstrated that ethanol treatment regulates the function and expression of GABAA receptors throughout the CNS. Conceivably, changes in receptor function may be associated with alterations of subunit composition. In the present study, a comprehensive (1–12 weeks) ethanol treatment paradigm was used to evaluate changes in GABAA receptor subunit expression in several brain regions including the cerebellum, cerebral cortex, ventral tegmental area (VTA) (a region implicated in drug reward/dependence), and the hippocampus (a region involved in memory/cognition). Expression of α1 and α5 subunits was regulated by ethanol in a region-specific and time-dependent manner. Following 2–4 weeks of administration, cortical and cerebellar α1 and α5 subunit immunoreactivity was reduced. In the VTA, levels of α1 subunit immunoreactivity were significantly decreased after 12 weeks but not 1–4 weeks of treatment. Hippocampal α1 subunit immunoreactivity and mRNA content were also significantly reduced after 12 but not after 4 weeks of treatment. In contrast, α5 mRNA content was increased in this brain region. These data indicate that chronic ethanol administration alters GABAA receptor subunit expression in the VTA and hippocampus, effects that may play a role in the abuse potential and detrimental cognitive effects of alcohol.  相似文献   

18.
Abstract: To elucidate mechanisms regulating the production of platelet-derived growth factor (PDGF) in the CNS, we analyzed the influence of a panel of cytokines on PDGF mRNA and protein levels in astrocyte-enriched cultures from the human embryonic brain and spinal cord. Using a specific ELISA, PDGF AB protein was detected in serum-free astrocyte supernatants and its levels were significantly increased after treatment of the cultures with transforming growth factor-β1 (TGF-β1) or tumor necrosis factor-α (TNF-α); the largest increase was detected after combined treatment with the two cytokines. Interleukin-1β (IL-1β) by itself had little or no effect but synergized with TGF-β1 in enhancing PDGF AB production. Supernatants from human astrocyte cultures stimulated the proliferation of rat oligodendrocyte progenitors, and most of the mitogenic activity could be accounted for by PDGF. By northern blot analysis, both PDGF A- and PDGF B-chain mRNAs were detected in untreated astrocytes. PDGF B-chain mRNA levels were increased by TGF-β1, TNF-α, TNF-α/TGF-β1, or IL-1β/TGF-β1, whereas PDGF A-chain mRNA levels were not consistently affected by cytokine treatments. These in vitro data indicate that TGF-β1, TNF-α, and IL-1β are able to stimulate astrocyte PDGF production. This cytokine network could play a role in CNS development and repair after injury or inflammation.  相似文献   

19.
The levels of GA1, 3-epiGA1 and GA8 in genotypes Le, le and led of Pisum sativum L. were determined by gas chromatography-selected ion monitoring (GC-SIM) after feeds of [3H, 13C]-GA20 to each genotype. The levels of endogenous and [13C]-labelled metabolites were determined by reverse isotope dilution with unlabelled GA1, 3-epiGA1 and GA8. The results demonstrate a quantitative relationship between the level of GA1 and the extent of elongation both on a per plant and a per g fresh weight basis. These results are consistent with previous findings in peas and other species possessing a predominant early 13-hydroxylation pathway for GA biosynthesis.
The levels of 3-epiGA1 also decreased in the genotypic sequence Le, le, led although not as rapidly as for the level of GA1. This may suggest that the alleles at the le locus also influence the formation of 3-epiGA1.  相似文献   

20.
Abstract: Recently, we reported that 6 R - l - erythro -tetrahydrobiopterin (6 R -BH4), a natural cofactor for hydroxylases of tyrosine and tryptophan, has a monoamine-releasing action independent of its cofactor activity. Here we attempted to determine whether 6 R -BH4 acts inside the cell or from the outside of the cell by using brain microdialysis in the rat striatum. For this purpose, sepiapterin, an immediate precursor of 6 R -BH4 in the salvage pathway, was used to selectively increase the intracellular 6 R -BH4 levels. Dialytic perfusion of sepiapterin increased tissue levels of reduced biopterin (mainly 6 R -BH4) but not the extracellular levels. Administration of sepiapterin increased the extracellular levels of 3,4-dihydroxyphenylalanine (DOPA) (an index of in vivo tyrosine hydroxylase activity) and of dopamine (DA) (an index of in vivo DA release). Either of the increases was eliminated after pretreatment with a tyrosine hydroxylase inhibitor α-methyl- p -tyrosine. Administration of 6 R -BH4 increased extracellular levels of reduced biopterin, DOPA, and DA. After pretreatment with α-methyl- p -tyrosine, the increase in DOPA levels was abolished, but most of the increase in DA levels persisted. The increase in DA levels also persisted after pretreatment with nitric oxide synthase inhibitors. These data demonstrate that 6 R -BH4 stimulates DA release directly, independent of its cofactor action for tyrosine hydroxylase and nitric oxide synthase, by acting from the outside of neurons.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号