摘要:

Abstract:Syntheticn‐butylβ‐carboline‐3‐carboxylate, an endogenous central benzodiazepine receptor inhibitor found in brain, was tritium‐labeled from the butenyl ester. Binding of this [3H]β‐carboline was concentrated particularly in the synaptosomal membrane fraction of the cerebral cortex; this fraction showed a single type of high‐affinity site (KD= 2.7 ± 0.1 nM) with aBmaxof 1.16 ± 0.08 pmol/mg of protein. The number of sites labeled was about half of that obtained with [3H]flunitrazepam binding (Bmax= 2.36 ± 0.06 pmol/mg of protein). On the other hand, in the cerebellum, both ligands bound to practically the same number of sites. When [3H]flunitrazepam binding was done in the presence of 10−11‐10−5Mbutylβ‐carboline, the differences between the two brain regions were more apparent. In cerebellar membranes the data fitted a straight line in the Eadie‐Hofstee plot; this finding and a Hill number near unity suggest a single type of binding site. In the cortical membranes the data of binding fitted a concave curve, and the Hill number was 0.6. These are characteristics of two types of binding sites with different affinities (KDi= 0.6–1.5 nMandKD2= 12–18 nM). The differentiation of a high‐ and low‐affinity site in the cerebral cortex was corroborated by experiments in which [3H]butylβ‐carboline binding was displaced by the triazolopyridazine CL 218,872. These results demonstrate that in the cerebral cortex there are two subtypes of sites (1 and 2) of central benzodiazepine receptors and that CL 218,872 binds preferentially to subtype 1. γ‐Aminobutyric acid (GABA) stimulated the binding of [3H]flunitrazepam, whereas the effect on the binding of [3H]butylβ‐carboline was negative. This finding, together with some pharmacological experiments in mice, suggests thatn‐butylβ‐carboline‐3‐carboxylate acts as an inverse agonist on the central benzodia

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02506.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:Addition of histamine (0.1 mM) to guinea‐pig hippocampal slices causes a 20‐ to 30‐fold increase in the accumulation of cyclic AMP compared with basal levels. This accumulation represents a balance between cyclic AMP production by adenylate cyclase and cyclic AMP breakdown mediated by phosphodiesterase (PDE). However, brain tissues are known to contain several different PDE isozymes. To determine which are involved in this response to histamine, the effect of isozyme‐specific PDE inhibitors on cyclic AMP accumulation was examined in the hippocampus. MB 22948 (0.1 mM), an inhibitor of PDEs I and II, had no significant effect on the response to either 1μMor 0.1 mMhistamine. SKF 94120 (0.1 mM), a PDE III inhibitor, was also without effect in the presence of 1μMhistamine, although with 0.1 mMhistamine, it caused a weak (1.25‐fold compared with control), but statistically significant, enhancement of cyclic AMP accumulation. However, both rolipram (0.1 mM), a PDE IV inhibitor, and 3‐isobutyl‐l‐methylxanthine (0.1 or 1 mM), an inhibitor of all forms of PDE, significantly increased cyclic AMP accumulation (2.8‐ to 6.5‐fold compared with controls), and the relative size of this effect decreased with increasing histamine concentration. It is concluded that PDE IV is the main PDE isozyme involved in cyclic AMP turnover in guinea‐pig hippocampal slices

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02507.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:The subcellular distribution of the protein tyrosine hydroxylase (TH) after fractionation of rat brain tissue was studied by a sensitive technique of immunoblot quantification in the dopaminergic nigrostriatal and the dorsal noradrenergic pathways and in the ventrolateral medulla. This repartition indicates that in all catecholaminergic regions of the cell bodies studied, the contribution of the nerve endings to the total TH amount is very low (<7%), in contrast to that observed in the terminal fields. The correlative subcellular determination of the TH amount and activity in the same tissue could be a useful approach for studying experimentally induced mechanisms of catecholamine synthesis modulation in different brain catecholaminergic pathways.

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02508.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:The effect of dexamethasone administration and withdrawal was studied with respect to blood‐brain barrier function. The tracersα‐[3H]aminoisobutyric acid (AIB) (MW 104) and [14C]sucrose (MW 342), which have a low permeability across the intact endothelium, were simultaneously injected intravenously in rats treated with dexamethasone and placebo‐treated control animals or in rats in which dexamethasone treatment was discontinued 3 days before the experiment. Unidirectional transfer constants (Ki) were determined in discrete brain regions. Steroid administration reduced the rate of influx of AIB and sucrose, whereas discontinuation of drug resulted in an increased permeability. These findings suggest that when exposure to glucocorticoids is prolonged, the efficiency of medical treatment of CNS diseases may decrease due to reduction of drug delivery to CNS. Thus, these experimental findings may have particular importance in the clinical setting of drug administration when considering the combination of steroids with other drugs, and may aid in understanding better the pathogenesis of some types of brain edema seen in patients from whom corticosteroid therapy has been wit

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02509.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:A pharmacological study was undertaken to determine whether the noradrenaline‐stimulated breakdown of inositol phospholipids and the potentiation of isoprenaline‐stimulated cyclic AMP by noradrenaline in rat cerebral cortex slices are mediated by the same α‐receptor subtype. The rank order of potency of a range of α1and α2antagonists suggests that both responses may involve an α1receptor, but there were several differences between the pharmacological profiles for the two systems. Although in both cases, all selective α1antagonists were more potent than α2antagonists, the rank orders and the absolute potencies differed for the two responses. The inhibition of the inositol phosphate response was characterised by a high α1/α2antagonist ratio, and in most cases, Hill slopes of inhibition were consistent with the involvement of a single receptor site. Inhibition of the cyclic AMP response had a much lower α1/α2antagonist ratio and generally exhibited Hill slopes less than one. Evidence has been provided suggesting that adenosine is involved in the potentiation of cyclic AMP and that other, as yet unidentified, factors may also be involved. Even in the absence of an adenosine component, the results presented support the suggestion that the potentiation due to noradrenaline is mediated by a receptor whose identity does not easily fit with the currently accepted classification of

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02510.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:Protein phosphorylation plays an important role in the regulation of neural functions. We have studied the phosphorylation of proteins in homogenates of segmental ganglia of the leechHirudo medicinalis.We describe a number of proteins whose phosphorylation is dependent on cal‐cium/calmodulin or cyclic nucleotides. Most of the proteins whose phosphorylation is increased in the presence of calcium seem to be substrates for cyclic nucleotide‐dependent protein kinases. Only two of the phosphoproteins described appear to be specific substrates for calcium/calmodulin protein kinase(s), and at least six phosphoproteins appear to be specific substrates for cyclic nucleotide‐dependent kinase(s). The leech nervous system, with large and identifiable neurons, provides a good tool for studies of neural functions, such as learning. The results are discussed in the context of the role of protein phosphorylation on learning proc

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02511.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:In the present study we have applied a brain microdialysis technique to investigate the effects of ouabain infusion on the release of dopamine, acetylcholine, and amino acids from striatal neurons in freely moving rats. Ouabain caused an increase in the dialysate levels of dopamine; its metabolite 3,4‐dihydroxyphenylacetic acid (DOPAC); and the amino acids glutamate, aspartate, taurine, glycine, alanine, serine, asparagine, and threonine. The ouabain‐induced increase in dopamine was dose dependent and explosive (100‐ fold at an infusion concentration of 1 mmol/L) and contrasted strongly with the small effect of the glycoside on the output of DOPAC. We investigated the nature of ouabain‐induced transmitter release by determining its sensitivity to coinfusion with tetrodotoxin or the calcium antagonist Mg2+.In the case of dopamine two mechanisms of ouabain‐induced release could be established. At lower infusion concentrations ouabain induced an exocytotic type of release whereas at higher concentrations the release was probably camer mediated. In the case of amino acids we noticed a calcium‐independent release which was nerve impulse flow dependent in the case of glutamate and aspartate and impulse flow independent in the case of alanine, serine, glycine, threonine, and asparagine. Ouabain induced a decrease in the release of acetylcholine an

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02512.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:Rat hippocampal formation slices were prelabelled with [3H]inositol and stimulated with carbachol for times between 7 s and 3 min. The [3H]inositol metabolites in an acid extract of the slices were resolved with anion‐exchange HPLC. Carbachol dramatically increased the concentration of [3H]inositol monophosphate, [3H]inositol bisphosphate (two isomers), [3H]inositol 1,3,4‐trisphosphate, [3H]inositol 1,4,5‐trisphosphate, and [3H]inositol 1,3,4,5‐tetrakisphos‐phate. The levels of [3H]inositol 1,4,5‐trisphosphate rose most rapidly; they were maximally elevated after only 7 s and declined toward control levels in 1 min followed by a more sustained elevation in levels for up to 3 min. When [3H]inositol 1,4,5‐trisphosphate was incubated with hippocampal formation homogenates in an ATP‐containing buffer it was very rapidly metabolised. After 5 min [3H]inositol 1,4‐bisphosphate, [3H]inositol 1,3,4‐trisphosphate, and [3H]inositol 1,3,4,5‐tetrakisphosphate could be detected in the homogenates. Under similar experimental conditions [3H]inositol 1,3,4,5‐tetrakisphosphate is metabolised to [3H]inositol 1,3,4‐trisphosphate and an inositol bisphosphate isomer that is not [3H]inositol 1,4‐bisphosphate. We conclude that like other tissues the primary event in the hippocampus following carbachol stimulation is the activation of phosphatidylinositol 4,5‐bisphosph

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02513.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:Dopamine was determined by microdialysis of the striatum of conscious rats. We investigated whether the release of dopamine, induced by nine different pharmacological treatments, was sensitive to calcium antagonism. Calcium antagonism was determined by Mg2+or Cd2+infusion. The following conditions were investigated: haloperidol, haloper‐idol plus GBR 12909, nomifensine, (+)‐amphetamine (all administered intraperitoneally), KC1, l‐methyl‐4‐phenyl‐pyridinium ion (MPP+), glutamate, ouabain, and 120 mmol/ L magnesium (all applied by infusion through the dialysis membrane). The results on calcium antagonism were combined with data on tetrodotoxin (TTX) sensitivity. With the combined data, three different types of dopamine release were characterized. First, action potential‐dependent dopamine release was observed in animals treated with saline, haloperidol, haloperidol plus GBR 12909, nomifensine, and ouabain. Second, action potential‐independent release was established in the case of (+)‐amphetamine, glutamate, MPP+, and 120 mmol/L Mg2+. Finally, K+‐induced dopamine release was classified as TTX independent and calcium dependent. It is concluded that brain dialysis is a powerful method for differentiating between different types of neuro

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02514.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract:Eight weeks of latent iron deficiency in weaned rats maintained on an experimental low iron content diet (18–20 mg/kg) did not significantly alter the packed cell volume and hemoglobin concentration; however, the hepatic and brain nonheme iron contents decreased by 66% and 21% (p<0.001), respectively. The tryptophan concentration decreased by 31% and 34% in liver and brain, respectively, in rats on experimental diet (p<0.01). The brain 5‐hydroxytryptamine and 5‐hydroxyindoleacetic acid contents were reduced by 21% and 23% (p<0.01 and p<0.02), respectively. However, in the brain, weight, protein, DNA, and the activities of monoamine oxidase, aldehyde dehydrogenase, and liver tryptophan oxygenase were found to remain unaltered.When rehabilitated with a diet containing 390 mg/kg iron, rats previously maintained on the experimental diet for 2 weeks showed partial recovery in tryptophan levels both in liver and brain. However, brain 5‐hydroxytryptamine and 5‐hydroxyindoleacetic acid levels remained unaltered. The hepatic iron content improved without any change in brain iron content. The latent iron deficiency produced significant alterations in the metabolism of 5‐hydroxytryptamine and brain iron content that could not be recovered 2 weeks after the iron reh

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1989.tb02515.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY