Structural alterations in synaptosomal membrane-associated proteins and lipids by transient middle cerebral artery occlusion in the cat

We have previously reported that ischemia reperfusion injury results from free radical generation following transient global ischemia, and that this radical induced damage is evident in the synaptosomal membrane of the gerbil. [Hall et al, (1995) Neuroscience 64: 81–89] In the present study we have extended these observations to transient focal ischemia in the cat. We prepared synaptosomal membranes from frontal, parietal-temporal, and occipital regions of the cat cerebral cortex with reperfusion times of 1 and 3 hours following 1 hour right middle cerebral artery occlusion. The membranes were selectively labeled with protein and lipid specific paramagnetic spin labels and analyzed using electron paramagnetic resonance spectrometry. There were significant motional changes of both the protein and lipid specific spin labels in the parietal-temporal and occipital regions with 1 hour reperfusion; but, both parameters returned to control values by 3 hours reperfusion. No significant changes were observed in the normally perfused frontal pole at either reperfusion time. These results support the argument that free radicals play a critical role in cell damage at early reperfusion times following ischemia.     

猫纹状皮层神经元整合野的形状和范围

用正弦调制的移动光栅测量了１２０个猫纹状皮层神经元在长度和宽度方向上的空间整合特性。结果表明：（１）大多数细胞的传统感受野具有长宽相近的结构,然而它们的整合野多数是宽而短或者窄而长的长条形。（２）整合野大小为传统感受野的２—７倍,平均为３．７倍。简单细胞与复杂细胞整合野的大小没有显著差别。（３）随着感受野的视网膜偏心度的增加,整合野大小有逐渐增大的趋势。（４）感受野靠近视网膜垂直中线的细胞,其整合野可以跨越中线进入同侧视野;在两半视野中整合野的范围没有显著差异,但是同侧视野整合野的作用强度明显弱于对侧视野。以上结果提示,初级视皮层神经元能够对大范围内的图形特征进行整合,这种整合作用来自两侧视野。     

Inhibition of nitric oxide synthase activity in cerebral cortical synaptosomes by nitric oxide donors: Evidence for feedback autoregulation

Despite evidence which supports a neurotransmitter-like role for nitric oxide (NO) in the CNS, relatively little is known regarding mechanisms which control NO formation within CNS neurons. In this study, isolated nerve endings (synaptosomes) from rat cerebral cortex were used to ascertain whether NO can autoregulate its own formation within neurons through feedback inhibition of the NO biosynthetic enzyme nitric oxide synthase (NOS). Under the conditions described here, N-nitro-l-arginine methyl ester-sensitive conversion ofl-[³H]arginine intol-[³H]citrulline (i.e., NOS activity) was found to be highly calcium-dependent and strongly inhibited (up to 60 percent) by NO donors, including sodium nitroprusside, hydroxylamine and nitroglycerin. The inhibitory effect of sodium nitroprusside was concentration-dependent (IC₅₀100 M) and prevented by the NO scavenger oxyhemoglobin.l-Citrulline, the other major end-product from NOS, had no apparent effect on synaptosomal NOS activity. Taken together, these results indicate that neuronal NOS can be inhibited by NO released from exogenous donors and, therefore, may be subject to end-product feedback inhibition by NO that is formed locally within neurons or released from proximal cells.     

The role of endozepine in the regulation of steroid synthesis

Endozepine has recently been isolated from various steroid-forming organs. The following article explores the role of endozepine in the regulation of steroid synthesis. Steroid hormone synthesis from cholesterol begins in the inner mitochondrial membrane, where cytochrome P450 converts cholesterol to pregrenolone. Scientists thought that ACTH would stimulate this conversion, but experiments showed no such stimulation. However, addition of aminoglutethimide to block side-chain cleavage caused the expected reaction of ACTH to take place. Next the role of protein synthesis on the actions of ACTH was explored. Then endozepine was isolated from bovine fasciculata based on stimulation of pregnenolone production by freshly prepared mitochondria. After further experimentation it was concluded that endozepine is a peptide with at least two groups of actions: It binds GABA_A receptors in the central nervous system, and it increases the mitochondrial synthesis of pregnenolone.     

Electrical consequences of spine dimensions in a model of a cortical spiny stellate cell completely reconstructed from serial thin sections

We built a passive compartmental model of a cortical spiny stellate cell from the barrel cortex of the mouse that had been reconstructed in its entirety from electron microscopic analysis of serial thin sections (White and Rock, 1980). Morphological data included dimensions of soma and all five dendrites, neck lengths and head diameters of all 380 spines (a uniform neck diameter of 0.1 m was assumed), locations of all symmetrical and asymmetrical (axo-spinous) synapses, and locations of all 43 thalamocortical (TC) synapses (as identified from the consequences of a prior thalamic lesion). In the model, unitary excitatory synaptic inputs had a peak conductance change of 0.5 nS at 0.2 msec; conclusions were robust over a wide range of assumed passive-membrane parameters. When recorded at the soma, all unitary EPSPs, which were initiated at the spine heads, were relatively iso-efficient; each produced about 1 mV somatic depolarization regardless of spine location or geometry. However, in the spine heads there was a twentyfold variation in EPSP amplitudes, largely reflecting the variation in spine neck lengths. Synchronous activation of the TC synapses produced a somatic depolarization probably sufficient to fire the neuron; doubling or halving the TC spine neck diameters had only minimal effect on the amplitude of the composite TC-EPSP. As have others, we also conclude that from a somato-centric viewpoint, changes in spine geometry would have relatively little direct influence on amplitudes of EPSPs recorded at the soma, especially for a distributed, synchronously activated input such as the TC pathway. However, consideration of the detailed morphology of an entire neuron indicates that, from a dendro-centric point of view, changes in spine dimension can have a very significant electrical impact on local processing near the sites of input.     

大脑皮层神经元膜蛋白构象改变的ESR研究

采用马来酰亚胺标记完整的大脑皮层细胞,观察由低氧引起的ESR谱线的变化及脑细胞脂质过氧化程度,低氧引起细胞过氧化物生成增加,膜蛋白构象改变．金属硫蛋白(10^-5mol/L)能明显抑制过氧化反应,具有一定的抗氧化作用．并对实验的分子机理进行了简要的讨论．     

Effect of low-molecular-weight proteins on protein (lysozyme) binding to isolated brush-border membranes of rat kidney

Filtered proteins including the low-molecular-weight protein lysozyme are reabsorbed by the proximal tubule via adsorptive endocytosis. This process starts with binding of the protein to the brush-border membrane. The binding of ¹²⁵I-labelled egg-white lysozyme (EC 3.2.1.17) to isolated brush-border membranes of rat kidney and the effect of several low-molecular weight proteins on that binding was determined. The Scatchard plot revealed a one-component binding type with a dissociation constant of 5.3 μM and 53.0 nmol/mg membrane protein for the number of binding sites. The binding of the cationic lysozyme was inhibited competitively by the addition of cationic cytochrome c to the incubation medium, while the neutral myoglobin had no effect. The anionic β-lactoglobulin A inhibited the lysozyme binding in a noncompetitive manner. These data suggest that the binding takes place between positively charged groups of the protein molecule and negative sites on the brush-border membrane, and, the competition between the cationic cytochrome c and the cationic lysozyme for the binding sites may be responsible for the inhibitory effect of cytochrome c on renal lysozyme reabsorption. The binding step at the brush-border membrane appears to be cation-selective.     

Sex differences in adrenocortical structure and function

Summary Adrenal glands of adult male hamsters are larger and secrete more cortisol than those of females. Stereology was therefore used to study zonal and cellular aspects of development of the adrenal cortex of male and female hamsters. Adrenal glands were studied at weekly intervals from day 21 to day 77 of postnatal ontogenesis. Within this period, body weight did not differ significantly between the sexes. During development, absolute and relative adrenal weights were higher in males; their zona glomerulosa (ZG), zona fasciculata (ZF) and zona reticularis (ZR) become markedly larger than those in females. No marked changes in the volume of individual ZG cells occurred although ZF cells and ZR cells become larger in male than female animals. The total number of adrenocortical cells increased within the period studied, a greater increase being observed in ZG and ZF in males. No distinct sex difference was observed in the number of ZR cells throughout development. From day 56 of postnatal life the adrenal cortex of male hamster contained more parenchymal cells than the female gland. These results thus indicate that sex differences in hamster adrenal cortex depend upon changes in number and size of parenchymal cells.Supported in part by a grant from the Committee of Zoology, Polish Academy of Sciences     

Effects of ACTH and 3′,5′-cyclic purine nucleotides on the morphology and metabolism of normal adult human adrenocortical cells in primary tissue culture

Summary Stereological studies showed that treatment of normal adult human adrenocortical cells in primary culture with ACTH or cyclic-AMP for 2 days results in similar increases in the volume of cells, of the mitochondrial and membrane space compartments and of the surface area of the smooth endoplasmic reticulum and mitochondrial cristae, and decrease in the lipid content of the cells. These changes were more marked after 8 days of treatment. Treatment for 2 days with cyclic-GMP had no striking effects on cell ultrastructure, whereas an 8-day treatment led to ultrastructural changes similar to those obtained after 2 days of ACTH-or cyclic-AMP-treatment. A discrete population of untreated cortical cells maintained a slow proliferation that was not effected by exposure to cyclic-GMP, but was significantly increased in cultures treated with ACTH or cyclic-AMP. Radioimmunological studies showed that untreated cortical cells kept secreting progesterone and cortisol and that ACTH, but neither cyclic nucleotide, increased the secretion rate per cell of both hormones. These results assign a major role to cyclic-AMP and a minor one to cyclic-GMP in the mediation of the differentiation-promoting and trophic effects, but not in the steroidogenic effects of ACTH on the human adrenal cortex.The authors wish to thank Miss A. Coi and Mr. G. Gottardo for their technical assistance. These investigations were partly supported by a contract with CNR-Italy (CT 74.00226/115.3439)