Tapering of human nerve fibres

To determine the tapering of human nerve fibres, rostral and caudal root pieces of cauda equina nerve roots were removed and nerve fibre diameter distributions were constructed for 4 myelin sheath thickness ranges for the two sites, and compared with each other. The reduction of the group diameter in the different alpha-motoneuron groups was 0.2 % per 13 cm. Accounting for systematic errors, there may be even less tapering. An identified single nerve fibre showed no tapering. Further, there is indication that gamma-motoneurons, preganglionic sympathetic and parasympathetic fibres and skin afferents also reduce their fibre diameter by 0.2 % per 13 cm or less. Consequently, a nerve fibre with a diameter of 10 microm would be reduced to approximately 9.8 microm at 1m from the cell soma. Preganglionic parasympathetic fibres were found to be represented in roots S1 to S5. At similar distances from the spinal cord, the mean diameter of ventral root alpha1-motoneuron (FF) axons increased from the thoracic towards the lumbo-sacral region before decreasing again in the lower sacral region. Usually no alpha1-motoneuron axons were found in S5 roots. The diameter distribution of unmyelinated nerve fibres of a ventral S5 root showed three peaks at 0.25, 0.95 and 1.2 microm. The unmyelinated fibres with diameters around 0.25 microm may represent parasympathetic fibres. In six selected areas of the ventral S5 root, 6.6 times more unmyelinated nerve fibres than myelinated fibres were found on the average.     

Effects of ultraviolet B irradiation on cutaneous leishmaniasis

Protection against many infectious diseases is mediated by cellular immunity in the competent host. Ultraviolet (UV) radiation, a component of sunlight, is a potent suppressor of cell-mediated immune responses. Suzanne Holmes Giannini discusses the possible relevance of ambient levels of UVB to pathogenesis and immunity in infectious diseases, with special reference to cutaneous leishmaniasis.     

Investigation of the relation between structure and function in myelinated nerve fibres with the aid of ultraviolet radiation

Ultraviolet radiation induces two photochemical alterations relevant to excitability in the nodal membranes: A selective blocking of the sodium permeability and a potential translation of the voltage dependent kinetic parameters of sodium inactivation and activation along the potential axis in the negative direction. The underlying processes are two different photoreactions, since 1) the action spectrum of the blocking effect shows a marked peak near 280 nm and rapidly decreasing sensitivity towards higher and lower wavelengths, while the action spectrum of the potential shift increases with lower wavelengths; 2) the blocking effect is enhanced by a more positive holding potential, while the potential shift is decreased; 3) the potential shift can be prevented intraaxonal application of l-cysteine or 2-mercaptoethanol, but the blocking effect is not affected.Paper presented at the Biomembrane Symposium of the Deutsche Gesellschaft für Biophysik, Freiburg, April 1975.     

长波紫外线辐射对脊椎动物的影响

臭氧层空洞的加剧使紫外辐射不断加强,造成的环境污染已经成为广为关注的问题,但大多数都集中在中波紫外线(UVB)的生物学作用及其与两栖动物衰减关系的研究,有关长波紫外线(UVA)对生物体损伤作用的研究却甚少。本文综述了近年来UVA对脊椎动物损伤的研究概况,从细胞结构、酶活性、遗传物质、膜结构以及免疫系统等方面阐述了UVA的损伤机理,并对低剂量辐射诱导兴奋效应对紫外损伤的保护作用进行了简要概述。最后分析和总结了关于UVA损伤研究所存在的问题及两栖动物作为实验用动物模型在研究紫外线损伤中的作用。     

Regulation of ultraviolet radiation induced cutaneous photoimmunosuppression by Toll-like receptor-4

UVB radiation is a potent immunosuppressive agent that inhibits cell-mediated immune responses. The mechanisms by which UVB radiation influences cell-mediated immune responses have been the subject of extensive investigation. However, the role of innate immunity on photoimmunological processes has received little attention. The purpose of this study was to determine whether Toll-like receptor-4 (TLR4) contributed to UV-induced suppression of contact hypersensitivity (CHS) responses. TLR4^−/− and wild type C57BL/6 (TLR4^+/+) mice were subjected to a local UVB immunosuppression regimen consisting of 100 mJ/cm² UVB radiation followed by sensitization with the hapten DNFB. Wild type TLR4^+/+ mice exhibited significant suppression of contact hypersensitivity response, whereas TLR4^−/− developed significantly less suppression. The suppression in wild type TLR4^+/+ mice could be adoptively transferred to naïve syngeneic recipients. Moreover, there were significantly fewer Foxp3 expressing CD4⁺CD25⁺ regulatory T-cells in the draining lymph nodes of UV-irradiated TLR4^−/− mice than TLR4^+/+ mice. When cytokine levels were compared in these two strains after UVB exposure, T-cells from TLR4^+/+ mice produced higher levels of IL-10 and TGF-β and lower levels of IFN-γ and IL-17. Strategies to inhibit TLR4 may allow us to develop immunopreventive and immunotherapeutic approaches for management of UVB induced cutaneous immunosuppression.     

Regulation of ultraviolet radiation induced cutaneous photoimmunosuppression by toll-like receptor-4

The open reading frame alr3199 of the nitrogen-fixing cyanobacterium, Anabaena sp. strain PCC7120 was cloned and overexpressed in Escherichia coli. Purified recombinant Alr3199 protein was found to be a functionally active deoxyribonuclease with novel features, such as (1) no homology to typical DNases (2) a Ca²⁺-dependent Nickase activity (3) presence of a di-hemerythrin domain, and (4) requirement of Fe²⁺ conjugated to hemerythrin domains for optimal activity. Both the DNase and Nickase activities were found to be associated with the N-terminal non-hemerythrin region, but were modulated by Fe²⁺ conjugated to the C-terminal hemerythrin region. This is the first report of a hemerythrin protein with DNase activity, tentatively designated as ‘HE-DNase’, and with a possible role in stress-induced DNA damage/repair in Anabaena.     

Effects of ultraviolet radiation on the membranes ofChara corallina

Summary The effects of 253.7 nm ultraviolet (UV) radiation on the membrane properties ofChara corallina have been studied. UV irradiation caused depolarization of the membrane potential (p.d.) and a decrease in membrane resistance. These effects were largely reversible with steady values being obtained within 40 minutes after the UV was turned off. The effects on ionic fluxes of Na⁺, K⁺ and Cl^– have also been studied using radioactive tracer techniques. The influxes were unchanged by irradiation. The chloride efflux was increased sevenfold during the irradiation period but recovered to the pre-irradiation value within 30 minutes after the irradiation period. The potassium efflux was also increased and reached a maximum 10 minutes after irradiation. The resting potential and the average depolarized p.d. reached during irradiation were in good agreement with those calculated from permeability coefficients indicated by the observed passive fluxes, using the Goldman equation for p.d. However, the plasmalemma resistance and its change due to irradiation did not match the values calculated from the same permeability coefficients used to estimate p.d. This disagreement, and an apparent imbalance in the charge transferred across the resting or irradiated plasmalemma, suggest the participation of another ion species as well as K⁺, Na⁺ and Cl^–.     

Mitochondrial accumulations in nerve fibres of human sympathetic ganglia

Summary The fine structure of mitochondrial accumulations in axonal swellings of human sympathetic ganglia is described. A typical swelling contained, in addition to regularly organized mitochondria, bundles of neurofilaments and vesicles as well as large dense-cored vesicles and myelin figures. Synaptic contacts between axonal swellings with mitochondrial accumulations and ganglion cells were not found.A three-dimensional model of the mitochondrial accumulation based on serial sectioning is presented. The possible degenerative and regenerative features of these accumulations are discussed. It is possible that mitochondrial accumulations are functionally active energy producers rather than results of degenerative processes.     

Effects of PGF2alpha on human melanocytes and regulation of the FP receptor by ultraviolet radiation

Prostaglandins are potent lipid hormones that activate multiple signaling pathways resulting in regulation of cellular growth, differentiation, and apoptosis. In the skin, prostaglandins are rapidly released by keratinocytes following ultraviolet radiation and are chronically present in inflammatory skin lesions. We have shown previously that melanocytes, which provide photoprotection to keratinocytes through the production of melanin, express several receptors for prostaglandins, including the PGE2 receptors EP1 and EP3 and the PGF2alpha receptor FP, and that PGF2alpha stimulates melanocyte dendricity. We now show that PGF2alpha stimulates the activity and expression of tyrosinase, the rate-limiting enzyme in melanin synthesis. Analysis of FP receptor regulation showed that the FP receptor is regulated by ultraviolet radiation in melanocytes in vitro and in human skin in vivo. We also show that ultraviolet irradiation stimulates production of PGF2alpha by melanocytes. These results show that PGF2alpha binding to the FP receptor activates signals that stimulate a differentiated phenotype (dendricity and pigmentation) in melanocytes. The regulation of the FP receptor and the stimulation of production of PGF2alpha in melanocytes in response to ultraviolet radiation suggest that PGF2alpha could act as an autocrine factor for melanocyte differentiation.     

Effects of ultraviolet radiation on corals and other coral reef organisms

The discovery of the importance of solar ultraviolet radiation (UVR) as a factor affecting the biology of coral reefs dates only to about 1980. Interest has heightened during the past five years owing to the demonstration of loss of stratospheric ozone through human activities. We have only begun to document gross, qualitative effects of UVR on coral reef organisms, usually in experiments comparing the biological response to the presence or absence of UVR through the use of UV-cutoff filters, or to varying levels of UVR in transplantation studies. Most such studies have not distinguished between the effects of UVA (320–400 nm) and those of UVB (290–320 nm), although in the context of global change involving stratospheric ozone loss, it is the latter wavelengths that are relevant. To date we have been addressing physiological and ecological questions, not yet attempting to evaluate quantitatively the impact of forecast increases in solar UVB penetration. Interacting and synergistic effects of UVR with increased temperature, pollutants, sedimentation, visible light, etc. have scarcely been studied but will be essential to understanding and predicting the fate of coral reefs under conditions of global change. Here we comprehensively review the effects of UVR on corals and other reef macroorganisms, mindful that although much is known of proximal effects, little of this knowledge is directly useful in making long-term predictions regarding the health of coral reefs. We conclude that even small anthropogenic increases in UVB levels will have sublethal physiological manifestations in corals and other reef organisms, but that this will have relatively small impact on the distribution of reef corals and coral reefs, perhaps affecting their minimum depths of occurrence.     

Modification of ultraviolet radiation effects on the membrane of myelinated nerve fibers by sulfhydryl compounds

Summary The modification of the ultraviolet blocking of sodium channels and of the ultraviolet-induced potential shift of the gating parameters by means of the sulfhydryl compoundsl-cysteine and 2-mercaptoethanol was investigated in the node of Ranvier under voltage-clamp conditions. The UV wavelength was 280 nm. The radiation-induced potential shift of the voltage-dependent gating parameters was prevented or even reversed by the action of the sulfhydryl compounds (internal application), while the blocking effect was not affected. It is concluded that the two radiation effects are caused by two separate photoreactions. Internally applied N-ethylmaleimide, binding specifically to protein-SH groups, exhibits an effect similar to the ultraviolet-induced potential shift, without affecting the maximum sodium permeability. Therefore, the ultraviolet-induced potential shift might be caused by a photocatalyzed oxidation of —SH groups of membrane proteins changing the surface charge density at the inner side of the nodal membrane.     

阳光紫外辐射对褐藻羊栖菜生长和光合作用的影响

为探讨经济褐藻羊栖菜对阳光紫外辐射变化的响应,我们在全波段阳光辐射(280－700 nm),去除UV-B辐射(320－700 nm)以及光合有效辐射PAR (400－700 nm)三种辐射条件下对其进行培养,测定了其光合作用与生长的变化。羊栖菜的生长是通过每两天测量一次藻体的湿重来测定的,光合放氧是用Clark型氧电极测定的,为了测定藻体叶绿素a和紫外吸收物质的含量,从250 nm到750 nm对羊栖菜的甲醇提取液进行扫描,叶绿素a的浓度用Porra的公式计算,紫外吸收物质的计算是根据Dunlap的方法先计算紫外吸收物质和叶绿素a的比率,然后乘以每单位藻体叶绿素a的含量。结果表明,当藻体接收较多的日辐射量时有较高的相对生长速率,当滤除UVR后,较高的太阳辐射也导致了较高的光合放氧。然而太阳紫外辐射能够抑制藻体的光合放氧和生长速率,降低叶绿素a的浓度,并且这种抑制作用随着辐射水平的升高而增强。此外,阳光紫外辐射也诱导产生了一定量的紫外吸收物质,但并不足以抵抗紫外辐射对藻体的伤害作用。     

Effects of ultraviolet radiation on carotenoid-containing and albino strains of Neurospora crassa

To determine the influence of carotenoids on UV sensitivity of Neurospora crassa conidia, the dose-response curves of 3 albino strains were compared to that of the wild type. In a control experiment the genetic background effects were eliminated by irradiating the wild type in which carotenoid synthesis had been inhibited by β-ionone, and comparing the dose-response curve to that of untreated wild type. All strains used had similar γ-ray survival curves and nuclei per conidium which precluded differences in UV sensitivity due to morphological differences.The albinos and β-ionone-treated strains showed a greater sensitivity (mean LD50 4.35·10³ erg/mm²) to UV irradiation than the wild type (LD50 7.30·10³ erg/mm²).     

Selective T cell killing of human lymphocytes by ultraviolet radiation

The effects of ultraviolet radiation (uv) on human B and T lymphocytes were studied. In vitro studies showed that T lymphocytes were more sensitive to uv than B lymphocytes as assessed by eosin-dye exclusion. Following uv exposure, the viable lymphocytes responded to mitogens (PHA, PWM), and functional B lymphocytes were present at a time when no viable T cells were detected. Varying doses of uv were required to abrogate different in vitro responses (proliferative response to antigen or allogeneic cells, MIF production, and cell-mediated lympholysis). In vivo, uv was able to diminish an established cutaneous delayed hypersensitivity response. In vitro uv treatment of parental mouse spleen cells eliminated a graft-versus-host reaction in F₁ recipients as determined by the spleen index. The basis for the differential effect of uv on B and T lymphocyte viability and functional responses is unknown.     

Pulse evolution on coupled nerve fibres

A numerical study of the coupled nerve fibre problem is given which verifies and extends the perturbation theory of Luzader. Pulses on adjacent fibres can couple together with two possible stable pulse separations.