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21.
Todd A. Crowl 《Hydrobiologia》1989,183(2):133-140
Laboratory experiments were performed in clear and turbid water to determine the effects of prey size, orientation, and movement on the reactive distance of largemouth bass (Micropterus salmoides) when feeding on crayfish (Procambarus acutus). In clear water, the reactive distance increased linearly with an increase in prey size, and prey movement resulted in a significant increase in the reactive distance. Prey orientation (head-on versus perpendicular) did not change the reactive distances. In moderately turbid water, the reactive distance did not increase with increased prey size, and prey movement did not result in any changes in the reactive distance. The absence of any effects of prey orientation in clear water or prey movement in turbid water is inconsistent with results from studies using different species (primarily planktivorous fish). I propose that largemouth bass change their foraging tactics as prey visibility changes. When prey are highly visible (low turbidity), predators attack (react) only after prey recognition, which is based on multiple cues such as prey size (length, width) and movement. When prey are less visible (high turbidity), predators attack immediately upon initial prey sighting, which does not depend on prey size or movement. 相似文献
22.
本实验观察了视前区(POA)内微量注入阿片样物质对丘脑束旁核(Pf)痛反应神经元电活动影响。结果如下:(1)POA 内微量注射高浓度吗啡(10μg/μl)能显著抑制 Pf 内大部分(20/26)痛兴奋神经元(PEN)的痛诱发放电,其中3个神经元注药后对伤害性刺激转变成抑制反应;POA 内微量注射低浓度吗啡(1μg/μl)也显著抑制 Pf 内大部分(19/23)PEN 的痛诱发放电。(2) POA 内微量注射两种浓度的吗啡,均使大多数痛抑制神经元(PIN,共27/33)的完全抑制时程缩短。上述结果提示,POA 内阿片样物质对 Pf 内痛反应神经元的电活动可能具有抑制作用。 相似文献
23.
Zinc is essential for normal growth, development and brain function although little is known about brain zinc homeostasis. Therefore, in this investigation we have studied65Zn uptake from blood into brain and other tissues and have measured the blood-brain barrier permeability to65Zn in the anaesthetized rat in vivo. Adult male Wistar within the weight range 500–600 g were used.65ZnCl2 and [125I]albumin, the latter serving as a vascular marker, were injected in a bolus of normal saline I.V. Sequential arterial blood samples were taken during experiments that lasted between 5 min and 5 hr. At termination, samples from the liver, spleen, pancreas, lung, heart, muscle, kidney, bone, testis, ileum, blood cells, csf, and whole brain were taken and analysed for radio-isotope activity. Data have been analysed by Graphical Analysis which suggests65Zn uptake from blood by all tissues sampled was unidirectional during this experimental period except brain, where at circulation times<30 min,65Zn fluxes were bidirectional. In addition to the blood space, the brain appears to contain a rapidly exchanging compartment(s) for65Zn of about 4 ml/100g which is not csf. 相似文献
24.
pH Dependence of Histidine Affinity for Blood-Brain Barrier Carrier Transport Systems for Neutral and Cationic Amino Acids 总被引:1,自引:1,他引:0
William H. Oldendorf Paul D. Crane† Leon D. Braun Eddy A. Gosschalk Jared M. Diamond† 《Journal of neurochemistry》1988,50(3):857-861
The effects of pH (3.5-7.5) on the brain uptake of histidine by the blood-brain barrier (BBB) carriers for neutral and cationic amino acids were tested, in competition with unlabeled histidine, arginine, or phenylalanine, with the single-pass carotid injection technique. Cationic amino acid ( [14C]arginine) uptake was increasingly inhibited by unlabeled histidine as the pH of the injection solution decreased. In contrast, the inhibitory effect of unlabeled histidine on neutral amino acid ( [14C]phenylalanine) uptake decreased with decreasing pH. Brain uptake indices with varying histidine concentrations indicated that the neutral form of histidine inhibited phenylalanine uptake whereas the cationic form competed with arginine uptake. Since phenylalanine decreased [14C]histidine uptake at all pH values whereas arginine did not, it was concluded that the cationic form of histidine had an affinity for the cationic carrier, but was not transported by it. We propose that the saturable entry of histidine into brain is, under normal physiological circumstances, mediated solely by the carrier for neutral amino acids. 相似文献
25.
Armando Tovar Jean K. Tews Nimbe Torres Alfred E. Harper 《Journal of neurochemistry》1988,51(4):1285-1293
Threonine entry into brain is altered by diet-induced changes in concentrations of plasma amino acids, especially the small neutrals. To study this finding further, we compared effects of various amino acids (large and small neutrals, analogues, and transport models) on transport of threonine and phenylalanine across the blood-brain barrier. Threonine transport was saturable and was usually depressed more by natural large than small neutrals. Norvaline and 2-amino-n-butyrate (AABA) were stronger competitors than norleucine. 2-Aminobicyclo[2.2.1]heptane-2-carboxylate (BCH), a model in other preparations for the large neutral (L) system, and cysteine, a proposed model for the ASC system only in certain preparations, reduced threonine transport; 2-(methylamino)isobutyrate (MeAIB; a model for the A system for small neutrals) did not. Phenylalanine transport was most depressed by cold phenylalanine and other large neutrals; threonine and other small neutrals had little effect. Norleucine, but not AABA, was a strong competitor; BCH was more competitive than cysteine or MeAIB. Absence of sodium did not affect phenylalanine transport, but decreased threonine uptake by 25% (p less than 0.001). Our results with natural, analogue, and model amino acids, and especially with sodium, suggest that threonine, but not phenylalanine, may enter the brain partly by the sodium-dependent ASC system. 相似文献
26.
Motoki Tagami Kazuo Yamagata Hideaki Fujino Akiyoshi Kubota Yasuo Nara Yukio Yamori 《Cell and tissue research》1992,268(2):225-232
Summary In this study bovine aortic endothelial cells were co-cultured with astrocytes from fetal Wistar Kyoto rats. Endothelial cells growing on type-I collagen, development. Although some cells appeared to be mature, horseradish peroxidase penetrated within 1 min of incubation through the intercellular junctions of these endothelial elements maintained on type-I collagen. In contrast, endothelial cells on type-IV collagen, co-cultured with astrocytes, were well developed; their intercellular junctions were well established, and plasmalemmal vesicles reduced in number. As a result, horseradish peroxidase was unable to penetrate through the endothelial cells grown on type-IV collagen and co-cultured with astrocytes because of the reduced extent of the junctional and vesicular transport. These findings reveal that (1) type-IV collagen is essential for the differentiation of endothelial cells, (2) endothelial cell-astrocyte interactions occur during co-culture, and (3) endothelial permeability depends on astrocyte-produced factors, in addition to type-IV collagen. 相似文献
27.
Zinc is essential for normal development and function of the CNS although much is to be learned about brain Zn homeostasis. In these experiments adult male Wistar rats within the weight range 500–600 g were used. Ventriculo-cisternal perfusion was performed to allow the measurement of65Zn fluxes between blood and csf across the choroid plexuses. Blood-brain or blood-cerebrospinal fluid barrier permeability to65Zn has been determined by graphical analysis in experiments that lasted between 5 and 180 minutes. Cerebral capillary permeability to65Zn was found to be low with a Kin of about 5×10–4ml/min/g. Choroid plexus permeability to65Zn was about 12 fold greater, although Zn influx to brain via this route was <5% that across cerebral capillaries. The autoradiographic distribution of65Zn in brain showed regional variation with lowest levels in white matter and high levels in the dentate gyrus and hippocampus. 相似文献
28.
To determine if alterations in lipid composition and/or membrane order of cerebral microvessels may contribute to the age-related changes in blood-brain barrier (BBB) function, cerebral microvessels isolated from male Fischer 344 rats at 3 (young), 12 (intermediate age), and 24 (aged) months of age were studied. The steady state fluorescence polarization of diphenylhexatriene incorporated into isolated cerebral microvessel membranes at 35°C, in aged rats was not different compared to young rats (0.2787±0.0029 vs 0.2847±0.0049). In addition, the thermotropic transition temperature of these membranes was not altered with age. Moreover, the fatty acid composition, the double bond index as well as cholesterol to phospholipid molar ratios were not significantly altered with age. In contrast, the concentration of conjugated dienes in lipid extracts of cerebral microvessels of aged rats (10.04±1.10 O.D./mg phospholipids) was significantly increased compared to the concentration in young rats (6.98±0.52 O.D./mg phospholipids) (p<0.01). It is concluded that aging is not associated with significant changes in lipid composition or membrane order of cerebral microvessels. However, the increased concentration of conjugated dienes in cerebral microvessels of aged rats is indicative of ongoing free radical damage in these microvessels which may contribute to the age-related changes in BBB function. 相似文献
29.
Thomas L. Pazdernik Matthew Layton Stanley R. Nelson Fred E. Samson 《Neurochemical research》1992,17(1):11-21
This overview presents data showing that glucose use increases and that excitatory amino acids (i.e., glutamate, aspartate), taurine and ascorbate increase in the extracellular fluid during seizures. During the cellular hyperactive state taurine appears to serve as an osmoregulator and ascorbate may serve as either an antioxidant or as a pro-oxidant. Finally, a unifying hypothesis is given for seizure-induced brain damage. This unifying hypothesis states that during seizures there is a release of excitatory amino acids which act on glutamatergic receptors, increasing neuronal activity and thereby increasing glucose use. This hyperactivity of cells causes an influx, of calcium (i.e. calcium stress) and water movements (i.e., osmotic stress) into the cells that culminate in brain damage mediated by reactive oxygen species.Special issue dedicated to Dr. Frederick E. Samson 相似文献
30.
Regional Kinetic Constants for Blood–Brain Barrier Pyruvic Acid Transport in Conscious Rats by the Monocarboxylic Acid Carrier 总被引:1,自引:1,他引:0
The present investigation using labeled pyruvate describes the regional distribution and kinetics of the monocarboxylic acid carrier at the blood-brain barrier of conscious rats. The experimental procedure involved the arterial injection of a single bolus of 200 microliter containing [1-14C]pyruvate, [3H]water, and varying concentrations of unlabeled pyruvate into the common carotid via an indwelling externalized catheter. The hemisphere ipsi-lateral to the injection and rostral to the midbrain was removed and dissected into five regions. A kinetic analysis revealed no significant regional differences in Km values with an overall average of 1.37 mM. However, there was regional variation in the density of the monocarboxylic acid carrier as indicated by varied levels of the kinetic constant Vmax. The cortex showed the highest Vmax value of 0.42 +/- 0.08 mumol/min/g whereas values for the caudate/putamen, thalamus/hypothalamus, and remaining portion of hemisphere ranged significantly lower at 0.22-0.27 mumol/min/g. The Vmax for the hippocampus was intermediate at 0.37 +/- 0.12 mumol/min/g. The nonsaturable carrier described kinetically by KD had an overall average of 0.034 ml/min/g. The present study confirms quantitatively previous results suggesting a variable regional distribution of the monocarboxylic acid carrier. 相似文献