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41.
Stomatal responses and water relations of Eucalyptus pauciflora in summer along an elevational gradient 总被引:1,自引:0,他引:1
Summary The spatial and temporal variation of lead conductance (g) in Eucalyptus pauciflora was analysed with respect to photon flux area density (I), temperature (T), water vapour concentration deficit (w), and leaf water potential () at four different sites between 940 m and 2,040 m altitude in the Snowy Mountains of south-eastern Australia. Along this altitudinal gradient the precipitation/evaporation ratio increases from 1 to 4. The results show that gas diffusion in this tree species is primarily controlled by I and w at all sites, independently of the specific soil moisture regime. Even under dry midsummer conditions with predawn leaf water potentials of-1 MPa at the lowest altitude, had no striking effect on g.The humidity threshold for the onset of stomatal closure does not vary greatly between the study sites (12.2±1.3 Pa kPa-1). The highest and lowest values observed for , the osmotic potential at water saturation (from pressure/volume curves), the mean and maximum g and stomatal dentity, all increase with elevation. The highest (least negative) osmotic potentials were obtained at all sites in midsummer. It therefore appears that there is no osmotic adjustment to drought in the seasonal course. The maximum difference between osmotic potentials obtained at the lowest and highest sites is 0.46 MPa. In general osmotic potential varies less than has been reported for other plant species exposed to varying water regimes. This may be the consequence of the pronounced feed-forward response of the stomata to evaporative demand, which led to only moderate tissue desiccation, never exceeding the turgor loss point. E. pauciflora is a tree species with a very conservative utilisation of soil water, which adjusts to drought via stomatal control of water loss, rather than via osmotic properties.These results explain previous reports of the comparatively high susceptibility of E. pauciflora to severe drought and its positive influence on the hydrological balance of mountain ecosystems in the Australian Alps. 相似文献
42.
B. Sporrong P. Kannisto Prof. Ch. Owman N. -O. Sjöberg B. Walles 《Cell and tissue research》1985,241(3):505-511
Summary With the use of an anti-human S-100 protein antibody, it was possible to reveal a characteristic cell type in the anterior lobe of the normal human pituitary. These cells, so-called folliculo-stellate cells, were present in all pituitaries studied but their number varied from one gland to another. Immunoreactive cells, isolated or grouped, were arranged close to various secretory granulated cells. Especially by use of double immunoenzymatic labeling, it was evident that these cells are spatially related either to somatotropes, prolactin cells and corticotropes, or to glycoprotein-containing cells. Such immunoreactive cells were rare or absent in pseudo-follicular arrangements of secretory granulated cells. Since it is now possible to identify this cell type by light microscopy and since no reliable functional significance is known, it seems more advisable to term this cell type stellate cell instead of folliculostellate cell. 相似文献
43.
Summary The structural and ultrastructural characteristics of the heart of Channichthys rhinoceratus, an antarctic teleost devoid of respiratory pigments, are described and compared with those obtained from the red-blooded related species Notothenia rossii.The heart of the icefish is characterized by a spongy myocardium supplied with a highly developed arterial coronary system. This vasculature includes a subepicardial system and an extensive intratrabecular capillary network. Arterial hilar network and Thebesian vessels may also be present. The bulbus arteriosus shows unusually large spheroid structures located in the middle layer of the wall.Both white- and red-blooded species display comparable myocardial cell morphology and organelle distribution. However, the mitochondrial cristae of the former are more densely packed and the sarcolemma possesses numerous caveolae. A large proportion of non-contractile cells is also found in the icefish ventricular wall. 相似文献
44.
A simplified method was developed for the bulk separation of neuronal perikarya and astroglial celis from adult rat brain without the involvement of density gradients. Activities of various enzymes involved in glutamate metabolism were estimated and compared with those of synaptosomes. The activities of glutamate dehydrogenase and aspartate aminotransferase were higher in synaptosomes than in neuronal perikarya or glia. Glutamine synthetase was distributed in all the three fractions while glutaminase activity was higher in astrocytes than in synaptosomes and was not detectable in neuronal perikarya. The significance of these results in relation to metabolic compartmentation was discussed. 相似文献
45.
T.T. Dolan A.S. Young G.J. Losos I. McMilian Ch.E. Minder K. Soulsby 《International journal for parasitology》1984,14(1):89-95
Dolan T. T., Young A.S., Losos G.J., McMillan I., Minder Ch.E. and Soulsby K. 1984. Dose dependent responses of Theileria parva stabilate. International Journal for Parasitology14: 89–95. A tick derived stabilate of Theileria parva (Maguga) was titrated in a large group of Boran (Bos indicus) cattle of the same age, sex and origin. The infectivity data was analysed using the independent action model. The cattle were identified as heterogeneous in their response to infection with 75% showing one ID50 (0.0014) and 25% showing another (0.01). The disease responses of the cattle given different dose levels were compared for a variety of parameters. The results obtained showed these parameters to be dose dependent including the time to onset of piroplasm parasitaemia. The stabilate is of large volume and can be used for controlled challenge in immunity studies and for comparison of susceptibility between cattle of different breeds and from different epidemiological backgrounds. 相似文献
46.
Male Long-Evans rats were injected with 0, 1, 3, or 6 mg/kg of cadmium chloride on the first day of life. Animals free of morphological stigmata at weaning were selected for study. Tissue concentrations of cadmium and operant behavior under various fixed-ratio (FR) schedules of reinforcement were evaluated when these rats were adults. Dose-related increases in cadmium were present in the brains, livers, and kidneys. Dose-related differences in behavior were most evident during the transition from fixed ratio 25 (FR 25 or 25 responses/reinforcer) to FR 75. An inverted U describes the relationship between response output during the transition to FR 75 and cadmium chloride dose response output increased at 3 mg/kg and decreased at 6 mg/kg. The rate decreases were not correlated with weight loss that appeared after some of the animals exposed to 6 mg/kg reached 60 days of age. Challenge doses of d-amphetamine revealed no interaction between neonatal exposure to cadmium and d-amphetamine. The occurrence of alterations in operant behavior in animals that appeared normal on a number of preweaning evaluations suggests that operant behavior in transition was sensitive to subtle effects not observed with other commonly used tests. The data provide evidence for delayed effects in the adult that are due to neonatal exposure to cadmium. 相似文献
47.
Correlation of neuronal size and peptide immunoreactivity in the guinea-pig trigeminal ganglion 总被引:2,自引:0,他引:2
Summary Frequency and size of guinea-pig trigeminal neurones immunoreactive with antisera to -neo-endorphin(-neo-END), dynorphin A-(DYN), vasoactive intestinal polypeptide-(VIP), somatostatin-(SOM), and substance P-(SP) are reported. Co-localisation of the various peptides to the same ganglion cells was investigated immunocytochemically in consecutive 7-m thick paraffin sections. According to their size, all peptide-immunoreactive neurones belong to the class of small ganglion cells. Within this cell group, SP-immunoreactive neurones appear to be the largest, followed by SOM-, VIP-, -neo-END- and DYN-immunoreactive ganglion cells. The observed differences in size are statistically significant with the exception of that between -neo-END and DYN. This finding correlates well with the observed co-occurrence of the two immunoreactive peptides. All -neo-END-immunoreactive perikarya are also reactive to VIP antisera. These neurones are significantly smaller than those containing VIP-immunoreactivity exclusively. Ganglion cells displaying co-existence of -neoEND- and SP-immunoreactivity or VIP- and SP-immunoreactivity are found too infrequently to allow morphometric analysis. Some non-immunoreactive ganglion cells are shown to be approached by dense baskets of VIP-, -neo-END- or SP-immunoreactive varicose fibres, indicating the presence of intraganglionic modulation sites. The combination of immunohistochemistry and morphometry presented in this study allows the differentiation of diverse populations of primary afferent neurones exhibiting peptide immunoreactivity, most likely reflecting their involvement in different central and peripheral reflex arcs and sensory modalities. 相似文献
48.
A neural cocktail-party processor 总被引:16,自引:0,他引:16
Sensory segmentation is an outstanding unsolved problem of theoretical, practical and technical importance. The basic idea of a solution is described in the form of a model. The response of neurons within the sensory field is temporally unstable. Segmentation is expressed by synchronization within segments and desynchronization between segments. Correlations are generated by an autonomous pattern formation process. Neuronal coupling is the result both of peripheral evidence (similarity of local quality) and of central evidence (common membership in a stored pattern). The model is consistent with known anatomy and physiology. However, a new physiological function, synaptic modulation, has to be postulated. The present paper restricts explicit treatment to the peripheral evidence represented by amplitude modulations globally present in all components of a sound spectrum. Generalization to arbitrary sensory qualities will be the subject of a later paper. The model is an application and illustration of the Correlation Theory of brain function.This work has been supported by Grant I/37-821 of the Stiftung Volkswagenwerk. 相似文献
49.
Ch. Franke H. Hatt J. Dudel 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1986,159(5):591-609
Summary Outside-out and inside-out patches of membrane were excised from different muscles of crayfish (Austropotamobius torrentium) and single channel currents elicited by synaptic transmitters and their analogues were measured with the patchclamp technique. If the Cl–-concentration was high on both sides of the membrane, glutamate even at concentrations <1 M elicited low amplitude single channel currents, which were identified to be Cl–-currents. The same channels were also activated by 10 M GABA. Glutamate and GABA showed competition in activating these inhibitory channels. Amplitude histograms of the single channel currents presented well defined peaks corresponding to 3 channel substatesI
1,I
2 andI
3, with conductances of about(I1)=22 pS in high chloride corresponding to a permeability
Cl(I1)=3.5× 10–14 cm3/s),(I2)=2(I1) and(I3)=3(I1). Glutamate activated preferably stateI
1, and GABA stateI
2, but both could activate all states at sufficient concentration. Distributions of the open times in the different states were plotted and could be fitted each with one or two exponentials described by time constants of(I1) of 1 and 6 ms,(I2) of 2 to 3 ms, and(I3) or 1 to 2 ms. The burst durations had components of 3 to 4 and of 30 to 40 ms. All these durations were approximately the same when the channels were activated by glutamate and GABA. The analogue quisqualate of glutamate, as well as the GABA analogue-guanidino propionic acid also elicited the respective patterns of states of the inhibitory channel. Quisqualate is by far the most effective agonist and glutamate is more effective than GABA at the inhibitory receptor. Picrotoxin blocked activation of the inhibitory channel by GABA more effectively than by glutamate. The importance of the activation of the inhibitory channel by glutamate as well as by GABA and their analogues is discussed. Elements of a tentative reaction schema are proposed. 相似文献
50.
Summary The immunohistochemical localization of neuropeptide Y (NPY) was correlated with those of dopamine--hydroxylase (DBH) and vasoactive intestinal polypeptide (VIP) by mapping serial 7 m paraffin sections at three levels of the guina pig lower brainstem: a) area postrema, b) dorsal motor nucleus of the vagus, and c) nucleus prepositus of the hypoglossal nerve. Based on differences in transmitter expression, three populations of NPY-immunoreactive (IR) neurons were distinguished: NPY-IR catecholaminergic cells (NPY/CA), NPY-IR VIP-ergic cells (NPY/VIP), and NPY-IR cells which were not reactive to either DBH or VIP. Within these populations, size differences among neurons in characteristic locations allowed differentiation among the following subpopulations: NPY/CA neurons in the lateral reticular nucleus — magnocellular part (mean neuronal size 538 m2) and parvocellular part (318 m2)-, in the vagus-solitarius complex (433 m2), and in the dorsal strip (348 m2); NPY/VIP neurons in the vagus-solitarius complex (368 m2) and in the nucleus ovalis (236 m2). Apart from scattered NPY-IR cell bodies in the regions listed above, NPY-IR cell bodies in the lateral portion of the nucleus solitarius and in the caudal part of the spinal nucleus of the trigeminal nerve did not exhibit IR to either DBH or VIP. NPY-IR neurons in the area postrema occurred too infrequently for co-localization studies. The differential distribution of heterogeneous NPY-IR cell subpopulations may reflect the involvement of NPY in a variety of neuronal functions.Supported by the Deutsche Forschungsgemeinschaft, grant He 919/6-1 相似文献