The distribution, density and uptake of twenty elements by aquatic invertebrates inhabiting a drainage system, that received excessive coal ash effluent (275 JTU of turbidity) at one end and thermal loading (44.5°C) at the other end, was studied for 15 months. The ash settling basin filled during the first eight months of sampling which resulted in the release of ash effluent directly into the receiving system. Density of invertebrates was lowest in the 300 m stream between the ash basin and swamp and highest 1200 m beyond the stream-swamp confluence where ash influence was minimal. Invertebrate density was lowest in the stations where turbidity from ash effluent was greatest. The most tolerant invertebrates to coal ash stress were odonates (Libellula sp. and Enallagma sp.), crayfish (Procambarus sp.), amphipods (Gammarus sp.) and gastropods (Physa. sp.), and midges (Chironomidae) when the basin was filling. During the period of ash overflow, all groups were either reduced in numbers or absent. In the thermally stressed station, Libellula sp. was the predominant invertebrate sampled when water temperature ranged from 25.5–45.5°C (257-1=28.7°C) all aquatic invertebrates were limited in numbers and density when temperature exceeded the lower and upper ranges of 10.0–38.0°C.This research was supported by AEC Contract AT (38-1-824)This research was supported by AEC Contract AT (38-1-824) 相似文献
In experiments on rats, we studied the characteristics of reflex discharges in the ventral root (VR) L5; the discharges were evoked by stimulation of segmental (peripheral nerve or dorsal root, DR) and suprasegmental vestibular
(stimulation of the round window of the labyrinth) inputs. Potentials were recorded within different time intervals (from
1 to 150 days) after transection of the sciatic nerve (SN); measures preventing regeneration of its fibers were used. Modifications
of the segmental responses related to post-denervational changes included four phases: (i) latent period, (ii) post-denervational
spinal hyperreflexia (PDSH), (iii) partial suppression of monosynaptic discharges (MDs) in the VR, and (iv) complete disappearance
of VR MDs resulting from late post-denervational changes. The latency of post-denervational modifications was about 18–48
h after the moment of transection of the SN. Within the PDSH phase, modifications were the greatest 3 to 5 days after transection;
these changes could be more adequately estimated in the case of stimulation of the DR on the side of transection and not under
conditions of stimulation of the central segment of the transected SN per se. Within this phase, the amplitudes of VR MDs and responses to vestibular stimulation were augmented two to three and four
to five times, as compared with the respective indices in intact animals. From the 7th to 10th day after the nerve transection,
the amplitude of VR MDs progressively dropped, and on about the 20th day these discharges practically disappeared, while polysynaptic
components of segmental responses were preserved. Vestibular responses within this period were, as earlier, considerably facilitated.
On the 60th and 150th days (within the phase of late post-denervational modifications) there were no VR MDs after stimulation
of segmental inputs, and polysynaptic responses were exclusively observed. The amplitude of discharges evoked by vestibular
stimulation became lower than in the PDSH state but remained significantly higher than the control values of this parameter.
Probable mechanisms of post-denervational modifications of the evoked spinal activity within different time intervals after
transection of the SN are discussed.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 37–46, January–February, 2007. 相似文献
Siphonophores are exclusively marine cnidaria and their predatory role in plankton food-webs is well recognised. In this study,
we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows
and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of
149 samples were collected using a 505 μm multiple closing net at 1–6 levels (0–100 m) of the water column, depending on the
bathymetry. Data on siphonophore species biovolumes (ml 100 m−3) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the ‘inner’
and the ‘outer’ assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore
species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical
distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger
than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially,
the lowest diversity and mean siphonophore biovolumes values were registered in the ‘inner assemblage’, where the highest
and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore
populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity,
since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps,
their prey. All the 23 species here registered were found in the ‘outer assemblage’; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the ‘outer’ group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the ‘inner assemblage’ during both seasons and, supporting previous
observations, this species might be considered as an indicator of nearshore waters.
Handling editor: K. Martens 相似文献
Development times of eggs, larvae and pupae of vectors of onchocerciasis (Simulium spp.) and of Onchocerca volvulus larvae within the adult females of the vectors decrease with increasing temperature. At and above 25°C, the parasite could reach its infective stage in less than 7 days when vectors could transmit after only two gonotrophic cycles. After incorporating exponential functions for vector development into a novel blackfly population model, it was predicted that fly numbers in Liberia and Ghana would peak at air temperatures of 29°C and 34°C, about 3°C and 7°C above current monthly averages, respectively; parous rates of forest flies (Liberia) would peak at 29°C and of savannah flies (Ghana) at 30°C. Small temperature increases (less than 2°C) might lead to changes in geographical distributions of different vector taxa. When the new model was linked to an existing framework for the population dynamics of onchocerciasis in humans and vectors, transmission rates and worm loads were projected to increase with temperature to at least 33°C. By contrast, analyses of field data on forest flies in Liberia and savannah flies in Ghana, in relation to regional climate change predictions, suggested, on the basis of simple regressions, that 13–41% decreases in fly numbers would be expected between the present and before 2040. Further research is needed to reconcile these conflicting conclusions. 相似文献
Radiation therapy causes both muscle and nerve tissue damage. However, the evolution and mechanisms of these damages are not fully understood. Information on the state of active muscle fibres and motoneurons can be obtained by measuring sEMG signals and calculating the conduction velocity (CV) and firing rate of individual motor units, respectively. The aim of this pilot study was to evaluate if the multi-channel surface EMG (sEMG) technique could be applied to the sternocleidomastoideus muscle (SCM) of radiotherapy patients, and to assess if the CV and firing rate are altered as a consequence of the radiation.
Surface EMG signals were recorded from the radiated and healthy SCM muscles of 10 subjects, while subjects performed isometric rotation of the head. CV and firing rate were calculated using two recently proposed methods based on spatio-temporal processing of the sEMG signals. The multi-channel sEMG technique was successfully applied to the SCM muscle and CV and firing rates were obtained. The measurements were fast and simple and comfortable for the patients. Sufficient data quality was obtained from both sides of seven and four subjects for the CV and firing rate analysis, respectively. No differences in CV or firing rate were found between the radiated and non-radiated sides (p = 0.13 and p = 0.20, respectively). Firing rate and CV were also obtained from a myokymic discharge pattern. It was found that the CV decreased significantly (p = 0.01) during the bursts. 相似文献
According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary‐type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non‐electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre‐existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation. 相似文献