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141.
142.
Sedimentation in the sea occurs through natural processes, such as wave and tidal action, which can be exacerbated during storms and floods. Changes in terrestrial land use, marine aggregate extraction, dredging, drilling and mining are known to result in substantial sediment deposition. Research suggests that deposition will also occur due to the modern development of marine renewable energy. The response to individual burial under three depths of sediment, three sediment fractions and five burial durations was investigated in two mussel species, Modiolus modiolus and Mytilus edulis in specialist mesocosms. Both mussel species showed substantial mortality, which increased with duration of burial and burial by finer sediment fractions. M. modiolus was better able to survive short periods of burial than M. edulis, but at longer durations mortality was more pronounced. No mortality was observed in M. modiolus in burial durations of eight days or less but by 16 days of burial, over 50% cumulative mortality occurred. Under variable temperature regimes, M. edulis mortality increased from 20% at 8°C to over 60% at 14.5 and 20°C. Only M. edulis was able to emerge from burial, facilitated by increased byssus production, laid mostly on vertical surfaces but also on sediment particles. Emergence was higher from coarse sediment and shallow burials. Byssus production in M. edulis was not related to the condition index of the mussels. Results suggest that even marginal burial would result in mortality and be more pronounced in warm summer periods. Our results suggest that in the event of burial, adult M. modiolus would not be able to emerge from burial unless local hydrodynamics assist, whereas a small proportion of M. edulis may regain contact with the sediment water interface. The physiological stress resulting in mortality, contribution of local hydrodynamics to survival and other ecological pressures such as mussels existing in aggregations, are discussed. 相似文献
143.
Distributions of time to fixation of neutral genes 总被引:1,自引:0,他引:1
Exact distributions of times to fixation are derived for neutral alleles in a discrete generation, constant census model that accommodates specified variations in gametic contributions per parent. This enables an evaluation of the performance of the effective number concept, and of diffusion equation approximations, used to characterize the time scale of drift events. Following simultaneous comparisons of modes, medians, means and standard deviations of exact and approximate distributions of times to fixation, it is concluded that diffusion equation methods, in conjunction with the appropriate effective number, do produce accurate results. 相似文献
144.
Connections between descending visual interneurons and metathoracic motoneurons in the locust 总被引:1,自引:1,他引:0
M. Burrows Dr. C. H. Fraser Rowell 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1973,85(3):221-234
Summary Connections between the four DMD neurons and metathoracic motoneurons in the locustSchistocerca were examined by recording extracellularly from the interneurons in the pro-mesothoracic connectives and intracellularly
from seventeen motoneurons. A DIMD or DCMD spike causes an EPSP in the fast extensor tibiae motoneuron, which can be modified
by changing the membrane potential. The EPSP always follows spikes at frequencies up to 200 Hz and with a latency of 0.9 ms,
suggesting that the connections are monosynaptic and chemically mediated. EPSPs from the DIMD or DCMD arrive at the same time,
their axons having the same conduction velocity, and appear simultaneously in the fast extensor tibiae motoneurons on both
sides of the ganglion. There is spatial and temporal summation between the inputs but on no occasion did the motoneurons spike.
Three inhibitory neurons are depolarized by DMD inputs and may on occasion spike, but it is not known whether these connections
are direct. Similarly the slow excitatory motoneuron to the anterior coxal adductor muscle is hyperpolarized by DMD input.
Other leg, flight or ventilatory motoneurons examined received no inputs from the DMD neurons. The connections shown are consistent
with the hypothesis that the DMD neurons are in some way involved with initiation of a jump, but to achieve this must act
synergistically with other inputs.
This work was supported in part by USPHS grant No. NS 09404-03 to C.H.F.R. Dr. Rowell wishes to thank Dr. J. Phillipson for
the use of facilities in the Oxford Department of Zoology during sabbatical leave. 相似文献
145.
Dr. Malcolm Burrows 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1973,83(2):165-178
Summary Two metathoracic flight motoneurons of the locustChortoicetes terminifera have been stained by injection of cobalt. The motoneurons innervate the tergosternal (hindwing elevator) muscle 113 and the first basalar (hindwing depressor) muscle 127. The somata of both are on the ventral surface of the ganglion (Fig. 1), and their axons in the ipsilateral nerve 3A. The main neuropilar segment and large medial dendrites of each follow parallel courses through the ganglion even though the two motoneurons subserve antagonistic functions (Fig. 3). Differences in the smaller dendrites add characteristic detail to each. The dendritic trees are complex and cover virtually all of the ipsilateral dorsal neuropile. No branches cross the mid-line so that electrotonic coupling is eliminated as a possible means of co-ordination of motoneurons of the two sides (Fig. 4). The general shape of the motoneurons is similar in different animals but there is variation in the number and extent of the small dendrites (Fig. 6).Beit Memorial Research Fellow. 相似文献
146.
Sequence of a cDNA for mouse thymidylate synthase reveals striking similarity with the prokaryotic enzyme 总被引:11,自引:0,他引:11
Perryman SM; Rossana C; Deng TL; Vanin EF; Johnson LF 《Molecular biology and evolution》1986,3(4):313-321
We report the nucleotide sequence of a cloned cDNA, pMTS-3, that contains a
1-kb insert corresponding to mouse thymidylate synthase (E.C. 2.1.1.45).
The open reading frame of 921 nucleotides from the first AUG to the
termination codon specifies a protein with a molecular mass of 34,962
daltons. The predicted amino acid sequence is 90% identical with that of
the human enzyme. The mouse sequence also has an extremely high degree of
similarity (as much as 55% identity) with prokaryotic thymidylate synthase
sequences, indicating that thymidylate synthase is among the most highly
conserved proteins studied to date. The similarity is especially pronounced
(as much as 80% identity) in the 44-amino-acid region encompassing the
binding site for deoxyuridylic acid. The cDNA sequence also suggests that
mouse thymidylate synthase mRNA lacks a 3' untranslated region, since the
termination codon, UAA, is followed immediately by a poly(A) segment.
相似文献
147.
Regulation of IgM and IgD expression in human B-lineage cells 总被引:2,自引:0,他引:2
W G Kerr L M Hendershot P D Burrows 《Journal of immunology (Baltimore, Md. : 1950)》1991,146(10):3314-3321
148.
M. Burrows H. J. Pflüger 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1988,163(4):425-440
1. | Two campaniform sensilla (CS) on the proximal tibia of a hindleg monitor strains set up when a locust prepares to kick, or when a resistance is met during locomotion. The connections made by these afferents with interneurones and leg motor neurones have been investigated and correlated with their role in locomotion. |
2. | When flexor and extensor tibiae muscles cocontract before a kick afferents from both campaniform sensilla spike at frequencies up to 650 Hz. They do not spike when the tibia is extended actively or passively unless it encounters a resistance. The fast extensor tibiae motor neurone (FETi) then produces a sequence of spikes in a thrusting response with feedback from the CS afferents maintaining the excitation. Destroying the two campaniform sensilla abolishes the re-excitation of FETi. |
3. | Mechanical stimulation of a single sensillum excites extensor and flexor tibiae motor neurones. The single afferent from either CS evokes EPSPs in the fast extensor motor neurone and in certain fast flexor tibiae motor neurones which follow each sensory spike with a central latency of 1.6 ms that suggests direct connections. The input from one receptor is powerful enough to evoke spikes in FETi. The slow extensor motor neurone does not receive a direct input, although it is excited and slow flexor tibiae motor neurones are unaffected. |
4. | Some nonspiking interneurones receive direct connections from both afferents in parallel with the motor neurones. One of these interneurones excites the slow and fast extensor tibiae motor neurones probably by disinhibition. Hyperpolarization of this interneurone abolishes the excitatory effect of the CS on the slow extensor motor neurone and reduces the excitation of the fast. The disinhibitory pathway may involve a second nonspiking interneurone with direct inhibitory connections to both extensor motor neurones. Other nonspiking interneurones distribute the effects of the CS afferents to motor neurones of other joints. |
5. | The branches of the afferents from the campaniform sensilla and those of the motor neurones and interneurones in which they evoke EPSPs project to the same regions of neuropil in the metathoracic ganglion. |
6. | The pathways described will ensure that more force is generated by the extensor muscle when the tibia is extended against a resistance. The excitatory feedback to the extensor and flexor motor neurones will also contribute to their co-contraction when generating the force necessary for a kick. |
149.
M. Burrows 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,165(5):687-695
Summary Changing the temperature from 10–40 °C modifies the transmission at an established monosynaptic connection between the fast extensor tibiae (FETi) and flexor tibiae motor neurons in the metathoracic ganglion of the locustSchistocerca gregaria (Forskål). Striking changes occur to the shape of the spikes, to membrane resistance, to the synaptic delay, and to the evoked synaptic potentials.In the presynaptic FETi motor neuron, raising the temperature reduces the amplitude of an antidromic spike recorded in the soma by a factor of 10 (40 mV to 4 mV), reduces the time taken to reach peak amplitude by 5 (3.5 to 0.7 ms) and decreases the duration at half maximum amplitude by 0.5. The conduction velocity of the spike in the axon is increased by 50% from 10 °C to 40 °C. Orthodromic spikes are affected by temperature in a similar way to the antidromic spikes.The membrane resistance of both pre- and postsynaptic motor neurons falls as the temperature is raised. The membrane resistance of FETi falls by a factor of 4 (about 4 M at 10 °C to 1 M at 40 °C). A contributory component to this fall could be the increase in the frequency of synaptic potentials generated as a result of inputs from other neurons. No temperature dependence could be demonstrated on the voltage threshold relative to resting potential for evoking orthodromic spikes, but because the resistance changes, the current needed to achieve this voltage must be increased at higher temperatures.The latency measured from the peak of the spike in the soma of FETi to the start of the EPSP in the soma of a flexor motor neuron decreases by a factor of 20 (10 ms at 10 °C to 0.5 ms at 40 °C).In a postsynaptic flexor tibiae motor neuron, the amplitude of the evoked synaptic potential increases by a factor of 3.4 (5 mV to 17 mV), its duration at half maximum amplitude decreases by 3 (7 ms at 12 °C to 2.3 ms at 32 °C) and its rate of rise increases by 3. An increased likelihood that spikes will occur in the flexor contributes to the enhanced amplitude of the compound EPSP at temperatures above 20 °C.Abbreviation
FETi
fast extensor tibiae motor neuron 相似文献
150.
Analysis of the axial filaments of Treponema hyodysenteriae by SDS-PAGE and immunoblotting 总被引:11,自引:0,他引:11
K A Kent R Sellwood R M Lemcke M R Burrows R J Lysons 《Journal of general microbiology》1989,135(6):1625-1632
Purified axial filaments from eight serotypes of Treponema hyodysenteriae and two non-pathogenic intestinal spirochaetes were characterized by SDS-PAGE and Western blotting. Axial filaments of all ten strains had similar SDS-PAGE profiles; five major axial filament polypeptides were identified, with molecular masses of 43.8, 38, 34.8, 32.8 and 29.4 kDa. Hyperimmune gnotobiotic pig serum raised against purified axial filaments of strain P18A (serotype 4) cross-reacted with all other serotypes and with the non-pathogens, and convalescent serum taken from a pig with persistent swine dysentery also showed a strong response to the axial filament polypeptides. Hyperimmune gnotobiotic pig serum raised against axial filaments failed to agglutinate viable organisms and did not inhibit growth in vitro. Hence, the axial filaments of T. hyodysenteriae have been identified as major immunodominant antigens, although the role that antibodies to these antigens play in protection has yet to be established. 相似文献