Main Memory Implementations for Binary Grouping

An increasing number of applications depend on efficient storage and analysis features for XML data. Hence, query optimization and efficient evaluation techniques for the emerging XQuery standard become more and more important. Many XQuery queries require nested expressions. Unnesting them often introduces binary grouping. We introduce several algorithms implementing binary grouping and analyze their time and space complexity. Experiments demonstrate their performance

The effect of DDD on single ranvier nodes of Xenopus laevis

Membrane potentials of single Ranvier nodes of myelinated nerve fibres were measured. DDD suppressed the rising phase of the action potential, probably by a reduction of the inward sodium current. This effect is in sharp contrast to that of DDT, which does not affect the rising phase but slows down the falling phase of the action potential by prolonging the inward sodium current

The effect of DDT and dieldrin on myelinated nerve fibres

The effects of the chlorinated hydrocarbon insecticides, DDT and dieldrin, on myelinated nerve fibres of the clawed toad, Xenopus laevis, were studied by recording compound action nerve fibres, and membrane potentials of single nodes of Ranvier. The effect of DDT (5 × 10−4 M) was found to be exclusively on the falling phase of the action potential; either it slowed down the whole falling phase or induced a large negative afterpotential. DDT did not affect threshold voltage, rate of rise and amplitude of the action potential, nor the testing potential. Dieldrin, even in high concentrations (10−3 M), had no appreciable effect on myelinated nerve fibres. DDT caused repetitive firing in sensory fibres only. The number of repetitive action potentials increased gradually with increasing amplitude of the negative afterpotential, while the interval between the action potentials decreased. These results indicate that the DDT-induced negative afterpotential is directly responsible for the repetitive activity. The possible mechanisms by which the negative afterpotential could induce a repetitive response were further investigated. It is suggested that the rate of recovery from sodium inactivation plays a major role in this process

Neurotoxicological effects and the mode of action of pyrethroid insecticides

Neuroexcitatory symptoms of acute poisoning of vertebrates by pyrethroids are related to the ability of these insecticides to modify electrical activity in various parts of the nervous system. Repetitive nerve activity, particularly in the sensory nervous system, membrane depolarization, and enhanced neurotransmitter release, eventually followed by block of excitation, result from a prolongation of the sodium current during membrane excitation. This effect is caused by a stereoselective and structure-related interaction with voltage-dependent sodium channels, the primary target site of the pyrethroids. Near-lethal doses of pyrethroids cause sparse axonal damage that is reversed in surviving animals. After prolonged exposure to lower doses of pyrethroids axonal damage is not observed. Occupational exposure to pyrethroids frequently leads to paresthesia and respiratory irritation, which are probably due to repetitive firing of sensory nerve endings. Massive exposure may lead to severe human poisoning symptoms, which are generally treated well by symptomatic and supportive measures

Effects of met-enkephalin on slow synaptic inhibition in frog sympathetic ganglion

The influence of met-enkephalin on slow inhibitory postsynaptic potentials (IPSP) in the frog sympathetic ganglion was studied with the help of a sucrose gap technique. Application of 1 μM met-enkephalin caused a hyperpolarization of the ganglionic neurones, probably via a postsynaptic mechanism. In addition, met-enkephalin depressed the amplitude of the slow IPSP by 40%. Both effects were completely antagonized by 1 μM naloxone. -ala-met-enkephalinamide (1 μM) and morphine (5 μM) also produced a hyperpolarization together with a depression of the slow IPSP. By varying the external potassium concentration it was shown that the depression of the slow IPSP was not due to the hyperpolarization of the ganglionic neurones by met-enkephalin. Further experimentation revealed that the sensitivity of the ganglion to exogenous dopamine, the putative transmitter for the slow IPSP, was only slightly suppressed by met-enkephalin. It is concluded that the depression of the slow IPSP by met-enkephalin is presynaptic in origin and may be the result of a decrease in the amount of transmitter released from the nerve terminals. The possibility that the reduction in transmitter release is brought about by a hyperpolarization of the nerve terminals is discussed. A hyperpolarization of the preganglionic nerve terminals was actually observed after application of 5 μM morphine

Negative temperature coefficient of the action of DDT in a sense organ

DDT induced repetitive spontaneuos activity inthe afferent nerve fibers of the lateral-line organ of the clawed toad, Xenopus laevis. The action of DDT increased markedly with lowered temperature. This temperature-effect was easily reversible. The results demonstrate that DDT has a definite negative temperature coefficient of activity in this sense organ