Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The experiments on an isolated frog neuromuscular preparation gave evidence that an exposure to stable magnetic fields of 1000-4000 Oe did not influence the time parameters, amplitude and pattern of the action potentials of the gastrocnemius muscle induced by ischiatic nerve stimulation with single impulses. Similar results were obtained from an analysis of electric responses of the upper cervical sympathetic mode to the stimulation of preganglionar fibers in in situ experiments on urethane anesthesized rabbits subjected to a total exposure of a stable magnetic field (500-3000 Oe). In addition, an exposure to a stable magnetic field of 4000 Oe brought about a decrease of the level of depression of the action potential of muscles after conditioning tetanus.
 ...
PMID:[Bioelectrical activity of the neuromuscular and sympathetic systems exposed to a constant magnetic field]. 50 28

1. Isometric twitch responses of single motor units in snake costocutaneous muscle have been recorded before and after conditioning tetanic stimulation. 2. Most units showed post-tetanic potentiation of twitch tension, associated with increased maximal rate of rise of twitch tension, and in some cases also associated with prolongation of twitch contraction time. A few units showed a short phase of actual depression of the post-tetanic twich responses, followed by potentiation. 3. The time course and magnitude of post-tetanic changes of twitch tension and maximal rate of rise of tension could be described by the sum of three processes which are assumed to be maximal close to the end of the conditioning tetanus: (i) a rapidly declining potentiation (called here early potentiation, which lasted less than 2 sec) which may have a purely mechanical origin; (ii) a much slower-declining potentiation (called here prolonged potentiation, which lasted up to 15 min); and (iii) a process which lasted up to 60 sec during which twitch potentiation was reduced. The latter process (called here depressed potentiation) was usually apparent as a marked trough in the plots of twitch amplitude versus time after the conditioning tetanus, and occassionally was evident as an actual transient depression of twitch amplitude after the tetanus compared with that before. 4. The effects of the prolonged potentiation and the depressed potentiation on the maximal effect of each process close to the end of the tetanus were extracted by fitting single exponential equations to different portions of the data, using a computer program. 5. Twitch potentiation associated with increased maximal rate of rise of tension seemed to be a separate phenomenon to that associated with prolongation of contraction time, seen when conditioning tetani of higher frequency and numbers of stimuli were employed. The depressed potentiation of twitch tension tended to be partly masked in cases where contraction time was prolonged, but this did not affect the depressed potentiation of maximal rate of rise of tension. 6. The post-tetanic potentiation shown by a unit was related to the contraction time of the unit, in addition to the well known relationship to the initial twitch-tetanus ratio. The depressed potentiation may correlat more closely with the initial twitch-tetanus ratio than with the unit contraction time. 7. The magnitude of maximal depressed potentiation shown by a unit may be directly correlated to that of maximal prolonged potentiation. 8. The time constant of decay for prolonged potentiation of twitch tension tended to be related inversely to unit contraction time and directly to unit size and the maximal value of prolonged potentiation oftwitch tension. The time constant of decay for prolonged potentiation of maximal rate of rise of tension tended to be related to unit size and initial twitch-tetanus ratio, and the time constant of decay for depressed potentiation of rate of rise of tension tended to be related to unit size. 9...
 ...
PMID:Post-tetanic potentiation of twitch motor units in snake costocutaneous muscle. 65 Apr 83

The effects of carbamazepine (CBZ) on post-tetanic potentiation (PTP) were evaluated using an in vivo cat coleus neuromuscular preparation. CBZ was administered i.p. and plasma CBZ concentrations were determined by gas liquid chromatography during PTP tests over a 90-min period. CBZ produced a concentration-dependent depression of PTP. Significant depression was first noted at about 12 microgram/ml and 50% depression occurred at 20 microgram/ml; this depression was time-dependent. No effect was observed on unpotentiated, supramaximal twitches. CBZ also modified the pattern of tetanic contraction; the most predominant change was an enhancement of the initial falling phase of the tetanus. Antidromically propagated post-tetanic repetitive afterdischarges (PTR) were monitored in single isolated vertral root filaments innerving the soleus muscle. CBZ inhibited PTR without affecting conduction velocity or the capacity of the fiber to follow the high frequency (tetanic) stimulation. These results are similar to those previously reported for phenytoin. CBZ inhibits PTP in this preparation by inhibition of PTR through a presynaptic effect; possible mechanisms are discussed. These observations may contribute to the understanding of the actions of this drug in epilepsy and neuromyotonia.
 ...
PMID:Carbamazepine suppression of post-tetanic potentiation at the neuromuscular junction. 73 33

2H2O (99.8%) Ringer's solution greatly reduces the twitch and tetanus of frog sartorius muscle and, as specially shown here, slows the onset features of the mechanical output of the twitch by: (a) increasing the time (LR) from stimulus to start of latency relaxation; (b) slowing the development of the latency relaxation, and (c) greatly decreasing the rate of onset of tension development. These changes reflect effects of 2H2O on excitation-contraction coupling and they represent the critical direct effects of 2H2O on muscle since it does not depress either the action potential or the intrinsic myofibrillar contractility. The increase in LR is attributed to slowed inward electrical propagation in the T-tubule. But the critical effect of 2H2O on frog muscle is to greatly depress mobilization of activator Ca2+. The depression of the Ca2+ mobilization and of its effects on the activation of contraction evidently result from (a) a lowered rate of release of Ca2+ from the sar coplasmic reticulum, as indicated by the slowed development of the latency relaxation, (b) a decreased amount of Ca2+ released in a twitch, and (c) a reduced speed of diffusion of the Ca2+ to the contractile filaments. The depressed mobilization of Ca2+ is apparently the essential cause of 2H2O's general depression of twitch and tetanus output.
 ...
PMID:Deuterium oxide effects on excitation-contraction coupling of skeletal muscle. 96 48

Brain-stem reflexes have been studied in four patients with generalized tetanus. Inhibitory cutaneous reflexes were abolished or severely depressed. The same held true, to a lesser degree, for excitatory cutaneous reflexes with long polysynaptic pathways. Proprioceptive reflexes behaved variably. The observations are discussed in regard to the possible sources of enhanced motoneuronal activity in tetanus. It is concluded that, besides depression of inhibitory synapses on motoneurons, interneuronal damage may contribute to the tetanus symptomatology.
 ...
PMID:Medullary actions of tetanus toxin. An electrophysiological study in man. 98 57

A report is made of five tetanus patients who were treated with large repetitive doses of Diazepam and became comatose. The period of impaired consciousness varied from thirteen to twenty-one days. None had significant respiratory depression, and full recovery occurred in all. It is proposed that Diazepam-induced prolonged coma should be regarded as a side-effect rather than a toxic effect and should caution rather than contra-indicate further use of large doses of the drug in the management of tetanus.
 ...
PMID:Favourable prognosis of prolonged coma associated with large doses of diazepam in severe tetanus. 100 86

1. The effect of active shortening on the time course and magnitude of isometric tension development during a single twitch and during an incompletely fused tetanus was studied at 0-2-1-2 degres C in isolated semitendinosus muscle fibres of the frog. 2. Active shortening caused a depression of the contractile force without markedly affecting the total duration of the twitch. The depressant effect increased with increasing amounts of sarcomere shortening. Sarcomere shortenings of 0-05 mum and 0-3 mum reduced the twitch force by approximately 5 and 20 percent of the maximal tetanic tension, respectively. 3. A given sarcomere shortening induced the same absolute amount of depression of the contractile strength when the movement was carried out at different times during the initial 200-250 msec after the stimulus. 4. The influence of load and velocity of shortening during the movement phase was studied. Differences in load ranging between zero and 1/3 of the maximal tetanic tension (with concomitant changes in speed of shortening from Vmax to approximately 1/5 of Vmax) did not affect the degree of depression markedly. Underthe conditions studied, the extent of movement appeared to be the only significant determinant of the depressant effect. 5. The reduction in force induced by active shortening persisted for 800-900 msec during an incompletely fused tetanus. 6. It is suggested that the depressant effect is based on a structural change in the myofilament system that is produced as the A and I filaments slide along each other during muscle activity.
 ...
PMID:Mechanical deactivation induced by active shortening in isolated muscle fibres of the frog. 107 34

Tetanus toxin administered to frogs in doses which produced general tetanus depressed the reciprocal inhibition of spinal reflexes. This depression was not associated with the block of the processes which led to depolarization fo the central terminals of the primary afferent fibers.
 ...
PMID:[Electrotonic potentials of spinal cord dorsal roots in frogs with experimental tetanus]. 108 68

The neuromuscular effects of d-tubocurarine (dTc), pacuronium, and succinylcholien (SCh) were studied in 37 unpremedicated adult surgical patients anesthetized with 1.25 MAC enflurance in oxygen. The relaxant doses that produced 50 per cent depression of twitch height (ED50) were 1.57, 0.29, and 4.9 mg/m2 for dTc, pancuronium, and SCh, respectively. These doses are approximately 3.1, 1.7, and 1.0 times less than the amount of dTc, pancuronium, and SCh required to produce 50 per cent depression of twitch height during halothane anesthesia but are the same as ED50 values during isoflurane anesthesia. In eight additional unpremedicated patients anesthesia was maintained at 0.71 MAC enflurane in oxygen (five patients) or 1.67 MAC enflurane in oxygen (three patients). Twitch depression following dTc, 1.5 mg/m2, was related directly to alveolar enflurane concentration. Ability to sustain tetanus decreased progressively with increasing tetanic frequencies and decreased with increasing alveolar enflurane concentrations. The authors concluded that smaller doses of dTc and pancuronium are needed for adequate relaxation during enflurane anesthesia than during equi-MAC halothane anesthesia, and that higher alveolar enflurane concentrations reduce the dose of dTc necessary to produce a given amount of paralysis. Also, neuromuscular effects of enflurane in combination with dTc or pancuronium are not significantly different from those seen suring equi-MAC isoflurane anesthesia.
 ...
PMID:Neuromuscular effects of enflurane, alone and combined with d-Tubocurarine, pancuronium, and succinylcholine, in man. 111 66

Pre- and postjunctional effects of three ethers (enflurane, diethyle ether, and methoxyflurane) and three non-ethers (chloroform, halothane, and trichloroethylene) were studied in the rat phrenic nerve diaphragm preparation using standard microelectrode recording techniques. Depression of postjunctional function included depression of the amplitude of miniature endplate potentials, inhibition of suxamethonium induced depolarization of the muscle endplate, prolongation of duration of the endplate potential, and increase in threshold for generation of the muscle action potential. The last two effects were more marked for the ethers than for the non-ethers. Effects on pre-junctional function included a slight increase in fluctuation of the endplate potential (EPP) amplitude associated with the thers and chloroform, a faster rate of decline of EPP amplitude during a tetanus in presence of the ethers, and prolongation of the normal facilitatory period during paired stimulation in the presence of chloroform. Chloroform had no effect on the rate of decline of EPP amplitude during tetanic stimulation and the ethers had no effect on the facilitatory period during paired stimulation. These results indicate that volatile anaesthetic agents depress synaptic transmission by acting on multiple sites, and that the pattern of this depression is different for each drug or group of similar drugs.
 ...
PMID:Comparative site of action of various anaestetic agents at the mammalian myoneural junction. 113 70


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>