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)

Tendon jerk (TJR) and Hoffmann (H) reflexes of the soleus muscle were studied in two men during a 26-day simulated oxygenhelium dive to a maximum pressure of 43 bars. The amplitude of the TJR response was observed to increase markedly after compression and also at the end of decompression. This biphasic pattern of enhanced reflectivity was reproduced by synchronised but much smaller variations in H reflex response. The positive facilitatory effects of applying Jenkdrassik's manoeuvre were reduced and the negative effects increased during hyperbaric exposure. Excitability cycles (twin-pulses methods) revealed modifications in one subject similar to those observed in clinical hyperreflexia, namely a shortening of Phase III and an enhancement of Phase IV. The other subject exhibited a notable depression of Phase IV. Abnormal EMG recordings are described including randomly-triggered slow wave potentials with no mechanical effects, and fixed, long latency late responses of a reflex nature with a definite mechanical effect. The contention that alterations in vestibulo-spinal relations may result in the release from tonic presynaptic inhibitory control of myotatic reflex arc excitability is discussed as a partial explanation for these and related findings.
 ...
PMID:Hyperbaric hyperreflexia: tendon-jerk and Hoffmann reflexes in man at 43 bars. 9 97

1. The excitability of relay cells of the lateral geniculate nucleus during a saccadic eye movement was studied in alert cats. Excitability was assessed by the firing probability of the cells in response to electrical stimulation of the optic chiasm. Modifications in the excitability were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in electro-oculogram and altering delays in the stimulus pulse. 2. The cells were classified into S and T cells, based on their response properties and the latencies to chiasmatic stimulation. With a saccade in a stationary patterned field, T cells showed a burst discharge, while the discharges of S cells were completely suppressed. 3. The excitability was depressed in both S and T cells for 150-200 msec after a saccade, when the eye movement occurred in light. However, the depression did not occur in complete darkness. 4. The depression occurred also in the absence of eye movement, when the patterned visual field was moved in a saccadic fashion. 5. The depression in S cells occurred during an inhibitory period. Since S cells do not receive signals on image movement directly from the retina, the depression was due to a recurrent inhibition by signals transferred through the T ganglion-relay cell channel. 6. The depression in T cells occurred concomitantly with the burst discharge. Since the recurrent inhibition was operating less effectively during the period, the depression may be due to a phasic occlusion of the test impulse by coincident high-rate firings in the same cell. 7. The impairment in transmission of visual information through the lateral geniculate nucleus during the period following eye movements has been discussed in connexion with a neurophysiological basis for saccadic suppression.
 ...
PMID:Depression in the excitability of relay cells of lateral geniculate nucleus following saccadic eye movements in the cat. 16 63

1. Excitability changes in primary afferents and inhibitory interactions in evoked spinal cord activity were investigated in unanesthetized stingrays (Dasyatis subina) with high cervical spinal transections. 2. Primary afferent excitability increases following a conditioning stimulus to an adjacent segmental nerve were demonstrated with the Wall (31) technique. 3. Stimulation of A-alpha,beta and A-delta afferent fibers produced excitability increases in both A-alpha,beta and delta-fibers of the adjacent segment. 4. The excitability increase had a latency of about 10 ms, it peaked around 25 ms, and the change lasted more than 100 ms. 5. The central afferent volley in A-alpha,beta fibers and the N1- and late negative waves due to postsynaptic activity of dorsal horn interneurons were reduced by conditioning volleys in adjacent afferent nerves. The time course of the inhibition paralleled that of the excitability increases in afferent terminal arborizations, suggesting that the depression of postsynaptic activity is, at least in part, due to presynaptic inhibition. 6. Reduction of evoked discharges and excitatory postsynaptic potentials was observed in recordings from interneurons with a time course similar to that of the primary afferent depolarization (PAD). 7. Conditioning volleys in afferents of adjacent peripheral nerves produced facilitation or inhibition of segmental reflexes.
 ...
PMID:Primary afferent depolarization and inhibory interactions in spinal cord of the stingray, Dasyatis sabina. 62 39

The effects of hydrostatic pressure on cardiac conduction and excitability were studied in 39 rabbit right atrial preparations. Increases in pressure significantly increased atrial conduction time, i.e., 41% at 150 ATA. Excitability, determined from strength-duration (S-D) curves, was depressed by pressure. The slope constant of the S-D curve increased 64% at 150 ATA. Rheobase and the X-asymptote were not affected significantly. The depression of excitability partially accounted for the slowed conduction. Frequency stress and pressure had an additive effect to produce even greater decreases in excitability and increases in conduction time. Atrial refractoriness to premature stimuli also increased as a function of pressure. Nitrous oxide (2.5 ATA) partially reversed the effects of 150 ATA of pressure on conduction time and excitability. The results suggest that pressure acts by altering basic functional components of the myocardial cell membrane. Some of these changes, particularly when combined with frequency stress, i.e., rapid heart rate, may pose a serious threat to humans exposed to hyperbaric environments.
 ...
PMID:Effects of hydrostatic pressure on conduction and excitability in rabbit atria. 67 27

1. The aim of this study was to investigate post-synaptic reciprocal Ia inhibition during the stretch reflex; particularly the extent to which an increased Ia excitation of the Ia inhibitory interneurones will be counteracted by recurrent inhibition from motor axon collaterals. For this purpose we investigated depression of monosynaptic test reflexes antagonist flexors (reciprocal inhibition) during static stretch of quadriceps or triceps surae in unanaesthetized decerebrate cats. 3. With increasing stretch of the extensor muscle there was first a linear augmentation of reciprocal inhibition, but along with the stretch reflex in the extensor a plateau appeared in the inhibition of the flexors, although the extensor stretch reflex (judged by the e.m.g.) increased with further stretching. Within the range of stretching of triceps surae which gave increased stretch reflexes the plateau in the reciprocal inhibition was usually maintained, while during stretching of quadriceps a second phase of augmenting reciprocal inhibition often appeared. Stretch beyond the level which increased the stretch reflex activity gave augmenting reciprocal inhibition both in case of quadriceps and triceps surae. 3. Excitability measurements from central terminals of Ia afferents revealed that the increasing reciprocal inhibition during increasing stretch reflex activity in quadriceps was associated with a primary afferent depolarization in knee flexor Ia afferents; there was no corresponding effect in ankle flexor Ia afferents during stretch reflexes in triceps surae. 4. The primary afferent depolarization evoked in knee flexor Ia afferents by electrical nerve stimulation was then compared with the presynaptic inhibition of knee flexor monosynaptic test reflexes produced by the same stimuli. The results suggest that the second phase of increasing reciprocal inhibition in knee flexors is due to presynaptic inhibition and accordingly that the depth of post-synaptic reciprocal inhibition remains constant at different degrees of stretch reflex activity in both knee and ankle extensors. 5. It is postulated that during increasing stretch reflex activity the increment in Ia excitation and recurrent inhibitio; on to the Ia inhibitory interneurones almost exactly balance each other. It is suggested that recurrent inhibition of Ia inhibitory interneurones may serve as a segmental autoregulatory mechanism to keep 'alpha-gamma-linked reciprocal inhibition' at a constant depth during different levels of agonist activity.
 ...
PMID:Reciprocal inhibition during the tonic stretch reflex in the decerebrate cat. 73 48

Direct cortical responses (DCRs) to paired stimuli were studied in chronic experiments in dogs during elaboration of classical and instrumental defensive conditioned reflexes. The DCRs were recorded with 20 to 250 ms intervals between stimuli. Paired and single electrical stimulations of the middle suprasylvian gyrus given with a frequency of one per second were used as conditioned stimuli and were reinforced in a similar way. During electrical cutaneous stimulation of the dog's paw and to an even greater extent during isolated action of the conditioned stimulus the initial negativity of the testing DCR became shorter and the degree of its depression diminished. In the case of a following period of facilitation, its degree became greater. It was higher at a distance of 4 to 5 mm from the point of stimulation than at a distance of 2 to 3 mm. During isolated action of the conditioned stimulus, the degree of facilitation was higher than at the period of the possible action of the unconditioned stimulus. The greatest shorterning of the DCR excitability cycle was observed immediately before and during the conditioned lifting of the dog's paw. Excitability cycles of DCR, and possibly of other evoked potentials as well, are a more sensitive indicator of the function state of the cerebral cortex than responses to single stimuli. For this reason it appears promising to use them in studying conditioned reflexes.
 ...
PMID:[Excitability cycles of direct cortical responses during elaboration of conditioned defense reflexes in dogs]. 121 Jun 76

The propagation mechanism of spreading depression (SD), which has been implicated in the pathophysiology of the neurological auras of migraine, remains enigmatic but is widely believed to depend primarily upon the behaviour of assemblies of neurons. It is proposed here, based upon a program of theoretical research, that the most essential constituent of SD is a slowly propagating, regenerative event in the neuroglial compartment. By altering the neuronal microenvironment, this glial spike helps trigger and coordinate the neuronal depolarization of SD; the glial spike is in turn facilitated by neuronally released agents acting at the neuroglial plasma membrane. The conduction velocity-determining propagation mechanism of SD is further proposed to be a wave of intracellular Ca(2+)-induced Ca2+ release (cytocal wave) that travels through the glial compartment of nervous tissue. Some implications for the improved understanding and clinical management of migraine are suggested. Excitability of glial cells of vertebrates has until now been demonstrated only in vitro, and its physiological significance has remained unknown. This work identifies a macroscopic reaction of neuronal tissue, known from the in vivo vertebrate brain for over 45 years, as a manifestation of neuroglial excitability.
 ...
PMID:The glial spike theory. I. On an active role of neuroglia in spreading depression and migraine. 136 95

Excitability of presynaptic terminals of low-threshold primary afferent fibers in the inferior alveolar nerve was tested in the trigeminal spinal nucleus of the ketamine-anesthetized, paralyzed guinea pig, by Wall's method. Fictive mastication was induced by repetitive stimulation of the cortical masticatory area, and was monitored by rhythmical burst activity in the jaw-opening anterior digastric motoneuron pool. The excitability was rhythmically modulated in a phase-linked manner during the masticatory cycle: it was decreased coincidentally with the digastric burst activity (jaw-opening phase) and increased during the middle and late periods of the interburst phase (jaw-closing phase) of the masticatory cycle. The results imply that presynaptic modulation of synaptic transmission of peripheral inputs from primary afferents to interneurons in the jaw-opening reflex pathway may contribute to the rhythmical modulation of the jaw-opening reflex evoked by innocuous stimulation of the intraoral structures during mastication; presynaptic inhibition contributing to the depression of the jaw-opening reflex during the jaw-closing phase and presynaptic facilitation to its enhancement during the jaw-opening phase.
 ...
PMID:Phase-linked modulation of excitability of presynaptic terminals of low-threshold afferent fibers in the inferior alveolar nerve during cortically induced fictive mastication in the guinea pig. 337 Apr 76

1. The excitability of the geniculo-striate pathway during a saccadic eye movement was studied in alert cats with chronically implanted electrodes. Excitability was assessed by the amplitude of post-synaptic components of field responses in both lateral geniculate nucleus and visual cortex to electrical stimulation of the optic chiasm. Modifications in amplitude were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in the electrooculograms and altering delays in the stimulus pulse.2. The post-synaptic component of the geniculate response was markedly depressed for about 150 msec, reaching a trough at approximately 100 msec after the initiation of an eye movement. This effect was dependent on the visual environment and was not observed in complete darkness. A similar depression occurred when the visual field was abruptly moved by retinal impulses generated by a quick displacement of the image of the visual world associated with an eye movement. The depression reflected a reduction of cellular discharge to the orthodromic volley and hence a suppression of the transmission of visual information through the lateral geniculate nucleus. This may be a mechanism for saccadic suppression.3. The post-synaptic components of the cortical response were enhanced for about 200 msec, reaching a peak at approximately 150 msec after the initiation of an eye movement. Although this facilitation occurred also in complete darkness, it did not occur when the visual field was abruptly shifted while the eyes were stationary. The fact that it occurred with eye movements and exclusively in the post-synaptic components suggests that it was caused by signals from a system closely related to eye movements. This may be a manifestation of the corollary mechanism.
 ...
PMID:Influence of eye movements on geniculo-striate excitability in the cat. 477 10

Digitalis intoxication is characterized by the appearance of most of the types of severe arrhythmias described and also by important disturbances of cardiac excitability and impulse propagation. Most of the antiarrhythmic agents that are used in the treatment of these conditions also depress excitability and impulse propagation. These characteristics are frequently responsible of severe complications. The purpose of this paper is to determine the type of interactions that exist between digitalis and some antiarrhythmic agents, and compare them with the effects of magnesium. The experiments were done in several groups, of dogs anesthetized with pentobarbital and with the chest open. Excitability, conduction time and functional refractory period were determined using the classical methods. The protocol used consisted in the comparison of the actions of toxic doses of digitalis on excitability and conduction times of the atrial and ventricular tissues, under control conditions and in the presence of therapeutic doses of procainamide, lidocaine and magnesium. The results showed that procainamide worsened the depression of excitability and conduction produced by digitalis intoxication, while lidocaine does not add to the digitalis effects and in some cases it produces a partial improvement of these parameters. Magnesium completely reverts the effects on excitability and conduction. These results provide us with rational pharmacological bases for the treatment of digitalis intoxication and suggest that magnesium could be very useful in the management of patients with severe digitalis intoxication.
 ...
PMID:[Effects of several anti-arrhythmia agents on excitability and conduction depressed by digitalis agents]. 624 58


1 2 3 Next >>