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At least 973 records · Page 54Linked to original sources
PubMed1993

Effects of inflammatory mediators on electrolyte transport across the porcine distal colon epithelium.

The epithelium from the porcine distal colon was mounted in Ussing chambers and bathed in plasma-like Ringer's solution. Histamine produced increases in current which were not affected by pretreatment with the neural conduction blocker tetrodotoxin. Both the H1-histamine antagonist pyrilamine and the cyclooxygenase inhibitor indomethacin produced dextral shifts in the histamine concentration-response curve. Replacement of Cl with gluconate or HCO3 with tris(hydroxymethyl)aminomethane(tris)-N-2- hydroxyethylpiperazine-N'-2-ethanesulfonic acid in the bathing solution inhibited the mucosal response to histamine by 74 and 23%, respectively. In addition, histamine increased the serosal-to-mucosal Na and Cl fluxes and inhibited the mucosal-to-serosal Na flux, resulting in a reduction of net Na and Cl absorption. Prostaglandin E2 also produced increases in short-circuit current which remained unaffected by tetrodotoxin. Replacement of either Cl or HCO3 inhibited these increases by 85%. Prostaglandin E2 inhibited the mucosal-to-serosal and net Cl fluxes. Leukotriene C4 produced oscillating increases in the short-circuit current which were completely blocked by tetrodotoxin. These increases in current were attributed to an increase in the serosal-to-mucosal Cl flux which resulted in a decrease in net Cl absorption. From these data it was concluded that: 1) histamine interacts with H1-receptors to increase Na and Cl secretion and inhibit Cl absorption; 2) prostaglandin E2 inhibits a HCO3-dependent Cl absorptive pathway, possibly involving Cl/HCO3 exchange and 3) leukotriene C4 acts on enteric nerves to stimulate Cl secretion.

Animals↗
PubMedDate not supplied

Spinal oscillators in man under normal and pathologic conditions.

1. Single-fibre action potentials (APs) were recorded from lower sacral nerve roots of brain-dead humans (HTs) and two paraplegics with thoracical spinal cord lesions. Impulse patterns of single oscillatory firing alpha 2 and alpha 3-motoneurons were identified and analysed. An alpha 2-motoneuron fired typically with 3 AP impulse trains every 160 msec. 2. In stable spinal oscillators of HTs the oscillation period was 70 msec plus 30 msec times the number of APs per impulse train; the respective values in paraplegics were 35 msec plus 40 msec times the number of APs per impulse train. These linear relationships indicate that spinal oscillators consist of at least 2 kinds of nerve cells. 3. Successive interspike intervals (IIs) of the impulse trains increased from about 3.5 msec to over 10 msec in paraplegics similarly as was the case in HTs. 4. The distributions of the first IIs (of impulse trains) and of the oscillation period of unstable continuously oscillatory firing alpha 2-motoneuron showed similar peaks. By relating the peak values of the first II and the oscillation period, a shortest II of 3.5 msec was obtained in a HT and a paraplegic, and a shortest oscillation period of 70 msec was measured in a HT and 40 msec in a paraplegic. The derivation of the shortest II of 3.5 msec from the oscillation itself is taken as an indication for alpha 2-motoneurons being included in the spinal oscillator function, since the shortest soma-dendritic spike intervals of motoneurons is expected to be 3.5 msec. 5. The spinal oscillator of a paraplegic showed more and higher activity changes than that in a HT as if spinal oscillators in paraplegics were insufficiently damped. 6. By interpreting the peaks in oscillation period distributions of unstable oscillators as being different oscillation loop pathways, it is speculated that the oscillators consist of the motoneuron, to which different interneuron pathways are connected. A contrasting of pathways with increasing excitation of the oscillator was observed. 7. The comparison of possible loop pathways of oscillation between paraplegics and HTs (closer to normal) indicates that the loss of descending tracts in paraplegics and the adaptation to it result in an increase of the oscillation pathways for alpha 2-oscillators from 1 to 3 in HTs to up to 6 in paraplegics. 8. Different measured and theoretically predictable spinal alpha 2-oscillators can cover altogether a frequency range between 5 and 10 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMedDate not supplied

Adaptive mechanisms of saccadic system in diagnostic use.

The possibilities of diagnostic use of saccades are given in pathological eye movements as well as in adaptive mechanisms. They are used to offset the degradation of oculomotor performance resulting from interference along the chain of neural conducting, in neuromuscular transmission and in muscle function. Pharmacological effects can be used to increase the influence of disorders or to detect adaptive mechanisms. During the pharmacological therapy with carbamazepine or diphenylhydantoin, adaptive processes can be measured.

Adaptation, Physiological↗
PubMedDate not supplied

[Long-term changes in the efficiency of the excitatory and inhibitory connections in the neuronal micronetworks of the motor cortex induced by tetanization of the thalamic nuclei and the sensory cortex].

Assumption was verified that tetanization which produces long-term potentiation (LTP) and long-term depression (LTD) in the efficacy of thalamo-cortical inputs and the inputs from the sensory cortex to motor cortex results also in long-term modifications of the efficacy of interneuronal interactions in the motor-cortical networks. It was shown that monosynaptic excitation of one of the neighbouring neurons in the motor cortex by rhythmical stimulation of some thalamic nuclei or the sensory cortex resulted in LTP or LTD in the efficacy of excitatory and inhibitory transmission between the neurons of the network. The efficacy of the synapses formed by the terminals of one axon on the neighbouring cells could be variously modified. If the network contained the neurons with multiple convergent inputs the tetanization resulted in the LTP of most of them. In the neuronal networks which contained local feed-forward inhibitory circuits, LTP (LTD) of the inhibitory input to the target cell was accompanied by LTD (LTP) of the excitatory input to the same target cell. Different patterns of modified interneuronal connections were caused by tetanization of different brain structures (thalamic nuclei or sensory cortex).

Animals↗
PubMed1995

Spinohypothalamic tract neurons in the cervical enlargement of rats: descending axons in the ipsilateral brain.

Spinohypothalamic tract (SHT) cells are spinal cord neurons with axons that project directly to or through the contralateral hypothalamus. Frequently, SHT axons decussate in the posterior optic chiasm, turn posteriorly and descend to unknown locations in the ipsilateral brain. We attempted to determine the course and the termination of these descending axons. Sixty neurons in the cervical enlargement of rats were antidromically activated initially from the contralateral hypothalamus and then from multiple anterior-posterior levels in the ipsilateral brain. Fifty-three (88%) were backfired with low currents at increased latencies from the ipsilateral brain. The axons of 35 neurons were surrounded with electrode penetrations from which high currents could not activate the neuron antidromically, suggesting the examined axons terminated in the surrounded areas. Seven SHT axons that were surrounded (20%) appeared to terminate in the contralateral hypothalamus, 5 (14%) in the ipsilateral hypothalamus, and 9 (26%) in the ipsilateral thalamus. Fourteen SHT axons (40%) ended in the ipsilateral midbrain mainly in the superior colliculus, cuneiform nucleus or nucleus brachium inferior colliculus. An additional 11 axons were followed even further posteriorly into the ventral pons or rostral medulla. Each of the 26 neurons that could be physiologically classified responded either preferentially or specifically to noxious mechanical stimuli. These results indicate that SHT axons course through a surprisingly long and complex path. After decussating in the hypothalamus, the axons of many SHT neurons descend into the ipsilateral posterior thalamus, midbrain, pons, or even rostral medulla. These axons may provide nociceptive information to a variety of nuclei throughout the diencephalon and brainstem bilaterally.

Animals↗
PubMed1977

[Synaptic organization of supraspinal control of the propriospinal neurons of the ventral horn of the cat and monkey spinal cord].

In experiments carried out on cats and monkeys synaptic actions evoked in propriospinal interneurons of the upper lumbar segments by reticulo-, vestibulo- and cortico-spinal volleys were investigated by means of intra- and extracellular recording. Propriospinal interneurons identified by antidromic invasion from the fibres of the ventrolateral funiculi were located in different zones of the ventral horn of the upper lumbar segments. In cats a monosynaptic effect could be evoked by a vestibulo- and reticulo-spinal volley. In monkeys monosynaptic brain-stem-propriospinal actions are complemented by cortico-propriospinal monosynaptic connections. The convergence of monosynaptic effects from different supraspinal sources was shown.

Animals↗
PubMed1996

U.S. Air Force pilot selection tests: what is measured and what is predictive?

Selection of military pilots has long included the use of multiple aptitude test batteries. Although the names and appearances of the tests used in pilot selection vary, most are to a large extent measures of general cognitive ability, or g. This is consistent with the central role played by cognitive ability measures in the prediction of numerous job training (r = 0.43) and performance (r = 0.34) criteria. Measures of specific cognitive abilities (e.g., verbal, quantitative, spatial, perceptual speed) have shown little incremental validity beyond g (increase in correlation of about 0.02). The incremental validity, beyond g, of measures of pilot job knowledge (e.g., aviation concepts, instruments, principles and terms; increase in correlation beyond g of about 0.08), psychomotor abilities, and personality scores (increase in correlation beyond g between 0.02 and 0.04) also has been small, but significant. The unavoidable requirement to reason in responding to test material causes g to be measured. In broad-ability-range samples, the positive correlations of the measures demonstrate that general cognitive ability is always present as a higher-order factor. Future measures of pilot aptitude may include tests based on cognitive components, chronometric methods, neural conductive velocity, or other methods. These measures, despite their appearance, have been shown to mostly measure g. Subsequently, we expect that future U.S. Air Force pilot selection tests will mostly be measures of g and will, therefore, continue to be predictive of performance.

Cognition↗
PubMed1977

[Study of the relationships between the "locomotor regions" of the subthalamus and midbrain in rats].

Responses of single neurons in the midbrain tegmentum to stimuli applied to the subthalamic "locomotor region" were recorded extracellularly. In various units the latencies of responses were from 1 to 13 ms. Thresholds of the unit responses usually were not higher than the thresholds for eliciting locomotion. Obtained data evidence for a direct and oligosynaptic connections between subthalamic and midbrain "locomotor region".

Animals↗
PubMed1977

[Recurrent inhibition of the sympathetic pregnaglionic neurons of the lateral horns of the spinal cord].

32.5% of the lateral horn sympathetic preganglionic neurons (B2-SPN) recorded in T3, T8-9 and L2 spinal segments of anaesthetized and immobilized cats were able to respond antidromically to repeated stimuli with time interval (16 ms and more) considerably exceeding the refractoriness of these neurons. This effect was not associated with axonal subnormality. A prolonged time interval between antidromic discharges correlated with the ability of orthodromic spikes to inhibit the generation of antidromic discharges throughout the same period which was substantially longer than the possible collision time. Preceding antidromic activation of a fraction of the described neurons partly inhibited the responses of other neurons in this segment elicited by stimulation of segmental nerves or spinal descending pathways. These data indicate that certain lateral horn sympathetic preganglionic neurons have a recurrent inhibitory mechanism.

Animals↗
PubMed1977

[Nature of the reflex excitation of the spinal motor neurons in children with isiopathic scoliosis].

In 32 girls from 12-14 years with expressed idiopathic scoliosis (III-IV stage) the authors studied H-reflexes, evoked from the soleus muscles. In 16 patients they established an expressed asymmetry in the expressivity of H-reflexes from the right and left sides. This asymmetry was found in a localization of the primary arch of spinal distortion in the sacral part. In a localization of the primary arch in the thoracal part, the asymmetry in the reflectory excitation of sacral motoneurons is not expressed. It is being assumed that changes in the motoneuron apparatus of the spinal cord are the reason of the appearance of a scoliotic deformation of the spine.

Adolescent↗
PubMed1976

Analysis of five tests commonly used in determining the ability to control single motor units.

A correlation regression analysis was used to analyze five individual test and two types of scores in terms of their predictive value in determining overall performance in single motor unit (SMU) control. Fine wire electrodes were inserted into the biceps brachii muscle of twenty-five women subjects. Each subject was tested for electrical silence, motor unit isolation, on-off control, frequency control and rhythm control. A detailed protocol and scoring criteria are described for each test. Ten predictors were analyzed--a time score and an error score for each of the five tests. A correlation regression analysis showed that the On-Off Control, the Rhythm Control and the Motor Unit Isolation tests have greater predictive value than the remaining tests. Furthermore, the error scores obtained from these tests are more reliable than the time scores in predicting overall performance in SMU control. The implications that the present findings may have on future studies are discussed.

Action Potentials↗