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F J Thompson

Publications and source records attributed to F J Thompson.

50 records · Page 3Linked to original sources
PubMed1985

Properties of spinal cord processing of femoral venous afferent input revealed by analysis of evoked potentials.

Two characteristics of spinal cord interneurons which receive inputs from femoral-saphenous venous afferents were examined. The shortest pathway between primary femoral-saphenous venous afferents and alpha-motoneurons was shown to be a di- or tri-synaptic circuit. In addition, the largest focal synaptic field potentials elicited by venous afferent stimulation at short latency were recorded from Rexed's lamina V. It was thus concluded that most of the first interneurons excited by venous afferents are found in this lamina.

Afferent Pathways↗
PubMed1983

Lumbar spinal cord responses to limb vein distention.

The purpose of this study was to determine if central neural responses were elicited by distention of limb veins, and to compare the pattern of these response to those produced in previous studies using electrical stimulation to excite limb venous afferent fibers. Spinal evoked potentials were measured in response to stretch of the wall of a segment of the femoral-saphenous vein by perfusion-distention or by mechanical stretch. These studies revealed that spinal cord evoked potentials were elicited by these procedures, and that the activated venous afferent fibers coursed through the saphenous nerve and entered the sixth lumber spinal cord segment. The minimum stretches which were required to elicit spinal evoked potentials were produced by perfusion pressures starting at 2-3 mm Hg, or by mechanical stretch of the wall of 5 micron/mm. A vein wall proprioceptor hypothesis is proposed and discussed in the light of these findings. In addition to the cord dorsum evoked potentials, distention or stretch of the vein wall elicited ventral root potentials (excitatory postsynaptic population potentials) which are known to be produced by excitatory inputs to motoneurons. A venous afferent mediated muscle-tonus venopressor mechanism hypothesis is proposed and discussed in the light of these and previous findings.

Afferent Pathways↗
PubMed1982

Interactions between femoral venous afferents and lumbar spinal reflex pathways.

This study reports findings of spinal reflex connections of afferent fibers electrically excited in the wall of the femoral vein. Condition-test experiments, and EMG recordings revealed that the femoral venous afferents have facilitatory connections to flexor and extensor motoneurons of both the proximal and the distal hindlimb muscles. Femoral venous afferent stimulation which produced facilitation, also produced inhibition of the test reflexes following the facilitation. Because the inhibition was enhanced by diazepam injection and because the inhibitory time-course correlated closely to the time-courses of both dorsal root potentials and individual tests of primary afferent depolarization, the inhibition was suggested to be produced by presynaptic inhibition. The potentially significant role of the venous afferent connections in a reflex-elicited skeletal muscle pump or in an increase in intramuscular venous counterpressure is discussed.

Afferent Pathways↗
PubMed1982

Origin and properties of spinal cord field potentials.

Electrical or natural stimulation of cutaneous, muscle, or visceral nerves evokes a field potential in the spinal cord; the field potential elicited by each type of afferent fiber differs in wave form. Cutaneous nerve-evoked spinal cord field potentials consist of a triphasic spike, one to three negative waves, and a slow positive wave. Muscle nerve-evoked spinal cord field potentials are composed of a triphasic spike, a slow positive wave, and one to three negative waves with different relative latencies and durations than the negative waves evoked by cutaneous nerves. Visceral nerve-evoked potentials in the spinal cord comprise only a single negative wave and a slow positive wave. The triphasic spike is a compound action potential propagating through the large primary afferent fibers; the negative waves are generated by dorsal horn interneurons; the positive wave is a reflection of primary afferent depolarization. A knowledge of the origin and properties of spinal cord field potentials has practical usefulness for both the experimental neurophysiologist and the clinician.

Electrodiagnosis↗
PubMed1981

Implementation and Service error: Veterans Administration health care and the commercial market option.

As government has attempted to deal with complex social problems, the inevitability of error has become increasingly apparent to students of public policy and implementation. This essay focuses on errors of service, initially drawing on the experience of the Veterans Administration (VA) medical system to explore problems of defining, detecting and correcting such errors when government directly delivers care. It probes the complex blend of errors of liberality and stringency that appeared to be present in the VA during the 1970s, the formidable barriers to error correction, and the steps taken by the VA in response to the problem. Second, the essay examines whether a commercial market strategy, as embodied by Medicare or Medicaid, offers certain advantages in dealing with service errors similar to those confronted by VA. The experience of Medicare and Medicaid casts doubt on whether a commercial market model yields superior results in coping with these kinds of error. Finally, the study points to some more general implications of the VA's experience for discussions of service problems in the health policy arena.

Aged↗
PubMed1980

Focal and generalized experimental seizures induced by homocysteine.

Electrocorticographic and behavioral effects of parenteral injections of homocysteine in rats are described. Homocysteine activates experimental foci and produces focal seizures in experimental animals with pre-existing lesions. It produces generalized ECoG seizures and generalized convulsions in unlesioned animals in higher doses.

Animals↗
PubMed1980

Projection of limb venous afferents to the feline motor-sensory cortex.

Previous studies have shown that the cerebral cortex has the capacity to exert a marked influence on the circulatory system. Recently low threshold femoral vein afferent fiber projections to the spinal cord were reported and were found to have powerful reflex connections to motor neurons. The venous afferents appeared to be attractive candidates to provide afferent input to the cortex by the activation of ascending sensory systems. Therefore the experiments described in this report were carried out to determine the existence and functional organization of venous afferent projections to the cerebral cortex in the cat. Femoral and brachial vein afferent fibers were excited in the vein wall by electrical stimulation. Cerebral cortical mapping of cortical evoked potentials revealed that femoral and brachial venous afferent fibers activate ascending sensory systems which activate cortical neurons. The primary projection focus of the hind limb venous afferents lay within the hindlimb 3a--4 gamma motor-sensory cortex on the medial postcruciate gyrus. The forelimb venous afferent primary projection focus lay within the forelimb 3a--4 gamma motor-sensory cortex on the lateral sigmoid gyrus. The venous afferent projection was proposed to be a component of a cortical control system which would facilitate optimal cardiovascular control.

Afferent Pathways↗
PubMed1975

Patterns of cortical projection to hindlimb muscle motoneurone pools.

This study was undertaken to examine the organization of the hindlimb area of the motor cortex. Two specific questions were posed. The first was: are the cortical neurones which control the excitability of a given motoneurone pool localized in a small zone of corjex or are they diffuse? The second question was: does microstimulation in the hindlimb area of the motor cortex activate spinal motoneurones in a reciprocal fashion, i.e., is cortically elicited facilitation of a muscle accompanied by inhibition of the antagonist? Intracortical microstimulation was used to condition monosynaptic reflexes of the cat hindlimb to study the organization of a cortical projection to lumbar motoneurone pools. Cortical neurones which produced facilitation or inhibition of a given monosynaptic reflex were localized within a small zone of the cortex. Facilitatory and inhibitory effective zones were found to have similar shape and size. Intracortical microstimulation elicited facilitation or inhibition of individual monosynaptic reflexes without eliciting reciprocal effects on the antagonists. The pyramidal tract was shown to play an important role in the mediation of cortically elicited facilitation as well as inhibition of the monosynaptic reflexes in the lumbar cord.

Animals↗
PubMedDate not supplied

Arterial supply of the feline motor cortex.

The arterial supply of the feline motor cortex is derived from both the anterior and middle cerebral arteries. The anterior cerebral artery supplies most of cortical area 6 (premotor cortex), the intrafundal cruciate and medial postcruciate cortex, (hindlimb motor cortex), and the midline and medial portions of the sensory areas 3a-7. The middle cerebral artery supplies the lateral prorean cortex, (lateral premotor cortex), precruciate and lateral sigmoid cortex, (forelimb motor cortex), and the remainder of the coronal and Sylvian cortical areas.

Animals↗