Biomedical subjects
Publications and source records attributed to Y S Chan.
Cerebral sparganosis is a rare disease; to date only eight cases have been described. Two new cases of cerebral sparganosis occurring in Chinese patients living in a metropolitan area are reported. Their clinical presentation and investigative results are presented and the operative and histological findings detailed. A brief review of the condition is given and the possible source of infection discussed.
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The effects of superfusion of morphine, met-enkephalin and D-ala2-met5-enkephalinamide on the spontaneous neural discharge rates of units in the spinal trigeminal nucleus and cuneate nucleus of decerebrate cats were studied. The drugs were superfused onto the dorsum of the exposed surface of the caudal medulla overlying these nuclei. Some of these neurons were identified by their response to innocuous mechanical stimuli delivered to the skin. In the caudal spinal trigeminal nucleus, morphine caused a dose-dependent suppression of the spontaneous discharge rate in the majority of the neurons studied. Endogenous opiate peptide, met-enkephalin or its synthetic analogue, D-ala2-met5-enkephalinamide caused an initial reduction, followed by a rebound of the discharge rate to the control value. These depressant effects of morphine and enkephalins were antagonized by concomitant superfusion of the opiate antagonist naloxone. In the main cuneate nucleus, however, similar doses of morphine, met-enkephalin and D-ala2-met5-enkephalinamide have little if any significant effect on the spontaneous activity of the neurons studied. These results provide electrophysiological evidence for the presence of opiate receptors in the caudal spinal trigeminal nucleus and the relative lack of such receptors in the main cuneate nucleus.
The responses of neurons sensitive to static tilt in the vestibular nuclei were examined in decerebrate cats during slow and constant velocity rotations about an axis tilted at various angles from the vertical. During any 360 degrees rotation, each unit showed a modulation of their firing rate, with a position-dependent maximum and minimum. Changes in amplitude of head displacement from 5 degrees to 25 degrees decreased the response gain of the units without affecting the locations of the discharge maxima and minima.
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In ketamine anesthetized cats, the contralateral labyrinth, the ipsilateral utricle, the ipsilateral horizontal and anterior semicircular canal nerves were completely destroyed, leaving the ipsilateral saccule intact. Neurons in the Deiters' nucleus, driven by electrical stimulation of the superior saccule, were responsive to static tilts in the antero-posterior direction. Results suggest that the saccule is capable of conveying information on head positional changes in the antero-posterior direction and that such information is retained at the level of the Deiters' nucleus.
A simple, low cost interspike interval analyzer for the analysis of trains of nerve impulses is described. The analyzer is built with readily available integrated circuits and has been used to analyze spike trains in the lateral vestibular nucleus of cats.
2 populations of cells were found in the Deiters' nucleus responsive to direct electrical stimulation of the ipsilateral saccule. Only those Deiters' neurons activated monosynaptically from the saccule could be driven antidromically from the oculomotor nucleus. Such an intracellular study provides strong evidence for a tri-neuronal arc in the sacculo-ocular reflex for vertical eye movements.
Computed tomographic arteriography is the technique of contrast enhancement by arterial perfusion during computed tomography. This technique appears to have significant advantages over conventional intravenous contrast enhancement in selected cases.
Computer assisted myelography (CAM) is a technique to examine the spinal subarachnoid space. Adjacent structures that may impinge on this space, such as the intervertebral disks, as well as structures contained in this space, such as the spinal cord, spinal roots, and vascular formation, may also be appraised by this method. At present, CAM is performed by subarachnoid introduction of water soluble contrast material followed by computed tomography in the axial transverse plane. The authors present their technique and their results with representative cases of intervertebral disk disease.
A patient was seen with symptomatic, rapidly expanding aneurysms that developed in both carotid arteries 4 years after bilateral radiation to the neck, left combined mandibular resection, and radical neck dissection. The presenting symptoms were pain and transient ischemic attacks of cerebrovascular insufficiency. The aneurysms were treated uneventfully be resection and vein-graft replacement at 15-day intervals. Microscopy demonstrated typical radiation changes. Effects of radiation on arteries are reviewed.
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Coliphage content of sewage collected from 11 different localities in Hong Kong was determined. The number of plaque-forming units (PFU) ranged from 0.036 x 10(3) to 15.9 x 10(3) per ml. In general, urban sewage tended to be richer than rural sewage both in PFU count as well as plaque morphological variation. Seventy-seven isolates were subjected to a host range study. Fifty per cent of these were able to grow on Escherichia coli K-12 as well as E. coli B. Approximately 32% were found to be male specific, and the remaining 18% were K-12 specific although sex-indifferent.
Single unit recordings were made in the Deiters' nucleus of cats in response to electrical stimulation of the superior area of the contralateral saccule and the ipsilateral oculomotor (IIIrd) nuclear complex. Correct placements of the stimulating and recording electrodes were identified by upward movements of the eyeballs associated with characteristic field potentials in the Deiters' nucleus. Stimulation of the contralateral saccule induced a negative N wave followed by positive P1 and P2 potentials. One hundred twenty-two units responded to contralateral saccular stimulation with a mean latency of 2.48 +/- 0.06 msec (SEM). Of these, only the responses of 31 cells could be made to collide with antidromic spikes evoked from ipsilateral IIIrd nuclear stimulation. This implies that the crossed sacculo-ocular pathway would involve at least four neurons with one commissural cell interposing between the bilateral vestibular nuclei.