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Biomedical subjects

J Leech

Publications and source records attributed to J Leech.

36 records · Page 2Linked to original sources
PubMed1985

An in vitro assay for sequestration: binding of Plasmodium falciparum-infected erythrocytes to formalin-fixed endothelial cells and amelanotic melanoma cells.

Erythrocytes infected with Plasmodium falciparum bind specifically to cultured endothelial cells and to a line of amelanotic melanoma cells. We have fixed endothelial cells and amelanotic melanoma cells in various ways and determined whether the fixed cells were still able to bind infected erythrocytes. Only cells fixed with 1.0-2.5% formalin in phosphate-buffered saline continued to bind infected erythrocytes as well as unfixed cells. The mechanism of binding to fixed and unfixed cells appeared to be identical for the following reasons. First, erythrocytes infected by parasite strains that bound to unfixed cells also bound to fixed cells while those that did not bind to unfixed cells did not bind to fixed cells. Second, immune serum that inhibited binding to unfixed cells also inhibited binding to fixed cells. Third, electron microscopy showed that knobs were the points of attachment between infected erythrocytes and both fixed and unfixed melanoma cells. Fixed cells gave reproducible results over at least 2 months. Thus, we have developed a simplified, reproducible assay for measuring binding of P. falciparum-infected erythrocytes to target cells.

Animals↗
PubMed1980

Reversed optokinetic nystagmus (OKN): mechanism and clinical significance.

We studied reversed optokinetic nystagmus (OKN) in 31 patients and found that it is actually the patient's own gaze-modulated spontaneous nystagmus shifted to the primary position of gaze by optokinetic stimulation. Two of our 31 patients were known to have congenital nystagmus. Most of the 29 others were adults who presented with neurological symptoms and nystagmus and were therefore suspected of having posterior fossa lesions. However, their nystagmographic findings and benign natural history suggest that they also had congenital nystagmus, which was unrecognized until they developed incidental neurological symptoms. These cases support the view that reversed OKN is pathognomonic of a benign, probably congenital, nystagmus.

Adult↗
PubMed1978

Clinical and theoretical aspects of head movement dependent oscillopsia (HMDO). A review.

Head movement-dependent oscillopsia (HMDO) with peripheral vestibular, brainstem and cerebellar lesions is reviewed. The differentiation of this kind of oscillopsia is based mainly on clinical grounds. HMDO with bilateral abolition of caloric responses, and in the absence of disease of the central nervous system, is due to bilateral vestibular disease. HMDO in patients with internuclear ophthalmoplegia and other brainstem signs is probably due to a lesion of VOR pathways in or near the medial longitudinal fasciculus. The occurrence of HMDO with ataxia of gait and cerebellar eye movement disorders (rebound nystagmus, flutter-like oscillations), in the absence of brainstem lesions (medial longitudinal fasciculus), is clinical evidence for HMDO due to a cerebellar lesion. An attempt is made to associate the different kinds of oscillopsia with current knowledge of the vestibulo-ocular reflexes.

Animals↗
PubMed1978

The relationship between head and eye movement in congenital nystagmus with head shaking: objective recordings of a single case.

Head shaking and congenital nystagmus were recorded in a patient presented with visual tasks. When she was at rest the nystagmus took a 6 cycles per second saw-tooth wave-form. When she was attentive the nystagmus beat at a 2 to 2.6 cycles per second with a saddle-shaped deformation which permitted foveation. The head shaking occurred occasionally when the patient was attentive and was phase-locked to the nystagmus with resemblances in wave form and direction. Deceleration of the head shaking to zero velocity and peak displacement (to the left) coincided with the onset of the saddle of the nystagmus and hence assisted foveation; all other parts of the head-shaking cycle were detrimental to vision. It is proposed that the head shaking has a common pathological origin with the nystagmus and that, just as an isolated congenital nystagmus wave form becomes altered with attention to permit periods of foveal fixation, the pattern of combined head and eye nodding in this patient provided similar peroids of fixation.

Adult↗
PubMed1977

Gaze failure, drifting eye movements, and centripetal nystagmus in cerebellar disease.

Three abnormalities of eye movement in man are described which are indicative of cerebellar system disorder, namely, centripetally beating nystagmus, failure to maintain lateral gaze either in darkness or with eye closure, and slow drifting movements of the eyes in the absence of fixation. Similar eye movement signs follow cerebellectomy in the primate and the cat. These abnormalities of eye movement, together with other signs of cerebellar disease, such as rebound alternating, and gaze paretic nystagmus, are explained by the hypothesis that the cerebellum helps to maintain lateral gaze and that brain stem mechanisms which monitor gaze position generate compensatory biases in the absence of normal cerebellar function.

Adult↗
PubMed1977

Coordination of the head and eyes in pursuit of predictable and random target motion.

Subjects were required to use their head and eyes in pursuit of visual targets which moved randomly or sinusoidally in the horizontal plane. All subjects disliked moving their heads to pursue the random motion, apparently because the motion broke fixation which resulted in a predominance of the vestibulo-ocular compensatory reflex over the smooth pursuit reflex. As a consequence gaze (head plus eye movement) was at times in the opposite direction to the motion of the target. In steady state pursuit of sinusoidal targets, eye movement consisted of a combination of pursuit and vestibulo-ocular reflex eye movements. At frequencies below 0.8 HZ, the vestibular reflex was used at times of minimum target velocity to stabilize fixation whereas during maximum target velocity the head movement was slowed and the smooth pursuit reflex predominated. At 1 HZ and over, there was a failure to suppress the compensatory vestibulo-ocular reflex; however, the saccades of vestibular nystagmus were used to "catch up" the target. There was a preference not to use the head in predictable pursuit.

Adult↗
PubMed1976

The assessment of position of stationary targets perceived during saccadic eye movement.

The experiment was performed to establish the accuracy with which visual targets perceived during saccadic eye movement are localised. Subjects were presented with the task of executing saccades of 30 degrees plus amplitude, passing through primary gaze, about the time of peak velocity a 5 ms red flash was presented at some random position (up to 30 degrees left or right of centre) on a horizontal visual display. Subjects were required to indicate the direction in which they thought the flash was localised by fixating in that direction. Observations were made under conditions of prolonged total darkness and in the presence of a contrasting background. Measurement was made of saccade velocity and eye displacement as an index of target positions. Eye displacement was linearly scaled with respect to true target direction. Targets were localised with an average error of 5 degrees-6 degrees although the variance was high. No systematic differences were found between conditions or subjects. Error was unrelated to saccade velocity. It is concluded that during saccadic eye movements the appreciation of target position is maintained with an acceptable degree of accuracy.

Eye Movements↗
PubMed1976

Internuclear ophthalmoplegia. An electro-oculographic study of peak angular saccadic velocities.

Peak angular saccadic velocities were measured during 30 degrees saccades in 18 patients with internuclear ophthalmoplegia who had full or nearly full adduction range, and 25 normal subjects. The following observations were made: 1. In the normal group adduction velocities were significantly faster than abduction velocities and centring movements were faster than decentring movements. 2. In patients with internuclear ophthalmoplegia adduction movements were significantly slower than in normal subjects and were significantly slower than abduction velocities. 3. Abduction velocities in patients with internuclear ophthalmoplegia were significantly slower than abduction velocities in normal subjects. It was concluded that measurements of peak angular velocities during saccades may be useful in detecting internuclear ophthalmoplegia or confirming the presence of suspected internuclear ophthalmoplegia. Slow abduction suggests that many patients with internuclear ophthalmoplegia (60 per cent in this series) have lesions affecting the supranuclear pathways subserving horizontal conjugate gaze.

Electrooculography↗
PubMed1976

A study of head and eye movement in spasmus nutans.

A case of spasmus nutans was studied using objective recordings of head and eye displacement in order to generate a precise description of the ocular oscillations and head nodding and to investigate their interrelationships. The ocularoscillations consisted of 11-Hz sinusoidal convergence movements. The head nodding consisted of a 3-Hz, 3 degrees peak to peak, sinusoidal oscillation in the horizontal plane. The occurrence of the nodding always abolished the ocular oscillation which was replaced by normal compensatory eye movements which assisted visual acuity. The hypothesis is made that the head nodding is not pathological; it is a learned behavioural pattern which permits the patient to nullify the pathological eye movements. In order to test this hypothesis further, objective evidence is required to determine the precise order of appearance of the abnormal head and eye movements in spasmus nutans.

Child, Preschool↗
PubMed1976

Analysis of a case of periodic alternating nystagmus.

A patient is described in whom there was periodic deviation of the eyes in darkness associated with alternating nystagmus. An exactly similar situation occurs in normal man subjected to a pendular stimulus. It is proposed that in this patient there was alternating activity of the vestibular nuclei on either side of the brain-stem as a result of a removal of cerebellar inhibition, and that this caused periodic shifts in the null region of Daroff and Dell'Osso.

Adolescent↗
PubMed1976

Perception of everyday visual environments during saccadic eye movements.

Subjects were required to execute saccadic eye movements in the horizontal plane which passed through primary gaze. During the saccades, visual images were projected onto a screen which subtended 40 degrees horizontaloy and 26 degrees vertically and was centered on primary gaze. Content, contrast, and intensity of the stimulus patterns and level of illumination of the laboratory background were manipulated to maximise pattern recognition. Little or no detail of the projected images could be discerned under any conditions. Only horizontal laminations were perceived as blurs of appropriate colour. It is concluded that there is no useful perception of the everyday environment during saccades.

Eye Movements↗
PubMedDate not supplied

The gene product of the Plasmodium falciparum 11.1 locus is a protein larger than one megadalton.

The Plasmodium falciparum 11.1 gene locus on chromosome 10 extends over 30 kb and contains approximately 22 kb of a tandemly repeated 27-bp sequence. Biochemical and size similarities have been noted between the reported 11.1 antigen and a variable-Mr, surface-radioiodinatable protein which appears to be involved in the cytoadherence of red blood cells infected with mature intraerythrocytic parasites to venular endothelium. We attempted to determine if these proteins were identical. Using rabbit antibody and affinity purified human immune sera specific for peptides encoded by the 27-bp repeat and a flanking 5' region, we have shown that the 11.1 locus encodes a protein of more than 1000 kDa. This protein cross-reacts with an uncharacterized 260-kDa protein, previously identified as the gene product of the 11.1 locus, and Pf155-RESA, but not with the radioiodinatable protein. The 11.1 protein that we have identified is a malarial protein of unprecedented size.

Animals↗
PubMedDate not supplied

Cryptosporidium parvum: in vitro cultivation in Madin-Darby canine kidney cells.

To facilitate studies of the biology of Cryptosporidium parvum, we have developed an in vitro culture system using Madin-Darby canine kidney (MDCK) cells as the host cell. Oocysts or free sporozoites were incubated 37 degrees C with monolayers of MDCK cells in supplemented RPMI 1640 medium and the cells were examined at various time intervals after initiation of the culture. High rates of infection (up to 90% of MDCK cells) were achievable. Sequential development of trophozoites, meronts, microgametocytes, and macrogametocytes was observed over a 72-h period of culture. Between 72 and 96 h we observed formation of oocyst walls, but fully sporulated oocysts were not observed. This culture system provides access to both the asexual and sexual intracellular stages of C. parvum.

Animals↗