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M H Rowe

Publications and source records attributed to M H Rowe.

At least 19 recordsLinked to original sources
PubMed2006

Autocorrelation analysis of hair bundle structure in the utricle.

The ability of hair bundles to signal head movements and sounds depends significantly on their structure, but a quantitative picture of bundle structure has proved elusive. The problem is acute for vestibular organs because their hair bundles exhibit complex morphologies that vary with endorgan, hair cell type, and epithelial locus. Here we use autocorrelation analysis to quantify stereociliary arrays (the number, spacing, and distribution of stereocilia) on hair cells of the turtle utricle. Our first goal was to characterize zonal variation across the macula, from medial extrastriola, through striola, to lateral extrastriola. This is important because it may help explain zonal variation in response dynamics of utricular hair cells and afferents. We also use known differences in type I and II bundles to estimate array characteristics of these two hair cell types. Our second goal was to quantify variation in array orientation at single macular loci and use this to estimate directional tuning in utricular afferents. Our major findings are that, of the features measured, array width is the most distinctive feature of striolar bundles, and within the striola there are significant, negatively correlated gradients in stereocilia number and spacing that parallel gradients in bundle heights. Together with previous results on stereocilia number and bundle heights, our results support the hypothesis that striolar hair cells are specialized to signal high-frequency/acceleration head movements. Finally, there is substantial variation in bundle orientation at single macular loci that may help explain why utricular afferents respond to stimuli orthogonal to their preferred directions.

Animals↗
PubMed1996

Linear and nonlinear contributions to step responses in cat retinal ganglion cells.

We measured excitatory and inhibitory step responses of cat retinal ganglion cells to square wave contrast reversal of stationary sinusoidal gratings. In most Y-cells the initial increase in firing rate (early peak) of the excitatory responses was followed by a distinct second increase in firing rate (late peak). Analysis of the spatial frequency and spatial phase dependence of the two peaks indicated that the early peak appears to be produced by the spatially linear center mechanism, while the late peak appears to be produced by the rectifying subunits described by Hochstein and Shapley (1976) Journal of Physiology, London, 262, 237-264, 265-284. These results indicate that the presence of two peaks in ganglion cell step responses is the result of two excitatory inputs with different time courses, and that inhibitory inputs are not required to explain the appearance of these responses.

Action Potentials↗
PubMed1996

Spatial and temporal properties of cat horizontal cells after prolonged dark adaptation.

We studied the change of spatial and temporal response properties for cat horizontal (H-) cells during prolonged dark adaptation. H-cell responses were recorded intracellularly in the optically intact, in vivo eye. Spatial and temporal properties were first measured for light-adapted H-cells, followed by a period of dark adaptation, after which the same measurements were repeated. During dark adaptation threshold sensitivity was measured at regular intervals. Stable, long lasting recordings allowed us to measure changes of sensitivity and receptive field characteristics for adaptation periods up to 45 min. Although cat H-cells showed no signs of dark suppression or light sensitization, they remained insensitive in the scotopic range, even after prolonged dark adaptation. Absolute thresholds were in the low mesopic range. The sensitization was brought about by a shift from cone to rod input, and by substantial increases of both spatial and temporal integration upon dark adaptation. The length constant in the light-adapted state was on average about 4 deg. After dark adaptation it was up to a factor of three larger, with a median ratio of 1.85. Response delays, latencies and durations for (equal amplitude) threshold flash responses substantially increased during dark adaptation.

Animals↗
PubMed1996

Gain control and hyperpolarization level in cat horizontal cells as a function of light and dark adaptation.

First a model is presented that accurately summarizes the dynamic properties of cat horizontal (H-) cells under photopic conditions as measured in our previous work. The model predicts that asymmetries in response to dark as compared to light flashes are flash-duration dependent. This somewhat surprising prediction is tested and confirmed in intracellular recordings from the optically intact in vivo eye of the cat (Experiment 1). The model implies that the gain of H-cells should be related rather directly to the sustained (baseline) membrane potential. We performed three additional experiments to test this idea. Experiment 2 concerns response vs intensity (R-I-) curves for various flash-diameters and background-sizes with background luminance varying over a 4 log unit range. Results support the assumption of a rather strict coupling between flash sensitivity (gain) and the sustained level of hyperpolarization. In Experiment 3 we investigate this relation for both dark and light flashes given on each of four background light levels. The results suggest that there are fixed minimum and maximum hyperpolarization levels, and that the baseline hyperpolarization for a given illumination thus also sets the available range for dark and light flash-responses. The question then arises whether, or how this changes during dark adaptation, when the rod contribution to H-cell responses gradually increases. The fourth experiment therefore studies the relationship between gain and hyperpolarization level during prolonged dark-adaptation. The results show that the rod contribution increases the polarization range of H-cells, but that the gain and polarization level nevertheless remain directly coupled. H-cell models relying on a close coupling between polarization level and gain thus remain attractive options.

Adaptation, Ocular↗
PubMed1992

Restenosis after directional coronary atherectomy.

OBJECTIVES: This study evaluates the incidence of restenosis after successful directional coronary atherectomy and identifies risk factors for restenosis. BACKGROUND: Directional coronary atherectomy has been shown to be a safe and effective treatment of obstructive coronary artery disease; however, information regarding restenosis is limited. METHODS: Between October 1986 and December 1989, 289 patients with 332 lesions were successfully treated with directional coronary atherectomy and followed up prospectively. Clinical follow-up information was available for 98% and angiographic follow-up information was obtained for 82% at approximately 6 months, or earlier if symptoms recurred. Angiograms were quantitatively analyzed. Restenosis was defined as greater than 50% stenosis at the site of intervention. RESULTS: Seventy-four percent of patients were either asymptomatic or clinically improved after the procedure. Thirty-two percent were subsequently treated by coronary artery bypass surgery (14%), percutaneous transluminal coronary angioplasty (4%) or repeat atherectomy (13%). Angiographic evidence of restenosis was observed in 42%. The restenosis rate in native coronary arteries was 31% for primary lesions and 28% and 49%, respectively, for lesions treated with one or two previous angioplasty procedures. The restenosis rate for saphenous vein grafts was 53% for primary lesions and 58% and 82%, respectively, for lesions treated with one or two previous angioplasty procedures. The median interval to angiographically documented restenosis was 133 days. A higher restenosis rate was associated with a saphenous vein graft, hypertension, a longer lesion (greater than or equal to 10 mm), a smaller vessel diameter (less than 3 mm), a noncalcified lesion and use of a smaller (6F) device. CONCLUSIONS: Restenosis remains a limitation of directional coronary atherectomy. A subset of patients with larger vessels, shorter lesions or lesions treated with a larger (7F) device may have a more favorable outcome.

Aged↗
PubMed1992

Effects of selective pressure block of Y-type optic nerve fibers on the receptive-field properties of neurons in the striate cortex of the cat.

In an aseptic operation under surgical anesthesia, one optic nerve of a cat was exposed and subjected to pressure by means of a special cuff. The conduction of impulses through the pressurized region was monitored by means of electrodes which remained in the animal after the operation. The pressure was adjusted to selectively eliminate conduction in the largest fibers (Y-type) but not in the medium-size fibers (X-type). The conduction block is probably due to a demyelination and remains complete for about 3 weeks. Within 2 weeks after the pressure-block operation, recordings were made from single neurons in the striate cortex (area 17, area V1) of the cat anesthetized with N2O/O2 mixture supplemented by continuous intravenous infusion of barbiturate. Neurons were activated visually via the normal eye and via the eye with the pressure-blocked optic nerve ("Y-blocked eye"). Several properties of the receptive fields of single neurons in area 17 such as S (simple) or C (complex) type of receptive-field organization, size of discharge fields, orientation tuning, direction-selectivity indices, and end-zone inhibition appear to be unaffected by removal of the Y-type input. On the other hand, the peak discharge rates to stimuli presented via the Y-blocked eye were significantly lower than those to stimuli presented via the normal eye. As a result, the eye-dominance histogram was shifted markedly towards the normal eye implying that there is a significant excitatory Y-type input to area 17. In a substantial proportion of area 17 neurons, this input converges onto the cells which receive also non-Y-type inputs. In one respect, velocity sensitivity, removal of the Y input had a weak but significant effect. In particular, C (but not S) cells when activated via the normal eye responded optimally at slightly higher stimulus velocities than when activated via the Y-blocked eye. These results suggest that the Y input makes a distinct contribution to velocity sensitivity in area 17 but only in C-type neurons. Overall, our results lead us to the conclusion that the Y-type input to the striate cortex of the cat makes a significant contribution to the strength of the excitatory response of many neurons in this area. However, the contributions of Y-type input to the mechanism(s) underlying many of the receptive-field properties of neurons in this area are not distinguishable from those of the non-Y-type visual inputs.

Animals↗
PubMed1991

Disruption of developmental timing in the albino rat retina.

We have examined the spatial and temporal gradients of two developmental processes in albino and pigmented rats: outer plexiform layer (OPL) development, and rate of cell production. The OPL first appears as a thin, discontinuous break in the cytoblast layer that is frequently interrupted by the profiles of migrating neuro- and glioblasts. In both strains, this occurs in an area temporal to the optic disc that corresponds to the eventual site of peak ganglion cell density, but is not located along the line of nasotemporal division. The OPL is first evident at P5 in pigmented animals, but its appearance in albino animals is delayed approximately 30 hours, and its development appears to follow a flatter spatial gradient than in pigmented animals. In pigmented animals OPL formation is complete over most of the retina by P10, but in albino animals at this age it is yet to be completely formed at any retinal location. Reductions in mitotic activity are also first evident in temporal retina, but unlike OPL development, appear to follow the same temporal-spatial gradient in both strains. Reductions in temporal retina are obvious by P4, and mitotic activity has ceased altogether in midtemporal retina by P6 and throughout most remaining retinal regions by P8. Thus, the initial reduction of mitotic activity precedes the onset of OPL formation in both strains, but OPL development lags behind the reduction of mitotic activity to a greater extent in albino than in pigmented animals. Some aspects of differentiation within the inner nuclear layer (INL) were also examined. Just prior to the time of the onset of OPL formation, three distinct sublaminae are apparent in the INL. Cells in the innermost sublamina appear to be in an early stage of differentiation. Cells in the middle sublamina appear to be postmigratory, but have not yet begun to differentiate. Cells in the outermost sublamina have the appearance of migrating neuroblasts. At least some of these outer cells appear to migrate across the developing OPL to the outer nuclear layer, since the outermost sublamina becomes thinner and eventually disappears at the same time that the OPL becomes a continuous, uninterrupted plexiform layer. Cells of the middle sublamina apparently begin differentiation at about the time that this migration is complete. Although this sequence is the same in both albino and pigmented strains, its onset is delayed in albino animals by the same amount as the onset of OPL formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Albinism↗
PubMed1991

Effect of lesion characteristics on outcome of directional coronary atherectomy.

Directional coronary atherectomy, a new transluminal procedure for treatment of obstructive lesions in coronary arteries by excision and removal of tissue, was performed on 447 lesions in 382 procedures. Successful outcome, defined as a reduction of stenosis by greater than or equal to 20% with a less than 50% residual stenosis, was achieved in 89.5% of lesions and mean stenosis was reduced from 75.9 +/- 13.3% to 14.5 +/- 22.1% (p less than 0.001). Complications included vessel occlusion during the procedure, 2.4%; vessel occlusion after the procedure, 1.3%; new lesion, 0.5%; nonobstructive guiding catheter-induced dissection, 0.3%; perforation, 0.8%; distal embolization, 2.1%; Q wave myocardial infarction, 0.8% and non-Q wave myocardial infarction, 4.2%. Twelve patients (3.1%) required coronary artery bypass surgery for these complications. The atherectomy success rate was greater than 80% and the combined atherectomy and angioplasty success rate was greater than 90% for complex morphologic features such as eccentric lesions, lengthy lesions, lesions with abnormal contour, angulated lesions, ostial lesions and lesions with branch involvement. In the presence of calcific deposition, atherectomy success rate was 52% for primary lesions and 83% for restenosed lesions. Among angiographically complex lesions, calcium was the predictor for failed atherectomy (p less than 0.0001). In summary, directional coronary atherectomy is safe and effective for treatment of obstructive lesions in coronary arteries in selected cases. In particular, it achieves a high success rate in lesions with complex morphologic characteristics, such as eccentricity, abnormal contour and ostial involvement.

Adult↗
PubMed1990

Comparison of dissection rates and angiographic results following directional coronary atherectomy and coronary angioplasty.

Directional coronary atherectomy is a new percutaneous transluminal technique for treating occlusive coronary artery disease. In this study, angiographic results (i.e., residual stenosis and angiographic evidence of postprocedure dissection) after directional coronary atherectomy and balloon angioplasty were compared. The atherectomy group consisted of 91 lesions in 83 consecutive patients who underwent either left anterior descending artery or right coronary artery atherectomy. The angioplasty group consisted of 91 lesions in 84 patients that were matched with the atherectomy lesions with respect to vessel and whether the lesion was a restenosis lesion. The mean preprocedure diameter stenosis was 76% in both groups as measured quantitatively with electronic calipers. After the procedure, the mean residual diameter stenosis of the atherectomy lesions was 13 +/- 17%, whereas for the angioplasty lesions it was 31 +/- 18% (p less than 0.001). Success rates in both groups were similar (94.5 and 93.4%, respectively). The incidence of postprocedure dissection was 11% in the atherectomy group and 37% in the angioplasty group (p less than 0.0001). Directional coronary atherectomy results in significantly improved postprocedure angiographic appearances due to significantly less severe residual stenosis and lower incidence of dissection.

Angioplasty, Balloon, Coronary↗
PubMed1990

Reduced conduction velocity of retinal Y-cell axons following early partial removal of their synaptic targets.

Following unilateral visual cortex ablation in neonatal kittens, the extraretinal conduction velocities of retinal Y-cell axons projecting to the lesioned hemisphere were measured and compared to the velocities of Y-cell axons projecting to the intact hemisphere. The extraretinal velocities of Y-cells projecting to the lesioned hemisphere were 16-28% lower than the velocities of Y-cells projecting to the intact hemisphere. This effect was seen in axons originating in both the ipsilateral and contralateral retinae. These data are consistent with the hypothesis that one factor regulating axon size is the amount of synaptic territory which is available to the cell. When the velocities of the unmyelinated intraretinal portions of Y-axons were examined in experimental animals, no significant differences could be detected between axons projecting to the lesioned hemisphere and those projecting to the intact hemisphere.

Action Potentials↗
PubMed1990

Evidence for degeneration of retinal W cells following early visual cortical removal in cats.

Size and distribution of ganglion cells surviving unilateral visual cortical removal at 5-7 days of age were examined in domestic cats. Such lesions were expected to result in a substantial loss of X cells in ipsilateral temporal and contralateral nasal retina, leaving ipsilateral nasal and contralateral temporal retina to serve as intact controls. A computer model of normal retinal ganglion cell topography was used to make qualitative predictions of the distribution of surviving ganglion cells. Contrary to expectations, a visual streak was no more prominent in the distribution of surviving cells than in the distribution of the normal ganglion cell population. The magnitude of ganglion cell loss, furthermore, was at least twice as great in nasal retina as in temporal retina. In nasal retina, the cell loss extended well into the small-medium size range, while in temporal retina, cell loss was restricted to the large-medium size range. Taken together, the differential magnitude of cell loss in nasal and temporal retina and the greater loss of small-medium cells in nasal retina cannot be explained by the exclusive degeneration of X cells and suggest that many of the degenerated ganglion cells were medium-sized W or gamma cells. These cells, therefore, share the susceptibility of retinal X cells to early cortical ablation. Surviving gamma cells in both nasal and temporal retina appeared to increase in soma size which may explain why their decreased numbers were not detected in previous physiological studies. Alpha cells, at least in nasal retina, decreased in some size.

Animals↗
PubMed1989

Early and late survival after coronary-artery surgery.

Between 1970 and 1985, 1801 patients underwent coronary-artery surgery without associated valvular surgery. Eighty-four per cent of patients were male and the mean (+/- SD) age was 55.7 +/- 8.3 years. Of the patients, 18.7% were from the Coronary Care Unit and 6.5% had diabetes. The hospital mortality rate for the whole group was 3.5%. Patients from the Coronary Care Unit had the highest (8.9%) hospital mortality rate compared with those patients who were not from the Coronary Care Unit (2.1%; P less than 0.001). Other factors which increased the hospital mortality rate significantly were the number of diseased vessels (P less than 0.01), the degree of left main coronary-artery stenosis (P less than 0.001), an earlier year of surgery (P less than 0.01) and female sex (P less than 0.01). After these were taken into account, no other factors (for example, age, preoperative infarction, presence of left-ventricular aneurysm, left-ventricular end-diastolic pressure, diabetes, use of mammary-arterial grafts or the need for endarterectomy) affected the mortality rate. Patients were followed-up for a mean (+/- SD) of 4.4 +/- 2.8 years. The five-year survival rate for all patients was 88% and the 10-year survival rate was 65%. Cox regression analysis showed that the significant indicators of decreased long-term survival were undergoing operation directly from the Coronary Care Unit (P less than 0.001), left main coronary-artery stenosis (P less than 0.01), the number of grafted vessels (P less than 0.01), concomitant surgery for aneurysm (P less than 0.001), year of surgery (P less than 0.01). Seventy-nine per cent of patients were free of angina pectoris at five years after operation. The year of surgery (P less than 0.001) and preoperative myocardial infarction (P less than 0.05) were the best predictors of recurrent angina. In the long term, recurrent angina remains a problem, although this may change with the increased use of mammary-arterial grafts.

Actuarial Analysis↗
PubMed1989

Effect of rapid mobilization on ejection fractions and ventricular volumes after acute myocardial infarction.

Despite the current practice of early mobilization and early hospital discharge after uncomplicated acute myocardial infarction (AMI), physicians are reluctant to permit normal physical and social activity for several weeks after the AMI "to allow the heart to heal." This study tested whether it was possible to identify a low risk group of patients on day 3 after AMI, and whether vigorous early mobilization from days 4 through 7 affected left ventricular function and volumes (studied by gated blood pool scan on days 4 and 14). There was 1 death in 3 months in 45 patients with uncomplicated AMI suitable for randomization to activity (group A) compared with 11 deaths in 55 patients unsuitable for rapid early mobilization (group B) (p less than 0.01). Early vigorous mobilization in 24 of the group A patients compared with sedentary care in 20 did not affect change in ejection fraction, end-diastolic volume, end systolic-volume, stroke volume, heart rate or cardiac output between days 4 and 14. A very low risk group suitable for early vigorous mobilization can be defined on day 3 after AMI; further, vigorous early mobilization does not affect left ventricular function or volumes. Early return to physical, social and occupational activity after uncomplicated AMI should result in marked reduction in direct and indirect costs of AMI.

Aged↗
PubMed1988

Spotty pigmentation and atrial myxoma: a case report of Carney's complex.

A case of atrial myxoma that was associated with marked spotty mucocutaneous pigmentation is described. The combination of these two conditions has been described as an easily-recognized syndrome which is familial. Other features which may be associated with the syndrome are cutaneous myxomas and endocrine tumours.

Adolescent↗
PubMed1988

Changes in inner plexiform layer thickness following neonatal visual cortical ablation in cats.

The effect of visual cortex removal at 5-7 days of age on the development of the inner nuclear and inner plexiform layers of the cat's retina was examined in animals which had survived 9-36 months after the cortical removal. The lesions were unilateral so that only the nasal or the temporal region of each retina was affected, and the affected regions were positively identified by HRP injection into the optic tract either ipsilateral or contralateral to the ablated hemisphere. Small sections of retina straddling the naso-temporal boundary were then embedded in plastic and sectioned radially for analysis. In this way, comparisons could be made between areas of retina which were closely matched in terms of location as well as histological history. Cells in the inner nuclear layer in affected regions of retina appeared normal both in number and size, even though ganglion cell density in these areas was clearly reduced. This indicates that, at least at this age, the survival of inner nuclear layer cells does not depend on the availability of ganglion cells as synaptic targets. Paradoxically, in the affected regions of retina there was an increase in the width of the inner plexiform layer which was not associated with any change in the thickness of other, more distal retinal layers. This could be due either to an increased growth of surviving ganglion cells and/or inner nuclear layer cells, or to an increase in the survival of cells in the ganglion cell layer, perhaps displaced amacrine cells, which have a greater dendritic volume than the lost ganglion cells.

Animals↗
PubMed1984

Morphology of identified relay cells and interneurons in the dorsal lateral geniculate nucleus of the rat.

The morphology of neurons in the lateral geniculate nucleus of the rat has been examined in both Golgi impregnated and in horseradish peroxidase (HRP) filled material. Two major classes of neurons are seen in Golgi material which encompass the variety of cells described in previous reports. Cells of one group (class A) are routinely labelled by injections of HRP into the visual cortex or optic radiations. This group also displays some morphological variation which may be related to the presence of parallel information channels in the retino-fugal pathway, but clear subgroups cannot be identified on the basis of morphological criteria alone. Cells of the other group (class B) are not labelled by HRP injections into visual cortex or the optic radiations, and are probably local circuit interneurons.

Animals↗
PubMed1982

Lack of binocularity in cells of area 19 of cat visual cortex following monocular deprivation.

We have studied the visual receptive field properties of neurons in cortical area 19 of monocularly deprived cats. Almost all visually responsive units responded to stimulation of the non-deprived eye only. Receptive field properties assessed through the non-deprived eye were found to be normal. Monocular deprivation appears thus to have sharply reduced the normal binocularity of neurons in area 19. Since the W-cell component of the visual pathways provide the predominant input to area 19, our results suggest that W-cells are vulnerable to environmental manipulation.

Animals↗