Cerebral oedema in diabetic ketoacidosis.
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Brain Edema↗
Biomedical subjects
P Hammond
Publications and source records attributed to P Hammond.
The development of the low profile Liverpool shear transducer.
The development of a shear transducer, small enough to be worn comfortably under a normal foot, is described, along with a microcomputer controlled data logger. Walks up to 8 s can be recorded and the information downloaded to any IBM compatible computer. Software then allows easy analysis of the peak shear stresses. Calibration curves show the transducers to have a linear response up to 35N and preliminary data from the measurement of shear stresses under the normal foot, and their relationship to vertical pressures, is presented. A patent application (number 9109463.1) has been filed for the device in the United Kingdom.
Adult↗
Binocular phase specificity of striate cortical neurones.
Sensitivity to binocular positional mismatch was evaluated in cat striate cortical neurones, for paired, dichoptically presented, moving sine-wave gratings whose interocular positional phase relationship was varied. Spatial frequency, orientation and velocity were optimized for each neurone. Binocular responses for each spatial phase were compared with monocular stimulation of either eye. Binocular responses ranged from facilitation, through complete or partial summation, to partial or binocular occlusion. Counter to previous reports, all functional classes of neurones (simple neurones; special, intermediate and standard complex neurones) were represented in phase-specific and phase-insensitive groups. Most simple neurones, together with a small minority of standard complex neurones, exhibited near-total phase-sensitive modulation, the most significant new finding being that a minority of simple neurones were relatively insensitive to binocular mismatch. The majority of complex neurones, of all types, showed shallower modulation depths (typically around 30%), distributed in a continuum, with no indication of bimodality. It is concluded that the property of positional sensitivity is not attributable solely to simple neurones; and that positional insensitivity is not seen only in complex neurones. At least some neurones of all functional categories evince either kind of behaviour. These results are interpreted as a two-stage mechanism for convergence and matching of inputs from the two eyes.
Animals↗
Orientation bias of cat dorsal lateral geniculate cells: directional analysis of the major axis of the receptive field centre.
The receptive field centre of cells in the dorsal lateral geniculate nucleus were mapped as iso-sensitivity contours. 94% of the cells were found to have elliptical centres, and analysis of the major axis orientation showed that 29% and 59% of units had their major axis oriented within +/- 20 degrees of the radial and horizontal directions, respectively. The data for Y-cells showed a greater dispersion in their orientation biases (R = 0.57) compared with X-cells (R = 0.79). Nevertheless, a horizontal orientation bias was found in both classes of cells: 47% of Y-cells and 73% of X-cells. In addition, an examination of the major axis orientations was undertaken for cells with receptive field centres located along the radial direction of 35 degrees below the horizontal meridian. In this 35 degree Radial Group a horizontal bias was also confirmed. Analysis of the dispersion of major axis orientations with eccentricity from the area centralis showed a statistically significant decrease in scatter and, hence, indicated an increase in the horizontal bias with eccentricity.
Animals↗
Interocular mismatch in spatial frequency and directionality characteristics of striate cortical neurones.
Spatial-frequency dependence of directional tuning and directional bias was compared, for both eyes, in four previously established discrete classes of binocular feline striate cortical neurones. Two classes (respectively direction-selective or bidirectional at optimal spatial frequency) were directionality invariant at all spatial frequencies. In the remaining two classes, both direction-biased at optimal spatial frequency, directional bias either altered or reversed with change in spatial frequency. In all four classes, the directional tuning of a majority of neurones sharpened at high spatial frequency through either eye, although the bandpass characteristics were sometimes dissimilar for the two eyes. All neurones were of the same type through either eye. Amongst the two classes of direction-biased neurones, the strength of bias was commonly different through the two eyes. Where reversal of bias occurred, that reversal took place at different spatial frequencies for each eye. Thus, the direction and orientation preferences of cortical neurones are fixed at optimal spatial frequency, but their envelope of tuning to a gamut of spatial frequencies is not. These differences are potentially related to binocular coding of visual perspective, including dynamic object rotation in visual space.
Animals↗
On the response of simple and complex cells to random dot patterns: a reply to Skottun, Grosof and De Valois.
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Animals↗
Directionality of cat striate cortical neurones: contribution of suppression.
Direction-selective or direction-biased striate cortical neurones were assessed for absence or incidence of suppression of firing, maximal at 90 degrees or 180 degrees ("null" suppression) to the optimal direction, in 327 neurones recorded from the striate cortex of cats anaesthetized with N2O/O2/halothane. Stimuli were light or dark bars moving over uniform or stationary textured backgrounds; or square-wave gratings of optimal spatial frequency and velocity. Five identified directionality groups were correlated with neuronal class and a range of other receptive field properties. Suppression maximal at 90 degrees to optimum was common amongst direction-biased neurones, rare amongst direction-selective neurones. In the latter group, null suppression (maximal at 180 degrees to optimum) was more prevalent than at 90 degrees. Standard complex cells constituted the majority of complex neurones. They were more commonly direction-biased and less commonly showed suppression than special complex cells. The latter comprised the majority of direction-selective neurones with 180 degrees suppression. Endstopping was seen more frequently in special complex cells, but for each functional class was similarly distributed between the different directionality groups. Based on the mean and mode of partially overlapping distributions, for all neuronal classes direction-selective neurones were more broadly tuned than direction-biased neurones. Special complex neurones were appreciably more broadly tuned than standard complex neurones; those with suppression at 180 degrees were the most broadly tuned neurones in the cortex. Direction-biased neurones with suppression at 90 degrees to optimum were more sharply tuned than those lacking such suppression. Direction-selective neurones had larger receptive fields than direction-biased neurones.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Areal influences on complex cells in cat striate cortex: stimulus-specificity of width and length summation.
In single neurones recorded from the striate cortex of cats anaesthetized with N2O/O2/halothane, receptive field dimensions, length specificity and areal extent of drive were assessed for different classes of visual stimuli. Receptive fields were mapped as rectangular minimum response fields (MRFs). Spatial summation along the axis of preferred orientation was assessed: for moving bars whose length was varied (length summation); and for height variation of a square-wave grating patch against a uniform grey background, or a patch of moving texture against a stationary background of similar texture. In complementary tests a moving square-wave grating background was progressively occluded by a uniform grey foreground mask of variable height; or a mask of stationary texture of variable height progressively occluded a background of moving texture. In parallel measurements, the width of grating or textured patches or masks was varied whilst maintaining height constant. Broadly speaking, the areal influence of each class of stimulus was comparable, and distinct from extra-receptive field phenomena in evoking responses from within the receptive field, but not from surrounding areas. The masking paradigm provided the most sensitive measure of receptive field height and width. However, in some neurones length summation, the degree of end-stopping, and the directional bias depended critically on the stimulus configuration used. Length summation tended to be more dramatic for short bars than for gratings. Length summation for texture was significantly more pronounced than for an oriented bar in special and in intermediate complex neurones. By contrast, endstopping was typically less intense for gratings than for bars, and least pronounced for texture. Because of stimulus specificity, complex neurones assigned to particular functional subgroups on the basis of their response to oriented bars may exhibit quite different patterns of behaviour for other classes of stimuli.
Animals↗
Influence of spatial frequency on tuning and bias for orientation and direction in the cat's striate cortex.
Directionality, orientation and spatial frequency tuning were determined for 108 neurones recorded extracellularly from the striate cortex of anaesthetized cats. Significant sharpening of orientation selectivity with increasing spatial frequency was seen in all simple neurones and the overwhelming majority of complex neurones. Orientation selectivity sharpened in 90 and broadened in only 10 of 100 fully characterized neurones. At least four distinct classes of neurone could be characterized on the basis of their directionality at optimal spatial frequency, and the presence or absence of changes in directionality over a range of spatial frequencies: in two classes, directionality was spatial-frequency dependent; in the remaining two it was invariant. With two exceptions Type A neurones (23 cells) were direction-selective; they were narrowly tuned for orientation and spatial frequency, and their directionality was invariant with spatial-frequency. The majority of neurones (52 cells) were Type B, most of which were direction-biased; their bias for direction varied systematically with spatial frequency. Type C were direction-biased and spatial-frequency selective (5 cells), but showed a clear reversal of bias with change in spatial frequency. Type D, a subset of direction-biased cells, were bidirectional and spatial-frequency invariant (8 cells), with comparable response strengths to motion in two opposing directions at all spatial frequencies. These response types crossed traditional boundaries between categories of simple and complex neurones, assigned on the basis of spatial summation, presence or absence of end-inhibition, and receptive field size.
Animals↗
Selective complexing of acetylcholinesterase in brain by intravenously administered monoclonal antibody.
Rats injected intravenously with monoclonal antibodies reactive with brain acetylcholinesterase (AChE) developed a prolonged depression of plasma AChE without changes in butyrylcholinesterase, lactic acid dehydrogenase, or hematocrit. One antibody, ZR1, accumulated in the brain and spinal cord. Within 3 days of injection, ZR1 bound to most of the AChE in cerebral cortex and certain other regions of the CNS. Examination of the molecular forms of cortical 10S AChE, whereas 4S AChE remained free. In vitro, however, ZR1 bound equally to solubilized 4S and 10S forms. These data provide direct evidence for the compartmentalization of different AChE forms in the CNS, 10S being mainly extracellular and 4S apparently intracellular. Development of a striking and persistent bilateral ptosis within hours of injection suggests that AChE in the autonomic nervous system is also accessible to antibodies and, furthermore, is the site of an immunopathological lesion. This novel model of cholinergic autoimmunity may have relevance for human neurological disorders of unknown etiology.
Acetylcholinesterase↗
The efficacy and safety of GR38032F in the prophylaxis of ifosfamide-induced nausea and vomiting.
The novel 5HT3 receptor antagonist GR38032F was evaluated in the control of emesis induced by the cyclophosphamide analogue ifosfamide. At a dose of 4 mg q 6 h, GR38032F was given to six patients receiving their first dose of ifosfamide infusion (4-6 g/m2 over 24 h); over the 42-h study period, major control of retching and vomiting was achieved in five patients. In the second phase of the study six further patients, in whom high-dose metoclopramide had failed to control emesis, were given 8 mg GR38032F q 6 h; major control of emesis was again observed in five patients. Toxicity attributed to GR38032F was minimal. This selective 5HT3 antagonist is effective and safe in the control of ifosfamide-induced emesis, even in patients resistant to high-dose metoclopramide.
Adult↗
Directional and orientational tuning of feline striate cortical neurones: correlation with neuronal class.
In a subset of 327 simple and complex cells from the striate cortex of cats anaesthetized with N2O/O2/halothane, a range of receptive field properties were compared. These included directional and orientational selectivity, tuning and symmetry; endstopping; receptive field dimensions; length summation; texture sensitivity; ocular dominance; and resting discharge levels. These properties were related to neuronal class (simple or complex) and to the special, intermediate and standard subdivisions of the complex cell category. Special complex cells showed a high incidence of direction selectivity, were less sharply tuned for orientation, more commonly endstopped, more strongly binocular, tended to have higher resting discharge levels and exhibited greater sensitivity to motion of randomly textured patterns than the other classes of neurones. The remaining classes of complex cells, together with simple cells, were more commonly direction-biased or bidirectional, and more selective for orientation than special complex cells. Standard complex cells were marginally more symmetrically tuned for orientation than the other groups. Simple cells represented the most sharply orientation tuned neurones in the cortex; unlike complex cells of all groups they were insensitive to texture motion, generally had lower levels of maintained discharge, and showed least integration of inputs between the two eyes. Assessed by appropriate measures (minimum response fields in special complex cells; length summation in standard complex cells), standard complex cells had significantly larger receptive fields than special complex cells.
Animals↗
Neural motion after-effects in the cat's striate cortex: orientation selectivity.
Single striate cortical neurones were recorded from adult cats, lightly anaesthetized with N2O/O2/halothane. The receptive fields for the dominant eye were subjected to direction-specific adaptation by a square-wave grating of optimal spatial frequency and velocity, drifting continuously in each neurone's preferred direction. Recovery of the neural motion after-effect induced by prior adaptation was assessed with the same grating pattern which now moved alternately in the preferred and opposite directions. In controls the same tests for recovery followed a period of exposure to a uniform field of identical luminance to the adapting grating. Three sets of measurements were made to establish whether the adaptation was orientation- as well as direction-specific. In the first, test grating orientation was maintained constant and optimal for each neurone whilst adapting orientation was systematically varied. In the second, test orientation was varied whilst maintaining adapting orientation constant. In the third set, adapting and test orientations were initially fixed at each neurone's optimum; they were next set, non-optimally to one side of the optimum. Results from the latter configuration were compared with similar tests in which the test grating remained at that non-optimal orientation whilst the orientation of the adapting grating was now altered to a new point on the other flank of each neurone's orientation tuning curve that was matched for strength of adaptation. Thus the degree of adaptation was identical in each case, but zero orientation difference between adapting and test gratings in one case was contrasted with a substantial orientation difference in the other. The results from all three sets of data were unequivocal: in simple neurones, and in standard and intermediate classes of complex neurones, but not in special complex neurones, the sequential effects of adapting gratings on the responses and sensitivity to subsequently presented test gratings were maximal when their orientations were matched and optimal for each neurone, less marked when orientations were matched but non-optimal. In conclusion, adaptation induced by pattern motion was orientation- as well as direction-specific only in standard (length summating) and intermediate complex neurones, and in simple cells; in special complex neurones it was not.
Adaptation, Ocular↗
Ambulatory infusion of bleomycin in patients receiving chemotherapy for germ cell tumors.
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Adult↗
Relationship between cortical lamination and texture sensitivity in complex neurones of the striate cortex in cats.
The present study provides detailed anatomical evidence that the strongly texture-sensitive complex neurones of the cat's striate cortex constitute a discrete subset of all complex neurones, and lie in two bands, deep in lamina III and in lamina V. Physiological properties of simple and complex striate cortical neurones were characterized extracellularly in lightly anaesthetized cats by use of micropipettes filled with 12% Fast Green FCF dye in 2.0 M sodium chloride. Complex neurones were further subdivided on the basis of their length-summating properties for an optimally oriented bar into "standard," "special," or "intermediate" categories and on the basis of their tuning and degree of sensitivity to motion of random texture. Extracellular dye marks were made at strategic locations along each microelectrode track, especially at the site of recording from strongly texture-sensitive complex neurones. Tracks were reconstructed with the aid of the histologically recovered dye marks in sections counterstained with cresyl violet to reveal cortical lamination. The results confirm and refine the inference made by Hammond and MacKay (Exp. Brain Res. 22:427-430, '75; Exp. Brain Res. 30:275-296, '77) and the gross observations from 2-deoxyglucose uptake studies by Wagner, Hoffmann, and Zwerger (Brain Res. 224:31-43, '81) concerning the laminar distribution of texture-sensitive complex neurones in the cat's striate cortex.
Animals↗
Neural correlates of motion after-effects in cat striate cortical neurones: monocular adaptation.
Motion after-effects were elicited from striate cortical cells in lightly-anaesthetized cats, by adapting with square-wave gratings or randomly textured fields drifting steadily and continuously in preferred or null directions. The time-course and recovery of responsiveness following adaptation were assessed with moving bars, gratings or textured fields. Results were compared with controls in which the adapting stimulus was replaced by a uniform field of identical mean luminance, and also assessed in relation to the strength and time course of adaptation. Within 30-60 s adaptation, firing declined to a steady-state. Induced after-effects were direction-specific, and manifest as a transitory depression in response to the direction of prior adaptation, recovering to control levels in 30-60 s. Maximal after-effects were induced by gratings of optimal drift velocity and spatial frequency. With rare exceptions after-effects were restricted to driven activity; no consistent effects on resting discharge were observed. The onset of adaptation, and the recovery period, were more rapid in simple cells, although after-effects of comparable strength were elicited from simple and from standard complex cells. Special complex cells, including many of the more profoundly texture-sensitive neurones in the cortex, were more resistant to adaptation. The results support the conclusion that psychophysically measured adaptation and induced motion after-effect phenomena reflect the known properties of cortical neurones.
Animals↗
Neural correlates of motion after-effects in cat striate cortical neurones: interocular transfer.
Interocular transfer of motion after-effects was assessed in the lightly-anaesthetized feline striate cortex. Neurones were adapted with square-wave gratings of optimal orientation and spatial frequency, or with randomly textured fields, drifting continuously at optimal velocity in their preferred or null directions. Neural after-effects were assessed as consequent changes in directional bias, using similar test patterns swept back-and-forth in the same directions and presented to the same or opposite eyes. All results were compared with controls, embodying similar tests following a period of exposure to a uniform background or stationary textured field. The majority of binocularly-driven complex and simple cells tested evinced positive interocular transfer of after-effects. After-effects, whether elicited monocularly or interocularly, were direction-specific. With gratings, after-effects elicited interocularly were always weaker than those obtained monocularly. After-effects evoked monocularly by texture adaptation were weak in comparison to those evoked by gratings; interocular transfer in this case was negligible. In neurones strongly dominated by one eye, adaptation of the non-driving eye yielded, at best, extremely weak after-effects through the other eye. In purely monocular neurones, no transfer could be induced. These results confirm the expectation that motion after-effects arise cortically rather than precortically. The partial interocular transfer seen in binocularly-driven cortical cells suggests that these neurones represent a second-stage processing of inputs from lower-order complex (or simple) cells, themselves driven monocularly or strongly dominated by one eye.
Animals↗
Butyrylcholinesterase in human brain and acetylcholinesterase in human plasma: trace enzymes measured by two-site immunoassay.
Enzyme-linked immunosorbent assays for acetylcholinesterase (AChE) and for butyrylcholinesterase (BuChE) were markedly more specific than conventional assays using selective enzyme inhibitors. The new assays were used with blood and brain samples containing traces of one enzyme dominated by large amounts of the other. The results showed that human plasma does contain AChE (8 ng/ml), even though its major cholinesterase is BuChE (3,300 ng/ml). BuChE immunoreactivity was not detected in human red blood cells but occurred in all brain regions. The cerebellum was the richest region tested (540 ng of BuChE/g of tissue), whereas the cerebral cortex was the poorest (240 ng of BuChE/g). However, because of the small local AChE content (99 ng/g), BuChE was the major cortical cholinesterase. The picture was reversed in the putamen, where BuChE immunoreactivity (340 ng/g) was far outweighed by that of AChE (6,100 ng/g).
Acetylcholinesterase↗