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Biomedical subjects

P Dean

Publications and source records attributed to P Dean.

At least 163 records · Page 9Linked to original sources
PubMed1981

Meridional variation in visual acuity of hooded rats reared in a carpentered environment.

Resolution acuity in people is frequently better for horizontal and vertical gratings than for obliques. An animal model of this oblique effect might be of help in elucidating its underlying neural mechanisms. Rats were chosen because laboratory rats area reared in a 'carpentered environment' apparently similar to those proposed to cause the oblique effect in people, and because electrophysiological experiments suggest that orientation selective units in rats' visual cortex may prefer horizontal and vertical stimuli. The acuity of eight laboratory-reared hooded rats was measured with high-contrast horizontal, vertical, and oblique gratings. The animals learned to detect low-frequency square-wave gratings with slightly fewer errors if they were horizontal or vertical than if they were oblique, but the effects of grating orientation on acuity were not significant. Refraction of the rats' eyes gave no evidence of astigmatism. These results suggest that the rat may not be a good animal model for studying the mechanisms that underlie meridional variations in acuity in people, and raise questions concerning both the neural bases of resolution acuity, and the validity of the 'carpentered environment' hypothesis.

Animals↗
PubMed1980

[Relation between cytomegalovirus infection and the so-called intolerance to azathioprine in renal transplantation].

Renal transplant recipients can develop hepatic function abnormalities or severe leucopenia after transplantation. Generally it is thought to be due to azathioprine intolerance and patients are treated by curtailment of immunosuppressive therapy, being subsequently at risk to lose their allograft because of rejection. Evidence of Cytomegalovirus (CMV) infection is also common after renal transplantation. It is generally thought that the majority of these infections are asymptomatic, but they can be accompanied by leucopenia and/or hepatic function abnormalities. Sixty-nine renal transplant recipients have been studied for at least three months in order to investigate the relationship between CMV and azathioprine intolerance after transplantation. Twenty-five out of 58 patients who underwent seroconversion to CMV (a fourfold or greater rise in titer of CMV antibodies) after transplantation or who had a high CMV titer (greater than or equal to 1 : 16) prior to transplant, developed azathioprine intolerance. None of 11 patients who before renal transplantation had low CMV titers and who did'nt underwent seroconversion did not tolerate azathioprine. Therefore the Authors advance the hypothesis that azathioprine intolerance following renal transplantation can be often due to an asymptomatic and unknown CMV infection.

Azathioprine↗
PubMed1980

Dissociation of d-amphetamine-induced locomotor activity and stereotype behaviour by lesions of the superior colliculus.

To investigate the role of the nigrotectal pathway in the expression of the behavioral effects of increased dopamine transmission, the behavior of rats with lesions of the superior colliculus was studied in open-field and hole-board after systemic administration of d-amphetamine. The rats with collicular lesions had higher locomotor activity scores than controls after saline injections, and after all doses of amphetamine studied (0.5-24 mg/kg): the difference was particularly marked at the highest doses used (16 and 24 mg/kg). Stereotyped behavior, on the other hand, was less pronounced in the rats with collicular lesions, who unlike controls rarely showed stereotyped sniffing, head waving, or forepaw padding while moving about in either apparatus, and never licked or gnawed in the hole-board. This evidence suggests that the nigrotectal pathway may play a role in the expression of some of the stereotyped behaviors observed after the administration of dopamine agonists, but that it is not necessary for the increased locomotor activity produced by such drugs.

Animals↗
PubMed1979

[Internal arteriovenous fistula in the antecubital region].

An assessment was made of the anterior cubital region as a vascular approach for primary and alternative dialysis. Reference is made to 36 fistulae in this area within 44 months' survival in the drawing of various conclusions with regard to surgical technique. End anastomosis of the median, cephalic or basilic vein laterally on the brachial or radial artery is recommended as a means of preventing or cutting down the more common complications associated with internal arteriovenous fitulae. The anastomosis should not exceed 6 mm in diameter. Complications led to loss of fistula function. In many cases, however, they did not prevent employment of the region for alternative approaches, such as superficialisation of the basilic vein or prosthesis.

Arm↗
PubMed1979

Visual cortex ablation and thresholds for successively presented stimuli in rhesus monkeys: II. Hue.

Rhesus monkeys were trained to discriminate successively presented hues. The smallest difference they could reliably detect was determined before and after either inferotemporal ablation, or a lesion intended to remove as much as possible of prestriate area V4 (Zeki, 1973). As a group, the animals with lesions of V4 showed good but not perfect retention of their preoperative performance, and their thresholds were unaltered. The inferotemporal group showed no retention of the simplest successive task, red versus green, but after relearning their thresholds too were unaltered. It appears that animals without inferotemporal cortex can form precise internal representations of hues, and that the basis of the inferotemporal learning impairment may depend upon the nature of the stimuli to be discriminated.

Animals↗
PubMed1979

Flow cytometry of mammalian sperm: progress in DNA and morphology measurement.

Variability in DNA content and head shape of mammalian sperm are potentially useful markers for flow cytometric monitoring of genetic damage in spermatogenic cells. The high refractive index and extreme flatness of the sperm heads produce an optical effect which interferes with DNA measurements in flow cytometers which have dye excitation and fluorescence light collection normal to the axis of flow. Orientation of sperm in flow controls this effect and results in coefficients of variation of 2.5% and 4.2%, respectively, for DNA measurements of mouse and human sperm. Alternatively, the optical effect can be used to generate shape-related information. Measurements on randomly oriented sperm from three mammalian species using a pair of fluorescence detectors indicate that large shape differences are detectable. Acriflavine-Feulgen stained sperm nuclei are significantly bleached during flow cytometric measurements at power levels routinely used in many flow cytometers. Dual beam studies of this phenomenon indicate it may be useful in detecting abnormally shaped sperm.

Animals↗
PubMed1978

Visual acuity in hooded rats: effects of superior collicular or posterior neocortical lesions.

The visual resolution acuity of hooded rats was measured with an avoidance technique, using large, high contrast square-wave gratings of high mean luminance. Measurements were taken before and after ablation of either posterior cortex or the superior colliculus. The cortical lesions included both striate and temporal cortex, and caused retrograde degeneration throughout the dorsal lateral geniculate nucleus. Neither group showed signs of detecting even coarse square-wave gratings when first tested after operation. The animals with collicular lesions quickly relearnt, and their acuity was unaltered. After extensive training 3 out of 4 cortical animals relearnt to detect gratings, and their acuity was reduced to about one-third of its preoperative value. It seems likely that in rats the geniculocortical pathway carries sufficient information for the normal detection of high spatial frequencies. Whether a pathway from superior colliculus to neocortex via a thalamic relay also carries this information is uncertain.

Animals↗
PubMed1978

Visual cortex ablation and thresholds for successively presented stimuli in rhesus monkeys: I. Orientation.

Rhesus monkeys were trained to discriminate gratings of different orientation presented one at a time. The smallest difference they could reliably detect was determined before and after removal of either inferotemporal, foveal prestriate or lateral striate cortex. Four animals with inferotemporal lesions had significantly higher thresholds after operation, which did not improve after extensive practice. Two monkeys with lateral striate ablation, and 1 out of 3 animals with foveal prestriate lesions were also impaired, but improved with practice. Monkeys without inferotemporal cortex may have imprecise internal templates for stimulus orientation, in accordance with the categorisation hypothesis of the inferotemporal defect.

Animals↗