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Biomedical subjects

J A Walker

Publications and source records attributed to J A Walker.

At least 109 records · Page 6Linked to original sources
PubMed1982

A disconnection analysis of hippocampal function.

A disconnection analysis determined the extent to which the fornix, hippocampus and entorhinal cortex are components of the same functional system in tasks that require working memory. Preoperatively, rats were trained to perform accurately on a radial arm maze. Then various combinations of unilateral and bilateral lesions were placed in the fornix and entorhinal cortex, either with or without a transection of the hippocampal commissures. When the lesions left intact at least one pathway through the hippocampus interconnecting the fornix and entorhinal cortex, rats performed normally. Either an uncrossed pathway (following a unilateral lesion of the fornix, transection of the hippocampal commissures, and an ipsilateral lesion of the entorhinal cortex) or a crossed pathway (following a unilateral lesion of the fornix and a contralateral lesion of the entorhinal cortex, leaving the hippocampal commissures intact) was sufficient. When the lesions produced a complete bilateral disconnection of the fornix and entorhinal cortex, rats performed poorly. The results indicate that the hippocampal system provides a functional connection between the subcortical structures associated with the fornix and the neocortical structures associated with the entorhinal cortex, and that without this connection normal processing of working memory can not occur.

Animals↗
PubMed1982

Achieving an esthetic appearance with a fixed prosthesis by submucosal grafts.

A review of a new plastic surgical procedure using autogenous grafts of dense connective tissue placed submucosally in anterior areas of collapsed, deformed edentulous ridges has been presented. This technique allows augmentation of an anterior, deformed edentulous ridge to a proper form, color, and texture before placement of a fixed prosthesis. Previous solutions to this problem have resulted in an esthetic compromise at best. Long-term follow-up shows good dimensional stability offering an acceptable solution to a difficult prosthetic problem.

Alveolar Ridge Augmentation↗
PubMed1982

Dialytic ascitic ultrafiltration in refractory ascites.

Nine patients with hepatic cirrhosis and refractory ascites underwent dialytic ascitic ultrafiltration with intraperitoneal reinfusion of the concentrated ascites. Ascites was removed via a peritoneal catheter and ultrafiltered using a hemodialyzer. The concentrate was continuously returned to the peritoneal space. A mean of 4.8 l of protein-free ascitic ultrafiltrate was removed without adverse effects over the course of the 3- to 5-h procedure. Preliminary evidence indicates a potential role for dialytic ascitic ultrafiltration in the management of refractory ascites.

Ascites↗
PubMed1980

Neuroanatomical bases of spatial memory.

Although many brain areas have been implicated in spatial memory processes, recent investigations have focused on the hippocampal formation. The present experiment was designed to determine the relative importance of the hippocampal system as compared to the amygdala, the caudate nucleus, or the frontal cortex. Groups of rats were trained to perform on an eight-arm radial maze and then given lesions in one of these brain areas. The post-operative performance of rats with lesions in the fimbria-fornix was never significantly greater than that expected by chance. In contrast, the performance of rats with lesions in the amygdala, the caudate nucleus or the sucal frontal cortex was not significantly different from that of controls. The performance of rats with lesions in the medial frontal cortex was substantially impaired relative to that of the controls during the first few post-operative test sessions, but improved so that by the end of testing the rats were performing as well as were controls. The recovery of function by the rats with lesions in the medial frontal cortex was a function of experience testing on the maze and not simply the passage of time following surgery. Thus, only rats with functional hippocampal systems were able to perform the maze task accurately while thos rats with lesions in the hippocampal system were not.

Amygdala↗
PubMed1980

The probability of surviving coronary bypass surgery. Five-year results from 1,718 patients.

This study of 1,718 men with bypass surgery from 1970 to 1974 in Milwaukee has indicated that the following factors are significantly associated with five-year survival: left ventricular end-diastolic pressure (LVEDP), plasma cholesterol level, coronary occlusion score, age, and left ventricular function (LVF). The 31 men with a previous stroke had a high risk (five-year survival was 32%). To serve as a guide to patient risk, a logistic model is used to predict five-year survival. These probabilities are tabulated for all combinations of LVEDP, age, LVF, occlusion score, and plasma cholesterol level.

Adult↗
PubMed1979

Circadian rhythm of luminance detectability in the rat.

Rats lived in a visual detection test environment which allowed for around-the-clock measurement of the detectability of a 500 nm stimulus of low luminance. Daily trends in visual sensitivity were compared with a behavioral activity measure, the rate of trial initiations in the self-paced testing procedure. Both variables showed circadian rhythms with periods exceeding 24 hr in the absence of day-night cues. However, the two oscillations were phase-displaced, such that maximal visual sensitivity occurred earlier than did maximal behavioral activity, each day. The temporal organization of visual sensitivity may underlie well-known photic influence on circadian rhythms and photoperiodic behavior.

Animals↗
PubMed1979

Spatial memory deficit following fimbria-fornix lesions: independent of time for stimulus processing.

The present experiment examined the possible role of stimulus processing time in the spatial memory deficit found following fimbria-fornix lesions in rats. Rats were trained preoperatively on a radial arm maze in a procedure that placed them at the end of each arm and confined them there for 30 seconds. This confinement period was markedly longer than the few seconds the rats normally spend there in the usual test procedure. Rats with fimbria-fornix lesions performed no better than expected by chance on the first choice after placements. Although performance on subsequent choices was above chance, this was due to a strong turning pattern; when this pattern was interrupted, performance was no greater than that expected by chance on all choices. These data demonstrate that the deficit in the radial arm maze resulted primarily from a difficulty in spatial memory, rather than from an insufficient time for processing stimulus information.

Animals↗
PubMed1978

Hippocampal connections and spatial discrimination.

Rats were tested in a new spatial discrimination procedure which measured working memory. Following preoperative testing, lesions were placed to disrupt each of the major extrinsic fiber connections of the hippocampal formation. Destruction of the entorhinal area, body of the fimbria-fornix anterior to hippocampus, septum, or postcommisural fornix produced a severe and consistent impairment in performance. Analysis of error patterns indicated that when animals with limbic lesions made errors, they were likely to make these errors in the same sequence as the original choices. These data support the hypothesis that the hippocampus has an important role in the processing of information about spatial location, and that normal performance on this task requires an intact hippocampal circuitry.

Acetylcholinesterase↗
PubMed1978

Dysphagia.

Explore the source record for details and available documents.

Adult↗
PubMed1978

Discussion of sensitivity to preservatives in anesthetics.

A 23-year-old woman with reported sensitivities to several drugs, including anesthetics, requested dental care. Because of the lack of evidence of allergic reactions to lidocaine, it was used in a dental emergency procedure. The patient had an allergic response. In an evaluation by an allergist, an allergy to methyl paraben was detected. The dental practitioner should be aware of possible allergies to preservative agents when a patient has a history of sensitivity to anesthetics. The practitioner's choice of anesthetics and OTC drugs for this type of patient is crucial.

Adult↗
PubMed1977

Studies of an outbreak of acute hepatitis A: I. Complement level fluctuation.

An outbreak of hepatitis A occurred in a rural elementary school in Colbert County, Alabama, in October and November 1972. The outbreak was caused by sewage-contaminated drinking water and involved 49 children and 1 adult. Acute and convalescent serum samples were obtained from the hepatitis patients, and from each of 24 unafflicted matched controls at the same time. Strinkingly, the levels of the third and fourth components of complement (C'3 and C'4) were markedly reduced in the acute samples from the sick children but returned to normal in the convalescent ones; the C'3 and C'4 levels in the healthy matched controls were not reduced. In addition, antigen-antibody complexes were found in convalescent sera from some of the sick children. These findings indicate that immune complexes are present in acture hepatitis A and suggest that the techniques for future virus isolation may have to be altered.

Acute Disease↗