Search PubMed⌕ Search

Biomedical subjects

M G Stewart

Publications and source records attributed to M G Stewart.

At least 91 records · Page 5Linked to original sources
PubMed1995

Clustering and co-localization of immunogold double labelled neural cell adhesion molecule isoforms in chick forebrain.

A quantitative immunoelectron microscopic study was carried out in the intermediate portion of hyperstriatum ventrale of chick forebrain (a region exhibiting learning-related morphological plasticity) in order to examine the fine distribution of the neural cell adhesion molecule (N-CAM). Antibodies against alpha 2,8 polysialic acid (PSA), characteristic for embryonic N-CAM, and those against the protein backbones of all N-CAM isoforms were sequentially labelled (post-embedding) with 5- and 15-nm gold particles, and binding to their epitopes was analyzed using the statistics of point processes. The results showed that: (1) PSA tends to form clusters (up to 200 nm in size), in contrast to the protein backbones of all N-CAM isoforms, and (2) the two tissue bound antibodies are co-localized spatially in clusters of sizes up to 100 nm. The data suggest that there is a spatial sub-cellular domain enriched in both PSA and protein isoforms of N-CAM.

Animals↗
PubMed1995

Nontuberculous mycobacterial mastoiditis.

Although nontuberculous mycobacterial (NTM) infections are recognized as an important cause of cervicofacial lymphadenopathy in children, NTM mastoiditis is rare. Further, NTM mastoiditis may be difficult to distinguish clinically from tuberculous mastoiditis since both may present with chronic, painless otorrhea and exuberant middle ear granulation tissue. The treatment of tuberculous mastoiditis is antituberculosis chemotherapy; however, most NTM infections are resistant to antituberculous agents, and the preferred treatment of NTM mastoiditis is mastoidectomy. We report a recent case of mastoiditis caused by Mycobacterium avium complex in an infant who presented with a temporal bone mass.

Child↗
PubMed1995

Late proptosis following orbital floor fracture repair.

OBJECTIVE: Late proptosis is an unusual complication of orbital floor fracture repair. We report 12 cases and propose a classification scheme and differential diagnosis for this rare complication. DESIGN: Retrospective multi-institutional case review. SETTING: Two tertiary referral centers. RESULTS: We report 12 cases of late proptosis following orbital floor fracture repair. Causes of late proptosis include peri-implant inflammation, capsular hemorrhage, gelatin film cyst, implant infection, sino-orbital fistula, intraorbital sinus mucocele, and carotid-cavernous fistula. We describe the treatment of each case individually; in most cases, the implant was removed. All 12 patients had a satisfactory outcome after treatment. CONCLUSIONS: Proptosis presenting 2 months or more after orbital floor fracture is rare. We classify the origin of late proptosis into three groups: implant, sinus, and neurovascular. We describe the diagnosis and management of this unusual complication.

Adult↗
PubMed1995

Quantification of dendritic spine populations using image analysis and a tilting disector.

A series of image analysis routines, stochastic geometry methodology, and a design-based stereological procedure have been developed to quantify objectively the length, layout, and the true density of neuronal dendritic spines observed at the light (or confocal) microscope level. First, the image of a dendritic fragment of interest (in the plane of view) is scaled to a standard brightness scale, and the dendritic profile is separated from the background using a computerized thresholding algorithm that analyzes the histogram of grey levels. Secondly, the resulting binary image of the dendrite is transformed to a midline skeleton that underlies the dendritic geometry. Thirdly, skeletal branch lengths are directly computed (in pixels), thus giving objective measures of visible spine lengths and inter-spine distances along the dendritic stem. These raw data are the basis for (1) an estimation of the distribution of 3D spine lengths, and (2) a nearest neighbour analysis of the spine layout along the dendrite. A design-based stereological routine, the tilting disector, is suggested for unbiased estimation of the true (3D) density of spines along dendrites. The routine involves tilting the dendritic fragment of interest around its longitudinal axis for a known angular sector and scoring the number of spines seen in one angular position and unseen in the other position. Data from a study of neuronal dendrites in the chick forebrain are presented.

Algorithms↗
PubMed1995

3-dimensional morphometry of intact dendritic spines observed in thick sections using an electron microscope.

An experimental technique is described which allows observation of fixed neuronal dendrites at magnifications from 10-12 K. The method uses 4-7-microns-thick sections of Epon-embedded tissue with nerve cells that are first impregnated by the rapid Golgi technique and then stained with gold particles/aggregates using a modified gold-toning procedure. A relatively high acceleration voltage (200 kV) is employed to observe in fine detail the dendritic fragments of interest at different angular positions in space, by using a eucentric goniometer stage with a tilt angle of +/- 45 degrees. Image analysis methodology is proposed which permits estimation of 3-dimensional (3D) lengths and of the volume of observed intact dendritic spines. The advantages of the technique with respect to 3D reconstruction methodology are discussed.

Animals↗
PubMed1995

Population trends in the fine spatial re-organization of synaptic elements in forebrain regions of chicks 0.5 and 24 hours after passive avoidance training.

Two regions in the forebrain of domestic chicks (Gallus domesticus), the intermediate and medial hyperstriatum ventrale and the lobus parolfactorius, have previously been shown to be important centres of biochemical, pharmacological and physiological change following one-trial passive avoidance training. The purpose of the present study was to examine, at the electron microscopic level, the fine spatial re-arrangement of synaptic structures in the intermediate and medial hyperstriatum ventrale (at 30 min), and in the lobus parolfactorius (at 24 h), post-training using comprehensive biometrical designs, image analysis and stochastic approaches. In intermediate and medial hyperstriatum ventrale, no significant differences in the numerical density of synapses either between control and trained chicks, or between hemispheres, were revealed using the disector method. However, after training, a nested-ANOVA demonstrated an increase in the thickness of pre- and post-synaptic electron densities (estimated via image analysis) only in the left intermediate and medial hyperstriatum ventrale, whereas synaptic apposition zone profiles increased in length bilaterally. In presynaptic terminals from the intermediate and medial hyperstriatum ventrale, stochastic analysis revealed that training resulted in the re-distribution of synaptic vesicles between two spatial pools relative to synaptic apposition zones, in both hemispheres producing a large number of synaptic vesicles closer to synaptic apposition zones; a nearest neighbour analysis of synaptic apposition zone profiles indicated that the lateral shape of the synaptic apposition zone after training is more complex in both hemispheres. In the lobus parolfactorius at 24 h post-training the main changes in synaptic fine structure involved a shift of synaptic vesicles away from synaptic apposition zones in the right hemisphere with the distance between synaptic apposition zones decreasing; in the left lobus parolfactorius, synaptic apposition zones became more regular/round in shape with a greater distance between them after training. These data suggest that the initial acquisition of memory involves population changes in the fine spatial organization of synaptic vesicles and synaptic apposition zones in synapses in the intermediate and medial hyperstriatum ventrale, which indicate a possible tendency towards greater synaptic efficacies. These changes are as dynamics as the molecular changes which have hitherto been considered the preserve of short-term correlates of memory formation.

Animals↗
PubMed1995

A comprehensive characterization of lymphoepithelial cyst associated with the pancreas.

BACKGROUND: Lymphoepithelial cyst of the pancreas is a rare but distinctive cystic lesion lined by a mature, keratinizing squamous epithelium and surrounded by lymphoid tissue. METHODS: To gain more insights into this entity, we describe 5 examples of lymphoepithelial cyst of the pancreas (2 of which were briefly described before) and compare them with similar cases in the literature for a total of 19 cases. RESULTS: The male:female ratio was 16:3; patients' ages ranged from 32 to 73 years (mean and median 51). The lymphoepithelial cyst was incidentally found at autopsy in 4 patients (21%) or during evaluation for unrelated diseases in another 4 patients (21%). In the remaining 11 patients, the cyst was associated with abdominal pain in 9 (47% of all patients), nausea/vomiting in 3 (16%), diarrhea in 1 (5%), and nonspecific systemic symptoms in 6 (32%) (some patients had more than 1 associated symptom). Computed axial tomography scan, with or without ultrasonographic study, was done in 16 cases and uniformly displayed a single, well-circumscribed, cystic mass protruding beyond the surface of the pancreas; the rest of the pancreas was normal. Intraoperatively, the cyst was readily apparent once the lesser sac was entered and the surface of the pancreas exposed; the cyst was located at the head (3 cases), neck (1 case), body (6 cases), and tail (9 cases). Surgery was done for all 15 clinical cases and included local excision of the cyst with a thin rim of attached, underlying pancreas (6 cases), or distal pancreatectomy with (4 cases) or without (3 cases) splenectomy. Follow-up information, available in 7 cases, showed that all symptoms disappeared and the patients were alive and well up to 6 years after surgery. CONCLUSIONS: This rare cyst of the pancreas has a uniform and characteristic clinicopathologic profile, enabling easy and accurate diagnosis. Although the histogenesis of lymphoepithelial cysts is not known, they are benign and can be cured by local excision.

Adult↗
PubMed1994

Training in chicks alters PSA-N-CAM distribution in forebrain cell membranes.

The intermediate and medial hyperstriatum ventrale (IMHV) in the chick is involved in memory formation following one-trial passive avoidance training. Possible links between neural cell adhesion molecule (N-CAM) distribution and memory consolidation were examined in an immunoelectron microscope study of IMHV 6 h after training. An antibody against alpha 2,8 polysialic acid (PSA), characteristic for embryonic N-CAM, and one against the protein backbones of N-CAM were labelled (post-embedding), separately, with 15 nm immunogold, and binding to their epitopes was analysed using the statistics of point processes. No difference in labelling levels between control and trained chicks, for either antibodies, was found, both groups of birds showing that cell membrane regions are 10-30 times more enriched in N-CAM isoforms, and have a two-fold greater proportion of PSA-N-CAM, than tissue as a whole. However, 375-400 nm regular arrays of labelled PSA-N-CAM were revealed statistically in cell membranes of control, but not trained, chicks, which may be related to the possible involvement of such membrane PSA domains in memory-related neuroplasticity.

Animals↗
PubMed1994

Connectivity of the lobus parolfactorius of the domestic chicken (Gallus domesticus): an anterograde and retrograde pathway tracing study.

In 1-week-old domestic chicks, the connectivity of the lobus parolfactorius (LPO), part of the avian basal ganglia, was investigated using Phaseolus vulgaris leucoagglutinin and horseradish peroxidase for anterograde and retrograde pathway tracing, respectively. Tyrosine hydroxylase immunocytochemistry was applied in combination with Phaseolus lectin to assess the overlap between LPO efferents and diencephalic and mesencephalic catecholamine centres. Anterograde projections from LPO were detected in the hyperstriatum, neostriatum, and paleostriatum. Intranuclear connections were also apparent within the LPO. Descending LPO efferents innervated the lateral mammillary and intramedial nuclei and the dorsomedial thalamic complex. Fibres from LPO were observed in the tectal gray, substantia nigra, area ventralis tegmentalis of Tsai, and the adjacent nucleus mesencephalicus profundus. Further caudally, projections from LPO reached the nucleus papillioformis, locus coeruleus, and subcoeruleus ventralis. LPO efferents were coextensive with tyrosine hydroxylase-positive cells in the nuclei mamillaris lateralis and intramedialis of the hypothalamus, area ventralis tegmentalis, substantia nigra, locus coeruleus, and subcoeruleus ventralis of mesencephalic and pontine tegmentum. Close contacts between LPO fibres and catecholamine cells were visible in the nigra and the area ventralis tegmentalis. Retrograde labelling from LPO was found in the archistriatum, dorsomedial thalamic complex, nuclei lateralis anterior and superficialis parvicellularis thalami, substantia nigra, central gray, area ventralis tegmentalis of Tsai, and locus coeruleus and in cells dorsal to the decussation of brachium conjunctivum. Reciprocal connections were verified between the LPO and the following areas: dorsomedial thalamic complex, central gray, substantia nigra, area ventralis of Tsai, and locus coeruleus.

Afferent Pathways↗
PubMed1994

Dendritic spine density in the lobus parolfactorius of the domestic chick is increased 24 h after one-trial passive avoidance training.

One to three day old chicks spontaneously peck at small objects. When presented with a chrome bead coated with the bitter tasting substance methyl anthranilate (MeA), chicks peck once, display a characteristic disgust response and subsequently avoid a similar bead. Chicks that are trained on a water coated bead continue to peck a similar bead on retrial. Twenty four hours after training on this one-trial passive avoidance paradigm, chicks were tested for retention. The brains of chicks displaying the correct behavioural response (> 90%) were removed and the lobus parolfactorius from each hemisphere was dissected from the brain and impregnated using a rapid Golgi technique. Analysis of large multipolar neurones by centrifugal dendritic branch order showed that there were significantly more spines on all orders examined in the left hemispheres of MeA-trained chicks compared to water-trained control chicks. Significantly higher spine densities were also found on 4th and 5th order branches of neurones in the right lobus parolfactorius of MeA-trained chicks compared to water-trained chicks. No significant difference in dendritic length was observed. These results suggest that substantial plasticity occurs in post-synaptic structures in the lobus parolfactorius following passive avoidance training. It is suggested that this plasticity is related to processes involved in long term information storage.

Animals↗
PubMed1994

Human papillomavirus in laryngeal and hypopharyngeal carcinomas. Relationship to survival.

OBJECTIVE: To determine the relationship between human papillomavirus (HPV) DNA detection in upper aerodigestive tract malignancies and patient outcome. DESIGN: Archival paraffin-embedded specimens from 78 previously untreated patients with squamous carcinomas of the larynx and hypopharynx were pathologically verified and analyzed by polymerase chain reaction for detection of HPV DNA. Charts were independently reviewed and coded until final analysis. SETTING: The University of Texas M. D. Anderson Cancer Center, Houston, a tertiary cancer referral center. RESULTS: DNA was successfully extracted from 65 archival patient samples (83%). The mean (+/- SEM) duration of follow-up for these patients was 42 +/- 21 months. Thirty specimens (46%) exhibited detectable HPV DNA. Detection of HPV was significantly related to decreased survival, independent of disease stage. Log rank testing revealed that HPV detection, pathologic vascular invasion, and nodal status were the most significant predictors of death of disease. CONCLUSIONS: Laryngeal and hypopharyngeal carcinomas with detectable HPV may represent a biologically distinct subset of tumors that carry a poorer prognosis than do cancers with no detectable HPV.

Adult↗
PubMed1994

Nontuberculous mycobacterial infections of the head and neck.

OBJECTIVE: To review the treatment and outcome of patients with nontuberculous mycobacterial infections of the head and neck. DESIGN: Retrospective examination of the medical records of patients treated by several surgeons during a 5-year period with a minimum 6-month follow-up. SETTING: Large teaching children's hospital. PATIENTS: Twenty-six children hospitalized for treatment of nontuberculous mycobacterial infections of the head and neck. MAIN OUTCOME MEASURES: Resolution of infection, recurrence, and need for additional surgical intervention for cure. RESULTS: Eleven patients initially were treated by incisional biopsy or incision and drainage procedures; eight patients developed recurrence or a draining sinus tract, necessitating a second surgical procedure. In contrast, 15 patients initially underwent complete excision; only one developed a recurrence (P < .01). Thus, eight (31%) of 26 patients required at least two surgical procedures owing to inadequate initial treatment. CONCLUSIONS: Excisional biopsy is both the diagnostic procedure and treatment of choice for nontuberculous mycobacterial adenitis.

Adolescent↗
PubMed1994

Atypical and malignant lipomatous lesions of the head and neck.

Although liposarcoma is the second most common soft-tissue sarcoma in adults, the incidence of liposarcoma of the head and neck is low. There are only 83 reported cases of head and neck liposarcoma. We report four cases of atypical and malignant lipomatous lesions of the head and neck and discuss their histologic classification and treatment implications. The histologic nature of liposarcoma is correlated clinically with treatment outcome. Recently, many authors have adopted the term atypical lipoma to describe well-differentiated lipomatous lesions in superficial extremity locations because of their tendency toward local recurrence only, without metastases or patient mortality. Although we accept the classification atypical lipoma for superficial, well-differentiated lesions, we believe that histologically similar lesions in nonsuperficial locations in the head and neck are best designated "well-differentiated liposarcoma."

Adult↗
PubMed1994

Transient cerebral ischemia disrupts performance on a one-trial passive avoidance task in the domestic chick and is associated with neuronal degeneration in the central nervous system.

We have examined the effects of transient cerebral ischemia on performance of a one-trial passive avoidance task by chicks. Transient forebrain ischemia was induced by bilateral carotid artery occlusion for a period of 10 min. In one experimental group, ischemia was produced prior to training on the avoidance task whereas in the other group ischemic intervention was not made until 3 h after initial training. Sham-operated groups were matched to each of the experimental groups. All four groups were tested for retention of the avoidance response 24 h post-surgery. The sham-operated birds and those receiving post-training ischemia showed good retention of the avoidance response, whereas in birds which received ischemia prior to training there was significant amnesia. Neuronal damage, determined qualitatively using a silver impregnation method, was observed in several forebrain regions including the hippocampus, hyperstriatal regions, paleostriatum primitivum, ventral archistriatum, and lateral corticoid area. Damage was also observed in the Purkinje cells of the cerebellum. The behavioural and anatomical effects of transient forebrain ischemia have not been previously investigated in an avian species and the finding of significant amnesia for a learning task following ischemia is in good agreement with several behavioural studies in mammals.

Animals↗
PubMed1994

Life-threatening presentations of fibrovascular esophageal and hypopharyngeal polyps.

Giant fibrovascular polyps of the esophagus and hypopharynx are benign tumors of the upper digestive tract. Although a rare cause of asphyxiation, laryngeal impaction by a regurgitated polyp of the esophagus may be the initial symptom that brings the patient to request medical attention. Two new cases of giant fibrovascular polyps with dramatic and potentially life-threatening presentations illustrate the unpredictable behavior of these unusual tumors. Both patients presented to the emergency center with a history of coughing and eructation followed by temporary airway obstruction that was relieved by clenching a regurgitated fleshy mass between the teeth. Diagnostic and therapeutic intervention requires aggressive airway management, radiographic and endoscopic evaluation, and definitive surgical treatment. Tracheotomy was required in one patient, and successful endotracheal intubation provided satisfactory airway control in the second. Esophagoscopy revealed the origin of both tumors to be near the cricopharyngeal muscle. Complete surgical excision was curative in both cases.

Aged↗
PubMed1994

Head and neck manifestations of erythema multiforme in children.

Erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis are related disorders of skin and mucous membranes, which are typically associated with antecedent medication use or infection. We review 108 cases of erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis from Texas Children's Hospital, Houston, Texas, from 1981 to 1991, and illustrate the characteristic skin and mucosal lesions. In addition, we describe in detail two unusual cases requiring intensive airway management. Head and neck manifestations were present in 4 of 79 patients (5%) with erythema multiforme and 26 of 28 patients (93%) with Stevens-Johnson syndrome. In Stevens-Johnson syndrome, mucosal involvement of the lip (93%), conjunctiva (82%), oral cavity (79%), and nose (36%) were most common. Antecedent medication use was identified in 59% of erythema multiforme patients and 68% of Stevens-Johnson syndrome patients. We note a striking increase in the number of cases in our series caused by cephalosporins. Fifty percent of Stevens-Johnson syndrome patients required supplemental hydration or alimentation because of the severity of the oral cavity involvement. The head and neck mucosal manifestations largely respond to local care, and the routine use of prophylactic antibiotics or systemic steroids is not recommended.

Adolescent↗