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Biomedical subjects

M G Stewart

Publications and source records attributed to M G Stewart.

At least 109 records · Page 6Linked to original sources
PubMed1993

Loss of glutamate immunoreactivity from mouse first somatosensory (SI) cortex following neonatal vibrissal lesion.

Whisker follicles were surgically ablated (lesioned) on two entire rows (B and C) of the left snout of two groups of Swiss mice, in the first 2 days after birth (neonatally lesioned) with the animals being allowed to survive for 4 weeks. In the second group at 8 weeks of age (adults), the whisker follicles of rows B and C were similarly lesioned and a survival period of 3 days allowed. Glutamate-immunoreactivity (Glu-IR) was examined in tangential sections of the first somatosensory (SI) 'barrel' cortex of these two groups (at which time it was also confirmed that the follicles had not regrown). In the neonatally lesioned mice, barrel rows B and C were more poorly defined in the right (experimental) hemisphere sections and a semi-quantitative study showed that there was a decrease in Glu-IR cell number (up to 41%) in rows B and C of the right hemisphere compared to the spared barrel rows (A and D). The loss appears to occur over almost the entire area of each deprived barrel rather than being confined to the sides or hollows. In contrast to neonatally lesioned animals, the barrels of the adult-lesioned mice appeared intact and visually similar in both the experimental (right) and control hemispheres (left). The only notable change in Glu-IR observed in the adult-lesioned animals was a decrease of 38% in the number of Glu-IR cells in the sides between the two deafferented rows of barrels (B and C), compared to the cell number between the unaffected barrels (D and E), a change also seen in the neonatally lesioned mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Quantitative autoradiographic demonstration of changes in binding to delta opioid, but not mu or kappa receptors, in chick forebrain 30 minutes after passive avoidance training.

Day-old domestic chicks (Gallus domesticus) were trained on a one-trial passive avoidance task in which the aversive stimulus was a bitter tasting substance, methylanthranilate. Thirty minutes later, localization of binding of highly specific ligands (([D-Ala2, Gly-ol]-enkephalin ([3H]DAGO) for mu (mu) receptor sites, [D-Pen2,D-Pen5]-enkephalin ([3H]-DPDPE) for delta (delta) sites, and [3H]-U- 69593 for kappa (kappa 1) sites) to opioid receptors in various regions of the forebrain of methyl-anthranilate trained (M-) and control (water trained (W-)) chicks was determined using quantitative receptor autoradiography. Significant differences in binding to delta ([3H]-DPDPE), but not mu or kappa receptors, were found in several regions of the forebrain, of trained compared to control chicks. There were decreases in binding in the hyperstriatum dorsale of the left hemisphere (14%) and a decrease in binding in the lateral hyperstriatum ventrale of the right hemisphere (14%). However, significant increases were observed in delta binding in the paleostriatum augmentatum of the right hemisphere (16%) and the lobus parolfactorius of both hemispheres (left, 20%; right, 21%). In a control experiment designed to determine whether the taste of methylanthranilate contributed to the increase in 3H-DPDPE binding, there was no significant difference in the level of binding between blindfolded birds in which methylanthranilate was placed in the beak, and blindfolded birds in which water was placed on the bead and inserted into the beak. These findings demonstrate that changes occur in an opioid receptor sub-type in specific regions of forebrain of the chick following passive avoidance training which may be related to events concerned with the process of memory formation.

Animals↗
PubMed1993

Spatial re-arrangement of the vesicle apparatus in forebrain synapses of chicks 30 min after passive avoidance training.

A quantitative ultrastructural study of synapses was carried out in the forebrain IMHV (intermediate and medial hyperstriatum ventrale) of 1-day-old chicks 30 min after training to avoid pecking at a bead coated with methyl anthranilate. In 10 birds (5 control and 5 trained), the length, curvature and the number of the synaptic active zone profiles were measured, and the active zone profile length was observed to increase in trained chicks. The spatial arrangement of synaptic vesicles with respect to the active zone was examined using a statistical stereological approach. This showed that vesicles are not located uniformly but accumulate in two spatial pools which appear to rearrange following training, with a greater number of vesicles near the active zone. These data may reflect subtle changes in the functional efficacy of synapses in the IMHV in the initial phases of memory formation.

Animals↗
PubMed1993

Long-term increases in the numerical density of synapses in the chick lobus parolfactorius after passive avoidance training.

Passive avoidance training has been shown to cause an increase in synaptic density (Nvsyn) in the lobus parolfactorius (LPO) of the one-day old chick. The present study was conducted to investigate the time-course over which this plastic change takes place. Two groups of chicks were trained to peck at either a water coated bead (Control) or a methyl-anthranilate coated bead (M-trained). M-trained chicks showed avoidance responses when offered a similar but dry bead, 30 min later. Right and left hemisphere LPOs were obtained at intervals of 1, 6, 12, 24 and 48 h after training. Synaptic counts were made using a 3-dimensional stereological probe; the 'dissector'. A significantly larger mean Nvsyn (31%) was found in the left hemisphere of M-trained chicks 24 h after training, compared with Control chicks, and the difference fell to 10% at 48 h post-training. M-trained chicks also had a greater Nvsyn (17%) in the right hemisphere at 48 h post-training. The bilaterality of these findings is of particular interest, since unilateral lesions of the LPO fail to produce amnesia for the avoidance task. The importance of these results in the process of memory formation is discussed.

Analysis of Variance↗
PubMed1993

7-Chlorokynurenate, an antagonist of the glycine binding site on the NMDA receptor, inhibits memory formation in day-old chicks (Gallus domesticus).

Unilateral intracranial injection into the left intermediate and medial hyperstriatum ventrale of 100 mumol.liter-1 7-chlorokynurenate, a highly selective antagonist of the glycine site on the N-methyl-D-aspartate receptor, prevents acquisition of memory for one-trial passive avoidance training in day-old chicks, in which the aversive stimulus is an unpleasant tasting substance, methyl anthranilate. Injections were given 30 min pretraining and the chicks were tested 30 min or 1 or 3 h post-training. Unilateral injections into the left intermediate and medial hyperstriatum ventrale were found to significantly block memory acquisition when birds were tested at all three time points, but unilateral injections in the right intermediate and medial hyperstriatum ventrale had no significant effect. Bilateral injections did not significantly increase the memory block. Injections of 7-chlorokynurenate given 5 min post-training failed to produce amnesia for the avoidance task when chicks were tested either 30 min or 1 h after training.

Animals↗
PubMed1993

Pediatric actinomycosis of the head and neck.

Actinomycosis is a rare soft tissue infection caused by a gram-positive, anaerobic bacteria. It is seen only approximately once a year in major medical centers, and is rarer still in the pediatric population. About 50% of all cases of actinomycosis involve the head and neck. The organism is very difficult to isolate in culture and the differential diagnosis is extensive, prompting one reviewer to name actinomycosis the "masquerader" of the head and neck. We review three cases of actinomycosis over the past ten years (1981-1990) at Texas Children's Hospital, Houston, Texas.

Actinomyces↗
PubMed1993

Effect of handedness on the middle latency auditory evoked potential.

The effect of handedness on the middle latency response of the auditory evoked potential was investigated by testing 16 right-handed and 16 left-handed young adults with normal hearing. Each handedness group contained eight males and eight females. Peaks PO, N(a),P(a),Nb,and Pb showed a progressive, statistically significant latency increase in left-handed subjects when compared with right-handed subjects. The latency difference was 1.1 ms at peak P(a) and 3.6 ms at peak Pb. There was no significant latency difference between males and females. Topographic brain mapping showed that the distribution of positivity of wave Pb was similar to the distribution for wave P(a) in both right- and left-handed subjects.

Acoustic Stimulation↗
PubMed1993

Short-term changes in the numerical density of synapses in the intermediate and medial hyperstriatum ventrale following one-trial passive avoidance training in the chick.

Previous ultrastructural studies using stereological counting techniques, based on assumptions regarding shape, size, and orientation of synapses, have suggested synaptic remodeling occurred at least 24 hr after one-trial passive avoidance training in day-old chicks. The present study estimates the mean synaptic density (Nv syn) in a region of the chick forebrain known to be involved in memory formation, the intermediate and medial hyperstriatum ventrale (IMHV), 1 and 24 hr following one-trial passive avoidance training. A stereological technique, the "disector," that makes no assumptions about size, shape, and orientation of synapses was used in the synaptic analyses. The density of axospinous synapses increased by approximately 77% at 1 hr posttraining in the right IMHV of chicks (M-trained) that learned to avoid a bitter-tasting bead, compared to those (W-trained controls) that peck a water-coated bead. A measure of the postsynaptic density size, the mean projected height of synapses (H), was 57% smaller 1 hr posttraining in the right IMHV of M-trained chicks. These differences were not found at 24 hr posttraining. We suggest that structural modification of synapses may be a key part of the processes involved in short-term memory formation.

Animals↗
PubMed1992

Structural asymmetry in the thalamofugal visual projections in 2-day-old chick is correlated with a hemispheric difference in synaptic density in the hyperstriatum accessorium.

Differences in visual discrimination ability between the left and right eyes of chicks, which are most prominent in young males, may result from a structural asymmetry in the organization of the visual projections from the thalamus to the visual Wulst. This asymmetry in projections is no longer present by 21 days in males when the contralateral projections from the right thalamus to the left hyperstriatum have developed. Since the asymmetry of the thalamo-hyperstriatal system results in a differential input of fibres to regions of the hyperstriatum which in turn project to the hyperstriatum accessorium (HA), one of the major differences expected within this region would be an asymmetry in the numerical density of synapses (Nv.syn/microns3). When this was examined in the hyperstriatum accessorium of 2-day-old male chicks, the density of synapses in the right HA was found to be significantly higher (22%, P less than 0.05) than in the left HA. The consequences of this asymmetry in synaptic density in the HA could be widespread and influential within the chick visual system.

Animals↗
PubMed1992

Examining the effects of amplification on the nasalance ratios of hearing-impaired children.

Nasalance scores were obtained for hearing-impaired children. Data speech samples obtained with and without personal amplification were compared for differences between gender and chronological age. Statistical comparisons are presented for each amplification condition. Significant differences for nasalance in the aided and unaided conditions were not evident although a high, positive correlation between conditions was reported. Nasalance, age and gender were not positively related. Dispersion of the nasalance scores for the two speech conditions was suggestive of persisting difficulties with velopharyngeal control during speech activities; mean scores revealed objective evidence of hypernasality.

Adolescent↗
PubMed1991

Loss of gamma-aminobutyric acid (GABA) immunoreactivity from mouse first somatosensory (SI) cortex following neonatal, but not adult, denervation.

Whisker follicles were surgically ablated (lesioned) on two entire rows (B and C) of the left snout of two groups of Swiss mice, in the first 2 days after birth, and in the second group at 8 weeks of age (adults). Two months after surgery GABA-immunoreactivity (GABA-IR) was examined in tangential sections of the first somatosensory (SI) 'barrel' cortex of these two groups (at which time it was also confirmed that the follicles had not regrown). In the adult-lesioned mice all of the barrels appeared intact and visually similar in both the experimental (right) and control (left) hemispheres. The staining pattern of immunopositive cells and puncta was qualitatively similar to that which we have described previously. However, in the neonatally-lesioned mice barrel rows B and C were not visible in the right hemisphere sections and there was a marked reduction in GABA-IR, with fewer immunopositive cells. Many of those that did show GABA-IR stained only weakly and the puncta were also fewer in number than in the left (control) hemisphere where the GABA-IR pattern and staining intensity was normal.

Aging↗
PubMed1991

An immunohistochemical study of spontaneous lymphomas in the C57B1/10J mouse.

Immunocytochemistry was used to examine 26 cases of composite lymphoma in the mouse mesenteric lymph node. The diagnosis was made by light microscopic criteria. A selection of polyclonal antibodies to light (Kappa and Lambda) and heavy chain (IgD, IgM, IgC, IgA, IgE) antigens was used together with three monoclonal antibodies to T cells, B cells (HLA-DR) and macrophages. Twenty lymphomas were classified as B cell and six as T cell. The B cells were subdivided into IgM and IgD (five), IgD (five), IgM (three) and IgA (one), three undifferentiated and, in three, there was insufficient tissue for further typing. There did not appear to be any correlation between the morphological appearance and the immunophenotype.

Animals↗
PubMed1991

An immunohistochemical study of spontaneous histiocytic tumours in the rat.

Immunocytochemistry was used to examine 18 cases of rat fibrous histiocytic tumours (11 malignant; seven benign). The diagnosis was made by light microscopic criteria and all cases were categorized as pleomorphic-storiform. A selection of polyclonal antibodies to histiocytic, muscle, neural and mesenchymal antigens was used. Fifteen tumours were positive with alpha 1-antitrypsin, four with alpha 1-chymotrypsin, ten with muramidase, five with desmin, 15 with neuron-specific enolase, 14 with S100, one with glial fibrillary acid protein and 12 with vimentin. Many tumours expressed several antigens, highlighting the confusion which has arisen with regard to the histiogenesis of fibrous histiocytic tumours in man, and supporting the concept of differentiation from a primitive mesenchymal common precursor able to differentiate in several directions.

Animals↗
PubMed1991

Application of nasometry to speech samples of hearing-impaired children.

Nasalance measurements from speech samples of 19 hearing-impaired children (12 boys, 7 girls, of M age 8.0 yr.) were computed via a Nasometer 6200 for three speaking conditions: unaided, aided, and FM amplification. The nasalance scores for each condition were compared with the device norms. Scores for each condition were correlated and then ranked by age for additional comparisons.

Child↗
PubMed1990

Distribution of mu, delta, and kappa opioid receptor binding sites in the brain of the one-day-old domestic chick (Gallus domesticus): an in vitro quantitative autoradiographic study.

Three highly specific opioid ligands--[D-Ala2,Gly-ol]-enkephalin (DAGO) for mu (mu) receptor sites, [D-Pen2,D-Pen5]-enkephalin (DPDPE) for delta (delta) sites, and U-69593 for kappa (kappa) sites--were used to determine the regional distribution of the three major subtypes of opioid receptor binding sites in the brains of 1-day-old domestic chicks by the technique of quantitative receptor autoradiography. Whilst there was a degree of heterogeneity in the binding levels of each of the ligands, some notable similarities existed in the binding of the mu and kappa ligands in several forebrain regions, and in the optic tectum of the midbrain where mu and delta binding was very high. In the forebrain there was a high level of binding of mu and kappa ligands in the hyperstriatum, and for the mu ligand there was a very distinct lamination of binding sites in hyperstriatum accessorium, intercalatum supremum, dorsale and ventrale. Levels of binding of the mu and kappa ligands were also high in nucleus basalis, and (for mu only) in the neostriatum. The distribution of binding of the delta specific ligand in the forebrain showed marked differences to that of mu and kappa, being particularly low in the hyperstriatum and neostriatum. Very high levels of labelling of delta binding sites were, however, found in the nucleus rotundus. Binding of the three ligands was generally low or absent in the cerebellum and medulla, apart from a distinct labelling of the granule cell layer by the mu-ligand. A kinetic analysis was made of the binding of the three ligands to whole forebrain sections using scintillation counting methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesics↗
PubMed1990

A system for the reconstruction and analysis of dendritic fields.

We report here the development of a fast and 'user friendly' Semiautomatic Neuron Reconstruction and Analysis System (SANRAS) based on a Zeiss Universal microscope, Kontron Microscope Control Processor (MCP), and Apple Macintosh SE microcomputer. Four programs for digitisation and analysis have been written; STAGE, CONVERTZ, RECON and SHOLL. Cells are digitised by superimposing ocular crosshairs on a dendrite and tracing directly, the stage position in x, y, and z co-ordinates being recorded by the computer at points indicated by a keypress. Cells can be digitised from serial thick sections and dendritic reconstructions can be visualised on screen, rotated and viewed from any angle. Output is given either to a Hewlett Packard colour plotter or to a laser printer, in graphical form, and as a summary of various metrical and topological parameters. Radial Scholl diagrams of dendritic trees may also be produced. Dendritic branching patterns of Golgi-impregnated neurons of the left and right intermediate medial hyperstriatum ventrale of the chick are described.

Animals↗
PubMed1990

The fate of transplanted encapsulated islets in spontaneously diabetic BB/Wor rats.

The present study was undertaken to determine whether the transplantation of encapsulated MHC identical islets into diabetic BB/Wor/BB rats could cure their diabetes. Islets were isolated from diabetes-resistant BB/Wor/WB rats and encapsulated in alginate-polylysine-alginate membranes. Five thousand islets were transplanted into the peritoneal cavity of spontaneously diabetic BB/Wor/BB rats (n = 9) that had been insulin dependent for more than five weeks. Similar diabetic animals were transplanted with 5,000 unencapsulated islets (n = 10) or with empty capsules (n = 3). After transplantation of free islets, the animals reverted to the insulin-dependent state after a median of 16 days (17 +/- 4 days, mean +/- SEM). After transplantation of encapsulated islets, the animals reverted to the diabetic state after a median of 59 days (54 +/- 10 days, mean +/- SEM). Light microscopic and electron microscopic analyses of capsules recovered from the peritoneal cavity after failure of graft function showed no evidence either of lymphocytic invasion of the capsules or of specific destruction of the islets. The capsules were, however, overgrown by a layer of histiocytes and numerous layers of fibroblasts. Empty capsules recovered after 15 and 60 days were overgrown to the same extent.

Alginates↗