Biomedical subjects

J S Dunbar

Publications and source records attributed to J S Dunbar.

8 recordsLinked to original sources

PubMed1992

Excitotoxic lesions of the pedunculopontine tegmental nucleus of the rat. I. Comparison of the effects of various excitotoxins, with particular reference to the loss of immunohistochemically identified cholinergic neurons.

The pedunculopontine tegmental nucleus (PPTg) has been shown to have cholinergic connections with the thalamus and basal ganglia. The ability of various doses of the excitotoxins (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) (AMPA), folate, ibotenate, kainate, N-methyl-D-aspartate (NMDA), quinolinate and quisqualate to make lesions in the PPTg was examined, with particular reference to their ability to destroy cholinergic neurons identified using choline acetyltransferase (ChAT) immunohistochemistry. All of the toxins induced convulsive activity on recovery from surgical anesthesia and all except folate made lesions in the PPTg and surrounding structures. The size of the lesions was computed following examination of Cresyl violet stained sections. The largest lesions were made by kainate = AMPA greater than NMDA = ibotenate greater than quisqualate = quinolinate. All of the toxins destroyed cholinergic neurons, higher doses producing greater loss than lower. The ratio of cholinergic cell loss to general neuronal loss (assessed by Cresyl violet staining) was also computed, revealing marked differences between the toxins. Statistical analysis showed that there were significant differences between excitotoxins in terms of this ratio, but these were accounted for by the low dose of quinolinate (24 nmol) producing a significantly greater ratio of damage (12.18:1) than every other toxin. (Next highest ratio: quisqualate 60 nmol, 6.22:1.) Between the other toxins (kainate, AMPA, ibotenate, quisqualate, NMDA and the high dose of quinolinate) there were no statistically significant differences. Intense calcium deposits (stained by Alizarin red) were found frequently and often defined the borders of the lesion. Tyrosine hydroxylase immunohistochemistry revealed axons running below and into the area of lesioned tissue suggesting strongly that fibers were undamaged by the lesions. We conclude that in the PPTg, different excitotoxins make discriminably different lesions, both quantitatively and qualitatively. Unlike excitotoxic lesions in the basal forebrain quinolinate, not quisqualate, made the most selective lesions of cholinergic neurons and, unlike excitotoxic lesions in the septal nuclei, non-myelinated fibers were spared by ibotenate. The implications of these data for research into brainstem mechanisms of Parkinson's disease are discussed.

Animals↗

PubMed1992

Excitotoxic lesions of the pedunculopontine tegmental nucleus of the rat. II. Examination of eating and drinking, rotation, and reaching and grasping following unilateral ibotenate or quinolinate lesions.

The pedunculopontine tegmental nucleus (PPTg) contains a population of cholinergic neurons thought to be part of the ascending reticular activating system, and non-cholinergic neurons. In the previous study it was shown that various excitotoxins made effective lesions of cholinergic neurons in the PPTg but that quinolinate made smaller lesions in the non-cholinergic population, making it more selective than any other excitotoxin. The purpose of the present experiment was, first, to make lesions of cholinergic neurons throughout the length of the PPTg by infusing toxin at two different sites within it; and second, to examine simple motor activities in rats bearing either quinolinate or ibotenate lesions of the PPTg, and contrast these with the deficits seen after 6-hydroxydopamine (6-OHDA) induced lesions of mesostriatal dopamine (DA)-containing neurons. Post-mortem examination was carried out using choline acetyltransferase (ChAT) and tyrosine hydroxylase (TOH) immunohistochemistry, and routine Nissl staining. Both quinolinate and ibotenate destroyed approximately 75% of ChAT-positive neurons in the PPTg, but damage to non-cholinergic neurons (assessed by Nissl staining) was twice as great following ibotenate as quinolinate. 6-OHDA induced almost complete lesions of mesostriatal DA neurons, assessed by TOH immunohistochemistry. DA depleted rats showed deficits in drinking and spilled more food in the first 2 weeks after surgery, and were unable to reach or grasp food pellets in the staircase test. They also showed strong ipsilateral turning in response to amphetamine and contralateral turning to apomorphine. Quinolinate lesioned rats had no eating or drinking impairment in the home cage but showed a reaching (though not grasping) disability in the staircase test. They had a mild ipsilateral bias following amphetamine. Ibotenate lesioned rats, despite having larger lesions than the quinolinate, showed no deficits in eating or drinking in the home cage, or reaching or grasping disabilities in the staircase test. They did have a mild contralateral bias in response to amphetamine. This dissociation of the effects of quinolinate and ibotenate lesions of the PPTg is consistent with the suggestion that the PPTg has two functionally distinct components, and is attributed to the differential lesion of non-cholinergic neurons by the two excitotoxins.

Animals↗

PubMed1979

Retropharyngeal abscesses in children revisited.

Retropharyngeal abscess appears in infancy and early childhood. Because of the advances in antibiotic therapy, the frequency of this disease has decreased considerably. If overlooked, however, the sequelae of retropharyngeal abscess can be disastrous. Of the typical signs and symptoms listed in presentation, the swelling of the posterior pharyngeal wall is referred to as an important diagnostic sign. This presentation will discuss the fallibility of this important sign in the evaluation of a retropharyngeal abscess in children. The size of the pediatric oral cavity and the presence of pooling secretions in the pharynx, due to retropharyngeal tissue swelling, make assessment of swelling of the posterior pharyngeal wall extremely difficult. Radiological assessment of retropharyngeal abscesses cannot differentiate between cellulitis and abscess formation. The presentation will discuss the radiological appearance of a retropharyngeal swelling and discuss the differentiation of abscess formation from cellulitis. The rationale for a therapeutic regime will be developed to validate the concept that with suggestive clinical signs, suggestive radiological diagnosis, and in spite of negative evidence of retropharyngeal swelling by oral examination, justification exists for an examination under anesthesia and incision and/or aspiration of the retropharyngeal abscess.

Abscess↗

PubMed1979

Antrochoanal polyps.

The antrochoanal polyp, a benign solitary polypoid lesion, usually arises in a maxillary sinus, opacifying and enlarging the sinus cavity without bone destruction. It passes through the ostium of the sinus into the choana, and from there into the posterior nasopharynx. The soft tissue mass does not erode or destroy contiguous soft tissue or bony structures. In this sequence of events, its radiologic findings are characteristic. Five case reports are presented, and the differential diagnosis is discussed.

Child↗

PubMed1979

Membranous laryngotracheobronchitis (membranous croup).

Membranous laryngotracheobronchitis (membranous croup), not previously described as a distinct entity, is characterized by diffuse inflammation of the larynx, trachea, and bronchi with adherent or semiadherent mucopurulent membranes in the subglottic trachea (conus elasticus) and in the upper trachea distal to the conus elasticus. We reviewed 28 cases of membranous croup diagnosed by endoscopy and/or radiographic examination. The importance of the recognition of membranous croup as a distinct entity is discussed. The characteristic radiologic findings consist of subglottic tracheal narrowing, irregularity of contour of the proximal tracheal mucosa, and sometimes detached or partially detached proximal tracheal membranes, which can be mistaken for tracheal foreign bodies.

Bronchitis↗

PubMed1976

The right pleuromediastinal reflection in children.

The authors review the anatomy of the pleural reflection of the right lung against the middle mediastinum in childhood. In 505 consecutive normal frontal radiographs of children, from birth to sixteen years, this pleural reflection (also known as the pleuro-esophageal line) was visible in 83%. The entire reflection from thoracic inlet to diaphragm was clearly seen in 13%, chiefly in upright, deep-inspiration, well penetrated radiographs. It is a radiographic landmark in the middle mediastinum, particularly well seen in childhood, and its use in assessment of mass lesions, cardiomegaly and lung collapse is described.

Adolescent↗

PubMed1975

Mechanicla properties and mineral content of avascular and revascularizing cortical bone.

The mechanical properties of avascular and revascularizing bone and their mineral content were studied in thirty adult dogs. The strength and mineral content of avascular bone decreased in the early phase of avascular necrosis, and with revascularization the bone-mineral content increased but the mechanical strength decreased further. In the normal bone the mechanical strength increased with an increase in mineral content.

Animals↗

PubMed1975

Contrast media used in cystourethrography. Experimental evaluation.

The effects of five iodinated contrast media and of physiologic saline on bladder capacity were studied. It was found that a significantly greater volume of sodium chloride was tolerated than of Cysto-Conray, Conray 30. Hypaque meglumine 30, Hypaque sodium, and Dimer X. Dimer X was tolerated in the smallest volume. The reason for the difference in volume tolerated is not known. The bladder mucosa showed dehydration changes 6 hr after saline cystogram with no change at 24 hr, 48 hr, 7 days, and 3 months. The contrast media produced dehydration and hydropic and desquamative changes in the bladder mucosa with at least one of these changes persisting up to 3 months. There was no significant difference in the severity of the changes produced by the various contrast media. No evidence of inflammatory changes was seen in the bladder mucosa or wall or in the ureter with any of the agents.

Absorption↗