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J S Dunbar

Publications and source records attributed to J S Dunbar.

At least 19 recordsLinked to original sources
PubMed1994

Outflow from the nucleus accumbens to the pedunculopontine tegmental nucleus: a dissociation between locomotor activity and the acquisition of responding for conditioned reinforcement stimulated by d-amphetamine.

Output of neuronal information from the nucleus accumbens to the ventral pallidum is known to be a critical pathway in the expression of locomotion and incentive-related behaviour. Some signals from this structure are relayed forward through the dorsomedial nucleus of the thalamus to the medial prefrontal cortex, but the other major pathway from this site is a descending innervation to the pedunculopontine tegmental nucleus. Information carried by these descending neurons has been linked with both the output of locomotor activity and incentive-related information. Previous studies carried out in this laboratory have shown no changes in locomotor activity--either spontaneous or in response to systemic administration of d-amphetamine or apomorphine--in rats with excitotoxic lesions of the pedunculopontine tegmental nucleus. The present experiments compare the effects of ibotenate lesions of this nucleus in tests of locomotor activity or the acquisition of responding with conditioned reinforcement, following injections of d-amphetamine directly into the nucleus accumbens. In general agreement with previous results, ibotenate lesions of the pedunculopontine tegmental nucleus did not alter locomotion stimulated directly from the nucleus accumbens. However, comparable lesions in a group of trained rats produced an array of deficits in the conditioned reinforcement paradigm. Most notably, these rats directed their attention almost entirely towards pressing the levers (practically ignoring the food-hopper panel), but did not appear to be able to discriminate between them, while controls focused almost all their efforts on pressing the reinforcing lever (virtually ignoring the non-reinforcing lever) and the food-hopper panel. These results indicate that pedunculopontine tegmental nucleus lesions disrupt an element of reward-related responding, but do not affect the production of locomotor activity. This highlights the unlikely existence of specific "locomotion-inducing" centres in the mesencephalon and implicates the pedunculopontine tegmental nucleus in the formation of stimulus-reward associations. These data are discussed with respect to a role for the pedunculopontine tegmental nucleus in response selection.

Animals↗
PubMed1993

Barbiturate anaesthesia reduces the neurotoxic effects of quinolinate but not ibotenate in the rat pedunculopontine tegmental nucleus.

We have previously demonstrated that ibotenate (IBO) injected into the pedunculopontine tegmental nucleus (PPTg) damages all neurones there while quinolinate (QUIN) makes relatively selective lesions of cholinergic neurones. We now compare the effects of two anaesthetics, sodium pentobarbitone and Avertin (tribromoethanol/tert-amylalcohol dissolved in ethanol, saline and phosphate buffer) on three doses of IBO and QUIN in the PPTg. Diaphorase-positive cell loss after QUIN was attenuated under barbiturate, the relative selectivity of QUIN for diaphorase-positive neurones was lost and lesion volumes were uniformly small compared with lesions made under Avertin anaesthesia. IBO toxicity was unaffected by anaesthesia. These data are discussed with reference to the actions of excitotoxins at glutamate receptor subtypes and interactions of barbiturates with the GABAA receptor.

Anesthesia, General↗
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↗
PubMed1987

Urography and voiding cystourethrography: findings in girls with urinary tract infection.

The voiding cystourethrogram and excretory urogram have been considered essential parts of the evaluation of girls with urinary tract infections. To evaluate the usefulness of these procedures, 523 examinations in girls with urinary tract infections were reviewed retrospectively. The major finding on voiding cystourethrograms was vesicoureteral reflux, occurring in 36% of the children. Of the total group, 8% had excretory urographic evidence of parenchymal scarring. Higher grades of reflux were associated with an increase in parenchymal scarring. All urethras were normal, and only one paraureteral diverticulum was identified. Bladder emptying was incomplete in 46% of the patients. Ovarian radiation doses were measured with "low-dose" and standard systems. On the basis of this study, traditional approaches to the standard workup are questioned.

Adolescent↗
PubMed1986

Normal left atrium: appearance in children on frontal chest radiographs.

The right lateral border of the left atrium can be seen in the anteroposterior radiographs of healthy children. Five hundred forty-three frontal radiographs, mostly of children, were reviewed, and the right lateral border of the left atrium was visualized in 30%, although it was very prominent in only 2.5% of cases. In a comparison of frontal angiocardiograms with plain chest radiographs, the shadow was demonstrated to be the lateral or inferior wall of the left atrium. Entities that simulate the left atrial shadow are presented, and ways to distinguish normal appearance from abnormalities are discussed.

Adolescent↗
PubMed1984

Pharyngonasal reflux: spectrum and significance in early childhood.

The radiographic and clinical findings of 57 infants and children demonstrating pharyngonasal reflux during barium swallow were reviewed. Pharyngonasal reflux is most frequent in the first 3 months of life and may occur in children with apneic episodes. Clinical symptoms in this group of children generally clear, even when reflux is severe. Pharyngonasal reflux may be associated with prematurity, neuromuscular disease, velopharyngeal incoordination, and other conditions but is usually of no consequence in very young infants.

Age Factors↗
PubMed1984

Nonpulmonary abnormalities recognizable in pediatric chest radiographs.

Systemic disorders can often be recognized or suspected from chest radiographs. This is often true in pediatric radiology. In this article, the author presents a sampling of metabolic, hematologic, and endocrine diseases as well as malformations that are recognizable on pediatric chest radiographs.

Adolescent↗
PubMed1983

Chest tube perforation of the lung in premature infants: radiographic recognition.

Newborn infants with severe respiratory distress syndrome have an increased incidence of pulmonary interstitial emphysema, pneumomediastinum, and pneumothorax. A chest tube inserted for treatment of a pneumothorax may inadvertently perforate the lung. Recognition of chest tube perforation can be suggested by the occurrence of: (1) persistent or repeated pneumothoraces despite the presence of a chest tube and (2) atelectasis and/or infiltrate near the end of the chest tube.

Humans↗
PubMed1981

Tracheal compression by the innominate artery in infancy and childhood.

The authors evaluated the normal radiographic anatomy of the innominate (brachiocephalic) artery in children. Review of 1,000 randomly selected lateral chest radiographs demonstrated anterior tracheal indentation in 30% of the children under the age of 2 years. In addition, 172 angiograms in children with congenital heart disease revealed that the innominate artery normally originates either completely or partially to the left of the trachea and crosses in front of it.

Adolescent↗
PubMed1980

Pulmonary vascular sling with tracheobronchial stenosis and hypoplasia of the right pulmonary artery.

We present a case of pulmonary sling associated with tracheobronchial stenosis, and with hypoplasia of the right lung and right pulmonary artery. Radiologic studies showed evidence of pulmonary sling and hypoplasia of the right lung; associated hypoplasia of the right pulmonary artery was also present, but not recognized initially. Narrowing of the distal trachea and right main bronchus was present, not due to compression by the anomalous left pulmonary artery, but to congenital stenosis of the trachea and right main bronchus associated with complete cartilaginous tracheobronchial rings.

Bronchial Diseases↗
PubMed1980

Intussusception complicated by distal perforation of the colon.

Three cases of perforation of the colon distal to an ileocolic intussusception are presented. Two cases were associated with attempted hydrostatic reduction of the intussusception, while the other was discovered at operation. The mechanism of this complication is not clear. When performing a contrast enhanced examination of the colon and there is a risk of perforation: (a) dilute water-soluble contrast medium should be used; (b) special attention should be paid to the colon distal to the intussusception; and (c) should contrast material be observed in the peritoneal cavity, the enema reservoir should immediately be lowered to the floor to siphon off the liquid from the colon.

Barium Sulfate↗