Biomedical subjects

D C Davies

Publications and source records attributed to D C Davies.

At least 55 records · Page 3Linked to original sources

PubMed1994

A Phaseolus lectin anterograde tracing study of the tectorotundal projections in the domestic chick.

The projection from the chick optic tectum to the nucleus rotundus was investigated by iontophoresis of the anterograde tracer Phaseolus vulgaris lectin (PHA-L) into the optic tectum and by Golgi impregnation. PHA-L labelled fibres were observed within the ipsilateral nucleus rotundus and to course through the supraoptic decussation to the contralateral nucleus rotundus. They appeared similar to fibres evident in Golgi impregnated material. Before reaching the nucleus rotundus, PHA-L labelled fibres gave off short terminal branches in the caudoventral thalamic nucleus. Within the ipsilateral nucleus rotundus, the labelled fibres formed an extensive fibre net with a dense core and a less dense periphery. PHA-L labelled fibres in the contralateral nucleus rotundus exhibited a qualitatively similar but sparser distribution. There appeared to be a topographic representation of the optic tectum within the nucleus rotundus. Electron microscopy revealed that PHA-L labelled tectal fibres established asymmetric synapses with principal neurons in the nucleus rotundus.

Animals↗

PubMed1992

The effect of the neurotoxin DSP4 on the development of a predisposition in the domestic chick.

Under certain conditions, dark-reared chicks preferentially approach objects resembling conspecifics. In the current study we investigated the effect of the catecholaminergic neurotoxin DSP4 on this predisposition. After hatching, chicks received an intraperitoneal injection of either DSP4 or vehicle (controls). The chicks were individually placed in running wheels for 2 x 1 hr, 24 hr before testing. The chicks were maintained in darkness until given a preference test, which involved the simultaneous presentation of an illuminated red box and a stuffed fowl at 36, 48, 60, 66, or 72 hr after hatching. The approach of each chick toward the two objects was recorded over 5 min and a preference score calculated. Control chicks placed in the running wheels at 24 and 36 hr posthatch and tested 24 hr later showed a significant preference for the fowl compared to the red box. In contrast, DSP4-treated chicks did not show such a preference at corresponding ages, but did express a greater preference for the fowl when placed in the running wheels at 42 and 48 hr posthatch and tested 24 hr later. These results suggest that experience of the running wheel or of associated factors, e.g., handling, must occur during a restricted period of time to influence the emergence of the predisposition to approach the stuffed fowl. DSP4 treatment delays the onset of this period.

Animals↗

PubMed1992

The effect of age and Alzheimer's disease on pyramidal neuron density in the individual fields of the hippocampal formation.

Pyramidal neuron density was determined at autopsy in the brains of 12 neurologically normal patients (age range 6-87 years) and 18 patients with histopathologically confirmed Alzheimer's disease (AD; age range 62-89 years). Paraffin wax sections were cut at the level of the central part of the cornu ammonis and stained with cresyl fast violet. Pyramidal neuron density was determined in the stratum pyramidale of the presubiculum, subiculum, prosubiculum and CA1-4. The width of the stratum pyramidale in these areas was also determined. There was no significant effect of age on pyramidal neuron density in any of the fields of the hippocampal formation. However, there was a significant decrease in pyramidal neuron density in the subiculum (44%), prosubiculum (28%) and CA1 (41%) of AD brains compared to controls. There was no significant effect of AD on pyramidal neuron density in the presubiculum, CA2 and CA3, but in CA4 it increased (23%) significantly. Pyramidal band width decreased significantly with age in the presubiculum but there was no effect of age on any other region of the hippocampal formation investigated. The width of the stratum pyramidale was significantly lower in the presubiculum (19%), subiculum (30%) and CA3 (17%) of AD compared with control brains. These data suggest that a reduction in pyramidal neuron density within the hippocampal formation does not occur in the absence of underlying pathology. In AD, pyramidal neuron loss predominantly occurs from that sector of the hippocampal formation which comprises the subiculum, prosubiculum and CA1.

Adolescent↗

PubMed1991

Can flow cytometry reduce the workload for cervical screening? The results of a series of 622 specimens.

A simple method permitting the flow cytometric examination of cervical specimens has been developed and an assessment made of the feasibility of relying on this method to screen women for cervical neoplasia. Examination of four flow cytometric parameters showed differences between morphologically normal and abnormal specimens and allowed identification of a proportion of the normal specimens. The system had a false negative rate of 8%. Our experience with cervical specimens has revealed a number of problems associated with their examination by flow cytometry and these are discussed.

Evaluation Studies as Topic↗

PubMed1990

Increased tau messenger RNA in Alzheimer's disease hippocampus.

The microtubule-associated protein tau is present in the pathologic hallmarks of Alzheimer's disease and its production and deposition have been implicated in the pathogenesis of the disease. We detected tau mRNA using in situ hybridization histochemistry in the hippocampus, visual cortex, and cerebellum, and compared its level in Alzheimer's disease with controls. The amount of tau mRNA also was determined as a ratio of total polyadenylated mRNA in each area. A significant and gene-specific increase in tau mRNA hybridization was found in hippocampal fields CA4 and CA3, with a similar trend in the dentate gyrus. In contrast, no change was found in the visual cortex or cerebellum in Alzheimer's disease. Increased hippocampal expression of tau mRNA also was present in cases of non-Alzheimer's dementia. Enhanced tau mRNA may be a marker of attempted plasticity involving the cytoskeleton in neuronal populations affected by various neurodegenerative disorders.

Aged↗

PubMed1989

Clinical experience with antithrombin III concentrate in treatment of congenital and acquired deficiency of antithrombin. The Antithrombin III Study Group.

Phase I clinical studies of antithrombin III (ATIII) concentrate demonstrated a mean in vivo incremental recovery of functional activity of 1.4 percent per unit/kg administered, an initial 50 percent disappearance time of 22 hours, and a biologic half-life of 3.8 days. Based on these observations, a treatment regimen designed to maintain plasma ATIII levels between 75 and 120 percent of normal has been developed. None of 10 subjects with congenital ATIII deficiency treated prophylactically had evidence of thromboembolism, including four pregnant women at the time of delivery. Five subjects treated for acute thrombosis and/or thromboembolism, four of whom were pregnant, recovered without further thrombotic extension or recurrence. Heparin resistance was reversed in two subjects, both pregnant. Nine subjects with acquired ATIII deficiency also received ATIII treatment for venous or arterial thrombosis or disseminated intravascular coagulation, all with low plasma ATIII levels. Two subjects with disseminated intravascular coagulation demonstrated improvement, one clinically, the other biochemically. All patients with congenital ATIII deficiency survived, but only five of nine with acquired deficiency survived, highlighting the importance in acquired ATIII deficiency of the underlying disease in prognosis. Survival rate was especially poor in subjects with arterial thrombosis in the setting of low plasma ATIII. Administration of ATIII concentrate was well tolerated. None of the subjects who received ATIII concentrate demonstrated evidence of an infectious transmissible agent. These studies demonstrate that it is now feasible to safely replace the deficient protein in congenital ATIII deficiency, either prophylactically or therapeutically.

Antithrombin III↗

PubMed1989

Amnesia of a passive avoidance task due to the beta 2-adrenoceptor antagonist ICI 118,551.

The selective beta 2-adrenoceptor antagonist ICI 118,551 induces amnesia in the domestic chick when given systemically, 10 min after a one-trial PAL task. Young chicks will spontaneously peck at a small bright bead. If the bead has been coated with a distasteful substance, the chicks will learn in a single trial not to peck at a similar bead on subsequent presentation. Administration of ICI 118,551 prevented retention of this task. Vehicle-injected chicks which learnt the task, avoided a similar bead to the training bead in the retention test, but did not avoid a bead of a different colour. The effect of ICI 118,551 is unlikely to be a direct effect on performance since amnesic chicks pecked both beads freely and equally in the test.

Adrenergic beta-Antagonists↗

PubMed1989

Surgical treatment of persistent ductus arteriosus at the University College Hospital, Ibadan.

Seventy-seven patients aged from 5 days to 30 years underwent surgical correction of persistent ductus arteriosus (PDA) between July 1975 and December 1985. Forty-seven percent presented before 5 years of age while 20% were aged above 15 years. The male:female ratio was 1:2. Additional cardiovascular anomaly was present in 14 patients, 8 of which were ventricular septal defect. Majority presented with congestive heart failure and or failure to thrive. Surgical closure was effected by ligation in 67 cases, division and suture in 5 and unspecified in 5 cases. Operative mortality was 2(2.1%) cases. Complications with superficial wound infections occurred in a minority of patients. We conclude that despite a large left to right shunt in most patients, attested to by their symptomatic status, and late presentation surgical closure can be accomplished with minimal morbidity and mortality in centres with limited facilities.

Adolescent↗

PubMed1988

Senile plaques are concentrated in the subicular region of the hippocampal formation in Alzheimer's disease.

The distribution of senile plaques within the hippocampal formation was examined at autopsy in the brains of 18 patients with Alzheimer's disease, ranging in age from 62 to 89 years. Wax sections were cut at the level of the central part of the cornu ammonis and stained by a silver impregnation method. Plaque surface density was determined in the stratum pyramidale of the presubiculum, subiculum, prosubiculum and CA1-4. Senile plaques were present in all 7 regions of the hippocampal formation. However, the number of senile plaques/mm2 was significantly greater in the subicular complex than in the cornu ammonis. There was no difference in plaque density between the individual regions of the subicular complex or between the 4 CA fields.

Aged↗

PubMed1988

The effects of hyperstriatal lesions on one-trial passive-avoidance learning in the chick.

The roles of different forebrain structures in memory formation in the chick were investigated using restricted radio-frequency lesions. Young chicks will spontaneously peck at a small bright bead. If the bead has been coated with a distasteful substance, the chicks learn not to peck a similar bead on subsequent presentation. Thus, in a single trial chicks learn not to peck at an aversive stimulus. Bilateral lesions of the intermediate part of the medial hyperstriatum ventrale (IMHV) prevented the acquisition of this 1-trial passive-avoidance learning task. However, neither bilateral lesions of the lateral cerebral area (LCA) nor sham operation affected learning. IMHV has previously been shown to be critically involved in the learning process of imprinting in the chick. The present experiment demonstrates that the role of IMHV in learning is not restricted to imprinting. The function of IMHV in imprinting has been suggested to be concerned with the recognition of objects. In the present study sham-operated and LCA-lesioned chicks recognized the visual characteristics of the training bead and did not avoid a bead of a different color in the test. We propose that IMHV-lesioned chicks fail to learn the task because they are unable to recognize the visual characteristics of the training bead and consequently cannot make the association between the bead and the unpleasant taste.

Animals↗

PubMed1988

Alzheimer's disease.

The current knowledge of the neuropathology, neurochemistry and genetics of Alzheimer's disease is reviewed. The hallmarks of neuropathology, namely neuritic plaques and neurofibrillary tangles, are described. The search for the aetiological agent(s) and a therapeutic strategy are briefly described and the location of a genetic locus for Alzheimer's disease on chromosome 21 is discussed. Future directions for research are suggested.

Alzheimer Disease↗

PubMed1987

Transmission electron microscopy of percutaneous fine needle aspirates from lung: a study of 70 cases.

Seventy consecutive lung fine needle aspirates (FNA) from 69 patients were examined by cytology/cell block histology, by transmission electron microscopy (TEM), and, where available, at histological follow up to determine the value of TEM in interpreting lung FNAs. Of 70 FNAs, 50 were suitable for TEM. Transmission electron microscopy was helpful in classifying seven of 10 poorly differentiated tumours, and two case histories are reported. In 26 of 30 well differentiated tumours TEM confirmed diagnosis by light microscopy. Two TEM false negatives, but no TEM false positives, were recorded. It is concluded that transmission electron microscopy of cells aspirated from lung can be helpful when unequivocal diagnosis has not been achieved.

Aged↗

PubMed1985

Selection of Swaledale sheep of reduced susceptibility to experimental scrapie.

A flock of 294 Swaledale sheep was injected with brain tissue from different sources so as to include strains of natural scrapie currently affecting the Swaledale breed. Discounting intercurrent deaths, 85 per cent of the flock developed clinical scrapie within an observation period of 2557 days (seven years). Scrapie cases fell into distinct early and late groups, occurring at (mean +/- sem) 287 +/- 7 days and 1207 +/- 38 days after injection, respectively. Breeding groups were formed from the survivors after the early cases had occurred and successive lamb crops were produced. Two groups of progeny and two groups of controls were injected with scrapie. The incidence of scrapie in the progeny (27 per cent) was much lower than in the controls (64 per cent). The incidence in the progeny was also assessed in relation to the response of their parents: it was high (about 40 per cent) when one or both parents developed late scrapie but otherwise very low (about 5 per cent). Hence the progeny of surviving parents had a greatly reduced susceptibility to the strains of scrapie used. Seventy-two of these selected progeny formed a nucleus flock which is being bred at Redesdale. The next stage of the experiment is to assess the effect of selected rams in recorded flocks with a high incidence of natural scrapie.

Animals↗

PubMed1985

Noradrenaline and learning: effects of the noradrenergic neurotoxin DSP4 on imprinting in the domestic chick.

The effects of the noradrenergic neurotoxin DSP4 on imprinting in domestic chicks were investigated. Chicks received either DSP4 or distilled water and were trained 60 hr after hatching by exposing them to either a rotating red box or a stuffed jungle fowl. Noradrenaline concentration was determined in Wulst and medial and basal forebrain samples. The medial forebrain sample comprised mainly the intermediate part of the medial hyperstriatum ventrale, a region previously shown to be intimately involved in imprinting. The DSP4 treatment reduced forebrain noradrenaline levels by about 65%. DSP4 profoundly impaired imprinting in box-trained chicks but not in fowl-trained chicks. In box-trained chicks, the strength of imprinting was positively correlated with noradrenaline concentration in both medial and basal forebrain samples. It is suggested on the basis of these and previous studies that some of the neural structures and mechanisms involved in imprinting on the fowl differ from those involved in imprinting on the box.

Animals↗

PubMed1985

Connections of the hyperstriatum ventrale of the domestic chick (Gallus domesticus).

The intermediate part of the medial component of the hyperstriatum ventrale (IMHV) of the chick telencephalon is implicated in the learning process of imprinting. The afferent connections of this region were investigated using the retrograde neuronal tracers horseradish peroxidase (HRP), nuclear yellow and fast blue. Labelled cells were found (i) ipsilaterally in the visual Wulst, neostriatum pars intermedia and caudalis, the posterior part of the hyperstriatum ventrale, the dorsal part of the archistriatum, paleostriatum augmentatum, dorsomedial part of the thalamus, and (ii) bilaterally in the hippocampus, area septalis, ventromedial part of the thalamus and the stratum album centrale of the tectum opticum. The efferent projections of the IMHV were studied using the anterograde tracer, [3H]leucine. Labelling was seen ipsilaterally over the dorsolateral part of the hemispherium telencephali, the paleostriatum augmentatum and the posterior and dorsal parts of the archistriatum. Double labelling with nuclear yellow and fast blue revealed (i) neurons in the IMHV which project to both the paleostriatum augmentatum and the archistriatum, and (ii) neurons in the hippocampus which project bilaterally to the IMHV.

Afferent Pathways↗

PubMed1984

Scheduling in the operating theatre.

The effect of scheduling on the use of operating theatre time has been studied. Scheduling involved determining the average length of common operations and fitting them into the calculated available operating time. The technique has been shown to reduce significantly the variation in length of operating sessions, and it ensures the best use of available operating time.

Appointments and Schedules↗

PubMed1983

Putative cholinergic afferents of the chick hyperstriatum ventrale: a combined acetylcholinesterase and retrograde fluorescence labelling study.

The retrograde fluorescent tracers Fast Blue and Nuclear Yellow were injected into the intermediate part of the medial hyperstriatum ventrale (IMHV) of the chick telencephalon. After the appropriate survival times, the brains were processed for acetylcholinesterase (AChE) histochemistry using the thiocholine technique. In some telencephalic regions, fluorescent retrograde labelling and brown AChE reaction product were observed simultaneously in the same neurones by using a combination of ultraviolet and bright-field illumination. These AChE-positive afferents of IMHV arose from the hippocampus, septum, septal nuclei, hyperstriatum ventrale and neostriatum.

Acetylcholinesterase↗

PubMed1983

Changes in telencephalic catecholamine levels in the domestic chick. Effects of age and visual experience.

The concentrations of adrenaline, dopamine and noradrenaline were measured in 3 regions of the domestic chick telencephalon: (a) the Wulst; (b) a medial forebrain sample comprising mainly the intermediate part of the medial hyperstriatum ventrale (IMHV); and (c) a basal forebrain sample comprising mainly paleostriatum augmentatum. There was no significant left/right hemispheric asymmetry in the concentration of any of these catecholamines in any region studied. Adrenaline was undetectable in the Wulst and medial forebrain samples and only trace amounts were found in the basal forebrain samples of 1-day-old, light-reared chicks. Dopamine concentrations of 9.13 +/- 1.13 (S.E.M.) ng/g were present in the Wulst, 16.66 +/- 2.56 ng/g in the medial forebrain and 121.19 +/- 33.06 ng/g in the basal forebrain samples at hatching. These levels did not alter with age or with visual experience of an imprinting stimulus during the first 50 h post-hatch. At hatching, noradrenaline concentrations of 35.83 +/- 8.61 ng/g were present in the Wulst, 26.09 +/- 3.75 ng/g in the medial forebrain and 53.13 +/- 7.85 in the basal forebrain samples. The noradrenaline concentrations in the Wulst and medial forebrain samples increased significantly over the first 50 h post-hatch in dark-reared chicks. Visual experience increased noradrenaline levels in all 3 regions of the telencephalon studied.

Aging↗