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D C Davies

Publications and source records attributed to D C Davies.

At least 37 records · Page 2Linked to original sources
PubMed2000

A comparative Golgi study of chicken (Gallus domesticus) and homing pigeon (Columba livia) hippocampus.

Neurons and fibres in the chick and homing pigeon hippocampus were described following Golgi impregnation. Two principal classes of neurons were distinguished: projection neurons with distant projecting axons and spiny dendrites, and local circuit neurons. In the homing pigeon and chicken hippocampus there are three types of projection neurons: pyramidal, pyramidal-like and multipolar. The pyramidal and pyramidal-like neurons are only found in the central 'pyramidal' layer of the hippocampus whereas multipolar neurons are present in the suprapyramidal, pyramidal and infrapyramidal layers. The axon of projection neurons typically emits several varicose collaterals from the initial section. Most of these collaterals extend along the infrapyramidal layer of the hippocampus, while others ascend to the pyramidal and suprapyramidal layers where they branch. The number of impregnated axon collaterals was higher in the homing pigeon than in the chick hippocampus. A variety of multi-angular/ovoid local circuit neurons ranging from small to large size are found in the homing pigeon and chick hippocampus. Their axons develop local arborization of varicose branches, the extent of which varies with the type of local circuit neurons. The density of GABA immunopositive local circuit neurons was found to be greater in the homing pigeon than in the chick. The profuse arborization of projection neuron axon collaterals and the higher density of GABA-immunopositive local circuit neurons in the homing pigeon hippocampus may underlie the differences in hippocampal function between the homing pigeon and chick, and this complex local connectivity may contribute to the ability of spatial orientation and memory.

Animals↗
PubMed2000

A golgi and a combined Golgi/GABA immunogold study of local circuit neurons in the homing pigeon hippocampus.

Three types of local circuit neurons have recently been reported in the homing pigeon hippocampus. The principal type appears to be constituted by the medium-sized angular or ovoid local circuit neurons that occur in all layers of the hippocampus. The current Golgi study has revealed that these neurons can be classified according to their axonal arborisation extension: (1) in all directions, (2) principally medio-laterally, or (3) dorso-ventrally. The local circuit neurons with dorso-ventral axon arborisation are present only in the subpyramidal layer. Serial sections of a Golgi-impregnated medium-sized, multiangular local circuit neuron in the pyramidal layer and a small, ovoid neuron in the suprapyramidal layer were investigated in the electron microscope. Some of these sections were processed for GABA immunogold cytochemistry. The soma and large dendrites of both neurons displayed GABA immunogold labelling. On the soma of medium-sized local circuit neuron there were numerous terminals; on the soma of the small one relatively fewer terminals were observed. The terminals contained round and/or flat synaptic vesicles. The long axonal branches of the neurons exhibited varicosities containing flattened or pleomorphic vesicles. Axo-dendritic, axo-somatic and a few axo-axonic synapses were observed. The large dense axon arborisation field of medium-sized local circuit neurons is properly situated to modulate intrinsic hippocampal activity and that of the small local circuit neurons is well situated to modulate the hippocampal input in the suprapyramidal layer.

Animals↗
PubMed2000

Pathophysiology of septic encephalopathy: a review.

OBJECTIVES: Encephalopathy is a common complication of sepsis. This review describes the different pathologic mechanisms that may be involved in its etiology. DATA SOURCES: The studies described here were derived from the database PubMed (http:¿¿www.nlm.nih.gov) and from references identified in the bibliographies of pertinent articles and books. The citations are largely confined to English language articles between 1966 and 1998. Older publications were used if they were of historical significance. STUDY SELECTION: All investigations in which any aspect of septic encephalopathy was reported were included. This selection encompasses clinical, animal, and in vitro cell culture work. DATA EXTRACTION: The literature cited was published in peer-reviewed clinical or basic science journals or in books. DATA SYNTHESIS: Contradictions between the results of published studies are discussed. CONCLUSIONS: The most immediate and serious complication of septic encephalopathy is impaired consciousness, for which the patient may require ventilation. The etiology of septic encephalopathy involves reduced cerebral blood flow and oxygen extraction by the brain, cerebral edema, and disruption of the blood-brain barrier that may arise from the action of inflammatory mediators on the cerebrovascular endothelium, abnormal neurotransmitter composition of the reticular activating system, impaired astrocyte function, and neuronal degeneration. Currently, there is no treatment.

Brain Diseases↗
PubMed1999

beta-Amyloid immunoreactivity in astrocytes in Alzheimer's disease brain biopsies: an electron microscope study.

The deposition of amyloid beta (A beta) protein plays a central role in the neuropathology of Alzheimer's disease (AD) and it constitutes the core of classical senile plaques. However, little is known about its intracellular distribution. An immunogold electron microscope study was therefore carried out on biopsies of brain tissue from patients with AD using a monoclonal antibody raised against residues 8 to 17 of the A beta protein. Specific A beta immunogold labeling was observed over extracellular amyloid fibrils associated with senile plaques. In addition, widespread intracellular A beta immunolabeling was observed adjacent to granular structures (30-40 nm in diameter) within membrane-bound processes. Pretreatment of some sections with amylase or omission of lead citrate staining from others strongly suggests that the electron-dense granular structures associated with A beta immunoreactivity are glycogen. Some of the A beta-immunolabeled processes contained gliofilaments and immunolabeling of alternate sections for glial fibrillary acidic protein confirmed that the A beta-immunolabeled processes were astrocytic. A beta immunolabeling was not observed over neuronal or microglial processes. Whether the presence of A beta protein in astrocytes is the result of synthetic or degradation processes requires further investigation.

Adult↗
PubMed1999

Faecal peritonitis causes oedema and neuronal injury in pig cerebral cortex.

Encephalopathy is a common complication of sepsis. However, little is known about the morphological changes that occur in the brain during sepsis. Faecal peritonitis was induced in pigs that were killed 8 h later and frontal cortex samples were taken immediately after death. The tissue was investigated using light and electron microscopy and compared with frontal cortex samples taken from sham-operated controls. Septic pigs had 49.5% more perimicrovessel oedema than sham pigs. However, the tight junctions between cerebral microvessel endothelial cells appeared morphologically intact in both septic and sham pigs. Sepsis also resulted in neuronal injury, disruption of astrocytic end-feet and swollen, rounded erythrocytes. These morphological changes may be sufficient to underlie the clinical features seen in septic encephalopathy.

Animals↗
PubMed1998

In vitro testing of calcium channel blockers and cytotoxic chemotherapy in B-cell low-grade non-Hodgkin's lymphoma.

The flux of calcium forms an important intracellular messenger system. The bcl-2 oncoprotein is thought to make cells resistant to a variety of insults, including cytotoxic drugs, by the suppression of apoptosis, which appears to involve the repartitioning of intracellular calcium. Three drugs that affect calcium pathways and may influence this repartitioning, i.e. dantrolene, azumolene (a water-soluble dantrolene analogue) and nimodipine, were studied in cell culture, using both a transformed follicle centre lymphoma cell line and primary culture of lymphoma cells in vitro in a manner that resulted in a growth pattern closely resembling that of the malignancy in vivo. Dantrolene and azumolene were potent inducers of cell death in both systems reducing the viable cell count by 70-90% in comparison with normal controls. Nimodipine, in comparison, appeared to have no significant effect. These results obtained in an in vitro setting suggest that further evaluation of dantrolene and azumolene for the treatment of low-grade non-Hodgkin's lymphoma is warranted.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Squatting facets on the neck of the talus and extensions of the trochlear surface of the talus in late Byzantine males.

Remodelling of bone occurs in response to physical stress. Habitual squatting is associated with modifications of the neck of the talus (squatting facets) and its trochlear/malleolar surfaces (trochlear extensions), and individual populations exhibit different incidences of these modifications that reflect their lifestyle. The occurrence of talar modifications was therefore investigated in a population of late Byzantine (13th century AD) adult male skeletons. Lateral squatting facets occurred most frequently (37.7%), but medial (0.6%), combined (0.6%) and continuous (gutter-like) facets (0.6%) were also observed. Lateral (8.0%), medial (10.9%) and continuous (lateral/central/medial) extensions (4.6%) of the trochlear surface were all present in the late Byzantine population. There was no evidence of side dimorphism. The occurrence of lateral squatting facets in the late Byzantine population was greater than that reported for modern Europeans, but similar to that reported for some populations of modern Indians. The frequency of occurrence of trochlear extensions in the late Byzantine population was substantially less than in modern Indian populations, but similar to modern Europeans. Therefore, it is unlikely that precisely the same factors determine the expression of squatting facets and trochlear extensions.

Adult↗
PubMed1997

Efferent connections of the domestic chick archistriatum: a phaseolus lectin anterograde tracing study.

The archistriatum of the domestic chick has been implicated in both fear behaviour and learning. However, relatively little is known about its organisation. The efferent connections of discrete anatomical regions of the chick archistriatum were therefore investigated by iontophoresis of the anterograde tracer Phaseolus vulgaris leucoagglutinin into its anterior, dorsal intermediate, ventral intermediate, medial, and posterior parts. The results of this study suggest that the chick archistriatum can be divided into two basic divisions according to whether they project to the following limbic structures: the hippocampal formation, septal areas, lobus parolfactorius, nucleus accumbens, ventral paleostriatum, and dorsomedial thalamus. The limbic archistriatum includes the posterior archistriatum and extends rostrally through the ventral intermediate archistriatum into the anterior archistriatum. The non-limbic archistriatum comprises the dorsal intermediate and medial archistriatum and largely gives rise to specific sensory, somatosensory, and motor telencephalofugal efferents. There may not be distinct borders between these two divisions of the chick archistriatum.

Animals↗
PubMed1997

Paired helical filament morphology varies with intracellular location in Alzheimer's disease brain.

Paired helical filaments (PHFs) are one of the hallmark pathologies of Alzheimer's disease (AD). PHFs occur in three intracellular locations, although hitherto, it was not known whether all PHFs are structurally homogeneous. Parietal cortex biopsies were taken from five patients with a clinical and histopathological diagnosis of AD and processed for electron microscopy. Photomicrographs were then taken of PHFs in neurofibrillary tangles (NFTs), neuropil threads (NTs) and neuritic plaque (NP) neurites and their dimensions measured. The mean half period, maximum and minimum widths of PHFs in NFTs were significantly smaller than those in NTs or NP neurites. The mean half period and maximum width of PHFs in NTs were similar to those in NP neurites. These results reveal the presence of two distinct PHF populations and investigation of their relationship may shed light on the pathogenesis of AD.

Adult↗
PubMed1995

The effect of archistriatal lesions on 'open field' and fear/avoidance behaviour in the domestic chick.

The chick archistriatum has been implicated in avoidance learning and filial imprinting. However, its role in these learning paradigms may be due to the inhibition of normal avoidance responses, since the avian archistriatum has been shown to play a role in fear/avoidance behaviour. The involvement of the archistriatum in the expression of unlearned fear/avoidance behaviour was therefore investigated in two day-old chicks. Chicks were exposed individually to a novel 'open field' for 5 min. Behaviour was recorded on videotape for analysis. In a separate but concurrent experiment, bilateral archistriatal lesions, sham archistriatal lesions or lateral cerebral lesions were made in day-old chicks which were then exposed to the 'open field' arena. At the end of each exposure a novel object was dropped near the chick. Chicks with archistriatal lesions generally displayed greater movement, more pecking behaviour and spent more time near the centre of the 'open field' than other chicks. There were no differences between the treatment groups in latencies to move or begin peeping. The behaviour of untreated chicks in the 'open field' was similar to that of sham-lesioned chicks and there was no effect of hatch on behaviour. Upon exposure to a novel object, indices of fear and avoidance were not changed in lesioned chicks. These results demonstrate that in the young chick, the archistriatum may be involved in the response to mild or intermediate levels of environment or isolation-related stress, but does not appear to be important for overt fear responses or avoidance of novel objects. Taken together with the results of previous work, the data suggests that the archistriatum may be directly involved in avoidance learning and imprinting.

Animals↗
PubMed1995

Myelinated axon number in the optic nerve is unaffected by Alzheimer's disease.

AIMS/BACKGROUND: Visual symptoms are a common but not invariable feature of Alzheimer's disease (AD) and such symptoms appear to become more pronounced as the severity of the dementia increases. Pathology in both the pregeniculate and cortical parts of the visual system has been suggested to underlie the visual deficits in AD. In order to investigate the former possibility, the effect of AD on the optic nerve was investigated. METHODS: Intraorbital segments of optic nerve were taken at autopsy from nine patients with AD and seven patients with no history of psychiatric or neurological disease and no abnormal neuropathology. All patients had functional vision before death and appeared free of retinal, optic nerve, or microvascular disease. The optic nerves were processed into resin, semi-thin sections cut perpendicular to the long axis of each optic nerve, and stained with paraphenylenediamine. The sections were then investigated using an image analysis system and standard morphometric techniques. RESULTS: There was no significant difference in the mean cross sectional neural area of AD compared with control optic nerves. Neither were there any significant differences between myelinated axon surface density, total axon number, or mean cross sectional axon area in AD compared with control optic nerves. CONCLUSION: These results indicate that optic nerve degeneration is not a feature of AD and suggest that the visual deficits in the disease result from cortical dysfunction. This view is supported by the fact that visuospatial dysfunction appears to be the most common visual problem in AD.

Aged↗
PubMed1995

Induction of CD80 expression in low-grade B cell lymphoma--a potential immunotherapeutic target.

The CD80 antigen (B7) is expressed on activated B lymphocytes. It is thought to be important in eliciting a T cell response via its ligands CD28 and CTLA-4 when antigen is presented in the presence of the MHC-1 peptide. Low-grade B cell lymphomas analysed by flow cytometry express CD80 very poorly. However, when grown in vitro using the IL-4/anti-CD40 stromal cell culture system, following depletion of T and IgD-bearing cells, a monoclonal B cell expansion occurs. Cells harvested at days 10-13 express the antigen strongly, regardless of the histological subtype of lymphoma. Further investigation of CD80-mediated immune functions may be possible using this system as a basis for testing immunotherapy.

B7-1 Antigen↗
PubMed1994

Termination pattern of medial hyperstriatum ventrale efferents in the archistriatum of the domestic chick.

The chick archistriatum receives afferents from the intermediate part of the medial hyperstriatum ventrale (IMHV) and projects to the lobus parolfactorius (LPO). There is functional evidence to suggest that the IMHV and the LPO are connected, but there is no anatomical evidence for a direct connection between the two structures. The aim of the current study was to characterize the termination pattern of medial hyperstriatal afferents within the archistriatum to determine whether the archistriatum may act as a relay between the IMHV and LPO. Following iontophoresis of Phaseolus vulgaris leucoagglutinin into the medial hyperstriatum ventrale (including the IMHV) of 1-week-old domestic chicks, anterogradely labelled fibers were observed to descend through the medial neostriatum and paleostriatum to enter the archistriatum. These medial hyperstriatum ventrale afferents arborised profusely to give varicose axon branches within all except the anterior part of the archistriatum. However, the greatest density was present in the ventral part of the intermediate archistriatum. Electron microscope examination of Phaseolus lectin immunocytochemistry and Golgi impregnation revealed that medial hyperstriatum ventrale axons formed multiple asymmetric synapses with dendritic spines (head and neck regions) on the terminal and preterminal dendritic segments of densely spiny archistriatal projection neurons. Medial hyperstriatum ventrale afferents were not observed to contact calbindin immunoreactive, presumptive "local circuit" neurons, within the archistriatum, despite a spatial overlap in their distribution. These results suggest that the archistriatum may be capable of mediating the transfer of information from the IMHV to the LPO.

Animals↗
PubMed1994

Archistriatal lesions impair the acquisition of filial preferences during imprinting in the domestic chick.

The avian archistriatum has been demonstrated to play a role in agonistic behaviours and avoidance learning. However, the extent of its role in learning is unknown. The involvement of the archistriatum in the learning process of filial imprinting was therefore investigated in day-old chicks. Bilateral archistriatal lesions, lateral cerebral area lesions or sham archistriatal penetrations were made in dark-reared, day-old chicks, which were subsequently exposed to either a rotating red box or blue cylinder for 2 x 1 h training sessions. Three hours later, the approach of chicks to their training object and to the other, novel object was measured. Chicks with archistriatal lesions ran a similar distance towards each stimulus and therefore failed to display a preference for their training object. However, chicks with sham archistriatal penetrations or lateral cerebral area lesions exhibited a significant preference for the object they had been trained upon. These results demonstrate that the archistriatum is essential for the expression of an imprinted preference. All chicks approached their training object significantly more on their second compared to their first training exposure, suggesting that some aspects of imprinting behaviour remain intact in chicks with archistriatal lesions. Taken together with the results of previous work, the current data suggest that the archistriatum may be involved in retention of significant aspects of the imprinting experience, or in motivation to approach imprinting objects.

Animals↗
PubMed1994

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

The avian archistriatum, part of which may be homologous with the mammalian amygdala, has been implicated in fear and avoidance behaviour. There is also evidence to suggest its involvement in learning. One-trial passive avoidance learning (PAL) has been used extensively to study memory formation in the chick. Young chicks will peck spontaneously at a small, visually conspicuous bead. If the bead has been coated with an aversive substance, the chicks show a disgust response and learn in a single trial not to peck a similar bead on subsequent presentation. Successful acquisition of this one-trial PAL task involves the formation of a learned association between the bead and a noxious taste, followed by the expression of an avoidance response. In view of the possible involvement of the archistriatum in avoidance and learning behaviour, its role in one-trial PAL was investigated by ablation. Bilateral electrolytic lesions of the entire archistriatum prevented the acquisition of the one-trial PAL task. Neither bilateral lesions of the lateral cerebral area nor sham operation affected learning. The impairment of one-trial PAL caused by archistriatal lesions was not due to effects on the visual or motor components of pecking behaviour. The archistriatum could therefore be directly involved in memory formation. It could also be involved in the organization of avoidance behaviour associated with the task, or it could form part of a circuit linking two other forebrain regions previously implicated in one-trial PAL, the intermediate part of the medial hyperstriatum ventrale and the lobus parolfactorius.

Amygdala↗
PubMed1994

Immunolabelling of hippocampal microvessel glucose transporter protein is reduced in Alzheimer's disease.

Changes in cerebral microvessel ultrastructure have been reported to occur in Alzheimer's disease (AD). In order to investigate whether these changes are associated with compromised blood-brain transport mechanisms, hippocampal formation sections from AD and age-matched normal brains were immunolabelled with an antibody to the GLUT-1 glucose transporter protein. GLUT-1 immunolabelling of microvessel endothelium was significantly reduced in the AD compared to normal hippocampal formation. Thus, AD is associated with a reduction in cerebral microvessel endothelium glucose transporter content, which may result in decreased glucose availability to the brain.

Aged↗
PubMed1994

The Golgi architecture of the domestic chick archistriatum.

Investigation of the chick archistriatum revealed that it was not possible to distinguish distinct sub-regions on the basis of their Golgi architecture, despite the fact that the pigeon archistriatum has been suggested to comprise "amygdaloid" and "sensorimotor" divisions. Nine sub-types of projection neuron and four of local circuit neuron were identified in the chick archistriatum. Projection neurons were generally larger with thicker dendrites than those in other regions of the chick telencephalon. A greater proportion of these projection neurons also had highly densely spiny dendrites. These findings suggest that archistriatal neurons receive a large, possibly complex afferentation and project considerable distances. Large and medium-sized local circuit neurons with varicose axon branches and relatively large neurogliaform cells were characteristic of the archistriatum. All types of archistriatal neuron were identified in both 28 and one day old chicks. However, presumptive highly densely spiny projection neurons appeared relatively immature in the one day old chick archistriatum.

Aging↗