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Biomedical subjects

R Davis

Publications and source records attributed to R Davis.

At least 451 records · Page 25Linked to original sources
PubMed1978

Dimensions of black suicide: a theoretical model.

This paper has two purposes: (1) to develop a theoretical model of suicide, based on the previous work of Henry and Short, and (2) to apply that model in the study of black suicides in Orleans Parish, Louisiana. In so doing, we are focusing on suicide among a traditionally low-status, low-suicide population group, one which Henry and Short cited in support of the positive relationship between status and suicide. The generality of the theory is thus examined in this and other ways. The theory of "external restraints" is only weakly sustained by this analysis. More adequate testing of the theory must await further data, with careful attention to the subjective aspects of hypothesized structural relationships.

Black or African American↗
PubMed1977

Subcellular distribution of thyrotropin-releasing hormone (TRH) in rat brain and hypothalamus.

TRH localization in rat brain and hypothalamic tissue was studied by determination of immunoassayable TRH in subcellular fractions prepared from homogenates of these tissues. In both hypothalamus and brain, most of the TRH was found in a crude mitochondrial fraction and its concentration was higher in the synaptosomal fraction isolated by density gradient centrifugation. Electron microscopy was used to verify the composition of the fractions. Exposure of the brain crude mitochondrial fraction to osmotic shock resulted in solubilization of TRH which then was sedimented by centrifugation at 96,000 X g. TRH added to brain homogenates in vitro was rapidly destroyed by incubation at 37 degrees C, but no endogenouse TRH was lost by such incubation. The localization of TRH of hypothalamic and brain tissue to subcellular fractions consisting largely of synaptosomes and synaptic vesicles is compatible with a neurotransmitter function for this substance.

Animals↗
PubMed1977

Observation and treatment of neonatal narcotic withdrawal.

A total of 110 infants born to mothers who were either in a methadone maintenance program, using heroin, or recently detoxified, were studied during the neonatal period. Of these infants, 93.6 per cent developed withdrawal symptoms. No significant differences were determined in therapeutic response among those infants treated with methadone, phenobarbital, and diazepam. There was a significant reduction in the frequency of withdrawal symptoms among infants born to mothers whose methadone dose at time of delivery was less than 20 mg (17.9 per cent). It is suggested that reduction of methadone dosage in late pregnancy results in reduced incidence of withdrawal but must be carefully carried out.

Diazepam↗
PubMed1977

Pharmacology of the brachium conjunctivum: red nucleus synaptic system in the baboon.

Acetylcholine, biogenic amines, and certain amino acids were applied by microiontophoresis to parvicellular and magnocellular red nucleus (RN) neurons of baboon while recording brachium conjunctivum (BC)-evoked and amino acid-evoked unit discharge from these neurons. Glycine, gamma-aminobutyric acid, and beta-alanine were potent depressants of BC-RN synaptic transmission, amino acid-evoked firing, and spontaneous activity of all RN neurons studied. Glycine was clearly more potent than the other 2 depressant amino acids. L-Glutamic and DL-homocysteic acid were strong excitants of all RN neurons tested. Dopamine, noradrenaline, and 5-hydroxytryptamine depressed the excitability of both parvicellular and magnocellular RN neurons; no excitatory effects were observed with these biogenic amines on RN neurons. Acetylcholine increased the rate of firing of spontaneously discharging parvicellular RN neurons and facilitated the amino acid-induced firing of these same neurons. Acetylcholine did not facilitate BC-RN synaptic transmission nor could this transmission be blocked by cholinergic antagonists. Unlike parvicellular RN neurons, the responsiveness of magnocellular neurons was either unaltered by acetylcholine or slightly decreased. These experiments demonstrate a difference in the pharmacologic responsiveness of parvicellular and magnocellular RN neurons to acetylcholine but do not provide evidence for a cholinergic input to RN via the brachium conjunctivum.

Acetylcholine↗
PubMed1977

The mammographic demonstration of malignant spicules.

A specimen of breast tissue containing a carcinoma with multiple spiculations was used as a test object and examined by a range of mammographic techniques. The images were compared with a photograph of the cleared specimen. A quantitative method of evaluating the performance of each technique is described and used to compare these images. Xeroradiography clearly excelled other imaging methods.

Breast Neoplasms↗
PubMed1977

Coronary xeroradiography.

Xeroradiography is shown to be especially helpful in coronary arteriography. Comparatively low concentrations of contrast medium are sufficient to provide adequate diagnostic details in the image. Selection injection techniques yield exceptional resolution of small vessels. The possibility of obtaining adequate coronary arteriograms by aortic root injections, with its inherently lower risk to the patient, is examined.

Angiography↗
PubMed1977

The advantages of xeroradiography for panoramic examination of the jaws and teeth.

Xeroradiography is an electrostatic imaging method which was significant advantages over conventional radiographic techniques. This article introduces the use of xeroradiography for panoramic examination of the jaws. The resultant images not only contain superior local contrast and detail when compared to conventional panoramic radiographs but also correlate well with histopathologic changes. The investigation indicates that xeroradiography is an important new diagnostic tool for detection of disease of the jaws and teeth.

Adolescent↗
PubMed1976

Brachium conjunctivum-red nucleus synaptic system in the baboon.

Electrophysiological properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system were studied in barbiturate-anesthetized baboon (Papio). Topographic recordings from the mesencephalon demonstrated that most of the BC-evoked activity was restricted to an area histologically identified as red nucleus; however, some brachium-evoked activity was recorded from the surrounding mesencephalic reticular formation. Short latency BC-evoked activity was also recorded from the pons in the region of nucleus reticularis tegmenti pontis. The majority of the BC fibers were found to conduct at a rate of 44 m/sec; a second group of BC fibers with a slower conduction velocity of 23 m/sec was also observed. Brachium-evoked responses recorded from magnocellular and pravicellular RN neurons were short latency responses consistent with monosynaptic activation of these RN neurons by the BC fibers. The BC-RN synaptic system was found to be a very secure synaptic system and could transmit activity at high rates of stimulation with little or no failure. The responsiveness of the BC fibers was found to be similar to that of optic nerve fibers and pyramidal tract fibers, both of which have been characterized as being similar to peripheral A fibers. The responsiveness of the BC-RN synaptic system began to decrease 5 msec after a single or repetitive transmission and was reduced to about 50% of normal responsiveness at 34 msec. This period of reduced postsynaptic responsiveness was associated with a reduction in presynaptic input to RN and suggest that a disfacilitation at the level of the deep cerebellar nuclei may be in part responsible for the subnormal responsiveness of the BC-RN synaptic system.

Animals↗
PubMed1976

Localization of acetylcholinesterase in a crustacean neuromuscular system.

1. The localization of acetylcholinesterase (AChE) was studied by light and electron microscopy (LM and EM) at the neuromuscular junctions (NMJs) of the abdominal superficial flexor muscle (SFM) and the claw adductor muscle (CAM) of the crayfish in view of reported pharmacological evidence of cholinergic transmission at the former but not at the latter site. 2. Survey of LM with the copper-thiocholine method disclosed staining for AChE, but not for butyrocholinesterase (BuChE), at numerous NMJs of the SFM; neither enzyme was detected at any NMJs of the CAM. 3. With the bis-(thioacetoxy) aurate (I) method, EM examination showed AChE-staining at NMJs of the SFM to be confined to the postjunctional membrane. 4. The published and present findings suggest a unique situation of more than one excitatory transmitter for the skeletal neuromuscular system in the crustacean studied.

Acetylcholinesterase↗
PubMed1976

Immunological status in tuberous sclerosis.

Cellular and humoral immunity, and lymphoid organ pathology, have been investigated in 10 institutionalized patients with tuberous sclerosis and 10 institutionalized matched controls without the disease. Type and incidence of infections and tumours were reviewed for each group, as was current medication. Elevated serum IgM levels were found in the patients with tuberous sclerosis, but no immunological deficiency of either cellular of humoral immunity was found, nor was there a difference in infection between the groups. Only patients with tuberous sclerosis had evidence of neoplasia. No morphological or histological abnormalities of lymph nodes, spleen or thymus were present. Explanations for the difference between tuberous sclerosis and ataxia telangiectasia are discussed, together with the effect of immuno-surveillance on the development of malignancy.

Adolescent↗
PubMed1976

In vivo transcription of R-plasmid deoxyribonucleic acid in Escherichia coli strains with altered antibiotic resistance levels and/or conjugal proficiency.

The amounts of plasmid deoxyribonucleic acid (DNA) and the levels of the in vivo transcription of the Escherichia coli plasmids R538-1 (repressed for conjugal transfer) and R538-1drd (derepressed for transfer) were determined by DNA-DNA hybridization and DNA-ribonucleic acid hybridization, respectively. The results demonstrate that the level of plasmid transcription is increased by two-fold in the strain carrying the derepressed plasmid, compared to an isogenic strain carrying the repressed plasmid, whereas the amount of plasmid DNA is approximately the same, suggesting that the transfer genes are under transcriptional control. Levels of plasmid DNA, plasmid DNA transcription, and chloramphenicol acetyltransferase activity were also compared in a mutant strain that carried the R538-1drd plasmid and was resistant to high levels of antibiotics. This strain produces about 13 copies of plasmid DNA per chromosome compared to five copies for the parent strain. The level of transcription of plasmid DNA was found to be twofold higher in the high-level resistant strain, whereas the level of chloramphenition, acetyltransferase activity was increased by 10-fold. In addition the levels of plasmid DNA transcription and chloramphenicol acetyltransferase activity in the high-level resistant strain were found to be further increased by the presence of high levels of chloramphenicol in the growth medium. The amount of plasmid DNA remained constant under these conditions, indicating that high levels of chloramphenicol can stimulate the expression of plasmid genes at the level of transcription in this strain.

Acetyltransferases↗