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Biomedical subjects

S Ramsay

Publications and source records attributed to S Ramsay.

66 records · Page 4Linked to original sources
PubMed1993

Transcriptional up-regulation of the mouse cytosolic glutathione peroxidase gene in erythroid cells is due to a tissue-specific 3' enhancer containing functionally important CACC/GT motifs and binding sites for GATA and Ets transcription factors.

Nuclear run-on experiments have shown that the high level of expression of the mouse cytosolic glutathione peroxidase mRNA in erythroid cells is due to up-regulation of the gene at the transcriptional level. Studies of the chromatin structure around the cytosolic glutathione peroxidase gene have revealed a series of DNase I hypersensitive sites (DHSS) in the 3' flanking region of the gene in erythroid and other high-expression tissues that are lacking in low-expression cells, in addition to a DHSS over the promoter region in both high- and low-expression tissues. Functional transfection experiments have demonstrated that one of the 3' DHSS regions functions as an enhancer in erythroid cells but not in a low-expression epithelial cell line; and site-directed mutagenesis and footprinting experiments reveal that the activity of the erythroid cell-specific enhancer requires a cluster of binding sites for the CACC/GT box factors and the GATA and Ets families of transcription factors.

Animals↗
PubMed1992

Regional response differences within the human auditory cortex when listening to words.

The relationship between activity within the human auditory cortices and the presentation rate of heard words was investigated by measuring changes in regional cerebral blood flow with positron emission tomography. We demonstrate that in the primary auditory cortices and middle regions of the superior temporal gyri there is a linear relationship between the rate of presentation of heard words and blood flow response. In contrast, the blood flow response in an area of the left posterior superior temporal gyrus (Wernicke's area) is primarily dependent on the occurrence of words irrespective of their rate of presentation. The primary auditory cortices are associated with the early processing of complex acoustic signals whereas Wernicke's area is associated with the comprehension of heard words. This study demonstrates for the first time that time dependent sensory signals (heard words) detected in the primary auditory cortices are transformed into a time invariant output which is channelled to a functionally specialised region--Wernicke's area. Wernicke's area is therefore distinguished from other areas of the auditory cortex by direct observation of signal transformation rather than by association with a specific behavioural task.

Adult↗
PubMed1992

The anatomy of phonological and semantic processing in normal subjects.

We assessed brain activation of nine normal right-handed volunteers in a positron emission tomography study designed to differentiate the functional anatomy of the two major components of auditory comprehension of language, namely phonological versus lexico-semantic processing. The activation paradigm included three tasks. In the reference task, subjects were asked to detect rising pitch within a series of pure tones. In the phonological task, they had to monitor the sequential phonemic organization of non-words. In the lexico-semantic task, they monitored concrete nouns according to semantic criteria. We found highly significant and different patterns of activation. Phonological processing was associated with activation in the left superior temporal gyrus (mainly Wernicke's area) and, to a lesser extent, in Broca's area and in the right superior temporal regions. Lexico-semantic processing was associated with activity in the left middle and inferior temporal gyri, the left inferior parietal region and the left superior prefrontal region, in addition to the superior temporal regions. A comparison of the pattern of activation obtained with the lexico-semantic task to that obtained with the phonological task was made in order to account for the contribution of lower stage components to semantic processing. No difference in activation was found in Broca's area and superior temporal areas which suggests that these areas are activated by the phonological component of both tasks, but activation was noted in the temporal, parietal and frontal multi-modal association areas. These constitute parts of a large network that represent the specific anatomic substrate of the lexico-semantic processing of language.

Adult↗
PubMed1989

Electrophysiological evidence for the dendritic localization of a calcium conductance in guinea-pig substantia nigra neurones in vitro.

Within the substantia nigra, anatomical, neurochemical and pharmacological findings strongly suggest that transmitter and protein are secreted from the dendrites of nigrostriatal neurones. This phenomenon may underlie a non classical modulatory cellular mechanism. Two conductances are generated in nigrostriatal neurones independent of somatic action potentials, that might mediate this modulation. However, these conductances have never been directly nor precisely located specifically within the dendrites. The aim of this study was to record the membrane properties of substantia nigra zona compacta neurones in response to selective sectioning of the population of long 'apical' dendrites i.e. the removal of the zona reticulata. Intracellular recordings from substantia nigra zona compacta neurones were made from mesencephalic slices of the guinea-pig brain maintained in vitro. In cells without the apical dendrites, the membrane potential, input resistance and mean firing frequency was not significantly different from the control neurones. However, removal of the substantia nigra zona reticulata virtually abolished one conductance in particular. This conductance, seen in control neurones, is a long lasting slow depolarization which is resistant to tetrodotoxin blockade of sodium channels: rather, it is mediated by the entry of calcium ions and is optimally deinactivated at a hyperpolarised membrane potential. Hence, this study strongly suggests that this conductance is generated exclusively in the 'apical' dendrites. It has been postulated that this long lasting calcium conductance is central to the modulation of nigrostriatal neuronal excitability. Thus, the 'apical' dendrites could play a specific and active role in the functioning of nigrostriatal neurones.

Action Potentials↗
PubMed1988

Comparison of propofol and thiopental for the induction of anesthesia.

We compared the safety, efficacy, and side effects of induction of anesthesia with propofol (2.5 mg/kg), a new intravenous agent, and thiopental (4.0 mg/kg) in 62 patients in American Society of Anesthesiologists class I or II. There was no significant difference between induction times for the propofol (40.0 +/- 2.0 sec) and thiopental (44.0 +/- 4.0 sec) groups. Propofol administration produced a significant fall (P less than .05) in systolic blood pressure (SBP), from 134.1 +/- 2.6 mm Hg before injection to 128.3 +/- 2.4, 118.2 +/- 2.7, and 114.4 +/- 2.8 mm Hg one, two, and three minutes after injection, respectively. Diastolic blood pressure (DBP) fell significantly (P less than .05) during the three postinjection periods. Heart rate (HR) rose significantly (P less than .05), from 78.6 +/- 3.1 beats per minute before injection to 89.4 +/- 3.4 beats per minute one minute after injection. In patients given thiopental, SBP fell significantly (P less than .05), from 131.7 +/- 2.7 mm Hg before induction to 126.4 +/- 3.4 and 126.9 +/- 4.0 mm Hg two and three minutes after injection, respectively. The DBP did not change significantly in the thiopental group, but the HR rose significantly (P less than .05), from 73.3 +/- 2.8 beats per minute before injection to 83.9 +/- 3.0, 90.1 +/- 2.3, and 84.2 +/- 2.4 beats per minute one, two, and three minutes after injection, respectively. In 94% of patients given propofol, there were apneic periods of more than 60 seconds, compared to 50% in the thiopental group (P less than .05). There was a significant difference (P less than .05) between groups for the incidence of pain on injection; 31% of the patients receiving propofol had pain, compared to 3% of those receiving thiopental.

Adolescent↗
PubMed1985

A study of institutionalized mentally retarded patients in Manitoba: over-representation by Canadian Indian children.

During analysis of data on 406 severely and profoundly mentally retarded children and their families in Manitoba a marked excess of Canadian Indian children was observed. There was no evidence to suggest that the over-representation by native children was due to an increased propensity of Indian families to institutionalize their children nor were these patients more profoundly retarded or more physically handicapped than the non-Indian children studied. Further analysis showed that Indian children were primarily over-represented in the groups with acquired retardation, autosomal recessive genetic disorders, idiopathic retardation with seizures and idiopathic retardation with malformations or dysmorphic signs. Review of other demographic findings indicated that other factors potentially predisposing to retardation, including low socioeconomic status, illegitimacy, high birth order, poor maternal reproductive history and increased consanguinity, were more common in the histories of native children. Severe and profound mental retardation has been said to occur equally in all strata of society. This evidently was not so in this Canadian population and the Indian child may be at special risk. Health care workers should be aware of possible predisposing factors for retardation in this group if reduction of the incidence of this major problem is to be achieved.

Adolescent↗
PubMed1982

A cytogenetic survey of 14,069 newborn infants. IV. Further follow-up on the children with sex chromosome anomalies.

Between 1970 and 1973, 14,069 consecutive liveborn infants at the Women's Centre, Winnipeg, were subjected to karyotypic analysis. The details of the materials and methods and the preliminary findings of the study have been previously published [1,2]. A total of 15 nonmosaic and 4 mosaic infants with sex chromosome anomalies were detected: 12 males and 7 females. These children have been followed wherever possible by physical and developmental evaluations, and preliminary findings have been reported previously [3]. In order to obtain further baseline data on these children while they were still prepubertal, it was decided to recontact all families and encourage them to present their children for further physical evaluation and psychologic testing. Details of these investigations and their results are given in this paper.

Child↗
PubMed1980

A study of institutionalized mentally retarded patients in Manitoba. I: Classification and preventability.

This preliminary report concerns the types, and the possibility of prevention, of mental retardation found among 406 patients less than 20 years of age and with IQs less than or equal to 50 who had been admitted to institutions for the retarded in Manitoba prior to 1977. The retardation appeared to be of genetic origin in 27.8 per cent of cases, and acquired in a further 30.3 per cent. 31 per cent of the genetic and 55 per cent of the acquired, or 25.4 per cent of the total group, are considered to have been avoidable, given the full application of current techniques and knowledge.

Adolescent↗