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Biomedical subjects

M Srinivasan

Publications and source records attributed to M Srinivasan.

At least 145 records · Page 8Linked to original sources
PubMed1988

Ventilatory effects of naloxone via the sympathoadrenal system in the neonate?

Rabbit pups responded to hypoxia (6% O2 in N2) with a biphasic respiratory pattern, an initial increase by 1 min followed by a decrease. Naloxone (0.8 mg/kg) was found to abolish the declining phase of hypoxia, showing a sustained increase of ventilation throughout the hypoxic challenge. Phentolamine (30 micrograms/kg), an alpha-blocker, had no effect on the normal hypoxic response. However, pretreating the pups with phentolamine and then administering naloxone resulted in a biphasic response to hypoxia. We propose that the naloxone effects on ventilation are mediated in conjunction with the adrenergic system.

Adrenal Glands↗
PubMed1988

Respiratory cytopathology in chlorine gas toxicity: a study in 28 subjects.

Bronchial brushings to evaluate cytopathologic changes were collected from 28 patients exposed to a toxic atmospheric level (66 parts/million) of chlorine gas. Postexposure smears collected on day 5 showed basal-cell and goblet-cell hyperplasia, acute inflammation, and chromatolysis of columnar epithelial cells. Columnar epithelial cell syncytia were observed in 15 (53.57%) smears. Nine (32.14%) smears showed abundant nonpigmented alveolar macrophages. Seven (25%) smears from mucosal erosions showed proliferating fibroblasts and capillary fragments; on day 15 and day 25 repeat smears from these seven cases showed evidence of epithelial regeneration and repair by fibrosis. This latter feature could lead to chronic ventilatory incapacitation in patients exposed to toxic levels of chlorine gas.

Adult↗
PubMed1988

Antigen-presenting function of B lymphocytes.

Here we review our current results studying B cells as APC and the mechanisms by which processed antigen is transported to and held on the cell surface for recognition by the specific T cell along with the MHC class II molecules. These studies were carried out using the globular protein cytochrome c as antigen for which the T-cell antigenic determinant was localized to a C-terminal 10-amino acid peptide fragment. For certain analyses, native cytochrome c or antigenic peptide fragments were covalently coupled to antibodies directed toward B-cell surface structures, allowing the targeting of antigen to the APC surface. Our findings indicate that all B cells function as APC and that the APC function is not differentially regulated in defined B-cell subpopulations. Using cytochrome c-antibody conjugates, it was shown that the surface Ig plays two significant roles in augmenting the B-cell APC function following antigen binding: signalling for enhanced APC function and concentrating antigen for subsequent internalization and processing. Both IgM and IgD appear to function identically in facilitating antigen processing in both immune and nonimmune B-cell populations. Furthermore, the surface Ig does not appear to be specially differentiated to function in concentrating antigen, as antigen artificially bound to other B-cell surface structures including MHC class I and class II molecules is also effectively presented. Lastly, evidence is presented that a previously described B-cell activating factor activity is strongly associated with the membranes of activated but not unactivated helper T cells, providing a mechanism by which the T-cell helper function can be focused on the specific antigen-presenting B cell. Concerning the mechanism by which processed antigen is presented at the B-cell surface, evidence is presented suggesting a role of peptide-binding chaperone proteins which may function to transport peptide to the APC surface and facilitate its association with the appropriate Ia. One candidate protein, PBP72/74, is described which binds peptides but not native antigens, is a member of the hsp70 family and appears to play a role in antigen presentation by the ability of antisera raised against it to block APC functions. Peptide-antibody conjugates were used to explore the spacial restrictions on MHC-restricted peptide presentation and it was shown that peptides covalently coupled to antibodies specific for Ig, class I or class II molecules are effective antigens in vitro even in the absence of processing.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Relationship between lesion extent in 'Wernicke's area' on computed tomographic scan and predicting recovery of comprehension in Wernicke's aphasia.

This study investigated the relationship between severity of auditory comprehension in Wernicke's aphasia and amount of temporal lobe damage within Wernicke's area (posterior two thirds of superior temporal gyrus region) as well as the total temporoparietal lesion size. There was a highly significant correlation between comprehension and the amount of temporal lobe lesion in Wernicke's area. There was no significant correlation between comprehension and the total temporoparietal lesion size. Patients with damage in only half or less than half of Wernicke's area had good comprehension at six months after the onset of stroke. Patients with damage in more than half of Wernicke's area had poor comprehension even one year after the onset of stroke. Additional anterior-inferior temporal lobe lesion extension into the middle temporal gyrus area was associated with particularly poor recovery.

Aged↗
PubMed1987

Bees perceive illusory colours induced by movement.

Certain black-and-white patterns, when rotated at appropriate speeds, can create the artificial perception of hues. We report that this illusion is not confined to human vision, but is also perceived by an insect, the honeybee. The findings suggest that certain features underlying the processing of colour information are shared by man and bee.

Animals↗
PubMed1987

Serum immunoglobulins in mycotic keratitis--an interim report.

Serum immunoglobulins were estimated in 34 patients selected randomly and 6 controls. 27 had fungal corneal ulcers and seven had bacterial corneal ulcers. The IgM was low in 7 patients who had fungal keratitis. One patient who had IgM only 25 mgs./100cc of serum immunoglobulin, developed fungal ulcer in both eyes (fusarium in one eye) within a year. IgG was increased in 16 patients. No control had rise of IgG or fall of IgM.

Humans↗
PubMed1985

Visual scanning behaviour in honeybees.

Freely flying bees were rewarded with sugar solution on a variety of black-and-white shapes as well as on coloured gratings in various training situations. In subsequent dual-choice tests, the bees' discrimination between the various shapes was measured. In addition, the bees were video-filmed while flying in front of the shapes. The scanning patterns thus obtained were then quantified in order to characterize scanning behaviour and its relationship to the geometrical parameters of the scanned shapes, investigate whether scanning plays a role in pattern discrimination and examine the influence of training on the characteristics of scanning. The scanning patterns clearly mirror the contours of the scanned shape in all cases, i.e. the bees fly along the contours contained in the shape. This behaviour does not depend on whether the scanned shape is one that was previously rewarded, or one that is completely novel to the bees. Comparison of the results of quantifying the scanning patterns with the results of dual-choice tests reveals that scanning behaviour is independent of discrimination performance. On the average, horizontal scanning directions occur more often than vertical directions. Variations of the training situation produce measurable differences in scanning behavior. However, except in the case of vertical scanning on a vertical grating, these differences are quite small, indicating that following contours is a largely stereotyped behaviour. Horizontal gratings are very well discriminated from vertical ones even if they offer contrast to only one receptor type, i.e. blue or green, demonstrating that the direction of contours is visible to the pattern recognition system even under these conditions. However, vertical and horizontal coloured gratings offering only blue-contrast do not elicit contour-following, whereas gratings offering only green-contrast do. Thus, the bees' scanning behaviour is colour-blind and most probably governed by the green receptors. We suggest that contour-following is the by-product of a behavioural mode which serves to prevent retinal image movement during flight in front of a contoured visual pattern.

Animals↗
PubMed1985

Temporal resolution of colour vision in the honeybee.

The temporal resolution of colour vision was measured in freely-flying honeybees by testing the performance of trained bees in discriminating between two stimuli, one of which presented a steady, homogeneous mixture of two colours, while the other offered a heterochromatic flicker between the two colours at various temporal frequencies. Pairwise combinations of the colours uv, blue and green were used, corresponding to the three receptor classes in the bee retina. For each colour combination, we determined a cutoff frequency beyond which discrimination no longer exists. For a given colour combination, the cutoff frequency depends upon the ratio of the intensities of the component colours, and is maximum at a particular ratio. The cutoff frequency at the optimum intensity ratio is approximately 100 Hz for each of the 3 colour combinations blue-green, green-uv and uv-blue, implying that colour computation requires ca. 10 ms. From the optimum intensity-ratios for the three colour combinations, we infer that the relative sensitivities of the green, blue and uv channels are approximately 1:1.3:24.

Animals↗
PubMed1984

Collateral pathways of the left gastric vein in portal hypertension.

Since June 1974, 347 percutaneous transhepatic portal venographic studies were performed on 246 patients with portal hypertension who had had bleeding gastroesophageal varices. Of 234 patients in whom left gastric veins (LGV) (coronary) were demonstrated, 177 (75.6%) had a single LGV and 57 (24.4%) had multiple left gastric veins (21.8% had two LGVs, 2.1% had three LGVs, and 0.5% had five LGVs). Of 193 patients undergoing selective left gastric venography, spontaneous portosystemic communications to the left renal vein were found in 55, to the inferior vena cava in two, to the inferior pulmonary veins in five, to the pericardiophrenic vein in eight, to the right inferior phrenic vein in three, and to the left intercostal veins in one. Interportal communications with the left gastric vein and varices occurred from the left portal vein in 13, from the gastroepiploic vein in one, and from a superior mesenteric vein branch in one. The predominant drainage of esophageal varices was to the azygos vein in 78 of 155 patients, to the hemiazygos vein in 13, and to multiple small unnamed veins in the mediastinum in 57. Opacified varices did not extend above the level of the azygos vein arch in 71 of 130 patients; however, 59 continued cephalad to the azygos arch and drained through more superior veins of the thorax. Knowledge of the anatomy and incidence of each of these portosystemic or interportal venous communications is important to properly treat bleeding esophageal varices by surgery or angiographic embolization.

Collateral Circulation↗
PubMed1981

The value of postcardiac infarction exercise stress testing: identification of a group at high risk.

We prospectively selected 154 patients who had survived acute myocardial infarction with electrical and/or mechanical complications to undergo an exercise stress test, four to six weeks after discharge from the Coronary Care Unit, Royal Melbourne Hospital. The patients exercised on a bicycle ergometer until they were unable to continue or had reached 70% of their predicted maximum heart rate for their age. Eighteen (11.7%) patients exhibited flat ST-depression of 1 mm or more on exercise. Six of these 18 patients later died (33.3%). Only seven (5.1%) of the 136 patients who exhibited no electrocardiographic change died during follow-up. We conclude that patients recording positive exercise stress test results after acute myocardial infarction, have a poorer prognosis and therefore should be considered for more intensive medical or surgical treatment.

Arrhythmias, Cardiac↗