Biomedical subjects
Publications and source records attributed to S Gagné.
A circuit for compensating the floating differential capacitance appearing between two recording microelectrodes is presented. It is shown how this floating capacitance can be neutralized so that current in any microelectrode can be injected without any significant crosstalk picked up by the other.
A low-cost and high-speed electromechanical shutter is described. The design makes use of a small magnet moving in a magnetic field and includes a specially developed electronic control for optimal operation. The opening and closing time of the shutter is below 200 microseconds with overall time for generating light flashes close to 1 ms.
OBJECTIVE: This research evaluates the psychometric properties of the French version of the Modified Mini-Mental State (3MS), an instrument for the screening of dementia, in a sample of patients seen in geriatric psychiatry. METHODS: Subjects (N = 94, 63 to 93 years of age) were outpatients of a service in geriatric psychiatry. In addition to the 3MS, a battery of tests evaluating the cognitive functioning and depressive symptomatology was administered. RESULTS: Test-retest reliability coefficient was 0.87 for a subsample of 35 subjects. An exploratory factor analysis revealed 4 factors accounting for 63.2% of the variance. Cut-off scores of 79 to 80 (with years of education > or = 8) and 71 to 72 (with years of education < or = 7) presented the best combination sensitivity/specificity, respectively 0.80 and 0.96. CONCLUSIONS: This study documents the psychometric properties of the French version of the 3MS for use in patients seen in geriatric psychiatry, in suggesting cut-off scores which take into account the level of education. This study underlines the influence of sociodemographic variables on test performance.
The polymerase chain reaction was used to amplify the spacer region located between the 16S and 23S ribosomal RNA genes of strains of Pseudomonas fluorescens and Pseudomonas putida isolated from peat bog, canola field, or arctic plants. Some of spacer region of four of the P. fluorescens strains examined, strains 64-3, 63-28, QP5, and R17-FP2, was about 515 base pairs (bp) in length, and contained the genes for tRNA(Ile) and tRNA(Ala). The DNA sequences of two strains from canola, 64-3 and 63-28, differed at only two positions. The sequences of the peat bog strains QP5 and R17-FP2 were identical. However, differences were noted between the DNA sequence common to the pair of strains 64-3 and 63-28 and the corresponding common sequence for strains QP5 and R17-FP2. These differences were mainly concentrated in two DNA segments of 10 and 19 bp, respectively. A probe for the 19-bp variable segment that occurs in the ribosomal spacer of strains QP5 and R17-FP2 recognized total DNA from these two strains, but not DNA from other bacteria of different origins. These results suggest the existence of a limited degree of variability within the 16S-23S ribosomal DNA spacer region, and that this variability may be useful to the recognition of particular Pseudomonas strains from environmental samples.
Pasteurella multocida type D toxin is a peptide shown to induce severe atrophic rhinitis in the pig as the result of an increased osteoclastic resorption of the ventral nasal turbinates. In the present study, the effects of the toxin on the histological, cytochemical and ultrastructural features of the osteoclast population of the rat were examined. Pasteurella multocida toxin induced atrophy of the ventral and dorsal nasal turbinates and thinning of the nasal bones. The number and size of the long bone metaphyseal osteoclasts were significantly increased, but not the number of nuclei per cell. Osteoclasts of toxin-treated rats had more developed clear zones and ruffled borders than those of the controls and their cytoplasmic vacuoles were more abundant and larger. We concluded that P. multocida toxin stimulates bone resorption by osteoclasts in the rat by increasing resorption activity and by increasing their number. Its action is not limited to the nasal turbinates but occurs also in the other bones, such as the long bones.
Research on atrophic rhinitis of pigs has shown that both Bordetella bronchiseptica infection and experimental treatment with acetic acid predispose the nasal mucosa to colonization with Pasteurella multocida. Gnotobiotic piglets aged 3 days were dosed intranasally with either B. bronchiseptica (n = 6) or acetic acid 1 per cent (n = 10) and killed at intervals up to the 4th day after treatment. Samples of the ventral turbinates were examined by light microscopy and scanning and transmission electron microscopy. Within 12 h acetic acid induced loss of cilia, oedema, focal cell exfoliations, mitochondrial swelling and inflammatory cell infiltration. Bordetella bronchiseptica induced only a limited oedema and loss of cilia. Colonization of cilia by the bacteria was observed 96 h after infection. We conclude that, although acetic acid and B. bronchiseptica do not induce the same modifications of the nasal respiratory epithelium, their action causes stagnation of nasal mucus, which results in a nasal environment favourable to colonization by Pasteurella multocida.
Left-handed and right-handed subjects were given two dichotic listening tasks using identical material. In one task, they were asked to determine whether or not a specific target word was present (verbal task). In the other task, subjects were asked to indicate whether or not one of the dichotically-competing words was spoken in a particular affective tone (emotion task). Overall, a right-ear advantage (REA) was found with the verbal task and a left-ear advantage (LEA) with the emotion task. Left-handers showed a slightly smaller REA than right-handers on the verbal task, but a slightly larger LEA on the emotion task. This finding suggests that left- and right-hemispheric functions are not related in a complementary fashion and that handedness effects for nonverbal tasks are different from those seen with verbal tasks. The emotional LEA was much larger for angry stimuli than for happy, sad, or neutral stimuli. Rather than providing evidence for a hemisphere by affective valence interaction, such results suggest a stimulus-specific effect.
We present models based on transmitter gating and competition for SUSTAINED and ON-OFF units located in the lamina of the fly visual system. Predictions of the models are compared with data in several experimental paradigms. The overshoot and the plateau of the response are explained by the adaptation process of transmitter dynamics. Furthermore, it is demonstrated that this transmitter adaptation when coupled with fast competition can explain response features arising from different combinations of ON and OFF field inputs.
The early receptor potential (ERP) of fly photoreceptors R1-6 has been recorded in the blowfly Calliphora erythrocephala, and quantitatively analyzed. Photoconversion of the native visual pigment (P) into the meta-state (M) does not induce a measurable ERP. Photoconversion of M into P induces a biphasic ERP, presumably due to the slow thermal decay of intermediate N, recently discovered by Roebroek, Gagné and Stavenga (1989). The experimentally measured ERP's are interpreted with an RC-model which incorporates the time constant of the flash, the time constant of the thermal decay of intermediate N, the electrical properties of the photoreceptor cell and the charge displacements within the visual pigment molecules occurring upon photoconversion. The model satisfactorily describes the ERP for the M to P conversion by assuming that effectively 0.03 electron charges are moved across the cell membrane during conversion of the M to the N state and that 0.04 electron charges are moved in the opposite direction during conversion of N to P. The net 0.01 electron charge movement during conversion of P to M would, according to the simple RC-model, induce a measurable ERP, in conflict with the experimental results. The longstanding enigma of the ERP of fly photoreceptors appears largely but not completely resolved.
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A mathematical analysis of the tip potential based on the main physicochemical phenomena occurring at the tip of a glass microelectrode is presented. The factors considered in the theoretical analysis are the diffusion of ions through the open tip, the conduction in the bulk solutions, the longitudinal conduction in the double layers at the glass-electrolyte interfaces, and to some extent, in a hydrated glass layer. A graphical analysis of the mathematical expressions as a function of the resistivity of test solutions is done and the distribution of the source potentials giving rise to the tip potential is studied. The experimental results presented in the paper confirm the validity of the proposed theoretical model. Comments for an improved use of glass microelectrodes in electrophysiological experiments are given throughout the paper.
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A study was made of 9 cases of left atrial myxoma with emphasis on the echocardiographic, haemodynamic and anatomical aspects and on the main clinical features. An epidemiological enquiry was made regarding the possibility of recurrences or familial cases. It was negative, suggesting that such cases are rare. The echocardiographic signs of left atrial myxoma are inconstant. The mitral diastolic EF slope is variable, the delay in appearance of the tumour echo behind the mitral valve in diastole is not constant, and the atrial "a" wave may be preserved. The echocardiographic features are a function of the size and shape of the myxoma, as well as the length and site of implantation of its pedicle.
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