Biomedical subjects

M Beauregard

Publications and source records attributed to M Beauregard.

At least 55 records · Page 3Linked to original sources

PubMed1992

Opposite effects of neurotensin on dopamine inhibition in different regions of the rat brain: an iontophoretic study.

Anatomical, biochemical and behavioral data suggest functional interactions between dopamine and neurotensin in regions of the brain receiving a co-existent and/or distinct innervation by these two transmitters. We therefore measured and compared the effects of iontophoretically applied dopamine and neurotensin in the prefrontal and anterior cingulate cortex (co-existent innervation) vs the nucleus accumbens and neostriatum (distinct innervation) of urethane-anesthetized rats. In every region, the firing rate of most spontaneously active neurons was depressed by dopamine. Neurotensin had no effect on the same cells, except for a few nucleus accumbens units which were inhibited by the peptide. When dopamine and neurotensin were concomitantly applied, the magnitude of maximal inhibitions induced by dopamine was modified in the majority of neurons tested. A significant decrease in dopamine inhibition was observed in 100% of anterior cingulate, 74% of prefrontal cortex and 48% of accumbens units. On the contrary, in neostriatum, dopamine inhibition was significantly increased in 60% of the units tested. In every region, the remaining neurons showed less than 30% changes in dopamine responsiveness, and were therefore considered unaffected by neurotensin. In the anterior cingulate cortex, inhibitions, respectively, induced by the dopamine D1 agonist, SKF 38393, and the D2 agonist, LY 171555, were also decreased by simultaneous application of neurotensin. Together with currently available data on the cellular localization of neurotensin receptors in rat brain, these results suggest that the modulation of dopamine inhibition by neurotensin may have opposite effects depending on whether the neurotensin receptors are located postsynaptically on target neurons (antagonistic effects) or presynaptically on dopamine terminals (potentiating effects).

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1991

Dopamine modulates the inhibition induced by GABA in rat cerebral cortex: an iontophoretic study.

Effects of iontophoresed gamma-aminobutyric acid (GABA) and two GABA agonists, 4,5,6,7-tetrahydroisooxazolo-[5,4-c]pyridine-3-ol (THIP) and baclofen were quantitatively compared in the anterior cingulate, frontal, and parietal cortex of urethane-anesthetized intact rats after catecholamine (CA) depletion with alpha-methyl-p-tyrosine (alpha-MPT) or selective dopamine (DA) denervation with 6-hydroxydopamine (6-OHDA). As assessed with to the IT50 index, the postsynaptic sensitivity to GABA was significantly higher in anterior cingulate than in frontal and parietal cortex. The responsiveness to GABA was also greater in frontal than in parietal cortex. Sensitivity to GABA was significantly reduced in both anterior cingulate and frontal cortex after CA depletion, and similarly, after DA denervation with 6-OHDA. The difference in the sensitivity to GABA between the three cortical regions in intact rats as well as after CA depletion did not seem to be correlated with either GABAA or GABAB receptors since the responsiveness to both GABA agonists in every region examined was comparable in intact rats, and remained unchanged after alpha-MPT treatment. This finding raises the possibility that some GABA receptors in the cerebral cortex may be pharmacologically distinct from the two main subtypes of GABA receptors, GABAA and GABAB. When GABA was administered by iontophoresis in the anterior cingulate cortex during continuous applications of subthreshold currents of DA, the inhibition induced by GABA was either increased or decreased. As DA innervation density is nearly two-fold greater in anterior cingulate than in frontal cortex, and 30-fold greater in anterior cingulate than in parietal cortex, these results suggest that responsiveness to GABA may be correlated with the regional density of DA innervation and that elevated levels of DA may enhance the sensitivity to GABA.

Animals↗

PubMed1991

Comparative analysis of the effects of iontophoretically applied dopamine in different regions of the rat brain, with special reference to the cingulate cortex.

A systematic comparison of the effects of iontophoresed dopamine (DA) was carried out in the neostriatum (NS), nucleus accumbens (Acb) and anterior cingulate (ACg), prefrontal (PF) and parietal (Par) cortex of urethane-anesthetized rats, before and after treatment with the specific DA uptake blockers GBR 12909 and Bupropion. Similar experiments were also conducted after DA denervation with 6-hydroxydopamine and after DA depletion with alpha-methyl-p-tyrosine. The average rate of spontaneous neuronal firing was comparable in all regions, except in the NS after DA depletion. A majority of the units were inhibited by DA in every region and condition tested. As assessed with the IT50 index, the responsiveness to DA was not markedly different between regions, indicating that the postsynaptic sensitivity to this amine is independent of the density of DA receptors and of DA innervation. In contrast, the average duration of DA inhibitions (RT90) was considerably longer (5-fold) in the intact ACg than in the PF, Par, NS, or Acb. Moreover, treatment with both DA uptake blockers reduced the duration of DA inhibitions in ACg (4- to 9-fold); while lengthening it in PF, NS and Acb; and having no apparent effect in Par. DA depletion and DA denervation also reduced the duration of the DA inhibitions in ACg without effect in Par. Taken together, these results provide further evidence for the existence of a presynaptic, positive-feedback mechanism in ACg, triggered by DA, and favouring the further release of this transmitter upon its reuptake in DA nerve terminals.

Animals↗

PubMed1991

Spectroscopic investigation of structure in octarellin (a de novo protein designed to adopt the alpha/beta-barrel packing).

We present here a spectroscopic structural characterization of octarellin, a recently reported de novo protein modelled on alpha/beta-barrel proteins [K. Goraj, A. Renard and J.A. Martial (1990) Protein Engng, 3, 259-266]. Infrared and Raman spectra analyses of octarellin's secondary structure reveal the expected percentage of alpha-helices (30%) and a higher beta-sheet content (40%) than predicted from the design. When the Raman spectra obtained with octarellin and native triosephosphate isomerase (a natural alpha/beta-barrel) are compared, similar percentages of secondary structures are found. Thermal denaturation of octarellin monitored by CD confirms that its secondary structures are quite stable, whereas its native-like tertiary fold is not. Tyrosine residues, predicted to be partially hidden from solvent, are actually exposed as revealed by Raman and UV absorption spectra. We conclude that the attempted alpha/beta-barrel conformation in octarellin may be loosely packed. The criteria used to design octarellin are discussed and improvements suggested.

Circular Dichroism↗

PubMed1991

[Health: this is what women have said...].

Co-authored by a number of prominent Québec women, including former federal health minister Monique Bégin, this award-winning anthology examines a number of issues from a feminist perspective. Among them: violence against women; nutrition; the reconciliation of motherhood with the world of work; infertility and new reproductive technologies; and the politics underlying the debate over midwives. The book should help women to grasp the important notion of autonomy in dealing with their state of health and at the same time touch all nurses, say the authors of the article.

Female↗

PubMed1990

Radioimmunoassay of serum pepsinogen in relation to gastric (pars oesophagea) ulceration in swine herds.

A radioimmunoassay for the detection of serum swine pepsinogens is described. The sensitivity and reproducibility of the assay were satisfactory for its clinical use. In normal pigs, the serum pepsinogen level was 1.51 +/- 0.56 ng/mL. Cases with parakeratosis, erosions and ulcerations of the pars oesophagea had elevated pepsinogen levels (5.15 +/- 1.98 ng/mL).

Animals↗

PubMed1989

Possible existence of a presynaptic positive feedback mechanism enhancing dopamine transmission in the anterior cingulate cortex of the rat.

A series of microiontophoretic and VTA stimulation experiments, conducted in intact, GBR-12909-treated, alpha-methylparatyrosine-depleted or 6-hydroxydopamine-denervated rats, provide suggestive evidence for the existence of a presynaptic, positive feedback mechanism triggered by dopamine reuptake and favoring the release of this transmitter in the anterior cingulate cortex.

Animals↗

PubMed1988

Removal of the 33, 23 and 18 kDa extrinsic proteins of photosystem II by sulfite treatment at alkaline pH.

We found that sulfite incubation of photosystem II submembrane fractions can induce selective depletion of the 18, 23 and 33 kDa polypeptides of the PSII oxygen evolving complex. When the sulfite treatment was done at pH 8.0, the 18 and 23 kDa proteins were removed efficiently from the PSII oxygen evolving complex. Under the same conditions, the 33 kDa subunit remained bound (even when 2 M sodium sulfite was used). However, in more alkaline conditions (pH 9.8), we show extensive removal of the 33 kDa in the presence of a low sulfite concentration (50 mM). The different extraction affinity for the 18, 23 and 33 kDa of the photosystem II complex was interpreted to mean that the 33 kDa polypeptides are bound to photosystem II by both electrostatic and hydrogen bonding forces.

Chlorophyll↗

PubMed1987

Photosynthetic action spectra of the energy storage in bundle sheath cells of Zea mays.

Photosynthetic action spectra (Formula: see text), (Carpentier, R., Larue, B. and Leblanc, R. (1984) Arch. Biochem. Biophys. 228, 534-543.), from 400 to 750 nm were studied in bundle sheath cells of maize. Photosynthetic action spectra in the presence of 10 mM ascorbate or 4 mM ribose-5-phosphate were increased and shifted through all the spectra. After the addition of 10 microM DCMU photosynthetic action spectra were remarkably diminished. On the basis of these results we suggest that the role of PSII in BS chloroplasts will be to prevent the overoxidation of PSI. It appears that in addition to PSII some endogen electron donor may regulate the PSI activity in bundle sheath cells.

Chloroplasts↗

PubMed1987

Study of Energy Storage Processes in Bundle Sheath Cells of Zea mays.

Photochemical energy storage in isolated bundle sheath cells from Zea mays was examined. Photoacoustic spectroscopy was used in this study to monitor energy storage processes. The presence of methyl viologen or addition of substrates which activated carbon fixation, prevented energy storage processes through the electron transport system. The energy storage was inhibited completely by dibromothymoquinone (DBMIB) and DCMU, inhibitors of noncyclic electron flow. However, the reductants such as dithiothreitol and ascorbate increased the energy storage. It was concluded that photosystem (PS) I may be reduced by some electron donor(s) other than water and that PSII only partially participates in PSI reduction. It is postulated that the role of PSII is to regulate PSI electron transport and prevent its overoxidation. In the presence of high level of malate, photoacoustic spectroscopy indicated a low energy storage which may be due to induction of energy utilization in carbon assimilation.

Journal Article↗

PubMed1983

Neonatal diarrhea of pigs in Quebec: infectious causes of significant outbreaks.

To evaluate the relative importance of the various enteropathogens causing neonatal diarrhea in Quebec farrowing operations, observations were made on 749 diarrheic pigs from 325 outbreaks of diarrhea. They were one to 15 days of age, and were obtained alive for necropsy generally within 48 hours of the onset of diarrhea. Some pigs were from severe, explosive outbreaks of diarrhea with high morbidity and mortality rates, while others were from herds with chronic neonatal diarrhea with lower morbidity and mortality rates. A combination of bacteriological, virological and histological methods were used to study the pigs. Viruses were incriminated in 60%, bacteria in 23% and coccidia in 15.3% of the 325 diarrhea outbreaks. Transmissible gastroenteritis virus was by far the most common enteropathogen with a prevalence of 52%; rotavirus was implicated in 9.2% of the outbreaks while adenovirus was incriminated in 0.30% of the outbreaks. Enterotoxigenic Escherichia coli were involved in 22.4% of the cases while Clostridium perfringens type C was an occasional finding. Coccidia involved in our herds were identified as Isospora suis. The disease was attributed to infection with a single etiologic agent in 590 diarrheic pigs (78%) while combinations of agents were present in only 90 (12%). The age-specific occurrence of the various enteropathogens was evaluated. Transmissible gastroenteritis virus was the most common enteropathogen in all age groups. Colibacillosis was common in pigs which became diarrheic under five days of age; in this age group, the enterotoxigenic E. coli were frequently found alone, but were usually combined with other agents in older pigs. The prevalence of coccidia was high in pigs which became diarrheic between five and 15 days of age. Rotavirus infection was common in diarrheic pigs older than ten days of age. Although individual baby pigs were commonly infected with a single enteropathogen, it was very common to see more than one agent involved in an outbreak of diarrhea, particularly when pigs of different ages were affected. Observations on the occurrence of the enteropathogens according to the seasons were also made. Occurrence of transmissible gastroenteritis was throughout the year with the highest prevalence during the fall, winter and spring months. Colibacillosis and coccidiosis were more common in the summer, fall and early winter months with the lowest prevalence in the spring months.

Adenoviridae↗

PubMed1973