Biomedical subjects

D Coulombe

Publications and source records attributed to D Coulombe.

9 recordsLinked to original sources

PubMed1992

Antihypertensive and hemodynamic effects of calcium channel blockade with isradipine after acute exercise.

In a randomized, double-blind, placebo-controlled, crossover study with two 4-week treatment periods, we investigated the effects of calcium channel blockade with 5 mg slow release oral isradipine on postexercise blood pressure and systemic hemodynamics (echocardiography) in ten hypertensive patients. The results show that the combination of exercise and isradipine treatment exerts additive antihypertensive effects in hypertensive patients after exercise. The antihypertensive effect of prior exercise with placebo was related to a significant fall in total peripheral resistance. After exercise during isradipine treatment, total peripheral resistance was lower than with placebo. Thus, isradipine exerts an additional antihypertensive effect during the postexercise period, which appears to be mediated by a further reduction of total peripheral resistance.

Adult↗

PubMed1992

Baroreflex regulation of forearm vascular resistance after exercise in hypertensive and normotensive humans.

The mechanisms underlying the antihypertensive period following a bout of exercise are not well understood. We examined the aftereffects of exercise on the linear relationship between forearm vascular resistance (FVR) and estimated central venous pressure (CVP) during leg raising and lower body negative pressure to determine whether an alteration of the baroreflex control of FVR was associated with the decreased blood pressure. Blood pressure, forearm blood flow (FBF), and estimated CVP were obtained in 13 hypertensive and 9 normotensive subjects evaluated in a randomized crossover fashion after 30 min of cycle ergometer exercise and after a nonexercise control period. In hypertensive subjects, the reduced blood pressure was accompanied by an increased baseline FBF after exercise. This resulted in a downward shift of the FVR-CVP relationship, while the slope was unchanged. In normotensive subjects, blood pressure and baroreflex control of FVR were unaffected by prior exercise. Four of the hypertensive subjects performed an additional study in which forearm skin was vasodilated with local heating to FVR levels similar to those observed after exercise. Results suggested that the aftereffects of exercise could not be attributed to changes in cutaneous blood flow. We speculate that modulation of the baroreflex control of FVR after exercise contributes to its antihypertensive effect.

Cold Temperature↗

PubMed1992

Aftereffects of exercise on regional and systemic hemodynamics in hypertension.

Several studies have indicated that a single bout of physical exercise induced a significant antihypertensive effect during the hours after the activity. However, little information is presently available on the underlying hemodynamic changes. We examined 13 essential hypertensive patients and nine normotensive subjects in a randomized, crossover study design during 3 hours after a 30-minute period of upright leg cycling at 50% of peak aerobic capacity and during 3 hours after a 30-minute control period of rest. Blood pressure, heart rate, cardiac output, total peripheral resistance, and regional vascular resistance in the forearm as well as venous plasma catecholamine concentrations were measured repeatedly. After exercise, systolic (-11 +/- 2 mm Hg) and diastolic (-4 +/- 1 mm Hg) blood pressures, total peripheral resistance (-27 +/- 5%), forearm vascular resistance (-25 +/- 6%), and plasma norepinephrine levels (-21 +/- 7%) were significantly (p less than or equal to 0.05) decreased, and cardiac output was increased (+31 +1- 8%) compared with control in hypertensive subjects. In contrast, in normotensive subjects blood pressure, forearm vascular resistance, and plasma norepinephrine were unchanged, and systemic hemodynamics changed to a lesser extent than in hypertensive subjects after exercise. It is concluded that a decrease in regional vascular resistance in skeletal muscles and possibly in the skin in hypertensive patients may contribute importantly to the antihypertensive effect of prior exercise. A decreased sympathetic nervous activity, as seen from lower plasma norepinephrine levels, may be involved in this effect.

Adult↗

PubMed1991

Interactions between amygdaloid and hypothalamic self-stimulation: a re-examination.

The function relating bar-pressing rate to the frequency of cathodal pulses was obtained in rats self-stimulating with amygdaloid (AMY) and lateral hypothalamic (LH) electrodes. The maximum self-stimulation (SS) rates in the AMY was found to be very low, compared to the LH. Concurrent stimulation with pairs of AMY-LH pulses did not shift the rate-frequency functional laterally, indicating the absence of summation of the two rewarding effects. In a second experiment, concurrent AMY-LH stimulation (using sub-threshold intensity LH pulses) facilitated bar-pressing for AMY stimulation (it increased the slope of the AMY rate-frequency function) without shifting this function laterally. In a third experiment, subjects were given a choice between a pulse frequency yielding maximal AMY rate and a series of higher pulse frequencies. Subjects consistently preferred the higher frequency values, attesting that the maximum AMY rates were not constrained by a saturating reinforcing effect. In a fourth experiment, subjects were given a choice between AMY stimulation and concurrent AMY-LH stimulation, using low intensity LH pulses. Subjects showed no preference for either stimulation condition, although rates were higher for the latter condition. These findings suggest that the maximum rate for AMY stimulation was constrained by factors interfering with bar-pressing and that the effect of these factors was attenuated by co-activation of the LH. In a fifth experiment, pre-treatment with phenobarbital mimicked the rate-enhancing effect of concurrent AMY-LH stimulation for 2 of the 4 subjects tested. This finding suggests that the LH pulses contributed to attenuate seizure activity accompanying AMY SS. In a final experiment, AMY SS rates were also increased by co-activation of rewarding sites in the rostral MFB but not the dorsal raphe, suggesting an anatomical specificity of this effect.

Amygdala↗

PubMed1991

Amygdaloid self-stimulation: a movable electrode mapping study.

The distribution of electrical self-stimulation foci within the amygdala (AMY) was mapped using movable electrodes in rats. Each barpress delivered a 0.4-s train of cathodal rectangular pulses of fixed intensity and duration and variable frequency. The rate-frequency function was recorded for successive dorsoventral sites. Self-stimulation was found throughout the AMY, except in the lateral nucleus. Depending on the site, maximum rates varied from 3 to 37 barpresses/min, whereas threshold frequencies varied from 9.2 to 40 pulses/train; no correlation between these two aspects of self-stimulation was found. Most threshold frequencies lay within the range of 10 to 20 pulses/train, which suggests a relatively homogeneous distribution of rewarding efficacy within the positive areas. The lowest threshold estimates are comparable to those usually obtained for pontine and medial forebrain bundle areas, which suggests that the AMY is an important focus for self-stimulation.

Amygdala↗

PubMed1989

Intensive language learning and increases in rapid eye movement sleep: evidence of a performance factor.

Ten anglophone students taking a 6-week French immersion course were recorded in the sleep laboratory during 4 consecutive nights before the course, during the course and after the course. There was a positive and significant (P less than 0.05) correlation between language learning efficiency and increases in the percentage of rapid eye movement (REM) sleep from pre-course to course periods. This observation suggests that learning performance may be an important factor in the relationship between information processing and REM sleep.

Adolescent↗

PubMed1987

Fitting intracranial self-stimulation data with growth models.

Until now, the problem of fitting self-stimulation rate-frequency functions has been dealt with by using linear models applied to the linear portion of the empirical curve. In this article, an alternative procedure is presented, together with three sigmoid growth models that seem to accurately fit rate-frequency data. From any of these models, it is possible to compute the two indices of stimulation efficacy in use in the parametric study of brain stimulation reward (M50 and theta 0), in addition to the inflection point of the curve, which can be used as an alternative to M50. Important relations allowing initial estimation of each parameter are provided, allowing use of computer programs derived from the Gauss-Newton algorithm for nonlinear regression. The considerations relevant to the choice of a nonlinear model are discussed in terms of each efficacy index.

Algorithms↗

PubMed1986

The curve-shift paradigm in self-stimulation.

Eleven rats were trained to press a lever in an operant chamber in order to earn rewarding trains of cathodal rectangular pulses of fixed intensity and variable frequency. The rate-frequency functions were examined under administration of two neuroleptics (pimozide and chlorpromazine) and three manipulations that interfered with bar pressing (muscular relaxation with methocarbamol, increased lever weight, and limitation of maximum response rates by an F1 reinforcement schedule). Chlorpromazine, and pimozide at low dosages produced a near parallel shift of the rate-frequency functions on the logarithmic axis of pulses, suggesting that these drugs decreased the reinforcing efficacy of the stimulation. The three conditions that interfered with bar-pressing decreased the asymptotic rates and produced small or moderate lateral shifts. Changes in the reinforcing efficacy of the stimulation following the above manipulations were inferred from the shift in the number of pulses required at zero and half-maximal performance (theta 0 and M50 indices, respectively). In the cases of the manipulations that interfered with bar-pressing, M50 indicated a larger artifactual change in the efficacy of the stimulation, compared to theta 0. This phenomenon was mainly due to the fact that the asymptote of the altered functions was shifted towards higher pulse numbers.

Animals↗

PubMed1986

The effects of pimozide on the reinforcing efficacy of central grey stimulation in the rat.

The present report describes the effects of the neuroleptic pimozide on the reinforcing efficacy of central grey stimulation. Six adult rats were implanted with a monopolar moveable stimulating electrode in the pontine central grey. Each bar-press in an operant chamber delivered a 0.3-s train of cathodal rectangular pulses of constant duration (0.1 ms) and intensity (from 180 to 440 microA depending on the subject) and of variable frequency. The function relating the rate of bar-pressing to the logarithm of the number of pulses per train (rate-frequency function) was recorded following administration of vehicle and increasing doses of pimozide (from 0.15 to 0.5 mg/kg). Pimozide produced a dose-dependent parallel shift of the rising segment of the rate-frequency function towards higher pulse numbers in 4 subjects, indicating that the drug reduced the reinforcing efficacy of the stimulation. In two subjects, the shift was accompanied by a decrease in slope of the rising segment. Depending on the subject, the greatest shift observed varied from 0.087 to 0.489 log units. Further attempt to increase the magnitude of shift with higher doses resulted in complete abolition of self-stimulation. The fact that pimozide reduced the value of reward in an area containing only marginal amounts of dopaminergic cells adds support to the hypothesis that dopamine modulates reward indirectly. The fact that the shift could not be increased with higher doses was interpreted as an indication that dopaminergic neurons are involved in a gate-like synaptic arrangement in which a limited decrease in dopaminergic activity is sufficient to obliterate the transmission in the reward pathway or the conversion of the signal into a reinforcing effect.

Animals↗