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Biomedical subjects

M Cabanac

Publications and source records attributed to M Cabanac.

At least 37 records · Page 2Linked to original sources
PubMed1998

Selective brain cooling and thermoregulatory set-point.

During heat stress, the function of selective brain cooling puts trunk core temperature in an open-loop situation. As a result, trunk core temperature deviates more than expected, while brain temperature remains lower than trunk temperature. Such an influence of selective brain cooling might explain why the set-point for temperature regulation was considered to be reset at higher values in various circumstances. In the present article it is argued that during muscular exercise and dehydration the set-point is not raised when core temperature is recorded on the tympanic membrane. During fever the set-point is raised less than would be expected from readings of rectal temperature. Data from experiments on humans are used to support and illustrate the claims.

Body Temperature Regulation↗
PubMed1997

Adrenalectomy lowers the body weight set-point in rats.

In order to evaluate the impact of a complete depletion of glucocorticoids on rats' body weight set-point, rats were adrenalectomized, and their set-points were estimated before, and after surgery. Body weight set-points were obtained from a quantitative behavioral method based on the rats' food-hoarding response to weight deficit. In addition, body fat contents were measured in vivo using a total body electrical conductivity analyzer (TOBEC). The hoarding of food showed that adrenalectomized rats had significantly lower body weight set-points than the sham-operated controls (337 +/- 11 g vs. 385 +/- 8 g) and were also significantly lighter. TOBEC measurements showed that the sham-operated control rats had a higher body fat content than the adrenalectomized rats ( 16.7 +/- 1.1% vs. 10.2 +/- 1.2%). The present study demonstrates that adrenalectomy lowers the body weight set-point in rats, suggesting that the concentrations of glucocorticoid hormones, and in turn, the hypothalamic corticotrophin releasing hormone (CRH) participates in the adjustment of the body weight set-point.

Adrenalectomy↗
PubMed1997

The food-hoarding threshold is not raised by acute intraventricular NPY in male rats.

We studied the influence of acute intracerebroventricular (i.c.v.) NPY on the relation existing in the rat between food-hoarding behavior and the body weight of the animals. Six male rats were trained to feed every day from 1000 to 1200 h. Then, their threshold for the onset of food hoarding was measured from the intercept of the regression line relating the food hoarded during meal time (Y axis) to the body weight (X axis). Thirty minutes before the hoarding session, the rats were injected i.c.v. with either 4 micrograms of NPY or saline control. The mean threshold for food hoarding was not modified after NPY. Mean food intake during the hoarding sessions was also unchanged. These results suggest that intracerebral NPY at 4 micrograms did not acutely alter the set-point for body weight regulation.

Animals↗
PubMed1996

The nature of the ponderostat: Hervey's hypothesis revived.

In 1969, Hervey hypothesized the long-term stability of body weight is actually mediated through the regulation of blood steroid concentration. We suggest that glucocorticoids are the regulated variable the concentrations of which entails bodyweight stability. A descriptive model of this regulation is proposed. Because steroids are soluble in lipids, it follows that their concentrations in the body depend in part of the volume of lipids stored. Low fat stores increase the glucocorticoid concentration in the blood, and conversely high fat stores lower the glucocorticoid concentration. Body weight could thus be the end product of the glucocorticoid levels. The set-point for body weight would be adjusted by intracerebral CRH.

Animals↗
PubMed1996

Ponderostat: hoarding behavior satisfies the condition for a lipostat in the rat.

The mass of food hoarded by rats given access to food only two hours per day is proportional to the rats' body weight deficit. The present work investigated whether this behavior might reflect the amount of body fat rather than body weight. The hoarding behavior of three rats was measured every other day at various body weights. After each hoarding session the animals were anesthetized and their percentage of fat was measured in vivo with a total body electrical conductivity method (TOBEC). The results showed that the amount of food hoarded in the two-hour sessions was inversely proportional to the fat content of the body. This result shows that, in the rat, the fat stored is correlated with the behavioral response leading to the defence of body weight, and therefore satisfies a condition necessary for a lipostat.

Adipose Tissue↗
PubMed1996

Ever higher: constant rise of body weight set-point in growing zucker rats.

The mass of food hoarded by rats given access to food only 2 h per day is proportional to the rats' body weight deficit. The intersect of the regression line of hoarded food plotted against body weight gives an indication of the body weight set-point. In the present work, the hoarding behavior of six obese and six control rats was measured every day at various body weights from 8 to 24 weeks of age. Every other week the animals were anesthetized and their percentage of fat was measured in vivo with a total body electrical conductivity method (TOBEC). Lean mass and body length of the obese, and their controls, increased similarly in both groups over the period of the measurements. On the other hand, the body weights increased more in obese, from 174 +/- 5 to 729 +/- 18 g (n = 6), than in controls, from 157 +/- 5 g to 452 +/- 14 g (n = 6). The body weight set-point, calculated every other week for both groups of rats, increased progressively with age. At the age of 24 weeks, the mean set-point for body weight regulation was 758 +/- 13 g in obese and 467 +/- 12 g in controls. This result suggests that the obese fa/fa rat defends its fat content, or a variable correlated to the fat content.

Age Factors↗
PubMed1996

On the origin of consciousness, a postulate and its corollary.

A hypothesis is presented according to which structure of consciousness is quadri-dimensional. The four dimensions are duration, quality, intensity, and affectivity. One may reach this conclusion by introspection alone, or by deduction along the following steps: (1) consciousness should be examined from the point of view of evolutionary psychology; (2) this leads to the following postulate--consciousness evolved from sensation; (3) the postulate entails a corollary-- consciousness has kept the quadri-dimensional structure of sensation. The above postulate could explain the phylogenetic origin of pleasure as the common currency, and in turn the tradeoffs for access to the behavioral final common path. It would also entail that joy is the transient sign of a useful conscious event, whereas happiness is the indifferent experience of a satisfied mind.

Consciousness↗
PubMed1996

Exercise hyperpnea and hyperthermia in humans.

The problem of the relative hyperpnea occurring at high levels of exercise remains unresolved. This study examined whether the hyperpnea observed in humans during exercise at approximately 70% of maximal work capacity was related to cranial (tympanic) and thoracic (esophageal) temperatures. Six trained male subjects pedaled at approximately 60 revolutions/min on an electrically braked cycle ergometer in a climatic chamber at 25 degrees C and approximately 35% relative humidity in two sessions. The subjects pedaled until exhaustion in two sessions. In one session work rate was increased by 40 W every 2 min and in the other session by 20 W every 2 min. In both exercise sessions, core temperature thresholds for ventilation were evident and subsequently tympanic and esophageal temperatures diverged. This suggested that the hyperpnea in humans observed after approximately 70% of an individual's maximal work rate was determined, in part, by core temperatures and revealed supportive evidence for selective brain cooling in humans.

Adult↗
PubMed1995

Palatability vs. money: experimental study of a conflict of motivations.

The pleasure of eating palatable food was pitted against the displeasure of giving money away in a situation where subjects had to spend money to buy their food. Ten healthy subjects taken individually had lunch in the laboratory on four different days. During the first session, they rated the palatability of small sandwiches, of ten different varieties. In the three following sessions, they were asked to eat the same number of sandwiches as in the first session and they had to buy each sandwich at a price that increased with palatability. The rate of the price increase was varied in the three sessions. As this rate increased, the subjects moved their preference to the less palatable sandwiches. The subjects' actual behavior was predictable from the quantitative relationship of pleasure ratings and price. This result supports the hypothesis according to which behavior tends to maximize multidimensional pleasure experience.

Adult↗
PubMed1995

Physical dilatation of the nostrils lowers the thermal strain of exercising humans.

Increased nasal air flow during exercise was examined as a possible heat loss avenue contributing to selective brain cooling in hyperthermic humans. On 2 separate days, eight subjects [mean (SE) age, 26.4 (1.2) years] exercised on a cycle ergometer in a warm room [28 (0.2) degrees C; 28 (5)% relative humidity] to induce a moderate level of hyperthermia. In one session the nostrils were physically dilatated [average dilatation 1.55 (0.17) times] and in the other they were not (control). Both sessions started with a 5-min resting period; then subjects pedaled at 60 W for 5 min, 100 W for 15 min, and 150 W for 20 min. During dilatation both tympanic temperature (Tty) and forehead skin blood flow, estimated by laser doppler velocimetry, were significantly lower than during the control exercise of 150 W. Rates of increase of Tty during the 100-W exercise were the same in both conditions; however, during the 150-W exercise with dilatated nostrils Tty increased at a rate significantly lower than during control [1.1 (0.3) degrees C.h-1 vs 1.5 (0.4) degrees C.h-1]. The change in the rate of increase of Tty between conditions was significantly correlated to the degree of nostril dilatation (r = -0.77, P = 0.02), suggesting that the lower Tty observed was due to nostril dilatation. Facial skin temperature was not significantly different between sessions. The results suggest that the nasal cavity may act as a heat exchanger in selective brain cooling of exercising humans.

Adult↗
PubMed1995

Nasal mucosal vasodilatation in response to passive hyperthermia in humans.

The present study was conducted to measure nasal mucosal blood flow (NMBF) during body warming. Five subjects [mean (SD) 24 (2) years], wearing only shorts and a thick felt hat with ear flaps, were immersed to the neck in a bath at 40 (0.5) degrees C. Tympanic (Tty), esophageal (Tes), mean unweighted skin (Tsk), nose skin and ear pinna skin were recorded at 1-min intervals. NMBF on the lower septal wall was estimated using a laser Doppler flow meter. At rest Tty and Tes were both 36.5 degrees C. Tty dropped significantly below Tes during body warming, despite impeded heat loss from the head due to the felt hat. Tty increased to 37.3 degrees C and Tes increased to 37.5 degrees C during the immersion. During the immersion all skin temperatures were steady or increasing, ruling out the possibility of a contamination of Tty from Tsk. Body warming significantly (P = 0.001) increased NMBF by approximately three times from resting values at the end of immersion. During the period of increasing core temperatures NMBF was significantly correlated to Tty (r = 0.93, P = 0.0001) and Tes (r = 0.97, P = 0.0001), suggesting the blood flow change in this tissue was a thermoregulatory response. The increased NMBF during hyperthermia supports the hypothesis of respiratory cooling involvement in selective brain cooling of humans.

Body Temperature Regulation↗
PubMed1995

Core temperature thresholds for hyperpnea during passive hyperthermia in humans.

Humans have higher ventilation when they are hyperthermic but it is not known whether core temperature thresholds for ventilation exist, nor has a physiological rationale been presented for this response. To examine this question, ventilation was studied in relation to core temperatures in humans rendered hyperthermic in a warm bath. Seven subjects [mean (SE), 23.3 (1.4) years] wearing only shorts and a thick felt hat with ear flaps were immersed to the neck in a bath at 41 (0.5) degrees C for 25 min. Tympanic (Tty), esophageal (Tes), thigh skin and forehead skin temperatures, heart rate, inspired minute ventilation (V1 at body temperature and pressure, saturated), ventilation frequency and oxygen consumption (VO2 at standard temperature and pressure, dry) were recorded at 30-s intervals. At immersion V1 briefly increased to 18.6 (3.0) l.min-1, returned to about the pre-immersion value, and significantly increased to 19.3 (3.0) l.min-1 by the end of immersion. VO2 increased significantly from the pre-immersion value of 0.27 l.min-1 to 0.67 l.min-1 by the first 0.5 min of immersion, but then returned to its pre-immersion value. Tty increased to 38.7 (0.2) degrees C and Tes increased to 39.0 (0.2) degrees C by the end of immersion. Core temperature thresholds for increases in V1 were evident at 38.1 degrees C when expressed against Tty and at 38.5 degrees C when expressed against Tes. The results indicated that during body warming core temperature thresholds for V1 are reached and subsequently a hyperpnea was evident, despite VO2 remaining at a resting value.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Ingestive response shows absence of taste aversion after bovine satietin in rats.

Six adult male rats (409 +/- 16 g) were equipped with chronically implanted oral catheters. Facial consummatory responses to gustatory stimuli, of 50 microliters 2.0 mol.1-1 banana or coconut flavoring, were recorded on a +4/-4 scale for 30 s. The new flavors were paired with IP injections on three different days. The rats were injected with either saline or 1 mg.kg-1 bovine serum satietin (bs-SAT). Food intake and body weight were reduced (p < 0.005) after satietin but not after saline. Both coconut and banana flavors aroused mild ingestive responses in the naive rats. Five days after the beginning of the pairing with IP injections, the rats' response to coconut and banana remained unchanged. The results show that satietin was able to reduce food intake and body weight but did not arouse taste aversion.

Animals↗
PubMed1995

Acute intraventricular CRF lowers the hoarding threshold in male rats.

The influence of intracerebroventricular rat-CRF on the food-hoarding behavior of rats has been studied in relation to the animals' body weights. A group of six male rats was trained to feed every day from 1000 to 1200 h. Then their threshold for the onset of food hoarding was measured from the intercept of regression line of food hoarded during meal time vs. body weight with the x-axis. Thirty minutes before the hoarding session, the rats received 4 micrograms CRF, or saline control, in the lateral ventricle. The mean threshold for food hoarding was significantly lowered to 299 +/- 61 g after CRF, from control 418 +/- 68 g. Mean food intake during the hoarding sessions was also diminished to 6.0 +/- 0.6 g after CRF, from control 14.5 +/- 0.5 g. These results suggest that the set-point for body weight regulation is acutely lowered by intracerebral CRF.

Animals↗
PubMed1995

Dissociation of anorectic and affective responses to epinephrine and glucose in rats.

The purpose of this study was to determine whether the anorexia following epinephrine and glucose IP injections is due to the activation of mechanisms of satiety. Epinephrine (100 micrograms.kg-1) and glucose (4 g.kg-1) were injected IP in rats. In control sessions for epinephrine test, rats received IP saline, and IM epinephrine. In control sessions for the glucose test, rats received IP NaCl, isoosmotic to the glucose solution. Food intake or taste reactivity to a sucrose solution was recorded after these treatments. Epinephrine and glucose decreased food intake by 75% (p < 0.001), and 49% (p < 0.01), compared to their controls. No change of taste reactivity responses was observed with any of these treatments. Twelve-hour fasting did not modify the general taste reactivity responses when compared to the responses evoked in rats fed ad lib. These results might be explained by the fact that anorexia could be obtained by a suppression of hunger without the activation of the mechanisms of satiety. This in turn would imply a possible dissociation between the signals and physiological pathways normally involved in hunger and satiety.

Affect↗