Showing papers by "Université de Montréal published in 1993"

Generalized Raking Procedures in Survey Sampling

Abstract: We propose the name generalized raking for the class of procedures developed in this article, because the classical raking ratio of W. E. Deming is a special case. Generalized raking can be used for estimation in surveys with auxiliary information in the form of known marginal counts in a frequency table in two or more dimensions. An important property of the generalized raking weights is that they reproduce the known marginal counts when applied to the categorical variables that define the frequency table. Our starting point is a class of distance measures and a set of original weights in the form of the standard sampling weights 1/π k , where π k is the inclusion probability of element k. New weights are derived by minimizing the total distance between original weights and new weights. The article makes contributions in three areas: (1) statistical inference conditionally on estimated cell counts, (2) simple calculation of variance estimates for the generalized raking estimators, and (3) presen...

Parental genomic imprinting of the human IGF2 gene.

Abstract: The mouse igf2 gene, coding for the insulin-like growth factor II (IGF-II) is parentally imprinted, only the gene copy derived from the father is expressed. To know whether IGF2, the human homologue, is also imprinted, we used an ApaI polymorphism at the 3' untranslated region in order to distinguish between mRNA derived from each copy of the gene in placentae from heterozygote human fetuses, studied after careful removal of the decidua. Six term and two pre-term placentae of heterozygotes were studied, and in each case the cDNA contained only one of the two alleles present in the genomic DNA. In three cases the mother was homozygous for the non-expressed allele, allowing assignment of paternal origin to the transcribed gene copy. We conclude that, as in the mouse, human IGF2 is parentally imprinted.

Cultural and reproductive success in industrial societies: Testing the relationship at the proximate and ultimate levels

Abstract: In most social species, position in the male social hierarchy and reproductive success are positively correlated; in humans, however, this relationship is less clear, with studies of traditional societies yielding mixed results. In the most economically advanced human populations, the adaptiveness of status vanishes altogether; social status and fertility are uncorrelated. These findings have been interpreted to suggest that evolutionary principles may not be appropriate for the explanation of human behavior, especially in modern environments. The present study tests the adaptiveness of social status with actual mating and reproductive data in a representative sample of males from an industrial society. Reproductive success, even when assessed by a more reliable measure of actual male fertility than the one commonly used, fails to correlate with social status. In striking contrast, however, status is found to be highly correlated with potential fertility, as estimated from copulation frequency. Status thus accounts for as much as 62% of the variance in this proximate component of fitness. This pattern is remarkably similar to what is found in many traditional societies and would result in a substantial positive relationship between cultural and reproductive success in industrial populations were it not for the novel conditions imposed by contraception and monogamy. Various underlying mechanisms are suggested for these findings, illustrating the value of current behavioral and reproductive data in the study of adaptation. It is concluded that evolutionary explanations of human behavior remain entirely relevant in modern societies.

The Effects of Product Market Competition on Collective Bargaining Agreements: The Case of Foreign Competition in Canada

Abstract: In this paper we estimate the effect of the financial conditions of firms on negotiated wage settlements and on employment using a sample of Canadian collective bargaining agreements from 1965 to 1983. We find that ordinary least squares estimates of the effect of quasi-rents per worker on wages are positive but very small. However, we find a much larger effect when we instrument quasi-rents with measures of foreign competition shocks. We conclude that standard estimates of rent-sharing based on contract data seriously understate the impact of product market competition on negotiated wage settlements.

Myoblast transfer in duchenne muscular dystrophy

Abstract: One biceps muscle of 8 patients with Duchenne muscular dystrophy was injected at 55 sites with a total of 55 million viable, purified, and contamination-free normal myoblasts (myoblast transfer). The other biceps of each patient was injected with a placebo to serve as a control. The procedure was blinded to the patients, parents, and investigators. Myoblasts derived from a biopsy specimen of the fathers were cultured and purified under strict conditions and carefully screened for microbial contamination. All patients received cyclophosphamide for immunosuppression for 6 or 12 months. No serious complications were observed after myoblast transfer, indicating that the procedure is safe. The overall therapeutic efficiency of myoblast transfer was poor as judged by the results in maximal voluntary force generation, dystrophin content of the muscle, magnetic resonance imaging of the muscle, and the lack of donor-derived DNA and dystrophin messenger RNA in the injected muscle. An improved efficiency of the take of myoblasts might be achieved by using younger cells and injecting the myoblasts with a myonecrotic agent (to increase the prevalence of regeneration) and a basal laminal fenestrating agent.

A Comparison of Management Patterns after Acute Myocardial Infarction in Canada and the United States

Abstract: Background There are major differences in the organization of the health care systems in Canada and the United States. We hypothesized that these differences may be accompanied by differences in patient care. Methods To test our hypothesis, we compared the treatment patterns for patients with acute myocardial infarction in 19 Canadian and 93 United States hospitals participating in the Survival and Ventricular Enlargement (SAVE) study, which tested the effectiveness of captopril in this population of patients after a myocardial infarction. Results In Canada, 51 percent of the patients admitted to a participating coronary care unit had acute myocardial infarctions, as compared with only 35 percent in the United States (P<0.001). Despite the similar clinical characteristics of the 1573 U.S. patients and 658 Canadian patients participating in the study, coronary arteriography was more commonly performed in the United States than in Canada (in 68 percent vs. 35 percent, P<0.001), as were revascularization pro...

Motor cortical activity during voluntary gait modifications in the cat. I. Cells related to the forelimbs

Abstract: 1. The discharge patterns of 91 identified pyramidal tract neurons (PTNs), located within the forelimb region of area 4 of the cat motor cortex, were recorded during the voluntary modifications of gait needed to step over obstacles attached to a moving treadmill belt. Recordings were made simultaneously from flexor and extensor muscles acting around the shoulder, elbow, wrist, and digits of the forelimb contralateral to the recording site. 2. Analysis of the changes in electromyographic (EMG) activity during the gait modification showed increases in the activity of most flexor muscles of the shoulder and elbow, as well as in the wrist and digit dorsiflexors, when the contralateral forelimb was the first to pass over the obstacle. This period of augmented activity could be subdivided into two parts: one associated with the initial flexion of the limb that was needed to bring it above and over the obstacle (phase I), and the second associated with increased wrist dorsiflexor muscle activity before foot contact (phase II). 3. The discharge frequency of a total of 57/91 (63%) of the recorded PTNs was significantly increased during the gait modification when the limb contralateral to the recording site was the first to step over the obstacle; six of these neurons also showed a significant decrease in their discharge in a different part of the step cycle. In a further 21/91 (23%) neurons, discharge frequency was only decreased, whereas the remaining 13/91 (14%) PTNs showed similar patterns of activity both during control walking and during the gait modifications. 4. Most of those neurons (47/57) in which significant increases in firing frequency were observed, discharged maximally during the period of increased activity of the physiological flexor muscles. Twenty-three of these cells (23/47) discharged maximally in phase I, and 12 (12/47) in phase II. A third population of PTNS (12/47) started to increase their discharge in the stance phase of the step cycle immediately preceding the modified cycle. Seven (7/57) PTNs increased their discharge during the stance phase of the modified cycle, and the remaining three could not be classified as being preferentially related to any one part of the step cycle. 5. The frequency modulation of 41/57 PTNs was less when the leg contralateral to the recording site was the second to encounter the obstacle. In many neurons there was also an appreciable change in the time in the step cycle that peak discharge occurred. These changes in amplitude and timing paralleled the changes observed in the temporal relationships of the muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased endothelin-1 content in blood vessels of deoxycorticosterone acetate-salt hypertensive but not in spontaneously hypertensive rats.

Abstract: Endothelin-1 (ET-1) is a powerful vasoconstrictor peptide produced in the endothelium of blood vessels that may play an important role in the control of local blood flow and could be involved in the pathogenesis of hypertension. We investigated immunoreactive ET-1 (ir-ET-1) levels in acid extracts from blood vessels of deoxycorticosterone acetate (DOCA)-salt and spontaneously hypertensive rats. We found that segments of thoracic aorta and the mesenteric vascular bed contain significantly more ir-ET-1 (11.84 +/- 0.84 and 17.30 +/- 1.89 fmol, respectively) than uninephrectomized control rats (1.78 +/- 0.20 and 9.19 +/- 0.63 fmol, respectively; p < 0.001). High performance liquid chromatography showed that ir-ET-1 of blood vessels of DOCA-salt hypertensive rats eluted in the same position as synthetic ET-1. Significantly increased ir-ET-1 was localized by immunohistochemistry in endothelial cells of aorta and large and small mesenteric arteries of DOCA-salt hypertensive rats. In contrast to the latter, in spontaneously hypertensive rats, vascular content of ir-ET-1 was similar to that of blood vessels of Wistar-Kyoto control rats, at both 6 and 16 weeks of age. High levels of vascular ET-1 may explain the downregulation of vascular endothelin receptors previously described in DOCA-salt hypertensive rats. Furthermore, this suggests that ET-1 may be involved in the maintenance of high blood pressure in mineralocorticoid hypertension.

Persistent neuropsychological deficits and vigilance impairment in sleep apnea syndrome after treatment with continuous positive airways pressure (CPAP)

Abstract: The obstructive sleep apnea syndrome is characterized by nocturnal sleep disturbance, excessive daytime sleepiness and neuropsychological deficits in the areas of memory, attention, and executive tasks. In the present study, these clinical manifestations were assessed in apneic patients before and 6 months after treatment with nasally applied continuous positive airway pressure (CPAP). CPAP treatment was found to restore normal respiration during sleep and to normalize sleep organization. Daytime vigilance greatly improved with treatment but some degree of somnolence as compared to normal controls persisted. Similarly, most neuropsychological deficits normalized with treatment. The exception was for planning abilities and manual dexterity, two neuropsychological deficits that have been found to be highly correlated with the severity of nocturnal hypoxemia. These results raise the possibility that anoxic brain damage is a pathogenic factor in severe obstructive sleep apnea syndrome.

The formalin test: a validation of the weighted-scores method of behavioural pain rating

Abstract: The formalin test was developed using an ordinal scale of weighted scores to rate the intensity of pain-related behaviours in animals. However, no studies have been carried out to establish the ordinal relationship of the behavioural categories used to generate the weighted pain intensity scores. The purpose of the present study was to evaluate the validity of the weighted-scores technique by assessing the ordinality of the behavioural categories associated with the specific category weights. The amount of time spent in each of 4 behavioural categories was measured as a function of the concentration of the formalin solution injected into the hindpaw of rats, and as a function of the dose of systemic morphine given to rats injected with a concentrated (5.0%) solution of formalin. The ordinal nature of the category weights was supported when the data were subjected to a polychotomous logistic regression for fitting an ordinal model.

IL-12 induces the production of IFN-gamma by neonatal human CD4 T cells.

Abstract: A major difference between "naive" and "memory" or "effector" Th cells is the spectrum of cytokines that they are capable of producing. After stimulation naive cells produce only IL-2, whereas memory cells produce several cytokines including IFN-gamma and IL-4. Using umbilical cord blood-derived CD4 T cells as a source of naive T cells, we first report that these cells are capable of producing large amounts of IFN-gamma when cultured with low concentrations of IL-12. The response is time- and dose-dependent, and it is observed at the protein and mRNA levels. IL-12 also induces neonatal CD4 T cells to produce lymphotoxin but not IL-2, TNF-alpha, or IL-4. The production of IFN-gamma by IL-12-stimulated neonatal T cells is associated with a small but significant T cell activation evidenced by DNA synthesis and by the expression of the activation markers CD25, CD71, and HLA-DR; moreover, it is inhibited by hydrocortisone, cyclosporin A, and transforming growth factor-beta. The response to IL-12 is enhanced and is much more rapid when CD4 T cells are cultured in the presence of accessory cells or of exogenous IL-1, IL-2, or TNF-alpha. Using a three-step culture system, we next show that IL-12 induces the maturation of resting naive CD4 T cells into cells producing both IL-2 and IFN-gamma but not IL-4 upon stimulation with PMA and ionomycin. Endogenously produced IFN-gamma plays a role in this IL-12-induced T cell maturation, as shown by the inhibitory effect of neutralizing IFN-gamma antibodies. Finally, we show that IL-12 supports the production of IFN-gamma during primary stimulation of neonatal T cells via the CD3/TCR complex by means of either immobilized anti-CD3 mAb or superantigen-coated (Staphylococcus enterotoxin B) fixed L cell transfectants expressing HLA-DR. It is suggested that IL-12 is involved in the selection of Th1 type immune responses.

Control of Trajectory Modifications in Target-Directed Reaching.

Abstract: Human reaching movements to fixed and displaced visual targets were recorded and compared with simulated movements generated by using a two-joint arm model based on the equilibrium-point (EP) hypothesis (λ model) of motor control (Feldman, 1986). The aim was to investigate the form of central control signals underlying these movements. According to this hypothesis, movements result from changes in control variables that shift the equilibrium position (EP) of the arm. At any time, muscle activations and forces will depend on the difference between the arm's EP and its actual position and on the limb's velocity. In this article, we suggest that the direction of EP shift in reaching is specified at the hand level, whereas the rate of EP shift may be specified at the hand or joint level. A common mechanism underlying reaching to fixed and displaced targets is proposed whereby the EP of the hand shifts in a straight line toward the present target. After the target is displaced, the direction of the ha...

Coping with job insecurity: How does personality make a difference?

Abstract: Reversing a long-standing tradition of neglect, occupational stress researchers have recently rediscovered the importance of personality disposition in understanding the transformation of stresses into strains and strains into symptoms. Two recent studies of job insecurity in our laboratory provided a fortuitous opportunity to explore the extent of this influence and the mechanisms by which it operates. The most important of our findings is that positive personality attributes impact as strongly on mental health as does negative personality disposition, albeit in the opposite direction. Thus, personality can cushion, as well as aggravate, the impact of occupational stress.

Determining Movement Onsets from Temporal Series

Abstract: With the advent of recent measurement techniques, kinematic and kinetic measures commonly are used to describe events over time. Often, the central and peripheral nature of the control processes involved are derived from these temporal series. For example, movement onset often arbitrarily defines the end of the central and the beginning of the peripheral processes. Because of its critical temporal location, we examined whether response dynamics (average movement velocity) affects the determination of movement onset. Interactive graphics and numerical methods of determining movement onsets from temporal series were evaluated on various kinematic signals. Variations in the initial rate of change in a given signal significantly affected the determination of movement onset. Consequently, measurements of component latency must be regarded with caution. A cursory description of related problems elucidated in previous research is discussed, and procedures that can minimize these artifacts are suggested.

Compensation for mechanically unstable loading in voluntary wrist movement

Abstract: In order to study the roles of muscle mechanics and reflex feedback in stabilizing movement, experiments were conducted in which healthy human subjects performed targeted wrist movements under conditions where the damping of the wrist was reduced with a load having the property of negative viscosity. If the movement speed and negative viscosity. If the movement speed and negative viscosity were sufficiently high, the wrist oscillated for several hundred milliseconds about the final target position. Subjects increased the activation of both wrist flexor and extensor muscles to increase joint stiffness to damp the oscillations. With practice, both the tendency to oscillate and the level of muscle activation were reduced. A small bias torque in either direction, added to the negative viscosity, enhanced the oscillations as well as the amount of flexor and extensor muscle activation during the stabilization phase of fast movements. The tendency for the wrist to oscillate was also seen during slow movements where the oscillations were superimposed upon the voluntary movement. We suggest that this reduction in mechanical stability is primarily of reflex origin. As wrist stiffness increases, the natural frequency of the wrist also increases, which in turn produces an increase in the phase lag of the torque generated by the myotatic reflex with respect to wrist angular velocity, effectively reducing damping. The oscillation frequency was often close to a critical frequency for stability at which torque, due to the myotatic reflex, lagged angular velocity by 180 degrees (6-7.5 Hz). Nevertheless, subjects were able to damp these oscillations, probably because the torque due to intrinsic muscle stiffness (in phase with position and hence lagging velocity by only 90 degrees) dominated the torque contribution of the myotatic reflex. Increasing stiffness with declining oscillation amplitude may also have contributed significantly to damping.

The Impact of Acquired Hearing Impairment on Intimate Relationships: Implications for Rehabilitation

Abstract: Hearing disabilities, due to their interactive nature, strongly affect intimate relationships. This paper reviews the literature on this dimension of the experience of hearing impairment. The effects of progressive hearing loss and of the coping process within the couple are examined borrowing concepts from symbolic interaction theory. A summary of the interactive dimensions of the effects of hearing impairment on the couple is drawn from the relevant studies. Specific needs have been identified for each partner in terms of information, support and communication facilitation. Implications are drawn for the audiological rehabilitation of hearing-impaired adults.

Empirical analysis of the influence of swimming pattern on the net energetic cost of swimming in fishes

Abstract: We tested the hypothesis that the energetics of swimming in a flume accurately represent the costs of various spontaneous movements using empirical relationships between fish swimming costs, weight, and speed for three swimming patterns: (1) ‘forced swimming’ corresponded to movements adopted by fish forced to swim against a unidirectional current of constant velocity; (2) ‘directed swimming’ was defined as quasi-rectilinear movements executed at relatively constant speeds in a stationary body of water and (3) ‘routine swimming’ was characterized by marked changes in swimming direction and speed. Weight and speed explained between 76% (routine swimming) and 80% (forced swimming) of net swimming cost variability. Net costs associated with different swimming patterns were compared using ratios of model predictions (swimming cost ratio; SCR) for various weight and speed combinations. Routine swimming was the most expensive swimming pattern (SCR for routine and forced swimming =6.4 to 14.0) followed by directed (SCR for directed and forced swimming =0.9 to 2.8), and forced swimming. The magnitude of the difference between the net costs of forced and spontaneous swimming increases with movement complexity and decreases as fish weight increases.