Artificial rearing of infant rats is a useful method for studying the role of early experiences in neural and behavioural development because it permits precise control over key features of the early environment without maternal influence. The present thesis examined the behavioural response of artificially reared rats towards natural and drug-mediated rewards, as well as novel environments. Male Sprague-Dawley rats were separated from their mother and litter-mates starting on post-natal day five and reared artificially (AR, n = 39), or they were reared naturally with a foster mother and litter (MR, n = 43). On post-natal day 21, half the rats from each rearing group were housed in isolation and the other half were group-housed with 3-4 rats per cage. Following three weeks in their respective housing conditions, all rats were exposed to three behavioural tests in the following order: open field, elevated plus-maze and sucrose preference. Additionally, one of the two cohorts used in adolescent behavioural testing was later tested in adulthood for conditioned place preference in response to morphine injection (intraperitoneal, 10 mg/kg). Adolescent AR rats were found to be more active in the open field and in the elevated plus-maze than MR rats. Furthermore, although there were no differences between the groups in fearfulness in the open field, in their first experience on the elevated plus-maze AR rats were more anxious than MR rats in exploring the open arms. AR rats also showed increased preference for sucrose consumption relative to chow, although their overall caloric intake during the 1h test was lower than that of MR rats. In adulthood, AR rats displayed a stronger conditioned place preference response to morphine. There were no significant effects of housing condition on any of these outcome measures. These findings support the potential of this model to contribute to the understanding of the role of early experience in the development of behavioural motivation.

Artificial rearing of infant rats is a useful method for studying the role of early experiences in neural and behavioural development because it permits precise control over key features of the early environment without maternal influence. The present thesis examined the behavioural response of artificially reared rats towards natural and drug-mediated rewards, as well as novel environments. Male Sprague-Dawley rats were separated from their mother and litter-mates starting on post-natal day five and reared artificially (AR, n = 39), or they were reared naturally with a foster mother and litter (MR, n = 43). On post-natal day 21, half the rats from each rearing group were housed in isolation and the other half were group-housed with 3-4 rats per cage. Following three weeks in their respective housing conditions, all rats were exposed to three behavioural tests in the following order: open field, elevated plus-maze and sucrose preference. Additionally, one of the two cohorts used in adolescent behavioural testing was later tested in adulthood for conditioned place preference in response to morphine injection (intraperitoneal, 10 mg/kg). Adolescent AR rats were found to be more active in the open field and in the elevated plus-maze than MR rats. Furthermore, although there were no differences between the groups in fearfulness in the open field, in their first experience on the elevated plus-maze AR rats were more anxious than MR rats in exploring the open arms. AR rats also showed increased preference for sucrose consumption relative to chow, although their overall caloric intake during the 1h test was lower than that of MR rats. In adulthood, AR rats displayed a stronger conditioned place preference response to morphine. There were no significant effects of housing condition on any of these outcome measures. These findings support the potential of this model to contribute to the understanding of the role of early experience in the development of behavioural motivation.

The objective of this thesis was to determine the association between exposure to parental BD during childhood and risk of mood disorder. Offspring of one parent with BD completed annual clinical assessments as part of a 16-year prospective cohort study. Clinical data in the parents from Ottawa and Halifax were mapped onto the first decade of their offspring’s life to estimate the timing, duration and severity of exposure to their illness. The duration of parental BD was associated with a 2 to 2.5 fold increased risk of any psychopathology (HR: 1.9, 95%CI: 1.0-4.0), and unipolar depression (HR: 2.6, 95%CI: 0.9-7.5), and a 7 fold increased risk of substance use disorders (HR: 7.1, 95%CI: 1.8-37.0). A longer duration of exposure to parental BD may be an important indicator of mood and non-mood psychopathology risk in offspring. This has implications for early intervention and preventive efforts in high-risk youth.

The aim of this project is to examine the relationships between two approaches to the measurement of life history strategies. The traditional method, termed here the biodemographic approach, measures developmental characteristics like birthweight, gestation length, inter-birth intervals, pubertal timing, and sexual debut. The alternative method under exploration, termed here the psychological approach, measures a suite of cognitive and behavioral traits such as altruism, sociosexual orientation, personality, mutualism, familial relationships, and religiosity. Although both approaches are supported by a large body of literature, they remain relatively segregated. This study draws inspiration from both views, integrating measures that assess developmental milestones, including birthweight, prematurity, pubertal timing, and onset of sexual behavior, as well as psychological life history measures such as the Mini-K and a personality inventory. Drawing on previous theoretical work on the fundamental dimensions of environmental risk, these measures are tested in conjunction with several scales assessing the stability of early environmental conditions, including both "event-based" measures that are defined with an external referent, and measures of internal schemata, or the predicted psychological sequelae of early events. The data are tested in a three-part sequence, beginning with the measurement models under investigation, proceeding to an exploratory analysis of the causal network, and finishing with a cross-validation of the structural model on a new sample. The findings point to exciting new directions for future researchers who seek to integrate the two perspectives.

Growing up in an adverse early environment is related to a number of negative health outcomes later in life, and dysregulation of the HPA axis may serve as the means by which this process occurs (Repetti et al., 2002). Indeed, early environment has been linked to altered physiological responses to general stressors in adulthood, but it remains unclear whether physiological responses to marital stress are also affected. Thus, the present work addresses two central questions in 129 newlywed couples: (1) How does growing up in an adverse early environment relate to physiological stress responses (assessed by cortisol) to a relationship conflict? (2) Does having a supportive spouse moderate this relation? The results provide some support for the link between early environment and cortisol reactivity among husbands, and marginal support for the moderating role of spousal support.

Le cadre neuroconstructiviste du développement cognitif, en considérant la variabilité des contraintes qui agissent dès la conception et façonnent le développement, apparaît pertinent pour considérer l’influence des expériences sensorielles précoces sur le développement neurocomportemental des nouveau-nés prématurés. Ils évoluent dans un environnement particulier et ont une vulnérabilité aux troubles neurodéveloppementaux, auxquels des atypies du traitement tactile et temporel sont associées. L’objectif de ce travail de thèse est d’étudier les compétences tactiles et temporelles des nouveaux nés prématurés, et d’évaluer l’effet de l’environnement précoce sur ces perceptions. La perception tactile passive et la cognition ont été étudié auprès de 61 nouveau-nés prématurés (nés entre 32 et 34SA) à 35 semaines d’âge corrigé. Les réponses d’orientation manuelle lors de stimulations tactiles passives du membre supérieur ont été mesurées lors d'un paradigme d’habituation et de déshabituation (changement de localisation ou pause dans la séquence de stimulation). Les prématurés montrent une réponse d'orientation manuelle aux stimuli, qui diminue lors de la répétition, indépendamment de son emplacement sur le bras. L'habituation est retardée chez les sujets nés le plus tôt, à un petit poids et ayant vécu davantage d’expériences douloureuses. Enfin, les prématurés perçoivent les changements de localisation du stimulus et l'intervalle interstimulus, ce qui suggère un développement prénatal des capacités de traitement temporel. Ces capacités de traitement temporel et leur utilisation pour générer une prédiction sensorielle ont été évaluées au cours d’une seconde étude. 19 nouveau-nés prématurés (nés entre 31 et 32 SA) ont été soumis à une séquence tactile (régulière ou irrégulière) aux âges corrigés de 33 et 35 SA. Les variations de flux sanguin cérébral été mesurées. Aux deux âges corrigés, les stimuli tactiles sont associés à une réponse hémodynamique au sein du cortex somatosensoriel. À 33 semaines d’âge gestationnel corrigé les omissions dans la séquence sont associées à une augmentation du flux sanguin cérébral, qui indique que les prématurés forment des prédictions sensorielles, indépendamment du groupe expérimental. Ce travail de thèse permet de mieux caractériser les capacités de traitement tactile et temporel des nouveau-nés prématurés, qui manquent d’investigations récentes et approfondies. De plus, il apporte des arguments rationnels qui pourraient permettre de proposer des thérapies sensorielles à ces patients, basées sur leurs capacités de perception. / The neuroconstructivist theoretical framework of cognitive development, taking into account the variability of the constraints that act from the conception to shape development, is relevant to consider the early influence of sensory experiences on the neurobehavioral development of preterm neonates. They evolve in a particular environment and are vulnerable to neurodevelopmental disorders, to which atypical tactile and temporal processing are associated. The aim of the thesis is to study tactile and temporal abilities in preterm newborns and to evaluate the effect of the early environment on these perceptions. We included 61 preterm neonates (born between 32 and 34 weeks of gestational age (wGA)). At 35 weeks of corrected gestational age, we measured orienting responses (forearm, hand, and fingers movements) during vibrotactile stimulation of their hand and forearm, during a habituation and dishabituation paradigm, the dishabituation being either a location change or a pause in the stimulation sequence. Preterm newborns displayed a manual orienting response to vibrotactile stimuli which significantly decreased when the stimulus was repeated, regardless of the stimulated location on the limb. Habituation was delayed in subjects born at a younger gestational age, smaller birth weight, and having experienced more painful care procedures. Preterm neonates perceived changes in stimulus location and interstimulus time interval, suggesting a prenatal development of temporal processing capacities. These temporal processing abilities and their use to generate sensory prediction are being evaluated in a second study. 19 premature neonates (born between 31 and 32wGA) were presented with a tactile sequence (regular or irregular) at 33 and 35 weeks of corrected GA. Variations in cerebral blood flow were measured. At both corrected GA, tactile stimuli are associated with a hemodynamic response in the primary somatosensory cortex. At 33 weeks of corrected GA, omissions in the sequence are associated with an increase in cerebral blood flow, which indicates that premature neonates form sensory predictions, regardless of their experimental group. This thesis work allows to better characterize the tactile and temporal processing abilities in premature neonates, which lack recent and thorough investigation. In addition, it provides rational arguments that could help to propose sensory therapies to these patients, based on their perceptual abilities.