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Nicotine has been shown to enhance multiple forms of learning and memory. However the substrates through which these effects occur are not well understood. To examine the specific substrates of nicotine's acute effects on trace fear conditioning, I infused nicotine into areas thought to support trace fear conditioning, the dorsal hippocampus, ventral hippocampus and medial prefrontal cortex. Additionally, we investigated the contributions of nicotinic acetylcholinergic signaling to trace fear conditioning by infusing the nicotinic antagonists dihydro-beta-erythroidine (DHbE) and methyllycaconitine (MLA) into these areas. Nicotine had different effects on both trace and contextual fear conditioning depending on dose and brain region, as did the nicotinic antagonists. In the dorsal hippocampus nicotine infusion enhanced both trace and contextual conditioning, although these effects were dissociable by dose and training protocol. Additionally, the high-affinity nicotinic antagonist DHbE produced selective deficits in trace conditioning, suggesting that while enhancement of nicotinic signaling can affect both contextual and trace learning, nicotinic activity in the dorsal hippocampus is critically involved in trace but not contextual conditioning. In the ventral hippocampus nicotine infusion produced deficits in both trace and contextual fear conditioning, without affecting delay conditioning, while the antagonists had no effect. This finding suggests that altered nicotinic signaling in the ventral hippocampus can suppress hippocampus dependent learning. In the mPFC nicotine selectively enhanced trace conditioning though both antagonists also enhanced trace fear conditioning. Unlike in the mPFC or dorsal hippocampus, where nicotine and antagonist induced effects occurred during training, effects in the ventral hippocampus occurred at both training and testing, suggesting that the ventral hippocampus may be able to modulate acquisition as well as expression of hippocampus dependent learning. Additionally, antagonist infusion into the mPFC during testing produced deficits in expression, suggesting that this area can modulate fear expression. Thus, the substrates of nicotinic acetylcholinergic contributions to trace and contextual fear conditioning are diverse. I put forth a multi-component model of these contributions, where trace fear conditioning is supported by dorsal hippocampus dependent maintenance of the CS during the trace interval, long-term storage in the mPFC and ventral hippocampal mediated acquisition and expression. / Psychology

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / La privation de sommeil post-apprentissage cause des déficits lors du rappel de certaines tâches chez l'humain et chez le rat. Néanmoins, peu d'études se sont penchées sur les effets d'une privation de sommeil totale ou sélective précédant l'apprentissage d'une tâche spatiale chez l'humain et le rat. Le présente étude comporte deux volets expérimentaux. Dans un premier temps, nous avons évalué les effets d'une brève privation de sommeil paradoxal (SP) chez le rat sur deux types de tâche spatiale : le labyrinthe aquatique de Morris (mémoire de référence) et une tâche d'alternance différée dans un labyrinthe aquatique (mémoire de travail). La privation de SP a été menée à l'aide de la méthode de la petite plate-forme; des enregistrements de sommeil ont été recueillis au cours de cette période. Dans un deuxième temps, nous avons évalué les effets d'une privation de sommeil totale (PST) sur l'orientation spatiale chez l'humain à l'aide d'un labyrinthe de dimension humaine. Les sujets ont été soumis à trois types de tâches spatiales : la construction, le rappel spontané et le rappel indicé de la carte cognitive. Puisque le cortex frontal est particulièrement vulnérable à une privation de sommeil et que la privation de sommeil totale et sélective post-apprentissage cause des déficits dans certaines tâches, nous supposons 1) qu'une brève privation de SP pré-apprentissage induira des déficits au niveau de la tâche d'alternance différée chez le rat et 2) qu'une PST pré-apprentissage induira des déficits au niveau de la construction, du rappel spontané et du rappel indicé chez l'humain. De plus, nous prévoyons que la méthode de la petite plate-forme sera efficace dans la réduction substantielle de SP. Nos résultats montrent que les rats privés de SP ont éprouvé davantage de difficultés dans l'encodage de la tâche de mémoire de travail que dans celle de mémoire de référence. Les enregistrements de sommeil révèlent une diminution significative et spécifique de SP par la méthode de la petite plate-forme. Chez l'humain, nos résultats démontrent que les sujets PST ont éprouvé plus de difficultés seulement dans la construction de la carte cognitive lors de l'apprentissage de l'itinéraire le plus complexe. Dans ces deux tâches (alternance différée chez le rat; tâche complexe chez l'humain), la mémoire de travail, qui dépend en partie du cortex frontal, aurait pu être surchargée. Ces résultats suggèrent donc une sensibilité particulière des fonctions du cortex frontal lors d'une privation de sommeil.

This dissertation investigates the complex interplay of age, sex and physiological responses to attentional tasks in childhood, employing heart rate and heart rate variability (HRV) as measures of the autonomic nervous system (ANS), and periodic electroencephalogram (EEG) alpha power and the aperiodic EEG measure of exponent of the spectral slope to assess central nervous system (CNS) activity. Through meticulous analysis of neurophysiological data, this study unveils developmental trajectories and sex-specific disparities in attentional processes. Initial examinations reveal age-related fluctuations in ANS and CNS responses, highlighting the dynamic nature of childhood neurodevelopment. Furthermore, sex-stratified analyses unveil distinct patterns of response, emphasizing the importance of considering sex as a pivotal factor in neurophysiological research. Surprisingly, despite expectations of developmental maturation, ANS reactivity to attentional challenges remains stable across childhood, challenging traditional developmental paradigms and prompting further exploration into underlying mechanisms. Moving forward, leveraging longitudinal mixed-effects modeling, cluster analysis, and assessments of neurobehavioral outcomes offers promising avenues for comprehensive understanding. This research significantly advances our understanding of childhood neurophysiology and lays the groundwork for targeted interventions and public health initiatives to optimize developmental outcomes.

Doctor of Philosophy / Department of Psychology / Stephen W. Kiefer / Exposing rats to differential rearing conditions, during early post-weaning development, has been shown to produce changes in a number of behaviors displayed during adulthood. The purpose of the current study was to investigate whether rearing alcohol-preferring (P) and non-preferring (NP) rats in an environmental enrichment condition (EC), a social condition (SC), or an impoverished condition (IC) would differentially affect the consumption of and operant responding for 10% ethanol. In Experiment 1 rats were tested for both limited access and free access (two bottle choice between water and ethanol) consumption of 10% ethanol. For, Experiment 2 rats were trained to respond in an operant chamber for ethanol and then provided concurrent access to 10% ethanol (right lever) and water (left lever). After concurrent access, rats were required to respond over a gradually increasing fixed-ratio schedule for 10% ethanol and finally a progressive ratio schedule for 10% ethanol, 15% ethanol, and 10% sucrose. For Experiment 3 rats were trained to respond for 10% sucrose and then assessed for the maintenance of operant responding for 10% sucrose. The data from this series of experiments shows that EC P rats consumed, responded for, and preferred 10% ethanol significantly less than their IC P counterparts. Also, EC P rats did not significantly differ from NP rats during any aspect of testing for all experiments. Experiment 3 failed to reveal a significant effect of rearing although there was a line effect that has been previously observed in the literature. Thus, it would appear from these results that rearing in an EC condition acts to protect alcohol-preferring rats from increased levels of consumption of, preference for, and responding for ethanol compared to rearing in an impoverished environment.