Stress has been shown to influence learning and memory in humans and rats (Diamond et al, 1996; Diamond et al, 1999; Krugers et al, 1997; Kirschbaum et al, 1996; Lupien et al, 1997). The hippocampus and is an area of the brain involved in memory function in humans and rats (Kirschbaum et al, 1996; Lupien et al, 1997) and is highly susceptible to stress (Diamond et al, 1990). Research has indicated that a number of stressors such as exposure to a predator (Diamond et al, 1999) can lead to stress effects. Recently efforts have been made to counteract the effects of stress on brain function and related behavioral performance. The antidepressant drug tianeptine has been used in this setting. Little is known about tianeptine's role in blocking stress effects on behavior and memory performance with regard to interactions with stress hormones, such as corticosterone. Here a set of experiments delineates the role of corticosterone and its link to stress effects on memory as well as an investigation into the actions of tianeptine and ADX in the blockade of stress effects on memory. First, I examined the effects of tianeptine on multi-day RAWM working memory training and a novel one-day learning and memory training task. Second, the effects of propranolol, an anti-anxiety medication, were tested with regard to the alleviation of stress effects on memory, allowing for a comparison between two anti-anxiety drugs, tianeptine and propranolol. Third, adrenalectomy (ADX) and the resultant depletion of adrenal hormones were examined in connection with learning and memory in the one-day learning task. Fourth, the effects and interactions of tianeptine and ADX were examined to see if tianeptine can exert its effects in the absence of adrenal hormones. Tianeptine blocked stress-induced memory errors in two different tasks and under ADX conditions. All effects were independent of corticosterone levels. In contrast, propranolol was ineffective in blocking stress-induced memory changes. The current data may prove useful in the development of antidepressant drugs and further the study of the mechanisms by which stress affects memory.

Several studies suggest profound effects on mood and cognition by neuroactive steroids. Estrogen alone or in combination with antidepressant drugs affecting the serotonin system has been used to treat mood disorders. On the other hand, progesterone is related to negative effects on mood and memory. A major part of the progesterone effects on the brain can be mediated by its metabolite allopregnanolone, which is also de novo synthesized in the brain, and affects the GABAA receptors. It would be of great importance to find a substance that antagonize allopregnanolone adverse effects. To investigate how long term supplementation of estradiol and progesterone, resembling postmenopausal hormone replacement therapy, affects serotonin receptors in different brain areas important for mood and memory functions, we used ovariectomized female rats. After 2 weeks of supplementation with 17β-estradiol alone or in combination with progesterone, or placebo pellets, estradiol alone decreases but estradiol supplemented together with progesterone increases 5HT1A mRNA expression in the hippocampus. Estradiol decreases the 5HT2C receptor gene expression, while estradiol in combination with progesterone increases the 5HT2A mRNA expression in the ventral hippocampus. Thus, estradiol alone has opposite effects compared to the estradiol/progesterone combination. To detect if acute tolerance develops to allopregnanolone, an EEG method was used where male rats by continuous allopregnanolone infusion were kept on anesthesia level of the silent second (SS). After different time intervals (first SS, 30 min or 90 min of anesthesia) several GABAA receptor subunit mRNAs were measured for detecting if changed expression of any GABAA receptor subunits is involved in development of acute tolerance. There is development of acute tolerance to allopregnanolone and brain regions of importance are hippocampus, thalamus and hypothalamus. The GABAA receptor alpha4 subunit in thalamus and alpha2 subunit in the dorsal hippocampus are related to development of acute tolerance. For assessing allopregnanolone behavioral effects, we studied how this neurosteroid affects spatial learning in the Morris water maze task Allopregnanolone inhibits spatial learning short after the injection and shows a specific behavioral pattern with swimming close to the pool wall. The steroid UC1011 can inhibit the increase in chloride ion uptake induced by allopregnanolone. UC1011 decreases allopregnanoloneinduced impairment of spatial learning in the water maze, as well as the specific behavioral swim pattern. In conclusion, the present work demonstrates that neuroactive steroids affect the 5HT and GABA systems in a brain region specific way. GABAA receptor subunit changes in hippocampus and thalamus are related to acute allopregnanolone tolerance. Allopregnanolone induces cognitive deficits, like spatial learning impairment and UC1011 can inhibit allopregnanolone-induced effects in vitro and in vivo. Key words: Estradiol, progesterone, HRT, allopregnanolone, UC1011, serotonin receptor, GABAA receptor, mRNA, Morris water maze, silent second, tolerance.

The anterior claustrum (CLA) has been implicated in epileptogenesis and epileptiform activity due to its abundant and widespread bilateral connections to some of the structures believed to play an important role in seizure generalization: the motor cortex, entorhinal cortex, limbic structures, and brainstem sites. Kindling in the CLA has been characterized as comprising two distinct phases: an early phase and a late phase. Early phase seizures progress quickly into generalized seizures, are short in duration, and resemble cortical seizures. Late phase seizures are characterized as being more severe in intensity, having longer durations, and resembling limbic-type seizures.<p>It is unknown whether kindling in the CLA will lead to changes in behaviour as seen after kindling of limbic sites. Thus, I measured the behavioural effects of kindling in the anterior CLA to investigate potential changes in learning, memory, and anxiety-related behaviours. I hypothesized that changes in behaviour would occur after kindling of late phase seizures, because of their close resemblance to limbic-type seizures, but not after kindling of early phase seizures. Anxiety-like behaviour was assessed in the elevated plus maze and open field. Object memory was assessed in an object recognition test, and spatial learning and memory were assessed in the water maze.<p>I found no significant changes in behaviour in the late phase group in comparison to the early phase and control groups. Thus, contrary to my hypothesis, late phase kindling of the CLA does not produce changes in learning and memory or alterations in anxiety-related behaviours.

Experience drives changes in gene expression that mold and reorganize neuronal circuits. In response to neuronal activity, the transcription factor CREB binds to a regulatory site on Bdnf promoter IV to modulate BDNF protein levels. CREB and BDNF are extensively implicated in animal behaviour, but the role of the interaction between these proteins has not been studied. I used transgenic mice carrying mutations at the CREB binding site of Bdnf promoter IV (CREmKI mutation) to specifically disrupt this interaction. F1 (N = 52) and F2 (N = 69) mice underwent a battery of behavioural tests. All mice showed normal motor learning and spatial memory. Critically, F1 mutants showed impaired auditory fear memory, while F2 mutants showed heightened anxiety. I suspect that differences in Bdnf expression and compensatory effects contributed to discrepancies between the two generations. My findings highlight the relevance of BDNF expression levels for memory- and anxiety-related behaviours.

Experience drives changes in gene expression that mold and reorganize neuronal circuits. In response to neuronal activity, the transcription factor CREB binds to a regulatory site on Bdnf promoter IV to modulate BDNF protein levels. CREB and BDNF are extensively implicated in animal behaviour, but the role of the interaction between these proteins has not been studied. I used transgenic mice carrying mutations at the CREB binding site of Bdnf promoter IV (CREmKI mutation) to specifically disrupt this interaction. F1 (N = 52) and F2 (N = 69) mice underwent a battery of behavioural tests. All mice showed normal motor learning and spatial memory. Critically, F1 mutants showed impaired auditory fear memory, while F2 mutants showed heightened anxiety. I suspect that differences in Bdnf expression and compensatory effects contributed to discrepancies between the two generations. My findings highlight the relevance of BDNF expression levels for memory- and anxiety-related behaviours.

La facilitación del aprendizaje y la memoria por la autoestimulación eléctrica intracraneal (AEIC) se ha observado principalmente en tareas de memoria implícita, como la evitación activa de dos sentidos, en ratas. En este trabajo pretendemos investigar si la AEIC post-entrenamiento, además de facilitar el aprendizaje y la formación de la memoria en paradigmas de memoria implícita, puede facilitar también el aprendizaje y la formación de la memoria en un paradigma de memoria espacial explícita o relacional, hipocampo-dependiente, en el Laberinto Acuático de Morris (LAM), en ratas Wistar. Dado que nuestra investigación previa ha puesto de manifiesto que el efecto de la AEIC para facilitar el aprendizaje y la memoria podría ser sensible a la capacidad básica o inicial de los sujetos para aprender las tareas, en el presente trabajo hemos realizado 4 experimentos consecutivos con ratas Wistar que han sido diseñados para dificultar progresivamente el aprendizaje en el LAM reduciendo, en cada siguiente experimento, la cantidad de ensayos de entrenamiento administrados. En cada experimento, los sujetos se dividieron en dos grupos, grupo AEIC y grupo Control y realizaron, en función del experimento, 8, 5, 3 o 1 ensayo diario. Inmediatamente después de cada sesión de entrenamiento los sujetos del grupo AEIC recibieron el tratamiento de AEIC (2000 trenes de corriente reforzante y estimulante a través de un electrodo crónicamente implantado en el hipotálamo lateral derecho de los sujetos) mientras que los sujetos Control no recibieron tratamiento alguno. Los ensayos tenían una duración de 2 minutos y se iniciaban desde una posición que variaba de uno a otro. Los animales debían nadar en la piscina hasta localizar una plataforma escondida que estaba señalizada por una pelota de playa colocada en la periferia de la piscina en el cuadrante derecho adyacente a la plataforma (experimento 1) o en el cuadrante opuesto al de la plataforma (experimentos 2, 3 y 4). Durante el entrenamiento en esta tarea de plataforma-escondida, registramos la latencia de nado y otras variables como la velocidad media de nado, el tiempo en paredes y la distancia total nadada de cada sujeto. Tres días después de la última sesión de entrenamiento, los sujetos realizaron el ensayo de prueba que consistió en dejar nadar al animal durante 60 segundos con la pelota presente pero sin la plataforma. En este ensayo de prueba registramos la media de tiempo que cada sujeto pasó en cada cuadrante así como las trayectorias de nado. A lo largo de las sesiones de entrenamiento observamos una fuerte y consistente facilitación de la ejecución en el LAM en aquellas ratas que habían recibido el tratamiento de autoestimulación tras un único ensayo de adquisición, es decir, cuando el aprendizaje fue más difícil (experimento 4). En este mismo experimento, durante el ensayo de prueba, los sujetos AEIC nadaron significativamente más tiempo en el cuadrante donde debería haberse encontrado la plataforma que en el resto de zonas de la piscina. Esta facilitación también se observó en la última sesión y en el ensayo de prueba de aquellas ratas que habían realizado tres ensayos por sesión (experimento 3). No obstante, no observamos diferencias entre los sujetos tratados y los controles cuando realizaron 8 o 5 ensayos diarios por sesión (experimentos 1 y 2 respectivamente). Estos hallazgos apoyan y confirman resultados previos de nuestro laboratorio en los que, como hemos comentado anteriormente, observamos que la capacidad de la AEIC post-entrenamiento para facilitar la consolidación de la memoria ha sido y es mayor en sujetos con bajos niveles iniciales de condicionamiento y claramente prueban que este tratamiento es capaz de facilitar la memoria explícita, relacional o hipocampo dependiente. / Learning and memory improvement by post-training intracranial self-stimulation has been observed mostly in implicit tasks, such as active avoidance, in rats. Here we wanted to know whether post-training self-stimulation is also able to facilitate a spatial hippocampus-dependent task in the Morris water maze. Four experiments were run with Wistar rats. In each of them subjects were given at least 5 acquisition sessions, one daily, consisting of two-minute trials. Starting from a variable position, rats had to swim in a pool until they located a hidden platform signalled by a cue located on its opposite site. Each daily session was followed by an immediate treatment of intracranial self-stimulation. Control subjects did not receive the self-stimulation treatment and were placed in their home cage. In the three successive experiments, independent groups of rats were given five, three and one trial per session, respectively. Temporal latencies and trajectories to locate the platform were measured for each subject. Three days after the last acquisition session, the animals were placed again in the pool, for 60 sec, but without the platform and the time spent in each quadrant and the swim trajectories were registered for each subject. A strong and consistent improvement of performance was observed in the self-stimulated rats when they were given only one trial per session, i.e. when learning was more difficult. These findings agree with our previous data showing the capacity of post-training self-stimulation to improve memory especially in rats with low conditioning levels (little training), and clearly prove that post-training self-stimulation can also improve explicit or relational memory.

Fructose consumption has increased exponentially during the past four decades. The physiological effects of a high fructose diet include obesity and insulin resistance. In animal models, the effects of a high fructose diet on fat distribution are inconclusive in that some studies find increases in body mass and lipids while others find no effect. Recent findings indicate that a high fructose diet causes hippocampal insulin resistance in hamsters, raising the possibility that the diet causes impairments in cognition. The following experiments tested the hypotheses that a high fructose diet alters fat distribution rather than total body mass and impairs hippocampal-dependent memory. Results indicated that the high fructose diet did not affect fat distribution, but did increase plasma triacylglycerides. Interestingly, the diet also impaired spatial reference memory in the Morris water maze, and this effect was correlated with plasma triacylglycerides. These results indicate that a high fructose diet impairs brain function.

Over the past five decades, per capita caloric intake has increased by approximately 28% in the United States. A hallmark of the current standard American diet is an excess of energy sources from saturated fat and refined carbohydrates. High energy diets such as the “Western” diet cause numerous pathologies, including non-alcoholic fatty liver disease (NAFLD), high blood pressure, dyslipidemia, and peripheral insulin resistance. High energy diets also negatively impact the hippocampus, a brain area important for learning and memory. It is not surprising, then, that high energy diets impair hippocampal-dependent memory. The experiments in this dissertation investigate possible diet-induced consequences that may contribute to the impairing effects of high energy diets on hippocampal-dependent memory. Our initial experiments found that diet-induced NAFLD impairs hippocampal-dependent memory, but these cognitive deficits were not due to decreases in insulin-like growth factor-1 (IGF-1) or hippocampal insulin signaling. Next, we found that a high energy diet increased the ability of epinephrine to increase blood glucose concentrations, indicating a novel way in which high energy diets impair liver function. The final set of experiments found that high energy diets do not necessarily impair memory but instead may prevent the memory-enhancing effects of acute stress. Taken together, these results indicate that high energy diets interact with acute stress to negatively impact hippocampal-dependent memory, and that hippocampal insulin resistance and IGF-1are not likely involved.

The anterior claustrum (CLA) has been implicated in epileptogenesis and epileptiform activity due to its abundant and widespread bilateral connections to some of the structures believed to play an important role in seizure generalization: the motor cortex, entorhinal cortex, limbic structures, and brainstem sites. Kindling in the CLA has been characterized as comprising two distinct phases: an early phase and a late phase. Early phase seizures progress quickly into generalized seizures, are short in duration, and resemble cortical seizures. Late phase seizures are characterized as being more severe in intensity, having longer durations, and resembling limbic-type seizures.<p>It is unknown whether kindling in the CLA will lead to changes in behaviour as seen after kindling of limbic sites. Thus, I measured the behavioural effects of kindling in the anterior CLA to investigate potential changes in learning, memory, and anxiety-related behaviours. I hypothesized that changes in behaviour would occur after kindling of late phase seizures, because of their close resemblance to limbic-type seizures, but not after kindling of early phase seizures. Anxiety-like behaviour was assessed in the elevated plus maze and open field. Object memory was assessed in an object recognition test, and spatial learning and memory were assessed in the water maze.<p>I found no significant changes in behaviour in the late phase group in comparison to the early phase and control groups. Thus, contrary to my hypothesis, late phase kindling of the CLA does not produce changes in learning and memory or alterations in anxiety-related behaviours.

Retrospective studies suggest that lifestyle activities may provide protection against Alzheimer s Disease (AD). However, such studies can be inaccurate and prospective longitudinal studies investigating lifestyle protection against AD are both impractical and impossible to control for. Transgenic (Tg+) AD mice offer a model in a well controlled environment for testing the potential for environmental factors to impact AD development. In an initial study, Tg+ and non-transgenic (Tg-) mice were housed in either environmentally enriched (EE) or standard housing (SH) from 2-6 months of age, with a behavioral battery given during the last 5 weeks of housing. In the Morris maze, platform recognition, and radial arm water maze tasks, Tg+/EE mice were completely protected from cognitive impairment present in Tg+/SH mice and comparable to control Tg-/SH mice in cognitive performance. The current study utilized the same cognitive-based behavioral battery and multimetric statis statistical analysis to investigate the protective effects of "complete" environment enrichment (EE) versus several of its components (physical activity, social interactions) in AD transgenic mice. The AD transgenic mice utilized develop beta-amyloid (AB) deposition and cognitive impairment by 6-7 months of age. Similar to our initial study, results show that "complete" EE (physical, social, and cognitive activities) from 2 to 8 months of age completely protected AD transgenic mice from cognitive impairment in tasks representing different cognitive domains - working memory, reference learning, and search/recognition. In strong contrast, Tg+ mice reared in environments that included physical activity and social interaction, or only social interaction, were not protected from cognitive impairment in adulthood -- enhanced cognitive activity was required over and above that present in these other environments. Through use of discriminant function analysis, EE and/or NT mice were consistently discriminated from the poorer performing other housing groups. The cognitive benefits observed in EE-housed Tg+ mice occurred without significant changes in cortical AB levels, plasma cytokine levels, or plasma corticosterone levels, suggesting involvement of mechanisms independent of these endpoints. However, EE-housed Tg+ mice did have decreased dendritic length of neurons in the parietal cortex (but not hippocampus). Noteworthy is that plasma cytokine levels and hippocampal dendritic length consistently correlated with cognitive measures, suggesting their involvement in underlying mechanisms of cognitive performance. The present work provides the first evidence that "complete" EE (including enhanced cognitive activity) is needed to provide cognitive protection against AD in a Tg+ model of the disease, while the physical and social activity components of EE do not alone lead to protection. These results suggest that humans desiring to gain maximal environmental protection against AD should live a lifestyle high in cognitive, social, and physical activities together.