RESUMEN
Upon stress exposure, a broad network of structures comes into play in order to provide adequate responses and restore homeostasis. It has been known for decades that the main structures engaged during the stress response are the medial prefrontal cortex, the amygdala, the hippocampus, the hypothalamus, the monoaminergic systems (noradrenaline, dopamine and serotonin) and the periaqueductal gray. The lateral habenula (LHb) is an epithalamic structure directly connected to prefrontal cortical areas and to the amygdala, whereas it functionally interacts with the hippocampus. Also, it is a main modulator of monoaminergic systems. The LHb is activated upon exposure to basically all types of stressors, suggesting it is also involved in the stress response. However, it remains unknown if and how the LHb functionally interacts with the broad stress response network. In the current study we performed in rats a restraint stress procedure followed by immunohistochemical staining of the c-Fos protein throughout the brain. Using graph theory-based functional connectivity analyses, we confirm the principal hubs of the stress network (e.g., prefrontal cortex, amygdala and periventricular hypothalamus) and show that the LHb is engaged during stress exposure in close interaction with the medial prefrontal cortex, the lateral septum and the medial habenula. In addition, we performed DREADD-induced LHb inactivation during the same restraint paradigm in order to explore its consequences on the stress response network. This last experiment gave contrasting results as the DREADD ligand alone, clozapine-N-oxide, was able to modify the network.
Asunto(s)
Clozapina , Habénula , Animales , Dopamina/metabolismo , Habénula/fisiología , Hipotálamo/metabolismo , Ligandos , Norepinefrina/metabolismo , Óxidos/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas , Serotonina/metabolismoRESUMEN
Working memory is a cognitive ability allowing the temporary storage of information to solve problems or adjust behavior. While working memory is known to mainly depend on the medial prefrontal cortex (mPFC), very few is known about how cortical information are relayed subcortically. By its connectivity, the lateral habenula (lHb) might act as a subcortical relay for cortical information. Indeed, the lHb receives inputs from several mPFC subregions, and recent findings suggest a role for the lHb in online processing of spatial information, a fundamental aspect of working memory. In rats, in a delayed non-matching to position paradigm, using focal microinjections of the GABAA agonist muscimol we showed that inactivation of the lHb (16 ng in 0.2 µL per side), as well as disconnection between the prelimbic region of the mPFC (mPFC/PrL, 32 ng in 0.4 µL in one hemisphere) and the lHb (16 ng in 0.2 µL in the lHb in the contralateral hemisphere) impaired working memory. The deficits were unlikely to result from motivational or motor deficits as muscimol did not affect reward collection or cue responding latencies, and did not increase the number of omissions. These results show for the first time the implication of the lHb in mPFC-dependent memory processes, likely as a relay of mPFC/PrL information. They also open new perspectives in the understanding of the top-down processing of high-level cognitive functions.
Asunto(s)
Habénula/fisiología , Memoria a Corto Plazo/fisiología , Corteza Prefrontal/fisiología , Animales , Agonistas de Receptores de GABA-A/farmacología , Habénula/efectos de los fármacos , Masculino , Memoria a Corto Plazo/efectos de los fármacos , Microinyecciones , Motivación/efectos de los fármacos , Motivación/fisiología , Muscimol/farmacología , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/fisiología , Pruebas Neuropsicológicas , Corteza Prefrontal/efectos de los fármacos , Ratas Long-Evans , RecompensaRESUMEN
Aging weakens memory functions. Exposing healthy rodents or pathological rodent models to environmental enrichment (EE) housing improves their cognitive functions by changing neuronal levels of excitation, cellular signaling, and plasticity, notably in the hippocampus. At the molecular level, brain derived-neurotrophic factor (BDNF) represents an important player that supports EE-associated changes. EE facilitation of learning was also shown to correlate with chromatin acetylation in the hippocampus. It is not known, however, whether such mechanisms are still into play during aging. In this study, we exposed a cohort of aged rats (18-month-old) to either a 6 month period of EE or standard housing conditions and investigated chromatin acetylation-associated events [histone acetyltranferase activity, gene expression, and histone 3 (H3) acetylation] and epigenetic modulation of the Bdnf gene under rest conditions and during learning. We show that EE leads to upregulation of acetylation-dependent mechanisms in aged rats, whether at rest or following a learning challenge. We found an increased expression of Bdnf through Exon-I-dependent transcription, associated with an enrichment of acetylated H3 at several sites of Bdnf promoter I, more particularly on a proximal nuclear factor κB (NF-κB) site under learning conditions. We further evidenced p65/NF-κB binding to chromatin at promoters of genes important for plasticity and hippocampus-dependent learning (e.g., Bdnf, CamK2D). Altogether, our findings demonstrate that aged rats respond to a belated period of EE by increasing hippocampal plasticity, together with activating sustained acetylation-associated mechanisms recruiting NF-κB and promoting related gene transcription. These responses are likely to trigger beneficial effects associated with EE during aging. SIGNIFICANCE STATEMENT: Aging weakens memory functions. Optimizing the neuronal circuitry required for normal brain function can be achieved by increasing sensory, motor, and cognitive stimuli resulting from interactions with the environment (behavioral therapy). This can be experimentally modeled by exposing rodents to environmental enrichment (EE), as with large cages, numerous and varied toys, and interaction with other rodents. However, EE effects in aged rodents has been poorly studied, and it is not known whether beneficial mechanisms evidenced in the young adults can still be recruited during aging. Our study shows that aged rats respond to a belated period of EE by activating specific epigenetic and transcriptional signaling that promotes gene expression likely to facilitate plasticity and learning behaviors.
Asunto(s)
Envejecimiento/fisiología , Envejecimiento/psicología , Ambiente , Hipocampo/crecimiento & desarrollo , Hipocampo/fisiología , Aprendizaje/fisiología , FN-kappa B/metabolismo , Plasticidad Neuronal/fisiología , Acetilación , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Cromatina/metabolismo , Epigénesis Genética , Femenino , Expresión Génica/genética , Aprendizaje por Laberinto/fisiología , Neurogénesis/fisiología , Ratas , Ratas Long-Evans , Memoria Espacial/fisiología , Sinapsis/fisiología , Factor de Transcripción ReIA/genética , Factor de Transcripción ReIA/metabolismoRESUMEN
Exposure of rodents to a stimulating environment has beneficial effects on some cognitive functions that are impaired during physiological aging, and especially spatial reference memory. The present study investigated whether environmental enrichment rescues these functions in already declining subjects and/or protects them from subsequent decline. Subgroups of 17-mo-old female rats with unimpaired versus impaired performance in a spatial reference memory task (Morris water maze) were housed until the age of 24 mo in standard or enriched environment. They were then trained in a second reference memory task, conducted in a different room than the first, and recent (1 d) and remote (10 d) memory were assessed. In unimpaired subgroups, spatial memory declined from 17 to 24 mo in rats housed in standard conditions; an enriched environment during this period allowed maintenance of accurate recent and remote spatial memory. At 24 mo, rats impaired at the age of 17 mo housed in enriched environment learned the task and displayed substantial recent memory, but their performance remained lower than that of unimpaired rats, showing that enrichment failed to rescue spatial memory in already cognitively declining rats. Controls indicated carryover effects of the first water maze training, especially in aged rats housed in standard condition, and confirmed the beneficial effect of enrichment on remote memory of aged rats even if they performed poorly than young adults housed for the same duration in standard or enriched condition.
Asunto(s)
Envejecimiento , Ambiente , Memoria a Largo Plazo , Memoria Espacial , Animales , Femenino , Ratas Long-EvansRESUMEN
Cocaine exposure induces changes in the expression of numerous genes, in part through epigenetic modifications. We have initially shown that cocaine increases the expression of the chromatin remodeling protein methyl-CpG binding protein 2 (MeCP2) and characterized the protein phosphatase-1Cß (PP1Cß) gene, as repressed by passive i.p. cocaine injections through a Mecp2-mediated mechanism involving de novo DNA methylation. Both proteins being involved in learning and memory processes, we investigated whether voluntary cocaine administration would similarly affect their expression using an operant self-administration paradigm. Passive and voluntary i.v. cocaine intake was found to induce Mecp2 and to repress PP1Cß in the prefrontal cortex and the caudate putamen. This observation is consistent with the role of Mecp2 acting as a transcriptional repressor of PP1Cß and shows that passive intake was sufficient to alter their expression. Surprisingly, striking differences were observed under the same conditions in food-restricted rats tested for food pellet delivery. In the prefrontal cortex and throughout the striatum, both proteins were induced by food operant conditioning, but remained unaffected by passive food delivery. Although cocaine and food activate a common reward circuit, changes observed in the expression of other genes such as reelin and GAD67 provide new insights into molecular mechanisms differentiating neuroadaptations triggered by each reinforcer. The identification of hitherto unknown genes differentially regulated by drugs of abuse and a natural reinforcer should improve our understanding of how two rewarding stimuli differ in their ability to drive behavior.
Asunto(s)
Cocaína/administración & dosificación , Inhibidores de Captación de Dopamina/administración & dosificación , Ingestión de Alimentos/fisiología , Proteína 2 de Unión a Metil-CpG/metabolismo , Proteína Fosfatasa 1/metabolismo , Animales , Encéfalo/efectos de los fármacos , Encéfalo/fisiología , Moléculas de Adhesión Celular Neuronal/metabolismo , Condicionamiento Operante/efectos de los fármacos , Condicionamiento Operante/fisiología , Proteínas de la Matriz Extracelular/metabolismo , Privación de Alimentos/fisiología , Expresión Génica , Glutamato Descarboxilasa/metabolismo , Masculino , Memoria/efectos de los fármacos , Memoria/fisiología , Proteínas del Tejido Nervioso/metabolismo , Distribución Aleatoria , Ratas Wistar , Proteína Reelina , Recompensa , Autoadministración , Serina Endopeptidasas/metabolismo , VoliciónRESUMEN
OBJECTIVE: Temporal lobe epilepsy is a relatively frequent, invalidating, and often refractory neurologic disorder. It is associated with cognitive impairments that affect memory and executive functions. In the rat lithium-pilocarpine temporal lobe epilepsy model, memory impairment and anxiety disorder are classically reported. Here we evaluated sustained visual attention in this model of epilepsy, a function not frequently explored. METHODS: Thirty-five Sprague-Dawley rats were subjected to lithium-pilocarpine status epilepticus. Twenty of them received a carisbamate treatment for 7 days, starting 1 h after status epilepticus onset. Twelve controls received lithium and saline. Five months later, attention was assessed in the five-choice serial reaction time task, a task that tests visual attention and inhibitory control (impulsivity/compulsivity). Neuronal counting was performed in brain regions of interest to the functions studied (hippocampus, prefrontal cortex, nucleus basalis magnocellularis, and pedunculopontine tegmental nucleus). RESULTS: Lithium-pilocarpine rats developed motor seizures. When they were able to learn the task, they exhibited attention impairment and a tendency toward impulsivity and compulsivity. These disturbances occurred in the absence of neuronal loss in structures classically related to attentional performance, although they seemed to better correlate with neuronal loss in hippocampus. Globally, rats that received carisbamate and developed motor seizures were as impaired as untreated rats, whereas those that did not develop overt motor seizures performed like controls, despite evidence for hippocampal damage. SIGNIFICANCE: This study shows that attention deficits reported by patients with temporal lobe epilepsy can be observed in the lithium-pilocarpine model. Carisbamate prevents the occurrence of motor seizures, attention impairment, impulsivity, and compulsivity in a subpopulation of neuroprotected rats.
Asunto(s)
Atención , Modelos Animales de Enfermedad , Epilepsia Parcial Compleja/psicología , Epilepsia del Lóbulo Temporal/psicología , Función Ejecutiva , Estado Epiléptico/psicología , Animales , Anticonvulsivantes/farmacología , Atención/efectos de los fármacos , Atención/fisiología , Encéfalo/efectos de los fármacos , Encéfalo/fisiopatología , Mapeo Encefálico , Carbamatos/farmacología , Recuento de Células , Epilepsia Parcial Compleja/inducido químicamente , Epilepsia Parcial Compleja/fisiopatología , Epilepsia del Lóbulo Temporal/inducido químicamente , Epilepsia del Lóbulo Temporal/fisiopatología , Función Ejecutiva/efectos de los fármacos , Función Ejecutiva/fisiología , Inhibición Psicológica , Carbonato de Litio , Neuronas/efectos de los fármacos , Neuronas/fisiología , Reconocimiento Visual de Modelos/efectos de los fármacos , Reconocimiento Visual de Modelos/fisiología , Pilocarpina , Ratas , Ratas Sprague-Dawley , Tiempo de Reacción/efectos de los fármacos , Tiempo de Reacción/fisiología , Aprendizaje Seriado/efectos de los fármacos , Aprendizaje Seriado/fisiología , Estado Epiléptico/inducido químicamente , Estado Epiléptico/fisiopatologíaRESUMEN
Engagement in cognitive activity in adulthood is one of the factors that enable successful cognitive aging, both in humans and rodents. However, some studies emphasize that the beneficial effect on cognition of such an activity may reflect carry over from one test situation to another, including memory for procedural aspects of the behavioral tasks, and thus question whether this effect can be limited to the trained cognitive domain or whether it can be transferred to an untrained ones. In the current study, we assessed whether adulthood intermittent working memory training has beneficial effect on long-term memory of aged rats using two very different test situations. To this aim, rats trained in a delayed non-matching to position task in operant box at 3 and 15 months of age were tested in a place learning task in water maze when they were 24 months. The two tasks differ with regard to the cognitive domain but also in their spatial ability requirement and the nature of the reinforcer used. During the memory tests, accuracy of the platform search indicated age-related impairment only in the aged-untrained group. Thus, intermittent training during adult life in a task involving working memory protects aged animals from the deleterious effects of aging on spatial reference memory. This result highlights the long-term beneficial effects of training on a working memory task on an untrained cognitive domain.
Asunto(s)
Entrenamiento Cognitivo , Memoria a Corto Plazo , Humanos , Ratas , Animales , Anciano , Memoria a Largo Plazo , Memoria Espacial , Trastornos de la Memoria/prevención & controlRESUMEN
Increasing evidence points to the engagement of the lateral habenula (LHb) in the selection of appropriate behavioral responses in aversive situations. However, very few data have been gathered with respect to its role in fear memory formation, especially in learning paradigms in which brain areas involved in cognitive processes like the hippocampus (HPC) and the medial prefrontal cortex (mPFC) are required. A paradigm of this sort is trace fear conditioning, in which an aversive event is preceded by a discrete stimulus, generally a tone, but without the close temporal contiguity allowing for their association based on amygdala-dependent information processing. In a first experiment, we analyzed cellular activations (c-Fos expression) induced by trace fear conditioning in subregions of the habenular complex, HPC, mPFC and amygdala using a factorial analysis to unravel functional networks through correlational analysis of data. This analysis suggested that distinct LHb subregions engaged in different aspects of conditioning, e.g. associative processes and onset of fear responses. In a second experiment, we performed chemogenetic LHb inactivation during the conditioning phase of the trace fear conditioning paradigm and subsequently assessed contextual and tone fear memories. Whereas LHb inactivation did not modify rat's behavior during conditioning, it induced contextual memory deficits and enhanced fear to the tone. These results demonstrate the involvement of the LHb in fear memory. They further suggest that the LHb is engaged in learning about threatening environments through the selection of relevant information predictive of a danger.
Asunto(s)
Condicionamiento Clásico/fisiología , Miedo/fisiología , Habénula/metabolismo , Memoria/fisiología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Amígdala del Cerebelo/metabolismo , Animales , Reacción Cataléptica de Congelación/fisiología , Masculino , Actividad Motora/fisiología , Corteza Prefrontal/metabolismo , Ratas Long-EvansRESUMEN
This study investigated if sub-populations of rats characterized by their basal level of impulsivity (BLI) in a delayed-reinforcement task, displayed differences in the functioning of neurotransmitter systems modulating impulsive choice behavior. For this, the effects of various doses of caffeine and d-amphetamine were investigated in three sub-populations of rats displaying pronounced differences in their impulsive choice behavior and their post-mortem serotonergic and dopaminergic functions were assessed. Caffeine and d-amphetamine reduce impulsive choice behavior only in the Medium BLI sub-population. Dopamine utilization was similar in the three sub-populations, but serotonin utilization was lower in the prefrontal cortex of the Medium and Very high BLI sub-populations as compared to the low BLI one. These results suggest that anti-impulsive effects of caffeine and d-amphetamine are dependent on the BLI of rats and that a low serotonergic function in the prefrontal cortex may be a trait marker of impulsivity evaluated by impulsive choice behavior.
Asunto(s)
Cafeína/farmacología , Estimulantes del Sistema Nervioso Central/farmacología , Dextroanfetamina/farmacología , Conducta Impulsiva/tratamiento farmacológico , Corteza Prefrontal/efectos de los fármacos , Análisis de Varianza , Animales , Conducta de Elección/efectos de los fármacos , Dopamina/metabolismo , Relación Dosis-Respuesta a Droga , Ácido Hidroxiindolacético/metabolismo , Conducta Impulsiva/metabolismo , Inhibición Psicológica , Corteza Prefrontal/metabolismo , Ratas , Ratas Long-Evans , Recompensa , Serotonina/metabolismo , Estadísticas no ParamétricasRESUMEN
The lateral habenula (LHb) is involved in emotional and cognitive behaviors. Recently, we have shown in rats that blockade of excitatory inputs to the LHb not only induced deficits of memory retrieval in the water maze, but also altered swim strategies (i.e., induced excessive thigmotaxis). The latter observation, although consistent with the occurrence of memory deficits, could also possibly be the consequence of an excessive level of stress, further suggesting a role for the LHb in the stress response in our behavioral paradigm. To test this hypothesis we performed in rats intra-LHb infusion of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 267â¯ng/side in 0.3⯵L), or vehicle, and assessed the responsiveness of the hypothalamo-pituitary adrenal (HPA) axis to environmental stressful or non-stressful situations. We have measured plasma corticosterone (CORT) concentrations at different time points before and following intra-LHb infusion of CNQX - or of the same volume of vehicle - in three conditions: during the probe test of a water maze experiment; in an anxiety test, the elevated plus maze; and in a home cage condition. Whereas there were no differences in the home cage condition and in the elevated plus maze, in the water maze experiment we observed that CNQX-treated rats presented, along with memory deficits, a higher level of blood CORT than vehicle-treated rats. These results suggest that perturbations of the modulation of the HPA axis are consecutive to the alteration of LHb function, whether it is the result of a defective direct control of the LHb over the HPA axis, or the consequence of memory deficits.
Asunto(s)
Habénula/fisiopatología , Sistema Hipotálamo-Hipofisario/fisiopatología , Aprendizaje por Laberinto/fisiología , Sistema Hipófiso-Suprarrenal/fisiopatología , Memoria Espacial/fisiología , Estrés Psicológico/fisiopatología , 6-Ciano 7-nitroquinoxalina 2,3-diona/farmacología , Animales , Cognición/efectos de los fármacos , Cognición/fisiología , Corticosterona/sangre , Antagonistas de Aminoácidos Excitadores/farmacología , Habénula/efectos de los fármacos , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Ratas Long-Evans , Memoria Espacial/efectos de los fármacosRESUMEN
Several studies have suggested a positive relationship between circulating corticosterone levels and contextual conditioning. However, a positive relationship between circulating corticosterone levels and cued conditioning has also been reported. This study further investigates the relationship between corticosterone and fear conditioning by modulating the predictive value of contextual and discrete tone cues in separate groups of rats. In a first experiment in which training parameters were chosen to induce strong conditioning (five foot-shocks), we used a correlational approach and investigated whether post-training corticosterone levels were related to subsequent expression of contextual and/or tone fear. In a second experiment, in which training parameters were chosen to induce lower conditioning (one and two foot-shocks), we investigated whether a post-training corticosterone injection enhanced the consolidation of contextual and/or tone conditioning. In the first experiment, the highest post-training corticosterone levels were obtained in rats trained with paired tones and shocks. Post-training corticosterone levels tended to be positively correlated with freezing scores during the tone-fear test and were negatively correlated with freezing scores during training although not during the context-fear test. In the second experiment, a post-training injection of corticosterone (3mg/kg) had no effect on subsequent freezing to contextual cues and to a tone that did not predict shock, whereas it was efficient in increasing fear conditioned to a predictive tone. Globally, these results suggest that the predictive value of the conditioned stimulus may be the main determinant of the facilitatory action of acutely enhanced corticosterone in fear conditioning.
Asunto(s)
Aprendizaje por Asociación/fisiología , Condicionamiento Clásico/fisiología , Corticosterona/sangre , Miedo/fisiología , Reacción Cataléptica de Congelación/fisiología , Análisis de Varianza , Animales , Corticosterona/fisiología , Señales (Psicología) , Ambiente , Masculino , Ratas , Ratas Long-EvansRESUMEN
In rats, some cognitive capabilities, like spatial learning and memory, are preserved from age-related decline by whole adult life enriched environment (EE) exposure. However, to which extent late EE contributes to such maintenance remains to be investigated. Here we assessed the impact of late housing condition (e.g., from the age of 18 months) on spatial learning and memory of aged rats (24 months) previously exposed or unexposed to EE from young adulthood. The results showed that late EE was not required for spatial memory maintenance in aged rats previously housed in EE. In contrast, late EE mitigates spatial memory deficit in aged rats previously unexposed to EE. These outcomes suggest that EE exposure up to middle age provides a "reserve"-like advantage which supports an enduring preservation of spatial capabilities in old age.
Asunto(s)
Envejecimiento/psicología , Ambiente , Memoria Espacial/fisiología , Animales , Modelos Animales de Enfermedad , Femenino , Aprendizaje por Laberinto , RatasRESUMEN
The present work aimed 1) to evaluate whether an increase in galanin or galanin receptors could be induced in the nucleus basalis magnocellularis (nbm) by degeneration of the basalocortical neurons from the cortex and 2) to analyze the consequences of such an increase on cortical activity. First, a mild ischemic insult to the frontoparietal cortex was performed to induce the degeneration of the basalocortical system; galanin immunoreactivity, galanin binding sites, and cholinergic muscarinic receptors were quantified through immunocytochemistry and autoradiography. Second, galanin infusions in the nbm were undertaken to mimic a local increase of the galaninergic innervation; cortical acetylcholine release, cerebral glucose use, and cerebral blood flow were then measured as indices of cortical activity. As a result of the cortical ischemic lesion, the postsynaptic M1 and presynaptic M2 muscarinic receptors were found to be reduced in the altered cortex. In contrast, galaninergic binding capacity and fiber density were found to be increased in the ipsilateral nbm in parallel with a local decrease in the cholinergic markers such as the muscarinic M1 receptor density. Galanin infusion into the nbm inhibited the cortical acetylcholine release and cerebral blood flow increases elicited by the activation of the cholinergic basalocortical system but failed to affect acetylcholine release, cerebral blood flow, and cerebral glucose use when injected alone in the nbm. These results demonstrate that degeneration of the basalocortical system from the cortex induces an increase in galaninergic markers in the nbm, a result that might suggest that the galaninergic overexpression described in the basal forebrain of patients with Alzheimer's disease can result from a degeneration of the cholinergic basalocortical system from the cortex. Because galanin was found to reduce the activity of the basalocortical cholinergic system only when this one is activated, galanin might exert its role rather during activation deficits than under resting conditions such as the resting cortical hypometabolism, which is characteristic of Alzheimer's disease.
Asunto(s)
Núcleo Basal de Meynert/metabolismo , Núcleo Basal de Meynert/patología , Corteza Cerebral/metabolismo , Corteza Cerebral/patología , Galanina/metabolismo , Vías Nerviosas , Acetilcolina/metabolismo , Animales , Núcleo Basal de Meynert/efectos de los fármacos , Sitios de Unión , Biomarcadores/metabolismo , Isquemia Encefálica/patología , Corteza Cerebral/efectos de los fármacos , Galanina/farmacología , Inmunohistoquímica , Masculino , Ratas , Ratas Sprague-Dawley , Receptor Muscarínico M1/metabolismo , Receptor Muscarínico M2/metabolismo , Receptores de Galanina/metabolismoRESUMEN
The selective alpha2-adrenoreceptor antagonist, atipamezole, improves behavioural performance of rats subjected to focal cerebral ischemia. The aim of the present study was to investigate whether the facilitatory effect of atipamezole on behaviour is related to altered neuronal activity in specific brain areas. The right middle cerebral artery of rats was occluded for 120 min using the intraluminal filament method. Starting on day 2 after induction of ischemia, atipamezole (1mg/kg, s.c.) or 0.9% NaCl was administered to ischemic or sham-operated rats once a day 30 min before the limb-placing test. [14C]Deoxyglucose ([14C]DG) uptake was used to measure neuronal activity 30 min after atipamezole or 0.9% NaCl administration on day 6 after ischemia. Ischemia induced a significant decrease in [14C]DG uptake in several cortical areas ipsilateral and contralateral to the lesion, in the ipsilateral thalamus, and bilaterally in the cerebellum and spinal cord. Administration of atipamezole normalised [14C]DG uptake particularly in the cerebellum and spinal cord both in sham-operated and ischemic rats and to a lesser extent in the thalamus in sham-operated rats. The pattern of altered cerebral [14C]DG uptake following alpha2-adrenoceptor blockade suggests that plasticity in the cerebellum and spinal cord contributes to the improved performance of ischemic rats in tests assessing tactile/proprioceptive limb-placing reactions.
Asunto(s)
Antagonistas de Receptores Adrenérgicos alfa 2 , Antagonistas Adrenérgicos alfa/farmacología , Química Encefálica/efectos de los fármacos , Ataque Isquémico Transitorio/metabolismo , Animales , Antimetabolitos/farmacología , Autorradiografía , Conducta Animal/efectos de los fármacos , Infarto Cerebral/patología , Desoxiglucosa/metabolismo , Imidazoles/farmacología , Ataque Isquémico Transitorio/patología , Masculino , Movimiento/efectos de los fármacos , Ratas , Ratas WistarRESUMEN
We assessed lifelong environmental enrichment effects on possible age-related modifications in emotional behaviors, spatial memory acquisition, retrieval of recent and remote spatial memory, and cholinergic forebrain systems. At the age of 1 month, Long-Evans female rats were placed in standard or enriched rearing conditions and tested after 3 (young), 12 (middle-aged), or 24 (aged) months. Environmental enrichment decreased the reactivity to stressful situations regardless of age. In the water maze test, it delayed the onset of learning deficits and prevented age-dependent spatial learning and recent memory retrieval alterations. Remote memory retrieval, which was altered independently of age under standard rearing conditions, was rescued by enrichment in young and middle-aged, but unfortunately not aged rats. A protected basal forebrain cholinergic system, which could well be one out of several neuronal manifestations of lifelong environmental enrichment, might have contributed to the behavioral benefits of this enrichment.
Asunto(s)
Envejecimiento/fisiología , Conducta Animal , Neuronas Colinérgicas/fisiología , Emociones/fisiología , Memoria/fisiología , Plasticidad Neuronal/fisiología , Medio Social , Animales , Modelos Animales de Enfermedad , Femenino , Aprendizaje por Laberinto/fisiología , Ratas , Ratas Long-Evans , Estrés Psicológico/fisiopatología , Estrés Psicológico/psicologíaRESUMEN
The recent literature provides evidence that epigenetic mechanisms such as DNA methylation and histone modification are crucial to gene transcription linked to synaptic plasticity in the mammalian brain--notably in the hippocampus--and memory formation. We measured global histone acetylation levels in the rat hippocampus at an early stage of spatial or fear memory formation. We found that H3, H4 and H2B underwent differential acetylation at specific sites depending on whether rats had been exposed to the context of a task without having to learn or had to learn about a place or fear therein: H3K9K14 acetylation was mostly responsive to any experimental conditions compared to naive animals, whereas H2B N-terminus and H4K12 acetylations were mostly associated with memory for either spatial or fear learning. Altogether, these data suggest that behavior/experience-dependent changes differently regulate specific acetylation modifications of histones in the hippocampus, depending on whether a memory trace is established or not: tagging of H3K9K14 could be associated with perception/processing of testing-related manipulations and context, thereby enhancing chromatin accessibility, while tagging of H2B N-terminus tail and H4K12 could be more closely associated with the formation of memories requiring an engagement of the hippocampus.
Asunto(s)
Aminoácidos/metabolismo , Hipocampo/metabolismo , Histonas/metabolismo , Acetilación , Aminoácidos/genética , Animales , Miedo/fisiología , Regulación de la Expresión Génica , Histonas/genética , Masculino , Aprendizaje por Laberinto/fisiología , Memoria/fisiología , Ratas , Ratas Long-Evans , Percepción Espacial/fisiologíaRESUMEN
Aged rodents exhibit memory and attention dysfunctions. Environmental enrichment (EE) attenuates memory impairments. Whether it may reduce attention deficits is not known. At the age of 1 month, Long-Evans female rats were placed in standard or EE conditions and tested after 3 (young), 12 (middle-aged) or 24 (aged) months of differential housing. Spatial reference memory was assessed in a water-maze task. Attention performance was evaluated in the five-choice serial reaction time (5-CSRT) task. EE improved spatial memory at all ages, but did not ameliorate 5-CSRT performance in young and middle-aged rats; it prevented, however, the degradation of attention performances detected in aged rats. The number of ChAT (+30 to +64%)- and p75(NTR)-positive (+35 to +44%) neurons was higher in the basal forebrain of aged enriched vs. standard rats, suggesting their EE-mediated protection. The weaker deficit of attention found in aged EE rats might be linked to a better survival in the very long term of neurons in the basalo-cortical system.
Asunto(s)
Envejecimiento/fisiología , Atención/fisiología , Ambiente , Vivienda para Animales , Aprendizaje por Laberinto/fisiología , Memoria/fisiología , Análisis de Varianza , Animales , Peso Corporal/fisiología , Encéfalo/metabolismo , Recuento de Células , Colina O-Acetiltransferasa/metabolismo , Femenino , Inmunohistoquímica , Actividad Motora/fisiología , Neuronas/metabolismo , Parvalbúminas/metabolismo , Ratas , Ratas Long-Evans , Tiempo de Reacción/fisiología , Receptor de Factor de Crecimiento Nervioso/metabolismo , Análisis de RegresiónRESUMEN
Cluster analysis of performance during acquisition of a place-learning task in the water maze distinguished between subpopulations of aged rats (25-27 months) classified as moderately (AMI) or severely impaired (ASI) in comparison with young adults (3-5 months). Using a slice-superfusion device, electrically or nicotine-evoked release of dopamine from striatum was assessed in the presence of GR-55,562 (5-HT(1B) receptor antagonist), methiotepin (mixed 5-HT(1/2) receptor antagonist) and/or sulpiride (D(2)/D(3) receptor antagonist). The main neuropharmacological results demonstrated age-related alterations in the 5-HT(1B)- and D(2)/D(3)-mediated modulation of electrically evoked striatal dopamine release. Regression analyses indicated a possible contribution of such alterations to the age-related behavioural deficits: the larger the deficit, the weaker the electrically evoked release under 5-HT(1B) and D(2)/D(3) receptor blockade. Extending our recent report on the modulation of striatal acetylcholine release in aged rats [Cassel et al., 2007. Neurobiol. Aging 28, 1270-1285], these new findings make dopaminergic and serotonergic functional alterations potential candidates to participate in age-related deficits in the water maze, most probably in interaction with formerly described cholinergic dysfunctions.
Asunto(s)
Envejecimiento/fisiología , Cuerpo Estriado/metabolismo , Dopamina/metabolismo , Aprendizaje por Laberinto/fisiología , Recuerdo Mental/fisiología , Receptores de Serotonina/metabolismo , Análisis y Desempeño de Tareas , Adaptación Fisiológica/fisiología , Animales , Femenino , Ratas , Ratas Long-EvansRESUMEN
To assess a possible role for serotonin in the mediation of the behavioral changes induced by enriched housing conditions (EC), adult female Long-Evans rats sustaining a serotonin depletion (150 microg of 5,7-dihydroxytryptamine, icv) and sham-operated rats were housed postoperatively for 30 days in enriched (12 rats/large cage containing various objects) or standard housing conditions (2 rats/standard laboratory cage). Thereafter, anxiety responses (elevated plus-maze), locomotor activity (in the home-cage), sensori-motor capabilities (beam-walking task), and spatial memory (eight-arm radial maze) were assessed. Monoamine levels were subsequently measured in the frontoparietal cortex and the hippocampus. Overall, EC reduced anxiety-related responses, enhanced sensori-motor performance and improved the memory span in the initial stage of the spatial memory task. Despite a substantial reduction of serotonergic markers in the hippocampus (82%) and the cortex (74%), these positive effects of EC were not altered by the lesion. EC reduced the serotonin levels in the ventral hippocampus (particularly in unlesioned rats: -23%), increased serotonin turnover in the entire hippocampus (particularly in lesioned rats: +36%) and augmented the norepinephrine levels in the dorsal hippocampus (+68% in unlesioned and +49% in lesioned rats); no such alterations were found in the frontoparietal cortex. Our data suggest that an intact serotonergic system is not a prerequisite for the induction of positive behavioral effects by EC. The neurochemical changes found in the hippocampus of EC rats, however, show that the monoaminergic innervation of the hippocampus is a target of EC.