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Transient intrauterine hypotension causes apoptosis in fetal rat brain and affects learning.

Hypotensive episodes are frequent during pregnancy, and their functional effect on fetal brain has not been studied. We produced systemic hypotension for 30 min during mid-gestation in pregnant rats and examined their offspring on postnatal days 1 and 28. When compared with sham controls, the brain of the hypotensive group contained more TUNEL-positive cells in the hippocampal and periventricular regions on both time points. Spatial learning assessed by water milk maze test was impaired in 28-day-old pups of the hypotensive mothers. According to these results, transient maternal hypotension can induce apoptotic cell death in fetal brain and affect learning. Similar mechanisms may be considered and investigated in the pathogenesis of human learning disorders.

Animals↗

Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production.

In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

Aging↗

Spatial memory in the rat requires the dorsolateral band of the entorhinal cortex.

The extensive connections of the entorhinal cortex with the hippocampus and the neocortex point to this region as a major interface in the hippocampal-neocortical interactions underlying memory. We asked whether hippocampal-dependent recall of spatial memory depends on the entorhinal cortex, and, if so, which parts are critical. After training in a Morris water maze, rats received fiber-sparing lesions in the dorsolateral band of the entorhinal cortex, which mediates much of the visuospatial input to the dorsal hippocampus. These lesions entirely disrupted retention and retarded new learning. Spatial memory was spared by lesions in the ventromedial band, which connects primarily with ventral hippocampus, but these lesions reduced defensive behavior on an elevated plus maze, mirroring the effects of damage to ventral hippocampus. The results suggest that the functional differences between dorsal and ventral hippocampus reflect their connectivity with modules of the entorhinal cortex that are differently linked to the rest of the cortex.

Animals↗

Behavioral analysis of CREB alphadelta mutation on a B6/129 F1 hybrid background.

The cyclic AMP (cAMP)-response element binding protein (CREB) is an activity-dependent transcription factor that plays a role in synaptic plasticity and memory storage in Aplysia, Drosophila, and rodents. Mice with targeted deletions of two CREB isoforms (alpha and delta; CREB alphadelta mice) have been characterized on a mixed genetic background of C57BL/6 (B6) and 129/SvEv (129), as well as on a defined F1 hybrid of B6 and FVB/N, and these results suggest that the phenotype of CREB alphadelta mice depends critically on genetic background. In an examination of the hypothesis that the role of CREB in learning and memory can be influenced by strain differences, we analyzed mice with the CREB alphadelta mutation on an F1 hybrid background of B6 and 129 strains. CREB alphadelta mice on this background had impaired short-term and long-term cued and contextual fear conditioning and normal spatial learning in the Morris water maze. Our results suggest that at least some aspects of hippocampal function are normal in CREB alphadelta mice, and that CREB alphadelta mice on the B6/129 F1 background have alterations in amygdala function. These studies underscore the importance of controlling for genetic background in the behavioral analysis of knockout and transgenic mice.

Animals↗

Age-independent and dose-response effects of ethanol on spatial memory in rats.

Results of previous studies have shown that ethanol impairs the acquisition of spatial memory in adolescent rats at doses below those required to impair the acquisition in adults. However, the previous work did not identify doses of ethanol that failed to impair acquisition in adolescents or that impaired acquisition in both adolescent and adult animals. This was our aim in the present study. Male, Long-Evans hooded rats (adolescent and adult) were treated intraperitoneally with 0.0, 0.5, or 2.5 g/kg of ethanol 30 min before daily training on a spatial or nonspatial version of the Morris water maze task. Twenty-four hours after training on the spatial task the animals were given a 1-min probe trial. The low dose of ethanol (0.5 g/kg) failed to impair the performance of animals from either age group on any tasks. It did, however, enhance the initial rate of acquisition on the spatial task. The 2.5-g/kg dose eliminated acquisition of spatial learning in animals of both ages and significantly attenuated performance on a nonspatial task in both age groups. However, the treatment effect in the nonspatial task was eliminated with controlling for baseline performance. These results establish a low dose of ethanol (0.5 g/kg) that does not impair acquisition of spatial memory in adolescent or adult rats. Moreover, the study findings show that 2.5 g/kg of ethanol markedly impairs acquisition of spatial memory in both adolescent and adult animals.

Aging↗

Network capacity analysis for latent attractor computation.

Attractor networks have been one of the most successful paradigms in neural computation, and have been used as models of computation in the nervous system. Recently, we proposed a paradigm called 'latent attractors' where attractors embedded in a recurrent network via Hebbian learning are used to channel network response to external input rather than becoming manifest themselves. This allows the network to generate context-sensitive internal codes in complex situations. Latent attractors are particularly helpful in explaining computations within the hippocampus--a brain region of fundamental significance for memory and spatial learning. Latent attractor networks are a special case of associative memory networks. The model studied here consists of a two-layer recurrent network with attractors stored in the recurrent connections using a clipped Hebbian learning rule. The firing in both layers is competitive--K winners take all firing. The number of neurons allowed to fire, K, is smaller than the size of the active set of the stored attractors. The performance of latent attractor networks depends on the number of such attractors that a network can sustain. In this paper, we use signal-to-noise methods developed for standard associative memory networks to do a theoretical and computational analysis of the capacity and dynamics of latent attractor networks. This is an important first step in making latent attractors a viable tool in the repertoire of neural computation. The method developed here leads to numerical estimates of capacity limits and dynamics of latent attractor networks. The technique represents a general approach to analyse standard associative memory networks with competitive firing. The theoretical analysis is based on estimates of the dendritic sum distributions using Gaussian approximation. Because of the competitive firing property, the capacity results are estimated only numerically by iteratively computing the probability of erroneous firings. The analysis contains two cases: the simple case analysis which accounts for the correlations between weights due to shared patterns and the detailed case analysis which includes also the temporal correlations between the network's present and previous state. The latter case predicts better the dynamics of the network state for non-zero initial spurious firing. The theoretical analysis also shows the influence of the main parameters of the model on the storage capacity.

Animals↗

Chronic infusions of GABA into the medial prefrontal cortex induce spatial alternation deficits in aged rats.

It has been proposed that functions associated with the prefrontal cortex could change as a consequence of aging. Previous experiments in young rats have demonstrated that anatomical lesions or chronic GABA infusions into this area produce deficits in spatial delayed alternation tasks. The present study examines the effect of chronic (7 days) GABA or saline infusion into the prefrontal cortex on the performance of delayed alternation task in old rats (24 months). The results suggested that aged rats needed more sessions to acquire the delayed alternation task. GABA infusions into the prefrontal cortex produced deficits in spatial alternation tasks similar to those previously observed in young rats. Performance rapidly recovered after the infusion period. Histological analysis showed similar lesion size in both groups. The results suggest that aged prefrontal cortex and/or related areas participating in the acquisition of the delayed alternation task are more sensitive to aging processes. Furthermore, the prefrontal cortex is important for the retention of a previously learned spatial delayed alternation task. The structures involved in functional recovery from these deficits appear to be fully functional in aged rats.

Aging↗

The effects of noradrenergic neurotoxin, DSP-4, on the performance of young and aged rats in spatial navigation task.

The present study investigated whether an overactive noradrenergic system is related to the impairment in learning/memory in aged subjects. The effects of partial noradrenaline depletion (using the noradrenergic neurotoxin DSP-4) on the acquisition of a water maze task was investigated in young and aged rats, and hippocampal noradrenaline content was correlated with spatial learning performance in similar rats. DSP-4 treatment impaired markedly the acquisition of the water maze task in aged rats, but improved it slightly in young rats. DSP-4 treatment decreased swimming speed, and this effect tended to be more marked in young rats. In the group of control rats, hippocampal noradrenaline tended to correlate positively with spatial bias in aged rats (the rats with the highest noradrenaline content in the hippocampus tended to have the best spatial learning/memory), but negatively in young rats. These results do not support the hypothesis that spatial learning/memory impairment is due to an overactive noradrenergic system in aged rats. Further studies are needed to clarify the reasons of the marked age-related difference in the effects of DSP-4 on the performance of water maze task in rats.

Aging↗

Age-related changes in spontaneous behavior and learning in NMRI mice from maturity to middle age.

Spontaneous behavior and learning and memory of 3-, 6-, 9- and 12-month-old virgin female NMRI mice were compared. Open field activity and spontaneous alternation in a Y-maze decreased in an age-related manner, reaching a statistical level of significance for the groups aged 9 and 12 months. Spatial learning was highly impaired in 9-and 12-month-old mice in the place version of a Morris-type water maze but not in the cued version of this task. Changes in motor activity, swimming ability or speed did not appear to account for these deficits. In a one-trial passive avoidance, performance was more variable, although a deficit in the oldest age group was clearly evident using a cutoff time of 120 sec. The passive avoidance was not attributable to reduced shock sensitivity. Together, these results suggest that the onset of aging in NMRI mice occurs at the age of 9 and particularly 12 months. NMRI mice of this age could, therefore, represent a viable animal model for the study of cognitive impairments in aging.

Aging↗

Binge pattern ethanol exposure in adolescent and adult rats: differential impact on subsequent responsiveness to ethanol.

BACKGROUND: Recent evidence indicates that adolescent animals are more sensitive than adults to the disruptive effects of acute ethanol exposure on spatial learning. It is not yet known whether adolescent animals are also more sensitive than adults to the enduring neurobehavioral effects of repeated ethanol exposure. In this study, animals were exposed to ethanol in a binge-pattern during either adolescence or adulthood. At a time when all subjects were adults, spatial working memory was examined in the absence and presence of an acute ethanol challenge. METHODS: Rats were exposed to ethanol (5.0 g/kg intraperitoneally) or isovolumetric saline at 48 hr intervals over 20 days. Exposure began on either postnatal day 30 (adolescent group) or 70 (adult group). Twenty days after the final injection, a time at which all animals were adults, the subjects were tested on an elevated plus maze and then were trained to perform a spatial working memory task on an eight-arm radial maze. At the beginning of each session of training on the working memory task, subjects retrieved food rewards on four of the eight arms. After a delay, subjects were placed on the maze and allowed to retrieve food from the remaining four arms. RESULTS: Prior exposure to ethanol did not influence behavior on the plus maze. Performance of the groups did not differ during acquisition of the spatial working memory task with a 5 min delay or during subsequent testing with a 1 hr delay. However, animals treated with ethanol during adolescence exhibited larger working memory impairments during an ethanol challenge (1.5 g/kg intraperitoneally) than subjects in the other three groups. CONCLUSIONS: The findings indicate that binge pattern exposure to ethanol during adolescence enhances responsiveness to the memory-impairing effects of ethanol in adulthood.

Aging↗

Obstructive jaundice in rats: cause of spatial memory deficits with recovery after biliary decompression.

Children with end-stage liver disease have been found to have cognitive deficits. The aim of this study was to examine whether cholestatic jaundice causes spatial deficits in rats and if these cognitive deficits are reversed by biliary drainage. Rats were randomly divided into three groups. In the first group, the bile duct was ligated for 3 weeks (BDL group); in the second group, the proximal bile duct was ligated with a Broviac CV catheter for 2 weeks followed by a tube bilioduodenostomy (TBD group); in the third group, a sham operation was performed (SHAM group). All the surviving rats were assessed for spatial learning and memory (a major cognitive function in rats) by the Morris water maze task about 3 weeks after the first operation. Blood was aspirated by cardiocentesis and assayed for total bilirubin, albumin, ammonia, and hemoglobin levels on the day following the water maze task. During the four consecutive acquisition trial days of the Morris water maze, jaundiced rats (BDL group) had a significant longer latency to escape than the SHAM group ( p < 0.05). Rats that underwent biliary decompression for 1 week (TBD group) showed improved status of the spatial deficit, as they required less time to reach the escape platform, approaching the performance of the SHAM group. The BDL group had a significantly higher serum ammonia level, higher bilirubin level, and lower hemoglobin level than the other two groups. After biliary decompression for 1 week, the serum albumin concentration in the TBD group still did not return to the level of the SHAM group. The results of this study suggest that long-term cholestasis results in spatial memory deficits in rats that correlate with anemia and hyperbilirubinemia encephalopathy. Early biliary decompression of obstructive jaundice improves spatial memory deficits, possibly related to the recovery of the serum ammonia and hemoglobin levels.

Analysis of Variance↗

Interactions between idiothetic cues and external landmarks in the control of place cells and head direction cells.

Two types of neurons in the rat brain have been proposed to participate in spatial learning and navigation: place cells, which fire selectively in specific locations of an environment and which may constitute key elements of cognitive maps, and head direction cells, which fire selectively when the rat's head is pointed in a specific direction and which may serve as an internal compass to orient the cognitive map. The spatially and directionally selective properties of these cells arise from a complex interaction between input from external landmarks and from idiothetic cues; however, the exact nature of this interaction is poorly understood. To address this issue, directional information from visual landmarks was placed in direct conflict with directional information from idiothetic cues. When the mismatch between the two sources of information was small (45 degrees), the visual landmarks had robust control over the firing properties of place cells; when the mismatch was larger, however, the firing fields of the place cells were altered radically, and the hippocampus formed a new representation of the environment. Similarly, the visual cues had control over the firing properties of head direction cells when the mismatch was small (45 degrees), but the idiothetic input usually predominated over the visual landmarks when the mismatch was larger. Under some conditions, when the visual landmarks predominated after a large mismatch, there was always a delay before the visual cues exerted their control over head direction cells. These results support recent models proposing that prewired intrinsic connections enable idiothetic cues to serve as the primary drive on place cells and head direction cells, whereas modifiable extrinsic connections mediate a learned, secondary influence of visual landmarks.

Aging↗

Enriched environment experience overcomes the memory deficits and depressive-like behavior induced by early life stress.

Stress in early life is believed to cause cognitive and affective disorders, and to disrupt hippocampal synaptic plasticity in adolescence into adult, but it is unclear whether exposure to enriched environment (EE) can overcome these effects. Here, we reported that housing rats in cages with limited nesting/bedding materials on postnatal days 2-21 reduced body weight gain, and this type of early life stress impaired spatial learning and memory of the Morris water maze and increased depressive-like behavior of the forced swim test in young adult rats (postnatal days 53-57). Early life stress also impaired long-term potentiation in hippocampal CA1 area of slices of young adult rats. Remarkably, EE experience on postnatal days 22-52 had no effect on spatial learning/memory and depressive-like behavior, but it significantly facilitated LTP in control rats, and completely overcame the effects of early life stress on young adult rats. These findings suggest that EE experience may be useful for clinical intervention in preventing cognitive and affective disorders during development.

Aging↗

Bacterial endotoxin-induced behavioral alterations in two variations of the Morris water maze.

Several studies report that lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) may affect behavior in a variety of learning tasks, including the Morris water maze (MWM), though the nature of these effects varies with testing parameters. The present study used C57BL/6J mice to evaluate the effect of a single intraperitoneal LPS injection 4 h prior to day 1 of testing, LPS before each day of testing, or saline prior to each test day, on performance in two variations of the MWM. In the first experiment, one that utilized a standard hidden platform, LPS clearly affected performance, as shown by increased latencies and greatly decreased swimming speeds. However, a modest effect on distance swam was only present during later test days. These data show a clear deficit in performance (driven by decreased swim speed), and some evidence for learning decrements on later test days. To explore to what degree the effects of LPS in the water maze were the result of alterations in performance factors such as motor behavior, a second experiment was conducted in which a highly visible jet-black platform was utilized. Despite eliminating the need for spatial learning, mice administered LPS still exhibited significantly increased latency scores and decreased swim speed. However, there was no difference between treatment groups in distance swam. These results reinforce the idea that, even when present, potential learning effects of LPS may sometimes be difficult to untangle from performance effects unrelated to learning, and underscore the need for utilizing behavioral tests that offer suitable control for LPS-induced performance effects.

Animals↗

[Analysis and course of cognitive deficits after rupture of aneurysms of the anterior communicating artery].

The aim of this study is to investigate general intellectual and memory performances at the secondary (3 weeks to 4.5 months) and late (10 to 16 months) stages following rupture of anterior communicating artery aneurysms (AACA). Twenty one patients presenting with selective lesion within frontal, or cingulate, callosal, caudate, basal forebrain areas were evaluated. At the secondary stage, the analysis of the general intellectual capacities revealed a drop of performance, prominent on performance IQ, which was more severe than the learning deficit. Specific cognitive evaluations revealed increase of the execution time, but performance was relatively preserved: in the Stroop test, focused attention disorder was moderate: the modified Wisconsin Card Sorting test was correctly performed in most cases; significant deficits of verbal short-term memory, long-term verbal and visuo-spatial learning, and access to semantic memory were observed. At the late stage, general intellectual performance improved, but did not reached the estimated prelesional level in most cases; specific cognitive disorders had most often disappeared. Most performances were best explained by the severity of lesions in the left cingulate cortex and corpus callosum area. These results show that the cognitive profile of AACA patients is different from classical descriptions of the "amnesic syndrome", and is also different at the secondary and late stages; this evolution has to be taken into account in studies describing cognitive deficits of such patients, or comparing them with others presenting with "annesic syndrome".

Adult↗

6-OHDA lesions of the nucleus accumbens accentuate memory deficits in animals with lesions to the forebrain cholinergic projection system: effects of nicotine administration on learning and memory in the water maze.

The separate and combined effects of lesions to the forebrain cholinergic projections system (FCPS) and to dopamine (DA) terminals in the nucleus accumbens (n.acc) were assessed in two water maze tasks: (1) standard acquisition using two trials/day with a 10 min intertrial interval (ITI) for 15 days with the platform in the same position and (2) a working memory task requiring matching to a platform position located by chance on Trial 1, with four trials/day separated by a 30-s ITI and a different platform position on each of 4 days. Effects of nicotine (0.1 mg/kg) were also examined in animals with FCPS, n.acc, and combined lesions in order to determine whether facilatory effects of nicotine in FCPS lesioned animals are mediated by dopamine release in the n.acc. The FCPS and combined lesion groups were impaired in both tasks, but the combined lesion group was substantially worse than animals with FCPS lesions alone. The n.acc lesion group did not differ from controls. Nicotine did not affect acquisition in either the FCPS or combined lesion group, but impaired learning in animals with n.acc lesions. In the working memory task nicotine exerted a nonspecific facilatory effect in the FCPS and combined lesion groups, by reducing latency to find the platform both on the first trial and on the subsequent matching to position trials. Choline acetyltransferase (ChAT) activity was reduced in hippocampus and cortex in the FCPS lesion group, whereas DA levels in n.acc were increased. Conversely, in the n.acc lesion group accumbal DA levels were reduced, while cortical and hippocampal ChAT activity was increased, suggesting that reciprocal changes were induced by the separate lesions. However the combined lesion group showed mixed and more widespread effects; ChAT activity was unaltered in cortex and substantially reduced in hippocampus, and DA levels were reduced in both n.acc and caudate. The results indicate that combined FCPS and n.acc lesions impair spatial learning and working memory far more severely than FCPS lesions alone, although this does not reflect simple additive reductions in DA and ChAT activity. Nicotine improved spatial search strategy, and effect detected in the in the working memory task with daily changes in platform position, rather than in the standard acquistion task, but did not appear specifically to improve working memory. Since the facilitatory effect of nicotine was seen in both FCPS and combined lesion groups, the findings suggest that nicotine-induced improvements do not depend on accumbal DA release.

Animals↗

Prenatal alcohol exposure alters GABA(A)alpha5 expression: a mechanism of alcohol-induced learning dysfunction.

OBJECTIVE: In a model for fetal alcohol syndrome (FAS), we have previously found an alteration in NMDA receptors suggesting mediation, at least in part, of alcohol-related learning deficit. NMDA and GABA receptors interact in a multisynaptic circuit for the regulation of the inhibitory tone through the CNS. The GABA receptor subunit GABA(A)alpha5 is involved in learning and is developmentally regulated, as it is excitatory in the perinatal brain and inhibitory in the adult. We were interested to evaluate alcohol's effect on GABA(A)alpha5 expression to further understand alcohol-induced learning dysfunction. STUDY DESIGN: Timed, pregnant C57B16/J mice were treated on gestational day 8 with alcohol (25% alcohol, 0.03 mL/kg i.p.) or control (saline). Embryos and brains were harvested 10 days after treatment, and brains from adult offspring were collected after evaluation in the Morris Water Maze, a well-established test for spatial learning. Gene expression included samples from at least 3 litters per timepoint, and calibrator-normalized relative real-time polymerase chain reaction (PCR) was performed to quantify GABA(A)alpha5 with GAPDH standardization. Statistical analysis included analysis of variance (ANOVA). RESULTS: Prenatal alcohol exposure significantly decreased GABA(A)alpha5 expression in the embryo (P < .02) and fetal brains (P < .01) 10 days after therapy. However, in adult brains GABA(A)alpha5 expression was increased versus controls (P < .01). As previously demonstrated, prenatal alcohol exposure resulted in deficits in adults learning the Morris Water Maze with controls learning faster (P < .05). CONCLUSION: Prenatal alcohol exposure alters developmental GABA(A)alpha5 expression. This may further explain the long-lasting damage of alcohol on learning skills. Both the alcohol-induced reduction in the GABA(A)alpha5 subunit during development and up-regulation in adult brain may be related to learning deficits resulting in decreased learning potential caused by the developmental defect and an increased inhibition of learning resulting from increased expression as an adult. In combination with our previous findings, these suggest that alcohol-induced learning impairment is likely the result of alterations of both NMDA and GABA expression and function.

Animals↗

Leptin facilitates learning and memory performance and enhances hippocampal CA1 long-term potentiation and CaMK II phosphorylation in rats.

Leptin, an adipocytokine encoded by an obesity gene and expressed in adipose tissue, affects feeding behavior, thermogenesis, and neuroendocrine status via leptin receptors distributed in the brain, especially in the hypothalamus. Leptin may also modulate the synaptic plasticity and behavioral performance related to learning and memory since: leptin receptors are found in the hippocampus, and both leptin and its receptor share structural and functional similarities with the interleukin-6 family of cytokines that modulate long-term potentiation (LTP) in the hippocampus. We therefore examined the effect of leptin on (1) behavioral performance in emotional and spatial learning tasks, (2) LTP at Schaffer collateral-CA1 synapses, (3) presynaptic and postsynaptic activities in hippocampal CA1 neurons, (4) the intracellular Ca(2+) concentration ([Ca(2+)](i)) in CA1 neurons, and (5) the activity of Ca(2+)/calmodulin protein kinase II (CaMK II) in the hippocampal CA1 tissue that exhibits LTP. Intravenous injection of 5 and/or 50mug/kg, but not of 500mug/kg leptin, facilitated behavioral performance in passive avoidance and Morris water-maze tasks. Bath application of 10(-12)M leptin in slice experiments enhanced LTP and increased the presynaptic transmitter release, whereas 10(-10)M leptin suppressed LTP and reduced the postsynaptic receptor sensitivity to N-methyl-d-aspartic acid. The increase in the [Ca(2+)](i) induced by 10(-10)M leptin was two times greater than that induced by 10(-12)M leptin. In addition, the facilitation (10(-12)M) and suppression (10(-10)M) of LTP by leptin was closely associated with an increase and decrease in Ca(2+)-independent activity of CaMK II. Our results show that leptin not only affects hypothalamic functions (such as feeding, thermogenesis, and neuroendocrine status), but also modulates higher nervous functions, such as the behavioral performance related to learning and memory and hippocampal synaptic plasticity.

Animals↗