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PubMed2003

Dietary fatty acids alter blood pressure, behavior and brain membrane composition of hypertensive rats.

The beneficial effect of dietary n-3 polyunsaturated fatty acids (PUFAs) on developing hypertension has been repeatedly demonstrated. However, related changes in brain membrane composition and its cognitive correlates have remained unclear. Our study aimed at a comprehensive analysis of behavior and cerebral fatty acid concentration in hypertension after long-term PUFA-rich dietary treatment. Hypertensive and normotensive rats were provided a placebo, or one of two PUFA-enriched diets with a reduced (n-6)/(n-3) ratio for 75 weeks. Exploratory behavior and spatial learning capacity were tested. Systolic blood pressure (BP) was repeatedly measured. Finally, brain fatty acid composition was analyzed by gas chromatography. Hypertensive rats exhibited more active exploration but impaired spatial learning compared to normotensives. Both diets reduced BP, increased PUFA and monounsaturated fatty acid (MUFA) concentration, and reduced saturated fatty acid content in brain. The level of cerebral PUFAs and MUFAs was lower in hypertensive than in normotensive rats. Furthermore, BP positively, while spatial learning negatively correlated with cerebral (n-6)/(n-3) PUFA ratio. We concluded that regular n-3 PUFA consumption could prevent the development of hypertension, but reached only a very delicate improvement in spatial learning. Furthermore, we consider a potential role of metabolically generated MUFAs in the beneficial effects of PUFA supplementation.

Animals↗
PubMed2006

Long-term administration of green tea catechins improves spatial cognition learning ability in rats.

Green tea catechins confer potent biological properties including antioxidation and free-radical scavenging. We investigated the effect of long-term oral administration of green tea catechins (Polyphenon E, PE: EGCG 63%; EC 11%; EGC 6%; ECG 6%) mixed with water on the spatial cognition learning ability of young rats. The learning ability of rats administered PE (0%, 0.1%, 0.5%) for 26 wk was assessed in the partially baited 8-arm radial maze. Relative to controls, those administered PE had improved reference and working memory-related learning ability. They also had lower plasma concentrations of lipid peroxides and greater plasma ferric-reducing antioxidation power than controls. Furthermore, rats administered PE had lower hippocampus reactive oxygen species concentrations than controls. We suggest that this improvement in spatial cognitive learning ability is due to the antioxidative activity of green tea catechins.

Animals↗
PubMed2006

Trimethyltin-induced alterations in behavior are linked to changes in PSA-NCAM expression.

The neurotoxic heavy metal trimethyltin (TMT) primarily damages neurons of the hippocampus and limbic areas of the temporal lobe, and causes a dose-dependent decrease in the polysialated form of the neural cell adhesion molecule (PSA-NCAM) in the mouse hippocampus. In the current study, we attempted to associate deficits in spatial learning following TMT exposure at various stages in learning with changes in levels of NCAM-180 and PSA-NCAM in both the hippocampus and frontal cortex. Mice were treated with TMT either before or after training on a spatial learning paradigm and examined for changes in NCAM and PSA-NCAM 12h later. In the first set of experiments, male BALB/c mice were injected with TMT (2.25 mg/kg) or saline i.p. and tested 24-168 h later using hidden and visible versions of the water maze, as well as light avoidance and motor activity. Mice in both treated and control groups which demonstrated a significant improvement in water maze performance also showed an elevation in hippocampal PSA-NCAM at all time points examined. TMT exposure impaired spatial learning and blocked learning-induced elevations in PSA-NCAM expression 24-96 h post-treatment, but these deficits disappeared by 168 h post-treatment. Mice exposed to TMT during reconsolidation of spatial learning (after repeated water maze training) demonstrated a mild and transient difference in escape latency compared to saline exposed mice. TMT administration during this period did not result in the attenuation of PSA-NCAM expression observed when animals were exposed before training. These results confirm a specific role for PSA-NCAM in acquisition and consolidation of spatial memory.

Animals↗
PubMed2000

Use of a delayed non-matching to position task to model age-dependent cognitive decline in the dog.

Spatial learning and memory in young and old dogs was studied in a series of experiments using a delayed non-matching to position (DNMP) paradigm. Past research from our laboratory has suggested that aged dogs perform more poorly on a version of the DNMP task compared to young dogs [Head et al., Spatial learning and memory as a function of age in the dog, Behav. Neurosci. 1995;109(5):851-585]. We have now extended these findings by testing a large number of dogs on three different variations of the DNMP paradigm to evaluate different aspects of spatial learning and memory. Our results indicate that: (1) aged dogs show impaired spatial learning compared to young dogs, (2) aged dogs display spatial working memory deficits compared to young dogs, (3) young dogs have a greater maximum working spatial memory capacity than old dogs and (4) we can use the DNMP paradigm to cognitively categorize different subsets of aged dogs. These data indicate that the DNMP paradigm can serve as a valuable tool to evaluate age-dependent cognitive dysfunction in the canine.

Age Factors↗
PubMed2000

Mice are not little rats: species differences in a one-day water maze task.

The present study examined species differences in spatial and non-spatial memory in the Morris water maze. Male Wistar rats and C57BL/6 mice were tested in a one-day water maze task in which spatial learning, retention, and non-spatial learning were assessed within 3 h. Rats and mice appeared to use different strategies for locating the hidden escape platform. Whereas rats evinced a clear spatial strategy, mice appeared to rely less on spatial cues and more on alternative non-spatial strategies. The sensitivity of this behavioral protocol to subtle species differences highlights the potential use of this one-day water maze task as a tool for evaluating rapidly learning and memory in rodents.

Animals↗
PubMed1995

Posttreatment with EPC-K1, an inhibitor of lipid peroxidation and of phospholipase A2 activity, reduces functional deficits after global ischemia in rats.

In this study the effect of an inhibitor of lipid peroxidation and of phospholipase A2 activity, EPC-K1, on spatial learning deficit and neuronal damage following transient cerebral ischemia was evaluated. Global ischemia was induced by four-vessel occlusion (4VO) for 20 min in rats. EPC-K1 (10 mg/kg IP) was administered either a) 15 min before induction of ischemia, b) immediately after, or c) 30 min after onset of reperfusion. One week after surgery spatial learning was tested in the Morris water maze. EPC-K1 reduced the deficit in spatial learning when given immediately or 30 min after the onset of reperfusion but not when applied 15 min before ischemia. Neuronal damage in the CA1 sector of the hippocampus produced by 4VO was slightly, but not significantly attenuated by posttreatment. The present data demonstrate that posttreatment with EPC-K1 exerts a protective effect on deficits in spatial learning induced by 4VO. These results support the hypothesis that lipid peroxidation and activation of phospholipase A2 contribute to functional alterations of the brain during reperfusion following forebrain ischemia.

Animals↗
PubMed2006

Mnemonic functions of the hippocampus: a comparison between animals and humans.

This review summarizes a series of experiments aimed at answering the question whether the hippocampus in rats and humans performs parallel functions focusing on studies that assess spatial and temporal pattern separation, sequential learning, spatial and temporal pattern association, spatial and temporal pattern completion, and short-term and intermediate-term memory. It is recognized that a comparison of the functions of the rat hippocampus with human hippocampus is difficult, because of differences in methodology, differences in complexity of life experiences, and differences in the degree of hippocampal damage as well as damage to interconnected brain regions. Yet, in general the data support the idea that with respect to spatial and temporal pattern separation, sequential learning, spatial and temporal pattern associations, spatial and temporal pattern completion, and short-term and intermediate-term memory, similar functions are observed in rats and humans with hippocampal damage using analogous tasks. These data provide support for evolutionary continuity in cognitive function assigned to the hippocampus of rats and humans.

Animals↗
PubMed2006

Oculomotor and manual indexes of incidental and intentional spatial sequence learning during middle childhood and adolescence.

The goal of this study was to examine incidental and intentional spatial sequence learning during middle childhood and adolescence. We tested four age groups (8-10 years, 11-13 years, 14-17 years, and young adults [18+ years]) on a serial reaction time task and used manual and oculomotor measures to examine incidental sequence learning. Participants were also administered a trial block in which they were explicitly instructed to learn a sequence. Replicating our previous study with adults, oculomotor anticipations and response times showed learning effects similar to those in the manual modality. There were few age-related differences in the sequence learning indexes during incidental learning, but intentional learning yielded differences on all indexes. Results indicate that the search for regularities and the ability to learn a sequence rapidly under incidental conditions are mature by 8 to 10 years of age. In contrast, the ability to learn a sequence intentionally, which requires cognitive resources and strategies, continues to develop through adolescence.

Adolescent↗
PubMed2001

Applications of the Morris water maze in the study of learning and memory.

The Morris water maze (MWM) was described 20 years ago as a device to investigate spatial learning and memory in laboratory rats. In the meanwhile, it has become one of the most frequently used laboratory tools in behavioral neuroscience. Many methodological variations of the MWM task have been and are being used by research groups in many different applications. However, researchers have become increasingly aware that MWM performance is influenced by factors such as apparatus or training procedure as well as by the characteristics of the experimental animals (sex, species/strain, age, nutritional state, exposure to stress or infection). Lesions in distinct brain regions like hippocampus, striatum, basal forebrain, cerebellum and cerebral cortex were shown to impair MWM performance, but disconnecting rather than destroying brain regions relevant for spatial learning may impair MWM performance as well. Spatial learning in general and MWM performance in particular appear to depend upon the coordinated action of different brain regions and neurotransmitter systems constituting a functionally integrated neural network. Finally, the MWM task has often been used in the validation of rodent models for neurocognitive disorders and the evaluation of possible neurocognitive treatments. Through its many applications, MWM testing gained a position at the very core of contemporary neuroscience research.

Animals↗
PubMed2000

A revised spatial serial learning and memory procedure using Corsi's Block-tapping apparatus.

The purpose of this study was to use Corsi's Block Tapping Test as a spatial analog of Benton's Serial Digit Learning Test, using the cognitive neuroscience approach utilized in the California Verbal Learning Test. 60 normal participants, ages 19-52 years, were included and administered an 8-block sequence for 9 trials or until they recalled the entire sequence for 3 consecutive errorless trials. The score was the number of blocks tapped in the correct serial order. An interference trial was administered. Following a 10-min. delay, free recall of the original sequence, cued recall, and recognition measures were obtained. Retroactive interference was significant, but no proactive interference emerged. Scores showed a strong primacy effect. Most participants who learned the sequence to the criterion of three successive errorless trials recalled the sequence after the 10-min. delay. Scores on the cued recall and recognition trials tended to support their validity as less demanding retrieval tasks. The use of this spatial learning and memory procedure allows finer discriminations among nonverbal memory deficits and may facilitate direct comparisons with scores on verbal memory tasks such as Serial Digit Learning and the California Verbal Learning Test.

Adult↗
PubMedDate not supplied

Serotonin, aging and cognitive functions of the hippocampus.

The cholinergic hypothesis of senile dementia /18/ does not provide a sufficient explanation for age-dependent spatial learning deficits; these are observed before an appreciable reduction of cholinergic markers can be detected. Behavioral deficits similar to those observed in old rats cannot be induced in young rats by comparable cholinergic lesions but do occur following combined cholinergic/serotonergic lesions. Serotonergic raphe grafts in the hippocampus (but not in the entorhinal cortex or hypothalamus) prevent such combined lesion-induced spatial learning deficits. The behavioral deficits are associated with a reduction of hippocampal commissure feed-forward inhibition. Similar reduced inhibition is found in old rats, deficient in their performance of a spatial learning water-maze task. Finally, treating old rats with the serotonergic precursor 5-hydroxytryptophan (5-HTP) reduces the age-dependent spatial learning deficits and restores hippocampal commissure feed-forward inhibition. Serotonin may act in parallel to the cholinergic innervation of the hippocampus by affecting inhibitory interneurons but in addition it may act by modulating acetylcholine release. Acetylcholine release is modulated by serotonin and the enhancing effects of serotonin releasing drugs on dentate granule cell excitability are mediated by acetylcholine. We thus propose that a reduction of serotonergic modulation of hippocampal interneuron activity and impaired modulation of cholinergic effects in the hippocampus contribute to age-dependent cognitive deficits.

Aging↗
PubMed2002

Attenuation of working memory and spatial acquisition deficits after a delayed and chronic bromocriptine treatment regimen in rats subjected to traumatic brain injury by controlled cortical impact.

Cognitive impairments are pervasive and persistent sequelae of human traumatic brain injury (TBI). In vivo models of TBI, such as the controlled cortical impact (CCI) and fluid percussion (FP), are utilized extensively to produce deficits reminiscent of those seen clinically with the hope that empirical study will lead to viable therapeutic interventions. Both CCI and FP produce spatial learning acquisition deficits, but only the latter has been reported to impair working memory in rats tested in the Morris water maze (MWM). We hypothesized that a CCI injury would impair working memory similarly to that produced by FP, and that delayed and chronic treatment with the D2 receptor agonist bromocriptine would attenuate both working memory and spatial learning acquisition deficits. To test these hypotheses, isoflurane-anesthetized adult male rats received either a CCI (2.7 mm deformation, 4 m/sec) or sham injury, and 24 h later were administered bromocriptine (5 mg/kg, i.p.) or vehicle, with continued daily injections until all behavioral assessments were completed. Motor function was assessed on beam balance and beam walking tasks on postoperative days 1-5 and cognitive function was evaluated in the MWM on days 11-15 for working memory (experiment 1) and on days 14-18 for spatial learning acquisition (experiment 2). Histological examination (hippocampal CA1 and CA3 cell loss/survival and cortical lesion volume) was conducted 4 weeks after surgery. All injured groups exhibited initial impairments in motor function, working memory, and spatial learning acquisition. Bromocriptine did not affect motor function, but did ameliorate working memory and significantly attenuated spatial acquisition deficits relative to the injured vehicle-treated controls. Additionally, the injured bromocriptine-treated group exhibited significantly more morphologically intact CA3 neurons than the injured vehicle-treated group (55.60 +/- 3.10% vs. 38.34 +/- 7.78% [p = 0.03]). No significant differences were observed among TBI groups in CA1 cell survival (bromocriptine, 40.26 +/- 4.74% vs. vehicle, 29.13 +/- 6.63% [p = 0.14]) or cortical lesion volume (bromocriptine, 17.78 +/- 0.62 mm3 vs. vehicle, 19.01 +/- 1.49 mm3 [p > 0.05]). These data reveal that CCI produces working memory deficits in rats that are similar to those observed following FP, and that the delayed and chronic bromocriptine treatment regimen conferred cognitive and neural protection after TBI.

Animals↗
PubMed1998

Is the hippocampus a Kalman filter?

Based on a large body of neurophysiological, neuroanatomical, and behavioral data, it has been suggested that the hippocampal formation serves as a spatial learning and localization system. This spatial representation is metric in nature and arises as a result of associations between sensory inputs and dead-reckoning information generated by the animal. However, despite the fact that these two information streams provide uncertain information (e.g., recognition errors, dead-reckoning drifts, etc.), the hippocampal computational models suggested to date have not explicitly addressed information fusion from erroneous sources. In this paper we develop a computational model of hippocampal spatial learning and relate its functioning to a probabilistic tool used for uncertain sensory fusion in robots: the Kalman filter. This parallel allows us to derive statistically optimal update expressions for the localization performed by our computational model.

Animals↗
PubMed2005

Reappearance of hippocampal CA1 neurons after ischemia is associated with recovery of learning and memory.

The pyramidal neurons of the hippocampal CA1 region are essential for cognitive functions such as spatial learning and memory, and are selectively destroyed after cerebral ischemia. To analyze whether degenerated CA1 neurons are replaced by new neurons and whether such regeneration is associated with amelioration in learning and memory deficits, we have used a rat global ischemia model that provides an almost complete disappearance (to approximately 3% of control) of CA1 neurons associated with a robust impairment in spatial learning and memory at two weeks after ischemia. We found that transient cerebral ischemia can evoke a massive formation of new neurons in the CA1 region, reaching approximately 40% of the original number of neurons at 90 days after ischemia (DAI). Co-localization of the mature neuronal marker neuronal nuclei with 5-bromo-2'-deoxyuridine in CA1 confirmed that neurogenesis indeed had occurred after the ischemic insult. Furthermore, we found increased numbers of cells expressing the immature neuron marker polysialic acid neuronal cell adhesion molecule in the adjacent lateral periventricular region, suggesting that the newly formed neurons derive from this region. The reappearance of CA1 neurons was associated with a recovery of ischemia-induced impairments in spatial learning and memory at 90 DAI, suggesting that the newly formed CA1 neurons restore hippocampal CA1 function. In conclusion, these results show that the brain has an endogenous capacity to form new nerve cells after injury, which correlates with a restoration of cognitive functions of the brain.

Animals↗
PubMed1992

Navigation by fragment fitting: a theory of hippocampal function.

This paper describes a computational theory of spatial learning and navigation and its possible realization in the hippocampus. In the theory, mammals store memories of their geographical environment as a large number of independent fragments. A typical fragment denotes a few prominent landmarks in some region, their geometric relations, and their nongeometric properties, such as smells and visual cues. Navigation involves piecing together current sense data and relevant fragments to form a local map of the animal's surroundings; this is like solving a jigsaw puzzle. This computational model has been implemented in a computer program, whose performance is broadly consistent with observed levels of animal performance, and laboratory results, in spatial learning. Possible realizations of the model in animal brains are discussed. Unlike some neural net models of spatial learning, the model is strongly geometric, and uses special neural structures to store and manipulate two-dimensional vectors and bearings. A possible neural architecture is described in which the hippocampus performs the geometric operations; this has a long-term memory for fragments (somewhere in the neocortex), which can associatively recall fragments into a number of parallel fragment fitters, in the dentate gyrus and CA3 regions. These vary the positions and orientations of their fragments, to optimize the fit of the fragments to each other and to the animal's recent sense data. A local map of the animal's surroundings is stored in CA1 and subicular regions, where matching of fragment positions and attributes takes place. Mismatches are passed back via the entorhinal cortex to improve the fit during the next hippocampal theta cycle. The model offers the potential for understanding current data on spatial learning, on the neuroanatomy of the hippocampus and on place cells in a coherent framework, as well as understanding the role of the hippocampus in nonpositional memory tasks. Comparisons with experimental data are given.

Animals↗
PubMed1999

An age-related decline in striatal taurine is correlated with a loss of dopaminergic markers.

Taurine is present in high concentration in the mammalian brain and is known to decline with aging. The present studies examined the relationship between the loss of striatal neurotransmitters and spatial learning ability in aged male Long-Evans rats. The effects of intrahippocampal infusions of neurotrophic factors-nerve growth factor (NGF) and brain-derived neurotrophic factor-were also examined for their ability to ameliorate the age-related decline in brain amino acid content. Taurine content was found to be significantly reduced in the striatum of aged rats (26 months old) that were impaired in spatial learning performance when compared to young unimpaired rats (5 months old). Aged rats that were behaviorally unimpaired had more modest reductions in taurine. Striatal dopamine content was also significantly reduced in aged learning-impaired rats. There was a significant (p < 0.001) correlation (r=0.61) between the striatal content of taurine and dopamine, but no such correlation was found for other striatal transmitters (glutamate, serotonin, norepinephrine). Treatment with neurotrophins had little effect on the age-related decline in striatal amino acids, although NGF treatment did improve spatial learning. These studies suggest (1) a link between age-related declines in striatal dopamine and taurine and (2) that NGF-induced improvement in spatial learning is not related to mechanisms involving changes in taurine or glutamate content.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2003

Combined uridine and choline administration improves cognitive deficits in spontaneously hypertensive rats.

Rationale. Hypertension is considered a risk factor for the development of cognitive disorders, because of its negative effects on cerebral vasculature and blood flow. Genetically induced hypertension in rats has been associated with a range of cognitive impairments. Therefore, spontaneously hypertensive rats (SHR) can potentially be used as a model for cognitive deficits in human subjects. Consecutively, it can be determined whether certain food components can improve cognition in these rats. Objective. The present study aimed to determine whether SHR display specific deficits in attention, learning, and memory function. Additionally, effects of chronic uridine and choline administration were studied. Methods. 5-7 months old SHR were compared with normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats. (a) The operant delayed non-matching-to-position (DNMTP) test was used to study short-term memory function. (b) The five-choice serial reaction time (5-CSRT) task was used to assess selective visual attention processes. (c) Finally, the Morris water maze (MWM) acquisition was used as a measure for spatial learning and mnemonic capabilities. Results. (1) SHR exhibited significantly impaired performance in the 5-CSRT test in comparison with the two other rat strains. Both the SHR and WKY showed deficits in spatial learning when compared with the SD rats. (2) Uridine and choline supplementation normalized performance of SHR in the 5-CSRT test. (3) In addition, uridine and choline treatment improved MWM acquisition in both WKY and SHR rats. Conclusion. The present results show that the SHR have a deficiency in visual selective attention and spatial learning. Therefore, the SHR may provide an interesting model in the screening of substances with therapeutic potential for treatment of cognitive disorders. A combination of uridine and choline administration improved selective attention and spatial learning in SHR.

Animals↗
PubMed1995

Paradoxical enhancement of long-term potentiation in poor-learning rats at low test stimulus intensities.

Much empirical evidence and numerous theoretical models point to modification of synaptic efficacy as a mechanism for memory formation. To evaluate theoretical models, it is necessary to obtain quantitative experimental data relating learning to experimentally induced synaptic efficacy changes (such as long-term potentiation, LTP). An important problem in this type of experiment is how to quantify the LTP induced by a given stimulation protocol. Of relevance is the informally well-known observation that LTP magnitude appears to vary as a function of the intensity of the stimulus used to evoke baseline responses. The present study found that using a measure of LTP that circumvents this variation, a strong negative correlation of learning with potentiation emerges. Spatial learning ability was compared with the magnitude of subsequent LTP induction as follows: rats underwent a day of spatial training in a watermaze followed by 5 days of bilateral perforant path tetanisation. Baseline electrophysiological responses were evoked over a range of stimulus intensities (input/output [IO] curves) before and after tetanisation. Although LTP was observed across the whole of the IO curve, it showed a smooth decline with increasing current. The animals were then grouped according to their watermaze performance and IO curves compared between good and poor learners. After tetanisation, there was a negative within-animal correlation between learning and evoked potential size with weak test stimuli and a positive correlation with strong stimuli. The decline of LTP across the IO curve differed between good and poor spatial learners; the poor learners showed higher percentage potentiation with test stimuli close to zero intensity, but a faster decrease in LTP across the curves. The findings are therefore: (1) the measured amount of LTP declined systematically with increasing stimulus strength, and (2) the parameters of the decline correlated with spatial learning ability. These results raise two important issues. First, because measured LTP varied systematically across the IO curve, it appears that for quantitative analyses the widely used method of LTP measurement using a single test stimulus intensity risks missing significant features of the data. It is suggested that a measure be used that incorporates data from a range of stimulus intensities. Second, when such a measure is used there is a striking negative correlation of spatial learning ability with LTP. These apparently paradoxical results are discussed.

Animals↗