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At least 703 records · Page 39Linked to original sources
PubMed2000

Long-term spatial memory in rats with hippocampal lesions.

In animal models of human amnesia, using lesion methods, it has been difficult to establish the role played by the hippocampus in the formation of long-term spatial knowledge. For example, lesions sustained after acquisition have generally produced a flat retrograde amnesia for spatial information. These results have not made it possible to dissociate the participation of the hippocampus in retrieval/performance processes from its participation in consolidation/retention. The present study was designed to investigate if electrolytic hippocampal lesions made before training lead to a deficit in the long-term retention of spatial knowledge when the rats show equal performance levels during the acquisition. Results show that lesioned rats learn a place response just as well as the control rats when, during the training, an intramaze cue orients the animal in its navigation towards the goal arm. One day after reaching criterion, lesioned and control rats remember the task perfectly during a transfer test in which the intramaze signal used previously is not present. However, 24 days later, the hippocampal animals manifest a profound deficit in the retention of the spatial information. When the spatial task learned during the acquisition phase requires only the use of a guidance strategy, control and lesioned animals show the same level of performance during the training phase and the same degree of retention during the retraining phase 24 days after criterion. Taken together, these results suggest that the hippocampus plays a crucial role in long-term retention of allocentric spatial information.

Amnesia↗
PubMed2006

Muscarinic receptor-mediated GTP-Eu binding in the hippocampus and prefrontal cortex is correlated with spatial memory impairment in aged rats.

The present study examined muscarinic receptor/G-protein coupling in the hippocampus and the prefrontal cortex of young and aged Long-Evans rats characterized for spatial learning ability in the Morris water maze. In a highly sensitive time-resolved fluorometry GTP-Eu binding assay, muscarinic-mediated GTP-Eu binding was severely blunted in hippocampus (-32%) and prefrontal cortex (-34%) as a consequence of aging. Furthermore, the magnitude of decreased muscarinic-mediated GTP-Eu binding was significantly correlated with the severity of spatial learning impairment in hippocampus and prefrontal cortex of aged rats and was specifically decreased in the subset of aged rats that were spatial learning impaired when compared to the aged unimpaired and the young rats. Western blot data indicated a preservation of the membrane-bound M1 receptor and the Galphaq/11 protein in both brain regions. These data demonstrate that muscarinic signaling is severely impaired as a consequence of normal aging in a manner that is closely associated with age-related cognitive decline.

Age Factors↗
PubMed1994

Levemopamil injection after cerebral oligemia reduces spatial memory deficits in rats.

Transient reduction of cerebral blood flow to oligemic levels as produced by bilateral clamping of carotid arteries (BCCA) in pentobarbital anesthetized Wistar rats leads to spatial orientation deficiencies in a water maze test 8-10 days after surgery. These deficiencies are more pronounced in 4-month-old than in 6-week-old animals. Levemopamil [(2S)-2-isopropyl-5-(methylphenethylamino)-2-phenylvaleronitril e hydrochloride], a Ca2+ channel blocker and 5-HT2 antagonist, prevents the deficiencies in groups of animals of both ages, even when administered 24 h after the transient vessel occlusion. Levemopamil did not influence the maze performance of sham-operated control rats. Levemopamil, therefore, appears to modulate mechanisms that are altered specifically either by, or as a consequence of, the BCCA procedure. Levemopamil did not influence the altered GABA or ACh content in different vulnerable brain structures following BCCA, showing that the substance acts via additional mechanisms affected by the BCCA procedure.

Acetylcholine↗
PubMed1999

Blockade of N-methyl-D-aspartate receptors in the insular cortex disrupts taste aversion and spatial memory formation.

The present experiments examined the effects of direct intracortical microinjections of the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid directly into the insular cortex of rats, before or immediately after training of conditioned taste aversion and the water maze spatial learning task. In the first series of experiments animals received bilateral injections of 2-amino-5-phosphonovaleric acid prior to taste aversion conditioning or spatial training. A strong disruptive effect was found in the acquisition of training tasks. To determine the possible involvement of N-methyl-D-aspartate receptors in the early post-training processes taking place in the cortex during both learning paradigms, in a second series of experiments, animals received bilateral 2-amino-5-phosphonovaleric acid microinjections 30, 60 or 120 min after the acquisition trial, and 15 min before the retention test. For spatial learning successive treatments were independently done either starting at the onset of the asymptotic phase of the learning curve, 0, 30 or 120 min after finishing the training session, as well as 15 min before the retention test trial. The conditioned taste aversion task remained sensitive to N-methyl-D-aspartate blockade during a period of at least 2 h after the first presentation of the gustatory stimulus, while in the case of the spatial learning task, a gradually decreasing effect was observed from the onset of the asymptotic phase onwards. Taken together, these results provide direct evidence for N-methyl-D-aspartate receptor involvement in cortical regulation of memory formation. Furthermore, our results suggest that in the same cortical region, a different time-course for the activation of N-methyl-D-aspartate-dependent mechanisms occurs during the early formation of cortically mediated memories, depending on the particular behavioural task.

2-Amino-5-phosphonovalerate↗
PubMed2001

Loss of the thalamic nuclei for "head direction" impairs performance on spatial memory tasks in rats.

This study sought to characterize the effects of removing the nuclei of primary importance in relaying the thalamic head direction signal to the hippocampal formation (the anterior dorsal [AD] and lateral dorsal [LD] nuclei) on the performance of a variety of spatial and nonspatial tasks. The results indicate that combined excitotoxic lesions of the AD and LD nuclei produce marked deficits on a variety of spatial tasks. These tasks included T-maze alternation and the ability to locate a hidden platform set at a fixed distance and fixed direction from a beacon in a Morris water maze. Although object recognition appeared unaffected, marked impairments were found in the ability to detect when an object was placed in a novel position (object-in-place memory).

Animals↗
PubMed1994

Effects of medial septal or unilateral hippocampal inactivations on reference and working spatial memory in rats.

The memory performances of rats receiving a reversible inactivation of either the medial septum or one side of the ventral hippocampus were compared in a radial arm maze task allowing the assessment of both working and reference memory. After pre-surgery training, rats were chronically equipped with bilateral cannulae into the ventral hippocampus and a single cannula into the medial septum. Following post-surgery retraining, animals received a series of test trials during which they received saline or lidocaine injections in either the medial septum or one side of the ventral hippocampus. Lidocaine injections in either structure resulted in both reference and working memory deficits. However, animals were more impaired after septal injections than after unilateral hippocampal injections. This result suggests that the septo-hippocampal formation acts as a functionally homogeneous structure essential for spatial processing.

Animals↗
PubMed2001

Evidence for a relationship between place-cell spatial firing and spatial memory performance.

The rat hippocampus contains place cells whose firing is location-specific. Although many properties of place cells have been uncovered, little is known about their actual contribution to the animal's spatial performance. In this study, we addressed this issue by recording place cells while rats solved a continuous spatial alternation task in which they had to alternate between the two arms of a Y-maze to get a food reward in the third (goal) arm. By manipulating the information available to the animals, we induced the cells to establish their fields in locations that were out of register relative to their standard position, thus making them inconsistent with the learned spatial task. When this happened, the rats' performance in the alternation task was markedly decreased. In addition, the nature of the behavioral errors during inconsistent field placements also changed dramatically in a way that was highly indicative of the rats' spatial disorientation. These results suggest that there is a functional relationship between the spatial firing patterns of place cells and the spatial behavior of the rat, thus strengthening the idea that these cells are part of a navigational system.

Animals↗
PubMed1999

Spatial memory impairment in ventral subicular lesioned rats.

The present study examined the effects of ibotenic acid lesions of the ventral subiculum (SUB) on the ability of rats to memorize a rewarded alternation test in a T-maze. Results indicated that rats with ibotenic acid lesions (IL) of the ventral subiculum were impaired in postoperative acquisition of the spatial discrimination task, making more errors than the vehicle treated and normal control rats. In addition, all rats, including the IL group of rats, were able to memorize an acquired spatial behaviour. These findings suggest that the SUB play an important role in spatial information processing in rats.

Animals↗
PubMed2006

The time course of spatial memory processing in the two hemispheres.

Previous studies have shown that memories for positions are often distorted in systematic ways, indicating the influence of categorical positions codes which can bias responses in object-relocation tasks towards stored spatial prototypes. In the present study, we examined the time course of these categorical influences. Subjects had to relocate the position of a tachistoscopically presented dot within a circle, which could appear in either the left visual field (i.e. initially to the right hemisphere) or the right visual field (i.e. initially to the left hemisphere). Three retention intervals between presentation and relocation were used: 500, 2000 and 5000 ms. Performance was most accurate with left visual field/right hemisphere presentation. Systematic distortions were found for angular errors (dot relocations regressed towards the 45 degrees with a quadrant) as well as for radial errors (dots were replaced in the direction of the circle's circumference, and this more so when the dot was further away from the circumference). Importantly, these categorical biases became stronger with retention interval and initial left hemispheric processing. These results suggest that categorical spatial coding might be the default manner in which spatial information is remembered over time. Finally, the left hemisphere may play an important role for such a categorical spatial coding.

Adult↗
PubMed1992

Effects of nicotine on spatial memory deficits in rats with septal lesions.

Impaired septohippocampal function has been implicated in the memory deficits associated with Alzheimer's disease (AD), and septal lesions have been used to model the cognitive deficits associated with AD. In this study, we assessed the effects of systemic administration of nicotine on lesion-induced deficits in the acquisition of a spatial discrimination version of the Morris water maze. Rats with radiofrequency lesions of the medial septum were required to learn which of two visible platforms in a pool of water provided a means of escape. On each of the first 4 days of training, the rats received an injection of (-)nicotine (0, 0.1 or 0.3 mg/kg, i.p.) before training. Nicotine markedly improved the performance of septal rats. This enhanced performance was maintained in rats subsequently tested 1 and 15 days later without additional drug treatment. Septal rats initially trained under nicotine were impaired, however, when the platform locations were reversed and training was conducted under saline. Our findings suggest that nicotinic receptor stimulation might be useful in the treatment of cognitive deficits.

Alzheimer Disease↗
PubMed1994

Prenatal irradiation and spatial memory in mice: investigation of dose-response relationship.

Pregnant CD1 mice were exposed on gestational day 18 to 250 kV X-rays at 0.1, 0.25, 0.35 and 0.5 Gy. The performances of 10 adult male offspring from each exposure condition were investigated on a spatial discrimination learning task in a radial arm maze. An impairment in the performance of this task was found which showed a correlation with dose. Compared with sham exposed control mice, performance was not significantly affected with irradiation at 0.1 Gy and was slightly but non-significantly reduced at 0.25 Gy. Irradiation at 0.35 Gy caused a significant impairment in performance, and exposure at 0.5 Gy resulted in a still larger impairment. The overall association between dose and behavioural impairment was best described by a linear relationship without a threshold, although at doses lower than about 0.25 Gy any impairment would appear to be too small to be detectable.

Animals↗
PubMed1985

Post-trial flicker stimulation interferes with spatial memory in the Morris water maze.

Rats (n = 20) trained under monocular viewing conditions in the working memory version of Morris water maze task received daily a single acquisition trial with a new location of the invisible escape platform followed after 15 min by a single retrieval trial. Escape latency decreased by 50% during retrieval. Flash stimulation (20 Hz, 0.6 J) during the entire 15-min delay disrupted retention, but this effect was not observed when the flashes started 3 or 5 min after acquisition. It is concluded that successful place learning requires a brief interference-free post-acquisition interval.

Animals↗
PubMed2004

Beta-sheet breaker peptide prevents Abeta-induced spatial memory impairments with partial reduction of amyloid deposits.

Current evidence supports the notion that beta-amyloid deposits or Abeta intermediates may be responsible for the pathogenesis in Alzheimer's disease (AD) patients. In the present work, we have assessed the neuroprotective effect of the chronic intraperitoneal administration of a five-amino-acid beta-sheet breaker peptide (iAbeta5p) on the rat behavioral deficit induced by the intrahippocampal Abeta-fibrils injection. At 1 month after the injection, animals showed a partial reduction of the amyloid deposits formed and a decreased astrocytic response around the injection site. More importantly, we report that following the iAbeta5p treatment, hippocampal-dependent spatial learning paradigms, including the standard Morris water maze and a working memory analysis, showed a significant prevention from impairments induced by Abeta deposits in the dorsal hippocampus. Thus, it is possible that a noninvasive treatment such as the one presented here with beta-sheet breaker peptides may be used as a potential therapy for AD patients.

Alzheimer Disease↗
PubMed1996

Topographic amnesia: spatial memory disorder, perceptual dysfunction, or category specific semantic memory impairment?

A 60 year old patient, SE, who presented with a severe difficulty in finding his way around previously familiar environments and a mild prosopagnosia is described. SE had herpes simplex encephalitis resulting in selective right temporal lobe damage. He showed normal spatial learning, but was severely imparied in his ability to recognise pictures of buildings and landmarks. The disorder was not confined to the visual modality, but rather involved a loss of knowledge about famous buildings and landmarks when tested from their spoken name. SE was contrasted with a more severely prosopagnosic patient, PHD, who showed normal ability to recognise buildings and landmarks, indicating that recognition of people dissociates from recognition of buildings/landmarks. It is concluded that SE's failure of place knowledge represents a category specific supramodal semantic memory impairment.

Agnosia↗
PubMedDate not supplied

Spatial memory and NGF levels in aged rats: natural variability and effects of acetyl-L-carnitine treatment.

The natural variability of behavioral performance of aged rats was used to evaluate the effect of acetyl-L-carnitine (ALCAR) on spatial learning and NGF levels in different brain areas. We used a cluster analysis procedure to subdivide the aged animals into three classes of performance (good, intermediate, and poor). These three classes were equally subdivided into controls and ALCAR-treated animals in order to investigate its effect on spatial retention. The stratification of animals prior to treatment allowed us to highlight the state dependency of the action of ALCAR. The effect of the molecule in improving spatial retention was evident only in the intermediate performance group. Furthermore, the drug reduced the NGF levels in the basal forebrain of treated animals, especially in the intermediate performance group. These results suggest a performance-dependent effect of ALCAR and a nonlinear relationship between NGF levels and learning ability in aged rats.

Acetylcarnitine↗
PubMed2000

Hemispheric differences in hippocampal volume predict verbal and spatial memory performance in patients with Alzheimer's disease.

Atrophy of the hippocampal formation, a region important for the acquisition of new declarative knowledge, has been well-documented in Alzheimer's disease (AD), although the relation of such atrophy to the extent of memory dysfunction in these patients has been less clear. In the present study, 18 patients with a clinical diagnosis of probable AD were studied with a high-resolution, quantitative magnetic resonance imaging (MRI) protocol, as well as the verbal and spatial versions of the Buschke controlled learning task. The volumes of the hippocampal formation and, as a control for generalized atrophy, parahippocampal gyrus and temporal neocortex were computed from gapless coronal slices taken perpendicular to the long axis of the hippocampus. To correct for individual differences in brain size, volumes of regions of interest were divided by total intracranial volume. Separate stepwise regression analyses (with age, right and left hippocampal, parahippocampal gyrus, and temporal lobe volumes as the independent variables) showed that left hippocampal volume was the best predictor of free recall and delayed free recall of verbal information (P = 0.0042 and P < 0.0001, respectively). Recall and delayed recall of the spatial location of verbal items were best predicted by right hippocampal volume (P = 0.0054 and P = 0.0118, respectively). Memory scores did not correlate either with parahippocampal gyrus or temporal lobe volume. Furthermore, the relation between hippocampal volume and memory function observed in cases with AD did not hold for healthy aged control subjects.

Aged↗
PubMed1990

Nerve growth factor levels and choline acetyltransferase activity in the brain of aged rats with spatial memory impairments.

Nerve growth factor (NGF) and choline acetyltransferase (ChAT) activity levels were measured in 7 different brain regions in young (3-month-old) and aged (2-years-old) female Sprague-Dawley rats. Prior to analysis the spatial learning ability of the aged rats was assessed in the Morris' water maze test. In the aged rats a significant, 15-30%, increase in NGF levels was observed in 4 regions (septum, cortex, olfactory bulb and cerebellum), whereas the levels in hippocampus, striatum and the brainstem were similar to those of the young rats. The NGF changes did not correlate with the behavioral performance within the aged group. Minor 15-30%, changes in ChAT activity were observed in striatum, brainstem and cerebellum, but these changes did not correlate with the changes in NGF levels in any region. The results indicate that brain NGF levels are maintained at normal or supranormal levels in rats with severe learning and memory impairments. The results, therefore, do not support the view that the marked atrophy and cell loss in the forebrain cholinergic system that is known to occur in the behaviorally impaired aged rats is caused by a reduced availability of NGF in the cholinergic target areas. The results also indicate that the slightly increased levels of NGF are not sufficient to prevent the age-dependent atrophy of cholinergic neurons, although they might be important for the stimulation of compensatory functional changes in a situation where the system is undergoing progressive degeneration.

Aging↗