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PubMed1992

Spatial memory in aged rats: population heterogeneity and effect of levocarnitine acetyl.

The existence in a population of aging rats of classes that display a different performance in the Morris water-maze test was investigated by cluster analysis procedure. These classes identified at 18 months of age showed a different response to levocarnitine acetyl and had a different behavioral profile when tested at 25 months of age. These findings demonstrate the need for an alternative interpretation of variability in animal populations as measured by the standard statistical analyses. The data analysis strategy we propose here will allow for the use of variability as a useful source of information.

Acetylcarnitine↗
PubMed1997

Symmetry and asymmetry of human spatial memory.

Six experiments investigated the limiting conditions on and the causes of asymmetries in estimates of euclidean distance. Participants estimated distances between locations on recently learned maps or between buildings on their college campus. Estimates between landmarks and neighboring nonlandmarks were often asymmetric, but estimates between other pairs of locations were typically symmetric. These and other results were inconsistent with the predictions of models that attribute asymmetries to stimulus or to retrieval bias. A contextual scaling model of asymmetry is proposed. According to this model, asymmetries in proximity judgments are caused by general principles of human memory and judgment: (a) Stimuli differ in the contexts they establish in working memory and (b) magnitude estimates are scaled by the context in which they are made.

Attention↗
PubMed1996

Bacterial alkaloids mitigate seizure-induced hippocampal damage and spatial memory deficits.

Studies of human patients with temporal lobe epilepsy and animal models of epilepsy have established relationships between seizures, excitotoxic hippocampal damage, and memory impairment. We report that bacterial alkaloids, recently shown to mimic actions of neurotrophic factors in cell culture, attenuate seizure-induced damage to hippocampal neurons and memory impairment in adult rats when administered subcutaneously. Intrahippocampal administration of convulsant doses of kainic acid (KA) to adult rats resulted in degeneration of neurons in CA3, CA1, and hilus. Rats administered KA exhibited (24 h later) deficits in performance on both goal latency and probe trial tasks in Morris water maze (MWM) tests of visuospatial memory. Seizure-induced damage to hippocampal neurons was significantly reduced, to varying extents, in rats administered the bacterial alkaloids K252a, K252b, or staurosporine (daily injections of 4 micrograms/kg body weight) prior to KA administration. The KA-induced deficits in MWM goal latency performance were abrogated in rats administered K252a or K252b, and K252a and staurosporine completely prevented seizure-induced impairment on the MWM probe trial. The alkaloids did not suppress electroencephalographic seizure activity, suggesting a dissociation between synchronization of activity and synaptically mediated excitotoxic injury to hippocampal neurons. Each alkaloid caused an increase in levels of protein tyrosine phosphorylation as determined by Western blot analysis of hippocampal tissue. Our data indicate that these bacterial alkaloids have potent antiexcitotoxic activities which may have clinical utility in epilepsy and other disorders that involve excitotoxic damage.

Alkaloids↗
PubMed1986

Landmark learning and visuo-spatial memories in gerbils.

The aim of this study is to understand what a rodent (Meriones unguiculatus) learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal. Gerbils were trained to find sunflower seeds on the floor of a light-tight, black painted room illuminated by a single light bulb hung from the ceiling. The position of the seed on the floor was specified by an array of one or more landmarks. Once training was complete, we recorded where the gerbils searched when landmarks were present but the seed was absent. In such tests, gerbils were confronted either with the array of landmarks to which they were accustomed or with a transformation of this array. Animals searched in the appropriate spot when trained to find seeds placed in a constant direction and at a constant distance from a single cylindrical landmark. Since gerbils look in one spot and not in a circle centred on the landmark, the direction between landmark and goal must be supplied by cues external to the landmark array. Distance, on the other hand, must be measured with respect to the landmark. Tests in which the size of the landmark was altered from that used in training suggest that distance is not learned solely in terms of the apparent size of the landmark as seen from the goal. Gerbils can still reach a goal defined by an array of landmarks when the room light is extinguished during their approach. This ability implies that they have already planned a trajectory to the goal before the room is darkened. In order to compute such a trajectory, their internal representation of landmarks and goal needs to contain information about the distances and bearings between landmarks and goal. For planning trajectories, each landmark of an array can be used separately from the others. Gerbils trained to a goal specified by an array of several landmarks were tested with one or more of the landmarks removed or with the array expanded. They then searched as though they had computed an independent trajectory for each landmark. For instance, gerbils trained with an array of two landmarks were tested with the distance between two landmarks doubled. The animals then searched for seeds in two positions, which were at the correct distance and in the right direction from each landmark.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Early post-natal administration of 5,7-dihydroxytryptamine destroys 5-HT neurons but does not affect spatial memory.

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) may play an important role in learning and memory. It has also been suggested that 5-HT abnormalities may mediate some aspects of the cognitive disorders associated with Korsakoff syndrome and Alzheimer's Disease. The effect of intracisternally applied 5-HT neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) on learning and memory in rodents was evaluated. Three-day-old rat pups were treated with pargyline (40 mg/kg, i.p.) followed by 5,7-DHT (50 micrograms/pup) and returned to the dam for a month. At 75 days of age, rats were tested on a learning set problem in the Morris water maze for 5 days followed by 30 days of testing in a 12-arm radial maze with 8 of the 12 arms baited. In the Morris water maze, the latency to locate the hidden platform did not differ significantly for 5,7-DHT treated and control rats (F less than 1.0). Similarly, 5,7-DHT treated rats performed comparably to controls on the 12-arm radial maze (F less than 1.0). At 106 days of age the assay of tryptophan hydroxylase activity in the dorsal raphe nuclei and hippocampus showed marked reduction (86%, 78%, respectively) in 5,7-DHT treated animals compared to vehicle injected controls. Immunocytochemical analysis was consistent with the biochemical results. In 5,7-DHT treated animals there was severe loss of neurons that bind 5-HT antibody in the dorsal and medial raphe nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

5,7-Dihydroxytryptamine↗
PubMed1984

Differential effects of frontal-lobe lesions on cognitive estimation and spatial memory.

Patients with unilateral frontal- or temporal-lobe excisions and normal control subjects were tested on the recall of objects and of their location in an array. An incidental-learning situation was used, in which the task was presented as a test of the ability to estimate the prices of the objects. Patients with right frontal-lobe lesions were the only group impaired on price estimation, but a correlation was obtained between error-score in price estimation and lesion-size for the left frontal-lobe group. In contrast to patients with extensive right hippocampal excisions, both frontal-lobe groups were accurate on location-recall when tested immediately and again 24 hr later.

Adolescent↗
PubMed1991

Spatial memory processing during hippocampal long-term potentiation in rats.

It was investigated in rats whether hippocampal long-term potentiation (LTP) influences working and/or reference memory processing in the radial maze. After preliminary training to an intermediate level of performance, experimental subjects received a series of high-frequency trains of electrical pulses applied to the right perforant path. Two control groups were adopted in order to control for possible effects of stimulation plus operation, and operation alone, respectively. Twenty-four hours after the experimental treatment, animals were administered one trial of radial maze training. This sequence of hippocampal stimulation and radial maze training was replicated 15 times. After a retention interval of 2 months, one radial maze trial was presented on each of 3 consecutive days. The analysis of field potential data showed that periodic LTP stimulation produced a state of hippocampal LTP confined to the initial portion of the acquisition phase. Evaluation of radial maze data revealed a marginal improvement of working memory performance in the experimental group during the rising phase of hippocampal LTP.

Animals↗
PubMed1994

A role for acetylcholine in spatial memory in turtles.

The present research was undertaken to determine whether acetylcholine plays a role in memory for a maze in turtles. Cholinergic cells have been observed in the basal forebrain of turtles, and the basal forebrain of turtles projects to the dorsal cortex, a region that has been implicated in associative function. In Experiment 1, turtles were trained on an X-maze for water reward and then given lesions of the dorsal cortex or basal forebrain or sham lesions and retested postoperatively on the maze. Both dorsal cortex and basal forebrain lesions impaired performance on the maze. In Experiment 2, turtles were trained on the maze and then given saline, scopolamine, or methylscopolamine on a 1-day retention test. Scopolamine in the higher doses impaired maze performance on the test day, but methylscopolamine did not. The highest dose of scopolamine had no effect on measures of general activity, showing that the effects of the drug were specific to the learned task.

Acetylcholine↗
PubMed1993

Effects of NBM lesions with two neurotoxins on spatial memory and autoshaping.

Four groups of Wistar rats received either vehicle, quisqualate, or one of two different ibotenic acid infusions into the basal forebrain. Following recovery from surgery, all rats were tested in three distinct behavioral paradigms: the Bättig radial arm maze, the Barnes circular platform, and autoshaping in an operant chamber. The results showed that the size and site of the ibotenic acid lesion had a profound effect on acquisition performance in some, but not all, procedures. Performance in the Bättig maze and acquisition of a food-rewarded lever press were in particular disrupted by ibotenic acid lesions. The severity of the reduction in cortical choline acetyltransferase (ChAT) did not correlate with performance in the tests. Quisqualate produced the largest reduction in ChAT levels but had no significant effect on performance in any of the three procedures used. Anatomic analysis revealed severe nonspecific damage to the striatum following ibotenic acid that was more pronounced in the group receiving a highly concentrated solution of ibotenic acid as compared to rats infused with a greater volume but less concentrated solution of the neurotoxin. Striatal damage was much less severe following quisqualic acid infusions. However, both types of neurotoxins produced equivalent nonspecific degeneration of the reticular thalamic nucleus. These data confirm reports that nonspecific damage appears to define the severity of ibotenic acid lesions on subsequent behavioral performance.

Animals↗