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PubMed1988

[Characteristics of the action of psychostimulants on learning and memory in rats].

The effects of intraperitoneal injections of psychostimulant drugs: centrophenoxine (50 mg/kg) and peptide analog of tuftsin TP-1 (300 micrograms/kg) on the processes of elaboration and retention of conditioned reflex have been experimentally studied. The animals were trained with food reward in 30 trials per day. Psychostimulant drugs or saline were injected after the 10th trial. The elaboration of conditioned reflex was continued 30 min later. The retention was tested 24 h, 7 and 30 days later. It was established that both drugs induce an increase in memory traces stability during 30 days. These findings provide direct evidence that psychostimulant drugs, centrophenoxine and peptide substance TP-1, when injected during consolidation phase can enhance memory storage processes.

Animals↗
PubMed1995

Conditional learning and memory impairments following neurotoxic lesion of the CA1 field of the hippocampus.

Monkeys with bilateral lesions of the CA1 field of the hippocampus produced by the injection of neurotoxin diagonally along the length of the hippocampus were found to have a severe impairment on the retention of a conditional task learnt prior to surgery and on the new acquisition of several types of this task. They were equally impaired on conditional tasks that required a spatial response or an object choice in response to either visual or spatial cues. They were not impaired on simple visual discrimination tasks, simple spatial discrimination tasks or reversal learning of these tasks. This patterns of impairment resembles that seen in the same species with neurotoxic lesions within the vertical limb of the diagonal band of Broca or transection of the fornix. Monkeys with subtotal lesions of the adjacent medial temporal area were not consistently impaired on any of these tasks. The results suggest that hippocampal lesions produce anterograde and retrograde amnesia for information other than reward association.

Animals↗
PubMed1997

Neonatal gamma-ray irradiation impairs learning and memory of an olfactory associative task in adult rats.

Adult neonatally gamma-irradiated rats were compared with control animals in a non-spatial olfactory associative task using two different procedures. Irradiation induced a clear reduction in the total mean area of the olfactory bulbs and hippocampus but not of the orbital prefrontal cortex, diagonal band and cell layers of the entorhinal and piriform cortex. The gamma-irradiation affected the granule cells of the olfactory bulbs and differentially altered the cell layers of the subfields of the ammonic fields and the dorsal and ventral blades of the dentate gyrus. In the CA1 ammonic field, dorsal and ventral blades of the dentate gyrus, the cellular loss was significant in comparison with control adult rats. The behavioural data indicated that irradiated rats were deeply disturbed in learning the odour-reward association, and substantially impaired in a reversal experiment, but not in the discrimination of the odours per se. The cellular loss in the olfactory bulbs, in the CA1 and in the ventral blade of the gyrus dentatus was positively correlated with the deficit in behavioural performance. The data support the findings that the hippocampal system participates in the odour-reward associations and facilitates the long-term storage of associations after learning is achieved in this olfactory associative task.

Animals↗
PubMed1993

Dynamics of the olfactory bulb: bifurcations, learning, and memory.

A mathematical model for describing dynamic phenomena in the olfactory bulb is presented. The nature of attractors and the bifurcation sequences in terms of the lateral connection strength in the mitral layer are studied numerically. Chaotic activity has only been found in the case of strong excitatory coupling. Synaptic modification-induced transition from oscillation to chaos is demonstrated. A model for a simple associative memory is also presented.

Animals↗
PubMed1994

Aging of nucleolar organizer region in rat basal forebrain neurons related to learning and memory.

The nucleolar organizer of rat basal forebrain neurons was studied with histochemical and morphometrical techniques, in order to analyze quantitatively the morphological correlate of activity as it changes during learning and aging of the brain. The learning abilities of adult (2 months) and senile (30 months) rats were tested with a conditioned response learning paradigm. Four groups of rats were defined: one group consisted of untrained adults, a second group consisted of trained adults, and the senile rats were subdivided into one group, which was able to learn and another group which was not able to perform the test. Frozen sections through the basal nucleus were silver stained to visualize the nucleolar organizer and the area of its profile was measured. The data showed that the nucleolar organizer in both the trained adult and the senile rats who were able to learn, was much larger than that in the untrained adults and the senile rats who were not able to learn. In the latter groups the nucleolar organizers were of equal size. An additional finding was, that the senile rats who could not be trained, showed a lower neuronal density in the basal nucleus compared with that of the trainable senile and adult rats. The changes in the size of the nucleolar organizer are interpreted as a morphological sign of learning-induced increases in transcription and synthesis of ribosomal RNA.

Aging↗
PubMedDate not supplied

Age-related learning and memory deficits in odor-reward association in rats.

In these experiments, potential cognitive deficits in aged rats were studied using an odor-reward association task. Aged Fischer 344 rats first performed to an odor-reward association task. After five daily sessions of 60 trials, the aged rats were globally impaired in comparison to the control rats. However, considering individual performance, 40% of the aged population performed as well as the control animals. These aged rats were then tested for retention at various times. They demonstrated an increased rate of forgetting which was confirmed by a final reversal experiment. The other group of aged rats remained severely impaired and unable to make the odor-reward association correctly until the inter-trial interval was decreased from 15 to 5 s. When they were submitted to a task requiring the learning and retention of 7 new odor pairs, these aged rats again performed poorly. A subsequent reversal session confirmed the rapid forgetting phenomenon for this aged group, even when the odor-reward associations were in fact made.

Aging↗
PubMedDate not supplied

Acetyl-1-carnitine. 2: Effects on learning and memory performance of aged rats in simple and complex mazes.

Acetyl-1-carnitine (AC) was administered via drinking water for six months to one group (OLD-AC) of male F-344 rats beginning at 16 months of age, while another group (OLD-CON) of rats was given water only during that period. The rats were maintained on this treatment throughout behavioral testing, which began at 22 months of age. Performance of the OLD-AC and OLD-CON rats was compared to that of young control (YG-CON) rats on the following set of tasks: spontaneous alternation in the arms of a T-maze, two-choice simultaneous discrimination in the stem of a T-maze, rewarded alternation in the arms of a T-maze, spatial discrimination and reversal on a circular platform, spatial working memory in the radial 8-arm maze, long-term memory in the 14-unit T-maze, and for preference of the light or dark chamber of a two-compartment box. AC improved the long-term memory performance in the split-stem T-maze and on the circular platform but had no discernable effects on performance of aged rats in the other tasks. Possible reasons for the selectivity of this agent's action on behavior are suggested.

Acetylcarnitine↗
PubMed1996

[Improvement of learning and memory functions by GABAB receptor antagonists in mice].

In one trial passive avoidance response in mice, the effects of gamma-aminobutyric acid (GABA)B receptor agonist baclofen and antagonist CGP35348 and CGP36742 on acquisition, consolidation and retrieval of memory were observed. The results showed that the antagonists could significantly promote the acquisition impairment induced by baclofen, the consolidation impairment induced by baclofen and NaNO2, and the retrieval impairment induced by baclofen and 30% alcohol. These results suggest that the GABAB receptor antagonists may become a novel type of drug for the treatment of Alzheimer's disease.

Animals↗
PubMed1999

The effects of chronic administration of hydrocortisone on cognitive function in normal male volunteers.

RATIONALE: Corticosteroids are elevated in certain neuropsychiatric disorders and this may contribute to the neuropsychological impairments reported in these disorders. OBJECTIVE: To examine the effects of hydrocortisone on learning, memory and executive function. METHODS: Hydrocortisone 20 mg was administered twice daily for 10 days to normal male volunteers in a randomized, placebo control, crossover, within-subject design. Learning, memory and executive function were measured using selected subtests from the Cambridge Neuropsychological Test Automated Battery. RESULTS: Hydrocortisone caused impairments of visuo-spatial memory. These included increased within search errors and impaired use of strategies on the spatial working memory subtest. In addition, administration of hydrocortisone was associated with more errors in the paired associate learning subtest, although no effect was found on the Tower of London. Hydrocortisone speeded response latencies in certain tests (pattern and spatial recognition memory). CONCLUSION: These results indicate that chronic administration of hydrocortisone leads to deficits in certain tests of cognitive function sensitive to frontal lobe dysfunction and may contribute to the cognitive impairment reported in certain neuropsychiatric disorders.

Adult↗
PubMed2000

Long-term consequences of early postnatal seizures on hippocampal learning and plasticity.

Neural activity influences the patterning of synaptic connections and functional organization of developing sensory and motor systems, but the long-term consequences of intense neural activity such as seizures in the developing hippocampus are not adequately understood. To evaluate the possibility that abnormal neural activity during early development may have long-term functional effects in hippocampal circuitry that plays a role in learning, memory and epilepsy, functional properties of hippocampal circuitry were assessed in adult rats that had experienced seizures induced by kainic acid on specific days during early postnatal development. Although previous studies have suggested that the immature hippocampus is relatively resistant to seizure-induced alterations compared with adults, independent behavioural and physiological experiments demonstrated that seizures evoked by kainic acid during early postnatal development induced a long-term loss of hippocampal plasticity manifesting as reduced capacity for long-term potentiation, reduced susceptibility to kindling, and impaired spatial learning, which was associated with enhanced paired-pulse inhibition in the dentate gyrus. The enhancement of inhibition and loss of plasticity were maximal when the seizures occurred on the first day of life, but were also observed when seizures were induced as late as postnatal day 14, which delimited a period of postnatal susceptibility in the developing rat hippocampus when disruption of normal neural activity by seizures produced consistent effects on a hippocampal-dependent behaviour and several forms of hippocampal plasticity implicated in learning, memory and the development of epilepsy in adulthood.

Age Factors↗
PubMed1990

Associative learning and memory for an antinociceptive response in the spinalized rat.

Prior research suggests that associative and memorial processes can modulate the activation of the endogenous antinociceptive systems. It has been generally assumed that forebrain systems play an essential role in mediating the impact of these processes. The present experiments explored whether the behavioral effects indicative of associative and memorial processes can be obtained in spinalized rats. Experiment 1 demonstrated that a conditioned nonopioid antinociception can be established after rats have experienced a spinal transection at the level of the 2nd thoracic vertebrae. Experiment 2 showed that a postshock distractor can speed the decay of shock-induced antinociception in the spinalized rat. These findings suggest that the circuitry needed to obtain associative and memorylike effects is present within the spinal cord.

Animals↗
PubMedDate not supplied

High doses of aspartame have no effects on sensorimotor function or learning and memory in rats.

Acute or repeated (14 days) intragastric administration of L-d-aspartyl-L-phenylalanine methyl ester (aspartame) suspended in saline and Tween-80 in doses of up to 1,000 mg/kg had no significant effect in male Fischer-344 rats on routine measures of sensorimotor function, including spontaneous motor activity, acoustic startle reflex and prepulse inhibition. Other experiments found that aspartame (500 or 1,000 mg/kg) had no significant effect on acquisition of passive or active avoidance or a spatial, reference memory task in the Morris water maze. A series of separate studies found that aspartame had no effects in rats fasted 24 hours prior to testing, or if it was suspended in carboxymethylcellulose or administered by the intraperitoneal route. Under the conditions of these experiments, large doses of aspartame have no significant neurobiological effects in adult rats as measured by procedures known to be sensitive to the neurobiological effects of neurotoxicants, including convulsants, organochlorine insecticides and heavy metals.

Animals↗
PubMed2001

Relationship between three intensity levels of Toxocara canis larvae in the brain and effects on exploration, anxiety, learning and memory in the murine host.

Outbred LACA mice were administered low (100 ova), medium (1000 ova), high (3000 ova) and trickle (4x250 ova) doses of Toxocara canis ova and the effect of infection was examined with respect to the number of larvae recovered from the brain and their behaviour. Recovery of larvae from the brain was generally low with the % recovery expressed in terms of the total dose administered being highest for the 3000 dose (6.1%) and 1000 dose (6%), followed by the 100 (4.4%) and trickle (3.5%) doses. The variation in larval recoveries was large between individual mice receiving similar doses. The level of infection in the brain was lower in mice receiving a multiple as opposed to an equivalent single dose of ova. Mice were then divided into three larval intensity groupings based upon the number of larvae recovered from their brain. The ranges for the groups were as follows: low intensity group, 0-15 larvae; moderate intensity group, 27-55 larvae; high intensity group, 66-557 larvae. Three behavioural tests were carried out on control and infected mice. Exploration and response to novelty was examined using a 'T' maze and learning was investigated by means of a water-finding task. Anxiety was measured using an elevated plus maze apparatus. Infected mice were less explorative and less responsive to novelty in the 'T' maze and this was particularly pronounced for the heavily infected mice. In the elevated plus maze, infected mice displayed reduced levels of anxiety to aversive and exposed areas of the maze, particularly in the case of the moderate and high intensity mice. There was evidence for impaired learning ability in the water task apparatus for moderate and high intensity mice. In general, the effects of infection on behaviour were more pronounced in the moderate and high intensity groups compared to the low intensity group.

Animals↗