Functional cooperation between the hippocampal subregions and the medial septum in unreinforced and reinforced spatial memory tasks.

Anatomical connections between the medial septum (MS) and hippocampus (Hipp) via the fimbria-fornix suggest that functional cooperation between these structures may be important for the acquisition and use of spatial reference memories. The present study examined the extent to which this was true for both an unreinforced learning task (object exploration task) and a reinforced learning task (Morris water maze task). In Experiment 1, we compared the performance of MS/Hipp contralateral- and MS/Hipp ipsilateral-lesioned rats.

Pretraining does not ameliorate spatial learning deficits induced by intrahippocampal infusion of AP5.

Previous studies show discrepancies concerning the effects of pretraining on spatial learning deficits induced by blockade of the N-methyl-D-aspartate (NMDA) receptor. These inconsistencies might be attributed to the differences in the nature of the pretraining tasks and the method of blocking NMDA receptors. In the present study, the authors pretrained rats in a spatial water maze task.

Functional differentiation and cooperation among the hippocampal subregions in rats to effect spatial memory processes.

We investigated the roles of the hippocampal subregions and intrahippocampal networks in effecting spatial reference and working processes. The results showed that the dentate gyrus plays a key role in encoding both types of spatial memory. Lesions in the dentate gyrus caused severe impairment in the acquisition of the Morris water maze and delayed matching-to-place tasks as compared to those in the other hippocampal subregions (Exp.

Hippocampal acetylcholine efflux increases during negative patterning and elemental discrimination in rats.

The purpose of this paper is to examine whether hippocampal acetylcholine (ACh) efflux increases during negative patterning (NP) discrimination tasks. For these tasks, a rat's response was rewarded when either a single stimulus A (tone) or stimulus B (light) was presented, but was not rewarded when the compound stimulus AB (tone+light) was presented to the NP group of rats. An elemental discrimination (E) task was given to another group (E group).

[The functional cooperation of the hippocampus and anterior thalamus via the fimbria-fornix in spatial memory in rats].

This study examined whether the cooperation of the hippocampus, and anterior thalamus via the fimbria-fornix is involved in the spatial memory. We compared the effect of contralateral lesions (Contra) with ipsilateral lesions (Ipsi) of the fimbria-fornix and anterior thalamus on the performance of an object exploration task and the Morris water maze task. If the hippocampus and anterior thalamus take part in a same functional system via fornix, the performance of Contra group will be more disruptive than that of Ipsi group.

Dissociation of the roles of NMDA receptor and hippocampus in rats' spatial learning: the effects of environmental familiarity and task familiarity.

In this study, we compared the effects of MK-801 and hippocampal lesions on re-training of Morris water maze place task in familiar and novel environments in rats. In Experiment 1, rats were pre-trained with the place task. After acquiring the task, rats were re-trained with the same task in a familiar environment following MK-801 injection, and were then trained with the same task in a novel environment following MK-801 injection.

Effects of post-training lesions in the hippocampus and the parietal cortex on idiothetic information processing in the rat.

Dead reckoning can be defined as the ability to navigate using idiothetic information based on self-movement cues without using allothetic information such as environmental cues. In the present study, we investigated the effects of hippocampal and parietal cortex lesions on homing behavior using dead reckoning in rats. Experimentally naive Wistar rats were trained with a homing task in which rats were required to take a food pellet from a cup in the arena and to return home with the pellet.

Open-field behaviors and water-maze learning in the F substrain of Ihara epileptic rats.

Purpose: Genetically epileptic model rats, Ihara epileptic rat (IER/F substrain), have neuropathologic abnormalities and develop generalized convulsive seizures when they reach the age of approximately 5 months. Because the neuromorphologic abnormalities are centered in the hippocampus, we expected to observe spatial cognitive deficits. The present study aimed to evaluate emotionality and learning ability of the F substrain of IER.

[Effects of ibotenic acid lesions to rat's hippocampus CA1 on place and cue learning in Morris water maze].

It is known that the multiple injections of ibotenic acid to the hippocampal CA1 (Cornu Ammonis 1) field of a rat cause cell loss and spatial learning impairment in the place task of Morris water maze. However, no study seems to have been conducted concerning the cue task of the maze. This study examined (1) whether cell loss in the CA1 field produced learning deficits in both the place and cue tasks; (2) whether training could remedy the deficit in spatial learning; and (3) whether the order of place training and cue training could change the performance outcome.

NMDA antagonist MK-801 does not interfere with the use of spatial representation in a familiar environment.

There is disagreement among researchers concerning whether glutamatergic N-methyl-D-aspartate (NMDA) receptors play a role in constructing spatial representations. Therefore, the authors reexamined the effects of the NMDA antagonist on a spatial discrimination task using rats in a water pool. The authors confirmed that MK-801 impaired acquisition of the spatial discrimination task (Experiment 1).

Arachidonic acid improves aged rats' spatial cognition.

To examine the effects of arachidonic acid (AA) on age-related cognitive deficits, F-344 rats were administered with an AA-supplemented powder diet from 79 weeks of age (OA group). For comparison, we also used an age-matched control group of animals (OC group) that were fed with a non AA-supplemented powder diet. When the subjects reached 87 weeks old, they were trained for Morris water maze place and cue tasks.

Long-term dietary restriction causes negative effects on cognitive functions in rats.

Long-term dietary restriction is reported to increase life span and improve age-related cognitive deficits. The present study shows that the restriction increases the life span of rats but decreases their cognitive ability. Thirty-two rats were divided into restricted and ad lib feeding groups at 2.

Medial prefrontal cortex and precision of temporal discrimination: a lesion, microinjection, and microdialysis study.

In this paper, we examined the role of the medial prefrontal cortex in temporal discrimination in three experiments using rats. Experiment 1 attempted to dissociate the roles of the medial precentral (PrCm) area from the prelimbic and infralimbic (PL-IL) area in temporal discrimination using fixed-interval (FI) schedule. The gradient of response rate distribution became more moderate by a lesion of the PrCm, but not by a lesion of the PL-IL.

Synaptic plasticity preserved with arachidonic acid diet in aged rats.

We examined whether synaptic plasticity was preserved in aged rats administered an arachidonic acid (AA) containing diet. Young male Fischer-344 rats (2 mo of age), and two groups of aged rats of the same strain (2 y of age) who consumed either a control diet or an AA ethyl ester-containing diet for at least 3 mo were used. In the Morris water maze task, aged rats on the AA diet had tendency to show better performance than aged rats on the control diet.

[Interactive effect of MK-801 and pre-training on spatial learning in rats].

In experiment 1, the effect of an NMDA receptor antagonist, MK-801, on the formation of the spatial representation was investigated. The administration of 0.1 mg/kg of MK-801 induced learning deficits in rats (n = 10) with the Morris watermaze task.

Effect of lesions in the lateral nucleus of the amygdala on fear conditioning using auditory and visual conditioned stimuli in rats.

The lateral nucleus of the amygdala (LA) is believed to be the site of auditory conditioned stimulus (CS) relay in classical fear conditioning. The present study attempts to determine whether the LA is specifically involved in fear conditioning using an auditory CS. Seven rats with lesions in the LA (Tone-Lateral group) and eight sham-operated rats in the control group were trained using an auditory CS (overtone based on an 800 Hz fundamental tone, 70 dB, 3.