Biomedical subjects

Hiroshige Okaichi

Publications and source records attributed to Hiroshige Okaichi.

12 recordsLinked to original sources

PubMed2006

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. METHODS: To determine whether deficits are caused by inborn neuropathologic abnormalities or by repeated generalized convulsions, we tested nine 6- to 12-week-old IER/F rats that had not yet experienced seizures (experiment 1) and nine 7- to 9-month-old IER/F rats that had repeatedly experienced seizures (experiment 2) with identical tasks: an open-field test and the Morris water-maze place and cue tasks. RESULTS: Both groups of IER/Fs showed behaviors that were different from those of control rats in the open-field test, and extensive learning impairments were seen in both the place task, which requires spatial cognition, and the cue task, which does not require spatial cognition but requires simple association learning. Their impaired performance of the cue task indicates that their deficiency was not limited to spatial cognition. CONCLUSIONS: Because young IER/F rats without seizure experiences also showed severe learning impairments, genetically programmed microdysgenesis in the hippocampus was suspected as a cause of the severe learning deficits of IER/Fs.

Age Factors↗

PubMed2006

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. After training, rats were divided into a control (CONT) group (n = 16), hippocampal lesioned (HIPP) group (n = 16), and parietal cortex lesioned (PARC) group (n = 16), and rats in the lesioned groups underwent surgery. After surgery, Test 1 (with four cups) and Test 2 (with one cup but the outgoing path was diverted by a barrier) were conducted. The HIPP group showed severe impairment in homing, but the performance of the PARC group did not differ from that of the CONT group. HIPP rats either approached wrong doors or ate the pellet in the arena. Circular statistics showed that homing directions of CONT and PARC rats showed concentration towards home, whereas those of HIPP rats did not. Our results exhibiting HIPP rats' failure in homing agree with many previous studies, but the results obtained from PARC rats were different from previous studies. These results indicate that the intact hippocampus is important for dead reckoning, but the role of the parietal cortex in dead reckoning is still not clear.

Animals↗

PubMed2006

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. In the familiar environment, MK-801 had no effect, but in the novel environment performance was impaired. In Experiment 2, after the place task training, the hippocampus was lesioned, and rats were re-trained with the same task in the familiar environment then retrained again in the novel environment. Rats showed severe impairment in both environments. These two experiments suggest different functions for NMDA receptors and the hippocampus. The results of Experiment 1 showed that NMDA receptors are not required for utilizing spatial representations but they play an important role in the construction of spatial representations. The results of Experiment 2 show that the hippocampus is necessary for both the utilization of spatial representations already formed and the formation of new spatial representations.

Animals↗

PubMed2006

[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. In the object exploration task, Contra and Ipsi groups did not differ from Control group in the performance of object recognition test. However, the performance of Contra group was significantly impaired in the spatial recognition test, compared with two other groups. In the Morris water maze task, only Contra group showed deficits in spatial learning but not the Ipsi group. These results indicate that contralateral, but not ipsilateral lesion caused deficits in spatial memory, supporting the notion that the functional cooperation of hippocampus and anterior thalamus via fornix is vital for spatial memory.

Animals↗

PubMed2005

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. Escape latencies of the OA group on the place task were significantly shorter than those of the OC group in the latter half of training. The probe test showed that OA rats remembered the trained platform position significantly better than OC rats. In the cue task training, the OC group was significantly slower than the OA group at the beginning of training, but their performance soon matched with that of the OA group. Fatty acids in the hippocampi were measured after the behavioral testing. There was no difference in AA composition in hippocampal phospholipids between the OA and OC groups. However, regression analysis conducted on AA composition and place task performance showed a significant correlation between these two parameters. The present study suggests that AA administration to aged animals can alleviate age-related deficits in spatial cognition.

Aging↗

PubMed2005

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). When rats were pretrained before drug treatment, MK-801 induced learning deficits in the novel environment but not in the familiar environment (Experiment 2). Moreover, in a familiar environment, MK-801 did not impair spatial learning, even when the task was completely novel for the rats (Experiment 3). These results suggest that NMDA receptors play an important role in the construction of spatial representations but not in the use of them.

Animals↗

PubMed2005

[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. Thirty-seven rats of Wistar strain were divided into Place-Cue (PC) group that received place training first and then cue training, and Cue-Place (CP) group that received training in the reverse order. Half rats in each group were damaged in the CA1 field by ibotenic acid injections. Results indicated that damage to CA1 pyramidal cells led to performance deficits only in the place task throughout training, regardless of the sequence of training. The results also indicated that training in the prior task affected learning in the succeeding task, only at the beginning of training, and the effect is transient.

Animals↗

PubMed2004

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. In experiment 2, the efflux of acetylcholine (ACh) in the PrCm area during temporal discrimination tasks was compared to that during non-temporal discrimination tasks. ACh efflux was not different between these two tasks. In experiment 3, microinjection of the anticholinergic drug scopolamine (10 microg) into the PrCm area made the gradient of response rate distribution moderate. These findings suggest that reduced activity of the ACh system within the PrCm area impairs the precision of temporal discrimination, even though enhancement of this system is not indispensable for performing temporal discrimination.

Acetylcholine↗

PubMed2004

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 2.5 months of age. The restricted rats were kept at a weight of 280g. The restricted rats were poor in performing the Morris water maze task at 7-12 months. At 17-18 months, they were poor in performing the delayed matching-to-place task. At 24-27 months, the surviving 13 restricted and 5 ad lib rats performed the spatial discrimination task. The restricted rats were also poor in performing this task. Injection of glucose prior to the discrimination task improved their performance to the level of the ad lib rats. These results suggest that dietary restriction is beneficial for longevity but has negative effects on the performance of cognitive tasks, and that the cause of the negative effects may be a reduced availability of glucose in the food-restricted aged rats.

Aging↗

PubMed2003

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. Long-term potentiation induced by tetanic stimulation was recorded from a 300 microm thick hippocampal slice with a 36 multi-electrode-array positioned at the dendrites of CA1 pyramidal neurons. The degree of potentiation after 1 h in aged rats on the AA diet was comparable as that of young controls. Phospholipid analysis revealed that AA and docosahexaenoic acid were the major fatty acids in the hippocampus in aged rats. There was a correlation between the behavioral measure and the changes in excitatory postsynaptic potential slope and between the physiologic measure and the total amount of AA in hippocampus.

Aging↗

PubMed2002

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, 3.7 s) paired with foot shock (1.0 mA, 0.5 s). Five rats with lesions in the LA (Light-Lateral group) and eight unoperated rats in the control group were trained using a visual CS (25 W light, 3.7 s). The behavioral index of fear conditioning was a potentiation of the startle reflex in the presence of CS. All rats in the control group and Light-Lateral group showed this potentiation, whereas those in the Tone-Lateral group did not. These results suggest that the LA is an input site of auditory CS information into the amygdala, and that it is not a site of visual CS information input in fear conditioning. Thus, each modality of CS may have a specific subnucleus of the amygdala that mediates fear conditioning.

Acoustic Stimulation↗

PubMed2002

[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. However, when rats (n = 10) were pre-trained in the same task without drug treatment, and then trained in the same task in a different environment under the influence of the same amount of the drug, their performance was not impaired. The result suggests that rats treated with MK-801 can acquire a spatial representation of their environment, and that the impairment shown by the drug-treated rats without pre-training may be due to the impairment in the learning of the problem-solving strategy required for the watermaze place task. Experiment 2 examined this possibility. Rats (n = 10) were pre-trained with a visual cue discrimination task without drug treatment and then trained in the place task with MK-801 (0.1 mg/kg) treatment. They did not show impairment in the place task, indicating that rats treated with MK-801 can learn a new problem-solving strategy. Thus the learning deficits of MK-801-treated rats that have not been pre-trained do not seem to be due to impaired acquisition of the spatial representation or of the learning of strategy required to solve the watermaze place task.

Animals↗