RESUMEN
We investigated whether systems consolidation of spatial memory could be detected in a non-navigational, spatial-learning test that takes advantage of rats' natural propensity to preferentially investigate an object that was displaced relative to spatial cues more than an object that remained stationary. Previous studies using navigational spatial-learning tests have generally failed to reveal temporally-graded retrograde amnesia, possibly because the hippocampus needs to be intact for the retrieval and/or processing of navigational information during the test. In the present study, the hippocampus of rats was kept inactivated, at two sites along its septo-temporal axis (dorsal and intermediate), for four consecutive days, beginning either 3h or 5 days after familiarization to two identical objects in an open field. Rats that had their hippocampus inactivated beginning 5 days but not 3h after familiarization showed evidence that they remembered the previous location of the displaced object. The results suggest that systems consolidation of spatial memories can be detected using a non-navigational test of spatial memory.
Asunto(s)
Amnesia Retrógrada/fisiopatología , Hipocampo/fisiopatología , Aprendizaje por Laberinto/fisiología , Refuerzo en Psicología , Retención en Psicología , Animales , Masculino , Ratas , Ratas Long-Evans , Retención en Psicología/fisiología , Percepción Espacial/fisiologíaRESUMEN
We investigated whether object familiarization was related to novel-object preference in the novel-object preference (NOP) test in rats. In Experiment 1, we found that no significant correlation existed between the time spent investigating 2 identical copies of a sample object and the degree of preference for a novel object. In Experiment 2, rats investigated 2 identical sample objects for a total of 5, 30, 60, 90 or 120s. Investigatory preference for the novel object was compared to chance expectancy as well as between the groups. Only the 90-s group and the 120-s group displayed above-chance investigatory preference for the novel object, but novel-object preference for these 2 groups did not differ from each other, suggesting that a minimal amount of sample object investigation is necessary for rats to develop a novel-object preference, beyond which no increase in novel-object preference was found. In Experiments 3 and 4, normal rats and rats with hippocampal lesions were given repeated test trials, with the same sample object presented with a different novel object, at 24-h and (Experiment 3) and 35-s intervals (Experiment 4). In both experiments, novel-object preference did not increase in magnitude with repeated sample object exposures, suggesting that increased familiarity with the sample object does not result in increased novel-object preference. Rats with lesions of the dorsal hippocampus showed an unreliable investigatory preference for the novel object. These results are discussed in terms of the potential limitations of the NOP test as a tool for the assessment of object-recognition memory in rats.
Asunto(s)
Conducta de Elección , Conducta Exploratoria , Animales , Conducta Animal , Habituación Psicofisiológica , Hipocampo/fisiología , Masculino , Memoria , Ratas , Ratas Long-Evans , Reconocimiento en Psicología , Conducta SocialRESUMEN
We investigated whether the ventral and dorsal hippocampus were differentially involved in incidental spatial learning. Rats with ventral and dorsal hippocampal lesions were tested on an unreinforced test of spatial memory that takes advantage of their natural propensity to explore novelty. Rats were presented with two copies of an identical object in a large circular open field arena. Subsequently, the rats were placed back into the open field with one of the objects displaced to an adjacent quadrant of the arena. Sham-operated rats and rats with ventral hippocampal lesions spent more time in the quadrant that contained the displaced object than in the quadrant that contained the non-displaced object, and more time investigating the displaced object than the non-displaced object. Rats with dorsal hippocampal lesions were impaired on both measures. Both sham and ventral hippocampal lesioned rats subsequently learned to retrieve a food pellet in the ends of each arm of a radial maze. Rats with lesions to the dorsal hippocampus showed no significant improvement in the number of errors made across training sessions and made significantly more errors, overall, than rats with ventral hippocampal or sham lesions. The findings suggest that an intact dorsal but not ventral hippocampus is necessary for spatial learning in rats.
Asunto(s)
Hipocampo/fisiología , Aprendizaje/fisiología , Percepción Espacial/fisiología , Análisis de Varianza , Animales , Conducta Exploratoria/fisiología , Hipocampo/efectos de los fármacos , Masculino , Aprendizaje por Laberinto/fisiología , Memoria/fisiología , N-Metilaspartato/toxicidad , Neurotoxinas/toxicidad , Ratas , Ratas Long-Evans , Conducta Espacial/fisiología , Factores de TiempoRESUMEN
A non-navigational test of incidental spatial learning was used to determine whether hippocampal damage causes temporally-graded retrograde amnesia (TGRA) for allocentric-spatial information. Rats were exposed to two identical objects in a circular open field for 7 min on seven consecutive days. In the 1-3 days after the last day of familiarization, rats received neurotoxic lesions of the hippocampal formation (HPC) or sham lesions. Another two groups received the same lesions 3 weeks after familiarization. The rats were then placed back in the open field with one object displaced, and the time spent in each of the quadrants as well as time spent exploring the objects was recorded. Rats that received HPC lesions 3 weeks but not 1-3 days after familiarization showed evidence of preserved remote spatial memory; however, their remote memory was expressed through different behavior than control rats. Rats with HPC lesions spent more time with the displaced object than with the object that remained in the same place, whereas control rats spent more time in the quadrant where the displaced object used to be. These results suggest that remote spatial memories may be preserved with a sufficiently long familiarization-to-surgery interval before HPC lesions, but that the nature of these memories may differ in quantity and/or quality from those of intact rats.