No abstract

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.

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. The authors then trained them with a novel spatial task in a novel environment under chronic blockade of hippocampal NMDA receptors by intrahippocampal infusion of 2-amino-5-phosphonopentanoic acid (AP5) using osmotic pumps. Although the rats had acquired the basic techniques needed to solve a water-maze spatial task during pretraining, those given high or low doses of AP5 showed acquisition deficits. As the spatial pretraining failed to ameliorate the acquisition deficits of a new task in a novel environment, it was suggested that NMDA receptors were necessary in forming spatial representations. Because neither dose of AP5 affected the performance of a spatial task in the retention phase, sensory motor disturbances could not have caused these deficits.

Our previous research using Octodon degus (degus) revealed that preweaning social isolation negatively affected object exploratory behavior. However, it remains unknown how social isolation affects animal psychology and other behaviors. The present study examined the effects of neonatal social isolation on degu emotion and mother–infant interactions before and after weaning. Because degus have a complex social repertoire, we predicted that they would be sensitive to social isolation and show similarities with humans in their social interaction. Pups in the isolation group were separated from their family seven times for 30 min a day from 8 to 15 days post-birth. Pups in the nonisolation group were reared with their family. At 2, 3, 4, 5, and 6 weeks of age, pups underwent a zero-maze test to measure anxiety and a mother–infant interaction test to assess mother–infant attachment. Isolated pups showed more activity in the zero-maze test than nonisolated pups at 3 weeks of age. We found no significant effects of social isolation on mother–infant interactions. These results suggest that while neonatal social isolation might affect emotion during weaning, it does not influence mother–infant relationships.