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Normal aging is characterized by slight impairments in spatial memory, and the modification of some electrophysiological parameters that underlie place learning and associated reference memory. However, the morphological mechanisms underlying these impairments remain unknown. In the present study, we analyzed the spine density and the proportion of thin, mushroom, stubby, wide, branched and double spines on pyramidal neuron dendrites in the hippocampal CA1 field of young and aged rats. These parameters were assessed both before and after evaluating place learning and reference memory in the Morris water maze. Aged rats adopted an egocentric strategy to resolve the task, swimming slower and further, and taking longer to locate the sunken platform. While probe trials revealed that aged animals could recall the platform position, these animals spent more time exploring incorrect quadrants than young rats. An increase in spine density was observed after task performance in both young and aged rats, but aging provoked a decrease in the density of thin spines. In addition, there was an increase in the density of mushroom and wide spines in aged animals after task performance as compared with the untested aged counterparts. Moreover, in aged animals there were fewer thin spines and more wide spines after task performance than in the young tested animals. These findings support the view that aging attenuates but does not abolish spatial memory, a process that may be associated with plastic changes in the type of dendritic spines on aged hippocampal CA1 neurons., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The involvement of the cerebellum in procedural learning is demonstrated in visuomotor-sequence tasks, as lesion of this area impedes the acquisition of new sequences. Likewise, the lateral cerebellum appears to be involved in the acquisition of new sequences, but not in the execution of learned sequences. In contrast, the dentate nucleus participates only in the execution of learned visuomotor sequences. In previous studies, disruption of the procedural elements of spatial navigation following cerebellar or dentate lesions has been reported. However, as praxic strategies (egocentric learning) are included in the procedural elements of the navigation, the participation of the cerebellar-dentate nucleus in egocentric procedural learning processes has not been evaluated. Therefore, using colchicine, bilateral lesions were made in the cerebellar-dentate nucleus of Sprague-Dawley rats, and these rats were given two tasks: egocentric-based motor sequence learning in the radial maze and egocentric navigation in the Morris water maze. The lesioned rats were unable to use the sequential information in the short term and showed delayed long-term acquisition, which was probably due to the inability to detect the sequence. No effects on the egocentric navigation task were observed. Our results indicate that the cerebellar-dentate nucleus is involved in the detection of egocentric sequential information but not in the use of this information in the navigation process. Further, they show differential involvement of the cerebellar-dentate nucleus in the execution of learned visuomotor sequences, as the dentate lesion disrupted the acquisition of new egocentric-motor-based sequences.