Transient spine density increases in the mid-molecular layer of hippocampal dentate gyrus accompany consolidation of a spatial learning task in the rodent
Section snippets
Training
The spatial learning task employed has been described in detail previously.18 Briefly, the water maze apparatus consisted of a large circular pool (1 m diameter, 80 cm high, temperature 26±1°C) with a platform (11 cm diameter) submerged 1.5 cm below the water surface. Both the pool and the platform were constructed of black polyvinyl plastic and offered no intra-maze cues to guide escape behaviour. The experimental room contained several extra-maze visual cues. During training the platform was
Results
The water maze task was acquired by all animals as the swim latency times became significantly reduced between the first and the fifth trial (median and interquartile ranges of 60, 8 versus 8, 3 s, respectively; P<0.05, Mann–Whitney U-test; Table 1). The passive control animals explored the water maze for a time matched to their trained counterparts but in the absence of the platform. The improved performance of the task in the trained animals persisted in the recall trial at 6 h post-training
Discussion
The experiments reported here imply that among the sequence of physiological processes initiated following acquisition of a spatial task is modulation of spine number in the mid-molecular layer of the dentate gyrus. Sensory information arrives at the hippocampus via the perforant path entorhinal cortical efferents, 80% of which terminate in the dentate molecular layer as axospinous synapses.5., 13., 27. Thus, the observed change in spine number most probably relates to the elaboration of
Acknowledgments
This work was supported by Enterprise Ireland.
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