Ultrastructural synaptic correlates of spatial learning in rat hippocampus
Section snippets
Spatial training in the rat
Seventeen male Sprague–Dawley rats (350–400 g) were employed. The water maze training protocol has been described previously.[18]Briefly, in the control, i.e. the non-spatial learning group (eight animals), a rat was released into the pool, at a pseudo-random location, and trained to find a visible escape platform. In the spatial learning group (nine rats), the platform was submerged so the animals once having found the platform, would subsequently have to rely on visible cues outside the maze.
Analysis of behavioural parameters
In the water maze, the decay of the escape latency with further training can be considered an indicator of the learning progress. We quantified the animal's performance in the water maze using the direct relationship between time of session and the escape latency decay, that is, as an exponential regression:where: t is the escape latency; T, time of training session; t0, “expected” initial escape latency; and α is the decay constant of the escape latency, which we consider as a
Discussion
The present study has employed a behavioural paradigm in which a comparison is made between a group of animals trained for a spatial memory task, and a group trained in conditions which do not require spatial memory, but are otherwise similar. Thus, animals in the control group were likely to experience motor activity, stress, visual and other sensory input matched with that in the test group, with the exception of the learning component related to the spatial task. However, it cannot be
Conclusion
In our experiments, training of rats on a hippocampal-dependent spatial learning task did not produce significant long-term changes in density or sizes of synapses, in either dentate gyrus, or CA1 areas of hippocampus when morphometric analyses were carried out on animals perfused six days after the last training session. However, more subtle, but significant, changes were found which indicate local re-arrangement of synaptic connections in CA1 associated with learning. These results provide
Acknowledgements
The study was partly funded by BBSRC Grant S02085 to MGS, by the Wellcome Trust and the European Neuroscience Program.
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