Male Long Evans rats' retention of a place memory acquired during a single massed training session in a water plus maze is short lived

While rats can retain a place memory acquired across several training days in the Morris water maze task (MWM) for long periods of time, retention of a place memory acquired during a single massed training session does not last very long (Bolding & Rudy, 2006). We hypothesized that reducing the searching area in the MWM by inserting a water plus-maze (WPM) might affect retention of a rapidly acquired spatial location. In Experiment 1, male Long Evans rats were given 10 trials on a place problem over a single massed training session in a WPM, followed by a 30-s no-platform probe trial given at 1 of 4 retention intervals: 30 min, 4 h, 24 h, or 48 h. Only the 30-min group showed a spatial bias, spending more time in the correct arm compared to the next preferred arm. In Experiment 2, the same rats were retrained on the spatial problem to determine if spatial bias would be evident at longer retention intervals when the duration of the probe trial was manipulated. No significant spatial bias was evident at the 4-h or 24-h retention intervals when rats were given 20-s or 60-s probe trials. Interestingly, in both experiments, first arm choice during the probe trials did not correlate with searching behaviour. The results from the present study extend Bolding and Rudy's (2006) findings in the open field MWM to the WPM and suggest that in a WPM first arm choice alone is not a representative measure of place memory retention.