The effect of AMPA receptor blockade on spatial information acquisition, consolidation and expression in juvenile rats

Improvement on spatial tasks in rats is observed during a late, postnatal developmental period (post-natal day (PND) 18 - PND 20). The developmental emergence of this spatial function occurs in conjunction with hippocampal connectivity changes and enhanced hippocampal-AMPA receptor-mediated synaptic responses. The current work investigated the effect of AMPAr blockade on the emergence and long-term storage of spatial information in juvenile rats and associated neural activity patterns in the dorsal hippocampus CA1 region. Male, Long Evans rats between the ages of PND 18 and PND 20 were systemically (i.p.) administered the AMPAr antagonist, NBQX, (0, 5 or 10 mg/kg) every day prior to hidden platform water maze training (PND 18, 19 and 20), every day immediately post-training or immediately before the probe test (PND 41). NBQX administration prior to training prolonged latencies, pathlength and increased thigmotaxis during the acquisition phase. Administration of NBQX immediately posttraining had no effect on the day-to-day performance. When given a probe test 3 weeks later, the saline group across all conditions spent more time in the target quadrant. Rats treated with pretraining 5 mg NBQX dose showed a preference for the target quadrant while the posttraining and pretesting 5 mg NBQX doses impaired the target quadrant preference. Groups injected with 10 mg of NBQX pretraining, posttraining or pretesting did not show a preference for the target quadrant. c-Fos labeling in the CA1 reflected these differences in probe performance in that groups showing greater than chance dwell time in the target quadrant showed more c-Fos labeling in the CA1 region than groups that did not show a target quadrant preference. These findings provide support for the critical role of AMPA receptor-mediated function in the organization and long-term storage of spatial memories acquired during the juvenile period.