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1.
Neurobiol Learn Mem ; 173: 107271, 2020 09.
Article in English | MEDLINE | ID: mdl-32565407

ABSTRACT

Preadolescent development is characterized by a reorganization of connectivity within and between brain regions that coincides with the emergence of more complex behaviors. The hippocampus is one such region that undergoes extensive preadolescent remodeling and as this process continues, spatial memory functions emerge. The current work investigated whether preadolescent spatial memories persist beyond 24 h and stabilize into the postadolescent period as remote memories supported by cortical networks in the anterior cingulate cortex (ACC). Male Long Evans rats were trained on the Morris water maze at different time frames from postnatal day (P) 18-26 and compared to P50 rats. Testing occurred at either a recent (24 h) or remote (3 weeks) timepoint. Spatial learning was evident in all age groups (P18, P20, P22, P24 and P50) across the 3 training days but only the P22 and P24 groups showed spatial learning that matched the P50 group. In light of this, the only group to show intact remote (3 week) memory was the P50 group. Spaced training in the P18 group did not improve retention at the recent or remote testing intervals. The P18 and P50 groups tested at 24 h showed more CA1 hippocampal c-Fos labeling than groups tested at 3 weeks. The P50 group tested at 3 weeks showed elevated c-Fos labeling in the anterior cingulate (ACC) compared to the P18 group tested at 3 weeks and the P50 group tested at 24 h. Spaced training in the P18 group was associated with elevated c-Fos labeling in the ACC at the 3-week test. Groups trained at P20, 22, and 24 showed more c-Fos labelling in the ACC than in the CA1. Results suggest that while spatial information processing emerges around P18/P20, remote spatial retention and the neural substrates that support retention are not in place until after P26 in rats.


Subject(s)
Gyrus Cinguli/physiology , Hippocampus/physiology , Maze Learning/physiology , Memory, Long-Term/physiology , Spatial Memory/physiology , Animals , Male , Proto-Oncogene Proteins c-fos/metabolism , Rats , Rats, Long-Evans
2.
Neurobiol Learn Mem ; 133: 145-156, 2016 09.
Article in English | MEDLINE | ID: mdl-27353718

ABSTRACT

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 10mg/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 3weeks later, the saline group across all conditions spent more time in the target quadrant. Rats treated with pretraining 5mg NBQX dose showed a preference for the target quadrant while the posttraining and pretesting 5mg NBQX doses impaired the target quadrant preference. Groups injected with 10mg 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.


Subject(s)
Behavior, Animal , CA1 Region, Hippocampal , Excitatory Amino Acid Antagonists/pharmacology , Memory Consolidation , Receptors, N-Methyl-D-Aspartate , Spatial Learning , Spatial Memory , Age Factors , Animals , Behavior, Animal/drug effects , Behavior, Animal/physiology , CA1 Region, Hippocampal/drug effects , CA1 Region, Hippocampal/physiology , Excitatory Amino Acid Antagonists/administration & dosage , Male , Memory Consolidation/drug effects , Memory Consolidation/physiology , Quinoxalines/administration & dosage , Quinoxalines/pharmacology , Rats , Rats, Long-Evans , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/physiology , Spatial Learning/drug effects , Spatial Learning/physiology , Spatial Memory/drug effects , Spatial Memory/physiology
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