Perforant path inputs to hippocampal subfields predict heterogeneous AMPA receptor subunit expression following rapid new spatial learning in a novel context.

Abstract

The hippocampus plays a critical role in spatial learning and memory. Its contribution to support these kinds of learning and memory functions relies on synaptic plasticity and related molecular mechanisms, well documented in the long-term potentiation (LTP) literature. The present experiment measures AMPA subunit expression, in a ratio of GluA2:GluA1 as an indicator of plasticity across the hippocampus, in rats that underwent new spatial learning in either a familiar or novel context. Statistically significant effects in this plasticity indicator were observed of context condition, time after task and hippocampal subfield. Based on the strong inputs of entorhinal cortex to hippocampus, we also identified differences in GluA2:GluA1 expression trends between time points and room conditions that mirror trends in medial and lateral entorhinal cortex connectivity between new room and same room context learning, respectively. Across the transverse axis in infrapyramidal dentate gyrus, CA3 and CA1, plasticity followed entorhinal cortex projection patterns. Along the transverse axis in the suprapyramidal blade of the dentate gyrus, and along the long axis in dentate gyrus and CA3, results did not follow entorhinal cortex subregion projection patterns. These latter results may be indicative of pattern separation in the dentate gyrus and emotional triage functions of the ventral hippocampus.