DIFFERENTIAL DISTRIBUTION OF ACTIVITY-INDUCED ARC RNA IN DEEP AND SUPERFICIAL LAMINA OF THE POSTERIOR PARIETAL CORTEX

S.N. Burke1*; M.K. Chawla¹; M.R. Penner¹;
M.J. Schaner¹; P.F. Worley²; B.L. McNaughton¹;
C.A. Barnes¹

1. NSMA, Univ Arizona, Tucson, AZ, USA

2. Neurosci & Neurol, Johns Hopkins Univ, Baltimore, MD, USA

Hippocampus and posterior parietal cortex (PPC) both contribute to spatial learning in rats and the interconnectivity between these regions could be important for spatial navigation. Output from the hippocampus is projected to layers II/III of the PPC while layer V of the PPC sends projections to the parahippocampal region, which then projects to the hippocampus. The output from the hippocampus could therefore affect the patterns of activity in superficial layers of the PPC more than the deep layers. The present study used compartment analysis of temporal activity (catFISH) with confocal microscopy to monitor the subcellular distribution of activity-induced Arc RNA in CA1, and superficial and deep layers of PPC. Because the time course for Arc RNA in the nucleus is distinct from the cytoplasm, its distribution can be used to infer the activity history of a neuron at two time points about 20 min apart. Rats traversed a track in the clockwise direction for 5 min in environment A, were returned to their home cage for a 20 min rest, and then traversed the track again for 5 min but in environment B. After the second track running epoch, the rats were sacrificed. In CA1, Arc distribution was consistent with two independent CA1 'maps' being activated. For deep layers of PPC, 75% of the cells expressing Arc RNA had overlapping nuclear and cytoplasmic expression, indicating that the same motion in two different environments activated similar cells in deep layers. In superficial layers of PPC, the patterns of Arc distribution were different. These neurons had less overlapping activation, suggesting that cells in superficial layers were more influenced by the visuo-spatial inputs in the two different environments than the cells in the deeper layers, possibly because of altered hippocampal input.

Support Contributed By: AG09219, AG18230 & T32 AG007434