DISTRIBUTION OF ACTIVITY-INDUCED ARC RNA CONFIRMS PLACE AND MOVEMENT ENCODING DISTINCTION BETWEEN HIPPOCAMPUS AND POSTERIOR PARIETAL CORTEX

S.N. Burke*; M.K. Chawla; M.R. Penner; B.L. McNaughton; C.A. Barnes

NSMA, Univ Arizona, Tucson, AZ, USA

Hippocampus & posterior parietal cortex (PP) both contribute to spatial learning in rats. CA1 neuronal ensembles encode position within a given environment, while specific movement encoding cells in PP provide a representation of the state of motion through it (e.g., left or right turning or forward movement; McNaughton et al., 1994). The present study used cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) with confocal microscopy to monitor subcellular distributions of activity-induced Arc RNA in CA1 & PP. Because the time course for Arc RNA in the nucleus is distinct from the cytoplasm, its distribution can reveal the activity history of a neuron at two time points about 20min apart. Rats traversed a track for two 5-min sessions with 20-min rest between sessions, & were then sacrificed. Group 1 traversed the track twice in the clockwise direction, first in Environment A & then Environment B. Group 2 traversed the track twice in Environment A; first clockwise, then counterclockwise. Consistent with previous neurophysiological & Arc studies, both groups showed patterns of Arc activation consistent with two independent CA1 maps being activated. For Group 1 in parietal cortex, 74% of the cells expressing Arc RNA had overlapping nuclear & cytoplasmic expression, indicating that the same motion in two different environments activated similar PP cells. Conversely, two different movement patterns made in the same environment (Group 2) resulted in a pattern consistent with activation of a subset of cells (45%) that reflect forward or general motion, another subset only activated by right turns (25%), & yet another only by left turns (30%). These results are consistent with neurophysiological recordings from the PP & support using catFISH as a technique to reveal neural networks participating in complex behaviors.

Support Contributed By: AG18230, AG09219, NS020331, MH01565 & AG07434

Arc, CA1, parietal cortex, catFISH