Reactivation of IEG expression in the rodent hippocampus.
1. ARL NSMA, Univ Arizona, Tucson, AZ,
2. Dept Neurosci, Johns Hopkins Univ, Baltimore, MD.
The transcription of the immediate-early genes Arc and Homer 1a (H1a) is dynamically regulated in response to synaptic activity, and both are thought to play critical roles in modifying glutamatergic signaling pathways. Previous studies (Vazdarjanova et al., 2002) have indicated that these genes are dynamically coupled in the same cells. Those cells transcribing Arc immediately following a stimulus also transcribe H1a ~30 minutes later. Moreover, previous data (Bottai et al., 2002) indicate that H1a transcripts are transported from the nucleus to the cytoplasm at ~60 minutes following stimulation. Combining these observations permits the expansion of the catFISH technique to capture activity during 3 behavioral episodes over the course of 60 minutes. This expansion of catFISH reveals that gene expression can be used to reliably mark neuronal activity with comparable cellular resolution at twice the delay interval. Moreover, making one of the behavioral episodes a period in which the animal remains in the home cage permits the exploration of IEG expression during periods of rest. Animals are known to transcribe IEGs in approx 5-10% of hippocampal principle cells during periods of rest, but it is not currently known how this rest activity relates to activity induced during active behavior. If animals engage in two exploration sessions 60 minutes apart, and the IEG transcription is examined during the intervening rest period, the overlap between the cell population transcribing IEGs during rest and those recruited during exploration are significantly greater than chance. Moreover, this same alignment of activity is not seen if an animal is permitted this rest prior to exploration, suggesting that this effect is a molecular correlate of the reactivation of the activity patterns seen electrophysiologically following exploration.
Support Contributed By: AG09219, NSERC
KEYWORDS: Plasticity, hippocampus, Arc, H1a, reactivation.