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Title: Immediate‐early gene Homer1a intranuclear transcription focus intensity as a measure of relative neural activation

Immediate‐early genes (IEGs) exhibit a rapid, transient transcription response to neuronal activation. Fluorescently labeled mRNA transcripts appear as bright intranuclear transcription foci (INF), which have been used as an all‐or‐nothing indicator of recent neuronal activity; however, it would be useful to know whether INF fluorescence can be used effectively to assess relative activations within a neural population. We quantified theHomer1a(H1a) response of hippocampal neurons to systematically varied numbers of exposures to the same places by inducing male Long‐Evans rats to run laps around a track. Previous studies reveal relatively stable firing rates across laps on a familiar track. A strong linear trend (r2 > 0.9) in INF intensity was observed between 1 and 25 laps, after which INF intensity declined as a consequence of dispersion related to the greater elapsed time. When the integrated fluorescence of the entire nucleus was considered instead, the linear relationship extended to 50 laps. However, there was only an approximate doubling ofH1adetected for this 50‐fold variation in total spiking. Thus, the intranuclearH1aRNA fluorescent signal does provide a relative measure of how many times a set of neurons was activated over a ~10 min period, but the dynamic range and hence signal‐to‐noise ratios are poor. This low dynamic range may reflect previously reported reductions in the IEG response during repeated episodes of behavior over longer time scales. It remains to be determined how well theH1asignal reflects relative firing rates within a population of neurons in response to a single, discrete behavioral event.

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Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
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Page Range / eLocation ID:
p. 481-490
Medium: X
Sponsoring Org:
National Science Foundation
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