Spatial experience induces a long-term sustained activity of the IEG Arc in the rat fascia dentata.
1. ARL NSMA
2. Evelyn F. McKnight Brain Inst., Univ. Arizona, Tucson, AZ
3. Inst. of Neurobiology, UNAM, Queretaro, Mexico
4. Physical Therapy and Neurological Surgery, Univ. California San Francisco, San Francisco, CA
5. Neurosci. and Neurol., Johns Hopkins Univ., Baltimore, MD
The induction of immediate early genes following spatial exploration represents the first major transcriptional activity that precedes changes in a variety of cellular responses including synaptic activity. Using cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH; Guzowski et al., 1999, Nature Neurosci., 2 (12): 1120-1124) and high-resolution confocal microscopy the transcriptional activity of Arc has been measured in the fascia dentata, CA1, CA3 and parietal cortex regions at 5 min, 45 min or 90 min following spatial exploration (Chawla et al., 2005). To more thoroughly examine the time course of Arc expression in hippocampal granule cells the time before sacrifice was extended to 120, 360, 480, 720 and 1440 min, in addition to measuring Arc activity following the 5 min behavior. Animals that explored a 60x60 cm square box, for 5 min showed Arc activation in ~ 2% of the granule cells (upper blade of the fascia dentata; Chawla et al., 2005), in ~ 35% of CA1 pyramidal cells, in ~ 25% of CA3 pyramidal cells and in ~ 50% of parietal cortical cells. Additionally, no transcription foci were detectable at the 45 or 90 min interval in cells from the CA1, CA3 or parietal cortex regions as reported previously. In the dorsal blade of the dentate gyrus sustained transcription of Arc is still present at the 480 min time point, by 720 min it is considerably reduced and returns to baseline by 1440 min. In all the groups, with the exception of the 5 min category, the proportion of cells with both, Arc foci and cytoplasmic Arc, out of the total active population is close to 50% or above. This indicates that even though only a subset (about half) of granule cells shows sustained Arc transcription, the same cells engage in the sustained transcriptional response for at least 8 hrs, returning to baseline by 24 hrs. The functional implication of this long lasting IEG transcriptional response in a subpopulation of granule cells awaits further investigation.
Grant/Other Support: AG009219; McKnight Brain Research Foundation; state of Arizona and ADHS; CONACyT P51028325
Keyword (Complete): behavior; hippocampus; fluroscence in situ hybridization; confocal microscopy