Environmental novelty is associated with a selective increase in Fos expression in the output elements of the hippocampal formation and the perirhinal cortex.
If the hippocampus plays a role in the detection of novel environmental features, then novelty should be associated with altered hippocampal neural activity and perhaps also measures of neuroplasticity. We examined Fos protein expression within subregions of rat hippocampal formation as an indicator of recent increases in neuronal excitation and cellular processes that support neuroplasticity. Environmental novelty, but not environmental complexity, led to a selective increase of Fos induction in the final "output" subregion of the dorsal hippocampal trisynaptic circuit (CA1) and a primary projection site (layer five of the lateral entorhinal cortex, ERC), as well as in the perirhinal cortex. There was no selective effect of novelty on Fos expression within "input" elements of the trisynaptic circuit (ERC layer two, the dentate gyrus or CA3) or other comparison brain regions that may be responsive to overall motor-sensory activity or anxiety levels (primary somatosensory and motor cortex or hypothalamic paraventricular nucleus). Test session ambulatory behavior increased with both novelty and environmental complexity and was not significantly correlated with Fos expression patterns in any of the brain regions examined. In contrast, the extent of manipulated environmental novelty was strongly correlated with Fos expression in CA1. These results support the prospect that a novelty-associated signal is generated within hippocampal neurocircuitry, is relayed to cortical projection sites, and specifically up-regulates neuroplasticity-supporting processes with dorsal hippocampal CA1 and ERC layer five. Whether novelty-dependent Fos induction in perirhinal cortex depends on this hippocampal output or reflects an independent process remains to be determined.
VanElzakker
Michael
M
Department of Psychology, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
Fevurly
Rebecca D
RD
Breindel
Tressa
T
Spencer
Robert L
RL
D000704:Analysis of Variance; D000818:Animals; D002452:Cell Count; D004777:Environment; D005106:Exploratory Behavior / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006624:Hippocampus / Q000378:metabolism*; D016014:Linear Models; D008297:Male; D000090204:Mesothelin; D016761:Oncogene Proteins v-fos / Q000378:metabolism*; D017397:Prefrontal Cortex / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013037:Spatial Behavior / Q000502:physiology
C000715529:Msln protein, rat; D016761:Oncogene Proteins v-fos; D000090204:Mesothelin