Fig. 2.

REM sleep-dependent gene expression. a Activity-dependent expression of Zif-268 as induced by unilateral high-frequency stimulation (HFS) into the main gateway to the HPC, the perforant path. As time passes, Zif-268 expression spreads from the DG in the HPC to cortical and other limbic regions in a hippocampofugal manner, especially during REM sleep and selective to the stimulated hemisphere. DG dentate gyrus, CA cornu ammonis, EC entorhinal cortex, LaD dorsolateral nucleus of the amygdala and the auditory (Au), primary somatosensory (S1), and primary motor (M1) cortices (modified from [158]). b Top left: rats exposed to novel objects in the dark were left undisturbed for 4 h and then killed after reaching criteria for specific behavioral states (WK, SWS and REM). Top right: model to interpret IEG expression results. Bottom: IEG (Arc and Zif-268) expression showed a marked difference between animals exposed (WK—EXP) and not exposed (WK—control) to novel objects, including in V1, despite lights off during experience. During SWS, IEG expression was generally downregulated, followed by a significant enhanced expression during REM sleep restricted to S1 (modified from [161]). c Same protocol as in b, but with 1-h sleep deprivation after experience, followed by animals killed after reaching criteria for specific behavioral states. Plot shows the housekeeping gene-normalized expression of different plasticity-related genes measured by real-time PCR during REM sleep relative to the expression of the same genes from rats not exposed to novel objects (control). Note a significant expression of IEGs and phosphatases during REM sleep restricted to the HPC 1 h after the experience (modified from [165]). d Summarized model for the REM sleep-induced experience-dependent IEG expression waves