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The basal expression of the proto-oncogene c-fos was studied by Northern blot analysis in different regions of the rat brain during 24 h. A striking spontaneous oscillation of c-fos mRNA expression was detected in animals kept in basal conditions with a 12 h light/12 h dark cycle. In these animals c-fos mRNA was just detectable during the rest hours (morning through afternoon), and was high during the activity hours (night). The periodicity of this oscillation persisted and became free-running when the animals were exposed for 6 consecutive days to constant light or darkness. It was thus demonstrated that the fluctuation of c-fos expression is circadian and is not created by the light-dark cycle, but the latter exerts a synchronizing effect. The oscillation of c-fos mRNA was modified by manipulations of the rest-activity cycle. In particular, the fluctuation observed in basal conditions was inverted, keeping the animals awake during the rest hours (diurnal) and allowing them to sleep in the activity period (nocturnal). These data indicated a close relationship between the oscillation of c-fos expression and the rest-activity cycle. Finally, electroencephalographic (EEG) monitoring was performed under behavioural control for 3 h before the animals were killed. These experiments confirmed that, irrespective of the time of day, the EEG pattern typical of a state of sleep (including both slow waves and paradoxical sleep) was associated with low or undetectable c-fos levels, whereas the protracted EEG desynchronization corresponding to wakefulness was associated with high c-fos expression.(ABSTRACT TRUNCATED AT 250 WORDS)

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We have previously shown that the local synthesis of two synaptic proteins of 66.5-kDa and 87.6-kDa is selectively enhanced in male adult rats trained for a two-way active avoidance task. We report here that a comparable but not identical response occurs in 2-year-old male rats trained for the same task. In the latter age group, the local synthesis of the 66.5-kDa protein markedly increases in cerebral cortex, brainstem, and cerebellum, with a somewhat lower increment in synthesis of the 87.6-kDa protein. On the other hand, the newly synthesized 87.6-kDa protein correlates with avoidances and escapes and inversely correlates with freezings in cerebral cortex and brainstem, whereas the correlations of the newly synthesized 66.5-kDa protein remain below significance. These correlative patterns are sharply at variance with those present in trained adult rats. Our data confirm that the local system of synaptic protein synthesis is selectively modulated by training and show that the synaptic response of old rats differs from that of adult rats as reflected in behavioral responses.