Circadian synaptic plasticity in the mouse barrel cortex

Mice show circadian rhythms in behaviour and metabolic processes but also in neuronal plasticity associated with the sensory input to the whisker representations in the somatosensory (barrel) cortex. We analyzed daily structural changes in the barrel cortex of the C57/BL mice in a light/dark (LD 12:12) regime and in constant darkness (DD). Using serial EM sections of the barrel cortex of mice sacrificed during their active or rest period, we observed up-regulation of the density of excitatory synapses located on single-synapse spines during the rest period in LD 12:12 and an increase in the density of inhibitory synapses located on double-synapse spines during the active period in LD 12:12 and DD. In conclusion, the mouse barrel cortex shows daily changes in the density of synapses and dendritic spines similar to the daily pattern of locomotor activity of the animals. Moreover, the excitatory and inhibitory synapses are differently regulated during the day/night cycle. This example of plasticity seems to be regulated by both, the circadian clock and light. Supported by a grant to MJ (2011/01/D/NZ3/00207).