The relation between motor activity and [3H]uridine uptake in the mouse brain

Using microautoradiography ex vivo we tested the effect of forced running on a roller drum for 3 h on the nuclear incorporation of [5-(3) H uridine] in mouse brain. Specific neuron types with increased nuclear labelling included primary motor cortex layer 5 nerve cells with nuclei greater than 12 mu m (+38%) and large neuron nuclei in putamen (+58%). Mice running for 45 min do not show any change in the labelling of nerve cell nuclei compared with mice moving freely in the cage. The [H-3]uridine uptake in other cell types, e.g. other neurons in cortical layer 5, neurons in sensory cortex and in the other cell layers in motor cortex, were not different from control mice. We conclude that RNA synthesis is normally low in adult mouse brain, but that physical exercise stimulates RNA synthesis in specific populations of large neurons in the motor system.