Effects of treadmill activity on cerebellar cyclic GMP

Ovariectomized, female Sprague-Dawley rats were trained to run on a treadmill for up to several minutes. On the day of the experiment the treadmill speed was adjusted to either 680, 1360 or 2720 cm/minute and separate groups of 5 rats were required to run at each of these speeds for either 15, 30, 45 or 60 seconds. Immediately after running on the treadmill, each rat was killed by microwave irradiation, and the cerebellum was collected for subsequent determination of cyclic guanosine monophosphate (cGMP). The time to the onset of an elevation of cGMP and the maximal elevation obtained were functions of the speed of running. The first significant increase in cerebellar cGMP over that observed in inactive control rats occurred within 15 seconds after the onset of running. Regardless of the speed of running, the cGMP content reached a plateau after 45 seconds.