MethodsRadiotelemeters were implanted in nNOS-KO mice and wild type littermates (WT), to provide continuous haemodynamic monitoring. After recovery, mice were placed in cages containing freely rotating voluntary running wheels. Heart rate was measured on a beat to beat basis. Activity state of the mouse for each individual heart beat was determined by logging individual wheel rotations and detecting movement of the animal within the cage. The following activity states were defined: wheel running, cage activity, and rest.