Abstract
Heart rate and locomotor activity of rats kept under 12L/12D illumination regimen was recorded every six minutes for ten days using implantable radio transmitters. Some of the rats then received bilateral radio frequency lesions into the suprachiasmatic nucleus (SCN). Control sham operations were performed on the rest of the animals. After recovery from surgery, recording of heart rate and locomotor activity was continued for ten days. SCN lesioned rats showed no significant diurnal fluctuation in heart rate, while normal and sham operated rats showed the normal diurnal rhythm in that function. The arrhythmic diurnal heart rate pattern of SCN rats appeared to be correlated to their sparadic activity pattern. The integrity of the suprachiasmatic nucleus therefore is necessary for the generation and/or the expression of diurnal rhythmicity in heart rate in the rat.