Factors in cerebrospinal fluid affecting motor activity in the rat.

Cerebrospinal fluid (CSF) was obtained from donor rats either during the dark or during the light period of their diurnal cycle, and infused into the lateral ventricle of recipient rats. Infusing recipient rats during their dark period with CSF from light-exposed donors reduced the motor activity, whereas, conversely, infusing them during their light period with CSF from dark-exposed rats increased the motor activity. Humoral factors may serve to regulate the level of motor activity and vigilance.