Stress and local cerebral blood flow: studies on restrained and unrestrained rats

The degree of stress has been compared between two protocols used for the measurement of local cerebral blood flow (LCBF) in conscious rats. The first method involved acute surgical procedures (cannulation of both femoral veins and arteries) under halothane anesthesia. It was followed by a recovery period (2-3 h) during which the rat was before LCBF measurement. The second method employed chronic cannulation of the abdominal aorta and vena cava, allowing the LCBF assays to be performed on freely moving rats. Plasma corticosterone and a glucose tolerance tests showed that the freely moving rats were less stressed than the gently restrained ones. The LCBF of the two groups were not significantly different except in the frontal and parietal cortex, where it was more elevated in the freely moving rats. LCBF may be sensitive to the environmental conditions in freely moving rats whereas these vascular effects may be reduced after 2-3 h of gentle restraint. The two protocols tested in this study could be considered as good methods for studying LCBF in conscious rats, although some stress remained in gently restrained rats. Freely moving rats can be used for behavioural studies providing that the time lag of the arterial samples is taken into account. Since the basal LCBF values of gently restrained rats are minimally affected by the stress inherent in the preparation, this convenient protocol could be considered as useful for numerous investigations.