Effect of sciatic nerve stimulation on pial arterioles in rats

The present study documents the microvascular response of the pial circulation in sensory hindlimb cortex to sciatic nerve stimulation. Rats, anesthetized with alpha-chloralose and urethan, were equipped with closed cranial windows, and pial arteriolar diameter was measured during stimulation of the contralateral sciatic nerve. The effects of varying stimulus frequency, intensity, and duration were examined. Optimal stimulus frequency was 5 Hz, but response diminished significantly beyond 10 Hz. Optimal stimulus intensity was 0.2 V. At higher stimulus strength, arteriolar dilation was reduced, but systemic blood pressure rose significantly. At low stimulus frequency and intensities, pial arterioles responded to stimulation with a consistent pattern: initial delay of 1.4 s followed by abrupt dilation to a peak magnitude, subsequent decline to a lesser but still dilated state, and recovery to a resting diameter after the cessation of stimulation. No consistent response profile was discernible at high stimulus intensity and/or frequency. This vasodilatory response was discretely restricted to a limited number of arterioles, confined to the hindlimb somatosensory cortex as confirmed by sensory evoked response. The response of the pial circulation provides a well-characterized model for analysis of brain microcirculation, which presumably is linked to cerebral metabolism.