Somatosensory pain does not affect total cerebral blood volume.

The effect of somatosensory pain on the total cerebral blood volume was investigated in anesthetized rats. Our results show for the first time that total cerebral blood volume remains unaltered in both brain hemispheres during 2.5 min noxious stimulation of the sensory C-fibres of the sciatic nerve. Regional cerebral blood flow was increased by 97% in the thalamus and by 47% in the hypothalamus at the same time. Blockade of the L-arginine-nitric oxide system reduced significantly the steady-state control level of total cerebral blood volume (i.l.: from 5.7+/-1.3 to 4.58+/-1.6 vol%, c.l.: from 5.0+/-0.6 to 4.24+/-0.9 vol%). Nitric oxide synthase blockade, however, did not affect either the stimulation induced increase of regional cerebral blood flow or the steadiness of total cerebral blood volume during the stimulation.