Influence of Nitrous Oxide on Local Cerebral Blood Flow in Awake, Minimally Restrained Rats

In order to evaluate the effect of 70–80% N2O on local cerebral blood flow (l-CBF) in the rat brain, we developed a procedure for measuring CBF by an autoradiographic [14C]iodoantipyrine technique in awake, minimally restrained animals. Results on l-CBF, as measured in 22 different structures, showed little variability between animals. In the majority of structures analyzed, 70–80% N2O failed to alter l-CBF. These included all cerebral cortical and most subcortical structures. However, nitrous oxide reduced CBF in the the inferior colliculus and the superior olive, in two of the limbic structures analyzed, and in the hypothalamus. In no structure, except the striatum ( p < 0.05), was a significant increase in l-CBF obtained in N2O-breathing animals. However, the results suggest that CBF may have been increased in the auditory cortex. Immobilization was found to reduce l-CBF in the cerebellum, inferior colliculus, superior olive, hippocampus, and septal nuclei. The results also suggest that the procedure somewhat increased CBF in frontal and parietal cortex. When the results obtained in awake, air-breathing animals were compared with those obtained in immobilized animals ventilated on N2O, there was no significant increase in any of the structures analyzed, although there were suggested increases in all cortical areas except the visual cortex. However, the data showed that ventilation with 70–80% N2O significantly decreased CBF in several structures (inferior colliculus, superior olive, hippocampus, amygdala, septal nuceli, and hypothalamus). In some of these, the effects of 70–80% N2O and of immobilization were obviously additive.