Regional differences in mechanisms of cerebral circulatory response to neuronal activation

Vibrissal stimulation raises cerebral blood flow (CBF) in the ipsilateral s pinal and principal sensory trigeminal nuclei and contralateral ventroposte romedial (VPM) thalamic nucleus and barrel cortex. To investigate possible roles of adenosine and nitric oxide (NO) in these increases, local CBF was determined during unilateral vibrissal stimulation in unanesthetized rats a fter adenosine receptor blockade with caffeine or NO synthase inhibition wi th N-G-nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI). Ca ffeine lowered baseline CBF in all structures but reduced the percent incre ase during stimulation only in the two trigeminal nuclei. L-NAME and 7-NI l owered baseline CBF but reduced the percent increase during stimulation onl y in the higher stations of this sensory pathway, i.e., L-NAME in the VPM n ucleus and 7-NI in both the VPM nucleus and barrel cortex. Combinations of caffeine with 7-NI or L-NAME did not have additive effects, and none alone or in combination completely eliminated functional activation of CBF. These results suggest that caffeine-sensitive and NO-dependent mechanisms are in volved but with different regional distributions, and neither fully account s for the functional activation of CBF.