EFFECT OF NEURONAL NO SYNTHASE INHIBITION ON THE CEREBRAL VASODILATORY RESPONSE TO SOMATOSENSORY STIMULATION

Whether nitric oxide (NO) mediates - or not - the local cerebral blood flow (CBF) increases occurring during functional brain activation is still a controversial issue. In the present study, we sought to determ ine whether neuronal NO synthase is involved in the cerebrovascular re sponse to activation of the trigeminal pathway in the rat. Local CBF w as measured using the autoradiographic [C-14]iodoantipyrine technique in control alpha-chloralose anesthetized rats and 30 min following adm inistration of 7-nitroindazole (7-NI), an inhibitor of the neuronal NO synthase. Unilateral whiskers stroking increased local CBF in all six regions of the trigeminal pathway. Under 7-NI, CBF was slightly decre ased and the vasodilatatory response to whisker stimulation was unalte red in the four trigeminal nuclei studied. In contrast, no significant vasodilatation was noted in the ventral posteromedial thalamic nucleu s and somatosensory cortex. These results suggest that the neuronal NO synthase mediates the hyperemia associated with somatosensory activat ion in second order relay stations but not in the site of termination of primary afferents.