Tryptophan hydroxylase activity in rat brain base arteries related to innervation originating from the dorsal raphe nucleus.

BACKGROUND AND PURPOSE Tryptophan hydroxylase activity was assayed in cell-free extracts of rat brain base arteries as marker of a serotonergic innervation. METHODS Estimation of the enzymatic activity was made in untreated male Sprague-Dawley rats (n = 53) and in those who underwent destruction of the dorsal and median raphe nuclei (n = 10). RESULTS Tryptophan hydroxylase activity was measured in rat cerebral arteries. The time-dependent 5-hydroxytryptophan production was undetectable in the absence of tryptophan or 6-methyltetrahydropterine and in the presence of 6-fluorotryptophan, and it was significantly reduced in the presence of p-chlorophenylalanine. Destruction of the dorsal raphe nucleus but not the median raphe nucleus brought about a significant reduction in enzyme activity. CONCLUSIONS These results suggest that rat cerebral arteries receive a serotonergic innervation arising from the dorsal raphe nucleus.