The pattern of cerebrovascular substance P (SP)-and calcitonin gene-related peptide (CGRP)-immunoreactive (IR) innervation was investigated in the quail. SP-and CGRP-IR nerves were relatively a few in the rostral part of the anterior circulation, and very scanty or lacking in its caudal part and the whole of the posterior circulation. A significant finding was that the anterior circulation in the majority of individuals is furnished with a varying proportion of SP-IR nerves with or without CGRP

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... immunoreactivity. There was a good correlation in the expression of CGRP immunoreactivity between SP-IR cells in the ophthalmic division of the trigeminal ganglion and SP-IR nerves supplying the major cerebral arteries. In the quail, SP-and CGRP-IR fiber bundles are usually present in the internal ethmoidal artery (IEA). From these and other findings, it is most probable that cerebral perivascular SP-and CGRP-IR nerves are mainly derived from the same categories of neurons in the primary sensory ganglion via the IEA. The close association of varicose SP-IR axons to the nerve cells in the pial arteries suggests that these intrinsic neurons may play some vasocontrolling roles through the modulatory effect of their pericellular SP-IR axons.-KEY WORDS: calcitonin gene-related peptide, cerebral artery, innervation, quail, substance P.