Substance P-like immunoreactivity in rat forebrain leptomeninges and cerebral vessels originates from the trigeminal but not sympathetic ganglia.

Substance P-like immunoreactivity (SPLI) is present in the pia mater, arachnoid and pial vessels (leptomeninges) of the rat. Unilateral electrolytic lesions of the trigeminal ganglion decreased levels of SPLI in leptomeninges on the lesioned side. Levels did not change following unilateral or bilateral superior cervical ganglionectomies or after i.c.v. injections of 6-hydroxydopamine, sufficient to deplete norepinephrine in pial arteries by more than 90%. SP levels did not decrease in leptomeninges or in blood vessels within the circle of Willis following treatment of adult or neonatal rats with capsaicin despite the fact that levels were reduced in the cornea and dorsal spinal cord in these same animals. These results suggest that not all substance P-containing sensory fibers are susceptible to the peptide-depleting effects of capsaicin.