Involvement of perivascular sensory fibers in the pathophysiology of cerebral vasospasm following subarachnoid hemorrhage

Abstract

The involvement of perivascular sensory fibers containing substance P (SP) and calcitonin gene-related peptide (CGRP) in the events occurring in conjunction with subarachnoid hemorrhage (SAH) has been studied in a rat model. Two days after blood injection, the time point at which maximum vasoconstriction is occurring in this model, immunocytochemistry and radioimmunoassay showed a reduction in SP- and CGRP-like immunoreactivity (LI). The quantitative measurements revealed a significant 50% reduction of CGRP-LI and a slight reduction of SP-LI in SAH as compared to con-trols. This partial reduction in neurotransmitter content (denervation) caused no change in the sensitivity of the rat basilar artery to SP or CGRP as studied using a sensitive in vitro method. However, the maximum relaxant response to CGRP was increased from 52 to 81% (p < 0.05), while there was no change in the maximum SP-induced relaxations. It is suggested that not only a pre-, but also a postsynaptic modulation of perivascular sensory fibers may occur in experimental SAH.