Neural basis for regulation of cochlear blood flow: Peptidergic and adrenergic innervation of the spiral modiolar artery of the guinea pig

The spiral modiolar artery is the terminal artery in the cochlea, and as such is expected to play a major role in the control of cochlear blood flow. In this study, we examined the distribution of adrenergic and peptidergic nerve fibres on the spiral modiolar artery of the guinea pig using histofluorescence and immunofluorescence techniques. The spiral modiolar artery was dissected from the modiolus so that the entire length of the vessel and its branches, could be observed. Noradrenaline was identified using the glyoxylic acid histofluorescence technique. The presence of the vasoactive peptides substance P, calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), was investigated using antibodies against these peptides. Each putative transmitter tested yielded labelled nerve fibres throughout the length of the spiral modiolar artery and its branches. Double-labelling experiments confirmed that CGRP and substance P are contained in the same fibres but that VIP and substance P appear to be contained in different populations of fibres. These results establish that nerve fibres containing vasoactive peptides and noradrenaline supply the spiral modiolar artery and suggest that they are involved in the regulation of cochlear blood flow.