The distribution of sympathetic fibers and calcitonine gene related pe
ptide (CGRP)-positive fibers was examine in endolymphatic sac of 10 gu
inea pigs by using immunohistochemical techniques to demonstrate tyros
ine hydroxylase (TH) and CGRP. A meshwork of TH-positive fibers, found
around the sigmoid sinus, sent branches to the distal and the interme
diate parts of the endolymphatic sac. In these areas. TH-positive fibe
rs traveled freely from blood vessels and formed a loose plexus beneat
h the lining epithelium. Such fibers were rare in the proximal portion
of the endolymphatic sac and in the endolymphatic duct. Seven days af
ter elimination of the ipsilateral superior cervical ganglion, some of
the TH-positive fibers were gone, however, there were still a few fib
ers in the endolymphatic sac as well as around the sigmoid sinus, thus
their origin remains obscure. CGRP-positive fibers also branched from
the fibers around the sigmoid sinus, and were distributed throughout
the endolymphatic sac, some occasionally extending to the endolymphati
c duct. They not only formed a dense plexus in the sublining space, bu
t also spread through the lining cell layer. Elimination of the ipsila
teral superior cervical ganglion did not affect the distribution of CG
RP-positive fibers, indicating that they are probably not sympathetic
fibers.