The data on the distribution of catecholaminergic cells and fibers in such
a significant subcortical relay auditory center as the inferior colliculus
(IC) are both few and controversial, and ultrastructural data are lacking.
Young adult mongrel cats of both sexes were used. Following routine prepara
tion procedures, the ultrathin sections were prepared for the ultrastructur
al examination of tyrosine hydroxylase (TH)-like immunoreactivity. TH-posit
ive neuronal perikarya were not detected in the IC. On the other hand, an a
ppreciable number of TH-immunoreactive unmyelinated axons and synaptic bout
ons were found in all subdivisions of the IC, most often in the nucleus ext
ernus, followed by the nucleus pericentralis, and a few were seen in the do
rsomedial part of the central nucleus. The boutons measured 0.5-1.8 mu m, c
ontained pleomorphic synaptic vesicles, and established symmetrical synapti
c contacts almost exclusively with dendrites of small caliber.