Ms. Malmierca et al., THE TOPOGRAPHICAL ORGANIZATION OF DESCENDING PROJECTIONS FROM THE CENTRAL NUCLEUS OF THE INFERIOR COLLICULUS IN GUINEA-PIG, Hearing research, 93(1-2), 1996, pp. 167-180
We describe the descending projections from the central nucleus of the
inferior colliculus (CMC) in guinea pig. Focal injections of the trac
er biocytin, made in physiologically defined frequency regions of the
CNIC, labelled laminated axonal terminal fields in the ipsilateral dor
sal nucleus of the lateral lemniscus, and bilaterally in the ventral n
ucleus of the trapezoid body and the dorsal cochlear nucleus. Labellin
g was also present in the rostral periolivary nucleus, but we could no
t distinguish a clear border between the terminal fields in this nucle
us and those in the ventral nucleus of the trapezoid body. Labelling o
bserved in the ventral nucleus of the lateral lemniscus, and to a less
er extent in the dorsal nucleus of the lateral lemniscus, was accompan
ied by retrogradely labelled somata and therefore we cannot conclude u
nequivocally that the CNIC projects to these lemniscal nuclei. Where t
he labelling was ordered topographically, its position varied as a fun
ction of the best frequency at the injection site. High-frequency regi
ons in the CNIC project to the medial parts of the ventral nucleus of
the trapezoid body and dorsal cochlear nucleus, while low-frequency re
gions in the CNIC project to the lateral parts of the ventral nucleus
of the trapezoid body and dorsal cochlear nucleus. Additional axonal l
abelling with terminal boutons, but with no apparent topographical arr
angement, was present in the ipsilateral horizontal cell group, sagulu
m, and also bilaterally in the superficial granule cell layer of the v
entral cochlear nucleus and layer 2 of the dorsal cochlear nucleus. Ou
r findings are consistent with the existence of tonotopically organise
d feedback projections from the CNIC to the brainstem nuclei that proj
ect to it.