L. Alibardi, Cytology, synaptology and immunocytochemistry of commissural neurons and their putative axonal terminals in the dorsal cochlear nucleus of the rat, ANN ANATOMY, 182(3), 2000, pp. 207-220
The first binaural integration within the auditory system responsible for s
ound localization depends upon commissural neurons that connect the two sym
metrical cochlear nuclei. These cells in the deep polymorphic layer of the
rat dorsal cochlear nucleus were identified with the electron microscope af
ter injection of the retrograde tracer, Wheat Germ Agglutinin conjugated to
Horseradish Peroxydase, into the contralateral cochlear nucleus. Commissur
al neurons are multipolar or bipolar with an oval to fusiform shape. Few co
mmissural neurons, most inhibitory but also excitatory, connect most of the
divisions of the rat cochlear nuclei. The most common type is a glycinergi
c, sometimes GABAergic, moderately large cell. Its ergastoplasm is organize
d into peripheral stacks of cisternae, and few axe-somatic synaptic boutons
are present. Another type of commissural neuron is a medium-sized, spindle
-shaped cell, glycine and GABA-negative, with sparse ergastoplasm and synap
tic coverage. A giant, rare type of commissural neuron is glycine-positive
and GABA-negative, with short peripheral stacks of ergastoplasmic cisternae
. It is covered with synaptic boutons, many of which contain round synaptic
vesicles. Another rare type of commissural neuron is a moderately large ce
ll, oval to fusiform in shape, immunonegative for both glycine and GABA, an
d contacted by many axe-somatic boutons. It contains large dense mitochondr
ia and numerous dense core vesicles of peptidergic type. Some labelled bout
ons, mostly inhibitory and probably derived from commissural neurons, conta
ct pyramidal, cartwheel, giant and tubercule-ventral neurons. The prevalent
inhibition of electrical activity in a cochlear nucleus observed after sti
mulation of the contralateral cochlear nucleus may be due to commissural in
hibitory terminals which contact excitatory neurons such as pyramidal and g
iant cells. Other inhibitory commissural terminals which contact inhibitory
neurons such as cartwheel and tubercule-ventral neurons, may explain the s
timulation of electrical activity in the DCN after contralateral stimulatio
n.