TY - JOUR
T1 - Projections from auditory cortex to the cochlear nucleus in rats
T2 - Synapses on granule cell dendrites
AU - Weedman, Diana L.
AU - Ryugo, David K.
PY - 1996/7/22
Y1 - 1996/7/22
N2 - Previous work has demonstrated that layer V pyramidal cells of primary auditory cortex project directly to the cochlear nucleus. The postsynaptic targets of these centrifugal projections, however, are not known. For the present study, biotinylated dextran amine, an anterograde tracer, was injected into the auditory cortex of rats, and labeled terminals were examined with light and electron microscopy. Labeled corticobulbar axons and terminals in the cochlear nucleus are found almost exclusively in the granule cell domain, and the terminals appear as boutons (1-2 μm in diameter) or as small mossy fiber endings (2-5 μm in diameter). These cortical endings contain round synaptic vesicles and form asymmetric synapses on hairy dendritic profiles, from which thin (0.1 μm in diameter), nonsynaptic 'hairs' protrude deep into the labeled endings. These postsynaptic dendrites, which are typical of granule cells, surround and receive synapses from large, unlabeled mossy fiber endings containing round synaptic vesicles and are also postsynaptic to unlabeled oxon terminals containing pleomorphic synaptic vesicles. No labeled fibers were observed synapsing on profiles that did not fit the characteristics of granule cell dendrites. We describe a circuit in the auditory system by which ascending information in the cochlear nucleus can be modified directly by descending cortical influences.
AB - Previous work has demonstrated that layer V pyramidal cells of primary auditory cortex project directly to the cochlear nucleus. The postsynaptic targets of these centrifugal projections, however, are not known. For the present study, biotinylated dextran amine, an anterograde tracer, was injected into the auditory cortex of rats, and labeled terminals were examined with light and electron microscopy. Labeled corticobulbar axons and terminals in the cochlear nucleus are found almost exclusively in the granule cell domain, and the terminals appear as boutons (1-2 μm in diameter) or as small mossy fiber endings (2-5 μm in diameter). These cortical endings contain round synaptic vesicles and form asymmetric synapses on hairy dendritic profiles, from which thin (0.1 μm in diameter), nonsynaptic 'hairs' protrude deep into the labeled endings. These postsynaptic dendrites, which are typical of granule cells, surround and receive synapses from large, unlabeled mossy fiber endings containing round synaptic vesicles and are also postsynaptic to unlabeled oxon terminals containing pleomorphic synaptic vesicles. No labeled fibers were observed synapsing on profiles that did not fit the characteristics of granule cell dendrites. We describe a circuit in the auditory system by which ascending information in the cochlear nucleus can be modified directly by descending cortical influences.
KW - centrifugal projections
KW - electron microscopy
KW - hearing
KW - ultrastructure
UR - http://www.scopus.com/inward/record.url?scp=0029783283&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029783283&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1096-9861(19960722)371:2<311::AID-CNE10>3.3.CO;2-U
DO - 10.1002/(SICI)1096-9861(19960722)371:2<311::AID-CNE10>3.3.CO;2-U
M3 - Article
C2 - 8835735
AN - SCOPUS:0029783283
SN - 0021-9967
VL - 371
SP - 311
EP - 324
JO - Journal of Comparative Neurology
JF - Journal of Comparative Neurology
IS - 2
ER -