Anatomical characterization of subcortical descending projections to the inferior colliculus in mouse

Descending projections from the thalamus and related structures to the midbrain are evolutionarily highly conserved. However, the basic organization of this auditory thalamotectal pathway has not yet been characterized. The purpose of this study was to obtain a better understanding of the anatomical...

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Bibliographic Details
Published in:Journal of comparative neurology (1911) 2017-03, Vol.525 (4), p.885-900
Main Authors: Patel, Mili B., Sons, Stacy, Yudintsev, Georgiy, Lesicko, Alexandria M.H., Yang, Luye, Taha, Gehad A., Pierce, Scott M., Llano, Daniel A.
Format: Article
Language:English
Subjects:
Animals
Auditory Pathways - cytology
colliculus
Female
GABA
Image Processing, Computer-Assisted
Inferior Colliculi - cytology
Male
Mice
Microscopy, Confocal
Neurons - cytology
RRID: AB_2619710
RRID:AB_2278725
RRID:AB_476667
RRID:AB_476894
RRID:AB_477329
RRID:IMSR_JAX:007677
RRID:SCR_001775
RRID:SCR_003070
RRID:SCR_013286
RRID:SCR_014235
RRID:SCR_014432
thalamocollicular
thalamotectal
thalamus
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Summary:Descending projections from the thalamus and related structures to the midbrain are evolutionarily highly conserved. However, the basic organization of this auditory thalamotectal pathway has not yet been characterized. The purpose of this study was to obtain a better understanding of the anatomical and neurochemical features of this pathway. Analysis of the distributions of retrogradely labeled cells after focal injections of retrograde tracer into the inferior colliculus (IC) of the mouse revealed that most of the subcortical descending projections originated in the brachium of the IC and the paralaminar portions of the auditory thalamus. In addition, the vast majority of thalamotectal cells were found to be negative for the calcium‐binding proteins calbindin, parvalbumin, or calretinin. Using two different strains of GAD‐GFP mice, as well as immunostaining for GABA, we found that a subset of neurons in the brachium of the IC is GABAergic, suggesting that part of this descending pathway is inhibitory. Finally, dual retrograde injections into the IC and amygdala plus corpus striatum as well into the IC and auditory cortex did not reveal any double labeling. These data suggest that the thalamocollicular pathway comprises a unique population of thalamic neurons that do not contain typical calcium‐binding proteins and do not project to other paralaminar thalamic forebrain targets, and that a previously undescribed descending GABAergic pathway emanates from the brachium of the IC. J. Comp. Neurol. 525:885–900, 2017. © 2016 Wiley Periodicals, Inc. The authors characterized a set of pathways from the posterior thalamus and related structures to the auditory midbrain. Among these pathways is a novel inhibitory projection from the brachium of the inferior colliculus to the auditory midbrain. These pathways may be important intermediaries of cortical control over the inferior colliculus.
ISSN:0021-9967
1096-9861
DOI:10.1002/cne.24106