title: Anatomical characterization of subcortical descending projections to the inferior colliculus in mouse.
abstract: 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.
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.|Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
authors: Mili B
authors: MB
authors: Patel
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Stacy
authors: S
authors: Sons
authors: Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Georgiy
authors: G
authors: Yudintsev
authors: Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Alexandria M H
authors: AM
authors: Lesicko
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Luye
authors: L
authors: Yang
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Gehad A
authors: GA
authors: Taha
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Scott M
authors: SM
authors: Pierce
authors: Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.|Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors: Daniel A
authors: DA
authors: Llano
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000166:cytology*; D005260:Female; D007091:Image Processing, Computer-Assisted; D007245:Inferior Colliculi / Q000166:cytology*; D008297:Male; D051379:Mice; D018613:Microscopy, Confocal; D009474:Neurons / Q000166:cytology*
keywords: GABA; 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; colliculus; thalamocollicular; thalamotectal; thalamus