title: Independent tonotopy and thalamocortical projection patterns in two adjacent parts of the classical primary auditory cortex in mice.
abstract: Amid recent amendment of delineation of a mouse auditory cortical map, a caudal auditory field, originally defined as the primary auditory cortex (AI), was divided into the AI and dorsomedial field (DM), based on distinct high frequency areas. A low frequency area was not previously established in the DM because responses to low frequency tones were weak in this area. This may lead to the misconception that the DM is an atypical region that lacks a low frequency band. In the current study, we confirmed that the DM has a low frequency area that is completely independent from the AI. First, we conducted flavoprotein fluorescence imaging with improved signal to noise ratio and revealed the presence of two separated low frequency areas in the AI and DM. Next, we injected a retrograde neural tracer along the tonotopic axis of the AI or DM to reveal the thalamic origins in the ventral division of the medial geniculate body (MGv). We found that neurons projecting to low frequency areas of the AI and DM occupied different locations within the MGv and mutually independent topographic organizations consisting of thalamic neurons projecting to the AI or DM. These results indicate that the AI and DM have distinct low frequency areas with distinct thalamic projections from the MGv. Our findings reaffirm that the AI and DM should be regarded as independent regions in the mouse auditory cortex.
authors.affiliation: Department of Neurophysiology, Brain Research Institute, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8585, Japan. Electronic address: tsukano-nii@umin.ac.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tsukano
authors.affiliation: Division of Neurobiology and Anatomy, Graduate School of Medicine and Dental Sciences, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Horie
authors.affiliation: Department of Otolaryngology, Graduate School of Medicine and Dental Sciences, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
authors.forename: Kuniyuki
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Neurophysiology, Brain Research Institute, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8585, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Hishida
authors.affiliation: Division of Neurobiology and Anatomy, Graduate School of Medicine and Dental Sciences, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8510, Japan.
authors.forename: Hirohide
authors.initials: H
authors.lastname: Takebayashi
authors.affiliation: Department of Neurophysiology, Brain Research Institute, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata 951-8585, Japan.
authors.forename: Katsuei
authors.initials: K
authors.lastname: Shibuki
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology*; D005829:Geniculate Bodies / Q000502:physiology*; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*
keywords: Dorsomedial field; Medial geniculate body; Mice; Primary auditory cortex; Tonotopy; Topology