Abstract
ObjectivesEcholocating bats show remarkable specialization which is related to analysis of echoes of biosonars in subcortical auditory brainstem pathways. The inferior colliculus (IC) receives inputs from all lower brainstem auditory nuclei, i.e., cochlear nuclei, nuclei of the lateral lemniscus, and superior olivary complex, and create de novo responses to sound, which is considered crucial for echolocation. Inside the central nucleus of the IC (ICC), small domains which receive specific combination of extrinsic inputs are the basis of integration of sound information. In addition to extrinsic inputs, each domain is interconnected by local IC neurons but the cell types related to the interconnection are not well‐understood. The primary objective of the current study is to examine whether the ascending inputs are reorganized and terminate in microdomains inside the ICC.MethodsWe made injection of a retrograde tracer into different parts of the ICC, and analyzed distribution of retrogradely labeled cells in the auditory brainstem of Japanese house bat (Pipistrellus abramus).ResultsPattern of ascending projections from brainstem nuclei was similar to other bat species. Percentages of labeled cells in several nuclei were correlated each other. Furthermore, within the IC, we identified that large GABAergic (LG) and glutamatergic neurons made long‐range connection.ConclusionsSynaptic organization of IC of Japanese house bat shows specialization which is likely to relate for echolocation. Input nuclei to the IC make clusters which terminate in specific part of the ICC, implying the presence of microdomains. LG neurons have roles for binding IC microdomains.
Highlights
Echolocating bats emit sound pulses with specific acoustical features to targets, and measure the distance to the target according to the echoes of the sound pulses
To analyze the echoes and pulses themselves, auditory nuclei of bats are remarkably hypertrophied (Zook & Casseday, 1982a), and show specialization related to echolocation (Covey & Casseday, 1995), which is obvious in the medial superior olive (MSO) of the superior olivary complex (SOC) (Casseday, Covey, & Vater, 1988; Covey, Vater, & Casseday, 1991; Grothe, Park, & Schuller, 1997; Grothe, Schweizer, Pollak, Schuller, & Rosemann, 1994) and monaural nuclei of the lateral lemniscus, namely intermediate nucleus (ILL) and compact and multipolar cell divisions of ventral nucleus (VLLc and VLLm) (Covey & Casseday, 1991)
We found that composition of brainstem input sources is related to the location inside the ICC
Summary
Echolocating bats emit sound pulses with specific acoustical features to targets, and measure the distance to the target according to the echoes of the sound pulses. We made injection of fluorogold (FG), a retrograde tracer, into different parts of the ICC, and analyzed distribution of retrogradely labeled cells in the entire auditory brainstem pathways of Japanese house bat (Pipistrellus abramus), which uses frequency modulated (FM) pulses for echolocation, to examine whether the ascending inputs are reorganized and terminate in small domains inside the ICC. By analyzing the distribution of retrogradely labeled cells inside the IC, we identified cell types that make long-range intrinsic connection inside the IC This species have been used frequently on biosonar studies (Fujioka et al, 2014; Sumiya, Fujioka, Motoi, Kondo, & Hiryu, 2017; Takahashi et al, 2014; Yamada, Hiryu, & Watanabe, 2016), the information about the organization of auditory pathways of this species has not been reported except for a single unit recording study from the IC Our study will give new neuroethological insights on biosonar
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
