Functional organization of the dorsal cochlear nucleus of the horseshoe bat (Rhinolophus rouxi) studied by GABA and glycine immunocytochemistry and electron microscopy

Unique among mammals, the dorsal cochlear nucleus (DCN) of horseshoe bats c onsists of two functionally and anatomically distinct subdivisions: a lamin ated ventral portion that processes the frequency range below the constant frequency (CF) component of the echolocation signal and a nonlaminated dors al portion that is specialized for processing the CF-signal range (76 kHz a nd higher). Using conventional transmission electron microscopy and postemb edding immunocytochemistry for the inhibitory neurotransmitters GABA and gl ycine on semithin-alternating sections, we present further evidence that th e ventral laminated subdivision of DCN conserves the main elements of micro circuitry and GABA/glycine labeling patterns typical for the mammalian DCN: (i) the main cell types and synaptic inventory of the granule cell/cartwhe el cell system of the superficial layers are present as well as (ii) the tu berculoventral cell system of the deep layers. The nonlaminated dorsal subd ivision lacks the granule cell/cartwheel cell system and is composed of a m ixture of fusiform projection neurons with tuberculoventral cell analogues. Thus the inhibitory tuberculoventral system known to play an important rol e in temporal and spectral processing in VCN is conserved throughout the DC N of horseshoe bats, whereas functional components of cerebellar-like circu its are reduced in a specialized region that processes the dominant biosona r component.