GAD‐ and GABA‐immunoreactivity in the ascending auditory pathway of horseshoe and mustached bats

Abstract

A comparative study of the immunostain to antibodies directed against glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) in the ascending auditory pathway was carried out in horseshoe bats (Rhinolophus rouxi) and mustached bats (Pteronotus parnellii). In both species GAD/GABA-positive puncta (presumed axonal boutons) and GAD/GABA-positive cells were found in the cochlear nucleus, the superior olivary complex, the nuclei of the lateral lemniscus the inferior colliculus, and the medial geniculate body. General features of the immunostaining pattern in the auditory pathway agree with observations in other mammals. Quantitative analysis of puncta distribution shows that many auditory centers are characterized by subregional differences in puncta density and distribution. This indicates local differences in putatively inhibitory input related to connectivity and tonotopic organization. The following species characteristic features were found: 1) The dorsal non-laminated portion of the dorsal cochlear nucleus in horseshoe bats lacks the GAD/GABA-immunoreactive cells typical for the ventral laminated portion and the dorsal cochlear nucleus of other species. Clearly, a cytoarchitectonic specialization is accompanied by a loss of putatively GABAergic local inhibitory circuits. 2) The ventral division of the medial geniculate body of the mustached bat lacks GAD/GABA-immunopositive cells. Such cells are present in the horseshoe bat and other mammals. This finding implies functional differences in the organization of the medial geniculate body within the same mammalian order.

Organization of projection from brainstem auditory nuclei to the inferior colliculus of Japanese house bat (Pipistrellus abramus)

“…No signal was detected in rat brain sections incubated with the antibody (1:3,000) preabsorbed with recombinant rat GAD67 protein (180 μg/ml). Furthermore, the staining pattern of the antibody was consistent with that in a previous study (Vater, Kossl, & Horn, 1992). …”

“…In the MSO of horseshoe and mustache bats, GABAergic neurons are sparsely present (Vater et al., 1992), while they are virtually absent in Japanese house bat (Ito et al., unpublished observation). Together, in horseshoe and mustache bats, MSO makes both excitatory and inhibitory influence on the IC in the same side, while in Japanese house bat it make excitatory influence on the bilateral IC.…”

The functional role of GABA and glycine in monaural and binaural processing in the inferior colliculus of horseshoe bats

“…The IC contains a significant proportion of GABAimmunoreactive cells which appear to encompass subclasses of disc-shaped and stellate cells (review: Oliver and Shneiderman 1991; horseshoe bat: Vater et al 1992b). Although direct evidence needs to be obtained, such cells could participate in local interactions within and across isofrequency laminae, thus contributing to inhibition observed at BF and in lateral sidebands of the tuning curves of single units.…”

“…In horseshoe bats, as in other mammals, the DNLL is composed of GABAergic projection neurons providing bilateral feedforward inhibition to the IC (cat: Adams and Mugnaini 1984;Shneiderman et al 1988;horseshoe bat: Vater et al 1990a). The intermediate nucleus and parts of the ventral nucleus of the lateral lemniscus and the LSO contain GABA-immunoreactive cell types which might include neurons projecting to the IC (Vater et al 1992b). Furthermore, the input from the contralateral IC (Schweizer 1981) might carry inhibitory components.…”

Influence of Benzodiazepines on Auditory Perception

“…GABA, the main inhibitory neurotransmitter of the central nervous system (Sivilotti and Nistri, 1991), is also largely present in the auditory system. A number of investigators have shown that neurons, fibers, and terminals containing GABA or its synthesizing enzyme glutamic acid decarboxylase are present in auditory structures at every level from the cochlear nucleus to the thalamus (eg Adams and Mugnaini, 1984;Muganini and Oertel, 1985;Thompson et al, 1985;Wenthold et al, 1986;Peyret et al, 1986;Moore and Moore, 1987;Helfert et al, 1989;Dupont et al, 1990, Vater et al, 1992Wynne et al, 1995, Fubara et al, 1996, as well as in the auditory cortex (eg Winer, 1986).…”