Structure of the Gaba-Ergic Inhibitory System in the Chicken Auditory Pathway Revealed by Immunocytochemistry

Abstract

The auditory system of birds has been shown to be an advantageous model to study audition in a higher vertebrate. From a neuroethologists view this notion is supported by the fact that birds, especially songbirds, have evolved a strikingly complex repertoire of communicative sounds which they use for intraspecific communication. The accuracy of sound analysis is also very similar to what is known from studies in mammals, including man (Dooling et al., 1975). The auditory pathway of birds has been shown to share multiple similarities with the mammalian auditory system. This includes not only the presence of comparable auditory nuclei (Boord, 1969), but also similar interconnectivities (Boord, 1969; Bonke et al., 1979). Due to the recent progress in immunocytochemistry it has become feasible to further characterize the structure of nuclei in the central nervous system by labeling neurons with a known transmitter content. Such studies can guide physiological experiments aimed at the function of neuronal circuits. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is present in a number of structures involved in sensory processing and has recently been shown to play an important role in telencephalic auditory processing in the chicken (Müller and Scheich 1987). I used the method of immunocytochemistry to describe the distribution of GABAergic perikarya and nerve terminals in the entire auditory pathway of the chicken. The results point out the importance of GABA as a neurotransmitter at all levels of auditory processing in the avian auditory pathway.