Patterns of γ‐aminobutyric acid and glycine immunoreactivities reflect structural and functional differences of the cat lateral lemniscal nuclei

The three nuclei of the cat lateral lemniscus (dorsal, intermediate, and ventral) were distinguished by their immunoreactivities for the putative inhibitory transmitters, γ‐aminobutyric acid (GABA) and glycine. Each nucleus had a distinct pattern of somatic and perisomatic labeling. The dorsal nucleus contained mostly GABA‐immunoreactive neurons (85%), with moderate numbers of GABA‐ and glycine‐immunoreactive puncta along their somata. The remaining neurons were nonimmunoreactive (15%). The intermediate nucleus contained mostly nonimmunoreactive neurons (82%), and these had numerous glycine‐immunoreactive and few GABA‐immunoreactive perisomatic puncta. The remaining neurons were immunoreactive for GABA only (10%), glycine only (2%), or both (6%). The ventral nucleus contained mostly glycine‐immunoreactive neurons (81%), and about half of these were also GABA‐immunoreactive. The remaining neurons were either nonimmunoreactive (8%) or GABA‐immunoreactive only (11%). Neurons in the ventral nucleus had fewer immunoreactive perisomatic puncta than neurons in either the dorsal or the intermediate nuclei. These differences in neuronal immunoreactivity and in the relative abundance of GABA‐and glycine‐immunoreactive perisomatic puncta among the three nuclei of the lateral lemniscus support connectional and electrophysiological evidence that each nucleus has a different functional role in auditory processing. In particular, this study demonstrates that the intermediate nucleus of the cat is cytochemically distinct from the dorsal and ventral nuclei in terms of the somatic and perisomatic immunoreactivity of its neurons for these two important inhibitory transmitters and may provide novel inputs to the inferior colliculus. J. Comp. Neurol. 389:264–276, 1997. © 1997 Wiley‐Liss, Inc.