SENSITIVITY OF AVIAN MESENCEPHALIC NEURONS TO AMINO ACIDS

It has been shown that in the avian optic tectum, L-glutamate may be an excitatory transmitter, whereas glycine and γ-aminobutyric acid (GABA) may be inhibitory transmitters. Tritiated glycine injections in the avian tectum label the cell bodies within the nucleus isthmus pars parvocellularis (Ipc). Electrical stimulation of Ipc results in the release of exogenous and endogenous glycine into tectal perfusate. It is, therefore, suggested that the isthmotectal pathway uses glycine as its transmitter. Tectal injections of of tritiated GABA also label Ipc cell bodies, indicating that the isthmotectal projection contains GABAergic fibers.