Tecto-isthmo-optic transmission in pigeons is mediated by glutamate and nitric oxide

The isthmo-optic nucleus of the centrifugal system in birds receives primar ily input from the ipsilateral tectum and projects to the contralateral ret ina. The present study using brain slices and microiontophoresis shows that synaptic transmission from the tectum to the centrifugal nucleus in pigeon s is excitatory, About 75% of tecto-isthmo-optic fibers are glutamatergic, mediated by alpha -amino-3-hydroxy-5-methyl-4-isoxazole propionic acid but not N-methyl-D-aspartate-receptors, and 25% of others may use nitric oxide as a transmitter or modulator. On the other hand, about 60% of isthmo-optic cells receive glutamatergic afferents, 20% receive nitric oxidergic affere nts, and 20% of others receive both glutamatergic and nitric oxidergic affe rents from the tectum, In the last group, it is more likely that both gluta mate and nitric oxide may cc-release from the same tecto-isthmo-optic termi nals. All the isthmo-optic cells examined in the present study also receive gamma -aminobutyric acid (GABA)ergic afferents via GABA(A) and GABA(B) rec eptors probably from some extratectal structures, (C) 2001 Elsevier Science Inc.