Excitatory and inhibitory transmission from the optic tectum to nucleus isthmi and its vicinity in amphibians.

Intracellular recordings were made from nucleus isthmi (NI) and its vicinity in toads (Bufo bufo gargarizans) in response to electrical stimulation of the bilateral optic tract. The results suggest that NI mainly receives its excitatory input from the ipsilateral tectum and its inhibitory input from the contralateral tectum. Tegmental cells in a region medioventral to NI were usually characterized by strong spontaneous activity and an excitatory-inhibitory sequence of postsynaptic potentials in response to stimulation of either side of the bilateral optic tract. Sixty of the recorded cells were stained with Lucifer yellow to show their morphological features and anatomical positions within NI and its vicinity.