The effect of acetylcholine on neurones of the amphibian nucleus isthmi.

In the bird, histochemical and biochemical data suggest that the tectal input into nucleus isthmi is of a cholinergic nature. In the present study the response of toad (Bufo bufo gargarizans) isthmic neurones to acetylcholine was investigated using conventional extracellular recording techniques and ionophoresis. The results show isthmic cells to be strongly excited by acetylcholine (ACh), whereas neurones in the neighbouring areas show minimal sensitivity. Atropine sulphate completely blocked the response to acetylcholine and greatly decreased activity induced by visual stimulus. The present data show that acetylcholine mimics one of the physiological transmitters in the nucleus isthmi.