Injection of nicotine into the superior colliculus facilitates occurrence of express saccades in monkeys

To clarify the role of cholinergic inputs to the intermediate layer of the superior colliculus (SC), we examined the effect of microinjection of nicotine into the SC on visually guided saccades in macaque monkeys. After injection of 0.4-2 mu l of 1-100 mM nicotine into the SC, frequency of extremely short latency saccades (express saccades; reaction time =70-120 ms) dramatically increased, for the saccades the direction and amplitude of which were represented at the location of the injection site on the collicular map. However, no marked change was observed for the relationship between the peak velocities and the amplitudes of saccades. These results suggested that activation of nicotinic acetylcholine receptors in the SC can facilitate initiation hut causes no major change in dynamics of visually guided saccades.