NITRIC-OXIDE PRODUCTION BY BRAIN-STEM NEURONS IS REQUIRED FOR NORMAL PERFORMANCE OF EYE-MOVEMENTS IN ALERT ANIMALS

Although nitric oxide (NO) is produced by discrete groups of neurons i n the brain, participation of NO in premotor structures directly invol ved in reflexively evoked, sensory-motor functions has not been demons trated so far. We now show that NO is a physiological mediator in the generation of a specific motor response in alert behaving animals. In the oculomotor system, numerous neurons expressing nitric oxide syntha se (NOS) are located in the prepositus hypoglossi, a nucleus involved in the control of horizontal eye movements. Unilateral inhibition of N OS within this nucleus results in severe ocular nystagmus with slow ph ases directed to the contralateral side. Accordingly, local increases of NO or cyclic GMP produced a nystagmus in the opposite direction. It is concluded that a balanced production of NO by prepositus hypogloss i neurons is a necessary condition for the normal performance of eye m ovements in alert animals.