THE interneuronal messenger nitric oxide1,2 (NO) may play a cen-tral role in the processing of olfactory information3. Several circuit elements in the mammalian olfactory bulb contain NO synthase4 or its functional equivalent, NADPH diaphorase5-7. The effects of NO on cellular excitability or circuit dynamics in the olfactory bulb are unknown, although NO effects on other rhythmic cells8 and circuits 9 have been described. I have studied the role of NO in central olfactory processing using the procerebral (PC) lobe, the major central site of odour processing in terrestrial molluscs10,11. As in the mammalian olfactory bulb during odour stimulation, the basic dynamics of electrical activity in the molluscan PC lobe is an oscillation12-14. Here I report an obligatory role for NO in the oscillatory dynamics of the PC lobe of Limax maximus. Nitric oxide mediation of the olfactory oscillation may relate to the highly developed odour sensitivity and odour-learning ability of Limax 15,16.
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