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We investigated the influence of modulating NO synthesis on oscillatory components of ON and OFF evoked field potentials in developing rat superior colliculus. Nitric oxide (NO) is involved in neuronal transmission by adjusting neurotransmitter release in adults and in stabilizing synaptic connections in developing brains. NO synthesis was decreased by inhibiting nitric oxide synthase (NOS) with an acute microinjection of N-nitro-l-arginine methyl ester (l-NAME); whereas NO synthesis was augmented by an acute microinjection of l-arginine (l-ARG). The study is focused on rhythmic activity by analyzing fast Fourier transform (FFT). Collicular responses were recorded in anesthetized rats, at post-natal days (PND) 13–19 and adults. This time window was chosen because it is centered on eye opening. NO down- and upregulation resulted in a dual effect depending on age and response-type. NO synthesis inhibition decreased the magnitude of oscillations in ON responses in the youngest animals (PND13–PND14), whereas oscillations of frequencies higher than 20 Hz in OFF responses were increased in all age groups of developing rats. In adults NO downregulation increased oscillations in ON responses and decreased oscillations in OFF responses. l-arginine application produced effects opposite to those seen with l-NAME. Our data together with results reported in the literature suggest that the temporal patterns of the evoked activity are NO-dependent. This sculpting action of the evoked firing may play a role in the synchronization of action potentials in afferent axons which in turn contributes to synaptic stabilization. [Copyright &y& Elsevier]