Administration of the NO-generating substance sodium nitrite to conscious non-immobilized rabbits at a dose of 11 mg/kg (s.c.) decreased the intensity and duration of the short-latency "modality-specific" components of the responses of neurons in the visual cortex (to flashes of light) and sensorimotor cortex (to pain reinforcement). Decreases in neuron activation in the visual cortex in response to flashes of light occurred independently of their biological significance. i.e., as the signal for a defensive reflex and on the background of conditioned inhibition. The long-latency activatory components of the response of sensorimotor and visual cortex neurons to pain reinforcement, the inhibitory pause in the responses of visual cortex neurons to flashes of light, and the disinhibitory effect of pain reinforcement showed smaller changes after sodium nitrite. The results obtained here support the suggestion that different neuromediators are involved in transmitting "modality-specific" and "modality-non-specific" influences to neocortical neurons during learning, and provide the basis for suggesting that sodium nitrite has a neurotropic action when given systemically.