Abstract
Background: The pioneering work of Robert F. Furchgott, Luis J. Ignaro and Ferid Murad has led us to investigate whether nitric oxide (NO) is present in the brain, its origin and whether it possesses a functional role in brain structures. This review is mainly an outline of own findings obtained by using the push-pull superfusion technique. Method: We have used the push-pull superfusion technique that makes it possible to determine quantitatively endogenous transmitters released from their neurons in the synaptic cleft. In some experiments, a NO sensor was inserted into the pushpull cannula for online determination of NO released in the synaptic cleft together with neurotransmitters. Results: The release rates of endogenous NO are not constant but oscillate according to an ultradian rhythm with an apparent frequency of about 24 min per cycle. Similar rhythmic changes have been found in the release of neurotransmitters in several brain regions, as well as in the EEG delta band. Endogenous NO modulates the release of acetylcholine, glutamate, aspartate, GABA, serotonin, histamine in distinct brain areas. The release of adenosine is also increased by NO suggesting the synchronous release of ATP. Endogenous NO influences various brain functions such as blood pressure regulation and responses to stress. Recordings of evoked potentials revealed that NO plays a crucial role in the integration of afferent signals. Furthermore, NO in involved in amphetamine-induced neurotoxicity. Conclusion: The multifarious influences of endogenous NO on central neuronal activity, brain functions and integration of afferent signals underpin its universal modulatory role in the brain.
Keywords: Endogenous nitric oxide (NO), push-pull superfusion, serotonin, acetylcholine, GABA, ultradian rhythm, oscillatory release, blood pressure regulation, evoked potentials.
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