Nitric Oxide Modulation of the Basal Ganglia Circuitry: Therapeutic Implication for Parkinson's Disease and Other Motor Disorders

Several recent studies have emphasized a crucial role for the nitrergic system in movement control and the pathophysiology of the basal ganglia (BG). These observations are supported by anatomical evidence demonstrating the presence of nitric oxide synthase (NOS) in all the basal ganglia nuclei. In fact, nitrergic terminals have been reported to make synaptic contacts with both substantia nigra dopamine-containing neurons and their terminal areas such as the striatum, the globus pallidus and the subthalamus. These brain areas contain a high expression of nitric oxide (NO)-producing neurons, with the striatum having the greatest number, together with important NO afferent input. In this paper, the distribution of NO in the BG nuclei will be described. Furthermore, evidence demonstrating the nitrergic control of BG activity will be reviewed. The new avenues that the increasing knowledge of NO in motor control has opened for exploring the pathophysiology and pharmacology of Parkinson's disease and other movement disorders will be discussed. For example, inhibition of striatal NO/guanosine monophosphate signal pathway by phosphodiesterases seems to be effective in levodopa-induced dyskinesia. However, the results of experimental studies have to be interpreted with caution given the complexities of nitrergic signalling and the limitations of animal models. Nevertheless, the NO system represents a promising pharmacological intervention for treating Parkinson's disease and related disorders.