Normal and Physio-Pathological Striatal Dopamine Homeostasis

The neurotransmitter Dopamine (DA) exerts a dual function in the striatum (STR), the latter comprising the caudate and putamen nuclei, the main structures in the central nervous system from which it is released. During the last 50 years, numerous studies have highlighted the role of DA in sensory/motor loops. Along with a phasic function exerted in synaptic or close apposition structures, a modulatory role for extracellular DA has also been demonstrated based on the slow and tonic extracellular diffusion of the amine. This duality is probably supported by a metabolic polymorphism, particularly of the release mechanism. The present chapter focuses on works carried out in vivo over the last two decades on the control of DA homeostasis in the STR during normal and pathological conditions. It is now generally accepted that the level of extracellular DA is not simply the consequence of dribbling from the synapse after phasic (firing-dependent) overflow but is maintained through tonic, largely non–synaptic, regulatory processes.