The differential distribution of the diverse dopaminergic systems indicates that dopamine influences a variety of brain functions. For instance, dopamine is involved in the modulation of arterial blood-flow, higher brain functions like cognition and learning and in anxiety-related behavior. Therefore it is not surpris ing that the dopaminergic systems serve as a target for antipsychotic drugs, i.e. in schizophrenia treatment. The classic domain for dopamine substitution, however, is Parkinsonism, where a degeneration of dopaminergic neurons in the substantia nigra is causal for the disease.
The nigro-striatal system is concerned with the initiation and maintenance of motor behavior. The mesolimbic and mesocortical systems appear to be involved in goal-directed and reward-mediated behavior and in motivation-dependent behavior. A dysfunction in these systems alters normal associative processes.
An enhancement of dopaminergic transmission in the mesolimbic system is linked with reinforcing effects of psychostimulant drugs. The hypothalamic-hypophyseal axis in the form of the tuberoinfundibular system plays a major role in the regulation of pituitary and hypothalamic peptides, for instance in the release of prolactin. An increase in dopamine activity in this system results in an inhibition of prolactin release. Thus, dopamine constitutes the prolaction-inhibiting factor.
It is thought that the dopaminergic tuberoinfundibular neurons are involved in the regulation of a-MSH and ^-endorphin and in the release of oxytocin and vasopressin from the pituitary.
With respect to the autonomic centers of the hypothalamus, dopamine seems to be an essential neurotransmitter, which impinges on arterial blood-flow regulation. Feeding, as well as drinking activities initiated by the ventromedial and lateral hypothalamic nuclei including the zona incerta, are also modulated by dopamine.
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