Dopamine is a chemical that your brain and other parts of your body produce to exert various effects throughout your body. The striatum is one part of the brain where dopamine exerts an effect. Disturbances in the actions of dopamine are at the root of abnormalities of several brain disorders such as Parkinson’s disease, schizophrenia and addiction and/or abnormal reward seeking behaviors.
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The striatum is a part of your brain that consists of two regions of gray matter called the caudate and putamen, which are separated by sheets of white matter. Its major output is to the basal ganglia, a group of deep brain structures that play a role in voluntary movement, eye movement and cognition. The striatum receives input from a large portion of the cerebral cortex, including the sensorimotor cortex, the premotor cortex and the frontal eye fields. The striatum also receives inputs from the intralaminar thalamic nuclei, substantia nigra, amygdala, hippocampus and midbrain raphe nuclei.
Dopamine is a catecholamine neurotransmitter and is especially important in the regulation of movement. The responsible set of dopamine-producing neurons has cell bodies in a region of the brain called the substantia nigra, which projects to the striatum. Non-striatal dopamine is made by proximal tubule cells of the kidney where it is thought to act locally. There are five known types of dopamine receptors in different parts of your body and with different effects.
There are five important paths along which dopamine is transmitted in your brain: The first is the mesolimbic-mesocortical pathway, which projects from the substantia nigra to the limbic system and neocortex, is involved in the reward system and is implicated in addiction. The second is the nigrostriatal pathway, which projects from the substantia nigra to the striatum and is described above. The third pathway is the tuberoinfundibular system in which nuclei in the hypothalamus produce and release dopamine into the portal circulation of the pituitary gland to inhibit secretion of prolaction from the anterior pituitary. The fourth dopaminergic system is the medullary-periventricular pathway, which consists of neurons in the motor portion of the vagus nerve. This pathway is suspected in eating behavior. The fifth pathway is the incertohypothalamic pathway, which may play a role in the anticipatory phase of sexual interaction.
Dopamine and Schizophrenia
The most widely accepted hypothesis as to the pathophysiology of schizophrenia proposes that the disease is due to excess dopamine activity in your mesolimbic system. This hypothesis is supported by the fact that dopamine receptor antagonists are effective antipsychotics.
Striatum and Dopamine in Movement Disorders
Degeneration of the dopamine-producing neurons in the substantia nigra causes an imbalance of dopamine and acetylcholine, which are neurotransmitters normally present in the striatum. This leads to the characteristic abnormalities of Parkinson’s disease. Neuron loss in a different part of your brain is the cause for the movement disorder known as Huntington’s disease.