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Pleasure and pain
Sub-Topics
Pleasure and Drugs
Avoiding Pain

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HelpDopaminergic Pathways in the Rat Brain
THE REWARD CIRCUIT

Studies of the brain circuits that use dopamine and the locations of the dopamine receptors in these circuits have identified eight major dopaminergic pathways in the brain. Three of these pathways are especially important. All three originate in the midbrain.

The first is the mesolimbic pathway–the bundle of dopaminergic fibres associated with the reward circuit. This pathway originates in the ventral tegmental area and innervates several structures of the limbic system, including the nucleus accumbens. The mesolimbic pathway is important for memory and for motivating behaviours. By blocking this pathway, antipsychotic drugs reduce the intense emotions caused by conditions such as schizophrenia.

The mesocortical pathway also originates in the ventral tegmental area, but projects to the frontal cortex and surrounding structures. Some evidence indicates that a malfunction in this pathway might be the cause of some of the symptoms of schizophrenia, such as hallucinations and disordered thinking. Medications that block this pathway reduce psychotic delirium, but also reduce the overall activity of the frontal lobes.
 

 


The third, nigrostriatal pathway projects axons from the substantia nigra to the striatum (caudate nucleus and putamen), which is involved in motor control. Degeneration of the neurons in this pathway is associated with the trembling and muscular rigidity symptomatic of Parkinson’s disease.

A fourth dopaminergic pathway worth mentioning is the tuberoinfundibular pathway, which connects the hypothalamus to the pituitary gland, where it influences the secretion of hormones such as prolactin.
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