The Dopamine Hypothesis Of Schizophrenia Essay

1459 words - 6 pages

The Dopamine Hypothesis of Schizophrenia

Schizophrenia is a disease that has plagued societies around the world for centuries, although it was not given its formal name until 1911. It is characterized by the presence of positive and negative symptoms. Positive symptoms are so named because of the presence of altered behaviors, such as delusions, hallucinations (usually auditory), extreme emotions, excited motor activity, and incoherent thoughts and speech. (1,2) In contrast, negative symptoms are described as a lack of behaviors, such as emotion, speech, social interaction, and action. (1,2) These symptoms are by no means concrete. Not all schizophrenic patients will exhibit all or ...view middle of the document...

(2) However, there are some problems with this evidense. Amphetamines only mimic the positive symptoms of schizophrenia. They do not produce any of the negative symptoms. Likewise, anti-psychotic drugs are only affective on the positive symptoms of the disease. There is still some evidense that schizophrenics do posess higher levels of dopamine, however, these increases are only found in the striatum of the brain (7). The striatum is a region of the brain that receives its inputs from and outputs to the cortex. Injury to the striatum results in problems with intiation and control of motor behavior. (9) Also, there is evidence that the prefrontal cortex produces lower levels of dopamine. (4) The prefrontal cortex is involved in the organization and coordination of information to and from the cortex. (7)

The major support and refutation of the dopamine hypothesis has come from the examination of dopamine receptors in these regions of the brain. There are two main types of dopamine receptors, D1 and D2. However, within the category of D2 receptors, there are three subtypes, D2, D3, and D4. (5) Through PET scan analysis of dopamine usage in the brain and post-mordum molecular analysis of brain tissue, researcher were able to determine relative levels of dopamine receptors in patients with schizophrenia compared to non-schizophrenics. Overall analysis of dopamine receptors in the brain indicate that the striatum, limbic system, and the cortex have more receptors than the rest of the brain, regardless of pathology. (6) Examination of the striatum (involved in production of emotions) does not show a difference in levels of any of the dopamine receptors in schizophrenic patients. However, a great deal of research indicates that the prefrontal cortex of schizophrenic patients has decreased levels of D1, D3, and D4 receptors. (3,4,6) One researcher was able to show that, in addition, the decreased level of D1 receptors was correlated with the severity of negative symptoms in patient. (3) Another researcher found that the control of production of D3 and D4 receptors could be altered by the alteration of levels of NMDA, a neurotransmitter that seems to have some regulatory control over the production of dopamine mRNAs. (6) Through the use of a NMDA antagonist, the researcher was able to decrease the level of D4 production and increase the level of D3 production in the limbic system. Administration of the NMDA antagonist also produced effects that mimic schizophrenia. Likewise, PCP, a drug that has its effects through the inhibition of NMDA, has been shown to produce effects that are similar to both the positive and negative symptoms of the disease. (5)

While all the research seems to indicate that dopamine is somehow involved in the production of the symptoms of schizophrenia, it is difficult to determine the exact involvment. It appears that the increased levels of dopamine in the striatum are responsible for some of the positive symptoms,...

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