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The Dopamine Transporter Protein: The Broker of Mental Activity and Mood
Both excessively high and excessively low concentrations of dopamine in the brain can have negative effects on mood and physiology. (Source: Chung Tzu-fa)
Both excessively high and excessively low concentrations of dopamine in the brain can have negative effects on mood and physiology. (Source: Chung Tzu-fa)

Psychiatrists worldwide typically rely on the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5) when diagnosing schizophrenia. Since the publication of DSM-1 in 1952, experts and researchers in relevant fields have regularly gathered to revise the DSM's content. Up until 2014, the following consensus concerning the diagnosis of schizophrenia prevailed: Persons with symptoms of hallucinations, delusions, incoherent speech, a blank expression, and disordered behavior were suspected to suffer from schizophrenia.

If the foregoing symptoms cause the deterioration of those life functions present prior to the emergence of the condition, the standard for diagnosis of schizophrenia was met. However, a consensus concerning the origin of this disorder has also been reached in functional pathology: The pathology of schizophrenia is connected with an imbalance in the secretion of the neurotransmitter dopamine in the brain.

Dopamine is one of the several dozen neurotransmitters secreted in the brain; one's mental stability and whether one's mood is excited or depressed are linked to the concentration of dopamine. The dopamine concentration is kept in a balanced state in the healthy brain. An excessively high concentration of dopamine may cause psychological symptoms, and is linked with schizophrenia, and an excessively low dopamine concentration may cause Parkinson's disease.

Special brain imaging techniques can be used to determine the dopamine concentration of the brain. Monitoring the synaptic cleft of neurons and presynaptic and postsynaptic neurons can indirectly gauge dopamine concentration. After a presynaptic neuron secretes dopamine, the dopamine will cross the synaptic cleft within several milliseconds, and bond to a special receptor on the postsynaptic neuron, which will trigger various changes in the postsynaptic neuron.

An interesting thing is that the nerve ending of the presynaptic neuron also has a dopamine transporter, which recovers dopamine from the synaptic cleft and pumps it back into the presynaptic neuron, allowing it to be reused. This recycling mechanism gives the dopamine transporter the ability to control dopamine concentration, which is why it is considered the broker of mental activity and mood.

Psychiatrist Chen Kao-chin of the National Cheng Kung University College of Medicine and Attached Hospital performed a long-term observational study in order to find out more about this phenomenon. Using single photon emission computed tomography (SPECT) imaging, Dr. Chen compared the availability of dopamine transporters in the corpus striatum of the brains of 47 patients recently identified as having schizophrenia but not yet taking medication with that of 112 healthy subjects. Dr. Chen's findings were that there was no difference in the availability of dopamine transporters between the two groups, and when the individuals in the two groups were mixed, the availability of dopamine transporters in women was higher than in men.

These conclusions verified a clinical research result concerning schizophrenia: The condition occurs in men and women at different ages, and tends to occur relatively early in men and later in women. This finding has caused researchers to wonder whether gender factors may play a certain role in the disorder. Because they have relatively high dopamine transporter availability, women may be better able to prevent excessively high synaptic dopamine concentration, and only suffer schizophrenia after this regulatory ability is overwhelmed. As a result, schizophrenia occurs later in women than in men.

Research has also found that dopamine transporter availability decreases with age, which is consistent with the finding of research on postsynaptic neuron receptors that the availability of dopamine receptors gradually falls with increasing age.

The sample in Dr. Chen's study was the largest in the world up to that time. To confirm the correctness of his conclusions, Dr. Shen also compiled and analyzed the results of the world's seven previous relevant studies (including his own study) on this subject, which were conducted between 1960 and 2010. The results of this analysis were consistent with his own finding that dopamine transporter availability in the corpus striatum of the brain did not vary between healthy subjects and persons recently found to have schizophrenia but not yet taking medication for the condition.

Translated by Glen E. Lucas
Date:14 Jun 2016

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