Brain Biochemistry Irregularities

The brain is a complex system of neurons, which form millions of connections.  These neurons communicate using several chemicals, called neurotransmitters.  Several different theories about the cause of schizophrenia propose that it is imbalances in these chemicals that cause some of the positive symptoms.

Dopamine Hypothesis 

The dopamine hypothesis states that there is too much of the neurotransmitter dopamine (too many messages are being sent between neurons) causing the symptoms.  This theory began with the accidental discovery of antipsychotic drugs, medications that help relieve some of the symptoms.  The first antipsychotics were discovered in the 1950’s by researchers who were looking for better drugs to treat allergies.  They noticed that, while they did nothing to help allergies, they did reduce schizophrenic symptoms.  They were soon widely prescribed for patients with schizophrenia.  Although this first drug had several side effects, it began the development of a long line of antipsychotics, some of which are still in use today.  Investigators have discovered that many of the antipsychotics act by blocking the dopamine from sending its message.  This would suggest that too much dopamine does in fact lead to schizophrenic symptoms.  Why might people with schizophrenia have overactive dopamine?  It has been hypothesized that people with this disorder have a larger than usual amount of receptors (when dopamine carries its message to another neuron, it binds to a receptor).  Although this theory does perhaps explain some of what is going wrong in a brain with schizophrenia, it in no way presents the whole picture.  The new atypical antipsychotics, which are often much more effective than the traditional antipsychotics, act by blocking receptors for neurotransmitters other than dopamine, suggesting that, while dopamine is a factor, there are other problems as well.

 Glutamate and NMDA receptors

NMDA receptors are a specific type of receptor found in the brain, and Glutamate is the neurotransmitter that binds to NMDA receptors.  It has been found that NMDA receptors are not functioning as well in brains of people with schizophrenia.  To compensate for the lower functioning NMDA receptors, the brain makes more neurotransmitters, which can then act at receptors other than the NMDA receptor. This increase in neurotransmitter could, as in the dopamine theory, cause too many messages to be sent, leading to the positive symptoms of schizophrenia.