Question

1.Explain the dopamine theory of schizophrenia. What are its deficiencies? Explain the alternative (or complementary) explanations that are available.

2.Describe the monoamine hypothesis for depression; include the evidence for it and a description of the effects of the drugs and ECT used to treat it.

Answer 1

The dopamine theory of schizophrenia states that the positive symptoms of schizophrenia (such as hallucinations and delusions) are caused by an excess of the neurotransmitter dopamine in the mid-brain; and decreased levels of dopamine in the prefrontal cortex. The theory was hypothesized based on the effects of medications that blocked dopamine (anti-psychotic medication).

Additionally, a study of patients with Parkinson’s disease exhibited psychotic symptoms as a result of the side effects of the medication prescribed to them. These medications increased dopamine levels and induced psychosis.

The dopamine theory was formulated based on the correlation between dopamine levels and psychotic symptoms. This evidence seems insufficient and does not take into consideration the role played by serotonin in the symptoms exhibited by patients with schizophrenia. Additionally, antipsychotics aimed at moderating dopamine levels only treat the positive symptoms of schizophrenia.

Imbalanced serotonin levels have been linked to the negative symptoms of schizophrenia (poor attention span, apathy, social withdrawal, etc.). Recent studies have also shown that medication used to moderate serotonin levels in patients with schizophrenia was more effective in managing symptoms in treatment-resistant schizophrenia.

Another alternative theory is the glutamate theory that suggests the inability of glutamate in stimulating receptors causes a deficiency that results in schizophrenia symptoms.

The monoamine theory suggests that symptoms of depression are caused by low levels of monoamine (serotonin, dopamine, and noreadrenaline/norepinephrine). Dopamine is responsible for energy levels and alertness, while norepinephrine is responsible for attention, motivation, rewards and pleasure. Serotonin is responsible for regulating levels of dopamine and norepinephrine, and low levels of serotonin directly impact the levels of dopamine and norepinephrine. As a result, low levels of serotonin causes low levels of dopamine and norepinephrine, which result in poor, attention, lack of pleasure, anxiety, low energy and alertness- all symptoms of depression.

Selective Serotonin Reuptake Inhibitors (SSRIs) are a class of drugs used to treat depression based on the hypothesis of the monoamine theory. These drugs block the absorption of serotonin in the brain, thereby increasing the availability of serotonin. While SSRIs help with regulating serotonin levels, they do have a number of side effects including nausea, weight gain, headaches, blurred vision, dry mouth, and diarrhea.

Electro Convulsive Therapy (ECT) has been used to treat depression in cases where a person does not respond to SSRIs. The procedure is performed under general anaesthesia and involves stimulating the brain through small electric currents that triggers a momentary seizure. ECT has been found to alter the chemical imbalances in the brain and alleviates certain symptoms of depression.