Biochemical Causes of Mood Disorders
Mood Disorders are accompanied by a number of abnormalities in the Central Nervous System. These include abnormalities in the body’s regulatory functions especially in the production and utilization of the chemical messengers in the brain known as neurotransmitters and in the production and impact of stress hormones. Much research on the relationship between neurotransmitters and depression has focused on dopamine, serotonin, and the catecholamine’s, norepinephrine and epinephrine. These neurotransmitters are thought to regulate several important behavioural systems relevant to mood disorders, including motivation concentration and interest in others (Rogeness, Javors & Pliszka 1992). According to the original catecholamine theory, low levels of norepinephrine lead to mania.
It turns out, however, that relationships between neurotransmission and depression are more complex than the original catecholamine theory envisioned (Rush 1993).
Current evidence suggests that dysregulation of serotonin, dopamine and norepinephrine is also associated with depression. One theory holds that low serotonin levels may allow other neurotransmitters such as dopamine and norepinephrine to swing increasingly out of control, leading to extreme moods.
Researchers are also using sophisticated technology particularly Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) to explore differences in the brain activity of depressed and non-depressed people. They have found for example, that blood flow appears to be increased in the frontal cortex and decreased in the parietal and posterior temporal lobes of depressed people relative to non-depressed individuals. PET scans of depressed persons have also revealed increased blood flow in the amygdala and thalamus. These structures from brain circuits that are involved in attention alertness and emotion and are influenced by the neurotransmitters we have described.
Neurotransmitters and Bipolar Disorder –
Imbalances in neurotransmitters have also been associated with bipolar disorder. The catecholamine theory would lead us to expect that norepinephrine levels should be elevated during manic episodes. Consistent with this hypothesis is evidence that lithium, the most effective medication for bipolar disorder lower norepinephrine activity in the brain (Bunney & Garland 1983).
Depression and the Endocrine System –
Depression has also been related to the functioning of the endocrine system. This system includes the hypothalamus, which regulates functions such as sleep and appetite; the pituitary gland which regulates growth the adrenal glands a key part of endocrine axis, which plays a critical role in the body’s response to stress. Biological challenge test show that depressed patients must have overactive HPAC system.