A2/A-level Biology - Depression

• Depression is an affective disorder.
• The causes of depression are complex and not fully understood.

• Depression occurs due to problems with serotonin in the brain. 
• It  can  be  triggered  as  a result  of  external  factors  such  as  relationship stress  or  bereavement,  or  can  be  purely  the result of chemical changes in the brain.
• Dopamine and noradrenalin may also play a role.

• Serotonin is the synaptic transmitter in a group of cells in the brain stem.
• It has axons spread throughout the brain into the cortex, the cerebellum and the spinal cord.
• Low levels of serotonin result in fewer nerve impulses travelling around the brain, suppressing the overall brain activity. 

• Intense feelings of sadness and guilt.
• Difficulty in initiating actions and making decisions.
• Loss of energy or restlessness.
• Disturbance of sleep.
• Irrational hopelessness.
• Frequent negative thoughts, low self-esteem.

• Scientists have found a gene (5-HTT) which appears to be linked to the production of serotonin in the brain.
• The gene codes for a reuptake protein that enables serotonin to be taken back into the presynaptic membrane after release into the synapse.
• People who are homozygous for the ‘short’ form seem most likely to experience depression after experiencing stressful events. Heterozygotes have an immediate risk and those homozygous for the ‘long’ form have a very low risk of depression.
• People who have homozygote long forms produce more reuptake proteins than heterozygotes who produce more than homozygous short forms.

• Talking therapies – can help a patient to come to terms with adverse life events.
• Use of drugs – SSRIs (selective serotonin reuptake inhibitors) inhibit the reuptake proteins in the presynaptic membrane, so that more serotonin remains in the synaptic cleft, more impulses travel along the post-synaptic axon to relieve the symptoms.
• Neurotransmitters – Tricyclic antidepressants (TCAs) increase the levels of serotonin and noradrenalin in the brain.
• Monoaminoxidase inhibitors inhibit the enzymes which usually cause the breakdown of neurotransmitters in the synapses of the brain.

That's the end of the topic!

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