4.2. Depression
Defining 'Depression'
In medicine, ‘depression’ can refer to one of two things (according to the DSM-V):
Major depressive episode (MDE), where a person experiences a persistent low mood and lack of interest in activities they used to find pleasurable, for two weeks or more.
Major depressive disorder (MDD), where a person has experienced two or more MDEs.
The fuller range of symptoms of depression are remembered and screened for using SIGECAPS mnemonic:
Sleep, lack of
Interest, loss of
Guilt, feeling of
Energy, lack of
Concentration, poor
Appetite, reduced
Psychomotor, retardation or agitation
Suicide, risk of
The definitions for mood disorders differs depending on what your reference is. For example, depression is classified as single episode depressive disorder or recurrent depressive disorder (of varying severities) in the ICD-11.
Depression can have biological, psychological and social components. Here, we will mainly consider the biological component, but we will also see how all three components can be intricately linked by concepts such as epigenetics and neuronal plasticity.
Biological Processes Underlying Depression
Serotonin is seen as neurotransmitter that has a major role in regulating mood. High levels of serotonin are associated with positive mood. Under normal circumstances, serotonin is released from the presynaptic terminal into the synaptic cleft. It then diffuses across the cleft and occupies postsynaptic receptors. It is then released from the receptors, taken back up into the presynaptic terminal, broken down and reassembled. It is thought that low levels of the neurotransmitter serotonin can result in depression, and this could be because of decreased production of serotonin, a decreased number of receptors or excessive reuptake. This is thought to occur in the:
Prefrontal cortex (dorsal and medial areas)
Limbic lobe (anterior cingulate cortex, hippocampus, amygdala and thalamus)
Other cortical areas (the insula)
Brainstem (the 'raphe nuclei' of the main neurotransmitters thought to mediate depression, e.g. serotonin, noradrenaline and dopamine)
Managing Depression
Due to its nature, depression can be treated with a mixture of biological, psychological and social interventions.
Biological interventions – this mainly involves the administration of anti-depressants. Examples of frequently prescribed anti-depressants are fluoxetine, citalopram and sertraline. These drugs are all termed selective serotonin reuptake inhibitors (SSRIs) and they work by blocking some of the serotonin reuptake channels in the presynaptic terminals of neurons. This means that less serotonin can leave the synapses and, as a result, more serotonin can occupy receptors on the postsynaptic membrane. Other drugs used to treat depression of greater intensity include venlafaxine (which is a serotonin and noradrenalin reuptake inhibitor, or SNRI), olanzapine (an atypical antipsychotic) and lithium (a mood stabiliser). Electroconvulsive therapy can be used for very hard-to-treat ('treatment resistant' or 'treatment refractory') depression.
Psychological interventions – examples of this include cognitive behavioural therapy (CBT), counselling and mindfulness. These therapies provide patients with new ways to think about and approach their problems, and may address some of the underlying issues that are triggering depression. Regular practice of mindfulness (a meditation-based therapy) has been shown to change the anatomy of the brain for the better. It is suggested that this is a result of neuronal plasticity, a feature of the brain that allows it to change its neuronal circuits over time when psychological therapies are consistently applied.
Social interventions – if social isolation is a trigger for depression, introduction to routine, creative activities with other patients may help to reverse some of the symptoms of depression.
