biological factors

BIOLOGICAL FACTORS• role of genes in contributing to the

risk of developing major depression• role of neurotransmitters serotonin

and noradrenaline in major depression

• the function of antidepressant medication in management

GENETICS

• A genetic link for depression is evident from– Family studies– Twin studies– Adoption studies

Family evidence

• Having a first degree relative (parent or sibling) with depression appears to be a risk factor for depression.

• One parent with depression, risk of offspring developing depression - 25-30%

• Two parents with depression, risk of offspring developing depression rises to about 70%

Twin studies• Major depression is more likely to occur in both

members of identical twins than non-identical twins.• According to one study, if one twin has major

depression…– 46% chance the other will develop major depression

(identical)– 20% chance the other will develop major depression (non-

identical)

Adoption Studies

• Wender et al. (1986) studied the biological relatives of adopted people who had been hospitalised for severe depression.

• There was a much higher incidence of severe depression in these relatives than in those of a non-depressed control group

• It is not yet clear HOW genes influence the development of depression.

• Social and psychological factors also influence the chance.

NEUROTRANSMITTERS

• Two neurotransmitters have been thought to be involved in depression, noradrenaline and serotonin.

• It has been thought that the low levels of these neurotransmitters leads to depression and high levels to mania.

• When neurotransmitters are released by the pre-synaptic neuron into the synaptic gap, they travel to the post-synaptic neuron. Any excess neurotransmitters are ‘taken back’ or ‘reabsorbed’ into the pre-synaptic neuron in a process known as reuptake.

Serotonin

• Involved with appetite, sleep patterns & mood.

• Low levels associated with– Sad and anxious moods, hunger, disruptions to the

sleep cycle• Low levels of serotonin has been found in the

cerebrospinal fluid of depressed patients (McNeal, 1986)

noradrenaline

• Involved with attention, alertness, states of arousal and the stress response

ANTI-DEPRESSANT MEDICATION

• Medications designed to relieve the symptoms of major depression

• Often prescribed along side other psychotherapies

• Can take 2-6 weeks before they become ‘active’– An indicator that other factors may be involved

• Types of neurotransmitters are classed based on whether they are designed to increase:– BOTH serotonin and noradrenaline in the brain– ONLY serotonin – most common in Australia– ONLY noradrenaline

Selective serotonin re-uptake inhibitors (SSRIs)

• Block the reabsorption of serotonin by the pre-synaptic neurons that release the neurotransmitter.

• A normal or relative high level of serotonin is then allowed to accumulate in the synapse and influence the activity of the post-synaptic neuron

• Fig 8.16 p264