Imbalances in Brain Chemicals Leading to Diseases
- Neurotransmitters are chemicals that transmit nerve impulses across synapses
- Some disorders and diseases are linked to an imbalance of neurotransmitters in the brain
- Two examples are
- Parkinson's Disease
- Depression
Parkinson's disease
- Parkinson's disease is a brain disorder that affects the co-ordination of movement, caused by the loss of neurones in some parts of the brain
- Symptoms include
- A tremor to the specific parts of the body
- Slow movement
- Stiff and inflexible muscles
- Difficulties with balance
- Changes to speech
- The lost neurones normally produce the neurotransmitter dopamine
- Dopamine is involved in muscle control
- Individuals that suffer from Parkinson's disease produce insufficient amounts of dopamine due to the loss of dopamine-producing neurones
- Less dopamine is released into the synaptic cleft meaning less is able to bind with receptors on the postsynaptic membrane
- Fewer sodium channels on the membrane are opened so depolarisation of the postsynaptic neurone does not occur
- This leads to fewer action potentials which creates the symptoms such as tremors and slow movement
- Different types of drugs can be used to treat this disease
- Dopamine agonists
- Produce the same effect as dopamine by binding to and activating the dopamine receptors on the postsynaptic membrane
- Dopamine precursors
- These are chemicals that can be converted into dopamine in the neurones
- E.g. L-dopa
- Enzyme inhibitors
- Monoamine oxidase B (MAOB) inhibitors inhibit the activity of enzymes that would normally break down dopamine in the synaptic cleft, raising levels of dopamine present in the brain
- Dopamine agonists
- Research into other treatments for Parkinson's disease is currently ongoing, with some promising future possibilities in the areas of
- Gene therapy
- This would involve the addition of genes to the affected cells in the brain to either increase dopamine production or prevent the destruction of dopamine-producing cells
- Stem cell therapy
- Stem cells could be used to replace the lost dopamine-producing cells in the brain
- Gene therapy
Depression
- Low levels of the neurotransmitter serotonin have been linked to depression
- Serotonin transmits nerve impulses through the areas of the brain that control mood
- Low levels of serotonin increase episodes of depression
- Other brain chemicals linked to depression include noradrenaline and dopamine
- Some drugs that have been developed for the treatment of depression, known as antidepressants, work by increasing the levels of relevant neurotransmitters in the brain
- SSRIs (selective serotonin reuptake inhibitors) are a class of antidepressant that prevent the uptake of serotonin at synapses; this increases the overall levels of serotonin in the brain
- TCAs (tricyclic antidepressants) increase levels of both serotonin and noradrenaline in the brain
- MAOB inhibitors inhibit enzymes that would otherwise break down neurotransmitters in the synaptic clefts in the brain