Drug Effects on Synapses (AQA A Level Biology)

Predicting the Effects of Drugs on a Synapse

• Chemical or drugs can have a major impact on the functioning of the brain and nervous system

• Some prescription drugs can have a beneficial effect on those suffering from neurological disorders while recreational drugs can have a damaging or even fatal effect

• Many drugs have been found to produce a specific effect on synaptic transmission

• They can have different modes of action such as:

  • Stimulating the release of a neurotransmitter

  • Providing the chemicals needed to synthesise neurotransmitters

  • Acting in the same way as a neurotransmitter by binding to the same specific receptor

  • Preventing the reuptake of the neurotransmitter by the presynaptic neurone

• Research is ongoing to further understand how several drugs work in the hopes that they can be used to treat nervous disorders

Dopamine

• There are many different neurotransmitters that bind to specific receptor molecules

• They are often restricted to certain regions of the brain so that they have a specific function

• Some are excitatory and some are inhibitory

  • Excitatory neurotransmitters result in the production of an action potential

  • Inhibitory neurotransmitters prevent the production of an action potential. They do this by causing potassium ions to leave the postsynaptic membrane

• Dopamine is a neurotransmitter involved in muscle control

• Individuals that suffer from Parkinson's disease produce insufficient amounts of dopamine

• There are two types of drugs that are used to treat this disease

  • A dopamine agonist - produces the same effect as dopamine by binding to the same receptors

  • A dopamine precursor - this can be used to synthesise dopamine in the neurones

Morphine

• Dopamine also plays a vital role in pain relief

• Chemicals called endorphins which are produced in the brain can stimulate the release of dopamine

• The endorphins attach to opioid receptors found on presynaptic neurones that release dopamine molecules

  • Exercise is a natural way to cause the release of endorphins

• Morphine is a chemical very similar in structure to endorphins and so it can provide pain relief by stimulating the release of dopamine

Cocaine

• Cocaine also affects levels of dopamine

• It binds to the dopamine transporter protein

• This prevents dopamine from binding to the transporter so it is not able to move through the membrane back into the presynaptic neurone

• As a result dopamine builds up in the synapses which can lead to feelings of pleasure

Cannabinoids

• Cannabinoids are compounds found in cannabis

• Cannabinoid receptors are located in the pre-synaptic membrane of neuromuscular junctions

• When a cannabinoid molecule binds to its specific receptor, it closes the calcium ion channels

• This leads to decreased muscle contraction

• There is currently research investigating whether cannabinoids could be an effective drug in treating multiple sclerosis (MS)

  • MS is a disease that involves damage to the myelin sheaths of neurones. Sufferers struggle to control muscle contraction

MDMA

• MDMA stimulates the release of multiple neurotransmitters most notably, serotonin

• Serotonin can affect people in many ways including their mood, anxiety and sleep

• When an individual takes MDMA they may feel extreme euphoria and enhanced touch and bodily sensations