6.2.9 Drug Effects on Synapses

• 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