Brain Inbalances

Many drugs that are aimed at effecting the nervous system interfere with the normal functioning on the synapse.
Below are 5 ways in which a drug can effect the synapse
-1- Effect the synthesis or storage of the neurotransmitter
-2- Effect the release of the neurotransmitter from the presynaptic membrane
-3- Effect the interaction of the neurotransmitter with the receptors on the post synaptic membrane
-4- Prevent the re-uptake of the neurotransmitter into the presynaptic membrane
-5- Inhibit the enzymes responsible for breaking down the neurotransmitter in the synaptic cleft, resulting in a high concentration of the neurotransmitter in the synapse. This results in repetition of the action potential in the postsynaptic membrane

Case study drugs

Serotonin selective reuptake inhibitor (SSRI) (Depression)
Effects serotonin levels in the brain. Serotonin is a neurotransmitter linked to feelings of reward and pleasure.
A lack of serotonin causes severe clinical depression.
SSRI help increase the levels of serotonin in the synapses by blocking the process which would normally remove serotonin.

Levodopa Drugs (L-dopa) (Parkinson's Disease)
These drugs effect the level of dopamine in the brain. Dopamine is a neurotransmitter that is active in neurons in the frontal cortex, brain stem and spinal cord. It is responsible for the control of movement and emotional responses.
A lack of dopamine is linked with Parkinson's Disease.
L-dopa drugs aim to increase the concentration of dopamine in the brain. Because Dopamine can not pass the blood brain barrier, L-dopa is used because it can and once in the brain in is used to make more Dopamine

Monoamine Oxidase B Inhibitor (MOAB) (Parkinson's Disease)
MOAB inhibitors have a similar effect to L-dopa except their mode of action works in a different way. MOAB inhibitor drugs inhibit the action of the enzyme MOAB in order to increase levels of Dopamine.
MOAB inhibitors are less frequently used then L-dopa because they have a lot of side effects.    

Ecstasy (MDMA)
MDMA drugs are illegal because they severely damage the brain function. It acts as a stimulant, increasing the heart rate and effects the serotonin levels in the brain.
MDMA blocks the serotonin reuptake transport system, meaning the synapses are completely flooded with serotonin, which cannot return to the presynaptic knob.
Long term use of MDMA results in over stimulation of neurons which causes damage to the presynaptic knob. This dramatically reduces the functionality of these neuron pathways, leading to depression.