When
alcohol is ingested, the ethanol travels to the brain through the bloodstream.
The ethanol causes slower brain activities as it increases inhibitory neurons
and decreases excitatory neurons. GABA is an inhibitory neuron which binds to
GABA receptors to open the chloride ion channels and thus make the inside of
the neuron more negative thus have lower responsiveness to stimuli. Ethanol
binds to the GABA receptor and allows the chloride channels to be opened longer
thus making it much more negative and thus increases the inhibitory effect.
Ethanol also inhibits glutamate (excitatory neuron) by binding to the glutamate
receptors and reducing positive ions from flowing in. This causes the reduced
excitatory effects and thus slows down brain activities. Alcohol affects the
reward pathway on dopamine and not on dopamine receptors directly. When the
GABA system is affected by alcohol, the neurons which go to the reward pathway
(VTA) releases dopamine. The endorphin system is also affected and causes
reward pathway to activate opioid peptides that releases dopamine. Dopamine
stimulates the nucleus accumbens and goes to the limbic system (amygdala and
hippocampus).

When the
drug cocaine is taken, it travels through the axons through action potentials
and reaches the axon terminal where neurotransmitters (monoamines – includes
dopamine) are released into the synaptic cleft via exocytosis. Dopamine then
binds to the dopamine receptors on the post-synaptic neuron and stimulates the
rewards pathway. Without the presence of cocaine, the dopamine would be
re-uptaken by the dopamine reuptake transporter on the pre-synaptic neuron.
This will decrease dopamine levels at the synaptic cleft and thus decrease
activities on the receptors. In the presence of cocaine, cocaine acts to
inhibit the dopamine reuptake transporter thus causing an accumulation of
dopamine at the synaptic cleft. This in turns increases activities on the
post-synaptic receptors. It would activate the mesolimbic rewards pathway from
the VTA to the nucleus accumbens to the amygdala(emotions) and
hippocampus(memory). 

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