Whenalcohol is ingested, the ethanol travels to the brain through the bloodstream.The ethanol causes slower brain activities as it increases inhibitory neuronsand decreases excitatory neurons. GABA is an inhibitory neuron which binds toGABA receptors to open the chloride ion channels and thus make the inside ofthe neuron more negative thus have lower responsiveness to stimuli. Ethanolbinds to the GABA receptor and allows the chloride channels to be opened longerthus making it much more negative and thus increases the inhibitory effect.
Ethanol also inhibits glutamate (excitatory neuron) by binding to the glutamatereceptors and reducing positive ions from flowing in. This causes the reducedexcitatory effects and thus slows down brain activities. Alcohol affects thereward pathway on dopamine and not on dopamine receptors directly. When theGABA system is affected by alcohol, the neurons which go to the reward pathway(VTA) releases dopamine. The endorphin system is also affected and causesreward pathway to activate opioid peptides that releases dopamine.
Dopaminestimulates the nucleus accumbens and goes to the limbic system (amygdala andhippocampus).When thedrug cocaine is taken, it travels through the axons through action potentialsand reaches the axon terminal where neurotransmitters (monoamines – includesdopamine) are released into the synaptic cleft via exocytosis. Dopamine thenbinds to the dopamine receptors on the post-synaptic neuron and stimulates therewards pathway. Without the presence of cocaine, the dopamine would bere-uptaken by the dopamine reuptake transporter on the pre-synaptic neuron.This will decrease dopamine levels at the synaptic cleft and thus decreaseactivities on the receptors. In the presence of cocaine, cocaine acts toinhibit the dopamine reuptake transporter thus causing an accumulation ofdopamine at the synaptic cleft.
This in turns increases activities on thepost-synaptic receptors. It would activate the mesolimbic rewards pathway fromthe VTA to the nucleus accumbens to the amygdala(emotions) andhippocampus(memory).