Early changes in the brain during exposure to addictive drugs involves the insertion of receptors into neuron membranes located within the

Early changes in the brain during exposure to addictive drugs involves the insertion of AMPA receptors into neuron membranes located within the VTA. AMPA receptor is an ionotropic transmembrane receptor for glutamate that is responsible in mediating fast synaptic transmission in the central nervous system. They provide initial depolarization that ultimately results in NMDA receptor activation. 

In some developing nations the percentage of the animal protein from fish in the diet can be as high as 25 percent.  about 85% of fish caught is used for human consumption.  the remainder is converted into fishmeal and fish oil.