User:Koberg27/Mesolimbic pathway

Goal: More in depth explanation on how addictive drugs alter the mesolimbic pathway. The section is a little disorganized and needs some work.

Lead
-define addictive drug

-reference addiction page

Article body
-define how drugs alter VTA

-define how drugs alter Nucleus Accumbens

-Make table for reference to the two bullet points above

-explain synaptic plasticity

The mesolimbic pathway and a specific set of the pathway's output neurons (e.g. D1-type medium spiny neurons within the nucleus accumbens) play a central role in the neurobiology of addiction.  Drug addiction is an illness caused by habitual substance use that induces chemical changes in the brain's circuitry. An addictive drug is defined as a substance that affects the mesolimbic system directly or indirectly by increasing extracellular levels of dopamine.

Common addictive substances such as cocaine, alcohol, and nicotine have been shown to increase extracellular levels of dopamine within the mesolimbic pathway, preferentially within the nucleus accumbens. The mechanisms by which these drugs do so vary depending on the drug prototype. For example, cocaine precludes the re-uptake of synaptic dopamine through blocking the presynaptic dopamine transporter. Another stimulant, amphetamine, reverses the dopamine transporter and induces the release of dopamine from synaptic vesicles. Non-stimulant drugs typically bind with ligand-gated channels or G protein-coupled receptors. Such drugs include alcohol, nicotine, and tetrahydrocannabinol (THC). These dopaminergic activations of the mesolimbic pathway are accompanied by the perception of reward. This stimulus-reward association shows a resistance to extinction and creates an increased motivation to repeat that same behavior that caused it. Additionally, drug intake changes synaptic plasticity in the ventral tegmental area and the nucleus accumbens. Repeated exposure to the drug can lead to lasting changes in the brain that gives rise to addictive behavior.