Reward system Addiction

mesocorticolimbic pathway

understanding pathways in drugs act , how drugs can alter pathways key when examining biological basis of drug addiction. reward pathway, known mesolimbic pathway, or extension, mesocorticolimbic pathway, characterized interaction of several areas of brain.

the projections ventral tegmental area (vta) network of dopaminergic neurons co-localized postsynaptic glutamate receptors (ampar , nmdar). these cells respond when stimuli indicative of reward present. vta supports learning , sensitization development , releases da forebrain. these neurons project , release da nucleus accumbens, through mesolimbic pathway. virtually drugs causing drug addiction increase dopamine release in mesolimbic pathway, in addition specific effects.
the nucleus accumbens (nacc) 1 output of vta projections. nucleus accumbens consists of gabaergic medium spiny neurons (msns). nacc associated acquiring , eliciting conditioned behaviors, , involved in increased sensitivity drugs addiction progresses. overexpression of Δfosb in nucleus accumbens necessary common factor in known forms of addiction; Δfosb strong positive modulator of positively reinforced behaviors.
the prefrontal cortex, including anterior cingulate , orbitofrontal cortices, vta output in mesocorticolimbic pathway; important integration of information helps determine whether behavior elicited. critical forming associations between rewarding experience of drug use , cues in environment. importantly, these cues strong mediators of drug-seeking behavior , can trigger relapse after months or years of abstinence.

other brain structures involved in addiction include:

the basolateral amygdala projects nacc , thought important motivation.
the hippocampus involved in drug addiction, because of role in learning , memory. of evidence stems investigations showing manipulating cells in hippocampus alters dopamine levels in nacc , firing rates of vta dopaminergic cells.

role of dopamine , glutamate

dopamine primary neurotransmitter of reward system in brain. plays role in regulating movement, emotion, cognition, motivation, , feelings of pleasure. natural rewards, eating, recreational drug use cause release of dopamine, , associated reinforcing nature of these stimuli. addictive drugs, directly or indirectly, act upon brain s reward system heightening dopaminergic activity.

excessive intake of many types of addictive drugs results in repeated release of high amounts of dopamine, in turn affects reward pathway directly through heightened dopamine receptor activation. prolonged , abnormally high levels of dopamine in synaptic cleft can induce receptor downregulation in neural pathway. downregulation of mesolimbic dopamine receptors can result in decrease in sensitivity natural reinforcers.

drug seeking behavior induced glutamatergic projections prefrontal cortex nucleus accumbens. idea supported data experiments showing drug seeking behavior can prevented following inhibition of ampa glutamate receptors , glutamate release in nucleus accumbens.