While our understanding of the neurobiological mechanisms underlying cocaine and opiate reward has historically been dopamine-focused, evidence from genetic and pharmacological approaches indicates that µ-opioid receptors (MORs) in the striatum are important contributors. Within the striatum, MORs are expressed in both dopamine D1-receptor and D2-receptor expressing GABAergic medium spiny neurons (MSNs), as well as in interneurons and various afferents. Thus, it remains unclear how these distinct MOR populations regulate drug reward.
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