Neurotransmitters other than DA (e.g., cannabinoids, opioids) are also involved with drug reward, and their relative contribution to a drug’s rewarding effects is determined in part by their pharmacological effects (e.g., endogenous opioids for heroin, alcohol, nicotine). Similarly, several neurotransmitters are also involved in the neuroadaptations associated with addiction (e.g., decreases in endogenous opioid signaling in cocaine addiction), including the central role of glutamate in the neuroplastic changes associated with chronic drug exposures (10, 11).
