A reward pathway in the dorsal raphe nucleus important to drug abuse begins with stimulation of glutamate neurons, according to a study from the National Institutes of Health.
Nerve cells in the dorsal raphe nucleus connect to the dopamine reward system, but many of the pathways are rich in serotonin. Serotonin-enhancing drugs have little risk for abuse and are not associated with drug reinforcement, leading scientists to believe that a different neurotransmitter was responsible for the role the dorsal raphe nucleus plays in reward, a press release from the NIH said. Glutamate, important in neural communication and learning, was the most likely option.
In a study on rodents, investigators from the National Institute on Drug Abuse (NIDA) used tracers to confirm that the reward pathways started with glutamate cells in the dorsal raphe nucleus, which connect to dopamine cells in the ventral tegmental area, which eventually lead to the nucleus accumbens, a brain structure important to reward, pleasure, and motivation. Further testing determined that glutamate, not serotonin, activates the reward pathway, the study published in Nature Communications found (2014 Nov. 12 [doi:10.1038/ncomms6390]).
The newly discovered glutamatergic pathway is “the first fully characterized link between electrically stimulated reward circuitry and the dopamine system on which it depends. The discovery of this specific brain pathway opens new avenues to examine its participation in a variety of disorders related to motivation,” Marisela Morales, Ph.D., NIDA scientist and senior author on the paper said in a press release.
The research was conducted at NIDA’s Intramural Research Program.