"Our data indicate that the brain becomes hypersensitive to rewards when this co-signaling of glutamate and dopamine does not function. Lower doses than normal are enough to increase the propensity to ingest the substance, and this is true of both sugar and cocaine," says Åsa Mackenzie, associate professor of neuroscience at Uppsala University and the researcher who led the study.
Addiction disorders are a major social problem, and we lack sufficient knowledge of how they arise and how various substances impact the brain. The brain's reward system gives us feelings of pleasure and happiness, for example when we have eaten or drunk something good, had sex, or worked out. This pleasure arises when certain signal substances, primarily dopamine, are released in the brain. But this reward system can be "kidnapped" by other rewarding substances, such as alcohol and abuser drugs like cocaine. They provide feelings of reward initially, but they are so strong that nerve cells in the system are rewired, and addiction occurs. More natural substance, such as food rich in sugar, can also produce addiction-like conditions.
The Uppsala researchers and their colleagues have recently shown that dopamine cells in the reward system can send signals in cooperation with glutamate, so called co-signaling. Its physiological role was not previously known, however. For instance, how important is it for the inclination to ingest reward substances?
In studies of mice that lack the ability to send the above signals because their glutamate transporter, so-called VGLUT, has been inactivated, the scientists studied how prone the mice were to ingest sugar and cocaine. The results showed that they both ingested more and responded to lower dosages than control mice. > > > > Read More
