This 2014 rodent study showed the opposing effects of neurochemicals orexin (excitator) and dynorphin (inhibitor) in the hypothalamus.
The hypothalamus plays a role in behaviors such as addiction and impulsiveness. Food and cocaine self-administration were the main techniques used.
Flooding the hypothalamus with orexin produced reward-seeking and motivated behavior. That was greatly reduced when dynorphin levels were increased, and depressive behavior set in.
http://www.pnas.org/content/111/16/E1648.full “Hypocretin (orexin) facilitates reward by attenuating the antireward effects of its cotransmitter dynorphin in ventral tegmental area”