1.   Both involve a chemical called dopamine.

2.   Cocaine use causes increased levels of a brain chemical called dopamine, which in turn constricts brain arteries.

3.   In particular, amphetamines act on a brain chemical called dopamine, which scientists believe is responsible for the euphoria the drugs produce and also their potential for abuse.

4.   Moreover, a brain chemical called dopamine regulates this clock.

5.   Nicotine works by stimulating the production of a chemical called dopamine.

6.   The cells produce a neuron-to-neuron signaling chemical called dopamine.

7.   The disease occurs when nerve cells that produce a crucial brain chemical called dopamine deteriorate and die.

8.   Without them, the brain cannot produce enough of a chemical called dopamine, a messenger that transmits signals within the brain.

9.   The work focused on a brain system in which brain cells signal each other by releasing bursts of a chemical called dopamine.