1.   Such canine Peter Pans even have low levels of the brain chemicals used in nerve transmission.

2.   That imbalance in brain chemicals also could lead to exaggerated responses to stress, resulting in extreme fatigue.

3.   The drug ketamine, an anesthetic used all over the world, blocks another brain chemical called glutamate.

4.   Pierce J. Howard, another expert, says new research indicates that physical exercise increases the amount of certain brain chemicals that stimulate growth of nerve cells.

5.   And some studies of antidepressants such as Prozac show these drugs, too, may help, specifically by raising levels of a brain chemical called serotonin.

6.   And scientists are still a long way from knowing how such brain chemicals act separately or together to influence behavior.

7.   And the sense of euphoria and inner peace just comes from various brain chemicals at work.

8.   Are there special brain chemicals that drive early neuroplasticity?

9.   At a recent meeting of the American Psychiatric Association in Miami, several studies suggested alcoholism may be related to deficiencies or surpluses in brain chemicals.

10.   Brain imaging specialists in New Mexico have found a link between variations in the levels of two brain chemicals and the results of IQ tests.