From Scientific American:
Neuroscientists have long believed that the tremors, stiffness and sluggish gait characteristic of Parkinson’s disease resulted from the death of neurons in a section of the midbrain that produce the neurotransmitter dopamine, which helps to maintain proper motion control.
A new study in mice, however, suggests that the disorder may actually be caused not only by hobbled dopamine-producing cells but also by neurons in the locus coeruleus region of the brain stem that produce norepinephrine, a chemical related to dopamine and associated with everything from anxiety to attention to blood pressure regulation. The new finding could lead to new therapies for combating the debilitating condition.
More here.