Epinephrine (aka adrenaline) is made from dopamine.

Because epinephrine is involved in the fight or flight response, it would seem reasonable that if overall dopamine supplies run low, then epinephrine production has priority.

If we have hypervigilant personalities and spend our lives with an increased need for epinephrine, then we are more likely to experience a chronic or recurring shortage of dopamine, the raw material for the epinephrine.

If we have a metabolic problem that limits the amount of dopamine we are capable of turning out, won't our lives and personalities reflect this chronic shortage of this important neurotransmitter, perhaps even generating the "Parkinson's personality"?

Since production of epinephrine/adrenaline worsens the shortage of dopamine, won't we learn early in life to suppress feelings, avoid emotions, etc in order to balance out as best we can?

Finally, while it is by no means certain that the death of neurons in the SN are cause rather than victim, what would be the net result on these neurons if they were forced to strain to function with this constant problem? Would they eventually die?