Carbidopa is used in the treatment of, among other diseases, Parkinson's disease (PD), a condition characterized by death of dopaminergic neurons in the substantia nigra.
Agonism of D2sh receptors inhibits dopamine release; antagonism increases dopaminergic release.
"The IRS2-Akt pathway in midbrain dopaminergic neurons regulates behavioral and cellular responses to opiates."