China group tours on Some cells in the substantia gelatinosa contain endorphins and are involved in regulation of pain. substantia nigra a region of gray matter in the midbrain, named for its dark pigmentation, that sends dopaminergic neurons to the basal ganglia. Depletion of dopaminergic neurons in this region is implicated in Parkinson’s disease. substitution n. in psychoanalytic theory, the replacement of unacceptable emotions or unattainable goals with alternative satisfactions or feelings. Substitution may be viewed as a positive adaptation or solution (e.g. China group tours 2016.