Can you tell me in Parkinson's disease, does dopamine loss occur merely in the striatum or does it occur in the s.niagra too?

Pigmented nuclei. The dopamine loss involves predominantly the basal ganglia area, but also involves dorsal vagal nucleus, substantial nigra, and areas of any dopamine interaction within brain and brain stem. But, to be complete, Parkinson's is a multi-neurotransmitter degenerative deficiency syndrome with other neurotransmitter systems involved.