New dopaminergic neurons in the Parkinson's disease striatum: Establishment of phenotype, function and origin.

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Parkinson s disease is usually associated with loss of dopamine cells that send nerves from the substantia nigra to the striatum. However, we have found large numbers of apparently new dopaminergic cells in post mortem tissue from the striatum of 10 patients with Parkinson s disease but not in 5 age-matched controls. Our aims are firstly to determine whether these cells are indeed dopaminergic neurons by establishing their neurochemical and morphological profiles. This is required to determine whether these apparently dopaminergic cells do indeed produce the neurotransmitter dopamine and to determine to what class of neuron they belong. The latter is important to establish whether they act locally in the striatum or extend their influence over a larger area of the brain. Secondly we shall assess their function in human and rat tissue. We shall determine whether their number is related to the severity of damage in Parkinson s disease, or whether L-DOPA therapy, which most patients receive, plays any role in their appearance. These experiments will lay the ground work to allow us to determine whether these cells are beneficial or harmful. Lastly, we shall determine where these cells come from. We shall determine whether they have always been present but have taken on a new function, or whether they are in fact new cells which have been born recently. This knowledge is essential if we are to be able to change their numbers to improve treatment of Parkinson s disease. We estimate that there are up to 66,000 of these dopaminergic cells in each striatum of patients with Parkinson s disease. This is enough to have a significant impact on the manifestation of the disease. These cells might be beneficial, allowing the brain to maintain essential functions for longer or they might be harmful playing a role in either development of Parkinson s disease itself or the harmful side effects of L-DOPA therapy.