Adrenal medulla graft induced recovery of function in an animal model of Parkinson's disease: possible mechanisms of action.

Following unilateral dopamine (DA) denervation of the striatum in animals, there is an asymmetry in the striatal DA system. Animals with such denervations will rotate vigorously when given dopaminergic drugs. Adrenal medulla grafts placed in the lateral ventricle adjacent to a DA-denervated striatum decrease rotational behaviour induced by DA receptor agonists or DA-releasing agents. This discussion reviews research on the use of adrenal medulla grafts to reverse behavioural deficits following DA-denervation of the striatum. Results from basic animal research and from the application of the procedure to patients with Parkinson's disease suggests that at least three different fundamental processes may mediate the functional effects of adrenal medulla grafts: (a) Adrenal medulla grafts may induce changes in the blood-brain barrier; (b) adrenal medulla grafts may induce an increase in serum DA; and (c) adrenal medulla grafts may have a trophic effect on the host brain. Hypotheses are proposed to explain the behavioural effects of adrenal medulla grafts in light of the processes that are thought to mediate their effects.