18. Novel Approach Using Fetal Dopaminergic Grafts In Situ Transduced with AAV-DREADDs Significantly Increases Behavioral Motor Recovery in a Rat Model of Parkinson's Disease

Over the past decades, cell replacement therapy has emerged as a possible therapeutic alternative for the treatment of Parkinson's disease. Although early trials showed great promise, later double blinded trials displayed varied clinical benefits. In order to improve therapeutic potential, we combined dopaminergic cell replacement therapy with designer receptors exclusively activated by designer drugs (DREADDs) which enable non-invasive, orthogonal, chemical modulation of neuronal activity. To date, most research has focused on optogenetics to achieve such control and though highly useful in pre-clinical research, broad clinical applications may be limited.In order to evaluate if activation of transplanted dopaminergic cells is sufficient to potentiate functional recovery, we grafted embryonic dopaminergic neurons from the ventral mesencephalon of TH-Cre expressing knock-in rats into the striatum of 6-OHDA lesioned wild-type rats View Large Image | Download PowerPoint SlideFigure 1 | Schematic showing the location of TH-Cre positive dopaminergic fetal grafts within the striatum as well as the injection site of the AAV-8 viral vector expressing either Dq or Ds between the grafts.Using AAV vectors, we expressed DREADDs capable of either increasing or silencing neuronal activity in Cre expressing neurons. Two different pathways (Gq and Gs coupled) were used to increase neuronal activity, either Gq alone or the combination of Gq/Gs. Systemically administered CNO, which serves as the ligand for the DREADDs significantly increased motor recovery in animals expressing Dq and Ds, while animals expressing receptors inducing neuronal silencing, displayed a significant loss of functional recovery. Interestingly, animals expressing the Gs coupled receptor displayed a larger functional recovery while also displaying motor behavior reminiscent of graft induced dyskinesia and increased rotational behavior. View Large Image | Download PowerPoint SlideFigure 2 | Animals expressing Dq/Ds receptors displayed a significant increase in rotational behavior following s.c. CNO administration, while Dq only and lesion controls displayed no significant increase.Taken together, our findings suggest that modulating activity of neurons used in cell replacement therapy may be able to increase functional recovery in patients with Parkinson's disease and the use of DREADDs may be a potent tool to dissect intracellular regulatory pathways.