Chronic high-frequency stimulation therapy in hemiparkinsonian rhesus monkeys using an implanted human DBS system

Deep brain stimulation (DBS) is routinely used in the treatment of Parkinson's disease, tremor disease, dystonia, and epilepsy. This study aims to establish a hemiparkinsonian monkey model and to investigate the effect of implanted human DBS system for the chronic alleviation of parkinsonian symptoms. Hemiparkinsonism was induced in four rhesus monkeys by unilateral infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. DBS leads were implanted stereotaxically in the right subthalamic (STN) of the monkeys. Subcutaneous extension wires were used to connect the leads to the internal pulse generators (IPG) for stimulation in two of the monkeys (human DBS test group). Post-operative imaging studies confirmed optimal locations of lead contacts. One week later, the IPG was turned on to determine the optimal stimulating parameters, using apomorphine (APO)-induced rotation as a behavioral readout. Animal behavior was scored on a scale of 0-10 over a 12-month period using the modified disability rating scale of hemiparkinsonian monkeys (DRSH). Parkinsonian symptoms in the group of monkeys with DBS improved dramatically (DRSH 3-4) compared to controls (DRSH 7-8). DBS leads were within the STN without intracranial hemorrhage, infection, or other serious complications. Histological examination showed cell necrosis and lymphocytic infiltration of the tissues around the lead and STN gliosis surrounding the lead contact. This study demonstrates that therapeutically effective human DBS systems can be established in relevant disease models in monkeys. Such combination of human DBS systems in hemiparkinsonian monkeys should be valuable in studying the mechanism of action and chronic consequences of DBS therapy in humans.