Electrophysiological localization of the substantia nigra in the parkinsonian nonhuman primate - Technical note

During ablative surgery and implantation of deep-brain stimulators for the treatment of movement disorders, electrophysiological techniques are often used for localization of subcortical targets. New restorative therapies for Parkinson disease, aimed at delivering drugs or cells to the substantia ni gra (SN), are becoming available. Therefore, precise surgical approaches to the dopaminergic cell-containing region of the SN are required to avoid da mage to nearby structures such as the corticospinal tract and subthalamic n ucleus. In a study conducted in nonhuman primates, the authors evaluated th e utility and accuracy of electrophysiological techniques in localizing the SN. Three adult rhesus monkeys were used as hosts for intranigal cell transplan ts. The monkeys were rendered hemiparkinsonian by intracarotid injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. With the aid of stereotactic guidance, chronic recording chambers were placed on the skull of each monk ey and directed at the SN. In each monkey, 20 to 40 trajectories were explo red with a microelectrode. Spontaneous and movement-related single-unit act ivities were recorded in the SN, pars reticulata, subthalamic nucleus, glob us pallidus, striatum, thalamus, and red nucleus. Motor and ocular response s to microstimulation in the subthalamic area were noted. Using the electro physiological and stereotactic information that was obtained, three-dimensi onal maps of the nigral complex were constructed to infer the location of t he SN pars compacta. The maps were subsequently used to guide intranigral p lacement of fetal dopaminergic cells. Accurate delivery was verified by his tological analysis. Based on the characteristic electrophysiological properties of the SN and s urrounding structures in the parkinsonian state, microelectrode recording t echniques may be used to ensure accurate placement of cell transplantation in the intranigral.