Optogenetic stimulation of the frontal eye field in an awake, behaving monkey.

Abstract

Optogenetics is a new tool in neuroscience that allows researchers to control neuronal activity with stimulation of exogenously expressed light-sensitive transmembrane ion channels. Since the introduction of this technique in 2005, it has been increasingly relied upon for its high spatial and temporal resolution; that is, the ability to depolarize or hyperpolarize spatially localized neurons of a defined genetic population with millisecond-scale induction and reversibility. Despite the methodological advantages of optogenetics, few groups have successfully implemented it in the study of visual processing in primates. Our laboratory applied optogenetics to the study of visual processing in the prefrontal cortex. We injected the excitatory opsin channelrhodopsin-2 (ChR2) into the frontal eye field of a cynomolgus monkey (Macaca fascicularis). ChR2 was carried with a lentivirus vector and expressed under control of the Thy 1 promoter (Lenti-Thy 1-ChR2(H134R)-eYFP). Injection sites were visually identified using anatomical landmarks in the right hemisphere, ventral to the dorsomedial aspect of the arcuate sulcus. Approximately 6 months after injection, we measured single unit activity in this region in the awake, behaving monkey using a single electrode coupled to an optic fiber and a monochromatic blue laser (473 nm). Measurements of neuronal activity during baseline and optical stimulation were carried out while the monkey fixated on a 1° fixation point on a projection screen. Light-induced neuronal activity was observed in multiple neurons over several weeks. These neurons exhibited up to 70-fold increases in firing rate during the optical stimulation compared to baseline activity. Preliminary immunohistological analyses of transfection efficiency of this viral construct in a separate brain region show transfection of both astrocytes and neurons; further analyses of the proportion and genetic identity of transfected cells are ongoing.

Meeting abstract presented at VSS 2013