Multichannel Microinjector Arrays for Efficient Viral Vector Delivery into Rhesus Monkey Brain

Effective delivery of viral vectors to target brain regions is critical for using genetically encoded molecular tools such as chemogenetics, optogenetics, and fluorescent indicators. Compared to rodent models, applications of genetically encoded tools in nonhuman primates have progressed slowly due to challenges in injecting larger volumes of brain tissue and the limited availability of transgenic lines. Stereotaxic and hand-held injections have been used to infuse viral constructs into the nonhuman primate brain, but at the cost of speed and dense expression, respectively. Here, we present a novel injection method using custom multichannel microinjector arrays to deliver viral vectors efficiently and with dense expression into cortical regions of rhesus macaques. We describe in detail the methods for building and implementing three types of multichannel microinjector arrays. In addition, we describe the methods for co-infusing manganese for postoperative validation of injection targeting using MRI.