Characterization of a Double-Barreled Device Designed for Real-Time Electrochemical Measurements and Precise Application of Neurochemical Modulators in the Brain

The growing field of neurochemical monitoring relies on rapid quantization techniques such as background-subtracted fast-scan cyclic voltammetry (FSCV), to measure of neurotransmitter fluctuations within discrete brain regions.  Neurotransmitter concentration changes can be pharmacologically manipulated leading to complex effects on multiple neuronal circuits or pathways.  However, comparative characterization of in-vivo methods that couple localized drug delivery and sensing is lacking. We present the characterization of a drug-delivery system that combines a carbon-fiber microelectrode for FSCV with a microsyringe cannula, by way of multi-barreled glass capillaries. This design allows small volumes of drugs to be delivered through the capillary adjacent to the carbon-fiber, ensuring discrete manipulation of the local environment. We characterize the use of this device with several local drug infusion methods. These include the use of air pressure to force fluid into the extracellular space (Picospritzer), the use of hydraulic pressure to deliver the drug (syringe pump), and drug delivery by way of iontophoresis, in which an  electric field  within the capillary causes migration of a charged chemical to the desired location. The most effective drug-delivery strategy generates a reproducible concentration profile for each infusion, giving a rapid and predictable on/off response. These results of this work will inform a broad cadre of neuroscience studies that utilize localized drug delivery for modulation of discrete neural circuits.