An implantable microelectrode array for simultaneous L-glutamate and electrophysiological recordings in vivo

Abstract

L-glutamate, the most common excitatory neurotransmitter in the mammalian central nervous system (CNS), is associated with a wide range of neurological diseases. Because neurons in CNS communicate with each other both electrically and chemically, dual-mode (electric and chemical) analytical techniques with high spatiotemporal resolution are required to better understand glutamate function in vivo. In the present study, a silicon-based implantable microelectrode array (MEA) composed of both platinum electrochemical and electrophysiological microelectrodes was fabricated using micro-electromechanical system. In the MEA probe, the electrophysiological electrodes have a low impedance of 0.018 MΩ at 1 kHz, and the electrochemical electrodes show a sensitivity of 56 pA µM−1 to glutamate and have a detection limit of 0.5 µM. The MEA probe was used to monitor extracellular glutamate levels, spikes and local field potentials (LFPs) in the striatum of anaesthetised rats. To explore the potential of the MEA probe, the rats were administered to KCl via intraperitoneal injection. K+ significantly increases extracellular glutamate levels, LFP low-beta range (12–18 Hz) power and spike firing rates with a similar temporal profile, indicating that the MEA probe is capable of detecting dual-mode neuronal signals. It was concluded that the MEA probe can help reveal mechanisms of neural physiology and pathology in vivo. Abnormal transmission of L-glutamate can cause neurological disorders such as Parkinson's disease, stroke and epilepsy. In their search for effective treatments, researchers are deploying extensive efforts to understand this key neurotransmitter, which regulates receptors located at chemical synapses. However, their attempts often fail to analyze the syntrophic complexity of biochemical and electrical events occurring in neurons. Now, Xinxia Cai and co-workers from the Institute of Electronics, Chinese Academy of Sciences, Beijing, China, have developed a silicon-based probe that simultaneously measures L-glutamate levels and electrical activity at various locations in the brain with high spatial and temporal resolution. The implantable array combines electrochemical and electrophysiological microelectrodes created through MEMS and nanotechnology. The team expects it to provide insight into physiological and pathological pathways in live brain tissue, paving the way to new diagnostic and therapeutic approaches.