Microtechnology for monitoring real-time electrical and chemical events at the neuronal level in freely behaving animals

Research in neuroscience is often performed on anesthetized animals or on tissue samples in vitro. Despite the valuable information that such research provides, insight into how the brain controls complex processes such as learning, motivation, and movement requires animals that are alert and capable of behaving. To address this need, we have developed a head-mounted system for recording both electrophysiological and electrochemical signals from virtually any brain region of freely behaving rodents. Our system is configured around a microdrive assembly that can accommodate either tungsten microelectrodes (5 mum diameter) for single-unit electrophysiology or glass-coated, carbon-fiber microelectrodes (5-10 mum diameter) for electrochemistry. Either type of electrode can be used in combination with multi-barrel glass pipettes far iontophoretic application of drugs or other substances directly to the recording site. For rats and mice, respectively, the entire system is small (7 and 3 mm diameter; 30 and 20 mm length) and lightweight (4.5 and 1.1 g). A flexible, shielded cable carries neuronal signals to conventional recording equipment via an electronic swivel, which allows for free behavioral expression. Further development of this system will help identify the neuronal mechanisms underlying normal as well as drug- and disease-related behavioral responses.