This protocol describes the methods used to evaluate the effects of gastric electrical stimulation (GES) on neural activity in the nucleus of solitary tract (NTS). Briefly, the multi-unit activity (MUA) and local field potential are accessed through multi-channel electrophysiological recording. The stimulation is applied during the imaging acquisition. The configuration of VNS was varied in terms of pulse parameters (amplitude, width) and polarity (proximal or distal coil of a bipolar electrode connected as the cathode).
The purpose of this study is to study how NTS neurons respond to GES with different parameter settings. To do so, we varied the stimulus parameters in terms of pulse amplitude (PA: 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6mA), width (PW: 0.1, 0.2, 0.3, 0.4, 0.5ms), and the pulse polarity. The pulse polarity can also be viewed as the current direction of the stimulus. For example, when delivering current through the bipolar electrode, the anode and cathode setting has two options which can result in two polarities of the stimulus. We altered the amplitude, pulse width, and pulse polarity. A total of 100 different parameter settings were tested for a single trail. The recording electrode was moved around to record from different groups of neurons in a single animal. The stimulation trail can be repeated multiple times on each animal but for different neurons.