Optical recording of spatiotemporal patterns of cardiorespiratory neuronal activity in the nucleus tractus solitarii network imaged in situ

The pattern and distribution of neuronal activity evoked by sensory input in the nucleus tractus solitarii (NTS) is not well understood. In the present study, we performed optical recordings (MiCAM02 system, Brain Vision Inc) in situ to investigate the spatiotemporal pattern of NTS neuronal activity in response to activation of cardiorespiratory inputs. The dorsal medullary surface was exposed and stained with the voltage‐sensitive dye, Di‐2‐ANEPEQ, at the level of calamus scriptorius. Graded electrical stimulation of the central vagus nerve and the brachial plexus (1 ms pulse, 200 ms duration, 1–10 Hz) at low frequency (<5 Hz) evoked a fast (50–75 ms), transient increase in optical activity that adapted rapidly; whereas, high frequency stimulation (>5 Hz) produced a sustained elevation of fluorescence that recovered following termination of the stimulus. In contrast, activation of peripheral chemoreceptors (NaCN, 0.03%) evoked a prolonged (4–6s) increase in optical activity that was superimposed by phasic changes in fluorescence coupled to the respiratory cycle. Synaptic blockade virtually abolished stimulus evoked fluorescence suggesting that optical signals represented post‐synaptic activity. These results suggest that optical imaging is capable of detecting differences in spatiotemporal patterns of neuronal activity in the NTS evoked by distinct populations of cardiorespiratory afferents. This work was funded by NIH HL059167.