Assessment of central chemosensitivity through simultaneous recording of single‐unit and whole‐nerve responses to CO2

Abstract

The isolated frog brainstem is an established preparation to quantify respiratory drive and the role of central CO2 sensitivity in control of breathing. Here, we establish a technique to quantify neuronal response to high CO2 (hypercapnia) and compare it to the concomitant response by the intact respiratory network. Recorded neurons were subsequently juxtacellularly labeled, facilitating identification of location and phenotype of respiratory CO2‐ sensitive neurons. Neurograms representing buccal and lung breathing were obtained with suction electrodes recording whole‐nerve activity in cranial nerves 5 and 7. Simultaneously, extracellular electrodes recorded single neurons in established CO2‐sensitive sites of the frog brainstem. Neural activity was recorded while brainstems were exposed to normocapnia and hypercapnia (1.5 and 5.0% CO2, balance O2). Neurons were then entrained to an injected current and juxtacellularly labeled with biotinamide. After electrophysiology experiments, brainstem slices were stained with streptavidin‐AlexaFluor and the recorded cells were imaged. Our results validate this technique, which is the first reported capacity to simultaneously assess CO2 sensitivity of the central network that controls breathing and a single neuron embedded in the network. We expect to use this technique to elucidate neural mechanisms responsible for respiratory drive. NSF IOS‐1022442