Activity of cardiorespiratory networks revealed by transsynaptic virus expressing GFP

A fluorescent transneuronal marker capable of labeling individual neurons i n a central network while maintaining their normal physiology would permit functional studies of neurons within entire networks responsible for comple x behaviors such as cardiorespiratory reflexes. The Bartha strain of pseudo rabies virus (PRV), an attenuated swine alphaherpes-virus, can be used as a transsynaptic marker of neural circuits. Bartha PRV invades neuronal netwo rks in the CNS through peripherally projecting axons, replicates in these p arent neurons, and then travels transsynaptically to continue labeling the second- and higher-order neurons in a time-dependent manner. A Bartha PRV m utant that expresses green fluorescent protein (GFP) was used to visualize and record from neurons that determine the vagal motor outflow to the heart . Here we show that Bartha PRV-GFP-labeled neurons retain their normal elec trophysiological properties and that the labeled baroreflex pathways that c ontrol heart rate are unaltered by the virus. This novel transynaptic virus permits in vitro studies of identified neurons within functionally defined neuronal systems including networks that mediate cardiovascular and respir atory function and interactions. We also demonstrate superior laryngeal mot orneurons fire spontaneously and synapse on cardiac vagal neurons in the nu cleus ambiguus. This cardiorespiratory pathway provides a neural basis of r espiratory sinus arrhythmias.