Fig. 2.

Viral transduction and optogenetic stimulation of the DVMN vagal preganglionic neurons in sheep. (a) Photomicrographs of coronal sections of the sheep brainstem taken at low (top) and high (bottom) magnification illustrating representative examples of ChIEF-tdTomato expression in the DVMN. Arrows point at the projecting axons of the transduced DVMN neurons. 4V, fourth ventricle. AP, area postrema. NTS, nucleus of the solitary tract. Scale bars: 400 μm (top), 100 μm (ai, aii). (b) Schematic drawing of the experimental setup in an anaesthetized sheep instrumented for stimulation of the DVMN neurons expressing ChIEF-tdTomato by application of blue laser light and recording of the efferent activity of the vagus nerve at the cervical level. (c) Stimulus-triggered averages (300 sweeps) of the evoked efferent vagus nerve mass action potentials induced by pulses of light of increasing duration delivered at 1 Hz to stimulate the DVMN neurons expressing ChIEF-tdTomato in sheep.