Identification of spinally projecting neurons in the rostral ventrolateral medulla in vivo

Putative sympathetic premotor neurons in the rostral ventrolateral medulla are critically important in the regulation of sympathetic vasomotor tone and are responsible for mediating many cardiovascular reflexes. In the rat, these neurons lie within a small area of the brainstem immediately caudal to the facial nucleus and can be distinguished from neighbouring cells by their axonal projections to the thoracic spinal cord, where they are thought to form synapses with sympathetic preganglionic neurons. This protocol describes the steps required for identification of sympathetic premotor neurons in acute experiments in vivo. It provides a detailed description of the methodology we use routinely to electrophysiologically map the topography of the facial nucleus and an account of the steps needed to conduct the antidromic collision test.