Proposed mechanism of hyperexcitability of the CB in SHR. The CB receives afferent (green) and efferent (red) innervation from the PG and SCG, respectively. Within the CB, connections are made with two main structures: Type A glomus cells and vasculature (arterioles, capillaries, and venules). Type A glomus cells receive inputs from purinergic PG afferent neurones positive for P2X3 receptors (P2X3R).¹³ In contrast, the vasculature is innervated by postganglionic sympathetic neurones (red) from the SCG. Both the CB vasculature and glomus cells express α₁-adrenoreceptors (α1R; Figure 6) and although glomus cells are not directly innervated by postganglionic sympathetic neurones, sympathetic varicosities were shown to be located close enough to glomus cells clusters to allow noradrenaline (NE) to diffuse and reach their receptors. In SHR, a more active sympathetic input to the CB exists compared with Wistar rats (Figures 3–5). In the SCG, a subpopulation of SIF (intense red) cells, organized in clusters, receive innervation from afferent purinergic PG neurones; these cells have been proposed to be ectopic glomus cells and could contribute to the CB-evoked sympatho-hyperreflexia and increased peripheral sympathetic outflow. Data from.^25,34,38,39