Neuroanatomical specificity of the circuits controlling sympathetic outflow to different targets

1. Despite the emerging framework that central neural pathways controlling the activity of the sympathetic nervous system are capable of producing highly selective responses, the specific neural pathways governing different sympathetic outflows are poorly understood. 2, Anatomical studies suggest that five brain areas, namely the rostral ventrolateral medulla, the rostral ventromedial medulla, the caudal raphe nuclei, the region containing the A5 noradrenergic neurons and the paraventricular hypothalamic nucleus, provide dominant supraspinal innervation of sympathetic preganglionic neurons. 3. The anatomical parcellation of different functions within and among these cell groups is uncertain. However, recent studies using transynaptic retrograde labelling of neural pathways connected to various sympathetic targets suggest that the circuits controlling these different targets may be partially distinct. Similarly, anatomical studies relying on stimulus-evoked expression of immediate early genes, such as c-fos, suggest that different sympathetic responses mag be controlled by distinct neural circuits. 4. Thus, although many similarities exist in the anatomical circuits innervating different sympathetic targets, possibly supporting the orchestration of global sympathetic responses, differences are also discernible.