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 hig hly selective responses, the specific neural pathways governing different s ympathetic outflows are poorly understood. 2, Anatomical studies suggest that five brain areas, namely the rostral ven trolateral medulla, the rostral ventromedial medulla, the caudal raphe nucl ei, the region containing the A5 noradrenergic neurons and the paraventricu lar hypothalamic nucleus, provide dominant supraspinal innervation of sympa thetic preganglionic neurons. 3. The anatomical parcellation of different functions within and among thes e cell groups is uncertain. However, recent studies using transynaptic retr ograde labelling of neural pathways connected to various sympathetic target s suggest that the circuits controlling these different targets may be part ially distinct. Similarly, anatomical studies relying on stimulus-evoked ex pression of immediate early genes, such as c-fos, suggest that different sy mpathetic responses mag be controlled by distinct neural circuits. 4. Thus, although many similarities exist in the anatomical circuits innerv ating different sympathetic targets, possibly supporting the orchestration of global sympathetic responses, differences are also discernible.