Fig. 3

Preganglionic autonomic neurons, key transcription factors in their embryonic development and the classification of autonomic nervous system domains. The figure schematically displays the sympathetic and parasympathetic domains of autonomic preganglionic neurons and provides classical and recent naming proposals for the distinct subdivisions. These are derived primarily from physiological and pharmacological studies (Langley [1] see figure 1), evolutionary comparison within vertebrates (Nilsson [200], see figure 2) and developmental studies of critical regulators of neuronal cell lineage (Brunet and colleagues first presented in Espinosa–Medina et al., [154], see figure 4). The transcription factors responsible for the current renaming proposal from sacral “parasympathetic” to “sympathetic” are depicted above the schematic illustration of consecutive domains of the central nervous system harboring preganglionic autonomic neurons. The expression patterns and function are discussed in the main text and Table 2. The illustration is modified from Osumi and colleagues [227] with the mesencephalon containing the neuronal cell bodies giving rise to preganglionic axons to the IIIrd cranial nerve (N. oculomotorius) and the parasympathetic ciliary ganglion. The schematic illustration of the metencephalon displays rhombomeres 1 to 7 with the neuronal cell bodies giving rise to the visceromotor axons in the VIIth (N. facialis) and Xth (N. vagus) cranial nerves. The source of the Vth (N. trigeminus) and IXth nerve (N. glossopharyngeus) are omitted for simplicity. Within the thoracolumbar sympathetic domain, three different axon trajectories are indicated: leftward orientation indicating the rostral direction of preganglionic axons towards the SCG, rightward orientation towards more caudally located ganglia in the paravertebral sympathetic chains, and downward orientation indicating projection to prevertebral sympathetic ganglia. In the sacral autonomic domain at the right end of the scheme, axon projections indicate nerve fibers not entering the paravertebral sympathetic chain and traversing abdominal space in the N. pelvicus and pudentus