Figure 5.

Models for postganglionic cholinergic neuronal differentiation in the sympathetic nervous system. (A) Sympathetic cholinergic neurons arise from principal ganglion cells via formation of fully functional noradrenergic neurons (NE) lacking cholinergic expression that synapse upon targets such as the sweat glands and induce the secretion from the target of factor(s) that induce the cholinergic phenotype and attenuate the expression of noradrenergic traits in the noradrenergic neuron (see ref. 5). (B) A proportion of the principal ganglion cells in the sympathetic chain express the cholinergic phenotype prior to innervation of target organs. Asterisk indicates a cholinergic (i.e., ChAT⁺/VAChT⁺) phenotype with noradrenergic [e.g., TH, dopamine β-hydroxylase (DBH), NET, but not VMAT] traits. Loss of noradrenergic traits in rat postganglionic cholinergic sympathetic neurons may occur as a direct result of interaction with the target, or may also be programmed in a target-independent manner.