Introduction: functional anatomy of central norepinephrine system in relation to neurological disorders

Catecholamine-containing neurons were first classified in the 1960s by Dahlstroem and Fuxe, following the method of Falck. In this work they described altogether 12 cell groups (A1–A12) in the rat central nervous system (CNS). Although several neuronal nuclei produce norepinephrine (NE) in the brain stem, given the wide contribution of the locus coeruleus (LC) compared with other nuclei, this main NE nucleus of the pons is considered apart from other NE systems. Thus, we routinely distinguish the LC complex as the rostral NE system, keeping it distinct from other NE nuclei forming the so-called “caudal” NE nuclear formations. In fact, the latter consist of scattered cell groups located in the lower brain stem, deep within the medullary ventrolateral reticular formation (A1), or placed within the dorsal vagal complex and the nucleus of the solitary tract (A2). These caudal NE nuclei, which form an interconnected network, send their large varicose axons to restricted target areas, following a fairly specific pattern in which distinct nuclei innervate discrete regions of the brain. This caudal component of the central NE system appears to be involved mainly in regulating vegetative functions and participates in neuroendocrine control.

The LC (A6) represents the most rostral NE complex, being localized in the pons (Figure 15.1a), in the upper part of the floor of the fourth ventricle. This rostral NE complex was originally called the nucleus pigmentosus pontis.