Figure 1.

Diagrammatic representations of the parcellation and nomenclature used to describe the locus coeruleus complex in mammalian species in a generalized coronal section through the rostral hindbrain of a mammal. (a) The alphanumeric nomenclature applied by Dahlström and Fuxe [2] for the rat brain. (b) The combined anatomical and alphanumeric nomenclature applied by Paxinos and colleagues in their rat atlases [63,64]. (c) The anatomical nomenclature applied by Swanson [65] in his rat atlases. (d,e) The mixed anatomical and alphanumeric nomenclature applied to a limited comparative sample by Kitahama and colleagues [61] and Smeets and González [3]. (f) The flexible alphanumeric nomenclature adopted in the current study based on observations made in approximately 80 mammal species from across the phylogenetic breadth of mammals (Table 1). Note how across mammal species in general the same broad organization and distribution of noradrenergic neurons is observed, but the nomenclature based on laboratory rodents is not encompassing and required modification to be applicable across mammalian species. 4V—fourth ventricle; Vmot—trigeminal motor nucleus; A4—dorsomedial division of the locus coeruleus; A5—fifth arcuate nucleus; A6—locus coeruleus; A6vc—ventral continuation of locus coeruleus; A7—subcoeruleus; A7d—nucleus subcoeruleus, diffuse portion; A7sc—nucleus subcoeruleus, compact portion; Cb—cerebellum; LC—locus coeruleus; LCd—dorsal locus coeruleus; LCv—ventral locus coeruleus; LSC—locus subcoeruleus; mcp—middle cerebellar peduncle; me5—fifth mesencephalic tract; py—pyramidal tract; scp—superior cerebellar peduncle; SLC—subceruleus nucleus; SON—superior olivary nuclear complex; SubCA—subcoeruleus nucleus, alpha part (SubCα); SubCD—subcoeruleus nucleus, dorsal part; SubCV—subcoeruleus nucleus, ventral part. See text for details of abbreviations used for the portions of the locus coeruleus complex.