Comparative and Developmental Notes

Abstract

Catecholamine (CA)-containing cells in the rostral midbrain tegmentum appear to be common to all tetrapods (see Parent et al. 1984b; Parent 1986). In reptiles and birds (see Sect. 3.1) the midbrain tegmentum contains a rather large number of CA cells that send their axons to the striatal regions of the telencephalon. In amphibians (Parent 1986), however, the rostral midbrain CA cell group is much less discrete than in amniotes, and no direct mesostriatal CA pathway has yet been demonstrated. In mammals, the topographical relationships between the pars compacta and the pars reticulata of the SN (Poirier et al. 1983; Parent 1986) and the development of the nuclei that form the VTA (Poirier et al. 1983; Halliday and Törk 1986) vary greatly among species. In Sect. 3.2 the cytoarchitecture, cytology, chemoarchitecture, and main fiber connections of the mammalian SN and VTA will be reviewed, with emphasis on data in rats and cats. Aspects of the development of these structures are discussed in Sect. 3.3.