“…These projection neurons possess spiny dendrites, and about half also contain enkephalin while the other half show colocalization of substance P (SP) and dynorphin (Brauth et al, 1983; Reiner et al, 1983, 1984; Reiner and Anderson, 1990; Anderson and Reiner, 1990a; Anderson and Reiner, 1991; Veenman and Reiner, 1994; Sun et al, 2005). These neurons account for the SP+ and enkephalinergic projections of MSt to the dopaminergic neurons of the substantia nigra pars compacta and the GABAergic neurons of the substantia nigra pars reticulata (Anderson et al, 1991; Medina et al, 1995; Veenman and Reiner, 1994), of which the SP+ projection is more prominent. The MSt neurons projecting to the substantia nigra and the ventral tegmental area send their axons through the ventral pallidum, and some have terminations there (Kitt and Brauth, 1981; Medina and Reiner, 1997; Person et al, 2008).…”