In addition to the role in stress responses reviewed above, effects of NK1R activation on catecholamine signaling in the mesolimbic, mesocortical, and nigrostriatal pathways also suggest a role in appetitive behaviors, including those related to drug seeking and taking. The catecholamine DA is classically associated with rewarding properties of addictive drugs and interacts with SP in pathways that drive drug seeking. For example, SP is co-localized with the D1 receptor in a subpopulation of medium spiny neurons (MSN) of the ventral striatum (Le Moine and Bloch, 1995). The majority of these neurons feed back onto the substantia nigra, a region that contains dopaminergic cell bodies and expresses NK1Rs (Futami et al., 1998; Le Moine and Bloch, 1995; Whitty et al., 1995). Infusion of SP or SP analogues into the substantia nigra or VTA stimulates the firing rate of these neurons and subsequent DA release in their terminal fields (Barnes et al., 1990; West and Michael, 1991), increases locomotor activity (Barnes et al., 1990; Eison et al., 1982; Elliott et al., 1992; Kelley et al., 1979; Placenza et al., 2004), and
