A,D. Two anteroposterior levels of the VP, defined by the presence of substance P-IR, at approximately +0.36 mm (A) and −0.12 mm (D). B-C. Sections proximal to tissue in panel D showing calbindin d28k-IR (B) and neurotensin-IR (C). E-F. Sections proximal to tissue in panel D showing calbindin d28k-IR (E) and neurotensin-IR (F). The VPdl subregion exhibits fibers with calbindin-d28k-IR but not neurotensin-IR. The VPvm subregion exhibits fibers with neurotensin-IR but not calbindin-d28k-IR, and the VPr and VPvl subregions do not express calbindin-d28k-IR or neurotensin-IR. This compartmentation of VP is observed across the anteroposterior extent of VP, except in the VPr (Zahm and Heimer, 1988, 1990; Zahm 1989; Zahm et al., 1996; Riedel et al., 2002; Tripathi et al., 2010, 2013). All sections are 30 μm thick. Neighboring locations to the VP are demarcated by dotted lines. Material from Dr. Root (Morales laboratory, NIDA).