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. Author manuscript; available in PMC: 2010 Jul 20.
Published in final edited form as: Neuropsychopharmacology. 2006 Nov 8;32(5):1098–1108. doi: 10.1038/sj.npp.1301228

Figure 1.

Figure 1

Mean (±1 SEM) active lever responding for rats in the NIC-Only, NIC + VS, and 2-Lever groups with access to 30 (a), 60 (b), or 90 μg/kg (c) nicotine infusions. For the 2-Lever group, responding on the infusion lever (■) is depicted separately from responding on the VS lever (□). The VS-Only group (0 μg/kg/infusion) is depicted in each panel for comparative purposes. When nicotine and VS were contingent upon a single response (NIC + VS groups) higher unit doses decreased response rate. In contrast, when nicotine and VS were contingent upon separate responses (2-Lever groups), higher unit doses still potently increased responding for VS.