To evaluate if ulnar stimulation could suppress NAc activity, we examined the expression of c-fos in the NAc by acute cocaine injection following surgical lesion of either DC, STT or LHb. The numbers of c-fos positive cells were significantly increased in cocaine-treated rats compared to controls. The cocaine-induced increase in c-fos positive neurons was attenuated by ulnar MS, which was prevented when the DC was lesioned, but not when the STT was lesioned (Fig. 6A1–6). In another set of animals, we repeated this experiment after disruption of the LHb. Electrolytic lesion of LHb prior to ulnar stimulation blocked the inhibitory effect of ulnar stimulation on cocaine-induced c-fos expression in the NAc (Fig. 6B1–5).Figure 6The effects of DC or LHb lesions on ulnar inhibition of cocaine-induced c-fos expression in the NAc. (A) The cocaine-induced increase in c-fos positive neurons in NAc (A2; Cocaine, n = 6) was attenuated by ulnar stimulation (A3; Cocaine + MS, n = 6), which was prevented when the DC was damaged (A4; DC X + Cocaine + MS, n = 6), but not STT (A5–6; STT + Cocaine + MS, n = 6). A1, control (Con); *p < 0.05, Bar = 20 µm. (B) The cocaine-induced increase in c-fos positive neurons in NAc (B2; Cocaine, n = 6) was attenuated by ulnar stimulation (B3; Cocaine + MS, n = 6), which was prevented when the LHb was damaged (B4–5; LHb X + Cocaine + MS, n = 6). B1, control (Con); *p < 0.05, Bar = 20 µm.