Fig. 2.

Effect of nicotine self-administration on stress-induced neuronal activation in prelimbic cortex. Photomicrographs (a–d) illustrate immunohistochemical labeling of c-Fos in coronal tissue sections of prelimbic cortex (PrL). Boxes indicate the locations of areas used for counting c-Fos⁺ neurons; these areas are shown in panels e-h at higher-magnification. Schematic representations of PrL (i) are adapted from Paxions and Watson 1997, with the position of the counting square (380 × 380 μm²) shown. Both the saline (a, e) and nicotine (b, f) rats expressed c-Fos at very low levels after sham-shock. Mild footshock stress greatly increased c-Fos expression in the saline group (c, g), but to a lesser degree in the nicotine group (d, h). Mean ± SEM number of stress-induced c-Fos⁺ neurons is shown in panel j. *: p < 0.01, compared to the corresponding sham-shock controls. #: p < 0.01, compared to saline rats receiving footshock. n=3 for sham-shock, and n=5 for shock groups in both the saline and nicotine rats in Figs. 2–5. Scale bars: panels a–d, 100 μm; panels e–h, 50 μm.