Figure 4.

Increased percentages of PCNA-positive foci following NNK exposure. The analysis was carried out using digitally recorded epi-fluorescence images of sections double-stained for PCNA and CGRP. A neuroendocrine focus (identified by CGRP reactivity) was regarded as positive if it contained one or more PCNA-reactive nuclei. 6wk: 6 weeks' solvent only (control) or NNK treatment; 6wk+6wk rec: 6 weeks' solvent only or NNK treatment, followed by recovery period of 6 weeks, denoted by “rec”; 24wk: 24 weeks solvent only or NNK-treatment; and 24wk+6wk rec: 24 weeks solvent only or NNK-treatment, followed by recovery period of 6 weeks. Mean ± SD is shown from N=6-10 animals per group. **: P<0.01, ***: P<0.001 between control vs. NNK treatment groups. Statistical analysis by unpaired t-test