To allow comparison to previously published work (Nixon & Crews, 2002) while maintaining temporal specificity needed to interpret effects on cell proliferation, rats were injected intraperitoneally (i.p.) with a single dose of BrdU nucleotide (200 mg in 0.9% saline/kg; Sigma, USA) immediately upon completion of the 7-wk exposure (day 0) or on days 3, 7 or 21 of abstinence (n=3–9/time-point). BrdU injections were performed starting at 09:00 hours (light off). Non-exposed controls (n=3–4/time-point) were injected in parallel. Animals were sacrificed 5 h after BrdU injection.
