The experimental timeline of operant training, dependence induction, BrdU injection, and perfusion are shown in Fig. 1a. Two sets of two groups of alcohol exposure were used: Set I, nondependent alcohol self-administering and alcohol-dependent animals perfused 2-4 h after the last air/alcohol vapor exposure; Set II, prolonged nondependent and prolonged dependent rats received one injection of BrdU and were continued on air/alcohol vapor exposure for 28 days beyond Set I perfusion date to measure BrdU survival, and were perfused 2-4 h after air/alcohol vapor exposure (Fig. 1a). The animals from the two nondependent groups did not differ in alcohol intake and self-administration behavior during baseline training (i.e., prior to air control). The animals from the two dependent groups did not differ in alcohol intake and self-administration behavior during baseline training (prior to alcohol vapors). Chronic intermittent exposure to alcohol vapors elicited increased alcohol self-administration in both groups of alcohol-dependent animals compared to baseline alcohol self-administration and compared to nondependent animals (post-vapor behavioral data was averaged from self-administration sessions over 5 days before day 77 Set I or Set II). Specifically,
