to exposure 1 (Fig. 1B and E). Because the increase in locomotor activity appeared to be limited to hyperactivity onset at 47% ethanol vapor (but not at higher concentrations; Fig. 1B), we determined the time of PS during the first exposure to 47% ethanol vapor (12.5 minutes) and split Dist into Dist onset (2 to 12.5 minutes) and Dist offset (12.5 to 25 minutes). This revealed that ΔDist increased during hyperactivity onset (2.32 m Exp 1 vs. 2.76 m Exp 2, p = 0.013, paired t-test) but not offset (2.89 m Exp 1 vs. 3.10 m Exp 2, p = 0.156) at 47% ethanol vapor concentrations. Earlier onset of locomotor activation during the second ethanol exposure at this low ethanol concentration may reflect sensitization to the locomotor activating effects of ethanol (Lister, 1987). Higher ethanol vapor concentrations that lead to overall increased hyperactivity in the rapid tolerance paradigm may be due to a mix of sensitization and tolerance.
