Fig. 5.

Locomotor activity recorded during place preference conditioning sessions with escalating doses of heroin (a) or saline (b) during the chronic heroin re-exposure period (Heroin/Heroin, black circles) or the chronic heroin exposure period (Saline/Heroin, white circles). Data from control rats conditioned with saline during chronic saline exposure or re-exposure were pooled (Saline/Saline, grey circles). The mean, averaged across all conditioning sessions, is shown to the right of each expanded dataset. All data are presented as mean ± S.E.M. * P<0.05, comparisons between Heroin/Heroin and Saline/Heroin groups; # P<0.05, compared to Saline/Saline control group