Fig. 7. Respiratory behavior after pretreatment with 0.1 µmol l^-1 cocaine in freely behaving snails over time. Comparison of animals pretreated with 0.1 µmol l^-1 cocaine and given operant training (shown in Fig. 6B) with freely behaving animals similarly pretreated but given no pneumostome stimulation (N=15) indicates that respiratory behavior does not change over the time frame used for trained animals. Values are mean ± s.e.m. for number of pneumostome openings. Training session 1; 2, Training session 2; MT, Memory Test; N.S.=not significant; E1-3, extinction training sessions. ^*P<0.05 compared with Training session 1 within the same treatment group.