Table 1.

Experimental cohorts

Cohort	na	Successful initiationb	Unsuccessful initiation	Ethanol preferencec	RRd	Extinctione	Prewaitf	Controlsg
1	8	6	2	yes	4	6	yes	no
2	6	3	3	no	4	3	yes	no
3	5	5	0	no	4	5	yes	no
4	12	5	1	no	20	11h	no	6
5	9	5	0	no	20	9	no	4
6	12	8	4	yes	20	0	no	no

^an = the number of rats that started the experiment

^bSuccessful initiation indicates the number of rats that met the criterion of consuming at least 0.3 g/kg of 10% ethanol in at least 4 of 5 consecutive days at the end of the initiation procedure.

^cEthanol preference indicates whether that cohort underwent the pre- and post-initiation two bottle choice procedure.

^dRR = the final intended response requirement during the training period

^eExtinction = the number of rats that went through the extinction procedure at the end of the training.

^fPrewait indicates whether that cohort had an extra 45 min wait period in the chamber before the session began.

^gControls = the number of rats that were never exposed to ethanol during the training.

^hThree controls were not included in the extinction analysis because they were not able to meet consistently the RR of 20.