Table 1.

Allocation of rats to experimental phases.

Experimental Phase	# Rats
Free Drinking (15 min delay) and Self-Administration	6
Free Drinking (15 min delay) Only	3
Free Drinking: 15 versus 60 min delay	11
Free Drinking: Effects of Delayed Opioid Antagonism	5
Free Drinking Anatomical Controls	4
Self-Administration and Extinction Learning	5
Extinction Learning Only	7
Extinction Learning and Retention	2
Extinction Retention Only	6
Extinction Learning/Retention and Reinstatement	4
Reinstatement Only	17
Rats excluded after pre-exposure	3
Rats excluded based on localization of injector tips	6
Total	79