Animals that had stabilized PR schedules within ± 3 BP and a minimum of FR-32 were then habituated to the microinjection process on two consecutive days. To lower the microinjectors into the bilateral intracerebral guide cannulae, animals were immobilized by gently wrapping them in a towel. Microinjectors were lowered into the guide cannulae over a 1 min period, approximately 1 min prior to putting the animal into the operant conditioning chamber. Microinjectors penetrated 3.5 mm beyond the guide cannulae into the lateral dorsal tegmental area (LDTg). Nothing was infused on these habituation days, and BP data were collected. The microinfusion experiment was then conducted starting at least two days after the microinjection habituation sessions. The experiment involved the delivery of aCSF or OxoSQ at two doses, 1 nmol and 10 nmol per side, into the LDTg in a counterbalanced order with baseline (i.e. no microinjection) days between infusions. In all cases where microinjections were delivered, injection volume was 0.1 μl per side delivered over 30 sec. In some animals, OxoSQ had sufficient suppressive effects on lever pressing to result in
