Table 1.

Treatment paradigms for chronic intraperitoneal injections of rats (see Fig. 2)

Day of treatment	Days 1–11		Day 12
Group	Initial	15 min later	Initial	15 min later
1	Saline	Saline	Saline	Saline	Control
2	Saline	Saline	Saline	Amph*	Acute amph
3	MK-801	Saline	MK-801	Saline	Chronic MK-801
4	Saline	Amph	Saline	Amph	Chronic amph
5	MK-801	Amph	MK-801	Amph	Chronic amph blocked by MK-801
6	MK-801	Amph	Saline	Amph	Chronic amph blocked by MK-801, unblocked at last injection

^*Amph, S(+)-amphetamine sulfate. Drug concentrations: amph, 4 mg/kg; MK-801, 1 mg/kg.