Table 1.

Subject groups, drugs injected and injection order.

Group	Cannula location	5 week access history	First drug	Second drug	N
1	core	IA	DAMGO	raclopride	9
2	core	WA	DAMGO	raclopride	7
3	core	CA	DAMGO	raclopride	7
4	shell	IA	DAMGO	raclopride	7
5	shell	WA	DAMGO	raclopride	7
6	shell	CA	DAMGO	raclopride	6
7	core	IA	naltrexone	SCH23390	11
8	core	WA	naltrexone	SCH23390	8
9	core	CA	naltrexone	SCH23390	9
10	shell	IA	naltrexone	SCH23390	7
11	shell	WA	naltrexone	SCH23390	6
12	shell	CA	naltrexone	SCH23390	8
13	core	IA	CTAP		11
14	core	WA	CTAP		11
15	shell	IA	CTAP		10
16	shell	WA	CTAP		8
17	core	IA	naltrindole	nor-BNI	12
18	core	WA	naltrindole	nor-BNI	11
19	shell	IA	naltrindole	nor-BNI	11
20	shell	WA	naltrindole	nor-BNI	8
21	core	none	(CTAP vs DAMGO)	-	19
				TOTAL	193

Three doses of the first drug were injected in random order, followed by three doses of the second drug in random order. See section 2.4 for doses. Each rat received a single vehicle (saline) injection on a randomly-determined day.