Table 2.

Net DAMGO-stimulated [³⁵S]GTPγS autoradiography in specific CNS regions of mice administered placebo pellet (placebo-P), morphine pellet (morphine-P) or morphine pellet plus supplemental morphine injection (morphine-P+morphine)

Region	Placebo-P	Morphine-P		Morphine-P+morphine
	(nCi g−1)	(nCi g−1)	(% Cont.)	(nCi g−1)	(% Cont.)
Nucleus accumbens	256±23	237±13	92±5.0	153±13*†	60±5.0
Caudate-putamen	201±17	191±16	95±7.9	120±10*†	60±4.9
Cingulate cortex	132±8	110±4	83±3.0	89±8*	67±6.0
Thalamus	188±20	183±22	97±11	130±21	64±11
Amygdala	230±9	210±17	91±7.3	197±15	86±6.5
Hypothalamus	143±13	180±12	110±7.3	123±11†	80±5.5
PAG	88±7	73±14	83±15	47±7*	53±7.9
Parabrachial nucleus	117±12	104±13	89±11	49±7*†	42±5.9
NTS	236±24	168±23*	71±9.7	157±10*	67±4.2
Spinal cord dorsal horn	187±9	147±11*	79±5.8	134±13*	72±6.9

Abbreviations: CNS, central nervous system; DAMGO, [D-Ala²,N-Me-Phe⁴,Gly⁵-ol]-enkephalin; GTPγS, guanylyl-5′-O-(γ-thio)-triphosphate; NTS, nucleus tractus solitarius; PAG, periaqueductal grey.

Mice were treated with placebo pellets, morphine pellets or morphine pellets+morphine and appropriate brain sections were processed for DAMGO-stimulated [³⁵S]GTPγS autoradiography as described in Materials and methods. Data are mean net DAMGO-stimulated [³⁵S]GTPγS binding±s.e. in nCi g⁻¹ from brains from 10 mice per group.

^*P<0.05 different from control (placebo-P) mice by Dunnett's test;

^†P<0.05 different from mice with morphine pellets implanted only (morphine-P) by Newman–Keuls test.