. 2007 Jun 18;151(8):1324–1333. doi: 10.1038/sj.bjp.0707328

Table 1.

Comparison of tolerance levels to the supraspinally mediated effects of acutely administered s.c. morphine in mice chronically given a placebo pellet, a morphine pellet or a morphine pellet plus supplemental morphine injection

Test	Placebo pellet ED₅₀ mg kg⁻¹ (95% CL)	Morphine pellet ED₅₀ mg kg⁻¹ (95% CL)	Potency ratio (95% CL)
Hot plate	3.2 (2.4–4.3)	23.1 (14.8–35.8)^a	7.3 (4.4–12.1)^b
Hypothermia^c	3.4 (2.0–5.8)	42.2 (18.4–96.6)^a	12.2 (6.6–27.1)^b
% Straub tail	3.5 (2.7–4.4)	23.0 (20.3–26.1)^a	6.4 (5.1–8.2)^b

	+Saline	+Morphine
Hot plate	4.1 (3.5–4.9)	144.5 (127.0–164.3)^a	35.4 (26.7–46.9)^b
Hypothermia^c	4.6 (3.9–5.6)	141.7 (103.2–194.7)^a	36.0 (29.3–44.3)^b
% Straub tail	4.7 (4.1–5.3)	113.9 (99.8–130.0)^a	24.7 (21.1–28.9)^b

Abbreviations: CL, confidence limits; ED₅₀, half-maximal effective dose; s.c., subcutaneously.

Mice were implanted with placebo pellet, 75 mg morphine pellet, placebo pellet+supplemental saline injection (+saline) or morphine pellet+supplemental morphine injection (+morphine), as described in Materials and methods. Thirty minutes after acute s.c. morphine treatment, the mice were assessed in the 56°C hot-plate test and for changes in body temperature (ΔT_b) and Straub tail. Data are mean values±95% CL from 30 mice per group, including six mice per morphine dose (four doses each and saline).

Significantly different than placebo-P group based on non-overlapping 95% CLs.

Significantly different potency ratio because the lower 95% CL is greater than 1.

Calculated as the ED_1.5 for a maximum ΔT_b of −3°C.