Table 2. Effect of chronic morphine with or without ULD naloxone enantiomers on mechanical withdrawal thresholds.

	Day 0 - Baseline		Day 7
Treatment	(# Withdrawals ± s.e.m.)		(# Withdrawals ± s.e.m.)
	control	TLR4 Mutant	control	TLR4 Mutant
SAL	2.3±0.6	1.6±0.2	3.3±0.3* #	2.6±0.3* #
MS	1.6±0.3	1.6±0.2	5.9±0.4#	6.5±0.3#
MS +(−)NLX	1.7±0.3	1.7±0.4	3.1±0.3* #	3.2±0.2* #
MS +(+)NLX	2.3±0.3	2.6±0.3	4.0±0.3* #	3.8±0.1* #

Control (C3H/HeOuJ) and TLR4 mutant (C3H/HeJ) mice were treated with vehicle (saline, SAL), escalating morphine (10–40 mg/kg, MS), MS and (−)naloxone (1 ng/kg, NLX), or MS and (+)naloxone (1 ng/kg) twice daily (i.p) for 7 days. Mechanical withdrawal thresholds were measured prior to the morning injection and are expressed as mean number of withdrawals to 10 repeated stimulations ± s.e.m.

*significantly different compared to morphine-treated group of same genotype.

^#significantly different compared to baseline (Day 0) response. Responses were not different between genotypes for any treatment at any time point.