Table 1.

Behavioral Responses of Intrathecal Administration of N/OFQ Over a Wide Range of Ultra-Low Doses as Compared to a Single Dose of DAMGO and Substance P.

	Warm Water Tail-Withdrawal Latency (sec)*
			Itch/Scratching†
Compound/Dose	46°C	50°C	Number/15 min
N/OFQ
0 (vehicle)	20 ± 0‡	1.6 ± 0.1	50.0 ± 12.9
1 fmol	20 ± 0	1.7 ± 0.1	33.8 ± 9.9
10 fmol	20 ± 0	1.6 ± 0.2	49.3 ± 15.7
100 fmol	20 ± 0	1.4 ± 0.2	44.3 ± 14.0
1 pmol	20 ± 0	1.7 ± 0.1	57.2 ± 15.3
10 pmol	20 ± 0	1.8 ± 0.1	57.5 ± 10.2
100 pmol	20 ± 0	1.9 ± 0.2	41.0 ± 15.1
1 nmol	20 ± 0	1.6 ± 0.2	35.2 ± 7.1
Substance P
100 nmol	4.9 ± 1.4§	1.2 ± 0.1	48.5 ± 8.6
DAMGO
10 nmol	20 ± 0	16.8 ± 2.1§	910.5 ± 103.9§

^*The latency was measured at 15 min after intrathecal administration of test compound.

^†The scratching number was scored between 15^th and 30^th min after intrathecal administration of test compound.

^‡Each value represents mean ± S.E.M. (n = 6).

^§The asterisk represents a significant difference from the vehicle condition (P < 0.05).