Table 1.

Characteristics of opioid agonists assessed with the AAT in amphibians

Opioid agonist	Type	Routea	Dosage rangeb	ED50c
Fentanyl	Mu	s.c.	0.1–30	1.4
CI-977 (Enadoline)	Kappa	s.c.	1–30	5.8
Levorphanol	Mu	s.c.	1–100	7.5
U50488H	Kappa	s.c.	1–100	8.5
Methadone	Mu	s.c.	10–300	19.9
Bremazocine	Kappa	s.c.	10–100	44.4
Morphine	Mu	s.c.	10–300	86.3
Buprenorphine	Mu	s.c.	30–300	99.1
Meperidine	Mu	s.c.	30–1000	128.1
Codeine	Mu	s.c.	10–1000	140.3
Nalorphine	Kappa	s.c.	100–300	320.9
Dermorphin	Mu	i.s.	0.003–0.3	0.04
DAMGO	Mu	i.s.	0.03–1	0.13
DSLET	Delta	i.s.	0.01–3	0.13
DADLE	Delta/mu	i.s.	0.03–3	0.14
Fentanyl	Mu	i.s.	0.3–10	0.94
Morphine	Mu	i.s.	0.3–10	2.26
DPDPE	Delta	i.s.	1–10	3.29
Deltorphin	Delta	i.s.	0.3–100	13.50
CI-977 (Enadoline)	Kappa	i.s.	0.3–30	13.51
Bremazocine	Kappa	i.s.	3–100	22.89
U50488H	Kappa	i.s.	3–100	36.82
Nalorphine	Kappa	i.s.	3–100	43.13
DADLE	Delta/mu	i.c.v.	0.1–10	1.3
Morphine	Mu	i.c.v.	0.1–10	2.0
DPDPE	Delta	i.c.v.	1–30	8.3
Fentanyl	Mu	i.c.v.	0.3–100	23.0
CI-977 (Enadoline)	Kappa	i.c.v.	3–100	35.5
U50488H	Kappa	i.c.v.	6–100	61.5

^aRoute of administration: s.c.= subcutaneous; i.s.= intraspinal; i.c.v.= intracerebroventricular (data from Refs. [50,53,59]).

^bEffective dosage range: in nanomoles per gram for s.c. administration; in nanomoles per frog for i.s. and i.c.v. administration.

^cDose that gives 50% analgesic effects: in nanomoles per gram for s.c. administration; in nanomoles per frog for i.s. and i.c.v. administration.