Delta opioid antagonist, 16-Me cyprenorphine, selectively attenuates conditional fear- and DPDPE-induced analgesia on the formalin test.
The effects of 16-Me cyprenorphine (M80) on the antinociception produced by reexposing rats to a chamber associated with footshock (1 mA, 0.75 sec) 24 hr earlier was assessed with the formalin test. In Experiment 1, intracerebroventricular administration of M80 dose-dependently (0.5-8 micrograms) reversed conditional analgesia. Experiment 2 demonstrated that M80 (5 micrograms) had no effect on baseline pain sensitivity, but completely reversed conditional analgesia. Experiment 3 demonstrated that 0.25 micrograms DAGO, 3.5 micrograms DPDPE, and 28 micrograms U50,488H all produced equivalent levels of antinociception on the formalin test. The 5 micrograms dose of M80 completely reversed the antinociception produced by DPDPE but did not influence that produced by DAGO or U50,488H. These data suggest, that at the doses employed, M80 is a selective delta-opioid receptor antagonist and that delta-receptors are involved in conditional fear-induced analgesia.
Fanselow
M S
MS
Department of Psychology, Dartmouth College, Hanover, NH 03755.
Calcagnetti
D J
DJ
Helmstetter
F J
FJ
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000037:antagonists & inhibitors*; D005239:Fear / Q000502:physiology*; D005260:Female; D005557:Formaldehyde; D007276:Injections, Intraventricular; D009019:Morphinans / Q000494:pharmacology*; D010147:Pain Measurement; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects*; D017465:Receptors, Opioid, delta
D000700:Analgesics; D004745:Enkephalins; D009019:Morphinans; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D005557:Formaldehyde; C051207:16-methylcyprenorphine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020881:Enkephalin, D-Penicillamine (2,5)-