Influence of omega-conotoxin on morphine analgesia and withdrawal syndrome in rats

• Published in: European journal of pharmacology Vol. 218; no. 1; p. 75
• Main Authors: Basilico, L, Parolaro, D, Rubino, T, Gori, E, Giagnoni, G
• Format: Journal Article
• Language: English
• Published: Netherlands 21.07.1992
• Subjects: Analgesia; Animals; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Calcium Channels - drug effects; Female; Mollusk Venoms - pharmacology; Morphine - pharmacology; Naloxone - pharmacology; omega-Conotoxins; Peptides, Cyclic - pharmacology; Rats; Substance Withdrawal Syndrome - prevention & control
• ISSN: 0014-2999
• DOI: 10.1016/0014-2999(92)90149-X

The effect of omega-conotoxin on opiate analgesia and withdrawal syndrome was investigated in rats. omega-Conotoxin given i.c.v. and i.p. caused weak analgesia in the tail-flick test. When the toxin (20 ng/rat) was given i.c.v. immediately before morphine (1.5 micrograms/rat i.c.v.) the resultant analgesic effect was additive. In contrast, the analgesia elicited by morphine (3 micrograms/rat i.c.v.) was greatly reduced after 24-h pretreatment with the toxin (20 ng/rat i.c.v.). The systemic administration of the toxin (10 micrograms/kg i.p.) did not affect morphine analgesia whether omega-conotoxin was coadministered with morphine (2.5 mg/kg i.p.) or was given 24 h before the opiate (5 mg/kg i.p.). omega-Conotoxin i.c.v. injected in morphine-dependent rats 15 min before naloxone challenge significantly attenuated the abstinence syndrome. On the contrary systemic administration of omega-conotoxin failed to suppress the morphine withdrawal syndrome. The present results suggest that omega-conotoxin affects both acute and chronic effects of morphine.