Abstract
Scratching induced by intrathecal (IT) administration of kainic acid (0.5 nmol) to rats was inhibited by IT pretreatment with the selective mu agonists levorphanol (30 and 90 nmol), [D-Ala 2,N-Met-Phe 4, Gly 5-ol]-enkaphalin (DAGO, 0.4 and 1.1 nmol), or morphine (90 nmol), the mixed mu-delta agonist [D-Ala 2,D-Leu 5]-enkaphalinamide (DADLE, 10 and 30 nmol), or the sigma/phencyclidine (PCP) agonists dextrorphan (90 nmol) or (+)-N-allyl-N-normetazocine ([+]-NAM, 90 nmol). The kappa agonists dynorphin (1.1 nmol) and ethylketocyclazocine (EKC, 90 nmol) had no significant effect, nor did the selective delta agonist [D-Pen 2,D-Pen 5]-enkaphalinamide (DPDPE, 90 nmol). The nonopioids (+)-3(3-hydroxyphenyl)-N-(1-propyl)piperidine([+])-3-PPP, 90 nmol) and PCP (90 nmol), selective for sigma and PCP sites, respectively, both antagonized kainic-induced scratching. Levorphanol- and DADLE-induced attenuation of scratching was partially antagonized by naltrexone. These findings suggest that opioid inhibition of kainic acid-induced scratching is mediated by classical mu receptors as well as sigma and PCP sites.
Published Version
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