Deltorphins antinociception

Delta receptors nevertheless mediate some delta agonist induced analgesia, as suggested by reduced DPDPE and deltorphin activity in the DOR mutant after ITH applications [52], or enhanced antinociceptive activity in MOR mutants subjected to CFA inflammation [65]. Delta receptors also depress respiratory neurons in slice preparations [66] and mediate SNC80-evoked convulsions [67]. 

An ITH injection of [D-Ala2]deltorphin II produces an acute antinociceptive tolerance [128], Concomitant pretreatment with lower doses of the PKC inhibitor calphostin C markedly prevents the development of acute tolerance to the ITH-administered [D-Ala2]deltorphin II-induced antinociception. On the other hand, the PKA inhibitor KT5720, has no effect on the development of acute tolerance to [D-Ala2]deltorphin II antinociception [128], It is therefore likely that PKC, but not PKA, plays an important role in the process of homologous desensitization of the spinal delta opioid receptor-mediated antinociception. 

An ITH injection of [D-Ala2]deltorphin II produces an acute tolerance to the antinociceptive effect of a subsequent ITH challenge of [D-Ala2]del-torphin II. The acute tolerance is developed within 3 h after a single injection [150] (Fig. 3A). The suppression of [D-Ala2]deltorphin II-induced antinociception lasts 3-9 h and completely subsides by 12 h [150]. It should be pointed... 

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