DIFFERENCES IN DELTA-OPIOID RECEPTOR ANTINOCICEPTION, BINDING, AND MESSENGER-RNA LEVELS BETWEEN BALB C AND CXBK MICE/

Mu and delta opioid receptors have been demonstrated to mediate supras pinal opioid antinociception. Whereas the recombinant inbred CXBK mous e is notably deficient in mu opioid receptor antinociception, binding density, and mRNA (MOR-1) levels, little is known about delta opioid r eceptor processes in this strain. The present study thus compared CXBK mice and their BALB/c strain progenitors with respect to delta opioid antinociception, whole-brain receptor binding levels, and mRNA (DOR-1 ) levels. Following intracerebroventricular injections of the selectiv e delta(1) and delta(2) opioids DPDPE and [D-Ala(2)]deltorphin II, res pectively, CXBK mice displayed relatively lower antinociception on the tail-flick test, resulting in significantly increased ED50 values for both agonists in this strain. Decreased whole-brain specific binding of [H-3][D-Ala(2)]deltorphin II, but not [H-3]DPDPE, was also observed in CXBK mice. Solution hybridization with a probe for the DOR-1 revea led increased transcript levels in the caudate-putamen, frontal cortex , and spinal cord of this strain. The present data demonstrate a defic iency in delta(1) and delta(2) opioid antinociception in CXBK mice con comitant with reductions in whole-brain delta, receptor binding and re gional increases in DOR-1. Whether these observations are causally rel ated remains to be clarified. (C) 1998 Elsevier Science B.V. All right s reserved.