Regional central nervous system densities of delta-opioid receptors in alcohol-preferring P, alcohol-nonpreferring NP, and unselected Wistar rats

The densities of delta-opioid receptors in the central nervous system of al cohol-naive, adult, male, alcohol-preferring P, alcohol-nonpreferring NP, a nd Wistar rats were examined with the use of quantitative autoradiography. Slides with coronal 20-mum sections through the regions of interest were in cubated in 5 nM [H-3]-[D-Pen(2),D-Pen(5)]enkephalin (DPDPE) to label delta- opioid receptor sites. Nonspecific binding was determined in the presence o f 10 muM naloxone. Significant differences between the P and the NP rat lin es were found in numerous cortical regions, the basolateral amygdala, and t he posterior hippocampus, with 10%-20% lower [H-3]-DPDPE binding found in t he P line. In most regions examined, binding levels in the Wistar rats were intermediate between those of the P and the NP rats. Significantly lower [ H-3]-DPDPE binding levels in the P rat may indicate fewer delta(1)-opioid r eceptors or decreased binding affinity. The lower binding in certain limbic regions, such as the basolateral amygdala and posterior hippocampus, as we ll as cortical differences in the P rat may be associated with the divergen t alcohol drinking behaviors found between the P and the NP lines. (C) 2001 Elsevier Science Inc. All rights reserved.