Distribution of opioid peptide mRNA and κ-opioid receptors in the limbic system of Fawn-Hooded and Wistar-Kyoto rats

Full text: Opioidergic mechanisms are implicated in alcohol-seeking behaviour. The aim of the present work was to examine whether there were differences in preproenkephalin (ppEnk) and preprodynorphin (ppDyn) mRNA expression, using in situ hybridization histochemistry (ISHH), and κ-opioid binding, using autoradiography, in the brain of Fawn-Hooded (FH) rats, an alcohol-preferring strain, compared with control Wistar-Kyoto (WKY) rats. Rats were stunned and killed by decapitation. For ISHH, antisense oligonucleotides (45-mers) to ppEnk and ppDyn were 3'-labelled with [33P]dATP and incubated with brain sections. For κ-opioid autoradiography, brain sections were incubated with [3H]U-69,593 (5 nM). Non-specific binding was determined with 10 μM naloxone. Sections were apposed to film for subsequent densitometric analysis. In comparison to WKY rats, FH rats had a decreased expression of ppEnk in the striatum (-24%) and nucleus accumbens (-17%), whereas ppDyn mRNA increased in the hippocampus (+34%) of FH rats compared to WKY rats. In comparison to WKY rats, FH rats had reduced κ-opioid binding in the central gray (-19%), the substantia nigra pars reticulata (-45%) and the lateral septal nucleus (-52%). Copyright (1998) Australian Neuroscience Society