κ 1 Receptor mRNA Distribution in the Rat CNS: Comparison to κ Receptor Binding and Prodynorphin mRNA

Abstract

Three opioid receptor types have been identified in the CNS and periphery that are referred to as μ, δ, and κ. The present study examines the mRNA distribution of the κ 1 receptor in the rat brain and compares it to the distribution of κ receptor-binding sites and prodynorphin mRNA using a combination of in situ hybridization and receptor autoradiographic techniques. κ 1 receptor mRNA was localized with a cRNA probe generated with a BamHI- HindIII cDNA fragment of the rat κ 1 receptor and corresponds to the last 45 bp of the protein coding region and 728 nucleotides of the 3′ untranslated region. Prodynorphin mRNA was localized with a cRNA probe corresponding to a 733-bp BamHI- HincII fragment of prodynorphin. κ receptor-binding sites were labeled in one of two ways: [ 3H]U69,593 or [ 3H]bremazocine in the presence of a 300-fold excess of DAMGO and DPDPE. A high degree of correspondence between the κ 1 receptor mRNA and κ receptor binding was observed in several brain regions, including the endopiriform nucleus, claustram, nucleus accumbens, olfactory tubercle, bed nucleus of the stria terminalis, medial preoptic area, paraventricular, supraoptic, suprachiasmatic, dorsomedial and ventromedial hypothalamic nuclei, basolateral, medial and cortical amygdaloid nuclei, midline thalamic nuclei, periaqueductal grey, parabrachial nucleus, locus coeruleus, and the nucleus of the solitary tract. Differences in the localization of κ 1 receptor mRNA and binding and the relationship between the distribution of κ 1 receptor and prodynorphin mRNAs are discussed.