Neuroanatomical patterns of the mu, delta, and kappa opioid receptors of rat brain as determined by quantitative in vitro autoradiography.

Abstract

Highly specific radioligands and quantitative autoradiography reveal strikingly different neuroanatomical patterns for the ,u, 8, and K opioid receptors of rat brain. The ,I receptors are most densely localized in patches in the striatum, layers I and III of the cortex, the pyramidal cell layer of the hippocampal formation, specific nuclei of the thalamus, the pars reticulata of the substantia nigra, the interpeduncular nucleus, and the locus coeruleus. In contrast, 8 receptors are highly confined, exhibiting selective localization in layers I, H, and VIa of the neocortex, a diffuse pattern in the striatum, and moderate concentration in the pars reticulata of the substantia nigra and in the interpeduncular nucleus. 8 receptors are absent in most other brain structures. This distribution is unexpected in that the enkephalins, the putative endogenous ligands of the 8 receptor, occur essentially throughout the brain. The K receptors of rat brain exhibit a third pattern distinct from that of the ,u and 8 receptors. K receptors occur at low density in patches in the striatum and at particularly high density in the nucleus accumbens, along the pyramidal and molecular layers of the hippocampus, in the granular cell layer of the dentate gyrus, specific midline nuclei of the thalamus, and hindbrain regions. K receptors appear to be uniformly distributed across regions in the neocortex with the exception of layer m, which revealed only trace levels of binding. An important conclusion of the present study is that 8 receptors occur at high density only in the forebrain and in two midbrain structures, whereas ,u and K receptors exhibit discrete patterns in most major brain regions.

Ultrastructural Immunocytochemical Localization of μ-Opioid Receptors in Rat Nucleus Accumbens: Extrasynaptic Plasmalemmal Distribution and Association with Leu5-Enkephalin

“…1). The light microscopic distribution of MOR-LI was similar to the known distributions of the receptor on the basis of receptor autoradiographic (Mansour et al, 1987;Tempel and Zukin, 1987), in situ hybridization (Mansour et al, 1995a) and immunocytochemistry of antipeptide antibodies raised against similar sequences taken from the same portion of the receptor (Arvidsson et al, 1995;Mansour et al, 1995b). The technique described here produced less intense neuronal perikarya immunoreactivity than that found with the same MOR serum using the conditions of A. Moriwaki and G. Uhl (unpublished observations).…”

“…A heterogenous distribution of -opioid receptors in the NAC has been shown using autoradiographic localization of selective radioligands (McLean et al, 1986;Mansour et al, 1987;Tempel and Zukin, 1987). Additionally, NAC neurons express mRNA for -opioid receptors as seen by in situ hybridization methods (Chen et al, 1993;Delfs et al, 1994;Zastawny et al, 1994;Mansour et al, 1995a).…”

Central Opioid Receptors Differentially Regulate the Nalmefene-Induced Suppression of Ethanol- and Saccharin-Reinforced Behaviors in Alcohol-Preferring (P) Rats

“…Thus, nalmefene produced a 20-fold greater potency in the NACC compared with the VTA in suppressing EtOH-maintained responding following bilateral infusions. The greater sensitivity of nalmefene in the NACC is likely due to the greater number of m-, and possibly d-opioid receptors in the NACC compared with the VTA (Mansour et al, 1987(Mansour et al, , 1995McBride et al, 1998a, b;Temple and Zukin, 1987).…”

Hedonic Hot Spot in Nucleus Accumbens Shell: Where Do μ-Opioids Cause Increased Hedonic Impact of Sweetness?

“…For example, -opioid receptors are particularly dense in the rostral and dorsal medial shell containing our hedonic hot spot, compared with other regions (Tempel and Zukin, 1987).…”