Differential expression of the K-2 opioid receptor protein under the effect of opioid agonists in embryonic chick neurons in vitro.

Neuronal cells cultured from 7-day-old chick embryos and differentiated under the chronic effect of opioid drugs were studied for kappa-opioid receptor expression. Plasma-membrane integrated receptors were measured by radioligand ([3H]-naloxone 1 nM, [3H]-ethylketocyclazocine, 4 nM) binding to intact neurons. These data were compared to the results of k-opioid receptor immunostaining (mAb KA8, Maderspach et al., 1991). The chronic presence of kappa-selective opioid agonist dynorphin1-13 (10(-6)-10(-7) M) or bremazocine (10(-7)-10(-8) M) between cultivation days 2-4 resulted in the significant (80%) down-regulation of the membrane integrated binding sites in concentration dependent fasion. Antagonists naloxone (10(-5) M) and norbinaltorphimine (10(-8) M) alone were ineffective, however, they essentially balanced the changes caused by the agonists. Mu ligand morphine was without effect while kappa-1 selective U 50488 H caused moderate decrease only at high concentrations. Interestingly, mAb KAB also caused down-regulation indicating that it has some agonist character. The down-regulation became measurable in short time (58% within 24 hours) and persisted during the three-day presence of the agonists. Kappa-receptor immunostaining of the neurons was not significantly influenced by the agonists. We suppose that the chronic opioid treatment may influence the intracellular traffic of the receptor protein.

Cellular distribution of the mRNA for the kappa-opioid receptor in the human neocortex: a non-isotopic in situ hybridization study.

Opioid receptors (OR) provide primary interaction sites of the human brain with opiates. Presently kappa-OR mRNA expression was studied in different cortical areas (A4, A10, A17) by in situ hybridization using digoxigenin-labeled oligonucleotides and an alkaline phosphatase-mediated color reaction. kappa-OR mRNA was expressed mainly in layers II/III and V pyramidal and layer VI multiform neurons. A4 giant pyramidal and A17 giant stellate neurons stood out labeled. These findings fit in with our data on kappa-OR protein distribution. Combined cellular assessment of protein and mRNA will enable the study kappa-OR expression under physiological and pathological conditions.