POSTSYNAPTIC AND EXTRASYNAPTIC LOCALIZATION OF KAPPA-OPIOID RECEPTOR IN SELECTED BRAIN-AREAS OF YOUNG-RAT AND CHICK USING AN ANTIRECEPTOR MONOCLONAL-ANTIBODY

kappa-opioid receptors were visualized by light and electron microscop ical immunohistochemistry in young rat and chick brains, using a monoc lonal antibody KA8 (IgG1, kappa) raised against a K-opioid receptor pr eparation from frog brain, which recognizes selectively the kappa-type receptor with preference for the kappa-2 subtype. The mosi pronounced kappa-opioid receptor-like immunoreactivity was observed in the hypot halamic nuclei of the rat brain and in the chick optic tectum, in regi ons where the functional significance of kappa-opioid receptors is wel l documented. Both neurons and glia were stained, the former on both s omata and dendrites. At the ultrastructural level, the receptor-like i mmunoreactivity was similar in both species. Immunoprecipitate decorat ed the inner surface of the plasma membrane of glial cells, neuronal s omata and dendrites, in a discontinuous arrangement. Ln the cytoplasm, labelling was associated with ribosomes, polyribosomes and rough endo plasmic reticulum membranes but not with Golgi cisternae. In the neuro pil, the immunoprecipitate was observed along the dendritic microtubul es and was also associated with postsynaptic sites. Nuclei and axons w ere devoid of label and immunoreactivity was never visible presynaptic ally. Our findings indicate that the antibody used in the present stud y marks various forms of the kappa-opioid receptor protein including t hose synthesised in ribosomes, transported along dendritic microtubule s and incorporated into postsynaptic and non-synaptic membranes. The a ntibody also recognizes glial opioid receptors. The observed subcellul ar distribution appears to be conserved in phylogenetically distant sp ecies.