Binding properties, regional ontogeny and localization of adrenergic receptors in chick brain

Publisher Website
Google Scholar
Abstract
The pharmacological properties of [3H]-WB4101, [3H]-clonidine and [3H]-dihydroalprenolol binding in chick brain membranes display the characteristics known for α1-, α2- and β-adrenergic binding sites, respectively. Kinetic studies performed at different embryonic and post-hatching ages have shown one binding component for each one of the above radioactive ligands. The ontogeny of α1, α2 and β binding sites was studied in cerebral hemispheres, optic lobes, brain stem and cerebellum. In all brain regions studied, the development of α2 binding sites precedes that of α1 and β, and a very significant decrease of α2 number was observed in the cerebellum, brain stem and optic lobes afterwards. The autoradiographic localization of adrenergic receptors was studied in the optic lobes and cerebellum. In the optic lobes the superficial layers of stratum griseum and fibrosum showed a strong selective labelling of α1, α2 and β binding sites and the strong selective labelling of α2 binding sites extended to the layer of stratum opticum. Among the nuclei located in the optic lobe only the nucleus mesencephalis lateralis pars dorsalis (MLD) exhibited a strong selective labelling for α1 binding sites while, for β binding sites, not only the MLD, but also the nucleus isthmic pars parvocellularis (Ipc) and the nucleus isthmic pars magnocellularisa (Imc) exhibited strong labelling. In the cerebellum strong selective labelling for α1 and β receptors was seen in the molecular layer. Labelling of the granule cell layer was almost equally strong for α1 but significantly less for β binding sites. No significant labelling could be detected for α2 binding sites.