A COMPARATIVE-STUDY OF THE BETA-ADRENOCEPTORS IN HIGHER VISUAL CENTERS OF BIRDS

This report describes the distribution of beta-adrenergic receptors in the telencephalic visual nuclei of chick, duck, pigeon, parakeet and goldfinch using [H-3]CGP 12177 (4-3-t-butylamino-2-hydroxypropoxy-[5,7 (3)H] benzimidazol-2-one) as a radioligand. The results reveal a predo minance of the beta(2)-adrenoceptor subtype in all the species studied and that this subtype fits the pharmacological profile described for mammals. It is also demonstrated that the autoradiographic interspecif ic differences described in previous studies are due to changes in B-m ax, while K-D values remain in a similar range (0.1-0.6 nM). The distr ibution of beta-adrenoceptors was fairly similar in the areas of the v isual Wulst of all five species studied while striking differences wer e found in the ectostriatum, the higher centre of the tectofugal pathw ay. Our findings support a role for ectostriatal beta-adrenoceptors in the visual adaptation and evolution of birds. (C) 1998 Elsevier Scien ce Ireland Ltd. All rights reserved.