ONTOGENY OF THE ALPHA(2)-ADRENERGIC RECEPTOR SYSTEM IN THE HYPOTHALAMO-LIMBIC SYSTEM OF THE PEKIN DUCK

The development of the central nervous alpha(2)-adrenergic system in t he duck was studied by semiquantitative autoradiography at the ontogen etic stages embryonic days 20 (E20) and 27 (E27) and postnatal days 3 (P3) and 14 (P14) by using the monoradioiodinated alpha(2)-agonist clo nidine ([I-125]CLO) as radioligand. All structures endowed with alpha( 2)-adrenoceptors in the adult animal were specifically labeled with [I -125]CLO by E20. A detailed analysis of the binding capacity for [I-12 5]CLO was performed for parts of several functional systems: hypothala mic structures (nucleus inferior hypothalami, nucleus magnocellularis preopticus, nucleus paraventricularis), limbic system (habenula, nucle us septalis lateralis, nucleus striae terminalis), circumventricular o rgans (organum pineale, organum subfornicale, plexus choroidei ventric uli tertii and ventriculi lateralis), visual system (hyperstriatum acc essorium, nucleus reticularis superior, tectum opticum), and associati ve cortex (hyperstriatum ventrale). Except for the nucleus inferior hy pothalami and the plexus choroideus ventriculi lateralis, all structur es showed a perinatal (E27-P3) maximum of alpha(2)-adrenoceptor-bindin g capacity with a subsequent decline to values of prehatching stages. This uniform expression pattern of alpha(2)-adrenoceptors indicates th at the days around hatching are a critical period for the development of the adrenergic system in the brain of the duck.