Laminar Distribution of Alpha-1-adrenoceptors and Beta-1-adrenoceptors in Ferret Visual-cortex

The distribution ofα1-andβ1-adrenoceptors has been examined in the ferret visual cortex (area 17), with an autoradiographic procedure using iodine-125 labeled hydroxy-iodophenyl-ethylaminomethyl-tetralone (HEAT) and iodocyanopindolol (ICYP), respectively. The density of ligand binding with ICYP, known to have selective affinity for β-receptors, was heavy over layers I-III, very low over layer IV, and medium over V and VI. In contrast, binding sites for HEAT, a new ligand selective for α-receptors, were diffusely distributed, although preferentially concentrated in layer IV and the upper layers. The distinct laminar distribution of these two receptor types may imply two cortical channels for norepinephrine influence;α1-receptors may be preferentially associated with enhancement of excitatory inputs to layer IV;β1-receptors, in contrast, with enhancement of inhibitory responses outside layer IV.