Laminar distribution of alpha 1- and beta 1-adrenoceptors in ferret visual cortex

The distribution of alpha 1- and beta 1-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 beta-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 alpha-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; alpha 1-receptors may be preferentially associated with enhancement of excitatory inputs to layer IV; beta 1-receptors, in contrast, with enhancement of inhibitory responses outside layer IV.