Tritium-sensitive film autoradiography of guinea pig brain α₂-noradrenergic receptors

Tritium-sensitive film autoradiography was used to determine the distribution of α-noradrenergic receptors (i.e. [³H]p-aminoclonidine binding sites) in guinea pig forebrain. α₂-Receptors are heterogeneously distributed throughout the forebrain. Many limbic system structures, such as bed nucleus of stria terminalis, medial preoptic area, medial amygdaloid nucleus and lacunosum molecular layer in hippocampus were heavily labeled. We did not quantify receptor density in areas containing principally white matter but the optical density in those areas was similar to film background suggesting a very low receptor density. Low receptor concentrations were also found in areas that do not contain a high percentage of white matter, such as lateral septum and ventromedial hypothalamic nucleus.