Development of β1 and β2 adrenergic receptors in baboon brain: An autoradiographic study using [125I]iodocyanopindolol

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Abstract
[125I]iodocyanopindolol (ICYP) autoradiography was used to investigate the temporal development and distribution of β1 and beta;2 receptors in brains of baboons at ages embryonic day 100 (E100), full‐term gestation (E180), and 3 years. In all brain regions examined, with the exception of the hippocampus, binding to β1 receptors exceeded that to β2 receptors. The highest densities of ββ1 receptors were found in the caudate nucleus, putamen, globus pallidus, substantia nigra, and cerebral cortex; intermediate receptor densities were observed in most nuclei of thalamus, and the lowest concentrations were in the hippocampus. At E100, β1 receptors were identified in the striatum, globus pallidus, and thalamus. During maturation, the number of β1 receptors declined in cortical areas but increased in the head of the caudate and putamen. Significant differences in the developmental distribution of β1 receptors during development were also detected: at E100 and E180 β1 receptors appeared as patches in the caudate and putamen, but by 3 years of age they were more homogeneously distributed in both regions; changes also occurred in the distribution of binding within cortical layers. Autoradiograms of [125I]ICYP and [3H]mazindol binding show overlapping patches of labeling in the E180 striatum, suggesting a possible developmental association between β receptors and dopamine high‐affinity uptake carrier sites. This study demonstrates that noradrenergic receptors in the primate forebrain undergo significant developmental reorganization with regional variations.