Ontogeny of β1- and β2-adrenergic receptors in rat cerebellum and cerebral cortex

The development of β₁- and β₂-adrenergic receptors was studied in rat cerebral cortex and cerebellum. In the cerebral cortex, which contains mostly β₁-adnergic receptors, total β-adrenergic receptor density increased sharply between postnatal days 10 and 21. The density of receptors remained fairly constant through 6 weeks of age and then subsequently declined. The proportion of β₁ and β₂ receptors was relatively constant throughout the development of the cerebral cortex. The development of the two receptor subtypes thus paralleled the development of total β-adrenergic receptors in the cerebral cortex.The ontogeny of β-adrenergic receptors in the cerebellum, which contains mainly β₂ receptors, was strikingly different from that observed in the cortex. Total cerebellar β receptor density exhibited a slow but steady increase from postnatal day 5 through day 42. The density of receptors then plateaued and remained constant until the animals were approximately 6 months of age. Unlike the results obtained in the cortex, the relative proportions of β₁ and β₂ receptors in the cerebellum changed markedly during development. Between postnatal days 8 and 13 approximately 18% of the receptors were of the β₁ subtype. This proportion steadily decreased with age, and in 3- and 6-month-old animals only approximately 2% of the receptors were of the β₁ subtype.The results demonstrate that two subtypes of β-adrenergic receptors can have different development patterns in the same brain area, and that a single receptor subtype can follow different development patterns in different brain regions. Possible correlations between the ontogeny of β₁ and β₂ receptors and various developmental events are discussed.