Ontogenic expression of two alpha-1 adrenergic receptor subtypes in the rat brain

alpha-1A/D and alpha-1B adrenergic receptor subtype mRNA expression was studied during pre- and postnatal rat brain development. Oligonucleotide probes were generated to distinguish these two homologous subtypes by in situ histochemical analysis in E14, E16, E19, P0, P8, P14, P21, and adult animals. alpha-1B adrenergic receptor mRNA expression was noted as early as the E14 animal and demonstrated specific regional and temporal expression. alpha-1A/D adrenergic receptor mRNA expression was limited in the E19 and P0 animal but increased in intensity with aging. Specific regional and temporal expression differed between the two subtypes. The regional localization for both subtypes appeared to be stable after P21 but the intensity of expression for both subtypes decreased between P21 and adulthood, which is a finding that correlates with previous ligand-binding data. Different subtypes of homologous receptors have very different ontogenic patterns of distribution and may account for previous discrepancies in ligand-binding data and differential tissue responses to various ligands during development.