Localization and diurnal expression of mRNA encoding the β₁-adrenoceptor in the rat pineal gland: an in situ hybridization study

Abstract.

The rat pinealocyte is stimulated by norepinephrine, which is released from sympathetic nerve fibers innervating the gland. Norepinephrine binds to β₁-adrenoceptors situated on the pinealocyte cell membrane. Ligand binding to these receptors exhibits a diurnal rhythm, with the largest number occurring in the late part of the light phase when the release of norepinephrine is minimal. By using in situ hybridization with a cDNA antisense oligonucleotide probe recognizing mRNA encoding the rat β₁-adrenoceptor, we have demonstrated a stronger hybridization signal in the rat pineal gland than in other brain regions. Cells containing β₁-mRNA are located in the superficial pineal gland, the deep pineal gland, and the pineal stalk. However, the number of receptors varies considerably between the individual pinealocytes. The β₁-mRNA in situ hybridization signal for mRNA encoding the β₁-adrenoceptor of the rat pineal has been quantified over a 24-h period; the strongest signal is found at mid-dark and the weakest signal at mid-light, indicating that the transcriptional regulation of β₁-mRNA synthesis in the rat pineal is diurnal. In addition, maximal receptor protein expression occurs late in the light phase in the rat pineal and is thus considerably delayed compared with its peak mRNA synthesis. This lag time indicates that the β₁-receptor is regulated at the translational or post-translational level. Removal of the sympathetic input to the pineal gland by superior cervical ganglionectomy decreases the β₁-mRNA signal in the gland.