Postnatal developmental regulation of neuronal nicotinic receptor subunit α7 and multiple α4 and β2 mRNA species in the rat

Abstract

This study examined the postnatal development of neuronal nicotinic receptor (nAChR) α7, α4 and β2 subunit mRNA in the Sprague Dawley rat brain. The hippocampus, septum and cortex were removed on postnatal day 1 (P1), P7, P14, or P28 and analyzed by sex. Northern analysis of cortical and pooled hippocampal and septal total RNA with 32 P - α-dCTP-labeled α7, α4 (recognizing α4.1 and α4.2 mRNA), and β2 nAChR cDNA probes identified three (2.4, 3.8 and 8.0 kb) α4, four (3.5, 5.0, 7.5 and 10.0 kb) β2 and a single 5.7 kb α7 mRNA species. Cortical α4 mRNA peaked on P14 and remained high on P28, whereas hippocampal/septal α4 mRNA was higher on P7 and P14 than on P1 and P28. Expression of cortical and hippocampal/septal β2 mRNAs decreased on P7, followed by a dramatic peak on P14. α7 mRNA peaked on P7. Throughout development, 2.4 kb α4 mRNA was more intense than 3.8 kb α4 mRNA, whereas 5.0 kb β2 mRNA was the most intense cortical and hippocampal/septal β2 mRNA species. The α4.1-specific cDNA probe detected similar-sized α4 bands as the pan-specific α4 cDNA probe, therefore precluding the identification of any band as α4.2-specific. These results suggest that postnatal expression of α4 and α7 but not β2 mRNAs is brain region-specific, and that the contribution of multiple nAChR subunit mRNA species in development may vary.