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

This study examined the postnatal development of neuronal nicotinic receptor (nAChR) alpha 7, alpha 4 and beta 2 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 P-32-alpha-dCTP-labeled alpha 7, alpha 4 (recognizing alpha 4.1 and alpha 4.2 mRNA), and beta 2 nAChR cDNA probes identified three (2.4, 3.8 and 8.0 kb) alpha 4, four (3.5, 5.0, 7.5 and 10.0 kb) beta 2 and a single 5.7 kb alpha 7 mRNA species. Cortical alpha 4 mRNA peaked on P14 and remained high on P28, whereas hippocampal/septal alpha 4 mRNA was higher on P7 and P14 than on P1 and P28. Expression of cortical and hippocampal/septal beta 2 mRNAs decreased on P7, followed by a dramatic peak on P14. alpha 7 mRNA peaked on P7. Throughout development, 2.4 kb alpha 4 mRNA was more intense than 3.8 kb alpha 4 mRNA, whereas 5.0 kb beta 2 mRNA was the most intense cortical and hippocampal/septal beta 2 mRNA species. The alpha 4.1-specific cDNA probe detected similar-sized alpha 4 bands as the pan-specific alpha 4 cDNA probe, therefore precluding the identification of any band as alpha 4.2-specific. These results suggest that postnatal expression of alpha 4 and alpha 7 but not beta 2 mRNAs is brain region-specific, and that the contribution of multiple nAChR subunit mRNA species in development may vary. (C) 1998 Elsevier Science B.V. All rights reserved.