Quantitative mRNA analysis of five C-terminal splice variants of the human5-HT4 receptor in the central nervous system by TaqMan real time RT-PCR

5-HT4 receptors mediate several physiological effects of 5-HT particularly in the central nervous system (CNS), heart and gut. Recently, several C-ter minal splice variants of the human 5-HT4 (h5-HT4) receptor have been descri bed, namely h5-HT4(a), h5-HT4(b), h5-HT4(c), h5-HT4(d), and h5-HT4(g). Prev ious tissue distribution data suggest some degree of specificity in the mRN A expression patterns of the different h5-HT4 receptor splice variants. How ever, comparison of the mRNA expression profiles of these splice variants i s difficult due to the non-quantitative methods used, and in addition, ther e is very limited data on the expression of each splice variant in human CN S subregions. In the present study we used a single technique, TaqMan real time quantitative RT-PCR, to investigate the mRNA distribution of 5-HT4 rec eptor C-terminal splice variants in multiple human CNS and peripheral tissu es. Using a primer/probe set that amplified all 5-HT4 splice variants (5-HT 4pan), the highest CNS expression of 5-HT4 receptor mRNA was observed in ba sal ganglia, amygdala and hippocampus, consistent with previous studies, h5 -HT4(a), h5-HT4(b), h5-HT4(c), and h5-HT4(g), were predominantly expressed in various CNS tissues, compared to most peripheral tissues, but there were differences in expression levels and distribution patterns of each variant . The distribution profile and expression levels observed for the 5-HT4(b) splice variant were virtually identical to that obtained with the 5-HT4pan primer/probe set, whilst the other splice variants were expressed at much l ower levels and with different patterns obtained with both 5-HT4(b) and 5-H T4(pan) primer/probe sets. Highest levels of 5-HT4(g) were observed in the hypothalamus and cortex, whilst the 5-HT4(d) variant was highest in the amy gdala. 5-HT4(c) expression was highest in the pituitary gland whilst 5-HT4( d) mRNA was only detected in the small intestine at very low levels and not in the CNS. In conclusion, we have shown quantitative differences in the m RNA distribution profiles of the 5-HT4 receptor C-terminal splice variants in human CNS subregions as well as peripheral tissues. In addition, our dat a suggests that the h5-HT4(b) variant is the most predominant form of the 5 -MT4 receptor in humans. (C) 2001 Elsevier Science B.V. All rights reserved .