Expression of brain and platelet serotonin transporters in sublines of rats with constitutionally altered serotonin homeostasis.

By selective breeding, two sublines of rats, termed Wistar-Zagreb 5HT rats, with constitutionally high or low values of platelet serotonin (5HT) level and activity of platelet serotonin transporter (5HTt) have been developed. Previous studies demonstrated significant differences between the sublines in the expression of platelet 5HTt at the level of both mRNA and protein. Neurochemical and behavioural studies demonstrated differences in functional activity of brain 5HTt indicating that, similarly to platelets, differences in mRNA level might be expected in brains of selected animals. In this work, semi-quantitative RT-PCR method for measuring the 5HTt expression in rat tissues was described and then used to quantify the 5HTt mRNA in brains and platelets of animals from high-5HT and low-5HT sublines. Three different housekeeping genes: GAPDH, beta-actin and cyclophylin B, were used as internal standards to normalise 5HTt signals. Significant differences in platelet 5HTt mRNA between the sublines were confirmed, as contrasted to only a tendency toward higher 5HTt mRNA levels in midbrain of animals from the high-5HT subline. Results indicate differences in transcriptional regulation of central and peripheral 5HT transporters, suggesting that homeostatic control in the brain counteract more efficiently the selection pressure than in the periphery.