Neuronal localization of 5-HT1A receptor mRNA and protein in rat embryonic brain stem cultures

The aim of the present work was to study the cellular localization of 5-HT1A receptor protein and mRNA in rat embryonic brain cultures. Primary cultures of the whole brain from rat fetuses at embryonic day (ED) 12 and of the brain stem at ED 14-ED 16 were stained with specific anti-5-HT1A receptor antibodies or a 40-mer biotin-labelled deoxyoligonucleotide complementary to the 5-HT1A receptor mRNA. The use of a biotinylated probe allowed the morphology of the cells to be preserved. 5-HT1A receptor mRNA was already detected in primary cultures from the brain of ED 12 embryos whereas the receptor protein first appeared two days later, at ED 14. Both 5-HT1A receptor mRNA and protein were found within neuron-like cells (labelled with antibodies against neuron specific enolase, microtubule-associated protein 2 or aromatic L-amino acid decarboxylase) but not in glial cells (specifically labelled with antibodies against glial fibrillary acidic protein, myelin basic protein or carbonic anhydrase II). Double staining with the 5-HT1A receptor mRNA probe and anti-5-HT antibodies suggests that 5-HT1A (auto)receptors are expressed by serotoninergic neurons during early ontogenesis.