NEURONAL LOCALIZATION OF 5-HT1A RECEPTOR MESSENGER-RNA AND PROTEIN INRAT 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. Prim ary 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 an ti-5-HT1A receptor antibodies or a 40-mer biotin-labelled deoxyoligonu cleotide complementary to the 5-HT1A receptor mRNA. The use of a bioti nylated probe allowed the morphology of the cells to be preserved. 5-H T1A receptor mRNA was already detected in primary cultures from the br ain of ED 12 embryos whereas the receptor protein first appeared two d ays later, at ED 14. Both 5-HT1A receptor mRNA and protein were found within neuron-like cells (labelled with antibodies against neuron spec ific enolase, microtubule-associated protein 2 or aromatic L-aminoacid decarboxylase) but not in glial cells (specifically labelled with ant ibodies against glial fibrillary acidic protein, myelin basic protein or carbonic anhydrase II). Double staining with the 5-HT1A receptor mR NA probe and anti-5-HT antibodies suggests that 5-HT1A (auto)receptors are expressed by serotoninergic neurons during early ontogenesis.