Identification and role of serotonin 5-HT1A and 5-HT1B receptors in primary cultures of rat embryonic rostral raphe nucleus neurons

Autoregulatory mechanisms affecting serotonin [5-hydroxytryptamine (5-HT)] release and synthesis during the early period of development were investiga ted in dissociated cell cultures raised from embryonic rostral rat rhombenc ephalon, The presence of 5-HT1A and 5-HT1B receptors in serotoninergic neur ons was assessed using binding assays. The involvement of 5-HT1A and 5-HT1B receptors in the control of the synthesis and release of [H-3]5-HT was stu died using biochemical approaches with several serotoninergic receptor liga nds. A mean decrease of 30% in [H-3]5-HT synthesis and release was observed in the presence of 5-HT (10(-8) M), the 5-HT1A agonist 8-hydroxy-2-(di-n-p ropylamino)tetralin (8-OH-DPAT), the 5HT(1B/1A) agonist 5-methoxy-3-(1,2,5, 6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969), the 5-HT1B agonist 3-(1,2,5 ,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP-93,129), and the 5-HT 1D/1B agonist sumatriptan, Inhibition of 5-HT synthesis and release induced by 8-OH-DPAT was blocked by chiral N-tert-butyl-3-[1-[1-(2-methoxy)phenyl] piperazinyl]-1-phenylpropionamide dihydrochloride quaternary-hydrate (WAY 1 00135) (10(-7) M) or methyl 4-[4-[4-(1,1,3-trioxo-2H-1,2-benzoisothiazol-2- yl)butyl]-1-piperazinyl]-1H-indole-2-carboxylate (SDZ 216-525) (10(-7) M), and that of CP-93,129 was blocked by methiothepin (10(-7) M). Paradoxically , extracellular levels of [3H]5-HT increased in the presence of 8-OH-DPAT a nd RU 24969 at 10(-6) M, 5-HT uptake experiments showed that these two agon ists interacted with the 5-HT transporter. 5-HT1 binding sites (620 fmol/mg of protein) and 5-HT1A (482 fmol/mg of protein) and 5-HT1B (127 fmol/mg of protein) receptors were detected in 12-day in vitro cell cultures. Experim ents carried out with tetrodotoxin suggested that 5-HT1A receptors are loca ted on nerve cell bodies, whereas 5-HT1B receptors are located on the nerve terminals. We concluded that autoregulatory mechanisms involving 5-HT1A an d 5-HT1B autoreceptors are functionally mature in cells from rostral raphe nuclei during the early period of development.