Phorbol ester differentially regulates oxytocin receptor binding activity in hypothalamic cultured neurons and astrocytes

Hypothalamic cultured neurons and astrocytes were used to investigate the c ellular mechanisms underlying the oxytocin receptor mediated downregulation through a possible involvement of protein kinase C (PKC). For this purpose , the effects of PKC activators. inhibitor and of OT on OT receptor binding activity were compared in both cultures. In neurons, phorbol-myristate-ace tate (PMA). a potent PKC activator. increased the binding of an OT receptor antagonist whereas in astrocytes. a decrease was observed. Pre-treatment o f the cells with bisindolylmaleimide (10(-4) M), a PKC inhibitor, prevented the PMA-induced up- and downregulation. In contrast, receptor downregulati on resulting from treatment of both cells with OT (10(-9) M) was not affect ed by the PKC inhibitor. On the other hand, when PMA (10(-7) M) was tested along with OT (10(-9) M), a subsequent decrease in ligand binding was obser ved in astrocytes. In neurons, PMA attenuated the OT-induced downregulation . Structural analysis of neuron and astrocyte OT receptor mRNA by RT-PCR, s ubcloning and sequencing, demonstrated identical sequence to rat uterine re ceptor. In conclusion. these data suggest that activation of PKC has opposi te effect on OT receptor binding activity in neurons and astrocytes but the y do not support the involvement of PKC in the OT-induced downregulation. ( C) 2001 Elsevier Science Inc. All rights reserved.