Effect of phorbol ester and serotonin on protein phosphorylation in the C.N.S. of Hirudo medicinalis

A wide variety of neurotransmitters and hormones mediate many of their functions through the activation of the protein kinase C ( PKC ). In nerve cells PKC has been shown to be involved in the regulation of ion channels and neurotransmitter release. Recently, since involvement of PKC has been suggested to playa crucial role in synaptic plasticity and in associative learning, we have started the study of PKC activity in the central nervous system of the leech H. medicinalis, which is considered a good model for associative and non associative learning processes. We have incubated segmental ganglia with physiological solution containing 32P - H3P04 and dibutyrate phorbol ester, an activator of PKC. The phosphoproteins have been separated by 2D-electrophoresis and detected by autoradiography. We have observed that the proteins of MWr 78, 74 and 71 Kua, pI:6; and 166 Kua, pI=5.3 show an increase in phosphorylation after phorbol ester treatment, whereas the proteins of 46, 40 and 30 Kua, pI= 6.5 show a decrease. Since in the leech serotonin mimics non associative learning, we are studying its effect on protein phosphorylation. Preliminary experiments indicate that serotonin increases the phosphorylation of the proteins 78 and 74 kD, pI=6 and other proteins not affected by the treatment with phorbol ester.