Effect of serotonin on protein phosphorylation and protein synthesis in the central nervous system of Hirudo medicinalis

In the leech, serotonin (5HT) -is involved in non associative learning. It is thought that t.he role of 5HT on short-term learning is due to the activation of different protein kinases and that new protein synthesis is involved in long term learning. With the aim of studying the molecular mechanism underlying learning in the leech, we have analyzed the effects of 5HT on 32P-phosphate and 35S-methionine incorporation into proteins by means of 2D-electrophoresis. 5HT prOduces an increase time- and dosedependent on protein phosphorylation. A group of proteins of 78 kDa and pI:6-6.5 phosphorylated following 5HT, 8Br-cAMP and phorbol ester treatment is present only in segmental ganglia. Long term learning, mimicked by repetitive 5HT treatment, modifies the incorporation of 35SL-methionine into several proteins.