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

In the leech, serotonin is involved in different behaviours, such as swimming, shortening~ and feeding. In addition, serotonin mimicks elementary forms of non associative learning such as sensitiation and dishabituation. Changes of the serotonin content in the central nervous system are correlated with variations of the learning capability [Catarsi et al. (1990) J. Compo Physiol. 167A, 469-474]. As in other invertebrates, some forms of short-term learning in the leech are not affected by the use of protein synthesis inhibitors, whereas some forms of long-term learning are blocked by those inhibitors. It is thought that the role of serotonin on short-term learning processes is due to the activation of different protein kinases and phosphorylation of preexisting proteins. At the aim of studying the molecular mechanism underlying long-term learning processes, segmental ganglia of leech nervous system have been labeled with [35S]-L- methionine and treated with serotonin. Proteins have been separated by means of two- dimensional electrophoresis and detected by autoradiography. Prediminary experiments indicated that serotonin treatment increases the incorporation of [3S] -L-methionine into proteins. Therefore, serotonin could exert its functions not only by modificating the phosphorylation level of some proteins, but also by increasing protein synthesis.