Effect of serotonin on protein phosphorylation in different regions of the central nervous system of Hirudo medicinalis

Serotonin is involved in several behaviors of the leech, such as swimming, shortening and feeding. In addition, serotonin exerts a pivntal role in elementary forms of non associative learning such as sensitization and dishabituation; seasonal variations of serotonin content in the central nervous system are correlated with changes in learning capability (Catarsi et al. (1990) J. Compo Physiol. 167A, 469-474). Since serotonin could mediate many of its functions through the activation of different protein kinases, we have compared the effect of serotonin on protein phosphorylation with that of activators of cAMP dependent protein kinase or protein kinase C. Phosphoproteins from different regions of leech central nervous system have been separated by means of two-dimensional electrophoresis and detected by autoradiography. Most of the phosphoproteins are similarly distributed in segmental, cephalic and caudal ganglia. However, some regional differences do exist: in the chains of segmental ganglia, a group of phosphoproteins of 78 kDa and pI = 6-6.5 is phosphorylated after treatment with serotonin, 8-Br-cAMP and dibutiryl phorbol ester; this group of phosphoproteins is not detected in either caudal or cephalic ganglion. Further investisations will clarify the role of these phosphoproteins in behaviors such as swimming, feeding and learning.