Tachykinin- and leucokinin-related peptides in the molluscan nervous system

Distribution of locustatachykinin-like immunoreactive (LomTKLI) and leucokinin like immunoreactive (LKLI) neurons in the central nervous system (CNS) of the pond snail, Lymnaea stagnalis was investigated and compared to that found in Helix pomatia. Occurrence of LomTKLI neurons in different ganglia of the freshwater bivalve, Anodonta cygnea, was also studied. Similar to Helix, the Lymnaea CNS contained LomTKLI and LKLI neurons mainly in the cerebral and pedal ganglia, but the number of labelled neurons was found to be significantly lower in Lymnaea (150-184 LomTKLI and 86-104 LKLI neurons). LomTKLI elements in anodonta ganglia were mainly confined to the neuropil, whereas the immunostained perikarya were only randomly distributed. LomTKLI and LKLI neurons were also demonstrated in a similar pattern of distribution in the intestine of Lymnaea and Helix. Analyzing the membrane effects of locustatachykinin-I, leucokinin-I and anodontatachykinin, Helix neurons were found to be either depolarized or hyperpolarized. Voltage-clamp experiments revealed the role of Ca- or K-currents in peptide effects. Our results indicate that the different tachykinin- and leucokinin-systems are involved in different central and peripheral regulatory processes of the molluscan nervous system.