Calexcitin (CE) is a low molecular weight Ca2+- and guanosine triphosphate- binding protein, which is phosphorylated during associative learning in both vertebrates and invertebrates. The purpose of this study was to determine the presence of CE in the central nervous system (CNS) of the pond snail Lymnaea stagnalis, which can acquire classical and operant conditioning. Immunoblotting of CE showed that the anti-CE antibody prepared from squid can detect Lymnaea CE. In the cerebral ganglia, CE-like immunoreactivity was exhibited in two pairs of cell clusters that receive taste signals from the superior or median lip nerves. In both pedal ganglia, CE-like immunoreactivity was detected in 1-4 cell of the PeA clusters, which are involved in the withdrawal response. Our results therefore showed that CE is involved in the feeding and withdrawal neural networks, suggesting that CE may function in associative learning of feeding and withdrawal behavior in L. stagnalis.
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