The gene expression of serotonin transporter after conditioned taste aversion learning in the CNS of Lymnaea stagnalis

摘要

In the pond snail Lymnaea stagnalis, based on the behavioral experiments for conditioned taste aversion (CTA) leaning, the neuromodulatory model including the serotonergic neuron, the cerebral giant cell (CGC) was proposed. We previously found that cyclic AMP-responsive element binding proteins (CREB) function as necessary players in synaptic plasticity in the CGC, under the control of the cAMPsignaling cascade. In the present study, we focused on serotonin transporter (SERT) to investigate the molecular mechanism for CTA learning and memory formation. First, we isolated a cDNA homologue of Lymnaea SERT (LymSERT) from the cDNA library of Lymnaea CNSs. The deduced LymSERT protein (631 amino acids) was highly identical to mammalian SERT in the functional region. We also cloned the promoter region of LymSERT gene which included several cyclic AMPresponsive element (CRE) sequences close to the transcription start site. The use of a luciferase reporter assay revealed that a 716 bp fragment of the 5′-flanking region of the transcription start site was sufficient to induce the gene expression by cAMP.We further performed real-time RT–PCR experiments and found that LymSERT mRNA level in trained animals was significantly higher than that in control animals.