Seasonal plasticity of synaptic connections between identified neurones in Lymnaea

Here we investigate the synaptic connectivity of the giant dopamine containing neurone (RPeDI) of Lymnaea stagnalis during the winter months, in wild and laboratory bred animals. RPeD1 is one of the three neurones forming the respiratory central pattern generator (CPG) in Lymnaea and initiates ventilation under normal circumstances. Many of the follower cells of RPeD1 are ventilatory motor neurones. The connections of RPeD1 to its follower cells were investigated using standard intracellular recording techniques and dopamine was applied to the follower cells using a puffer pipette. During February and early March, RPeD1 was functionally disconnected from its follower cells, but connections reappeared towards the end of March. Most functionally disconnected cells failed to respond to applied dopamine, consistent with the hypothesis that there is down regulation of dopamine receptors in the follower cells of RPeD1 in the winter months. Behaviourally, Lymnaea that survive the winter, are not active at this time and do not indulge in lung ventilation, but stay quiescent. Thus functional disconnection of neurones from the CPG may be either a cause or a consequence of this change in behaviour.