Download An octopaminergic system in the CNS of the snails, Lymnaea

Octopamine: a new feeding modulator in Lymnaea
Á. Vehovszky, C. J. H. Elliott, E. E. Voronezhskaya, L. Hiripi, and K. Elekes
The role of octopamine in the feeding system of the pond snail Lymnaea stagnalis was studied
applying behavioural tests on intact animals, and a combination of electrophysiological analysis and
morphological labelling in the isolated central nervous system.
Octopamine antagonists phentolamine, demethylchlordimeform (DCDM) and 2-chloro-4methyl-2-(phenylimino)-imidazolidine (NC-7) were injected into intact snails and the sucrose induced
feeding response of animals was monitored. Snails which received 25-50 mg/kg phentolamine did not
start feeding in sucrose, and the same dose of NC-7 reduced the number of feeding animals by 80-90
percent 1-3 hours after injection. DCDM treatment reduced feeding by 20-60 percent. Additionally,
both phentolamine and NC-7 significantly decreased the feeding rate of those animals which still
accepted food after 1-6 hours of injection.
In the central nervous system a pair of buccal neurons was identified by electrophysiological
and morphological criteria. After double labelling (intracellular staining with Lucifer yellow followed
by octopamine-immunocytochemistry) these neurons were shown to be octopamine immunoreactive
and called OC (Octopamine Containing) neurons.
Synchronous intracellular recordings demonstrated that the OC neurons share a common
rhythm with feeding neurons either appearing spontaneously or evoked by intracellularly stimulated
feeding interneurons. OC neurons also have synaptic connections with identified members of the
feeding network: electrical coupling was demonstrated between OC neurons and members of the B4
cluster motoneurons, moreover chemically transmitted synaptic responses were recorded both on
feeding motoneurons (B1, B2 cells) and the SO modulatory interneuron after the stimulation of OC
neurons. However, elementary synaptic potentials (PSPs) could never be recorded on the follower cells
of OC neurons. Prolonged (20-30 seconds) intracellular stimulation of OC cells activated the buccal
feeding neurons leading to rhythmic activity pattern (fictive feeding) in a way similar to octopamine
applied by perfusion onto isolated central nervous system (CNS) preparation.
Our results suggest that octopamine acts as a modulatory substance in the feeding system of
Lymnaea stagnalis and the newly identified pair of OC neurons belongs to the buccal feeding network.