Non-synaptic integration of the cell bodies of neurons into the central nervous system of the snail.

Single neurons (soma and proximal process) were isolated from the serotonergic (5-HT-ergic) PedA cluster in experiments on the pond snail Lymnaea stagnalis, and changes in the electrical activity of isolated neurons were observed during repeated movement of these cells towards and away from the surface of the CNS. The position of cell bodies of 5-HT-ergic neurons had excitatory effects on the isolated neuron. This effect was maximal (at 10(-8)-10(-7) M 5-HT) when neurons were brought close to the PedA cluster and were further enhanced by addition of the 5-HT precursor 5-hydroxytryptophan at concentrations of (1-2) x 10(-4) M. The results obtained here provide evidence 5-HT-ergic neurons cooperate during 5-HT-dependent behaviour, this being based on excitatory interactions at the level of cell bodies.