Role of electrical activity in trophic factor-mediated synapse formation

In vitro cell culture and electrophysiological techniques were used in this study to test the hypothesis that trophic factor-induced excitatory synapse formation between the presynaptic neuron, visceral dorsal 4 (VD4), and the postsynaptic neuron, left pedal dorsal 1 (LPeD1) involves the modulation of spontaneous electrical activity in soma-soma paired neurons. This study demonstrates that chronic exposure to trophic factors does not affect the spontaneous electrical activity levels of LPeD1 and VD4 neurons, when tested after synapse formation. However, a significantly larger proportion of paired cells demonstrated spontaneous electrical activity in both neurons when chronically exposed to trophic factors. To further test the hypothesis that the trophic factors contained in Lymnaea brain-conditioned media modulated the spontaneous electrical activity of soma-soma paired neurons, I investigated the acute effects of trophic factors on the spontaneous activity of paired neurons during synapses formation. This analysis revealed that the trophic factors contained in Lymnaea brain-conditionioned media had a specific and significant effect on the spontaneous spiking activity of LPeD1. This effect was not mediated by receptor tryrosine kinases. Furthermore, this study demonstrated that the trophic factor-induced increase in spiking activity of LPeD1 was not necessary for synapse formation.