Activity-induced large amplitude postsynaptic mPSPs at soma-soma synapses between Lymnaea neurons.
Spontaneous transmitter release has been observed at various synapses that permit analysis at a sufficient resolution as a miniature postsynaptic potential (mPSP). However, the precise mechanisms that regulate spontaneous transmitter release have not yet been fully defined. Activity and ligand-mediated modulation of large amplitude, spontaneous events significantly enhances postsynaptic excitation in the absence of action potential activity suggesting a more complicated role for this mode of transmitter release, and thus warrants further analysis. Here, we used Lymnaea soma-soma synaptic connections to demonstrate that a transient increase in both the frequency and amplitude of spontaneous events (mPSPs) occurs following a short burst of action potentials in the presynaptic cell. These events were of presynaptic origin and the increase in mPSP amplitude could also be achieved with a stimulatory concentration of ryanodine. Ryanodine also occluded the activity-induced increase in mPSP amplitude implicating calcium release from these channels in the production of large amplitude spontaneous transmitter release events. This suggests that presynaptic activity triggers ryanodine receptor-mediated large amplitude minis, indicating that although these events are action potential-independent, they are nevertheless responsive to the prior activity of the synapse.
Dunn
T W
TW
Faculty of Medicine, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
McCamphill
P K
PK
Syed
N I
NI
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D008195:Lymnaea; D055369:Miniature Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012433:Ryanodine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D012433:Ryanodine