Axonal speeding: shaping synaptic potentials in small neurons by the axonal membrane compartment.
The role of the axonal membrane compartment in synaptic integration is usually neglected. We show here that in interneurons of the cerebellar molecular layer, where dendrites are so short that the somatodendritic domain can be considered isopotential, the axonal membrane contributes a significant part of the cell input capacitance. We examine the impact of axonal membrane on synaptic integration by cutting the axon with two-photon illumination. We find that the axonal compartment acts as a sink for signals generated at fast conductance synapses, thus increasing the initial decay rate of corresponding synaptic potentials over the value predicted from the resistance-capacitance (RC) product of the cell membrane; signals generated at slower synapses are much less affected. This mechanism sharpens the spike firing precision of fast glutamatergic inputs without resorting to multisynaptic pathways.
Mejia-Gervacio
Sheyla
S
Laboratoire de Physiologie Cérébrale, UFR Biomédicale, Université Paris 5, 45 Rue des Saints Pères, 75006 Paris, France.
Collin
Thibault
T
Pouzat
Christophe
C
Tan
Yusuf P
YP
Llano
Isabel
I
Marty
Alain
A
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000502:physiology*; D019771:Axotomy / Q000379:methods; D002118:Calcium / Q000378:metabolism; D002531:Cerebellum / Q000166:cytology; D003712:Dendrites / Q000502:physiology / Q000528:radiation effects; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D066298:In Vitro Techniques; D009431:Neural Conduction / Q000502:physiology; D009474:Neurons / Q000166:cytology* / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D002118:Calcium