Action potentials initiate in the axon initial segment and propagate through axon collaterals reliably in cerebellar Purkinje neurons.
Purkinje neurons are the output cells of the cerebellar cortex and generate spikes in two distinct modes, known as simple and complex spikes. Revealing the point of origin of these action potentials, and how they conduct into local axon collaterals, is important for understanding local and distal neuronal processing and communication. By using a recent improvement in voltage-sensitive dye imaging technique that provided exceptional spatial and temporal resolution, we were able to resolve the region of spike initiation as well as follow spike propagation into axon collaterals for each action potential initiated on single trials. All fast action potentials, for both simple and complex spikes, whether occurring spontaneously or in response to a somatic current pulse or synaptic input, initiated in the axon initial segment. At discharge frequencies of less than approximately 250 Hz, spikes propagated faithfully through the axon and axon collaterals, in a saltatory manner. Propagation failures were only observed for very high frequencies or for the spikelets associated with complex spikes. These results demonstrate that the axon initial segment is a critical decision point in Purkinje cell processing and that the properties of axon branch points are adjusted to maintain faithful transmission.
Foust
Amanda
A
Department of Neurobiology, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Popovic
Marko
M
Zecevic
Dejan
D
McCormick
David A
DA
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology*; D001703:Biophysics / Q000379:methods; D002531:Cerebellum / Q000166:cytology*; D004558:Electric Stimulation / Q000379:methods; D049452:Green Fluorescent Proteins / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics; D066298:In Vitro Techniques; D051379:Mice; D008822:Mice, Transgenic; D009412:Nerve Fibers / Q000502:physiology; D009479:Neuropeptides / Q000235:genetics; D018408:Patch-Clamp Techniques / Q000379:methods; D011689:Purkinje Cells / Q000166:cytology*; D056969:Voltage-Sensitive Dye Imaging / Q000379:methods; D016875:tau Proteins / Q000235:genetics
D020662:Guanine Nucleotide Exchange Factors; D009479:Neuropeptides; C104971:Pcp2 protein, mouse; D016875:tau Proteins; D049452:Green Fluorescent Proteins