Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential

Abstract

Traditionally, neuronal operations in the cerebral cortex have been viewed as occurring through the interaction of synaptic potentials in the dendrite and soma, followed by the initiation of an action potential, typically in the axon. Propagation of this action potential to the synaptic terminals is widely believed to be the only form of rapid communication of information between the soma and axonal synapses, and hence to postsynaptic neurons. Here we show that the voltage fluctuations associated with dendrosomatic synaptic activity propagate significant distances along the axon, and that modest changes in the somatic membrane potential of the presynaptic neuron modulate the amplitude and duration of axonal action potentials and, through a Ca2+-dependent mechanism, the average amplitude of the postsynaptic potential evoked by these spikes. These results indicate that synaptic activity in the dendrite and soma controls not only the pattern of action potentials generated, but also the amplitude of the synaptic potentials that these action potentials initiate in local cortical circuits, resulting in synaptic transmission that is a mixture of triggered and graded (analogue) signals.

Analog and digital, continuous and discrete

“…Recent work by a number of researchers (e.g. Shu et al (2006) and Alle and Geiger (2006)) has cast doubt on the conventional view of neural firing as an "allor-none" phenomenon. Instead, the post-synaptic potential invoked by some neurons may vary as a function of the input received.…”

Axonal bleb recording

“…Consequently, a new method [1][2][3][4] has recently been developed for patch-clamp recording from the thin axons of both projection neurons and interneurons. We expect that this new method will facilitate studies on axon physiology.…”

“…The mossy fibers are projection axons of the hippocampal granule cells in the dentate gyrus, sending signals to the CA3 region. The MFB is an enlarged axon terminal (3)(4)(5) μm in diameter) forming synaptic contacts onto CA3 neurons [23][24][25] . In hippocampal slices maintained in vitro, it is possible to make simultaneous paired recording from the soma and the MFB of a given granule cell, or a presynaptic MFB and a postsynaptic CA3 pyramidal neuron.…”

“…At the cut end, the ax- Different recording configurations can be used on the axonal blebs ( Fig. 1), including cell-attached, whole-cell, outside-out patch and giant outside-out patch recordings [1][2][3][4] .…”

“…The thin structure of most axons in the central nervous system (CNS) prevents direct access of patch pipettes to the axonal membrane; therefore, it was impossible to probe the properties and functions of axonal ion channels and neurotransmitter receptors. A recently developed axonal recording method, known as the axonal bleb recording [1][2][3][4] , has been successfully used in studies on the physiology of CNS axons.…”