Figure 8. Action potentials are not decremental in the distal axon during a burst discharge.

A, pairs of simultaneous recorded somatic whole-cell (top traces) and axonal cell-attached (V_pipette = -65 mV) (bottom traces) recordings at different distances from the soma during burst firing. During an action potential burst the amplitude of somatically recorded action potentials decreases, in some trials later somatically recorded action potentials show inflections in their rising phase (**) and can apparently fail (*). Simultaneous axonal recordings show that when action potential invasion of the soma almost fails (**) two axonal events are recorded, and that when somatic failure occurs the axonal action potential is largely unchanged (axonal recording 25 μm from the base of the soma, two consecutive records). The decrement in axonal action potentials during a burst is dependent upon the distance of the axonal recording from the soma. Note that each action potential of a burst is of a similar amplitude at the most distal axonal recording site (40 μm from the base of the soma). B. the relative amplitude of the second, third, fourth and fifth action potentials in a burst during cell-attached axonal recordings at different distances from the soma. Action potential amplitude was normalised to that of the first action potential in the burst. Total of 14 cells represented. C, simultaneous somatic and axonal whole-cell recording during burst firing. Note all action potentials in the burst are generated first in the axon.