Fig. 4.

Dendrotomy abolishes some forms of bursting in Purkinje cells and layer 5 pyramidal cells. (Aa) Simultaneous recordings of somatic membrane potential (Middle) and dendritic Ca²⁺ fluorescence (Bottom) before (black) and after (red) dendrotomy. The stimulus was a 500-msec-long 7-nA current step applied at the soma (Top). The Purkinje cell in which these recordings were made is shown at right before dendrotomy. Red line, location of the Ca²⁺-imaging line scan; dashed white line, approximate site of dendrotomy. (Ab) Expanded views of the somatic membrane potential recorded in this cell, showing the first and last 50 msec of the response to the current step. Before dendrotomy, there was a rapidly inactivating burst of sodium APs at the beginning of the step, followed by slower rhythmic bursting during the latter part of the step (Left, arrow). After dendrotomy, the fast initial burst remained, but the late rhythmic bursting was abolished (Right). (Ac) Response of a different Purkinje cell to a 1-msec-long current step applied before (Left, 1.4-nA step) and after (Right, 0.5-nA step) dendrotomy. A second, attenuated sodium AP appears after dendrotomy (arrow). (Ba) A similar experiment was done on the layer 5 pyramidal cell (Right). The stimulus was a 100-Hz train of five 3-msec-long 2.2-nA current steps (Top). This stimulus elicited both a train of five APs (Middle) and, in control conditions, a Ca²⁺ transient (Bottom Left) recorded in the primary apical dendrite ≈90 μm from the soma (at red line in fluorescence image). After dendrotomy (at the dashed white line in the fluorescence image), the Ca²⁺ transient was abolished (Bottom Right). (Bb) Voltage response of this cell to a 450-pA current step applied at the soma. In control conditions (Left), the cell showed an initial burst of APs (arrow). After dendrotomy, bursting was abolished (Right). (Bc) Expanded view of the first AP in a train elicited in the same layer 5 cell before (black) and after (red) dendrotomy, showing the reduction in amplitude of the afterdepolarization (arrows).