Figure 1.
Increasing glutamate release from individual pyramidal cells with cesium dialysis promotes disynaptic inhibition.
A
, IPSCs can be generated between pyramidal cell pairs in L2/3 with a cesium-based internal solution. Left, A paired recording from two nearby L2/3 pyramidal cells with a cesium internal solution in both cells. A brief depolarizing voltage step (40 mV for 1 ms) applied to one pyramidal cell (top) yields an unclamped spike (or “action current”). This spike produces a large IPSC in the other pyramidal cell (bottom; 0 mV). Right, Summary data of the latencies and amplitudes of IPSCs generated with cesium internal solutions. IPSCs were observed in 16 of 69 (23%) total recordings with a cesium internal.
B
, Repatching with a cesium-based internal solution generates IPSCs between pyramidal cell pairs. Left, A pair of pyramidal cells, in which one cell contains a potassium internal (top) and the other contains a cesium internal (bottom; 0 mV). Action potentials triggered in the pyramidal cell filled with potassium do not produce IPSCs in the pyramidal cell filled with cesium. Right, When the same pyramidal cell is repatched with a cesium-based internal solution, action currents (as in
A
) now produce IPSCs in the other pyramidal cell.
C
, Repatching pyramidal cells with a cesium-based internal solution doubles the size of EPSPs onto FS interneurons. Left, Paired recordings performed between a layer 2/3 pyramidal cell and an FS interneuron. The pyramidal cell is first patched with a potassium internal solution (green) and subsequently repatched with a cesium internal solution (black, as in
A
). Right, Summary data. Switching from a potassium- to a cesium-based internal solution produced a 2.2-fold increase in the EPSPs recorded in FS interneurons (n = 8).
D
, The increase in FS interneuron EPSPs does not result from the voltage-clamp paradigm per se. Left, EPSP generated in an FS interneuron by triggering a spike (black) or an action current (blue) in the presynaptic pyramidal cell recorded in the current clamp or voltage clamp configuration, respectively. Right, Summary data. Note the lack of difference in the amplitude of the EPSP evoked with either recording configuration. ss, Somatosensory.