Figure 7. PF-evoked Ca²⁺ transients in axon varicosities.

(A₁) Fluorescence image of a stellate cell shows the dendritic position of the extracellular pipette used to stimulate PFs. Magnified view of an axonal varicosity (boxed inset) used for Ca²⁺ imaging. (A₂) NMDAR-mediated EPSP evoked (V_rest= −70 mV) by focal stimulation of PFs (50 Hz, 80 ms). (B) PF stimulation evoked Ca²⁺ transients in the dendrite and axon varicosity of the cell shown in A₁. The PF-evoked axonal Ca²⁺ transient is shown (bottom) at higher gain. (C₁) Somatic voltage clamp did not alter the dendritic Ca²⁺ transient. (C₂) Somatic voltage clamp eliminated the Ca²⁺ transient in an axon varicosity evoked by dendritic PF stimulation. (D) An axonal Ca²⁺ transient evoked by dendritic PF stimulation. PF stimulation near the axon (middle) failed to evoked a Ca²⁺ in an axon varicosity. The axonal signal with no stimulation (bottom). (E) Summary data show that local stimulation of PFs near axon varicosities failed to evoke a Ca²⁺ transient.