Figure 1. Bath applied NMDA evokes Ca²⁺ entry in stellate cell dendrites and axons.

(A) Two-photon fluorescence image of a cerebellar stellate cell filled via patch pipette with 50 µM Alexa 594 and 200 µM Fluo-5F. Magnified views show a dendrite (left boxed inset) and an axon studded with varicosities (right boxed inset). The axon segment shown in the right inset is not part of the cell shown in A. (B) A sequence of frame scans show that application of NMDA (10 µM, 0 mM Mg²⁺) increases Ca²⁺ in a segment of dendrite (frame 540s) while somatic depolarization (frame 1460s) resulted in very little Ca²⁺ entry. Plot shows the average Ca²⁺ increase in dendritic segments elicited by NMDA superimposed on the average somatic membrane potential. Images and voltage sweeps taken every 20 seconds. (C₁) Sequence of frame scans from an axon segment showing action potential-evoked Ca²⁺ entry. (C₂) Frame scans from the same axon segment show Ca²⁺ entry induced by bath applied NMDA (10 µM, 0 mM Mg²⁺) and somatic depolarization (frame 540 s and 1420 s, respectively). Plot shows the average change in Ca²⁺ recorded in axon segments and somatic membrane potential. (D) Dependence of axonal Ca²⁺ elevation on distance from the axon hillock (10 µM NMDA, 0 mM Mg²⁺).