Figure 3. Glutamate receptors are absent from distal dendrites.

A) 2-photon fluorescence image of a SAC (z-projection) with targeted locations of glutamate uncaging sites along one dendritic path. Colors correspond to current responses in B.

B) Voltage clamp recordings (holding potential = −72 mV) from the cell in A in response to glutamate uncaging at 40 dendritic sites. Black arrowheads indicate the timing of the 100 µs laser uncaging pulses at different dendritic sites (moving outward from the soma to the distal dendrites from left to right and bottom to top). Traces are averages of 10 sweeps.

C) Locations where uncaging-evoked EPSCs indicated the presence of putative postsynaptic sites (black dots). Each row represents a different dendrite (n = 20 dendrites from 15 cells). Dashed lines: the entire path lengths from the soma to the end of the dendrite; solid lines: the path lengths sampled by uncaging. Locations of the last synapses in each dendrite are connected by the grey line.

D) Histograms of the putative postsynaptic sites as a function of path length (top) or path length normalized to the dendritic length of each dendrite.

E) Starburst amacrine cell excitatory receptive field size determined using spot stimulation (‘Spots’), ring stimulation (‘Rings’), or glutamate uncaging (‘Uncaging’). Error bars are S.D.

See also Figures S2–3.