Figure 6.

Focal glutamate uncaging at individual dendritic spines evokes uEPSPs that attenuate with distance from the soma. a, Alexa 594 reconstruction of a part of a pyramidal thalamorecipient neuron showing three sites of two-photon glutamate uncaging (arrows). b, The top shows mEPSPs recorded in a thalamorecipient pyramidal neuron (black trace) and an example of a uEPSP (blue trace) in response to a single pulse of glutamate uncaging in the same neuron. The bottom shows the same uEPSP (blue trace) superimposed against the averaged mEPSP (black trace) from the same neuron. Miniature EPSPs (amplitude, 0.44 ± 0.15 mV; 20–80% rise time, 9.8 ± 3.5 ms; 80–20% decay time, 24.0 ± 15.7 ms) were not significantly different from uEPSPs evoked on the secondary dendrites (amplitude, 0.45 ± 0.12 mV; 20–80% rise time, 8.9 ± 6.9 ms; 80–20% decay time, 22.8 ± 8.3 ms; n = 51; p > 0.05, Mann–Whitney U test). c, Representative traces of uEPSPs (top black traces) evoked by two-photon uncaging (arrow) measured at the soma and calcium transients (middle blue traces) and Alexa 594 bleaching (red traces) measured in a dendritic spine of the same neuron. d, Peak uEPSPs as a function of distance generated at mushroom spines along basal and apical dendrites of thalamorecipient neurons. Each data point is an average of 5–16 uEPSPs; length constants were calculated from raw data (n = 168 uEPSPs generated along basal dendrites at a total of 17 sites in 7 neurons; n = 162 uEPSPs generated along apical dendrites at a total of 17 sites in 8 neurons).