Fig. 7: SynTagMA identifies active neurons during behavior.

a Nuclei of CA1 neurons expressing AAV2/9-hSyn-postSynTagMA imaged in vivo through a chronic cranial window using 980 nm and 1070 nm to excite green and red SynTagMA fluorescence, respectively. Ten 2 s, 405 nm, 12.1 mW mm⁻² light pulses were applied in an awake mouse after which a small percentage of nuclei became photoconverted (magenta). b Photoconversion relative to baseline under ketamine-xylazine anesthesia (n = 1105 nuclei), after violet light (n = 1105 nuclei) and under awake conditions (n = 1576 nuclei). c Closed loop paradigm: a head-fixed mouse was trained to stop at a certain position on the running belt to receive a water reward (teardrop). Nuclear fluorescence in CA1 was continuously monitored during 4 laps, followed by 15 laps where 405 nm, 12.1 mW mm⁻², 2 s light pulses were triggered during water reward. d Mouse engaged in the task. Note spout for water delivery. e 2P image of CA1 cell body layer during running. Eight nuclei that later became photoconverted are marked by white circles. Yellow circles are eight randomly selected non-converted nuclei used for comparison of calcium signals. f Black trace is running speed during the first 4 laps with times of reward delivery (teardrop/dashed line). Magenta and green traces are the average green SynTagMA fluorescence of the 8 photoconverted nuclei and the 8 non-converted nuclei indicated in e, respectively. At right is the photoconversion of the individual nuclei. Note the consistent dips in the magenta trace (i.e., high calcium) just before the water reward/photoconversion light would be triggered. g Interneurons expressing AAV2/9-mDlx-postSynTagMA-2A-mCerulean imaged through a chronic cranial window under isoflurane anesthesia (mCerulean fluorescence not shown). At high magnification, green fluorescence reveals PSD spots on the dendrite. Red spots at baseline are autofluorescent material, unrelated to SynTagMA. Violet light (20 flashes, 0.2 Hz, 3 s duration, 0.42 mW mm⁻²) was applied to photoconvert postSynTagMA. h Photoconversion of synapses on dendrite A (n = 54 synapses) and B (n = 58 synapses) indicate higher activity levels in dendrite A. Scale bars: 50 µm (a, e); 20 µm and 2 µm (g). All experiments were performed in at least two mice and found to be reproducible.