Fig. 6: Moderate ChR2 expression is associated with subtle reductions in CF signaling and abolishes learning to a sensory US.
From: Climbing fibers provide essential instructive signals for associative learning
a, Experimental scheme. A visual CS was paired with a sensory airpuff US in a traditional classic conditioning experiment in CF-ChR2 animals. b, CF-ChR2-puff animals, without any photostimulation, unable to learn to an airpuff US (blue, N = 6 mice), but recovered learning (CF-ChR2-LE-puff, light blue, N = 4 mice) on lowering ChR2 expression. Shadows correspond to ±s.e.m. (%CR at the last learning session: CF-ChR2-puff versus CF-ChR2-LE-puff, ***P = 7.75 × 10−5, two-sample Student’s t-test). c, Animals with both expression levels exhibiting robust UR blinks on CS + US trials (CF-ChR2-puff, blue, N = 6 mice and CF-ChR2-LE-puff, light blue, N = 4 mice, ±s.e.m. in shadows). d, Average eyelid traces ± s.e.m. (shadows) from CS-only trials of the last training session revealing no learning in CF-ChR2-puff animals (blue, N = 6 mice and CF-ChR2-LE-puff, light blue, N = 4 mice). e, Spontaneous (Spont.) CSpk firing rate for each Purkinje cell recorded from control (black, N = 26 cells from 4 mice), CF-ChR2-LE (light blue, N = 20 cells from 4 mice) and CF-ChR2 (blue, N = 15 units from 5 mice) mice. Controls versus CF-ChR2: *P = 0.04, two-sample Student’s t-test (26 versus 15 cells); controls versus CF-ChR2-LE: P = 0.24 NS, two-sample Student’s t-test (26 versus 20 cells). f, Probability of an airpuff-evoked CSpk for each Purkinje cell recorded. Controls versus CF-ChR2: ***P = 0.00003, two-sample Student’s t-test (26 versus 15 cells); controls versus CF-ChR2-LE: P = 0.16 NS, two-sample Student’s t-test (26 versus 20 cells). g,h, SSpk statistics for each Purkinje cell recorded from control (black), CF-ChR2-LE (light blue) and CF-ChR2 (blue) mice. g, SSpk spontaneous firing rate: controls versus CF-ChR2, P = 0.41 NS, two-sample Student’s t-test (26 versus 15 cells); controls versus CF-ChR2-LE, P = 0.07 NS, two-sample Student’s t-test (26 versus 20 cells). h, SSpk coefficient of variation (CV). Controls versus CF-ChR2: P = 0.33 NS, two-sample Student’s t-test (26 versus 15 cells); controls versus CF-ChR2-LE: P = 0.26 NS, two-sample Student’s t-test (26 versus 20 cells).
