Fig. 4
From: High frequency neural spiking and auditory signaling by ultrafast red-shifted optogenetics
f-Chrimson expression after postnatal AAV-transduction of SGNs. a Scheme of the future oCI as implanted into the human ear: the oCI passes through the middle ear (limited left by ear drum and right by inner ear) near the ossicles, enters the cochlea and spirals up in scala tympani. It will likely contain tens of microscale emitters (orange spots on oCI) that stimulate (orange beams) SGNs housed in the modiolus (central compartment of the cochlea), that encode information as APs. SGNs form the auditory nerve (right) which carries the information to the brain (not displayed). b pAAV vector used in the study to express f-Chrimson-EYFP under the control of the hSynapsin promoter (top) upon early postnatal injection of AAV2/6 into scala tympani via a posterior tympanotomy (lower left) to expose the round window (white circle in right lower panel). c Photocurrents of a representative culture f-Chrimson-EYFP-positive SGN isolated from an injected ear at postnatal day 14. Light pulses of 2 ms duration were applied at the indicated intensities in the focal plane and photocurrents recorded at −73 mV at room temperature. Scale bar: 2 ms, 50 pA. d Fraction of EYFP-positive (EYFP+) SGNs (identified by parvalbumin immunofluorescence, parvalbumin+) and e density of parvalbumin+ SGNs (#cells per 104 µm2) obtained from data as in f. Symbols mark results from individual animals (n = 5), box–whisker plots show 10th, 25th, 50th, 75th and 90th percentiles of the injected (orange) and non-injected control (magenta) cochleae (Kruskal–Wallis ANOVA, P = 0.6538, H = 0.98; post-hoc Dunn’s test for comparison of expression, P > 0.05 for all pairwise comparisons; Mann–Whitney U test for comparison of density, Lapex vs. Rapex, Lmid vs. Rmid, Lbase vs. Rbase, P > 0.05 for all comparisons). f Projections of confocal cryosections with YFP (green) and parvalbumin (magenta) immunofluorescence of SGNs in three cochlear regions (scale bar: 50 µm). Insets (scale bar: 10 µm) show close-up images of single z-sections of the same images
