Spontaneous activity in CSF-contacting neurons requires Pkd2l1. Immunohistochemistry for zebrafish Pkd2l1 in 30 hpf a Tg(pkd2l1:gal4; UAS:TagRFP-CAAX) or b Tg(pkd2l1−/−; pkd2l1:GCaMP5G) embryos. Right: magnification of the area in the gray box. No Pkd2l1 was detected in pkd2l1−/− embryos. Scale: 20 µm. c Calcium imaging traces from ventral CSF-cNs in 24–26 hpf Tg(pkd21l:GCaMP5G) embryos. Traces represent cells with the median integral values taken from all embryos. Scale: 30 s, 100% ΔF/F. d Integral quantification of CSF-cN calcium activity. Each point reflects the average calcium activity for all cells from one embryo (n = 22 pkd2l1+/+, n = 32 pkd2l1+/−, n = 12 pkd2l1−/− embryos, p = 1.94 × 10‒13, comparison between pkd2l1+/+ and pkd2l1−/−, linear mixed models). The central mark on the box plot indicates the median, the bottom and top edges of the box indicate the 25th and 75th percentiles. The whiskers extend to the most extreme data points not considered outliers. e Gap-free voltage-clamp (VC) recordings from ventral CSF-cNs show extensive single channel opening exclusively in pkd2l1+/+ embryos. Scale: top: 10 s, 20 pA; bottom: 20 ms, 10 pA. f Channel opening frequency in ventral CSF-cNs of pkd2l1+/+ and pkd2l1−/− embryos (n = 8 pkd2l1+/+ CSF-cNs from eight embryos, n = 3 pkd2l1−/− CSF-cNs from two embryos). Error bars represent s.e.m. g Distribution of channel amplitudes at −85 mV in gap-free voltage-clamp recordings of pkd2l1+/+ CSF-cNs (mean amplitude 26.0 ± 5.1 pA). h Representative firing of a ventral CSF-cN at 28 hpf. Six out of seven ventral CSF-cNs fired single or repetitive action potentials in response to 10–20 pA of injected current. Scale: 100 ms, 20 mV
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