Fig. 5: Histamine feedback sustains ACh cotransmission.
From: A single photoreceptor splits perception and entrainment by cotransmission
a, ACh-mediated circadian photoentrainment requires HisCl1. Average actogram of CHO flies (left: n = 61) and CHO flies with HisCl1 rescued in R8 photoreceptors (right: n = 71). b, Light step-induced AMA responses in wild-type (black), CHO (orange) and CO (blue) flies. Left: representative voltage responses (current clamp). Middle: representative current responses (voltage clamp). Right: pooled peak and steady voltage response amplitudes (top), current response amplitudes (middle) and firing rates (bottom). Light: 470 nm, 60 s, intensities of 0.0094, 0.19 and 1.88 × 106 photons μm−2 s−1. c, HisCl1 in R8 photoreceptors restored steady depolarization in CHO flies. Top: representative recordings in CHO flies with HisCl1 rescued in R8 photoreceptors; middle and bottom: pooled data. Light: 470 nm, 60 s, intensities of 0.0094, 0.19 and 1.88 × 106 photons μm−2 s−1. d, Negative histamine feedback to histamine release. Left: Histamine-mediated hyperpolarization in ort-expressing AMA neurons is increased in HO flies when ACh-mediated depolarization is blocked by MCA. Right: pooled steady and peak response amplitudes and their corresponding ratios. Light: 470 nm, 60 s, 1.88 × 106 photons μm−2 s−1. e, Normal ACh sensitivity in CHO flies. Left: representative ACh-induced depolarization before, during and after light stimulation; right: pooled data. Light: 470 nm, 60 s, 1.88 × 106 photons μm−2 s−1. f, Frequency dependence of light-pulse-induced responses in AMA neurons. Left: representative responses to light pulses of 0.2 Hz and 1 Hz; right: pooled peak response ratios between the first and fiftieth pulses. Light pulses: 470 nm, duration of 100 ms, 5.65 × 107 photons μm−2 s−1. g, Circadian photoentrainment of CHO flies to brief light pulses. Average actograms to 100-ms flashes at 0.2 Hz (n = 63), 1 Hz (n = 65), 2 Hz (n = 60) and 5 Hz (n = 54). h, A model of negative histaminergic feedback in R8 photoreceptors. Pooled data are shown as mean ± s.e.m. *P < 0.05; **P < 0.01; ***P < 0.001; NS, not significant. Statistical analysis is summarized in Supplementary Table 2.
