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Fig. 1. Axon removal reveals dendritic origin of sAPs in DA neurons. (A) Fluorescence images of a DA neuron in a midbrain slice and pacemaking and spontaneous firing diagram. The yellow rectangular area containing an axon is expanded into the middle images before and after axon removal at the red line. Right, spontaneous firing traces recorded in the cell-attached mode before and after axon removal. (B) Mean spontaneous firing frequencies before and after axon removal. (C) ISI variances before and after axon removal. (D) Ca2+ spikes were measured in two opposite proximal primary dendrites, P1 (ABD, blue circles) and P2 (nABD, red circles). (E) Before axon-cutting, Ca2+ spikes always developed immediately after sAPs from the ABD (P1, blue) and later at the nABD (P2, red). Black line represents AP appearance timing. AP propagation direction was marked with arrow in an insert. (F) Time-lags between APs and rising-points of Ca2+ spikes (mean time lag: P1 = 0.473 ± 0.046, P2 = 10.39 ± 1.04, n = 3). (G) Variances in the time-lags before and after axon removal. (H) Ca2+ spikes were measured in two opposite proximal primary dendrites (P1 and P2) after axon removal. The order of the two dendritic Ca2+ spikes varied. The case in which the Ca2+ spike occurred first at the nABD, immediately after sAP, is presented. (I) The order of Ca2+ spikes between two primary dendrites with the time-lags (mean time lag: P1 = 10.86 ± 2.69, P2 = 6.85 ± 2.19, n = 3). (J) Incidence of AP initiation in the ABD (P1) and nABD (P2) changed dramatically after axon removal (from P1 = 100% and P2 = 0% to P1 = 55.56%, and P2 = 44.44%, n = 3). Values are presented as mean ± SE. DA, dopamine; ISI, interspike interval; ABD, axon-bearing dendrite; nABD, non-axon-bearing dendrite; AP, action potential; sAPs, spontaneous action potentials; AIS, axon initial segment. **p < 0.001.
Korean J Physiol Pharmacol 2024;28:165-181 https://doi.org/10.4196/kjpp.2024.28.2.165
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