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Fig. 3. Variable initiation of sAPs from multiple PDCs in the primary dendrites in acutely dissociated, AIS-disabled DA neurons. (A) The red fluorescence image with differential interference contrast image of an acutely dissociated DA neuron loaded with Fluo 4-AM and Ca2+ measuring sites (S, soma; P, proximal dendrite; and D, distal dendrite). (B) After sAP, the Ca2+ spike started immediately from the PDC (red) and then propagated into the soma (black) and distal dendritic region (blue). Normalized traces expanded from the inset. (C) The Ca2+ spike started from the soma and propagated directionally to the proximal and distal dendritic regions. Normalized traces expanded from the inset. (D) Distribution of the time-lags of Ca2+ spike onsets between the dendritic regions and the soma. Black circles indicate Ca2+ propagation from the soma to the dendrite. Red circles indicate Ca2+ propagation from the proximal dendrite to the soma. Gray closed circles indicate time-lags in the distal dendritic region. Right, time lags of Ca2+ onset are represented by a bar graph (P→S: –6.06 ± 1.66 ms, 13/24, S→P: 6.75 ± 2.33 ms, 11/24). (E) Initiation order of Ca2+ spikes among three different parts, including two opposite proximal primary dendrites. Two individual PDCs, P1 (red closed circles) and P2 (green closed circles), alternatively generated APs, but in some cases (*), two proximal dendrites independently generated Ca2+ spikes earlier than the somatic one (black closed circles). (F, G) The order of generation of Ca2+ spikes between two opposite primary dendrites and their statistics (P1 and P2 > S; both P1 and P2 Ca2+ spikes preceded the soma Ca2+ spikes; P1 > S or P2 > S, either P1 or P2 generated the earliest Ca2+ spike; S, the soma Ca2+ spikes preceded both the P1 and P2 Ca2+ spikes; n = 13). (H) Schematic models of sAP generation in multipolar DA neurons. In normal DA neurons with an attached axon, sAPs always begin in the AIS and propagate into the soma and other primary dendrites. When the AIS is disabled or removed, the excitable PDCs of many primary dendrites depolarize independently, and the one that first reaches the AP threshold fires first. Values are presented as mean ± SE. sAPs, spontaneous action potentials; PDCs, proximal dendritic compartments; AIS, axon initial segment; DA, dopamine; AP, action potential.
Korean J Physiol Pharmacol 2024;28:165-181 https://doi.org/10.4196/kjpp.2024.28.2.165
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