Scientific Reports (Oct 2024)

Plateau depolarizations in spontaneously active neurons detected by calcium or voltage imaging

  • Katarina D. Milicevic,
  • Violetta O. Ivanova,
  • Darko D. Lovic,
  • Jelena Platisa,
  • Pavle R. Andjus,
  • Srdjan D. Antic

DOI
https://doi.org/10.1038/s41598-024-70319-4
Journal volume & issue
Vol. 14, no. 1
pp. 1 – 14

Abstract

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Abstract In calcium imaging studies, Ca2+ transients are commonly interpreted as neuronal action potentials (APs). However, our findings demonstrate that robust optical Ca2+ transients primarily stem from complex “AP-Plateaus”, while simple APs lacking underlying depolarization envelopes produce much weaker photonic signatures. Under challenging in vivo conditions, these “AP-Plateaus” are likely to surpass noise levels, thus dominating the Ca2+ recordings. In spontaneously active neuronal culture, optical Ca2+ transients (OGB1-AM, GCaMP6f) exhibited approximately tenfold greater amplitude and twofold longer half-width compared to optical voltage transients (ArcLightD). The amplitude of the ArcLightD signal exhibited a strong correlation with the duration of the underlying membrane depolarization, and a weaker correlation with the presence of a fast sodium AP. Specifically, ArcLightD exhibited robust responsiveness to the slow “foot” but not the fast “trunk” of the neuronal AP. Particularly potent stimulators of optical signals in both Ca2+ and voltage imaging modalities were APs combined with plateau potentials (AP-Plateaus), resembling dendritic Ca2+ spikes or “UP states” in pyramidal neurons. Interestingly, even the spikeless plateaus (amplitude > 10 mV, duration > 200 ms) could generate conspicuous Ca2+ optical signals in neurons. Therefore, in certain circumstances, Ca2+ transients should not be interpreted solely as indicators of neuronal AP firing.