Single infrared light pulses induce excitatory and inhibitory neuromodulation

Xuedong Zhu; Jen-Wei Lin; Ahmet Turnali; Michelle Y Sander

doi:10.1364/BOE.444577

Single infrared light pulses induce excitatory and inhibitory neuromodulation

Biomed Opt Express. 2021 Dec 16;13(1):374-388. doi: 10.1364/BOE.444577. eCollection 2022 Jan 1.

Authors

Xuedong Zhu^{1

2

3}, Jen-Wei Lin⁴, Ahmet Turnali^{5

3}, Michelle Y Sander^{1

2

5

3

6}

Affiliations

¹ Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02215, USA.
² Neurophotonics Center, Boston University, 24 Cummington Mall, Boston, MA 02215, USA.
³ Photonics Center, Boston University, 8 Saint Mary's Street, Boston, MA 02215, USA.
⁴ Department of Biology, Boston University, 5 Cummington Mall, Boston, MA 02215, USA.
⁵ Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary's Street, Boston, MA 02215, USA.
⁶ Division of Materials Science and Engineering, Boston University, 15 Saint Mary's Street, Brookline, MA 02446, USA.

Abstract

The excitatory and inhibitory effects of single and brief infrared (IR) light pulses (2 µm) with millisecond durations and various power levels are investigated with a custom-built fiber amplification system. Intracellular recordings from motor axons of the crayfish opener neuromuscular junction are performed ex vivo. Single IR light pulses induce a membrane depolarization during the light pulses, which is followed by a hyperpolarization that can last up to 100 ms. The depolarization amplitude is dependent on the optical pulse duration, total energy deposition and membrane potential, but is insensitive to tetrodotoxin. The hyperpolarization reverses its polarity near the potassium equilibrium potential and is barium-sensitive. The membrane depolarization activates an action potential (AP) when the axon is near firing threshold, while the hyperpolarization reversibly inhibits rhythmically firing APs. In summary, we demonstrate for the first time that single and brief IR light pulses can evoke initial depolarization followed by hyperpolarization on individual motor axons. The corresponding mechanisms and functional outcomes of the dual effects are investigated.