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. 2024 Apr 16;19(4):e0296607.
doi: 10.1371/journal.pone.0296607. eCollection 2024.

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus

Katayoon Montazeri  1 , Mohammad Farhadi  1 , Abbas Majdabadi  2 , Zainab Akbarnejad  1 , Reza Fekrazad  3 , Ali Shahbazi  4 , Saeid Mahmoudian  1
Affiliations

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus

Katayoon Montazeri et al. PLoS One. .

Abstract

Tinnitus is a common annoying symptom without effective and accepted treatment. In this controlled experimental study, photobiomodulation therapy (PBMT), which uses light to modulate and repair target tissue, was used to treat sodium salicylate (SS)-induced tinnitus in a rat animal model. Here, PBMT was performed simultaneously on the peripheral and central regions involved in tinnitus. The results were evaluated using objective tests including gap pre-pulse inhibition of acoustic startle (GPIAS), auditory brainstem response (ABR) and immunohistochemistry (IHC). Harmful neural plasticity induced by tinnitus was detected by doublecortin (DCX) protein expression, a known marker of neural plasticity. PBMT parameters were 808 nm wavelength, 165 mW/cm2 power density, and 99 J/cm2 energy density. In the tinnitus group, the mean gap in noise (GIN) value of GPIAS test was significantly decreased indicated the occurrence of an additional perceived sound like tinnitus and also the mean ABR threshold and brainstem transmission time (BTT) were significantly increased. In addition, a significant increase in DCX expression in the dorsal cochlear nucleus (DCN), dentate gyrus (DG) and the parafloccular lobe (PFL) of cerebellum was observed in the tinnitus group. In PBMT group, a significant increase in the GIN value, a significant decrease in the ABR threshold and BTT, and also significant reduction of DCX expression in the DG were observed. Based on our findings, PBMT has the potential to be used in the management of SS-induced tinnitus.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Diagram of methods.
Abbreviations: GPIAS (Gap Prepulse Inhibition of Acoustic Startle), ABR (auditory brainstem response), SS (sodium salicylate), Cont. (control), PBMT (photobiomodulation therapy), IHC (immunohistochemistry).
Fig 2
Fig 2. Laser irradiation in the PBMT group.
The distance between the tip of the optical fiber and the animal’s head was fixed at 8 cm by the mechanical holder, at which the diameter of the laser beam becomes 2 cm, which covers the entire surface of the animal’s brain. (a) laser radiation to the skull from the upper side (b) laser radiation to the left and right hearing area from the lateral side.
Fig 3
Fig 3. Between-groups comparison of GIN and PPI values in control, tinnitus and PBMT groups.
Abbreviations: GIN (gap-in-noise), PPI (pre-pulse inhibition), PBMT (photobiomodulation therapy).
Fig 4
Fig 4
ABR waveforms in (A) Control group (B) Tinnitus group C) PBMT group. * The highest mean amplitude was produced at 90 dB SPL and in wave II of ABR. In each row, the bold line represents the grand average of the waveforms.
Fig 5
Fig 5. Between groups comparison of BTT and threshold in control, tinnitus and PBMT groups.
Abbreviations BTT (brainstem transmission time), PBMT (photobiomodulation therapy), dB (decibel), ms (millisecond).
Fig 6
Fig 6. Doublecortin (DCX) expression in 3 brain regions (coronal sections) in the control (Cont), Tinnitus (TIN) and PBMT (PBMT) groups.
DCX expression indicated as brown infiltration. (A) DCX expression in the paraflocculus (B) DCX expression in the dentate gyrus (C) DCX expression in the dorsal cochlear.
Fig 7
Fig 7. Bar graphs of DCX expression evaluated in three brain regions in the control (Cont), Tinnitus (TIN) and PBMT (PBMT) groups.
(A) DCX expression in Paraflocculus (B) DCX expression in dentate gyrus (C) DCX expression in dorsal cochlear nucleus.
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