Safety evaluations for transtympanic laser stimulation of the cochlea in Mongolian gerbils (Meriones unguiculatus)

• Published in: Neuroscience research Vol. 212; pp. 31 - 40
• Main Authors: Okamoto, Aya, Uenaka, Miku, Ito, Yuki, Kuroki, Yuta, Miyasaka, Tomohiro, Toda, Koji, Hiryu, Shizuko, Kobayasi, Kohta I., Tamai, Yuta
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.03.2025; Elsevier
• Subjects: Acoustic Stimulation; Animals; Auditory perception; Auditory Perception - physiology; Auditory Perception - radiation effects; Auditory prosthesis; Cochlea - physiology; Cochlea - radiation effects; Conditioning, Classical; Gerbillinae; Head-fixed classical conditioning; Infrared laser stimulation; Lasers - adverse effects; Male; Infrared laser stimulation; Auditory prosthesis; Auditory perception; Head-fixed classical conditioning
• ISSN: 0168-0102; 1872-8111; 1872-8111
• DOI: 10.1016/j.neures.2024.10.004

Infrared laser stimulation of the cochlea has been proposed as a possible alternative to conventional auditory prostheses. Whereas previous studies have focused primarily on the short-term effects of laser stimulation, the practical application of this technics requires an investigation into whether prolonged laser exposure can induce neural responses and safely. This study assessed the effect of laser-induced damage to the cochlea on auditory perception using Mongolian gerbils (Meriones unguiculatus) trained with a classical conditioning task. The broadband noise was presented as a conditioned stimulus, and reward licking was recorded as a conditioned response. After training, the subject’s cochlea was exposed to a continuous pulsed laser for 15 h. Broadband noise of various intensities was presented without pairing it with water before and after laser exposure to assess the decrease in auditory perception due to laser-induced injury. The licking rate did not change after laser exposure of 6.6 W/cm2 or weaker but drastically decreased after 26.4 W/cm2 or higher. These findings showed, for the first time, that the safety margin of long-term, at least several hours, cochlear laser stimulation exists and will contribute to the appropriate delimitation of the safe and effective laser stimulation parameters in future research. •The laser with high energy density caused thermal elevation of the cochlear surface.•The spatial injury profile depends on the thermal distribution of the cochlea.•The injury threshold for laser stimulation is between 6.6 and 26.4 W/cm2.