Objective: Despite 6%–20% of the adult population suffering from tinnitus, there is no standard treatment for it. Placenta extract has been used for various therapeutic purposes, including hearing loss. Here, we evaluate the effect of a novel neuroprotective protein composition (NPPC) extract on electrophysiological and molecular changes in the medial geniculate body (MGB) of tinnitus‐induced rats. Methods: To evaluate the protein analysis by western blot, the rats were divided into three groups: (1) saline group (intraperitoneal injection of 200 mg/kg saline twice a day for 28 consecutive days, (2) chronic Na‐Sal group received sodium salicylate as in the first group, and (3) chronic treatment group (received salicylate 200 mg/kg twice daily for 2 weeks, followed by 0.4 mg NPPC daily from day 14 to day 28). Single‐unit recordings were performed on a separate group that was treated as in group 4. Gap‐prepulse inhibition of the acoustic startle (GPIAS) and pre‐pulse inhibition (PPI) was performed to confirm tinnitus in all groups at the baseline, 14th and 28th days. Results: Western blot analysis showed that the expression of γ‐Aminobutyric acid Aα1 subunit (GABA Aα1), N‐methyl‐d‐aspartate receptor subtype 2B (NR2B or NMDAR2B), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptors subunit GluR1 (GluR1), and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptors subunit GluR2 (GluR2) decreased after Na‐Sal injection, while NPPC upregulated their expression. MGB units in rats with tinnitus showed decreased spontaneous firing rate, burst per minute, and a spike in a burst. After NPPC administration, neural activity patterns showed a significant positive effect of NPPC on tinnitus. Conclusion: NPPC can play an effective role in the treatment of tinnitus in salicylate‐induced rats, and MGB is one of the brain areas involved in these processes. Level of Evidence: NA.
The generous support of the Iran National Science Foundation (INSF), as well as ENT and Head & Neck Research Center, Iran University of Medical Sciences to assign credit to the research line auditory neuroscience, is gratefully acknowledged. Also, all authors would like to appreciate the late Professor Alexander Borisovich Poletaev (*06 November 1951—† March 6th, 2021). He was the first to report the evident positive effects of the protein fraction of porcine placental extract introduced by Alexander Anikin, in terms of having prominent neuroprotective properties, initially named X‐proteins (XP). He also generously provided the placenta extract extraction method to this research group. The authors further thank all colleagues as well as administrative personnel at Shefa Neuroscience Institute, Tehran, Iran, who contributed to data collection.
This study was financially supported by the Iran National Science Foundation (INSF, Synergy Grant Code no. insf‐98020383‐1400/03/23 and 95830795), and ENT and Head and Neck Research Center, Hazrate Rasoul Akram Hospital, the Five Senses Institute, School of Medicine, Iran University of Medical Sciences, Tehran, Iran (Ethical approval no. IR.IUMS.REC.1398.233).
© 2023 The Authors. Laryngoscope Investigative Otolaryngology published by Wiley Periodicals LLC on behalf of The Triological Society.
- startle reflex
- placenta extract
- single unit recording
- sodium salicylate