Background: Histamine is a widely distributed biogenic amine with multiple biological functions mediated by specific receptors that determine the local effects of histamine. This review aims to summarize the published findings on the expression and functional roles of histamine receptors in the inner ear and to identify potential research hotspots and gaps. Methods: A search of the electronic databases PubMed, Web of Science, and OVID EMBASE was performed using the keywords histamine, cochlea*, and inner ear. Of the 181 studies identified, 18 eligible publications were included in the full-text analysis. Results: All four types of histamine receptors were identified in the mammalian inner ear. The functional studies of histamine in the inner ear were mainly in vitro. Clinical evidence suggests that histamine and its receptors may play a role in Ménière’s disease, but the exact mechanism is not fully understood. The effects of histamine on hearing development remain unclear. Conclusions: Existing studies have successfully determined the expression of all four histamine receptors in the mammalian inner ear. However, further functional studies are needed to explore the potential of histamine receptors as targets for the treatment of hearing and balance disorders.

Hair cells (HCs) in the mammalian cochleae cannot spontaneously regenerate once damaged, resulting in permanent hearing loss. It has been shown that Atoh1 overexpression induces hair cell-like cells (HCLCs) in the cochlea of newborn rodents, but this is hard to achieve in adult mammals. In this study, we used a three-dimensional cochlear culture system and an adenoviral-mediated delivery vector to overexpress Atoh1 in adult mouse cochleae. HCLCs were successfully induced from 3 days after virus infection (3 DVI) in vitro, and the number increased with time. HCLCs were myosin7a positive and distinguishable from remnant HCs in a culture environment. Meanwhile, patch-clamp results showed that noninactive outward potassium currents (sustained outward potassium currents) could be recorded in HCLCs and that their magnitude increased with time, similar to normal HCs. Furthermore, transient HCN currents were recorded in some HCLCs, indicating that the HCLCs experienced a developmental stage similar to normal HCs. We also compared the electrophysiological features of HCLCs from adult mice with native HCs and found the HCLCs gradually matured, similar to the normal HCs. Meanwhile, HCLCs from adult mice possessed the same bundles as developmental HCs. However, these HCLCs did not express prestin, which is a special marker for outer hair cells (OHCs), even at 13 DVI. These results demonstrate that Atoh1 overexpression induces HCLC formation in the adult mammalian cochlea and that these HCLCs were functional and experienced a developmental process similar to that of normal HCs.

The histamine H3 receptor (H3R) is a crucial regulator of synaptic plasticity, neurotransmitter release, and neural signaling within the central nervous system. However, its role in the cochlea remains poorly understood, even though mast cells, a rich endogenous source of histamine, have recently been documented in the mammalian cochlea. This study examined H3R expression and localization in the postnatal day 4–5 (P4-5) C57BL/6 mouse cochlea and evaluated its functional consequences under antagonist treatment. RT-qPCR analysis showed significantly higher H3R mRNA levels in the modiolus compared to the organ of Corti and the lateral wall. Immunofluorescence staining confirmed H3R localization in hair cells (HCs) and spiral ganglion neurons (SGNs). Dissected cochlear explants exposed to two distinct H3R antagonists—ciproxifan and pitolisant—at concentrations of 10µM, 50µM, and 100µM, displayed different responses: ciproxifan induced dose-dependent HC loss. In contrast, pitolisant caused no loss of HC but led to stereociliary abnormalities at higher concentrations. Both antagonists disrupted type II SGN neurite projections, redirecting their normal basal-directed trajectory toward the apical region. These findings implicate H3R in maintaining cochlear structural integrity and guiding SGN neurite development during early postnatal maturation. Further investigation into H3R-mediated mechanisms may reveal new therapeutic targets for hearing preservation and repair.