Tumor Microenvironment in Sporadic Vestibular Schwannoma: A Systematic, Narrative Review.

Although diagnosis and treatment of vestibular schwannomas (VSs) improved in recent years, no factors have yet been identified as being capable of predicting tumor growth. Molecular rearrangements occur in neoplasms before any macroscopic morphological changes become visible, and the former are the underlying cause of disease behavior. Tumor microenvironment (TME) encompasses cellular and non-cellular elements interacting together, resulting in a complex and dynamic key of tumorigenesis, drug response, and treatment outcome. The aim of this systematic, narrative review was to assess the level of knowledge on TME implicated in the biology, behavior, and prognosis of sporadic VSs. A search (updated to November 2022) was run in Scopus, PubMed, and Web of Science electronic databases according to the PRISMA guidelines, retrieving 624 titles. After full-text evaluation and application of inclusion/exclusion criteria, 37 articles were included. VS microenvironment is determined by the interplay of a dynamic ecosystem of stromal and immune cells which produce and remodel extracellular matrix, vascular networks, and promote tumor growth. However, evidence is still conflicting. Further studies will enhance our understanding of VS biology by investigating TME-related biomarkers able to predict tumor growth and recognize immunological and molecular factors that could be potential therapeutic targets for medical treatment.

Detection of Lymphatic Vessels in the Superficial Fascia of the Abdomen.

Recently, the superficial fascia has been recognized as a specific anatomical structure between the two adipose layers-the superficial adipose tissue (SAT) and the deep adipose tissue (DAT). The evaluation of specific characteristics of cells, fibers, blood circulation, and innervation has shown that the superficial fascia has a clear and distinct anatomical identity, but knowledge about lymphatic vessels in relation to the superficial fascia has not been described. The aim of this study was to evaluate the presence of lymphatic vessels in the hypodermis, with a specific focus on the superficial fascia and in relation to the layered subdivision of the subcutaneous tissue into SAT and DAT. Tissue specimens were harvested from three adult volunteer patients during abdominoplasty and stained with D2-40 antibody for the lymphatic endothelium. In the papillary dermis, a huge presence of lymphatic vessels was highlighted, parallel to the skin surface and embedded in the loose connective tissue. In the superficial adipose tissue, thin lymphatic vessels (mean diameter of 11.6 ± 7.71 µm) were found, close to the fibrous septa connecting the dermis to the deeper layers. The deep adipose tissue showed a comparable overall content of lymphatic vessels with respect to the superficial layer; they followed the blood vessel and had a larger diameter. In the superficial fascia, the lymphatic vessels showed higher density and a larger diameter, in both the longitudinal and transverse directions along the fibers, as well as vessels that intertwined with one another, forming a rich network of vessels. This study demonstrated a different distribution of the lymphatic vessels in the various subcutaneous layers, especially in the superficial fascia, and the demonstration of the variable gauge of the vessels leads us to believe that they play different functional roles in the collection and transport of interstitial fluid-important factors in various surgical and rehabilitation fields.

Liquid Crystalline Nanoparticles Conjugated with Dexamethasone Prevent Cisplatin Ototoxicity In Vitro.

The conjugation of drugs with nanoparticles represents an innovative approach for controlled and targeted administration of therapeutic agents. Nanoparticle-based systems have been tested for the inner ear therapy, increasing the drug diffusion and being detected in all parts of the cochlea when locally applied near the round window. In this study, glycerol monooleate liquid crystalline NanoParticles were conjugated with Dexamethasone (NPD), a hydrophobic drug already used for inner ear treatments but defective in solubility and bioavailability. NPD has been tested in vitro in the cell line OC-k3, a model of sensory cells of the inner ear, and the therapeutic efficacy has been evaluated against cisplatin, a chemotherapeutic compound known to induce ototoxicity. After comparing the physical chemical characteristics of NPD to the equivalent naïve nanoparticles, an initial investigation was carried out into the nanoparticle's uptake in OC-k3 cells, which takes place within a few hours of treatment without causing toxic damage up to a concentration of 50 µg/mL. The NPD delivered the dexamethasone inside the cells at a significantly increased rate compared to the equivalent free drug administration, increasing the half-life of the therapeutic compound within the cell. Concerning the co-treatment with cisplatin, the NPD significantly lowered the cisplatin cytotoxicity after 48 h of administration, preventing cell apoptosis. To confirm this result, also cell morphology, cell cycle and glucocorticoids receptor expression were investigated. In conclusion, the NPD system has thus preliminarily shown the potential to improve the therapeutic efficacy of treatments delivered in the inner ear and prevent drug-induced ototoxicity.

Erratum: miR-199a-3p increases the anti-tumor activity of palbociclib in liver cancer models.

[This corrects the article DOI: 10.1016/j.omtn.2022.07.015.].

miR-199a-3p increases the anti-tumor activity of palbociclib in liver cancer models.

Palbociclib is in early-stage clinical testing in advanced hepatocellular carcinoma (HCC). Here, we investigated whether the anti-tumor activity of palbociclib, which prevents the CDK4/6-mediated phosphorylation of RB1 but simultaneously activates AKT signaling, could be improved by its combination with a PI3K/AKT/mTOR inhibitor in liver cancer models. The selective pan-AKT inhibitor, MK-2206, or the microRNA-199a-3p were tested in combination with palbociclib in HCC cell lines and in the TG221 HCC transgenic mouse model. The combination palbociclib/MK-2206 was highly effective, but too toxic to be tolerated by mice. Conversely, the combination miR-199a-3p mimics/palbociclib not only induced a complete or partial regression of tumor lesions, but was also well tolerated. After 3 weeks of treatment, the combination produced a significant reduction in number and size of tumor nodules in comparison with palbociclib or miR-199a-3p mimics used as single agents. Moreover, we also reported the efficacy of this combination against sorafenib-resistant cells in vitro and in vivo. At the molecular level, the combination caused the simultaneous decrease of the phosphorylation of both RB1 and of AKT. Our findings provide pre-clinical evidence for the efficacy of the combination miR-199a-3p/palbociclib as anti-HCC treatment or as a new approach to overcome sorafenib resistance.

Neuron Compatibility and Antioxidant Activity of Barium Titanate and Lithium Niobate Nanoparticles.

The biocompatibility and the antioxidant activity of barium titanate (BaTiO3) and lithium niobate (LiNbO3) were investigated on a neuronal cell line, the PC12, to explore the possibility of using piezoelectric nanoparticles in the treatment of inner ear diseases, avoiding damage to neurons, the most delicate and sensitive human cells. The cytocompatibility of the compounds was verified by analysing cell viability, cell morphology, apoptotic markers, oxidative stress and neurite outgrowth. The results showed that BaTiO3 and LiNbO3 nanoparticles do not affect the viability, morphological features, cytochrome c distribution and production of reactive oxygen species (ROS) by PC12 cells, and stimulate neurite branching. These data suggest the biocompatibility of BaTiO3 and LiNbO3 nanoparticles, and that they could be suitable candidates to improve the efficiency of new implantable hearing devices without damaging the neuronal cells.

Immune Response After Cochlear Implantation.

A cochlear implant (CI) is an electronic device that enables hearing recovery in patients with severe to profound hearing loss. Although CIs are a successful treatment for profound hearing impairment, their effectivity may be improved by reducing damages associated with insertion of electrodes in the cochlea, thus preserving residual hearing ability. Inner ear trauma leads to inflammatory reactions altering cochlear homeostasis and reducing post-operative audiological performances and electroacoustic stimulation. Strategies to preserve residual hearing ability led to the development of medicated devices to minimize CI-induced cochlear injury. Dexamethasone-eluting electrodes recently showed positive outcomes. In previous studies by our research group, intratympanic release of dexamethasone for 14 days was able to preserve residual hearing from CI insertion trauma in a Guinea pig model. Long-term effects of dexamethasone-eluting electrodes were therefore evaluated in the same animal model. Seven Guinea pigs were bilaterally implanted with medicated rods and four were implanted with non-eluting ones. Hearing threshold audiograms were acquired prior to implantation and up to 60 days by recording compound action potentials. For each sample, we examined the amount of bone and fibrous connective tissue grown within the scala tympani in the basal turn of the cochlea, the cochleostomy healing, the neuronal density, and the correlation between electrophysiological parameters and histological results. Detection of tumor necrosis factor alpha, interleukin-6, and foreign body giant cells showed that long-term electrode implantation was not associated with an ongoing inflammation. Growth of bone and fibrous connective tissue around rods induced by CI was reduced in the scala tympani by dexamethasone release. For cochleostomy sealing, dexamethasone-treated animals showed less bone tissue growth than negative. Dexamethasone did not affect cell density in the spiral ganglion. Overall, these results support the use of dexamethasone as anti-inflammatory additive for eluting electrodes able to protect the cochlea from CI insertion trauma.

Effectiveness of micronized nasal irrigations with hyaluronic acid/isotonic saline solution in non-polipoid chronic rhinosinusitis: A prospective, randomized, double-blind, controlled study.

BACKGROUND: Sodium hyaluronate has been proposed as a treatment for improving the symptoms of chronic rhinosinusitis. The present study evaluated the effect of the intranasal administration of hyaluronic acid in a group of patients affected by chronic rhinosinusitis without nasal polyps (CRSsNP). MATERIALS AND METHODS: Thirty subjects aged 18-65 years affected by CRSsNP were enrolled. The subjects were randomly administered hyaluronic acid or isotonic saline solution by nasal nebulizer twice per day for 30 days. They were evaluated before (T0) and after the treatment (T1) with Sino-Nasal Outcome Test-22, visual analogue scale for rhinorrhea, nasal obstruction, facial pain and hyposmia/hypogeusia, nasal endoscopy, active anterior rhinomanometry, peak nasal inspiratory flow and nasal cytology. RESULTS: Comparing the study and the control group, at T1 no significant differences were observed in both objective and subjective parameters. Being included in the study group rather than in the control group did not have a significant effect on the variation of the considered parameters between T0 and T1. Considering the effects of the micronized douches independently from the type of solution used (either hyaluronic acid or isotonic saline solution), although no difference emerged between study and control group for any of the objective parameters, there was an improvement of Sino-Nasal Outcome Test-22 scores (p = .0005), visual analogue scale for nasal obstruction (p = .0006) and for hyposmia/hypogeusia (p = .04). CONCLUSIONS: The treatment with micronized nasal douches can improve the sino-nasal symptoms of CRSsNP, in particular nasal obstruction and olfactory ability. No advantage of the use of hyaluronic acid over isotonic saline solution emerged.

Cisplatin-Induced Ototoxicity: Updates on Molecular Targets.

Cis-diamminedichloridoplatinum (II) (cisplatin) is a chemotherapeutic drug currently prescribed for the treatment of many types of human cancer, but its use is associated with numerous adverse effects, one of which is ototoxicity. Cisplatin-induced hearing loss is mainly attributed to oxidative stress, but recent data suggest that inflammation could be the trigger event leading to inner ear cell death through endoplasmic reticulum (ER) stress, autophagy, necroptosis, and then intrinsic apoptosis. In this review, we look at the molecular targets of cisplatin, and the intracellular pathways underlying its ototoxicity. Special attention is devoted to signal transduction processes involving cisplatin that may promote the development of new strategies to prevent cisplatin-induced hearing loss, an adverse event with severe social impacts.

Polydimethylsiloxanes biocompatibility in PC12 neuronal cell line.

Cochlear implants, the only way to recover from severe/profound hearing loss, may cause adverse effects, among which reactions to silicone materials coating implant electrodes, leading to apoptosis and necrosis of spiral ganglion cells. Our aim was to evaluate whether three polydimethylsiloxane (PDMS) compounds (hexadimethylsiloxane, octamethyltrisiloxane, decamethylcyclopentasiloxane) used in silicone rods could exert toxic effects on an in vitro neuronal cell model (PC12). Cell viability, morphology and mRNA expression levels of apoptotic markers were evaluated on PC12 cells at different PDMS dilutions up to 6 days of exposure. The results showed that at the highest concentrations tested cell viability was reduced by hexadimethylsiloxane and octamethyltrisiloxane at all times of exposure, but only from 72 h onwards by decamethylcyclopentasiloxane. The number of neurites per cell was not affected by hexadimethylsiloxane, but was significantly reduced from 24 h onwards by octamethyltrisiloxane and decamethylcyclopentasiloxane. Neurite length was reduced by hexadimethylsiloxane only at 24 h, and by octamethyltrisiloxane and decamethylcyclopentasiloxane at all exposure intervals. In controls exposed to silicone or glass rods cell viability was reduced only after 24 h, but neurite number and length was never reduced at any exposure interval. Biomolecular investigations showed that apoptotic markers did not change in any experimental condition, suggesting that PDMS are biocompatible. The reduction of cell viability and neurite number and length caused by exposure to these compounds was probably caused by a PDMS surface film formed over the cell medium, preventing air exchange, and not by the release of cytotoxic molecules.

Evaluation of toxicity of glycerol monooleate nanoparticles on PC12 cell line.

An innovative approach to improve drug delivery is the use of glycerol monooleate nanoparticles. Numerous studies describe their high versatility, low toxicity and ability to carry relatively high loads of conjugated compounds including scarcely soluble ones, providing sustained drug release and increasing drug diffusion and half-life. Despite a growing interest in their potential use for therapeutic applications, there are surprisingly few literature data concerning the toxic effects of these nanoparticles at high concentrations in vitro and in vivo, and their effects on cell metabolism. We produced and characterized from a physical-chemical point of view glycerol monooleate nanoparticles and tested them on the PC12 cell line, a rat model of neuronal differentiation. The toxicity of these nanoparticles was evaluated by molecular methods on cell viability, cell cycle, nanoparticle uptake and induction of apoptosis. The results showed that glycerol monooleate nanoparticles up to 100 µg/mL had no toxic effects on PC12 cells, did not induce significant changes in the cell cycle nor cause apoptosis. The nanoparticles entered PC12 cells 8 h after treatment, successfully delivering the conjugate compound inside cells. Overall, glycerol monooleate nanoparticles did not exhibit significant toxicity on PC12 cell line in concentrations up to 100 µg/mL, supporting their therapeutic use as drug delivery systems.

Human mesenchymal stromal cell therapy for damaged cochlea repair in nod-scid mice deafened with kanamycin.

BACKGROUND: Kanamycin, mainly used in the treatment of drug-resistant-tuberculosis, is known to cause irreversible hearing loss. Using the xeno-transplant model, we compared both in vitro and in vivo characteristics of human mesenchymal stromal cells (MSCs) derived from adult tissues, bone marrow (BM-MSCs) and adipose tissue (ADSCs). These tissues were selected for their availability, in vitro multipotency and regenerative potential in vivo in kanamycin-deafened nod-scid mice. METHODS: MSCs were isolated from informed donors and expanded ex vivo. We evaluated their proliferation capacity in vitro using the hexosaminidase assay, the phenotypic profile using flow-cytometry of a panel of surface antigens, the osteogenic potential using alkaline phosphatase activity and the adipogenic potential using oil-red-O staining. MSCs were intravenously injected in deafened mice and cochleae, liver, spleen and kidney were sampled 7 and 30 days after transplantation. The dissected organs were analyzed using lectin histochemistry, immunohistochemistry, polymerase chain reaction (PCR) and dual color fluorescence in situ hybridization (DC-FISH). RESULTS: MSCs showed similar in vitro characteristics, but ADSCs appeared to be more efficient after prolonged expansion. Both cell types engrafted in the cochlea of damaged mice, inducing regeneration of the damaged sensory structures. Several hybrid cells were detected in engrafted tissues. DISCUSSION: BM-MSCs and ADSCs showed in vitro characteristics suitable for tissue regeneration and fused with resident cells in engrafted tissues. The data suggest that paracrine effect is the prevalent mechanism inducing tissue recovery. Overall, BM-MSCs and ADSCs appear to be valuable tools in regenerative medicine for hearing loss recovery.

Regenerative medicine in hearing recovery.

Hearing loss, or deafness, affects 360 million people worldwide of which about 32 million are children. Deafness is irreversible when it involves sensory hair cell death because the regenerative ability of these cells is lost in mammals after embryo development. The therapeutic strategies for deafness include hearing aids and/or implantable devices. However, not all patients are eligible or truly benefit from these medical devices. Regenerative medicine based on stem cell application could play a role in both improvement of extant medical devices and in vivo recovery of auditory function by regeneration of inner ear cells and neurons. A review of recent literature on the subject indicates that two promising approaches to renewal and differentiation of cochlear tissues are transplantation of stem cells and in situ administration of growth factors. Rather than directly regenerating dead cells, these procedures apparently induce, through various pathways, differentiation of resident cochlear cells. More studies on the possible adverse effects of transplanted cells and the recovery of tonotopic sensorineural activity or required. To date, no reliable clinical results have been obtained in the field of cochlear regeneration.

Coenzyme Q10 plus Multivitamin Treatment Prevents Cisplatin Ototoxicity in Rats.

Cisplatin (Cpt) is known to induce a high level of oxidative stress, resulting in an increase of reactive oxygen species damaging the inner ear and causing hearing loss at high frequencies. Studies on animal models show that antioxidants may lower Cpt-induced ototoxicity. The aim of this study is to evaluate the ototoxic effects of two different protocols of Cpt administration in a Sprague-Dawley rat model, and to test in the same model the synergic protective effects of a solution of coenzyme Q10 terclatrate and Acuval 400®, a multivitamin supplement containing antioxidant agents and minerals (Acu-Qter). The Cpt was administered intraperitoneally in a single dose (14 mg/kg) or in three daily doses (4.6 mg/kg/day) to rats orally treated or untreated with Acu-Qter for 5 days. The auditory function was assessed by measuring auditory brainstem responses from 2 to 32 kHz at day 0 and 5 days after treatment. Similar hearing threshold and body weight alterations were observed in both Cpt administration protocols, but mortality reduced to zero when Cpt was administered in three daily doses. The Acu-Qter treatment was able to prevent and completely neutralize ototoxicity in rats treated with three daily Cpt doses, supporting the synergic protective effects of coenzyme Q terclatrate and Acuval 400® against Cpt-induced oxidative stress. The administration protocol involving three Cpt doses is more similar to common human chemotherapy protocols, therefore it appears more useful for long-term preclinical studies on ototoxicity prevention.

A soft-surgery approach to minimize hearing damage caused by the insertion of a cochlear implant electrode: a guinea pig animal model.

OBJECTIVE: A "soft surgery" technique was applied, using various types of specifically designed dummy electrodes, to mimic cochlear implantation in a guinea pig model, and the degree of hearing-preservation/cochlear damage was assessed. METHODS: Tricolor guinea pigs were divided into 3 groups: group A were implanted with electrodes without any contacts or wires (soft electrode), group B were implanted with electrodes having a metallic wire inside (stiff electrode), and group C underwent a cochleostomy procedure without implantation. Compound action potentials, in the range of 4 to 32 kHz, were used to assess electrophysiologic changes in the hearing function presurgery and postsurgery. Data were collected before surgery, at times t = 0 (immediately after surgery) and at 3, 7, 14, and 30 days. RESULTS: At low frequencies (4-8 kHz), an immediate elevation of hearing threshold was observed in all 3 groups. Higher threshold shifts were more consistent for group B implanted with a stiff electrode, in comparison to the other 2 groups. Animals from group C presented a recovery from hearing loss, starting 3 days after surgery. At high frequencies (16-32 kHz), the elevation of hearing threshold was higher, as compared with the data from the low frequencies. Group C animals presented oscillatory threshold shifts twice, and the recovery to normal threshold values occurred approximately at t = 14 days. CONCLUSION: The data suggest that cochleostomy is minimally harmful to the inner ear and that a soft electrode might better preserve the inner ear integrity than a rigid electrode.

Cochlear implants and drug delivery: In vitro evaluation of dexamethasone release.

Anti-inflammatory drugs can minimize the trauma and inflammation in the inner ear caused by cochlear implantation surgery. For this reason, much effort has recently been devoted to finding the best way to administer these anti-inflammatory drugs for a prolonged time and in a personalized dosage. One solution is constructing an electrode with a dispenser filled with anti-inflammatory drugs with a dosage adapted to suit each new cochlear implant user. The purpose of this study was to measure in vitro, by high-performance liquid chromatography-mass spectrometry assay, the amount of dexamethasone released in 78 days in a physiological solution by a filled dispenser. The drug release continued for more than 2 months in three different phases: (1) during the first 1-5 days, (2) within about 2 weeks, and (3) from about 3 weeks until the end of experiment. This release trend is in accordance with the 3 main phases of damage caused by the cochlear implantation: (1) insertion trauma within the first 2 days, (2) inflammation within 2 weeks, and finally (3) an intracochlear chronic fibrosis reaction. Future animal model studies should consider using this dispenser in order to establish its effectiveness in preventing damage caused by cochlear implantation.

Correlation of adverse effects of cisplatin administration in patients affected by solid tumours: a retrospective evaluation.

Cisplatin is the most common antineoplastic drug used for the therapy of solid tumours. To date, researchers have focused on the dosage to be administered for each specific tumour, mainly considering the local adverse effects. The aim of this study was to correlate the severity of the adverse effects with: i) the dosage of cisplatin; ii) the specific site of the tumour; iii) the association with other drugs; and iv) the symptoms. We analysed data from 123 patients with 11 different tumour classes undergoing therapy from 2007 to 2008 at St. Anna Hospital (Ferrara, Italy), using the Spearman non-parametric correlation index. Even though significant correlations were found among the variables, the overall results showed that the main factor influencing the severity of the adverse effects was the dosage of cisplatin administered.

Ultrastructure and distribution of superficial neuromasts of blind cavefish, Phreatichthys andruzzii, juveniles.

Transmission and scanning electron microscopy (TEM, SEM) were used to study the ultrastructure of superficial neuromasts in 15 six-month old blind cavefish juveniles, Phreatichthys andruzzii (Cyprinidae). In five specimens examined with SEM, the number of superficial neuromasts over the fish body (480-538) was recorded. They were localized mainly on the head (362-410), including the dorsal surface, the mentomandibular region, and laterally from the mouth to the posterior edge of the operculum. Neuromasts were also present laterally on the trunk and near the caudal fin (116-140). A significantly higher number of neuromasts were present on the head compared to the trunk (t-test, P < 0.05). Superficial neuromasts of the head and those along the trunk were similar in ultrastructure. Each neuromast comprised sensory hair cells surrounded by nonsensory support cells (mantle cells and supporting basal cells) with the whole covered by a cupula. Each hair cell was pear-shaped, 15-21 microm high and 4-6 microm in diameter, with a single long kinocilium and several short stereocilia. Most support cells were elongated, with nuclei occupying a large portion of the cytoplasm. In the margin of the neuromast, mantle cells were particularly narrow. Both types of support cells had well-developed Golgi apparatus and rough endoplasmic reticulum. The number of hair cells and nonsensory support cells of the anterior lateral line (head) did not differ significantly from those of the posterior lateral line (trunk) (t-test, P > 0.05).

Cochlear repair by transplantation of human cord blood CD133+ cells to nod-scid mice made deaf with kanamycin and noise.

We investigated the fate of human cord blood CD133+ hematopoietic stem cells (HSC) transplanted intravenously (IV) into irradiated nod-scid mice previously made deaf by ototoxic treatment with kanamycin and/ or intense noise, to verify whether HSC engraft the cochlea and contribute to inner ear restoration, in vivo. We tested the presence of HLA.DQalpha1 by PCR, used for traceability of engrafted cells, finding evidence that HSC migrated to various host tissues, including the organ of Corti (OC). By histology, antibody and lectin-staining analysis, we confirmed that HSC IV transplantation in mice previously damaged by ototoxic agents correlated with the repair process and stimulation ex novo of morphological recovery in the inner ear, while the cochlea of control oto-injured, nontransplanted mice remained seriously damaged. Dual color FISH analysis also provided evidence of positive engraftment in the inner ear and in various mouse tissues, also revealing small numbers of heterokaryons, probably derived from fusion of donor with endogenous cells, for up to 2 months following transplantation. These observations offer the first evidence that transplanted human HSC migrating to the inner ear of oto-injured mice may provide conditions for the resumption of deafened cochlea, emerging as a potential strategy for inner ear rehabilitation.

Rodlet cells and the sensory systems in zebrafish (Danio rerio).

This preliminary work was designed to study, using routine procedures for light and transmission electron microscopy, the presence of rodlet cells (RCs) in or near the sensory systems of 12 adult specimens (4.0 +/- 1.2 cm, LT +/- SD) of zebrafish, Danio rerio Hamilton, 1822. Rodlet cells, characterized by a distinctive cell cortex (range, 0.4-1.5 microm in thickness) and conspicuous inclusions named "rodlets," have a round to ovoid nucleus with irregular outline. Mature RCs are 11.5 +/- 1.2 microm (mean +/- SD) long and 7.8 +/- 1.1 microm (mean +/- SD) wide. These cells are more numerous near neuromasts enclosed by an epithelial roof and/or ossified canal wall. In contrast, very few RCs were noticed near superficial neuromasts. Based on the presence of RCs around the two cranial neuromasts of each fish, a variable number from 1 to 15 rodlet cells was found (10.4 +/- 3.6, mean +/- SD). The RCs were located 1.5 microm (minimal) to 73.3 microm (maximal) from the neuromast (27.9 +/- 17.2, mean +/- SD). Moreover, RCs were found in olfactory epithelium and in proximity to some taste buds. Interestingly, RCs were absent in the inner ear, eye, and brain.