Tinnitus update: what can be done for the ringing?

Physicians will frequently encounter patients who report tinnitus. Tinnitus is a symptom whereby there is the perception of sound or sounds in the ear or head in the absence of an external source of sound. Most individuals experiencing tinnitus will have a neutral reaction to the percept, but in a small proportion of patients, tinnitus can be a debilitating symptom. When it causes burden, patients can be affected in multiple different facets of life, including impairment in sleep, hearing cognition and psychological and psychiatric well-being, often resulting in high healthcare utilisation and societal costs. Hence, chronic, disabling tinnitus is a complex condition with multifactorial causes and multiple perpetuating biopsychosocial factors. Despite efforts to increase knowledge about its pathophysiology and research into treatments, little impact on real-world clinical practice has been seen. There are no proven effective pharmacological treatments or complementary medicines specifically for chronic, disabling tinnitus. Despite this, there is a role for treating this condition through a multidisciplinary approach specifically targeting comorbid active psychiatric conditions, using hearing aids in appropriate clinical settings such as in those with a coassociated confirmed hearing loss, and specialised cognitive behavioural therapy for patients reporting bothersome tinnitus. Cognitive behavioural therapy remains the most valuable evidence-based intervention in this regard. This narrative review attempts to summarise the current understanding in terms of pathophysiology, assessment and treatment of tinnitus for the internal physician who may encounter patients with disabling, chronic tinnitus.

Plasma Gelsolin Inhibits Natural Killer Cell Function and Confers Chemoresistance in Epithelial Ovarian Cancer.

Plasma gelsolin (pGSN) overexpression in ovarian cancer (OVCA) disarms immune function, contributing to chemoresistance. The aim of this study was to investigate the immunoregulatory effects of pGSN expression on natural killer (NK) cell function in OVCA. OVCA tissues from primary surgeries underwent immunofluorescent staining of pGSN and the activated NK cell marker natural cytotoxicity triggering receptor 1 to analyze the prognostic impact of pGSN expression and activated NK cell infiltration. The immunoregulatory effects of pGSN on NK cells were assessed using apoptosis assay, cytokine secretion, immune checkpoint-receptor expression, and phosphorylation of STAT3. In OVCA tissue analyses, activated NK cell infiltration provided survival advantages to patients. However, high pGSN expression attenuated the survival benefits of activated NK cell infiltration. In the in vitro experiment, pGSN in OVCA cells induced NK cell death through cell-to-cell contact. pGSN increased T-cell immunoglobulin and mucin-domain-containing-3 expression (TIM-3) on activated NK cells. Further, it decreased interferon-γ production in activated TIM-3+ NK cells, attenuating their anti-tumor effects. Thus, increased pGSN expression suppresses the anti-tumor functions of NK cells. The study provides insights into why immunotherapy is rarely effective in patients with OVCA and suggests novel treatment strategies.

Consumption of Soya Isoflavones Improved Polycystic Ovary Syndrome (PCOS)-Associated Metabolic Disorders in a Rat Model.

Polycystic ovary syndrome (PCOS) is associated with increased risks for certain metabolic disorders such as insulin resistance, non-alcoholic fatty liver disease (NAFLD), and suppressed ovarian follicular development. This study aimed to examine whether soya isoflavones (ISF) mitigate these PCOS-associated metabolic disorders in a rat model. Weanling Sprague-Dawley female rats were randomly divided into 6 groups and were treated with either 0 or 83 µg/day dihydrotestosterone (DHT) to induce PCOS and fed diets containing 0, 0.5, or 1g ISF/kg diet for 8 weeks. DHT treatment increased food intake, body weight gain (BWG, p<0.001), percentage of primordial follicles (60% vs 50.9%, p<0.05), and accumulation of lipid droplets in the livers. It also elevated serum total cholesterol (TC), free cholesterol (FC), triglycerides, non-esterified fatty acids (NEFA), and leptin, and hepatic TC and NEFA. Additionally, DHT treatment reduced the percentage of primary follicles (13.8% vs 30.2%, p<0.05), ovary weight, and length (p<0.001), as well as insulin sensitivity (p<0.01) compared to the Control. ISF intake at 1g/kg reduced BWG, serum TC, FC, NEFA, leptin, and hepatic triglycerides and DHT-induced insulin resistance (p<0.01). ISF intake at both levels decreased DHT-induced lipid droplet accumulation in the livers, and changes in the percentages of primordial and primary follicles. Dietary soya ISF alleviated DHT-induced BWG, insulin resistance, and hepatic lipid droplet accumulation, as well as suppressed ovarian follicular development. This suggests that consumption of soya foods or ISF supplements may be beneficial for the individuals with PCOS, mitigating the associated metabolic disorders such as diabetes and NAFLD.

Sudden unilateral audiovestibular loss due to acute labyrinthine haemorrhage can be missed on early MRI brain sequences: case report.

Background: Labyrinthine haemorrhage is a rare vascular disorder often presenting with the triad of acute vertigo, sudden sensorineural hearing loss and tinnitus. There are minimal reports on imaging progression over the acute period. Index case: A woman in her mid-40s presented with acute vertigo, sudden left-sided hearing loss and tinnitus, consistent with acute unilateral audiovestibular loss. Left peripheral vestibular hypofunction was confirmed acutely on video head impulse testing, and pure tone audiometry showed a profound left sensorineural hearing loss. An MRI brain including diffusion-weighted imaging within 24 hours was normal. Delayed MRI brain and internal acoustic canal after 7 days demonstrated increased 3D fluid-attenuated inversion recovery and T1 signal throughout the left cochlea and semicircular canals, without contrast enhancement. This was consistent with labyrinthine haemorrhage. She received early oral prednisone followed by three doses of intratympanic dexamethasone. At 12 months follow-up the patient remained profoundly deaf, however, balance and vestibular symptoms improved with early vestibular physical rehabilitation. Conclusion: We report a case of acute labyrinthine haemorrhage missed on an early MRI brain sequence. This diagnosis should be considered in presentations of acute audiovestibular loss, and delayed MRI including internal auditory canal sequences may be important for diagnosis.

The regulation of plasma gelsolin by DNA methylation in ovarian cancer chemo-resistance.

BACKGROUND: Ovarian cancer (OVCA) is the most lethal gynecologic cancer and chemoresistance remains a major hurdle to successful therapy and survival of OVCA patients. Plasma gelsolin (pGSN) is highly expressed in chemoresistant OVCA compared with their chemosensitive counterparts, although the mechanism underlying the differential expression is not known. Also, its overexpression significantly correlates with shortened survival of OVCA patients. In this study, we investigated the methylation role of Ten eleven translocation isoform-1 (TET1) in the regulation of differential pGSN expression and chemosensitivity in OVCA cells. METHODS: Chemosensitive and resistant OVCA cell lines of different histological subtypes were used in this study to measure pGSN and TET1 mRNA abundance (qPCR) as well as protein contents (Western blotting). To investigate the role of DNA methylation specifically in pGSN regulation and pGSN-induced chemoresistance, DNMTs and TETs were pharmacologically inhibited in sensitive and resistant OVCA cells using specific inhibitors. DNA methylation was quantified using EpiTYPER MassARRAY system. Gain-and-loss-of-function assays were used to investigate the relationship between TET1 and pGSN in OVCA chemoresponsiveness. RESULTS: We observed differential protein and mRNA expressions of pGSN and TET1 between sensitive and resistant OVCA cells and cisplatin reduced their expression in sensitive but not in resistant cells. We observed hypomethylation at pGSN promoter upstream region in resistant cells compared to sensitive cells. Pharmacological inhibition of DNMTs increased pGSN protein levels in sensitive OVCA cells and decreased their responsiveness to cisplatin, however we did not observe any difference in methylation level at pGSN promoter region. TETs inhibition resulted in hypermethylation at multiple CpG sites and decreased pGSN protein level in resistant OVCA cells which was also associated with enhanced response to cisplatin, findings that suggested the methylation role of TETs in the regulation of pGSN expression in OVCA cells. Further, we found that TET1 is inversely related to pGSN but positively related to chemoresponsiveness of OVCA cells. CONCLUSION: Our findings broaden our knowledge about the epigenetic regulation of pGSN in OVCA chemoresistance and reveal a novel potential target to re-sensitize resistant OVCA cells. This may provide a future therapeutic strategy to improve the overall OVCA patient survival.

A perspective on psychedelic teratogenicity: the utility of zebrafish models.

Psychedelic drugs have experienced an unprecedented surge in recreational use within the past few years. Among recreational users, the risks of psychedelic use by pregnant and breastfeeding women are severely understudied and there is little information on the potential teratogenic effects of these drugs. We provide an overview of the previous data on psychedelic teratogenicity from rodent studies and human surveys, discuss their limitations, and propose the utility of the zebrafish as a potential effective model for investigating psychedelic teratogenicity. Recent years have validated the use of zebrafish in the study of fetal exposure and developmental biology; we highlight these properties of the zebrafish for its suitability in psychedelic toxicity research.

The zebrafish for preclinical psilocybin research.

In this review, we discuss the possible utility of zebrafish in research on psilocybin, a psychedelic drug whose recreational use as well as possible clinical application are gaining increasing interest. First, we review behavioral tests with zebrafish, focussing on anxiety and social behavior, which have particular relevance in the context of psilocybin research. Next, we briefly consider methods of genetic manipulations with which psilocybin's phenotypical effects and underlying mechanisms may be investigated in zebrafish. We briefly review the known mechanisms of psilocybin, and also discuss what we know about its safety and toxicity profile. Last, we discuss examples of how psilocybin may be employed for testing treatment efficacy in preclinical research for affective disorders in zebrafish. We conclude that zebrafish has a promising future in preclinical research on psychedelic drugs.

Neuropeptide Y directly reduced apoptosis of granulosa cells, and the expression of NPY and its receptors in PCOS subjects.

BACKGROUND: Most women with anovulatory infertility show polycystic ovarian syndrome (PCOS), and androgen excess is known as a key factor involved in pathogenicity of PCOS. However, the mechanism of follicular developmental arrest in PCOS is not completely understood. The reproductive function of Neuropeptide Y (NPY) in the ovary during folliculogenesis was previously reported; NPY function in apoptosis and proliferation of granulosa cells (GCs) is follicular-stage dependent. The objective of this study was to investigate the role of NPY in ovarian follicular development and the pathogenesis of PCOS. METHODS: To simulate the PCOS phenotype using a rat model, 21-day old Sprague Dawley rats were implanted with dihydrotestosterone (DHT) capsule (83 µg/day) and euthanized after 28 days. mRNA and protein content of NPY and its receptors were assessed in GCs from DHT treated rats using RT-qPCR and Western blot, respectively. Proliferation and apoptosis of GCs was assessed using Ki67- and TUNEL assays. Finally, NPY levels were measured in human follicular fluid (FF) from matched PCOS and non-PCOS patients using ELISA. RESULTS: GCs from DHT treated rats (PCOS-GCs) contained significantly less NPY protein and Npy mRNA by 0.16- and 0.56-fold, respectively, and more NPY receptor type 2 and 5 protein by 2.21- and 3.17-fold, respectively, when compared to sham control. Addition of recombinant NPY to PCOS-GCs culture did not alter Ki67-positive but significantly decreased TUNEL-positive cells by 0.65-fold, but not to baseline levels. There was no significant difference in NPY levels in FF between PCOS and non-PCOS subjects. CONCLUSIONS: These results indicate that DHT modulates expression of NPY and its receptors, NPY decreases DHT-induced GCs apoptosis. That alterations in NPY's function might be involved in follicular developmental failure of PCOS.

The ram cichlid (Mikrogeophagus ramirezi) learns an associative task: a new fish species for memory research.

Fish are the most species rich and evolutionarily oldest vertebrate taxon. This represents opportunities for biologists who intend to employ laboratory animals in their comparative or translational research. Yet, the overwhelming majority of such studies use a single fish species, the zebrafish, a suboptimal strategy from the comparative standpoint. Neuronal plasticity (learning and memory) is perhaps one of the most complex biological phenomena from a mechanistic standpoint, and thus its analysis could benefit from the use of evolutionarily ancient and simple vertebrate model organisms, i.e., fish species. However, learning & memory research with the zebrafish has been replete with problems. Here, we employ a novel fish species, the ram cichlid, we argue will be particularly appropriate for this purpose for practical as well as ethological/ecological reasons. First, we investigate whether the ram cichlid exhibits innate preference for certain colours (red, blue, yellow or green) in a four-choice task, the plus maze. Subsequently, we pair the apparently least preferred colour (green, the conditioned stimulus or CS) with food reward (the unconditioned stimulus, US) in the plus maze, a CS-US associative learning task. After eight pairing trials, we run a probe trial during which only the CS is presented. At this trial, we find significant preference to the CS, i.e., acquisition of memory of CS-US association. We argue that our proof-of-concept study demonstrating fast acquisition of CS-US association in the ram cichlid, coupled with the universal utility of some genome editing methods, will facilitate the mechanistic analysis of learning and memory.

Obesity and PCOS radically alters the snRNA composition of follicular fluid extracellular vesicles.

Introduction: The ovarian follicle consists of the oocyte, somatic cells, and follicular fluid (FF). Proper signalling between these compartments is required for optimal folliculogenesis. The association between polycystic ovarian syndrome (PCOS) and extracellular vesicular small non-coding RNAs (snRNAs) signatures in follicular fluid (FF) and how this relates to adiposity is unknown. The purpose of this study was to determine whether FF extracellular vesicle (FFEV)-derived snRNAs are differentially expressed (DE) between PCOS and non-PCOS subjects; and if these differences are vesicle-specific and/or adiposity-dependent. Methods: FF and granulosa cells (GC) were collected from 35 patients matched by demographic and stimulation parameters. FFEVs were isolated and snRNA libraries were constructed, sequenced, and analyzed. Results: miRNAs were the most abundant biotype present, with specific enrichment in exosomes (EX), whereas in GCs long non-coding RNAs were the most abundant biotype. In obese PCOS vs. lean PCOS, pathway analysis revealed target genes involved in cell survival and apoptosis, leukocyte differentiation and migration, JAK/STAT, and MAPK signalling. In obese PCOS FFEVs were selectively enriched (FFEVs vs. GCs) for miRNAs targeting p53 signalling, cell survival and apoptosis, FOXO, Hippo, TNF, and MAPK signalling. Discussion: We provide comprehensive profiling of snRNAs in FFEVs and GCs of PCOS and non-PCOS patients, highlighting the effect of adiposity on these findings. We hypothesize that the selective packaging and release of miRNAs specifically targeting anti-apoptotic genes into the FF may be an attempt by the follicle to reduce the apoptotic pressure of the GCs and stave off premature apoptosis of the follicle observed in PCOS.

Modelling accessibility of adult neurology care in Australia, 2020-2034.

Introduction: In 2015/2016, annual national expenditure on neurological conditions exceeded $A3 billion. However, a comprehensive study of the Australian neurological workforce and supply/demand dynamics has not previously been undertaken. Methods: Current neurological workforce was defined using neurologist survey and other sources. Workforce supply modelling used ordinary differential equations to simulate neurologist influx and attrition. Demand for neurology care was estimated by reference to literature regarding incidence and prevalence of selected conditions. Differences in supply versus demand for neurological workforce were calculated. Potential interventions to increase workforce were simulated and effects on supply versus demand estimated. Results: Modelling of the workforce from 2020 to 2034 predicted an increase in neurologist number from 620 to 89. We estimated a 2034 capacity of 638 024 Initial and 1 269 112 Review encounters annually, and deficits against demand estimated as 197 137 and 881 755, respectively. These deficits were proportionately greater in regional Australia, which has 31% of Australia's population (Australian Bureau of Statistics) but is served by only 4.1% of its neurologists as determined by our 2020 survey of Australia and New Zealand Association of Neurologists members. Nationally, simulated additions to the neurology workforce had some effect on the review encounter supply deficit (37.4%), but in Regional Australia, this impact was only 17.2%. Interpretation: Modelling of the neurologist workforce in Australia for 2020-2034 demonstrates a significant shortfall of supply relative to current and projected demand. Interventions to increase neurologist workforce may attenuate this shortfall but will not eliminate it. Thus, additional interventions are needed, including improved efficiency and additional use of support staff.

The Application of an Extracellular Vesicle-Based Biosensor in Early Diagnosis and Prediction of Chemoresponsiveness in Ovarian Cancer.

BACKGROUND: Ovarian cancer (OVCA) is the most fatal gynecological cancer with late diagnosis and plasma gelsolin (pGSN)-mediated chemoresistance representing the main obstacles to treatment success. Since there is no reliable approach to diagnosing patients at an early stage as well as predicting chemoresponsiveness, there is an urgent need to develop a diagnostic platform for such purposes. Small extracellular vesicles (sEVs) are attractive biomarkers given their potential accuracy for targeting tumor sites. METHODS: We have developed a novel biosensor which utilizes cysteine-functionalized gold nanoparticles that simultaneously bind to cisplatin (CDDP) and plasma/cell-derived EVs, affording us the advantage of predicting OVCA chemoresponsiveness, and early diagnosis using surface-enhanced Raman spectroscopy. RESULTS: We found that pGSN regulates cortactin (CTTN) content resulting in the formation of nuclear- and cytoplasmic-dense granules facilitating the secretion of sEVs carrying CDDP; a strategy used by resistant cells to survive CDDP action. The clinical utility of the biosensor was tested and subsequently revealed that the sEV/CA125 ratio outperformed CA125 and sEV individually in predicting early stage, chemoresistance, residual disease, tumor recurrence, and patient survival. CONCLUSION: These findings highlight pGSN as a potential therapeutic target and provide a potential diagnostic platform to detect OVCA earlier and predict chemoresistance; an intervention that will positively impact patient-survival outcomes.

Granulosa cell-derived miR-379-5p regulates macrophage polarization in polycystic ovarian syndrome.

Polycystic ovarian syndrome (PCOS) is associated with hyperandrogenemia and ovarian antral follicle growth arrest. We have previously demonstrated that androgen-induced exosomal release of miR-379-5p (miR379) from preantral follicle granulosa cells increases the proliferation of target cells via phosphoinositide-dependent kinase 1 (PDK1) upregulation. Androgen also increases inflammatory M1 macrophage abundance, but reduces anti-inflammatory M2 polarization in rat antral and preovulatory follicles. However, the role of small extracellular vesicles (sEVs; also known as exosomes) secretion in determining the cellular content and function of miRNAs in exosome-receiving cells is largely unknown. Our objectives were to determine: 1) the regulatory role of granulosa cells (GC)-derived exosomal miR379 on macrophage polarization and ovarian inflammation; 2) whether miR379-induced M1 polarization regulates GC proliferation; and 3) if this regulated process is follicular stage-specific. Compared with non-PCOS subjects, PCOS subjects had a higher M1/M2 ratio, supporting the concept that PCOS is an inflammatory condition. Ovarian overexpression of miR379 increased the number of M1 macrophages and the M1/M2 ratio in preantral follicles specifically. Transfection of macrophages with a miR379 mimic reduced the cellular content of PDK1 and induced M0→M1 polarization; whereas its inhibitor polarized M0→M2. Conditioned media from macrophages transfected with miR379 mimic and follicular fluid from PCOS subjects had higher galectin-3 content, a pro-inflammatory cytokine which specifically suppresses human antral follicle GC proliferation. These results indicate that miR379 inhibits M2 macrophage polarization, a condition which suppresses GC proliferation in a follicle stage-dependent manner, as exhibited in PCOS.

Androgen-induced exosomal miR-379-5p release determines granulosa cell fate: cellular mechanism involved in polycystic ovaries.

Polycystic ovarian syndrome (PCOS) is a complex multi-factorial syndrome associated with androgen excess and anovulatory infertility. In the current study, we investigated the role of dihydrotestosterone-induced exosomal miR-379-5p release in determining the destiny of the developing follicles. Our hypothesis was that androgen regulates granulosa cell miR-379-5p content by facilitating its exosomal release in a follicular-stage dependent manner, a process which determines granulosa cell fate. Compared to human non-PCOS subjects, individuals with PCOS exhibit higher follicular fluid free testosterone levels, lower exosomal miR-379-5p content and granulosa cell proliferation. Androgenized rats exhibited lower granulosa cell miR-379-5p but higher phosphoinositide-dependent kinase-1 (PDK1; a miR-379-5p target) content and proliferation. Androgen reduced granulosa cell miR-379-5p content by increasing its exosomal release in preantral follicles, but not in antral follicles in vitro. Studies with an exosomal release inhibitor confirmed that androgen-induced exosomal miR-379-5p release decreased granulosa cell miR-379-5p content and proliferation. Ovarian overexpression of miR-379-5p suppressed granulosa cell proliferation, and basal and androgen-induced preantral follicle growth in vivo. These findings suggest that increased exosomal miR-379-5p release in granulosa cells is a proliferative response to androgenic stimulation specific for the preantral stage of follicle development and that dysregulation of this response at the antral stage is associated with follicular growth arrest, as observed in human PCOS.

Effects of different handling methods on the behavior of adult zebrafish.

The zebrafish is an important biomedical research organism. In most research, zebrafish are removed from their home tank and subsequently their phenotype is measured. The method of handling the fish, however, may significantly affect a variety of phenotypes. This is particularly problematic for studies of brain function that measure behavioral or neuronal responses. Nevertheless, the potential effects of handling have not been analyzed, and in fact are usually ignored. Here, we explore the effects of two usual and two rarely or never-before employed handling methods on the behavior of adult zebrafish. We exposed each fish to one of four handling methods, a between subject experimental design: (1) net chasing followed by air-suspension, (2) gentle net catching (without chasing) followed by air-suspension, (3) gentle net catching followed by being placed in a beaker (no chasing and very short air-suspension), (4) transportation in home tank and pouring the fish directly into the test tank (no chasing, netting or air-suspension). With these handling methods, the fish were placed in a test tank and their swim path was videorecorded and analyzed. Handling significantly affected swim path parameters, duration and frequency of immobility, absolute turn angle and its temporal variance and velocity, but not the distance to bottom. The behavioral effects confirmed that chasing and netting induce robust behavioral changes, and that pouring the fish from its home to its test tank is least aversive for zebrafish. We recommend using this latter method to reduce experimental error variation and increase reproducibility of results.

Predicting chemoresponsiveness in epithelial ovarian cancer patients using circulating small extracellular vesicle-derived plasma gelsolin.

BACKGROUND: Resistance to chemotherapy continues to be a challenge when treating epithelial ovarian cancer (EOC), contributing to low patient survival rates. While CA125, the conventional EOC biomarker, has been useful in monitoring patients' response to therapy, there are no biomarkers used to predict treatment response prior to chemotherapy. Previous work in vitro showed that plasma gelsolin (pGSN) is highly expressed in chemoresistant EOC cell lines, where it is secreted in small extracellular vesicles (sEVs). Whether sEVs from tumour cells are secreted into the circulation of EOC patients and could be used to predict patient chemoresponsiveness is yet to be determined. This study aims to identify if sEV-pGSN in the circulation could be a predictive biomarker for chemoresistance in EOC. METHODS: Sandwich ELISA was used to measure pGSN concentrations from plasma samples of 96 EOC patients (primarily high grade serous EOC). sEVs were isolated using ExoQuick ULTRA and characterized using western blot, nanoparticle tracking analysis, and electron microscopy after which pGSN was measured from the sEVs. Patients were stratified as platinum sensitive or resistant groups based on first progression free interval (PFI) of 6 or 12 months. RESULTS: Total circulating pGSN was significantly decreased and sEV-pGSN increased in patients with a PFI ≤ 12 months (chemoresistant) compared to those with a PFI > 12 months (chemosensitive). The ratio of total pGSN to sEV-pGSN further differentiated these groups and was a strong predictive marker for chemoresistance (sensitivity: 73.91%, specificity: 72.46%). Predetermined CA125 was not different between chemosensitive and chemoresistant groups and was not predictive of chemoresponsiveness prior to treatment. When CA125 was combined with the ratio of total pGSN/sEV-pGSN, it was a significant predictor of chemoresponsiveness, but the test performance was not as robust as the total pGSN/sEV-pGSN alone. CONCLUSIONS: Total pGSN/sEV-pGSN was the best predictor of chemoresponsiveness prior to treatment, outperforming the individual biomarkers (CA125, total pGSN, and sEV-pGSN). This multianalyte predictor of chemoresponsiveness could help to inform physicians' treatment and follow up plan at the time of EOC diagnosis, thus improving patients' outcomes.

Common Aquarium Plants as an Enrichment Strategy in Zebrafish Facilities.

An increasing number of laboratories utilize zebrafish as this species is now represented in practically every subfield of biology research. Environmental enrichment has been shown to improve welfare and health of a large number of species of animals studied in laboratories, kept in zoos, or used in agriculture. However, most laboratories keep zebrafish in barren tanks. Artificial and live aquatic plants have been used in a variety of contexts for aquarium fish, and they have also been suggested as a potential enrichment strategy for the zebrafish. However, no systematic studies have been conducted to investigate their beneficial effects in zebrafish husbandry and biology research. In this study, we review some of the potential benefits of using live plants, and argue that systematic analyses for proper choice and use of live plants in zebrafish husbandry are sorely needed. We provide a few examples of aquatic plant species out of the large variety produced for the aquarium hobby that could be adopted to the zebrafish laboratory setting as environmental enrichment. We speculate that once systematic analyses have been conducted, they will show benefits of this ethologically/ecologically relevant enrichment method, one of which will be healthier and less stressed fish leading to increased reproducibility of results in zebrafish research.

The effect of fish density and tank size on the behavior of adult zebrafish: A systematic analysis.

The zebrafish has been employed in several fields of biology due to its translational relevance and its simplicity and ease of maintenance. As a result, zebrafish are kept in thousands of laboratories around the world. Current industry standards favor keeping the largest possible number of fish in the smallest possible volume of water to increase efficiency and reduce costs. However, physiological and psychological stress resulting from such crowding may impact a variety of phenotypes, from brain function and behavior to cardiovascular function and cancer. Nevertheless, surprisingly little is known about what constitutes an optimal housing environment for the zebrafish, e.g., no systematic analyses have been performed to test the role of housing density and tank volume despite recent sporadic reports implying negative effects of the standard practice of crowding. Here, we conduct the first proof of concept analysis examining the potential impact of housing density and tank volume on the behavior of zebrafish. We randomly assigned adult zebrafish to one of three tank sizes (1.5, 10, or 50 L) with one of three housing densities (1, 2, or 4 fish/L), a 3 × 3 between subject experimental design, and maintained the fish in their corresponding condition for 2 weeks. Subsequently, we tested the behavior of the fish singly in a novel open tank for 12 min and quantified several of their swim path parameters using a video-tracking system. We found significant additive and interacting effects of tank size and/or housing density on swim path parameters including immobility, swim speed, turn angle, and distance to bottom and to stimulus. Although we had only three fish densities and three tank sizes and we did not explore the effects of more extreme conditions and although the interpretation of the above behavioral effects is speculative at this point, the results already demonstrate that both tank size and housing density exerts significant effects on the zebrafish and thus should be considered in zebrafish husbandry.