Study on Laser-Induced Olfactory Bulbectomy in Zebrafish as a Novel Model for Affective Syndrome

Background

Affective disorders, such as depression, are common mental health issues worldwide. Although rodent models have played a significant role in depression research, their cross-species applicability has limitations. Zebrafish (Danio rerio), as an emerging model in neuroscience research, has gradually become an important tool for studying affective disorders due to its high genetic and physiological homology with humans. Olfactory bulbectomy (OBX) is a classic animal model of depression that induces neurochemical and behavioral deficits by removing the olfactory bulbs, mimicking symptoms of depression. However, the applicability of the OBX model in non-mammalian species remains unclear. This study aims to develop a zebrafish-based OBX model using laser technology for non-invasive olfactory bulb ablation, exploring its potential in affective disorder research.

Source of the Paper

This paper was co-authored by Evgeny V. Nekhoroshev, Maxim A. Kleshchev, Andrey D. Volgin, and others, with the research team from the Scientific Research Institute of Neurosciences and Medicine in Novosibirsk, Russia, Sirius University of Science and Technology, and research institutions in Brazil, Azerbaijan, China, and other countries. The paper was published in 2025 in the European Journal of Neuroscience, titled Laser-induced olfactory bulbectomy in adult zebrafish as a novel putative model for affective syndrome: a research tribute to Brian Leonard.

Research Process and Experimental Design

1. Animals and Housing

The study used 3-5-month-old wild-type zebrafish, with a male-to-female ratio of approximately 1:1. The zebrafish were randomly divided into four groups: sham-operated control (sham), sham-operated + fluoxetine treatment (sham+fl), olfactory bulbectomy (ZOBX), and olfactory bulbectomy + fluoxetine treatment (ZOBX+fl). Each group consisted of 16-18 fish.

2. Laser-Induced Olfactory Bulbectomy (ZOBX)

The study employed a novel non-invasive laser technique, using a 405-nanometer laser diode to precisely ablate the zebrafish olfactory bulbs. During the procedure, zebrafish were anesthetized and immobilized under a microscope, receiving two 4-second laser pulses at 500 milliwatts each. The sham group underwent the same procedure but with a significantly reduced laser intensity (5%) to avoid tissue damage.

3. Behavioral and Pharmacological Testing

On days 7 and 14 post-surgery, the research team conducted behavioral tests, including: - Novel Tank Test: Assessing locomotor activity and anxiety-like behavior in a new environment. - Zebrafish Tail Immobilization Test (ZTI): Evaluating despair-like behavior.

Additionally, the study validated the impact of ZOBX on zebrafish olfactory function through Y-maze testing and alarm substance (AS) testing.

4. Neurohistological Validation

On day 7 post-surgery, the research team sectioned zebrafish brains and used Nissl staining to assess olfactory bulb tissue damage. Fluorescence microscopy and image analysis software were used to quantify neuronal staining areas, verifying the effectiveness of laser ablation.

Key Findings

1. Behavioral Results

• Novel Tank Test: ZOBX zebrafish exhibited significantly reduced locomotor activity and increased anxiety-like behavior, characterized by decreased distance moved and shorter time spent in the top zone. Fluoxetine treatment partially reversed these behavioral deficits.
• Tail Immobilization Test: ZOBX zebrafish displayed despair-like behavior in the tail immobilization test, which was significantly improved by fluoxetine treatment.

2. Olfactory Function Validation

• Y-Maze Test: ZOBX zebrafish showed a significantly weakened response to food odor, with increased latency to enter the food arm and reduced time spent there.
• Alarm Substance Test: ZOBX zebrafish exhibited a significantly reduced response to alarm substance, indicating impaired olfactory function.

3. Neurohistological Results

Nissl staining revealed significant damage to the olfactory bulb tissue in ZOBX zebrafish, with a marked reduction in neuronal staining area, confirming the effectiveness of laser ablation.

Conclusions and Significance

This study is the first to establish a laser-induced olfactory bulbectomy model (ZOBX) in zebrafish and validate its potential for modeling affective disorders. The results demonstrate that ZOBX can induce depression-like and anxiety-like behaviors in zebrafish, which can be partially reversed by fluoxetine treatment. Additionally, the study validated the impairment of olfactory function in ZOBX zebrafish through behavioral and neurohistological analyses. This model not only extends the application of the OBX model to non-mammalian species but also provides a new tool for high-throughput drug screening in affective disorder research.

Highlights of the Study

1. Innovative Method: The first use of laser technology for non-invasive olfactory bulb ablation in zebrafish, offering a new experimental model for affective disorder research.
2. Cross-Species Applicability: Validates the applicability of the OBX model in zebrafish, providing important insights for cross-species affective disorder research.
3. High-Throughput Potential: The low cost and high-throughput nature of the zebrafish model enable rapid screening of antidepressant drugs.

Additional Valuable Information

The study also discussed the limitations of the ZOBX model, such as the lack of research on molecular markers and neurophysiological changes. Future studies could further explore the effects of ZOBX on zebrafish neuroplasticity, immune responses, and cognitive functions to comprehensively evaluate its application value in affective disorder research.

This study provides new perspectives and tools for understanding the mechanisms of affective disorders and developing therapeutic interventions, offering significant scientific and practical value.