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Early development of functional spatial maps in the zebrafish olfactory bulb
Jun Li1, Julia A Mack, Marcel Souren
1Department of Biomedical Optics, Max-Planck-Institute for Medical Research, 69120 Heidelberg, Germany.
Summary
Zebrafish olfactory bulb maps form early, with amino acids activating the lateral region and bile acids the medial region. This spatial organization persists as the brain develops.
Area of Science:
- Neuroscience
- Developmental Biology
- Olfactory System Research
Background:
- The adult olfactory bulb (OB) exhibits a chemotopic map where odorant chemical classes activate specific glomerular regions.
- In zebrafish, distinct odorants like amino acids and bile acids activate specific OB regions (lateral and medial, respectively).
Purpose of the Study:
- To investigate the developmental trajectory of spatial olfactory response maps in zebrafish.
- To determine when and how the functional organization of the olfactory bulb emerges during early development.
Main Methods:
- Utilized a transgenic zebrafish line expressing Ca2+ indicator protein inverse pericam in mitral cells.
- Employed two-photon Ca2+ imaging to reconstruct high-resolution, three-dimensional activity patterns in the olfactory bulb.
- Monitored odor responses at various developmental stages, from 2.5 to 6 days postfertilization (dpf).
Main Results:
- Odor responses were first detected in the zebrafish OB at 2.5-3 dpf.
- Early in development (2.5-3 dpf), amino acids and bile acids evoked distinct spatial activity patterns in the lateral and medial OB, respectively.
- This coarse spatial organization of olfactory activity maps was maintained between 2.5 and 6 dpf, despite an increase in responsive units and ongoing glomerular refinement.
Conclusions:
- A fundamental spatial organization of olfactory functional maps is established very early in zebrafish OB development, preceding full glomerular differentiation.
- This early-established spatial map persists throughout development, suggesting a foundational role in olfactory processing, glomerular differentiation, and later map refinement.