BDNF Expression in Larval and Adult Zebrafish Brain: Distribution and Cell Identification

Abstract

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, has emerged as an active mediator in many essential functions in the central nervous system of mammals. BDNF plays significant roles in neurogenesis, neuronal maturation and/or synaptic plasticity and is involved in cognitive functions such as learning and memory. Despite the vast literature present in mammals, studies devoted to BDNF in the brain of other animal models are scarse. Zebrafish is a teleost fish widely known for developmental genetic studies and is emerging as model for translational neuroscience research. In addition, its brain shows many sites of adult neurogenesis allowing higher regenerative properties after traumatic injuries. To add further knowledge on neurotrophic factors in vertebrate brain models, we decided to determine the distribution of bdnf mRNAs in the larval and adult zebrafish brain and to characterize the phenotype of cells expressing bdnf mRNAs by means of double staining studies. Our results showed that bdnf mRNAs were widely expressed in the brain of 7 days old larvae and throughout the whole brain of mature female and male zebrafish. In adults, bdnf mRNAs were mainly observed in the dorsal telencephalon, preoptic area, dorsal thalamus, posterior tuberculum, hypothalamus, synencephalon, optic tectum and medulla oblongata. By combining immunohistochemistry with in situ hybridization, we showed that bdnf mRNAs were never expressed by radial glial cells or proliferating cells. By contrast, bdnf transcripts were expressed in cells with neuronal phenotype in all brain regions investigated. Our results provide the first demonstration that the brain of zebrafish expresses bdnf mRNAs in neurons and open new fields of research on the role of the BDNF factor in brain mechanisms in normal and brain repairs situations.

Neuroanatomical distribution and functions of brain‐derived neurotrophic factor in zebrafish (Danio rerio) brain

“…Nevertheless, BDNF mRNAs were still detected in the pallium, OT, pharyngeal epithelium, and rhombencephalon. In‐situ hybridization studies in 7‐day‐old zebrafish larvae have confirmed the presence of BDNF mRNA in a variety of brain regions including the olfactory rosettes, anterior telencephalon (tel), OT, and midbrain tegmentum (Cacialli et al, ). Interestingly, double staining studies suggest that in each of these regions, the BDNF‐expressing cells are postmitotic in nature and do not express the radial glial marker aromatase B.…”

“…In the adult zebrafish brain, BDNF mRNA‐expressing cells are present in the olfactory bulb (glomerular cell layer), pallium (medial, lateral and posterior parts), subpallium (posterior zone and entopeduncular nucleus), diencephalon (parvocellular and magnocellular nuclei of preoptic area and the entopeduncular and suprachiasmatic nuclei), habenula, ventrolateral, and ventromedial nuclei of the ventral thalamus, dorsal thalamus (anterior, dorsal, posterior and central posterior nuclei), posterior tuberal nucleus, preglomerular nuclei, hypothalamus, synencephalon (nucleus of the medial longitudinal fascicle, dorsal and ventral periventricular pretectal nuclei), mesencephalon (torus longitudinalis), OT (periventricular gray zone), tegmentum (central nucleus of the torus semicircularis and the interpeduncular nucleus), medulla oblongata (secondary gustatory nucleus and the vagal lobe), and superior and inferior reticular formation (Cacialli et al, ) (Figure e). The BDNF protein has also been detected in the purkinje cells of the cerebellum (Gatta et al, ).…”

“…Similarly, BDNF mRNAs were also never expressed in aromatase B and BLBP (radial glial markers)‐positive cells. However, the MAP2 and acetylated tubulin (neuronal markers)‐positive cells showed co‐expression of BDNF mRNAs (Cacialli et al, ). This suggests that neurons may serve as the major source of BDNF in the adult zebrafish brain.…”

Morpho‐Functional Features of the Gonads of Danio rerio: the Role of Brain‐Derived Neurotrophic Factor

“…In teleost fishes, BDNF and its specific receptor TrkB have been largely documented in CNS and PNS during development as well as adulthood (Vissio et al, ; Dalton et al, ; Germanà et al, ; D'Angelo et al, ; Sánchez‐Ramos et al, ; D'Angelo et al, ; De Felice et al, ; Gatta et al, ; Cacialli et al, ; Gatta et al, ; Montalbano et al, ). p75 is primarily expressed in neuronal cells during zebrafish development (Han et al, ).…”

Cellular and molecular attributes of neural stem cell niches in adult zebrafish brain

“…However, the potential role of BDNF in adult neurogenesis remains uncharted. In zebrafish, a recent report suggests that BDNF is abundantly expressed in several regions of the forebrain (Cacialli et al, ). Interestingly, BDNF was observed to be expressed by neurons and not by radial glia or progenitor cells in adult zebrafish brain (Cacialli et al, ).…”