# Neurotrophin
**Neurotrophins** are a family of secreted growth factors that regulate the survival, development, and function of neurons, acting through a two-receptor system of [Trk receptor](https://www.edgepedia.org/trk-receptor) tyrosine kinases and the p75 neurotrophin receptor (p75^NTR).[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) • [2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf) Mammals have four neurotrophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5).[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) The discovery of NGF by [Rita Levi-Montalcini](https://www.edgepedia.org/rita-levi-montalcini) and Stanley Cohen in the 1950s earned the two the 1986 [Nobel Prize in Physiology or Medicine](https://www.edgepedia.org/nobel-prize-in-physiology-or-medicine).[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11201509/) • [4](https://www.nobelprize.org/prizes/medicine/1986/press-release/1000/)
| Key fact | Detail |
|---|---|
| Family members | Four in mammals: NGF, BDNF, NT-3, and NT-4/5, functioning as homodimers in both neural and non-neural tissues[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) |
| Receptors | Three selective Trk tyrosine kinases (TrkA, TrkB, TrkC) plus p75^NTR, which binds all four neurotrophins[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) • [5](https://www.ncbi.nlm.nih.gov/books/NBK11134/) |
| Ligand specificity | TrkA binds NGF, TrkB binds BDNF and NT-4/5, TrkC binds NT-3[5](https://www.ncbi.nlm.nih.gov/books/NBK11134/) |
| Proneurotrophins | Neurotrophins are synthesized as precursors; proneurotrophins preferentially activate p75^NTR (with sortilin or SorCS2), while only mature neurotrophins activate Trk receptors[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) |
| Discovery | NGF identified in the 1950s by Levi-Montalcini and Cohen at Washington University; Nobel Prize 1986[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11201509/) • [4](https://www.nobelprize.org/prizes/medicine/1986/press-release/1000/) |
| Therapeutic barrier | Neurotrophins are large polar proteins that do not cross the blood-brain barrier; BDNF has a serum half-life of about 10 minutes[6](https://onlinelibrary.wiley.com/doi/10.1155/2014/601084) • [7](https://pmc.ncbi.nlm.nih.gov/articles/PMC3542569/) |
| Clinical record | Roughly 3 dozen clinical reports over 25 years established no neurotrophic factor as a treatment for any human disease until cenegermin, a recombinant human nerve growth factor, was approved for neurotrophic keratitis[8](https://pubmed.ncbi.nlm.nih.gov/27063798/) • [19](https://www.ema.europa.eu/en/medicines/human/EPAR/oxervate) |
## The four mammalian neurotrophins
NGF is the prototypic member, and BDNF, NT-3, and NT-4/5 are structurally and functionally related to it.[9](https://www.ncbi.nlm.nih.gov/books/NBK6480/) Neurotrophins act as homodimers and have functions in both neural and non-neural tissues, controlling adult physiology as well as embryonic development.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) NGF plays a major role in maintaining the cholinergic baso-cortical and baso-hippocampal circuits involved in memory and higher cognition, and is considered critical for the integrity of cholinergic neurons during development and adulthood.[2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf) BDNF controls hippocampal synaptic plasticity, learning, and memory.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/)
**Receptor binding.** The selective actions of the neurotrophins arise from the Trk receptor family: TrkA is primarily a receptor for NGF, TrkB for BDNF and NT-4/5, and TrkC for NT-3.[5](https://www.ncbi.nlm.nih.gov/books/NBK11134/) A neuron's expression of a particular Trk subtype therefore determines which neurotrophins it can respond to.[5](https://www.ncbi.nlm.nih.gov/books/NBK11134/) The second receptor class, p75^NTR, binds all neurotrophin species.[5](https://www.ncbi.nlm.nih.gov/books/NBK11134/) • [10](https://www.ncbi.nlm.nih.gov/books/NBK28185/)
## Discovery history
The discovery of NGF traces to the 1950s and the collaboration between the Italian developmental biologist Rita Levi-Montalcini and the American biochemist Stanley Cohen at [Washington University in St. Louis](https://www.edgepedia.org/washington-university-in-st-louis).[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11201509/) In 1947 Levi-Montalcini went to Washington University to work with the embryologist [Viktor Hamburger](https://www.edgepedia.org/viktor-hamburger), who was studying nerve tissue growth in chick embryos.[11](https://www.mayoclinicproceedings.org/article/S0025619611627390/pdf) Stanley Cohen joined the group as a young postdoc in 1953 and isolated the NGF protein in the late 1950s.[12](https://www.sfn.org/-/media/SfN/Documents/TheHistoryofNeuroscience/Volume-1/c7.pdf) To determine whether the biologically active molecule was a nucleic acid or a protein, the pair used snake venom, a rich source of phosphodiesterase, in their early characterization experiments.[13](https://www.sciencedirect.com/science/article/pii/S0962892404001436) Together they isolated NGF, which enhances the growth of nerve cells, and created antibodies that inhibited NGF's activity.[14](https://www.nichd.nih.gov/newsroom/news/021420-cohen)
In 1986, Levi-Montalcini and Cohen shared the Nobel Prize in Physiology or Medicine for their discoveries of growth factors; Cohen's later work at [Vanderbilt University](https://www.edgepedia.org/vanderbilt-university) produced the independent discovery of epidermal growth factor (EGF).[4](https://www.nobelprize.org/prizes/medicine/1986/press-release/1000/) • [14](https://www.nichd.nih.gov/newsroom/news/021420-cohen) The discovery of BDNF was a direct result of the earlier work on NGF, the first growth factor characterized and shown to be essential for development of the vertebrate nervous system.[15](https://journals.physiology.org/doi/10.1152/physrev.00038.2024)
## Receptor signaling
**Trk signaling.** Neurotrophin binding promotes formation of Trk dimers and trans-phosphorylation of cytoplasmic tyrosine residues, recruiting adapter proteins that activate the ras/ERK1/2, PI3 kinase/Akt, STAT, and phospholipase Cγ pathways.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) A distinctive feature is retrograde signaling through signaling endosomes: endocytosed neurotrophin/Trk complexes are transported along the axon back to the cell body, where they control gene transcription.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) In sympathetic neurons, NGF/TrkA complexes remain intact as endosomes acidify and engage retrograde transport, whereas NT-3 dissociates from TrkA at acidic pH and is recycled locally without producing signaling endosomes.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) TrkA was first identified not as a neuronal receptor but as an oncogene generated by fusion of a tyrosine kinase domain with nonmuscle tropomyosin, causing ligand-independent activation.[15](https://journals.physiology.org/doi/10.1152/physrev.00038.2024)
**p75^NTR signaling.** Historically, p75^NTR was the first neurotrophin receptor identified, reported in 1986 and 1987.[16](https://pmc.ncbi.nlm.nih.gov/articles/PMC3063094/) It is a member of the death domain-containing subgroup of the TNF receptor superfamily, and its signaling often opposes Trk signaling: in sympathetic neurons, TrkA promotes axon growth and survival while p75^NTR promotes axon degeneration and cell death.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) p75^NTR can also act as a coreceptor, pairing with Trk receptors to enhance binding affinity of mature neurotrophins, with NogoR and Lingo-1 to mediate the inhibitory effects of CNS myelin, and with other ligand-binding partners.[16](https://pmc.ncbi.nlm.nih.gov/articles/PMC3063094/) In some contexts p75^NTR mediates neurotrophin-induced cell death; NGF kills cultured mature oligodendrocytes via a p75-mediated mechanism.[9](https://www.ncbi.nlm.nih.gov/books/NBK6480/) • [17](https://pmc.ncbi.nlm.nih.gov/articles/PMC8095803/)
**Proneurotrophins.** Neurotrophins are synthesized as precursors that are cleaved to release a prodomain peptide and the mature neurotrophin, and receptors may be exposed to both forms.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) p75^NTR binds both forms and is activated more effectively by proneurotrophins, an effect dependent on sortilin or SorCS2 binding a conserved motif in the prodomain; only mature neurotrophins activate Trk receptors.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) In sympathetic neurons this produces opposite outcomes from the same ligand family: proNGF, which activates p75^NTR but not TrkA, promotes cell death, while mature NGF, which activates both receptors, promotes survival.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) Mature and pro-forms of BDNF likewise exert opposite effects on adult neurons, with mature BDNF generally neuroprotective and the pro-form promoting a degenerative pattern.[2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf)
## Evolution
The neurotrophin system is ancient: orthologs of neurotrophins, p75^NTR, and Trk receptors are found in invertebrates as diverse as sea urchins, mollusks, and round worms, giving the system roughly half a billion years of evolution.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/) The entire signaling system has, however, been lost in the *Caenorhabditis* and *Drosophila* lineages, which deprives researchers of convenient genetic model organisms for studying it.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/)
## Therapeutic challenges
The growth- and survival-promoting effects of neurotrophins motivated many attempts to use them to prevent neuronal death in neurological disease, but translation has been difficult.[6](https://onlinelibrary.wiley.com/doi/10.1155/2014/601084) Neurotrophins are relatively large, polar molecules that cannot readily cross the blood-brain barrier and must be administered directly into the central nervous system.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC3542569/) They also have short biological half-lives; BDNF's serum half-life is approximately 10 minutes.[6](https://onlinelibrary.wiley.com/doi/10.1155/2014/601084) Over 25 years, about 3 dozen clinical reports have examined neurotrophic factors in neurodegenerative disease, and none has produced efficacy data robust enough to establish them as treatments for any human disease.[8](https://pubmed.ncbi.nlm.nih.gov/27063798/) NGF- and BDNF-based clinical trials for Alzheimer's disease and ALS have failed, probably due to poor brain penetration and insufficient target engagement.[2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf) Intraventricular NGF infusion has been associated with significant side effects, including hyperinnervation of cerebral blood vessels, hypophagia, [Schwann cell](https://www.edgepedia.org/schwann-cell) hyperplasia, and neuropathic pain.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC3542569/)
**Alternative strategies.** Approaches under investigation include small-molecule Trk receptor agonists with longer half-lives and blood-brain barrier permeability, intranasal delivery, nanocarriers, and focused ultrasound to transiently open the barrier.[6](https://onlinelibrary.wiley.com/doi/10.1155/2014/601084) • [2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf) A mutated form of NGF has been proposed as a substitute for the wild-type molecule without its pain-related side effects.[2](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf) [Antidepressant](https://www.edgepedia.org/antidepressant) drugs act as allosteric potentiators of BDNF signaling through binding to TrkB, and agonist TrkB antibodies are being developed for neurodegenerative disorders.[18](https://www.sciencedirect.com/science/article/pii/S0968000424000379)
## References
1. [Mark Bothwell (2016). Recent advances in understanding neurotrophin signaling. F1000Research.](https://pmc.ncbi.nlm.nih.gov/articles/PMC4965695/)
2. [Triaca, Imbimbo, and Nisticò (2022). Editorial: Neurotrophins Biodelivery to CNS. Frontiers in Neuroscience.](https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2022.916563/pdf)
3. [The History of Nerve Growth Factor: From Molecule to Drug. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC11201509/)
4. [The Nobel Prize in Physiology or Medicine 1986, Press Release. NobelPrize.org.](https://www.nobelprize.org/prizes/medicine/1986/press-release/1000/)
5. [Neurotrophin Receptors. Neuroscience, NCBI Bookshelf.](https://www.ncbi.nlm.nih.gov/books/NBK11134/)
6. [Cai et al. (2014). Potential Therapeutic Effects of Neurotrophins for Acute and Chronic Neurological Diseases. BioMed Research International.](https://onlinelibrary.wiley.com/doi/10.1155/2014/601084)
7. [Current advances in using neurotrophic factors to treat neurodegenerative disorders. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC3542569/)
8. [Bartus and Johnson (2016). Clinical tests of neurotrophic factors for human neurodegenerative diseases, part 1. PubMed.](https://pubmed.ncbi.nlm.nih.gov/27063798/)
9. [Neurotrophins. Madame Curie Bioscience Database, NCBI Bookshelf.](https://www.ncbi.nlm.nih.gov/books/NBK6480/)
10. [Classes of Growth Factors Acting in the Nervous System. Basic Neurochemistry, NCBI Bookshelf.](https://www.ncbi.nlm.nih.gov/books/NBK28185/)
11. [Rita Levi-Montalcini: Nobel Prize for Work in Neurology. Mayo Clinic Proceedings.](https://www.mayoclinicproceedings.org/article/S0025619611627390/pdf)
12. [The History of Neuroscience in Autobiography, Volume 1 (Society for Neuroscience).](https://www.sfn.org/-/media/SfN/Documents/TheHistoryofNeuroscience/Volume-1/c7.pdf)
13. [Rita Levi-Montalcini: the discovery of nerve growth factor and modern neurobiology. ScienceDirect.](https://www.sciencedirect.com/science/article/pii/S0962892404001436)
14. [Stanley Cohen, Nobel Winner and Longtime NICHD Grantee, Dies. NICHD.](https://www.nichd.nih.gov/newsroom/news/021420-cohen)
15. [The physiopathology of brain-derived neurotrophic factor. Physiological Reviews.](https://journals.physiology.org/doi/10.1152/physrev.00038.2024)
16. [Understanding Proneurotrophin Actions: Recent Advances and Challenges. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC3063094/)
17. [Pathophysiological Mechanisms for Actions of the Neurotrophins. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC8095803/)
18. [TrkB transmembrane domain: bridging structural understanding with therapeutic strategy. Trends in Biochemical Sciences.](https://www.sciencedirect.com/science/article/pii/S0968000424000379)
19. [Oxervate, European Medicines Agency (EMA)](https://www.ema.europa.eu/en/medicines/human/EPAR/oxervate)
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*Topic: Encyclopedia › Life and health › Human health and medicine › Human structure and function › Nervous and sensory systems › Neuroscience as a discipline › Subfields and history of neuroscience › Molecular and developmental neuroscience*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license