Neurotrophin
Neurotrophins ( Gr. Νεῦρον neũron 'nerve' and τροφος trophos 'food', for example “nerve nutrients”) are endogenous signal substances that cause targeted connections between nerve cells . They ensure the continued existence of neural connections. Neurotrophins are small basic proteins with a molecular mass of about 13 kDa .
Classification
There are five types of neurotrophins:
- NGF - nerve growth factor
- BDNF - brain-derived neurotrophic factor
- NT-3 - neurotrophin 3
- NT-4 - neurotrophin 4
- NT-5 - Neurotrophin 5, as NT-4 and NT-5 have similar properties, they are often grouped together as NT-4/5
These can bind to membrane receptors . There are two types of receptors for neurotrophins:
- p75 neurotrophin receptor (p75NTR), a receptor of the TNF receptor family
- Receptors of the tyrosine kinase receptor family (Trk A, Trk B and Trk C)
The p75NTR is able to bind all five neurotrophins, but the affinity is comparatively low. The receptors of the Trk family, on the other hand, have more affinity and specifically only bind certain neurotrophins:
- Trk A - NGF
- Trk B - BDNF, NT-4 and NT-5
- Trk C - NT-3
The binding of neurotrophins to p75NTR leads to programmed cell death (see apoptosis ) of the cell. Binding to receptors of the Trk family, on the other hand, triggers a cascade of kinases that have an anti-apoptotic effect. The central enzyme in this mechanism is protein kinase B , also known as "AKT", especially in the Anglo-American language area . Because of this ambivalent behavior, neurotrophins are no longer viewed as neurostimulators, but as neuromodulators .
history
The term neurotrophin was introduced with the neurotrophin hypothesis by Viktor Hamburger and Rita Levi-Montalcini . It assumes that immature neurons compete for limited trophic factors presented by target cells. Only those neurons that successfully make synaptic connections get enough of these trophic factors to survive.
Neurons that are not receiving enough trophic factors are removed by apoptosis .
If neurotrophins are present, they bind to cell surface receptors of the Trk family. A cascade of kinases is then triggered, the target proteins of which lead to the suppression of apoptosis .
psychology
Neurotrophins contribute to memory formation and play a major role in building and breaking down new nerve networks.
Experts in neurotrophin research at the Ruhr University in Bochum suspect that neurotrophin levels change when you fall in love . Scientists from the Italian University of Pavia found elevated neurotrophin levels in test subjects who were newly in love and suspect that this is responsible for the typical euphoria at the beginning of a romance. After a year, no more elevated values were found.
Individual evidence
- ↑ Being in love lasts only one year. ( Memento of the original from December 4, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Psychologie Heute, December 5, 2005.
literature
- J. Yuan, BA Yankner: Apoptosis in the nervous system . In: Nature . No. 407, 2000, pp. 802-809; doi : 10.1038 / 35037739 .