Neuron growth factor, commonly referred to as nerve growth factor or NGF, is a type of protein naturally produced in living organisms that is important to the nervous systems of vertebrates. It is essential for the survival and development of nerve cells in the sensory and sympathetic parts of the nervous system. NGF is part of a larger category of molecules called neurotrophins that also includes the proteins brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4, all of which are involved in development or maintenance of the nervous system. The plural term nerve growth factors is sometimes used to refer to all types of neurotrophin.
Sensory neurons detect sensory stimuli from the environment, such as light, vibrations, pressure, and so on and translate them into nervous signals. These are then transmitted through nerves to the central nervous system, where they are interpreted by the brain and translated into the familiar mental experiences of images, sounds, and other sensations. The sympathetic nervous system extends into most of the organs of the body and is involved in the regulation of many of the involuntary functions that keep the body functioning, including heart rate, respiration, and digestion. During times of stress or danger, it is also essential to the physiological changes that occur to produce the fight-or-flight response. The role of neuron growth factor in maintaining these systems makes it essential to human life.
Molecules of neuron growth factor bind to proteins called receptors on the cell membranes of sympathetic and sensory neurons. It is known to bind with two types of receptors, commonly called low-affinity nerve growth factor receptors (LNGFR) and high-affinity nerve growth factor receptors (TrkA). The neuron growth factor molecules cause the nerve cell's axon, a structure that transmits electrical nerve impulses through the cell, to grow and branch. It also prevents programmed cell death, or apoptosis, from occurring in the cells.
Neuron growth factor is the subject of research for the role it plays in many health problems and its possible medical uses. It has shown the ability to promote regeneration of peripheral nerves in animal tests and may also be able to repair the damage to the insulating material of nerve axons, called myelin, that causes the symptoms of demyelinating diseases such as multiple sclerosis. Diminished levels of NGF are also associated with mental disorders such as anorexia nervosa and schizophrenia, as well as some cardiovascular and metabolic disorders.
The biochemistry of emotions also involves neuron growth factor. People who fall in love have dramatically increased NGF levels for approximately the first year of the romantic relationship, compared to people who are single or in long-standing relationships. Research in this area is still in its early stages, and the psychological effects of NGF are not yet fully understood.