Answer: "Trophic support" refers to a variety of chemical signals that neurons need to continue living.
Neurons are energetically expensive cells. They use a lot of oxygen, and require a large expenditure of energy in the form of ATP to do their normal functions. As part of homeostatic adjustment, the body prefers to minimize extra energy usage. However, since neurons are critically important for healthy functioning, they receive signals in the form of chemicals that tell them to continue working. These chemicals are called trophic factors.
Many of these trophic factors are synthesized and released by glial cells of the nervous system, the non-neuronal cells that interact closely with the neurons. Glial cells, particularly the astrocytes and Schwann cells, are well known producers of trophic support molecules.
One of the best characterized trophic support molecules is called brain derived neurotrophic factor, or BDNF. BDNF is a large protein. BDNF is normally synthesized and produced by cells of the nervous system, and is important for making changes in neurons or for growth of the nerve cells. BDNF signals through the activity of several different receptors, the most well-known being the TrkB receptor.
Other neurotrophic factors used by the nervous system that are important as trophic support molecules include nerve growth factor (NGF), neurotrophin-3, glial-derived neurotrophic factor (GDNF), and the ephrins.