NGF is necessary for the survival of effector neurons in a certain period of embryonic development. In vitro experiments have proved that nerve cells can neither grow axons nor survive if NGF is not added to the medium. NGF and its receptors are also widely distributed in the central nervous system. NGF produced in hippocampus and cerebral cortex can be retrograde transported to forebrain basal nucleus through cholinergic nerves, maintaining the survival and function of cholinergic neurons. In the early stage of embryonic development, the content of central nerve growth factor determines the density of cholinergic nerves. The content of NGF in cerebellum and hypothalamus without cholinergic innervation is also high, which indicates that NGF has nutritional effect on other types of neurons except cholinergic nerves.