NGF is produced by every peripheral tissue/organ that is innervated by sensory afferents and/or sympathetic efferents, as well as by central and peripheral nervous system and immune cells . The largest amount of the neurotrophin is produced in mice submaxillary glands, as revealed by immunofluorescence staining depicted in panel A, that are the source for murine NGF used in several clinical trials. When intravenously injected in rats (B), NGF levels quickly increases in the bloodstream, reaching a peak within 30 min and remaining above baseline levels up until 72 h. Peripheral NGF injection induces peculiar effects on immune circulating cells, such as the overexpression of its receptor TrkA on circulating lymphocytes (C) or degranulation of peritoneal mast cells (D). Radiolabelled, intra-cerebroventricular injected NGF is captured by TrkA-expressing neurons, such as cholinergic neurons in the basal forebrain complex (E).