Endocrine hormone of the central and peripheral nervous systems that binds and activates the G protein-coupled receptors GALR1 (galr1a and galr1b) and GALR2 (galr2a and galr2b). This small neuropeptide may regulate diverse physiologic functions including contraction of smooth muscle of the gastrointestinal and genitourinary tract, growth hormone and insulin release and adrenal secretion. Strongly expressed in brain and stomach, moderately in the eye, and very weakly in heart, kidney and gills. Not detected in liver. In embryos and larvae, detected mainly in nerve cells in the preoptic-hypothalamic regions and fibers innervating several brain regions (at protein level) (PubMed:22522977, PubMed:27315774). In embryos, detected in the anterior commissure, postoptic commissure, hypothalamus, pituitary gland, ventral hindbrain and the white matter of the ventral spinal cord (at protein level) (PubMed:27315774, PubMed:30903017). In larvae, detected in brain regions including telencephalon, hypothalamus, mesencephalon, medulla oblongata and pituitary at 30 hpf onwards (at protein level) (PubMed:22522977). Both isoforms are maternally expressed and detected throughout embryonic development (PubMed:22522977). Low-level expression detected throughout the developing embryo at 6-24 hours post-fertilization (hpf) with more focused expression detected in specific groups of neurons in the brain at 28 hpf onwards (PubMed:22522977). Belongs to the galanin family.