Involved in oxygen transport in the brain (By similarity). Hexacoordinate globin, displaying competitive binding of oxygen or the distal His residue to the iron atom. Capable of penetrating cell membranes. Monomer. Located in the soma (perikaryon) of most nerve cells in brain. Has ability to penetrate cell membranes and translocate into cells. Detected in brain, eye and gill, but not in muscle and blood (at protein level). Particularly high expression in the periventral zone of tectum opticum, with significant expression detected in white matter, preglomerular nucleus, posterior tubular nucleus, torus longitudinalis, hypothalamus, pituitary gland, posterior tuberculum, hypothalamus, synencephalon and formatio reticularis. Detected also in brain regions of the visual system, predominantly in parts of tectum opticum and torus semicircularis, area dorsalis telencephali and medulla oblongata. Strong expression observed in sensory epithelium of peripheral olfactory organ, and outer and inner nuclear layers and ganglion cell layer of retina. Expressed at low levels during the early stages of development, with levels increasing strongly around hatching period at 72 hours post-fertilization. Expression levels remain high in the adult stage. By hypoxia. Expression is significantly up-regulated by severe hypoxia in brain but not in eye. Belongs to the globin family.