Neuroepithelial cells of the gill and their role in oxygen sensing.

A highly sensitive oxygen (O(2)) sensing mechanism is critical for the survival of all vertebrate species. In fish, this requirement is fullfilled by the neuroepithelial cells (NECs) of the gill. NECs are neurotransmitter-containing chemosensory cells that are diffusely distributed within a thin epithelial layer of the filaments and respiratory lamellae of all gill arches, and are innervated by afferent fibers from the central nervous system. In acute cell culture, NECs respond immediately, and in a dose-dependent manner, to acute changes in O(2) tension. Thus, hypoxic stimulation of gill NECs appears to initiate the production of adaptive, cardiorespiratory reflexes that contribute to the maintenance of O(2) uptake in order to meet metabolic demands. This review covers the current evidence for the status of NECs as the primary peripheral O(2) sensors in fish. We have included an overview of the phylogeny of O(2) sensing structures among vertebrate groups, and morphological and physiological evidence for the importance of NECs in O(2) sensing.