ABSTRACT
Positioned strategically at the interface between respiratory water and arterial blood flows, the secretory neuroepithelial cells NECs present in the gill filaments of fishes and exhibit morphofunctional features of O2 chemoreceptors present in the lungs of air-breathing vertebrates.
Our anatomical and physiological knowledge about the indolamine secretory properties, hypoxia sensitivity and complex innervations of the fish gill NECs are reviewed in a comprehensive description of the fish gill nervous system. Acting as receptosecretory paraneurons, the fish gill NECs are probably involved in local and central control of branchial functions through the paracrine production of serotonin and their synaptic relationships with the sympathetic and intrinsic branchial nervous systems. In response to hypoxia, NECs could locally adapt the respiratory surface through direct serotonin-mediated effects on the branchial vasculature. Vasomotor responses to hypoxia may also be mediated by a central reflex triggered by the NECs through their afferent synapses to the CNS which in turn would act on the filament vasculature via branchial autonomic motor innervation and intrinsic neurons.
