The sphincter of the efferent filament artery in teleost gills: II. Sympathetic innervation

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Abstract
In addition to the cholinergic innervation described in the sphincter of the efferent filament arteries (Bailly and Dunel‐Erb, ′86), an aminergic component has been demonstrated by specific techniques. The Falck fluorescence technique reveals a network of nerve fibers displaying a green fluorescence characteristic of catecholamines. At the ultrastructural level two types of fibers are present, one with clear vesicles and another with densecored vesicles. Axo‐axonal synaptic relationships exist between the two types. Results of 5‐ and 6‐OHDA (hydroxydopamine) treatments confirm the presence of an aminergic component.These observations support the notion of a dual innervation: cholinergic and adrenergic of, respectively, parasympathetic and sympathetic origin. The presence of presynaptic modulation is suggested. The aminergic component could inhibit or reduce the release of acetylcholine from cholinergic nerve endings. These results suggest that the sympathetic innervation modulates the vasoconstriction effect of the parasympathetic component.