Distribution of acetylcholine and catecholamines in fish gills and their potential roles in the hypoxic ventilatory response.

Carotid body glomus cells in mammals contain a plethora of different neurochemicals. Several hypotheses exist to explain their roles in oxygen-chemosensing. In the present study we assessed the distribution of serotonin, acetylcholine and catecholamines in the gills of trout (Oncorhynchus mykiss) and goldfish (Carassius auratus) using immunohistochemistry, and an activity-dependent dye, Texas Red hydrazide (TXR).

A comparative analysis of putative oxygen-sensing cells in the fish gill.

We investigated the distribution of serotonin (5-HT)-containing neuroepithelial cells (NECs), the putative O(2) sensing cells, in the gills of four species of fish: trout (Oncorhynchus mykiss), goldfish (Carassius auratus), trairão (Hoplias lacerdae) and traira (Hoplias malabaricus) using immunohistochemical markers for 5-HT, synaptic vesicles and neural innervation. We found that all fish had a cluster of innervated, serotonergic NECs at the filament tips, but there were species-specific distributions of serotonin-containing NECs within the primary gill filaments. Trout gill filaments had a greater number of serotonin-containing NECs than both trairão and traira, whereas goldfish primary filaments had none.