Branchial innervation

Abstract

Inspection of the dorsal end of fish gills reveals an impressive set of nerve trunks, connecting the gills to the brain. These trunks are branches of cranial nerves VII (the facial) and especially IX (the glossopharyngeal) and X (the vagus). The nerve trunks carry a variety of nervous pathways to and from the gills. A substantial fraction of the nerves running in the branchial trunks carry afferent (sensory) information from receptors within the gills. There are also efferent (motor) pathways, which control muscles within the gills, blood flow patterns and possibly secretory functions. Undertaking a more careful survey of the gills, it becomes evident that the arrangement of the microanatomy (particularly the blood vessels) and its innervation are strikingly complex. The complexity not only reflects the many functions of the gills but also illustrates that the control of blood flow patterns in the gills is of crucial importance in modifying the efficiency of its chief functions: gas transfer and salt balance. The "respiratory-osmoregulatory compromise" is maintained by minimizing the blood/water exchange (functional surface area of the gills) to a level where excessive water loss (marine teleosts) or gain (freshwater teleosts) is kept low while ensuring sufficient gas exchange. This review describes the arrangement and mechanisms of known nervous pathways, both afferent and efferent, of fish (notably teleosts) gills. Emphasis is placed primarily on the autonomic nervous system and mechanisms of blood flow control, together with an outline of the afferent (sensory) pathways of the gill arches.

Characterisation of putative oxygen chemoreceptors in bowfin (Amia calva)

“…In other species, intrinsic bipolar neurons innervate the eFA sphincter, thus they are likely to be involved in regulating blood flow through the gill (Jonz and Nurse, 2003). Gill blood flow is modulated during hypoxia by the contraction of the eFA sphincter, which causes an increase in branchial blood pressure, which in turn causes an increase in lamellar recruitment increasing the functional surface area for gas exchange (reviewed by Sundin and Nilsson, 2002). ) and (C) cell length (μm) in Type I cells in various locations in the gill filament of bowfin exposed to normoxia or to sustained hypoxia with or without access to air.…”

“…Serotonin caused a dilation of the CVS in Atlantic cod (Gadus morhua) (Sundin, 1995), increasing blood flow to the mitochondrion-rich cells. It has also been suggested that dilation of the CVS could divert plasma from the arterio-arterial pathway increasing the haematocrit in the lamellae and improving oxygen uptake (Sundin and Nilsson, 2002), but no anastomoses between these two circulations have been found in bowfin (Olson, 1981). It is also possible that these cells contained synaptic vesicles not labelled by the SV2 antibody.…”

Serotonergic and cholinergic elements of the hypoxic ventilatory response in developing zebrafish

“…Gill NECs are characterized by having cytoplasmic synaptic vesicles containing neurotransmitters and are believed to release their contents across a chemical synapse onto afferent nerve terminals (Dunel-Erb et al, 1982;Jonz and Nurse, 2003;Perry et al, 2009). Chemoreceptor responses are then carried from the gills to the central nervous system by afferent fibres of the glossopharyngeal and vagus nerves (Milsom and Brill, 1986;Burleson and Milsom, 1993;Sundin and Nilsson, 2002).…”

Acetylcholine-Containing Neuroepithelial Cells in Fish Gill Support the Cholinergic Hypothesis of O2 Chemoreception

“…The carotid body and first gill arch are innervated by the glossopharyngeal (cranial nerve IX) nerve (Sundin and Nilsson, 2002;Gonzalez et al, 1994). The branchial neuroepithelial cells of fish gills are the phylogenetic precursors to glomus (O 2 -sensing cells of the mammalian carotid body.…”