Characterization of Individual Projections Reveal That Neuromasts of the Zebrafish Lateral Line are Innervated by Multiple Inhibitory Efferent Cells

Abstract

The zebrafish lateral line is a sensory system used to detect changes in water flow. It is comprized of clusters of superficial hair cells called neuromasts. Modulation occurs via excitatory and inhibitory efferent neurons located in the brain. Using mosaic transgenic labeling we provide an anatomical overview of the lateral line projections made by individual inhibitory efferent neurons in 5-day old zebrafish larvae. For each hemisphere we estimate there to be six inhibitory efferent neurons located in two different nuclei. Three distinct cell types were classified based on their projections; to the anterior lateral line around the head, to the posterior lateral line along the body, or to both. Our analyses corroborate previous studies employing back-fills, but our transgenic labeling allowed a more thorough characterization of their morphology. We found that individual inhibitory efferent cells connect to multiple neuromasts and that a single neuromast is connected by multiple inhibitory efferent cells. The efferent axons project to the sensory ganglia and follow the sensory axon tract along the lateral line. Time-lapse imaging revealed that inhibitory efferent axons do not migrate with the primordium as the primary sensory afferent does, but follow with an 8–14 h lag. These data bring new insights into the formation of a sensory circuit and support the hypothesis that different classes of inhibitory efferent cells have different functions. Our findings provide a foundation for future studies focussed toward unraveling how and when sensory perception is modulated by different efferent cells.

Petrosamine isolated from marine sponge Petrosia sp. demonstrates protection against neurotoxicity in vitro and in vivo

“…The lateral line is a sensory system used by aquatic animals to detect water flow. This morphological structure is modulated by sensory organs and neuromasts [ 37 ]. Neuromasts are innervated by sensory neurons, situated in two ganglia, that leads to the anterior lateral line projected in the head and posterior lateral line along the body.…”

“…Neuromasts are innervated by sensory neurons, situated in two ganglia, that leads to the anterior lateral line projected in the head and posterior lateral line along the body. Thus, neuromasts are clusters of superficial hair cells, allowing fish to sense mechanical changes in water, playing a crucial role in behaviours such as rheotaxis, predator avoidance and schooling [ 37 ]. The localization of apoptotic cells detected coincides with that of neuromasts, according to the observed pattern of green spots.…”

Physiological responses of mechanosensory systems in the head of larval zebrafish (Danio rerio)

“…We then were interested in how tactile and flow stimuli in the zebrafish head are encoded, especially by the anterior lateral line, and how it might be different from stimuli encoding by the posterior lateral line system. There is evidence, for example, that the anterior lateral line is targeted in a specific way by efferent innervations ( Manuel et al, 2021 ). The anterior lateral line also appears to differ from the posterior lateral line regarding the distribution of synapses of its projections in the hindbrain ( Valera et al, 2021 ) and may play a distinct role in behavior ( Groneberg et al, 2015 ).…”

Neuromasts and Olfactory Organs of Zebrafish Larvae Represent Possible Sites of SARS-CoV-2 Pseudovirus Host Cell Entry

“…8A ). Both anterior and posterior neuromasts project neurons to and receive neurons from anterior and posterior lateral line ganglia, respectively, which in turn connect to specific cellular domains in the rhombencephalon ( 41 , 45 , 87 ). Thus, both lateral line systems present possible direct routes for viral entry from the aquatic environment into the central nervous system (CNS) via the neuromast hair cells.…”

“…Here, we used the zebrafish (both embryos and larvae) as an in vivo model to explore SARS-CoV-2 pseudovirus entry into the cells that form the peripheral anterior organs, specifically the anterior neuromasts ( 41 , 42 ), and olfactory organs ( 43 , 44 ). These peripheral sense organs present a direct host cell entry site and thus a possible pathway for SARS-CoV-2 to enter sensory neurons that project from the anterior neuromasts to the anterior lateral line ganglion ( 45 ) and from the olfactory epithelia to the olfactory bulbs ( 46 , 47 ), thus providing a possible direct route to the brain and spinal cord ( 48 – 51 ). In humans, elevated levels of ACE2 expression in the olfactory neuroepithelium have been reported ( 52 ), and the nasal tract has been reported as a common site of exposure and entry of SARS-CoV-2 ( 53 ).…”