Neuronal labeling patterns in the spinal cord of adult transgenic Zebrafish

Abstract

We describe neuronal patterns in the spinal cord of adult zebrafish. We studied the distribution of cells and processes in the three spinal regions reported in the literature: the 8th vertebra used as a transection injury site, the 15th vertebra mainly used for motor cell recordings and also for crush injury, and the 24th vertebra used to record motor nerve activity. We used well-known transgenic lines in which expression of green fluorescent protein (GFP) is driven by promoters to hb9 and isl1 in motoneurons, alx/chx10 and evx1 interneurons, ngn1 in sensory neurons and olig2 in oligodendrocytes, as well as antibodies for neurons (HuC/D, NF and SV2) and glia (GFAP). In isl1:GFP fish, GFP-positive processes are retained in the upper part of ventral horns and two subsets of cell bodies are observed. The pattern of the transgene in hb9:GFP adults is more diffuse and fibers are present broadly through the adult spinal cord. In alx/chx10 and evx1 lines we respectively observed two and three different GFP-positive populations. Finally, the ngn1:GFP transgene identifies dorsal root ganglion and some cells in dorsal horns. Interestingly some GFP positive fibers in ngn1:GFP fish are located around Mauthner axons and their density seems to be related to a rostrocaudal gradient. Many other cell types have been described in embryos and need to be studied in adults. Our findings provide a reference for further studies on spinal cytoarchitecture. Combined with physiological, histological and pathological/traumatic approaches, these studies will help clarify the operation of spinal locomotor circuits of adult zebrafish.

Zebrafish spinal cord repair is accompanied by transient tissue stiffening

“…However, the absolute values of zebrafish spinal cord tissue stiffness were almost an order of magnitude lower as compared to their rodent counterparts [24, 38]. The distribution of individual regions of interest furthermore mirrored the symmetry of the spinal cytoarchitecture of adult zebrafish as described in [37]. Each tissue region contains a specific set of cell bodies, processes and filaments that vary in structural arrangement and/or density and consequently amount to distinct tissue architectures.…”

“…Each tissue section was divided into nine regions of interest (ROIs) based on the fluorescence pattern (Fig.1b) of the transgenic fish line Tg(mbp:GFP, alpha1-tubulin:mls-dsRed). The ROIs corresponded furthermore to distinct structural features of the spinal cytoarchitecture as described in [37]. ROI 1 comprises the dorsal horn (dh, Fig.1b), ROI 2 contains the dorsal longitudinal fasciculi (dlf, Fig.1b), ROI 3 and 4 comprise the ventral horns (vh, Fig.1b) and ROI 5 contains the ventral (vlf, Fig.1b) and medial longitudinal fasciculi (mlf, Fig.1b).…”

“…Each tissue region contains a specific set of cell bodies, processes and filaments that vary in structural arrangement and/or density and consequently amount to distinct tissue architectures. Gray matter regions consist of densely packed processes, synapses, neurofilaments and neuronal cell bodies, whereas white matter regions contain ascending and descending myelinated axon tracts that run in parallel to the anterior-posterior axis of the spinal cord and are crosslinked by oligodendrocytes [37]. The dorsal horn exhibited the highest elasticity values in uninjured specimen and displayed a tissue architecture that was dominated by the presence of densely packed cell bodies.…”

“…The increased apparent Young’s moduli of tissue sections located at the 28 th vertebra might arise from a more densely packed spinal cord tissue due to the caudally decreasing diameter of the spinal cord and/or altered structural properties of individual tissue components. For instance, sensory fibers and processes of radial glia, both of which display progressively increasing densities toward the caudal part of the spinal cord [37], might serve to explain the increase of tissue elasticity in ROIs 5. Apart from that, it is currently not known if and how the spinal composition changes in the most caudal spinal cord parts.…”

Large scale analysis of the diversity and complexity of the adult spinal cord neurotransmitter typology

“…The zebrafish is an important model organism for high-throughput studies on neuronal circuits' functions and behavior, and much is known about the different cell types in the zebrafish spinal cord (Ampatzis et al, 2013;Bernhardt et al, 1990Bernhardt et al, , 1992Björnfors and El Manira, 2016;Bradley et al, 2010;Böhm et al, 2016;Djenoune et al, 2017;Hale et al, 2001;Higashijima et al, 2004a;2004b;Kimura et al, 2008;Liao and Fetcho, 2008;McLean et al, 2007;Menelaou et al, 2014;Satou et al, 2012;Stil and Drapeau, 2016). However, the number and identity of the spinal excitatory and inhibitory neurons that process sensory-related information are unknown, as are the neurotransmitter identities of the neurons that control and gate motor commands.…”