Neuronal Labeling Patterns in the Spinal Cord of Adult Transgenic Zebrafish Aur  elie Stil, Pierre Drapeau Hospital Research Centre (CRCHUM) and Department of Neurosciences, Universit e de Montr eal, Montr eal, Quebec, Canada H2X 0A9 Received 22 April 2015; revised 13 September 2015; accepted 14 September 2015 ABSTRACT: We describe neuronal patterns in the spinal cord of adult zebrafish. We studied the distribu- tion 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 inter- neurons, ngn1 in sensory neurons and olig2 in oligoden- drocytes, 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 ven- tral 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 popula- tions. Finally, the ngn1:GFP transgene identifies dorsal root ganglion and some cells in dorsal horns. Interest- ingly 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/trau- matic approaches, these studies will help clarify the operation of spinal locomotor circuits of adult zebra- fish. VC 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 642–660, 2016 Keywords: adult zebrafish; spinal cord; locomotor cir- cuits; neuronal patterns; transgenic lines INTRODUCTION Zebrafish embryos are a prevalent non-mammalian vertebrate used in developmental and biomedical research. Although less common, studies in adult zebrafish are now widespread in several exciting fields of research. Because they have the capacity to spontaneously regenerate many organs such as fins, retina, heart, brain and spinal cord, adult zebrafish are used as models to assess regenerative processes in traumatic conditions (Gemberling et al., 2013). In this regard and unlike mammals, zebrafish, as other teleosts, have the impressive capacity to regenerate the spinal cord and recover locomotor activity after an injury (Becker et al., 1997) and therefore consti- tute a model of choice to study the trauma-induced plasticity and re-growth of the spinal tissue (for review, see Vajn et al. 2013). Recent studies have already elucidated some key extrinsic and intrinsic determinants for axonal regeneration and cell replacement such as FGF (Goldshmit et al., 2012b) and Notch (Dias et al., 2012) signaling. Correspondence to: P. Drapeau (p.drapeau@umontreal.ca) Contract grant sponsors: Groupe de Recherche sur le Syste`me Nerveux (GRSNC, FRSQ) (to A.S.), CIHR and NSERC of Canada (to P.D.). Research Centre of the University of Montreal Hospital Centre (Canada). In memory of Laurent Vinay, whose inspiration shines all over... Ó 2015 Wiley Periodicals, Inc. Published online 26 September 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/dneu.22350 642