Central projections and connections of lumbar primary afferent fibers in adult rats: effectively revealed using Texas red-dextran amine tracing

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Date: Oct. 2017
From: Neural Regeneration Research(Vol. 12, Issue 10)
Publisher: Medknow Publications and Media Pvt. Ltd.
Document Type: Report
Length: 4,555 words
Lexile Measure: 1520L

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Byline: Shi-de. Lin, Tao. Tang, Ting-bao. Zhao, Shao-jun. Liu

Signals from lumbar primary afferent fibers are important for modulating locomotion of the hind-limbs. However, silver impregnation techniques, autoradiography, wheat germ agglutinin-horseradish peroxidase and cholera toxin B subunit-horseradish peroxidase cannot image the central projections and connections of the dorsal root in detail. Thus, we injected 3-kDa Texas red-dextran amine into the proximal trunks of L[sub]4 dorsal roots in adult rats. Confocal microscopy results revealed that numerous labeled arborizations and varicosities extended to the dorsal horn from T12-S4, to Clarke's column from T[sub]10-L2, and to the ventral horn from L[sub]1-5. The labeled varicosities at the L[sub]4 cord level were very dense, particularly in laminae I-III, and the density decreased gradually in more rostral and caudal segments. In addition, they were predominately distributed in laminae I-IV, moderately in laminae V-VII and sparsely in laminae VIII-X. Furthermore, direct contacts of lumbar afferent fibers with propriospinal neurons were widespread in gray matter. In conclusion, the projection and connection patterns of L[sub]4 afferents were illustrated in detail by Texas red-dextran amine-dorsal root tracing.

Introduction

Spinal cord injury can be disastrous, often leading to lifelong disability and seriously impacting patients' physical and mental health, and the outcomes of current treatments are still poor (Schonherr et al., 2000; Dunn et al., 2009; Mulcahey et al., 2010; Byrnes et al., 2012; Tian et al., 2014). For more than 16 years, we have been attempting to repair spinal cord transection by intercostal nerve-lumber dorsal root anastomosis, obtaining a number of promising outcomes (unpublished). The vertebrate central pattern generators (CPGs) located in the spinal cord form the neuroanatomical basis of our novel treatment strategy for spinal cord injury. CPGs are comprised of afferent nerves, interneuron units and efferent nerves. The interactions between the elements of CPGs cause neural oscillations and rhythmic impulses, and the interplay among CPGs harmonically generates different modes of locomotion, such as swimming, walking and running (McCrea and Rybak, 2008; Rybak et al., 2015). Although there have been significant advances in CPG research, the precise neural mechanisms underlying coordinative locomotion remain unclear. Signals from lumbar primary afferents are important for locomotion modulation of the hind-limbs (Menard et al., 2002; Sirois et al., 2013), and their projection scopes and synaptic connections with the propriospinal neurons in the spinal cord may be beneficial for elucidating the mechanisms of CPGs. However, quantitative analysis of varicosities from the dorsal root in the spinal cord has not previously been reported. In the current study, we applied 3-kDa Texas red-dextran amine (TRDA) for fine labeling of nerve fibers and varicosities (Fritzsch, 1993), and obtained images of the whole central projections and connections of lumbar afferent fibers by directly injecting TRDA into the proximal trunks of the L[sub]4 dorsal root.

Materials and Methods

Animals

A total of 20 adult female specific-pathogen-free Sprague-Dawley rats (weighing 260-300 g, aged 7-8 weeks), supplied by the Laboratory Animal Center of the Academy of Military Medical Sciences (SCXK-(Army)-2012-004), were housed in temperature- and humidity-controlled rooms (25 [+ or -] 1[degrees]C;...

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Gale Document Number: GALE|A514278600