AUTHOR=D'Acunzo Pasquale , Badaloni Aurora , Ferro Mattia , Zimarino Vincenzo , Ripamonti Maddalena , Malgaroli Antonio , Consalez G. Giacomo TITLE=A conditional transgenic reporter of presynaptic terminals reveals novel features of the mouse corticospinal tract JOURNAL=Frontiers in Neuroanatomy VOLUME=7 YEAR=2014 URL=https://www.frontiersin.org/journals/neuroanatomy/articles/10.3389/fnana.2013.00050 DOI=10.3389/fnana.2013.00050 ISSN=1662-5129 ABSTRACT=

In many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), synaptic alterations precede the demise of the neuronal cell, making synapses a useful vantage point from which to monitor the onset and progression of clinical signs and pathological changes. While murine models of ALS display many features in common with the clinical picture observed in patients, corticospinal tract (CST) involvement is usually less severe in mice than the picture observed in humans. In this paper we describe the characterization of a new conditional transgenic line obtained by targeted integration of a GFP-VAMP2 fusion gene into the Rosa26 locus, and devised to permit the detection of genetically defined presynaptic terminals in wild type mice and murine models of neural disorders. This reporter molecule is selectively enriched in presynaptic boutons, significantly reducing the background signal produced by fibers of passage. The specific features of this reporter line allow us to strongly support the view that murine CST terminals give rise to very few direct contacts with spinal motor neurons. Moreover, the evidence described here reveals the existence of previously uncharacterized, putative direct connections between CST presynaptic boutons and Renshaw neurons in the spinal cord. These results constitute a proof of concept for the potential application of this indicator line to morphological analyses of wild type and diseased synapses.