Review Excitatory components of the mammalian locomotor CPG Ole Kiehn ⁎ , Katharina A. Quinlan, Carlos Ernesto Restrepo, Line Lundfald, Lotta Borgius, Adolfo E. Talpalar, Toshiaki Endo Mammalian Locomotor Laboratory, Department of Neuroscience, Karolinska Institutet, Retzius väg 8, 171 77 Stockholm, Sweden ARTICLE INFO ABSTRACT Article history: Accepted 1 July 2007 Available online 7 November 2007 Locomotion in mammals is to a large degree controlled directly by intrinsic spinal networks, called central pattern generators (CPGs). The overall function of these networks is governed by interaction between inhibitory and excitatory neurons. In the present review, we will discuss recent findings addressing the role of excitatory synaptic transmission for network function including the role of specific excitatory neuronal populations in coordinating muscle activity and in generating rhythmic activity. © 2007 Elsevier B.V. All rights reserved. Keywords: Spinal cord Commissural interneuron Locomotion Motor neuron Transcription factor Contents 1. Introduction .......................................................... 57 2. Excitatory synaptic transmission is involved in many CPG functions ........................... 57 2.1. Rhythmic activation of motor neurons ........................................ 57 2.2. Rhythmic activation of interneurons ......................................... 57 2.3. Rhythm-generation .................................................. 58 3. Candidate excitatory CPG interneurons ........................................... 58 3.1. Excitatory commissural interneurons ........................................ 58 3.1.1. Intersegmental networks ........................................... 58 3.1.2. Intrasegmental networks ........................................... 59 3.1.3. Genetic determination of the intrasegmental CIN pathway ........................ 59 3.2. Ipsilaterally projecting excitatory interneurons ................................... 60 BRAIN RESEARCH REVIEWS 57 (2008) 56 – 63 ⁎ Corresponding author. E-mail address: O.Kiehn@ki.se (O. Kiehn). Abbreviations: 5-HT, 5-hydroxytryptamine; AP-5, D(-)-2-Amino-5-phosphonopentanoic acid; AMPA, alpha-amino-3-hydroxy-5-methyl- 4-isoxazolepropionic acid; Chx10, ceh-10 homeo domain containing homolog; CIN, commissural interneuron; CNQX, 6-Cyano-7- nitroquinoxaline-2,3-dione; CPG, central pattern generator; Dbx, developing brain homeobox; DTA, diphtheria toxin A subunit; En1, engrailed 1; EphA4, Ephrin receptor A4; EphrinB3, Ephrin ligand B3; Evx-1/2, even skipped homeotic gene 1/2 homolog; Gata 2/3, Gata binding protein 2/3; HB9, homeobox gene HB9; IN, interneuron; MN, motor neuron; NMDA, N-methyl-D-aspartic acid; RC, Renshaw cell; Sim1, single-minded homolog 1; VGLUT2, vesicular glutamate transporter 2 0165-0173/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.brainresrev.2007.07.002 available at www.sciencedirect.com www.elsevier.com/locate/brainresrev