title: Development of an inhibitory interneuronal circuit in the embryonic spinal cord.
abstract: Locally projecting inhibitory interneurons play a crucial role in the patterning and timing of network activity. However, because of their relative inaccessibility, little is known about their development or incorporation into circuits. In this study, we characterized the functional onset, neurotransmitters, rostrocaudal spread, and funicular distribution of one such spinal interneuronal circuit during development. The R-interneuron is the avian homologue of the mammalian Renshaw cell. Both cell types receive input from motoneuron recurrent collaterals and make direct connections back onto motoneurons. By stimulating motoneurons projecting in a given ventral root and recording the response in adjacent ventral roots, we demonstrate that the R-interneuron circuit becomes functional between embryonic day 6 (E6) and E7. This ventral root response is observed at E11 and at E14 until it can no longer be detected at E16. Using bath-applied neurotransmitter receptor antagonists, we were able to demonstrate that the circuit is predominately nicotinic and GABAergic from E7.5 to E15. We also found a glutamatergic component to the pathway throughout this developmental period. The R-interneuron projects three or more segments both rostrally and caudally through the ventrolateral funiculus. The distribution of this circuit may become more locally focused between E7.5 and E15.
authors.affiliation: Department of Physiology, Emory University, School of Medicine, Atlanta, GA 30340, USA.
authors.forename: Huaying
authors.initials: H
authors.lastname: Xu
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Whelan
authors.forename: Peter
authors.initials: P
authors.lastname: Wenner
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002642:Chick Embryo; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004622:Embryo, Mammalian; D004625:Embryo, Nonmammalian; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007395:Interneurons / Q000145:classification / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008464:Mecamylamine / Q000494:pharmacology; D009415:Nerve Net / Q000166:cytology / Q000196:embryology*; D009433:Neural Inhibition / Q000502:physiology*; D016571:Neural Networks, Computer; D018733:Nicotinic Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology* / Q000196:embryology; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000196:embryology / Q000502:physiology; D013331:Strychnine / Q000494:pharmacology
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018684:Glycine Agents; D018733:Nicotinic Antagonists; D008464:Mecamylamine; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D013331:Strychnine; D001640:Bicuculline