Development of an Inhibitory Interneuronal Circuit in the Embryonic Spinal Cord

Abstract

2004; doi:10.1152/jn.01091.2004. 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.

Connexin hemichannels contribute to spontaneous electrical activity in the human fetal cortex

“…1 E, Left Lower), and total surface area (525.3 ± 106.3 mV·s vs. 890.1 ± 172.5 mV·s; P < 0.05; Fig. 1 Spontaneous network activity in developing circuits (37)(38)(39)(40)(41)(42)(43) generally comprises AP-mediated release of neurotransmitters and neuromodulators (44). To determine whether spontaneous electrical activity in human SP neurons at midgestation (17-23 gw) was also driven by AP-mediated release of neurotransmitters, we blocked AP initiation with bath application of tetrodotoxin (TTX; 1 μM).…”

Primary Afferent Synapses on Developing and Adult Renshaw Cells

“…This anatomical organization is not too different to the one reported here, except that, because of the shorter distances of lumbar segments in the neonatal mouse, the axons spread among more segments. Recently, Xu et al (2005) described a progressive focusing of recurrent inhibition such that its intersegmental spread becomes restricted with development in chick embryos. The mechanisms responsible for this restriction are not known.…”

Imaging the spatiotemporal organization of neural activity in the developing spinal cord

“…For example, in the chick embryo, imaging has been used to examine the formation of synaptic connections in the spinal cord (Arai et al, 1999;Xu et al, 2005), the vestibulocochlear nuclei , the vagal pathway (Sato et al, 2004), the auditory system (Momose- and to monitor the repair of spinal cord lesions (Sholomenko and Delaney, 1998). The technique has also been applied to the rat spinal cord to study the organization of developing spinal circuitry both in vitro (Ziskind-Conhaim and Redman, 2005) and in vivo (Sasaki et al, 2002).…”