Reorganization of Locomotor Activity during Development in the Prenatal Rat^a

Abstract

Development of neuronal circuits generating locomotor activity was studied using an isolated lumbar spinal cord preparation from fetal and neonatal rats. Bath application of N-methyl-D-aspartate (NMDA) or 5-HT evoked patterned motor activity resembling that seen during normal fictive locomotion on embryonic day (E) 20.5. Glycine-mediated inhibition was essential to the formation of this coordinated motor activity. In preparations from fetuses at the earlier stages (E14.5-E16.5), we observed spontaneous motoneuronal activity and chemically induced rhythmic bursts, which were synchronized on the two sides in the corresponding ventral roots. The spontaneous activity was not blocked by kynurenate, the glutamate receptor blocker, although it was completely abolished by strychnine, the glycine receptor antagonist. A brief application of glycine evoked excitatory responses resembling the spontaneous bursts in both time course and amplitude. It is concluded that glycine functions transiently as excitatory transmitters at these stages. These results suggest that functional change in glycine-induced responses during development plays an important role in differentiation of the neuronal circuits generating locomotion.

Ion Channel Development, Spontaneous Activity, and Activity-Dependent Development in Nerve and Muscle Cells

“…Activity up to stage E17.5 was blocked by strychnine (437,498) and bicuculline (498), indicating that the classic inhibitory transmitters lead to spontaneous activity at early stages. In addition, because of the change in the Cl Ϫ reversal potential during the same range of developmental stages, GABAergic blockers initially caused an early abolition of activity, while the same blockers used at later stages caused an augmentation of activity (311,498). Ren and Greer (498) also showed that nicotinic receptor blockade led to cessation of spontaneous activity at E13.5-E17.5.…”

Ontogeny of Modulatory Inputs to Motor Networks: Early Established Projection and Progressive Neurotransmitter Acquisition

“…These CPGs are present very early in development (Sillar et al, 1997;Fenelon et al, 1998b;Kudo and Nishimaru, 1998;Branchereau et al, 2001) and also express multiple outputs in response to distinct modulatory environments (Sillar et al, 1998;Branchereau et al, 2001). The basic organization of CPGs for locomotion is highly conserved from lamprey to larval Xenopus to neonatal rats (Sillar et al, 1997).…”

Serotoninergic Modulation of Chloride Homeostasis during Maturation of the Locomotor Network in Zebrafish

“…Many regions of the developing CNS, including the brain (O'Donovan, 1999;Ben-Ari, 2001;Zhang and Poo, 2001) and the spinal cord (Kudo and Nishimaru, 1998;Nakayama et al, 1999;Branchereau et al, 2000;Hanson and Landmesser, 2003;Ren and Greer, 2003;Yvert et al, 2004), exhibit a characteristic recurrence of spontaneous neural network activity. During that period, GABA and glycine can exert excitatory effects (Cherubini et al, 1991;Ben-Ari, 2001;Payne et al, 2003;Rivera et al, 2005), and this excitation has been implicated as a fundamental developmental process (Zhang and Poo, 2001;Payne et al, 2003;Rivera et al, 2005).…”