Abstract
One of the first functionally identified groups of inhibitory neurons in the mammalian central nervous system are Renshaw cells (RCs, Renshaw 1946). RCs are excited by axon collaterals from motor neurons (MNs), and provide recurrent inhibition of MNs (Eccles et al. 1954). It has been shown by studies using cat spinal cord since then that, 1) excitatory synaptic inputs from MNs are mediated by acetylcholine (Curtis and Ryall 1966) and 2) these inputs are the main driving force for RC activity during locomotion (Noga et al 1987). We examined the physiological nature of RCs in detail using visually guided whole cell recording in isolated spinal cord preparations from glutamic acid decarboxylase (GAD) 67-EGFP knock-in mouse neonates. Among the GFP-positive cells in the lumbar ventral horn, RCs were uniquely identified by electrically stimulating the adjacent ventral root to evoke a short latency EPSC and by filling the cell with alexa-dyes to confirm its expression of calbindin-28k after recording. The short latency EPSCs that were reduced to 20-40% of control in amplitude by nicotinic receptor blockers and further reduced by blocking ionotropic glutamate receptors indicating that glutamate is also mediating synaptic inputs to RCs from MNs. During the locomotor-like rhythmic activity evoked by bath-application of 5-HT and NMDA, RCs fired rhythmically and modulated not only by excitatory synaptic inputs but also inhibitory ones. These results show that such technique is a powerful tool to reveal the neuronal mechanisms of motor control. [J Physiol Sci. 2006;56 Suppl:S37]
