Abstract
Spinal motoneurones (Mns) constitute the final output for the execution of motor tasks. In addition to innervating muscles, Mns project excitatory collateral connections to Renshaw cells (RCs) and other Mns, but the latter have received little attention. We show that Mns receive strong synaptic input from other Mns throughout development and into maturity, with fast-type Mns systematically receiving greater recurrent excitation than slow-type Mns. Optical recordings show that activation of Mns in one spinal segment can propagate to adjacent segments even in the presence of intact recurrent inhibition. While it is known that transmission at the neuromuscular junction is purely cholinergic and RCs are excited through both acetylcholine and glutamate receptors, here we show that neurotransmission between Mns is purely glutamatergic, indicating that synaptic transmission systems are differentiated at different postsynaptic targets of Mns.
Highlights
MethodsAll experiments were carried out in accordance with the Animal (Scientific Procedures) Act (Home Office, UK, 1986) and were approved by the UCL Ethical Committee, under project licence number 70/7621
Motoneurones (Mns) are the ultimate neural targets of effector commands issued from the central nervous system
We show here that Mns themselves form an interconnected network and that activity in one segment of the spinal cord can propagate reciprocally to neighbouring segments, constituting a positive feedback loop that can amplify the strength of motor output
Summary
All experiments were carried out in accordance with the Animal (Scientific Procedures) Act (Home Office, UK, 1986) and were approved by the UCL Ethical Committee, under project licence number 70/7621. Intramuscular injections were performed under inhaled isofluorane anaesthesia and by a surgical procedure supervised and approved by the Veterinary Surgeon named by the Home Office, UK. Animals were administered terminal anaesthesia via intraperitoneal injection of a mixture of ketamine and xylazine (80 mg/Kg and 10 mg/Kg, respectively)
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