Abstract
Renshaw recurrent inhibition (RI) plays an important gated role in spinal motion circuit. Peripheral nerve injury is a common disease in clinic. Our current research was designed to investigate the change of the recurrent inhibitory function in the spinal cord after the peripheral nerve crush injury in neonatal rat. Sciatic nerve crush was performed on 5-day-old rat puppies and the recurrent inhibition between lateral gastrocnemius-soleus (LG-S) and medial gastrocnemius (MG) motor pools was assessed by conditioning monosynaptic reflexes (MSR) elicited from the sectioned dorsal roots and recorded either from the LG-S and MG nerves by antidromic stimulation of the synergist muscle nerve. Our results demonstrated that the MSR recorded from both LG-S or MG nerves had larger amplitude and longer latency after neonatal sciatic nerve crush. The RI in both LG-S and MG motoneuron pools was significantly reduced to virtual loss (15–20% of the normal RI size) even after a long recovery period upto 30 weeks after nerve crush. Further, the degree of the RI reduction after tibial nerve crush was much less than that after sciatic nerve crush indicatig that the neuron-muscle disconnection time is vital to the recovery of the spinal neuronal circuit function during reinnervation. In addition, sciatic nerve crush injury did not cause any spinal motor neuron loss but severally damaged peripheral muscle structure and function. In conclusion, our results suggest that peripheral nerve injury during neonatal early development period would cause a more sever spinal cord inhibitory circuit damage, particularly to the Renshaw recurrent inhibition pathway, which might be the target of neuroregeneration therapy.
Highlights
Recurrent inhibition (RI) is a basic type of neuronal circuit throughout the central nervous system
Our current research further investigated the relationship between recurrent inhibition (RI) changes and the motoneuron functional self-regulation in adult rats after transient neonatal sciatic nerve crush injury, which had a significant meaning to identify mechanism of nerve regeneration
monosynaptic reflexes (MSR) were recorded in the two branches of the sciatic nerve, lateral gastrocnemius-soleus (LG-S) and medial gastrocnemius (MG) nerve, respectively, by stimulating the peripheral sectioned spinal root L5 (Figures 1(a) and 5(a))
Summary
Recurrent inhibition (RI) is a basic type of neuronal circuit throughout the central nervous system. Renshaw cells and motoneurons form a recurrent inhibitory circuit that controls motor output. Individual Renshaw cell receives inputs from particular motor pools and spreads its inhibitory output to the same motoneurons, their synergists (i.e., motor pools exerting a similar action on the same joint), and sometimes selo ected motor pools across joints [2]. The regenerated muscle and motoneuron were functionally disturbed, such as denervated amyotrophy and myoceptor degeneration [11]. These factors restricted functional recovery of the injured neurons. The findings that motoneuron was able to resubject muscle by regeneration and full or nearly full recovery in adult animals with sciatic nerve injury [12], but with reduced excitatory postsynaptic
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