Differential synaptic effects on physiological flexor hindlimb motoneurons from cutaneous nerve inputs in spinal cat

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Reflexes

Background:

• Previous work showed superficial peroneal nerve stimulation caused mixed effects on extensor digitorum longus (EDL) motoneurons, unlike tibialis anterior (TA) and semitendinosus (St).
• Understanding ipsilateral cutaneous reflexes is crucial for motor control and rehabilitation.

Purpose of the Study:

• To characterize the organization of ipsilateral cutaneous reflexes by examining postsynaptic potentials (PSPs) in St, TA, and EDL motoneurons.
• To investigate responses to superficial peroneal and saphenous nerve stimulation in decerebrate, spinal cats.

Main Methods:

• Recorded postsynaptic potentials (PSPs) in St, TA, and EDL motoneurons following superficial peroneal and saphenous nerve stimulation.
• Varied stimulus intensity to differentiate responses mediated by large (Aα) and small (Aδ) cutaneous fibers.
• Analyzed PSPs for excitation (EPSP) and inhibition (IPSP), noting latencies and motoneuron type.

Main Results:

• TA and St motoneurons typically showed an initial EPSP followed by an IPSP with low-intensity stimulation; higher intensity enhanced late excitation.
• EDL motoneurons exhibited variable initial inhibition or excitation with superficial peroneal stimulation; saphenous nerve evoked excitation, sometimes preceded by inhibition.
• Short-latency (<1.8 ms) EPSPs and IPSPs were observed, suggesting disynaptic linkages in both excitatory and inhibitory cutaneous reflex pathways.

Conclusions:

• Removal of higher center influences reveals specialized inhibitory reflex pathways from superficial peroneal and saphenous nerves to EDL motoneurons.
• The findings suggest disynaptic connections as the minimal linkage for both excitatory and inhibitory cutaneous reflex pathways.
• These results contribute to understanding spinal reflex organization and its modulation.