Neural pathways between sacrocaudal afferents and lumbar pattern generators in neonatal rats

Area of Science:

• Neuroscience
• Spinal Cord Research
• Locomotion Control

Background:

• Understanding the neural control of locomotion is crucial for neuroscience.
• Sacrocaudal afferent input's role in activating lumbar pattern generators is not fully understood.

Purpose of the Study:

• To investigate the projections of sacrocaudal afferents (SCA) onto lumbar pattern generators in neonatal rat spinal cords.
• To elucidate the synaptic mechanisms and pathways involved in SCA-evoked locomotor rhythms.

Main Methods:

• Isolated spinal cords of neonatal rats were used.
• Locomotor-like rhythms were induced by SCA stimulation.
• Synaptic transmission in the sacrococcygeal (SC) cord was blocked using low-calcium/high-magnesium solutions and modulated with calcium.
• Pharmacological agents, including CNQX (non-NMDA antagonist), NMDA antagonists, and adrenoceptor antagonists, were employed.
• Midsagittal splitting and funiculi interruption experiments were conducted.

Main Results:

• SCA stimulation induced a locomotor-like rhythm in the majority of preparations.
• The SCA-evoked lumbar rhythm depended on synaptic transmission in the SC cord and non-NMDA receptor activation.
• NMDA receptors and alpha1/alpha2 adrenoceptors in the SC cord were not essential for this rhythm.
• Crossed and uncrossed ascending/propriospinal pathways were coactivated by SCA stimulation.
• These pathways ascend through the lateral, ventrolateral, and ventral funiculi to the thoracolumbar cord.

Conclusions:

• SCA-induced lumbar rhythm generation involves synaptic activation of SC relay neurons.
• Non-NMDA receptors are critical for the functional activation of these SC relays.
• Ascending propriospinal pathways originating from the SC cord are essential for transmitting the locomotor command to the lumbar cord.