Distribution of the motoneuronal pools controlling the hindlimb muscles in the lumbar spinal cord of the Acomys cahirinus.

The motoneuron pools innervating major functionally distinct hindlimb muscles were mapped in the spinal cord of Acomys cahirinus using the fluorescent retrograde tracer Fast Blue. The dorsoventral, mediolateral, and rostrocaudal distributions of motoneuron pools in the lumbar spinal cord were characterized for the targeted muscles: (i) motoneuron pools innervating the m. iliacus (hip flexor) extend from the middle part of segment L1 to the caudal part of segment L3 and are located in the ventrolateral column; (ii) motoneuron pools innervating the m. vastus lateralis (knee extensor) extend from the caudal part of segment L2 to the caudal part of segment L3 and are located in the central column; (iii) motoneuron pools innervating the m. tibialis lateralis (ankle dorsiflexor) extend from the middle part of segment L3 to the middle part of segment L4 and are located in the dorsolateral column; (iv) motoneuron pools innervating the m. gracilis anterior (hip adductor, hip extensor) extend from the rostral part of segment L1 to the caudal part of segment L5 and are located in the central column; (v) motoneuron pools innervating the m. semitendinosus (hip extensor, knee flexor) extend from the caudal part of segment L2 to the middle part of segment L5 and are located in the central column; (vi) motoneuron pools innervating the m. soleus (ankle plantarflexor) extend from the caudal part of segment L3 to the middle part of segment L5 and are located in the dorsolateral column; (vii) motoneuron pools innervating the m. gastrocnemius medialis (knee flexor, ankle plantarflexor) extend from the middle part of segment L4 to the caudal part of L5 and are located in the dorsolateral column; and (viii) motoneuron pools innervating the m. gluteus medius (hip rotator, hip extensor) extend from the middle part of segment L3 to the caudal part of segment L5 and are located in the ventrolateral column. These findings represent the first detailed mapping of motoneuron pools in Acomys cahirinus and may prove valuable for studies investigating the locomotor system in precocial species.