The central distribution pattern of primary afferent fibers innervating the thigh muscle posterior iliotibialis in the chicken.

The anatomical relationship between motoneuron dendrites and primary afferent fibers innervating the same muscle were examined by using a modified cholera toxin tracing method. The cholera toxin B subunit conjugated with latex beads was injected into the posterior iliotibial muscle (PIT) of chicken. Both motoneuron dendrites and primary afferent fibers were intensely labeled. Labeled primary afferent fibers innervating the PIT were mainly located in laminae I (ventral part), V (lateral part), VI, VII (except ventromedial part) and lateral motor column (LMC, lamina IX) of the lumbar spinal cord. Numerous labeled primary afferent fibers were observed in proximity to the motoneuron pool of the PIT located in the dorsolateral region of the LMC; primary afferent fibers were closely apposed to somatic profiles of the PIT motoneurons.