ORGANIZATION OF FORELIMB MOTONEURON POOLS IN 2 BAT SPECIES (EPTESICUS-FUSCUS AND MYOTIS-LUCIFUGUS)

The present investigation provides further evidence of the conservatio n of motor nuclei in amniotes. The position of six forelimb and should er motor pools were mapped in two species of bat, Eptesicus fuscus and Myotis lucifugus. The intraspinal locations of motor pools were revea led by labeling with the retrograde neuronal tracer WGA-HRP injected i nto the bellies of six muscles: m. pectoralis, m. spinodeltoideus, mm. triceps brachii (long and lateral heads), m. infraspinatus, m. supras pinatus, and m. biceps brachii. The positions of the labeled motor poo ls were reconstructed from serial transverse and horizontal sections o f the spinal cord. WGA-HRP-labeled cells were located midway between c ervical spinal nerves four and five to midway between cervical spinal nerve eight and the first thoracic spinal nerve. Individual motor pool s formed fusiform clusters of cells with little intermingling of neuro ns between adjacent motor pools. The pectoralis motor pool contained s ignificantly more motoneurons than all other motor pools for M. lucifu gus. The pectoralis poor in E. fuscus contained more motoneurons than the biceps, supraspinatus, and infraspinatus, but not the spinodeltoid or the triceps brachii. The biceps, spinodeltoid, infraspinatus and s upraspinatus pools were located rostrally; the pectoralis and triceps pools caudally. The pectoralis pool was the most medial and the spinod eltoid pool was the most lateral. These data suggest that the location s of shoulder and forelimb motor pools are ontogenetically and phyloge netically conserved across tetrapods and independent of the function o f the muscles in adults.