AN HRP STUDY OF LOCALIZATION AND TOPOGRAPHICAL MAPPING OF THE MOTONEURONS SUPPLYING THE RAT SERRATUS ANTERIOR MUSCLE

Abstract

Shoulder movements are a complex motor act, controlled by many muscles attached to thescapula and the vertebral column. These muscles are innervating by motoneurons (Mns) located in theventral horn of the spinal cord. Motoneurons of the ventral horn are arranged such that several groups ofMns can be distinguished in a transverse section through the spinal cord. The anatomical or functionalimplication of these groups is still unknown. The present research was designed to determine thelocation and topographical mapping of Mns to the rat serratus anterior (SA) muscle.Thirty young adult male rats weighing 180-250g were used in this study. The location anddistribution of the Mns in the rat cervical spinal cord to the serratus anterior (SA) muscle of the rat havebeen studied using horseradish peroxidase (HRP) intramuscular injection and the application of a HRPnerve dipping method to the long thoracic nerve. Following the intramuscular injection of HRP and alsoa nerve dipping for the long thoracic nerve, labeled motoneurons were identified ipsilaterally to the sideof HRP application forming two main cell columns extended rostrocaudally in the ventral horn of bothsides. The column G5 extended longitudinally from the caudal half of the fifth (C5) to the rostral half ofthe seventh (C7) cervical segments in group five. The column G7, located mainly in the rostral half ofthe C7 in group seven. The serratus anterior labeled motoneurons showed a rostrocaudal somatotopicdistribution in each of the columns G5 and G7.These results suggest that there is a specific functional role for motoneurons, and also thatmotoneurons are arranged in the form of a motor pool with a musculotopic pattern of distributioncorresponding to the embryonic origin and anatomical position of the muscles they innervate to.