Reticulospinal fibers of the opossum, Didelphis virginiana. II. Course, caudal extent and distribution.

Abstract

AbstractLesions were placed in the deep midbrain tegmentum and within areas of the pontine and medullary reticular formation which were determined by the retrograde degeneration method to give rise to reticulospinal fibers. The location of each lesion was verified histologically and the spinal cords processed by either the Nauta or Fink‐Heimer method. Control material for the origin of degenerated fibers was provided by previous studies on corticospinal, tectospinal and rubrospinal fibers in the same form.Fibers degenerating as a result of mesencephalic tegmental lesions followed the ipsilateral ventral funiculus and could be traced as far caudal as midthoracic levels. They ended in Rexed's laminae VII and VIII.Lesions of the pontine reticular formation resulted in the degeneration of fibers within the ventral funiculus of the spinal cord. The great majority of these fibers followed an ipsilateral course. Such pontospinal fibers were present throughout the length of the spinal cord; their terminal distribution appears to take place mainly within laminae VII and VIII. At certain levels, however, such fibers could be traced into lamina IX.Lesions in the medial medullary reticular formation resulted in fiber degeneration chiefly within the ipsilateral ventral and lateral funiculi. However, a few fibers were present on the side opposite the ablation. This fiber system extends throughout the length of the spinal cord and distributes itself in laminae VII and VIII and, at certain levels, also in lamina IX. Lesions isolated to the lateral, parvocellular portion of the medullary reticular formation resulted in fiber degeneration located within the propriospinal bundles of the lateral funiculus which could be traced to rostral cervical levels. Such lesions also interrupted the rubrospinal tract in the its medullary trajectory.