Development of motor systems: a comparative approach.
Anurans offer a unique opportunity to study the development of neuronal connections. Transition from the aquatic limbless tadpole to the juvenile occurs over a protracted period of time during which the animal is accessible for experimental studies. Moreover, tract-tracing studies have demonstrated that their descending brain stem pathways show remarkable similarities in origin, course and site of termination to those of mammals. A developmental sequence in the formation of descending pathways to the spinal cord has been shown implying that reticulospinal and vestibulospinal fibers innervate spinal segments very early in development, whereas the red nucleus projects spinalwards definitely later in development. In anurans, this developmental sequence parallels the changes observed in locomotor pattern. The ingrowth of descending pathways into the spinal cord possibly occurs along so-called 'pre-existing' tracts. Several hypotheses on guidance cues in axonal pathfinding will be discussed.
ten Donkelaar
H J
HJ
Department of Anatomy and Embryology, University of Nijmegen, The Netherlands.
D000818:Animals; D001921:Brain / Q000196:embryology*; D001933:Brain Stem / Q000196:embryology; D009046:Motor Neurons; D009434:Neural Pathways / Q000196:embryology; D009893:Opossums; D013116:Spinal Cord / Q000196:embryology*; D014982:Xenopus laevis / Q000196:embryology