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Avian brainstem and descending spinal projections associated with locomotion Webster, Deirdre M.S.


Electrical microstimulation studies in the decerebrate bird have previously identified brainstem regions that play a role in the initiation of locomotion. This thesis was designed to identify the neuroanatomical connections of these physiologically defined locomotor regions. The experiments were conducted on the Pekin duck, Anas platyrhynchos; Canada goose, Branta canadensis; Sulphur-crested cockatoo, Cacatua galerita; and Eastern rosella, Platycercus eximius. A variety of retrograde tracer chemicals (e.g. wheat germ agglutinin-horseradish peroxidase and fluorescent tracer True Blue) were injected into either the cervical or lumbar spinal cord alone or in conjunction with a more rostral subtotal lesion of the spinal cord to determine (1) the origins of spinal projections to the spinal cord, and (2) the funicular organization of these pathways at the lumbar level. The distribution of retrogradely labelled neurones was similar in all avian species examined. There were no direct telencephalic projections to the spinal cord. Descending brainstem-spinal spinal pathways from previously identified "locomotor sites" in the ventromedial medulla (nucleus reticularis medullaris centralis and nucleus reticularis, gigantocellularis) projected to the lumbar level via the ventrolateral funiculus, whereas dorsolateral "locomotor sites" (nucleus reticularis parvocellularis, nucleus and descending tract of the trigeminal nerve) only projected as far as the cervical spinal cord. The afferent projections to these identified brainstem locomotor regions were determined by discrete injections of retrograde fluorescent tracers into the ventromedial or dorsolateral pontomedullary locomotor sites. Afferent input originated principally from the pontomedullary reticular formation and the mesencephalon. The similarity of avian spinal and brainstem connections to those previously described for mammals indicates considerable conservation of the origins and organization of descending locomotor pathways between mammalian and non-mammalian species.

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