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|Title:||Reticular Pathways Controlling Lateral Head Movements in the Rat|
|Author(s):||Sirkin, David Winsor|
|Department / Program:||Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Following upon the discovery that pontine reticular formation (PRF) lesions in the rat abolish certain head movements, it was decided to further characterize the effects of PRF lesions on head movements in the rat and to begin to determine what output pathways from the PRF might mediate its role in head movement control.
In the first study, PRF lesions were produced electrolytically, and effects on orienting responses to a stationary visual stimulus as well as responses to full-field optokinetic stimulus were observed. Unilateral lesions abolished ipsiversive orienting movements and quick phases of optokinetic head nystagmus. Some also had a temporary effect on slow phases. Effects of bilateral lesions were bilateral. A class of fast head movements that are abolished by PRF lesions thus emerges. It includes quick phases of head nystagmus, spontaneous turns in the open field, and visual orienting movements. It is analogous to the class of fast eye movements that are abolished by PRF lesions, which includes quick phases of nystagmus and saccades.
In the second study, spinal projections from the PRF in the rat were traced with the autoradiographic method. The spinal projections from the medial PRF appeared to course in the medial reticulospinal tract. Since the recent literature indicates that the PRF controls horizontal eye movements via direct projections to extraocular muscle motoneurons, it is suggested that, by analogy, the PRF might control head movements via its efferents descending in the medial reticulospinal tract and innervating the ventral horn in the spinal cord.
In the third study, lesions were made where medial reticulospinal axons course in the medulla to test this hypothesis. Some lesions abolished fast head movements, but the effects were not as longlasting as those produced by PRF lesions. These results are consistent with a major role for medial reticulospinal fibers in the control of head movements, but this role remains to be conclusively demonstrated.
The main conclusions drawn are the eye and head movement control systems are organized similarly, and that the PRF plays parallel critical roles in the two systems.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
|Date Available in IDEALS:||2015-05-14|