Publication Date
2014
Document Type
Thesis
Committee Members
David Ladle , Ph.D. (Advisor); Mark Rich, M.D., Ph.D. (Committee Member); Robert Putnam, Ph.D. (Committee Member)
Degree Name
Master of Science (MS)
Abstract
In animals proprioceptive Ia afferents enable the animal to sense the location, orientation and movement of its limbs in space. These Ia afferents make connections with many different types of neurons within the spinal cord such as; motor neurons, Ia Inhibitory interneurons, and other interneurons. Ia Afferents connect with IaINs that project to antagonist muscle MNs to ensure that contraction of the antagonist muscle group is inhibited. For example the quadriceps Ia afferents contact IaINs that contact PBST motor neurons to inhibit excitation and thus contraction. The way in which the connectivity of these Ia afferents is established is not entirely understood. Complete genetic control of connectivity would be overly complicated, and while it probably does play a part there seems to be changes in the connectivity that occur during development, and even after birth some refinement may occur. To investigate plasticity in connectivity, we mapped the connections of Ia afferents of the quadriceps and obturator nerves onto Ia inhibitory interneurons of animals at and shortly after birth (P0/P1 timepoint). The known characteristics of Ia Inhbitory interneurons were used to identify them, glycine being used as the neurotransmitter, calbindin contacts from Renshaw cells, and afferent contact. The IaINs were placed into three categories those receiving quad afferent contact, those receiving obturator afferent contact, and those receiving both afferent contact. Out of the 437 Ia inhibitory interneurons analyzed in 3 animals 26.5% received contacts from both quadriceps and obturator Ia afferents. This is surprising because Adductor afferents should not contact the same IaINs as quad afferents, because there is no reciprocal inhibition seen in the PBST when the obturator is stimulated as it is with stimulation of the quad nerve. This suggests that there are some activity dependent changes that occur to refine the circuit of reciprocal inhibition after birth.
Page Count
76
Department or Program
Department of Neuroscience, Cell Biology and Physiology
Year Degree Awarded
2014
Copyright
Copyright 2014, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
