Serotonin (5-HT) is a well-known modulator of spinal cord excitability and motor output. In the spinal cord, the actions of 5-HT are primarily mediated by the 5-HT1AR, 5-HT2Rs and the 5-HT7R. Following a spinal cord transection, which results in a loss of supraspinal input, 5-HT agonists such as quipazine are used to provide excitation to the spinal cord to facilitate locomotor recovery. This is characterized by rhythmic alteration of left and right hindlimbs and ipsilateral flexor and extensor muscles. However, whether 5-HT has a global effect on spinal cord excitability or is confined to a specific motor group (i.e. flexors or extensors) is currently unknown. Furthermore, quipazine is used in conjunction with activity based interventions to enhance recovery following a spinal cord injury. However, the influence of limb activity on the responsiveness of the injured spinal cord to quipazine has not been examined. Lastly, the recovery of locomotion is at least in part thought to occur through an up-regulation of 5-HT receptors, although this has not been investigated in lumbar spinal cord. Chapter 2 examines whether quipazine had a differential effect on flexor and extensor motor output assessed by recording flexor and extensor reflexes, motoneurons and Ia extracellular field potentials pre- and post-quipazine. It was determined that following an acute spinal transection, quipazine induced a larger flexor monosynaptic reflex (MSR) compared to the extensor MSR due to pre-synaptic but not motoneuron modulation. Chapter 3 examines the influence of a chronic spinal transection with and without passive cycling on the hindlimb flexor and extensor MSR, both pre- and post-quipazine. It was found that three months post STx, the extensor but not flexor MSR demonstrated a hyperexcitable response, which was attenuated with passive cycling. Further, three months of passive cycling extensor MSR response to quipazine was similar to that seen in the control intact group. Chapter 4 examined 5-HT receptor expression in flexor and extensor motoneurons three months post spinalization with or without passive cycling. Following a chronic STx, the 5-HT1AR and 5-HT2CR are down regulated, whereas the 5-HT2AR is up-regulated. Passive cycling further enhanced the 5-HT2AR expression as well as up-regulated the 5-HT7R in extensor but not flexor motoneurons. Chapter 5 discusses the results and significance of these findings in detail.

In young healthy adults, characteristic obstacle avoidance reflexes (stumble corrective) were elicited with electrical stimulation during walking that were dependent on the anatomical location of cutaneous afferents stimulated (sole versus dorsum of the foot). We previously demonstrated an age-related erosion of these stumble corrective responses when the perturbation was applied to the dorsum of the foot. However, it is unknown whether similar age-related reflex erosion is present with stimulation to the sole of the foot. The purpose of this study was to identify age-dependent differences in stumbling reactions to electrically evoked stimulation of the tibial nerve at the ankle during walking in healthy young (19-39) and older adult (70 years and older) groups. Electromyograms (EMG) of the tibialis anterior (TA), soleus (SOL), medial gastrocnemius (MG), biceps femoris (BF) and vastus lateralis (VL) were recorded along with gait kinematics including angular displacement and velocity at the ankle and knee joint as well as toe clearance relative to the walking surface. The main finding of this study was the significant erosion of the kinematic and EMG stumbling reactions seen in the older adults compared to the young. Specifically, during mid-swing phase, there was reduced peak toe clearance and significantly smaller amplitudes in ankle dorsiflexion and knee flexion angular displacement as well as absent responses in TA and MG in older adults compared to the young. Further, these degraded responses were superimposed on altered mid-swing phase kinematics during unstimulated walking in the older adults showing reduced toe clearance, knee flexion and increased ankle dorsiflexion compared to the young. This combination of degraded reflexes and altered unstimulated kinematics resulted in significantly reduced toe clearance in the older adults and could suggest that these adults are in the prodromal stage of fall risk. / Graduate / 0566

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 84-92)

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 55-62).

Thesis (M.A.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

Experiments were carried out to investigate the extent to which habituation of the flexor reflex depended on mechanisms operating at spinal interneurones. An attempt was made to cause selective degeneration of interneurones in the spinal cord of the rat by subjecting the cord to a period of ischaemia. Ischaemia was produced by temporary occlusion of the thoracic aorta. The flexor withdrawal reflex was tested 3, 7 or 14 days after occlusion. When compared with data from control animals it was found that ischaemia had resulted in both a qualitative change and a quantitative diminution in the amount of habituation which occurred during the presentation of 400 uniform stimuli. It was concluded that this impairment of the habituation process was a consequence of degeneration of interneurones which normally cause progressive inhibition of the excitatory flexor reflex pathway. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

No description available.

No description available.