Effects of therapeutic interventions on the organization of the rat sensorimotor cortex

Patrick Daniel Ganzer

doi:10.17918/etd-7002

A spinal cord injury (SCI) not only impacts the spinal circuitry, but also affects the cortical sensory and motor representations in the brain. After injury, these representational maps of body parts on the surface of the brain can reorganize, which is defined as an extension of cortical representations of intact body areas into the cortical regions normally devoted to the deafferented body areas. In fact, cortical reorganization within these sensory and motor representations can play a major role in recovery after SCI. Therefore, it has been suggested that therapeutic interventions should act at, and therefore potentially promote, plasticity at all levels of the sensorimotor system. Unfortunately, the impact of rehabilitative strategies on cortical reorganization remains largely unknown. Both serotonergic (5-HT) pharmacotherapy and exercise therapy can act above and below the level of a SCI, and are each involved in the promotion of plasticity. Importantly, these interventions have been shown to improve locomotor recovery after SCI. However, their effects on cortical organization after SCI are unknown. In this thesis work, we have utilized 5-HT pharmacotherapy and passive bicycling exercise to promote recovery in the adult rat completely transected as an adult at spinal level T8/9. We hypothesized that these two therapeutic interventions used in combination would promote significant sensorimotor cortical reorganization, the magnitude of which would be correlated to locomotor recovery. To assess this hypothesis, we have utilized high resolution electrophysiological mapping techniques to investigate the somatosensory (single neuron mappings) and motor (intracortical microstimulation) representations in cortex after injury and therapy. These quantifications of sensory and motor cortical reorganization are then compared to locomotor recovery measures across therapy groups. Our results show that a combination of chronically administered 5-HT pharmacotherapy and passive bicycling exercise promotes significant reorganization of functionally relevant representations in the somatosensory and motor cortices, the magnitude of which is correlated to locomotor recovery. Interestingly, lesioning these new cortical circuits significantly reduced the achieved locomotor recovery seen in these animals. Therefore, the cortical reorganization induced by this combination therapy may play a major role in locomotor recovery, equating to new supraspinal control strategies and eventually weight-supported stepping.

Effects of therapeutic interventions on the organization of the rat sensorimotor cortex

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Effects of therapeutic interventions on the organization of the rat sensorimotor cortex

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