Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2011)

Cortical sensory maps are highly organized structures that contain point-to-point representations of sensory inputs. This organization emerges in-part from horizontal connections that limit activity-flow across representational borders (local-circuit constraint properties). Interestingly, this organization undergoes experience-dependent modifications throughout life. This dissertation examines changes in local-circuit constraint properties during cortical reorganization.

Synaptic plasticity of horizontal connections could modify activity-flow across borders. Very little is known about inhibitory synaptic plasticity, its relationship to excitatory synaptic plasticity, and their relationship to functional organization. To investigate this, we located the forepaw/lower jaw (FP/LJ) of the primary somatosensory cortex (SI) in vivo, and used whole cell-patch electrophysiology to record excitatory and inhibitory responses of horizontal connections in vitro. Connections that remained within the representation (continuous) and those that crossed from one representation to another (discontinuous) were both examined before and after tetanization, allowing us to examine differences associated with borders. Tetanic stimulation induced diverse forms of synaptic plasticity, with long-term potentiation (LTP) dominating for excitation and long-term depression dominating for inhibition. The border did not restrict this plasticity in either case. In contrast, tetanization elicited LTP of monosynaptic inhibitory responses in continuous, but not discontinuous connections. These results demonstrate that continuous and discontinuous horizontal connections are capable of diverse plasticity responses that could theoretically functionally reorganize the cortex.

Axon remodeling could also change activity-flow across borders. To investigate this, we examined axon remodeling during long-durations of reorganization. We located the FP/LJ border and then iontophoresed a retrograde axonal tracer near the border at different durations of forelimb-denervation or sham-denervation. In sham-denervated animals, neurons close to the border had axonal projections oriented away from the border (axonal bias). Forelimb denervation resulted in a sustained change in border location and a significant reduction in the axonal bias after 6 weeks of denervation, but not after 4 or 12 weeks. The change in axonal bias resulted from axon sprouting across the border at 6 weeks, followed by the retraction of those axons by 12 weeks. This suggests bidirectional axonal rearrangements are associated with relatively long-durations of reorganization. Thus, diverse synaptic and morphological plasticity mechanisms could contribute to functional reorganization.

    Cover page: Plasticity of Local-Circuit Constraint Properties During Functional Reorganization of Adult Cortex
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2019)
    This report describes the successful management of a case of central neurogenic hyperventilation (CNH) refractory to high dose sedation by increasing the mechanical dead space. A 46-year-old male presented with a history of multiple neurological symptoms. Following an extensive evaluation, he was diagnosed with primary diffuse CNS lymphoma and started on high dose steroids. After initial symptomatic improvement, the patient developed increasing respiratory distress and tachypnea. He was intubated and transferred to the neurointensive care unit (neuro ICU). While in the ICU the patient remained ventilator dependent with significant tachypnea and respiratory alkalosis resistant to fentanyl and propofol. This prompted an attempt to normalize the PaCO2 via an increase of the mechanical dead space. This approach successfully increased PaCO2 and bridged the patient until ongoing therapy for the underlying disease resolved the pervasive breathing pattern typical of CNH. Further investigation is warranted to evaluate this strategy, which upon review of the literature appears underused.
      Cover page: Refractory Central Neurogenic Hyperventilation: A Novel Approach Utilizing Mechanical Dead Space.Creative Commons 'BY' version 4.0 license
      Top