Ailing Li

Graduation Semester and Year

2014

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Psychology

Department

Psychology

First Advisor

Yuan Bo Peng

Abstract

Nociceptive stimuli can activate peripheral nociceptors to produce nociceptive signals which can be projected to the spinal cord and further up to the thalamus and many other cortical and subcortical areas through ascending pathways. Nociceptive information can be processed in various brain areas (e.g., somatosensory cortex and anterior cingulate cortex); it can change activities in those brain areas and eventually result in morphological changes following long-term stimulation. The medial prefrontal cortex (mPFC) has been proven to be involved in higher cognitive functions and emotional processing. It receives projections from brain areas that are involved in nociception. Morphological changes of the mPFC happened in chronic pain patients and rats with neuropathic pain, and decreased single neuronal activity has been observed in rats after the induction of arthritic pain. In this study, both single cell activity of spinal cord dorsal horn (DH) and the local field potential (LFP) of the mPFC were investigated in response to peripheral graded electrical stimulation of L5 spinal nerve (SN) by a customized wireless module (10Hz, 1ms, 5s, from 0.1v to 5v with 0.5v increment). It was found: (1) The DH neuronal activity was significantly increased by L5 SN stimulations equal to or higher than 0.5v (p < 0.05), intensity-dependently. Significant after-discharge was also observed at high-intensity stimulations from 3.5v to 5v. Electrical stimulation at 1v or higher showed similar DH response to phase I response after formalin injection. (2) In anesthetized animal, LFP was reduced bilaterally in mPFC by L5 SN stimulation, with slightly different pattern in each side. The inhibition became significant starting at 1v for contralateral and 3v for ipsilateral mPFC. Similar inhibition of LFP was observed in mechanical (pinch) and chemical (formalin injection) nociceptive stimulation. (3) The inhibition of LFP in mPFC by L5 SN stimulation and formalin injection was not observed in the freely moving animal. In conclusion, the electrical stimulations of L5 SN at intensities that induced comparable DH response as formalin injection reduced the LFP in mPFC under anesthesia. The inhibition was similar to that induced by mechanical and chemical noxious stimulus. However, such mPFC inhibition was not observed in freely moving animal which might be due to additional emotional and cognitive processing during awake state that has masked the effect.

Disciplines

Psychology | Social and Behavioral Sciences

Comments

Degree granted by The University of Texas at Arlington

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