Digitized Honors Theses (2002-2017)

Date of Award

5-2006

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biomedical Sciences

Faculty Mentor

Cindy Stanfield

Abstract

A major part of the nociceptive modulatory system is the Rostroventral Medula (RVM). Within, the RVM three types of cells are involved in pain modulation. ON cells are activated by noxious heat to the tail of rats. OFF cells are inhibited by noxious heat to the tail. Neutral cells are unresponsive to noxious heat to the tail of rats. ON and OFF cells are a heterogeneous group of cells with different subpopulations. Each subpopulation has different response patterns and it has been proposed that pain modulation might be only one among the numerous functions of ON and OFF cells.

Some ON cells start firing one second, or less, before the tail flick response (TFR) in rats (Abrupt ON cells), while others start firing more than one second before the TFR (Gradual ON cells). Some OFF cells stop firing one second, or less, before the TFR (Abrupt OFF cells), whereas others start decreasing their activity more than one second before the tail flick response occurs (Gradual OFF cells). Our hypothesis was that Abrupt cells respond only to noxious stimuli whereas Gradual cells respond to both innocuous and noxious stimuli.

Extracellular recordings of RVM cells were obtained in lightly anesthetized rats.

After classification of the cell as ON, OFF, or NERUTRAL, the rat was exposed to innocuous and noxious somatic stimuli like touch, brush, airpuffs, pinch, and heat to various locations on the body. Contrary to the hypothesis, both Abrupt and Gradual cells responded to innocuous as well as somatic stimuli. However, Abrupt ON cells responded only to high intensity innocuous stimuli (brush), whereas Gradual ON cells responded to low intensity innocuous stimuli (airpuffs), and high intensity innocuous stimuli (brush). Gradual ON cells were most responsive to brush on the back and Abrupt ON cells on the tail. Gradual OFF cells were most responsive to brush to the back, whereas Abrupt OFF cells were equally responsive to brush to the tail and back.

These results showed that subpopulations of ON and OFF cells exist with different response patterns of each population. Further studies should be conducted with larger groups of Abrupt and Gradual cells to determine whether more differences exist.

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