Undergraduate Honors Theses

Thesis Defended

Spring 2015

Document Type


Type of Thesis

Departmental Honors


Integrative Physiology

First Advisor

Dr. Christopher A. Lowry

Second Advisor

Dr. David Sherwood

Third Advisor

Dr. Ryan Bachtell


Chronic stress is a major risk factor for developing anxiety and depressive disorders. Improving stress resilience can reduce this risk and previous studies have shown positive effects of chronic exercise on stress resilience through unknown mechanisms. In this study, we are trying to understand the effects of voluntary or forced exercise on the rat brain serotonin (5-hydroxytryptamine; 5-HT) system. Specifically, we analyzed serotonergic neuron activation in the dorsal raphe nucleus (region of the brain abundant in serotonergic neurons) and its relation with stress resilience in rats. The objective of the experiment was to determine whether forced or voluntary exercise activates serotonergic neurons within anatomically and functionally distinct subregions of the dorsal raphe nucleus, including the dorsal (DRD), ventral (DRV), ventrolateral /ventrolateral periaqueductal gray (DRVL/VLPAG), and interfascicular (DRI) parts. Of particular interest, DRD serotonergic neurons are thought to project to areas controlling anxiety-related behavior and anxiety states, while DRVL/VLPAG serotonergic neurons are involved in inhibition of panic-like behavioral responses and sympathetic outflow, and DRI serotonergic neurons project to areas in the forebrain thought to be associated with stress resilience. In our studies, rats exposed to repeated forced exercise, but not repeated voluntary exercise, responded with decreased c-Fos expression in serotonergic neurons in the rostral DRD and increased c-Fos expression in serotonergic neurons in the caudal DRD, ventral part of the dorsal raphe nucleus (DRV), and DRI. Immunohistochemical staining of FosB to detect chronic changes in serotonergic neuronal activation revealed consistent results. These results suggest that repeated forced exercise, but not repeated voluntary exercise, activates DRI serotonergic neurons, an effect that may contribute to the recently described stress resilience effects of forced exercise. These results also suggest that the stress resistance effects of chronic voluntary and forced exercise may involve different mechanisms.