DOI
https://doi.org/10.25772/X0SQ-3G82
Defense Date
2013
Document Type
Thesis
Degree Name
Master of Science
Department
Physiology
First Advisor
John Grider
Abstract
The enteric nervous system controls the gut through the release of specific neurotransmitter and neuromodulators at specific sites such as mucosal secretory cell or smooth muscle cell. In the present study, we have examined the response to one of these neurohumoral agents, Neurotensin, in the rat distal colon. Neurotensin is a paracrine and endocrine modulator of the digestive tract. Even though these effects have been seen in colonic preparations, there are very few functional studies of the effects of Neurotensin in the rat colon, especially the distal colon. In the current study we propose the following hypothesis that Neurotensin will lead to contractile effect on basal tone and phasic contraction in the distal rat colon and will mediate this process primarily through the NT1 receptor. This hypothesis is based on evidence from the mixed action of Neurotensin in other regions of the gut and the more widespread distribution of the NT1 receptor. We have identified two specific aims to investigate this hypothesis. Aim 1 is to investigate the role of Neurotensin in tonic contraction and phasic contraction of the distal rat colon. In this aim, we will expose distal rat colon strips to varying doses of Neurotensin and record changes in basal tone and phasic activity. For our second aim, we will investigate the receptors mediating these responses to Neurotensin. In this aim, we will introduce NT1, NT2, and nonspecific inhibitors to distal rat colon and observe modulation in Neurotensin effects. We will also determine the existence of the receptors via Western Blot. The rat distal colon did respond in a dose-response fashion to varying doses of Neurotensin, but elicited different effects dependent on the strip preparation. When the mucosa was intact, circular muscle responded with an inhibitory effect to phasic activity, but there was little to no change in tonic activity. When the mucosa was removed, the circular muscle responded to Neurotensin by eliciting an increase in tonic activity, but had no effect on phasic activity. The use of SR48692, a specific NT1 receptor inhibitor, showed that the effects that were observed due to Neurotensin were not mediated through the NT1 receptor. With the use of SR142948, a non-selective NT1/NT2 inhibitor, the effects of Neurotensin was completely abolished. This led us to believe that the observed effects were mediated through a Neurotensin receptor and that receptor is likely the NT2 receptor. This was confirmed by the use of the specific NT2 receptor antagonist, levocabastine. The existence of the receptor in rat colon had to be confirmed in order to ensure that the effects observed were mediated through the NT2 receptor and not from an outside mediator. Western Blot analysis confirmed the existence of the NT2 receptor within the mucosa, within the muscle, and within the intact preparation of the distal rat colon. Although these results conflict with our hypothesis, it provides for an interesting template and avenue of exploration.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
October 2013