Near-infrared Optical Probe Development to Monitor Female Sexual Arousal Response in a Rat Model

Abstract

Aging leads to the decline of estrogen levels in women, which can result in female sexual dysfunction (FSD). With diminished ovarian estrogen, the vaginal wall becomes thinner and physical characteristics, such as elasticity, expandability, and flexibility, worsen. Postmenopausal women, in particular, experience discomfort when it comes to having intercourse because menopause entails low desire or interest, diminished arousal, orgasmic difficulties, and dyspareunia. Female sexual dysfunction is widely reported to be prevalent all over the world; there is a growing interest in it, and a few studies have been carried out on the matter. Laser Doppler flowmetry (LDF) is currently used in clinics to diagnose female sexual dysfunction (FSD). However, mostly LDF only can collect information from arteries in the surface while Near-infrared spectroscopy (NIRS) is sensitive to both arteries and microvessels and this makes NIRS more attractive in preclinical female sexual studies. Besides, NIRS can collect information from the surface and the subsurface of the vagina. In this study, an optical probe based on NIRS was designed to monitor vaginal hemodynamics and temperature induced by apomorphine (APO) administration which is induced sexual arousal. This work is structured in three parts 1) to develop a probe for rat vaginal hemodynamic measurement, 2) to monitor different vaginal hemodynamic and temperature response depending on anesthetic agents, and 3) to monitor vaginal hemodynamic changes during apomorphine administration in an ovariectomized rat model. For the 1st chapter, an optical probe was developed as considering the size and shape of the vaginal wall of the animal after dissection. The NIRS based probe was inserted to the vagina to measure the changes of oxyhemoglobin (OHb), deoxyhemoglobin (RHb), and total hemoglobin (THb) concentrations along with temperature from the animal vaginal wall. For the 2nd chapter, animal experiments were performed using female rats with two widely used anesthetic agents in preclinical studies: ketamine and isoflurane. The developed NIRS based probe was used to measure the changes of oxyhemoglobin (OHb), deoxyhemoglobin (RHb), and total hemoglobin (THb) concentrations along with temperature from the animal vaginal wall. For the 3rd chapter, a rat whose bilateral ovaries have been removed was used as a menopause model. In the menopause model, changes of oxyhemoglobin (OHb), deoxyhemoglobin (RHb), and total hemoglobin (THb) concentrations and temperature were monitored from the animal vaginal wall. Moreover, hormone (17 beta-estradiol), lubrication from the vagina, and body weight information were obtained after hemodynamic response measurement. All measurements were taken every two weeks after ovariectomy surgery (OVX). To accomplish all the chapters, Sprague Dawley rat (SD, 180-200 g) model was used and a respiratory challenge was applied to the animals to verify the developed probe. Apomorphine (APO) was administered as a sexual stimulant, and ovariectomized (OVX) surgery was performed to mimic human menopause. From all results, we can find out the optical probe based on NIRS could be a useful tool to diagnose female sexual dysfunction of the vagina.