Abstract

Adult rats make ultrasonic vocalizations (USVs) that exhibit acoustic characteristics indicative of an immediate emotional state and its underlying neural activation. As an integral part of the rats' behavioral repertoire, USVs can be translated to human behavior, including clinical models of human diseases and disorders. Although female rats are used as predictive models of sexual function and dysfunction in women, their USVs have not yet been incorporated into existing preclinical behavioral paradigms. Female rats reliably emit USVs in response to the application of temporally-distributed, manual clitoral stimulation (CLS). It is unclear, however, whether the emissions are reflective of the hedonic properties of CLS or those of general arousal. Thus, the experiments in the thesis aimed to characterize the acoustic properties of CLS-elicited USVs to clarify their communicative function. The experiments described in Chapter 2 determined that female rats emit hedonic USVs when distributed CLS is delivered with a soft-bristle paintbrush. The ovarian hormones estradiol and progesterone modulated the acoustic parameters of hedonic USVs whereas chronic administration of the selective serotonin reuptake inhibitor fluoxetine attenuated their emission concurrently with decreases in sexually appetitive behaviors like solicitations. The experiments described in Chapter 3 explored whether altering the tactile quality of distributed CLS alters its hedonic value and its capacity to serve as a reinforcer in partner-preference conditioning. Compared to CLS applied with a soft-bristle brush, CLS applied with a hard-bristle brush elicited distinct subtypes of low frequency USVs associated with aversion. The experiment described in Chapter 4 found that the tactile quality of distributed CLS also altered the pattern of Fos protein expression in brain areas involved in sexual reward, aversion, and sensory integration. Exposure to a neutral odour previously associated with rough-bristle CLS increased the number of neurons expressing Fos protein in brain regions subserving aversive responses and decreased expression in regions subserving reward. An opposite pattern was expressed in response to the same odour associated with soft-bristle CLS, whereas the odour associated with sham CLS did not alter Fos expression in those areas. Taken together, the data show that CLS-induced USVs can be used as a measure of both appetitive and aversive sexual affect, as well as provide a foundational model of anticipatory-induced clitorodynia.