Imaging the influence of hormones on pain processing in humans

• Main Author: Vincent, Katy
• Published: University of Oxford 2010
• Subjects: 616.0472
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599898

The details of the interactions between steroid honnones and the pain experience are only just beginning to be understood. This thesis uses both behavioural measures and functional magnetic resonance imaging (FMRI) to investigate the relationships between steroid hormones and the response to experimental noxious thennal stimuli of the ann and abdomen. In the first half of this thesis, the hypothesis that central actions of steroid honnones modulate the pain experience by specific interactions with endogenous pain modulatory systems was investigated. As expected, no influence of the menstrual cycle on the perception of noxious stimuli could be demonstrated in healthy women with either naturally controlled cycles or those using the combined oral contraceptive pill (COCP). However, the corre lations of brain activity in response to noxious stimuli and the specific serum honnone levels were in the predicted brain regions, supporting influences of estradiol on opiates; progesterone on y-aminobutyric acid (GABA); and cortisol on the endocannabinoid system. Furthennore, imaging data suggest that the observed increase in sensit ivity to noxious stimuli in the women using the COCP is likely mediated by reduced activ ity of the endogenous opioid system, secondary to low serum estradiol levels. In the second half of this thesis, the hypothesis that repeated episodes of menstruation are associated with long-lasting alterations in the central processing of noxious stimuli was addressed. In agreement with this hypothesis, dysmenorrhoea was associated with an increase in sensitivity to noxious stimulation of both sites, that persisted beyond the time of menstruation. Negative correlations between the duration of symptoms and both brain activity in response to the stimuli and serum cortisol levels suggest the development of a maladaptive response to repeated episodes of pain. However, when comparing healthy, pain-free male and female subjects, corre lations with age were only observed in female subjects and only in response to abdominal stimuli, suggesting the development of an adaptive response to menstruation in painfree women. This