title: Brain imaging reveals that engagement of descending inhibitory pain pathways in healthy women in a low endogenous estradiol state varies with testosterone.
abstract: The combined oral contraceptive pill (COCP) has been implicated in the development of a number of chronic pain conditions. Modern COCP formulations produce a low endogenous estradiol, low progesterone environment similar to the early follicular phase of the natural menstrual cycle, with a variable effect on serum androgen levels. We used behavioural measures and functional magnetic resonance imaging to investigate the response to experimental thermal stimuli in healthy women, in both a natural and COCP-induced low endogenous estradiol state, to investigate whether alterations in central pain processing may underlie these observations in COCP users. Although COCP users overall did not require lower temperatures to obtain a fixed pain intensity, alterations in the brain response to these stimuli were observed. In a subgroup of COCP users with significantly reduced serum testosterone, however, lower temperatures were required. Region-of-interest analysis revealed that within key regions of the descending pain inhibitory system, activity in response to noxious stimulation varied with serum testosterone levels in both groups of women. Of particular interest, in COCP users, activity in the rostral ventromedial medulla increased with increasing testosterone and in those women with low testosterone, was significantly reduced compared to controls. These findings suggest that, in a low endogenous estradiol state, testosterone may be a key factor in modulating pain sensitivity via descending pathways. Specifically, failure to engage descending inhibition at the level of the rostral ventromedial medulla may be responsible for the reduction in temperature required by COCP users with low circulating testosterone.
authors: Centre for Functional Magnetic Resonance Imaging of the Brain, Nuffield Department of Clinical Neurosciences, Nuffield Division of Anaesthetics, University of Oxford, UK Nuffield Department of Obstetrics and Gynaecology, University of Oxford, UK.
authors: Katy
authors: K
authors: Vincent
authors: Catherine
authors: C
authors: Warnaby
authors: Charlotte J
authors: CJ
authors: Stagg
authors: Jane
authors: J
authors: Moore
authors: Stephen
authors: S
authors: Kennedy
authors: Irene
authors: I
authors: Tracey
mesh_terms: D000328:Adult; D001921:Brain / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D003277:Contraceptives, Oral, Combined / Q000494:pharmacology; D004958:Estradiol / Q000097:blood*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008597:Menstrual Cycle / Q000097:blood / Q000187:drug effects; D009434:Neural Pathways / Q000098:blood supply / Q000187:drug effects / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010146:Pain / Q000378:metabolism / Q000473:pathology*; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation / Q000009:adverse effects; D011601:Psychophysics; D013739:Testosterone / Q000097:blood*; D013997:Time Factors; D055815:Young Adult
chemical_list: D003277:Contraceptives, Oral, Combined; D013739:Testosterone; D004958:Estradiol; D010100:Oxygen