Hormones, Mood and Cognition
Abstract: Ovarian steroid hormones are neuroactive steroids with widespread actions in the brain, and are thus able to influence mood, behavior and cognition. In this thesis the effects of progesterone withdrawal and the direct effects of the progesterone metabolite allopregnanolone are evaluated. Allopregnanolone, through binding to the GABAA receptor complex, enhances inhibitory neurotransmission, thus exerting anxiolytic, sedative and antiepileptic effects. The acoustic startle response (ASR) is a withdrawal reflex evoked by sudden or noxious auditory stimuli, and can be measured in humans as an eye blink. ASR is significantly increased in several anxiety disorders, and notably also during progesterone withdrawal. Sensorimotor gating can be assessed by measuring prepulse inhibition of the startle response (PPI). The CNS circuits regulating PPI are sensitive to hormone fluctuations. GABAergic drugs are involved in cognitive impairment and animal studies have indicated that allopregnanolone may inhibit learning.The main purpose of this research was to evaluate the behavioral effects of progesterone withdrawal on the startle response and sensorimotor gating in PMDD patients and healthy controls, in healthy third trimester pregnant women and healthy postpartum women. A second aim was to evaluate allopregnanolone effects on memory and cognition in healthy women and also on the startle response and PPI. We found that PMDD patients have an increased startle response across the menstrual cycle and a deficiency in sensorimotor gating during the late luteal phase. Ovarian steroids affect sensorimotor gating; pregnant women have lower levels of PPI than late postpartum women. Acutely administered allopregnanolone did not affect the ASR or PPI. Allopregnanolone impairs episodic memory in healthy women.In conclusion, our studies suggest that ovarian steroids, including allopregnanolone, do not influence the startle response. Ovarian steroids affect sensorimotor gating; pregnancy, a condition with high levels of ovarian steroids, suppresses PPI. Theoretically, the variability in PPI across reproductive events is due to effects mediated by the progesterone or estradiol receptors but is not mediated by allopregnanolone. PMDD patients display decreased PPI during the late luteal phase, suggesting underlying pathophysiology in common with other anxiety disorders. The most vulnerable memory system, the episodic memory, is impaired by the allopregnanolone in healthy women.
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