11. Neuroimaging menstrual cycle associated changes in appetite

Abstract

The menstrual cycle provides a unique physiological paradigm in which to study ingestive behaviour. Caloric intake varies during the menstrual cycle in response to changes in ovarian steroid levels. Food intake is highest during the luteal phase and early follicular phase before declining in the second week of the follicular phase, reaching a nadir around the time of ovulation. This reduction in caloric intake is the result of the periovulatory increase in estrogen which exerts an anorexigenic effect at the level of the brain. Increased food intake in the early follicular phase and luteal phase results from reduced estrogen signaling due to low estrogen levels and increased progesterone levels respectively. In addition to altering expression of hypothalamic neuropeptides that respond to hormonal signals of energy balance, ovarian steroids influence non-homeostatic ingestive behavior by affecting corticolimbic brain regions. Neuroimaging studies demonstrate that activation of the amygdala/hippocampal complex, ventral striatum, and prefrontal cortex by rewarding stimuli is increased during the late follicular phase compared to the luteal phase or early follicular phase. This difference may result from ovarian steroid effects on the mesolimbic dopamine system. Thus, increased dopamine signaling during the periovulatory period may be the key molecular mechanism responsible for reduced food intake at this time of the menstrual cycle. It is imperative that future neuroimaging studies involving women and reward incorporate menstrual cycle phase into the study design.