15 General introduction Neuroendocrinal regulation of social avoidance Hypothalamus Pituitary Male Testes Female Ovaries GnRH FSH, LH Testosterone Amygdala Striatum PFC Social threat A. B. Figure 1.2. Illustration of the HPG-axis and a simplified model of the approach enhancing properties of testosterone. A: Illustration of the hypothalamic–pituitary–gonadal axis (HPG-axis) activity of which leads to testosterone production. B: Simplified neural model of the proposed threat approach enhancing properties of testosterone based on neuroimaging studies verifying effects of testosterone administration during social threat challenges (such as visual presentation of an angry facial expression): testosterone enhances amygdala activity, dopaminergic projections from the amygdala to the striatum, and has been associated with reduced connectivity between the prefrontal cortex (PFC) and the amygdala. Note. GnRH = Gonadotropin-releasing hormone, FSH = Follicle-stimulating hormone, LH = Luteinizing hormone. + indicates excitatory connection; - indicates inhibitory connections. 1
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