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Article

Dayna L. Averitt, Rebecca S. Hornung, and Anne Z. Murphy

The modulatory influence of sex hormones on acute pain, chronic pain disorders, and pain management has been reported for over seven decades. The effect of hormones on pain is clearly evidenced by the multitude of chronic pain disorders that are more common in women, such as headache and migraine, temporomandibular joint disorder, irritable bowel syndrome, chronic pelvic pain, fibromyalgia, rheumatoid arthritis, and osteoarthritis. Several of these pain disorders also fluctuate in pain intensity over the menstrual cycle, including headache and migraine and temporomandibular joint disorder. The sex steroid hormones (estrogen, progesterone, and testosterone) as well as some peptide hormones (prolactin, oxytocin, and vasopressin) have been linked to pain by both clinical and preclinical research. Progesterone and testosterone are widely accepted as having protective effects against pain, while the literature on estrogen reports both exacerbation and attenuation of pain. Prolactin is reported to trigger pain, while oxytocin and vasopressin have analgesic properties in both sexes. Only in the last two decades have neuroscientists begun to unravel the complex anatomical and molecular mechanisms underlying the direct effects of sex hormones and mechanisms have been reported in both the central and peripheral nervous systems. Mechanisms include directly or indirectly targeting receptors and ion channels on sensory neurons, activating pain excitatory or pain inhibitory centers in the brain, and reducing inflammatory mediators. Despite recent progress, there remains significant controversy and challenges in the field and the seemingly pleiotropic role estrogen plays on pain remains ambiguous. Current knowledge of the effects of sex hormones on pain has led to the burgeoning of gender-based medicine, and gaining further insight will lead to much needed improvement in pain management in women.

Article

Caleigh Guoynes and Catherine Marler

How hormones and neuromodulators initiate and maintain paternal care is important for understanding the evolution of paternal care and the plasticity of the social brain. The focus here is on mammalian paternal behavior in rodents, non-human primates and humans. Only 5% of mammalian species express paternal care, and many of those species likely evolved the behavior convergently. This means that there is a high degree of variability in how hormones and neuromodulators shape paternal care across species. Important factors to consider include social experience (alloparental care, mating, pair bonding, raising a previous litter), types of care expressed (offspring protection, providing and sharing food, socio-cognitive development), and timing of hormonal changes (after mating, during gestation, after contact with offspring). The presence or absence of infanticide towards offspring prior to mating may also be a contributor, especially in rodents. Taking these important factors into account, we have found some general trends across species. (1) Testosterone and progesterone tend to be negatively correlated with paternal care but promote offspring defense in some species. The most evidence for a positive association between paternal care and testosterone have appeared in rodents. (2) Prolactin, oxytocin, corticosterone, and cortisol tend to be positively correlated. (3) Estradiol and vasopressin are likely nuclei specific—with some areas having a positive correlation with paternal care and others having a negative association. Some mechanisms appear to be coopted from females and others appear to have evolved independently. Overall, the neuroendocrine system seems especially important for mediating environmental influences on paternal behavior.

Article

Danielle S. Stolzenberg, Kimberly L. Hernandez-D'Anna, Oliver J. Bosch, and Joseph S. Lonstein

For female mammals, caring for young until weaning or even longer is an extension of the reproductive burden that begins at insemination. Given the high price females potentially pay for failing to transmit genetic material to future generations, a multitude of interacting endocrine, neuroendocrine, and other neurochemical determinants are in place to ensure competent maternal caregiving by the time the offspring are born. Achieving this high maternal competency at parturition seems effortless but is quite a feat given that many nulliparous and parentally inexperienced female mammals are more prone to ignore, if not outright harm, conspecific neonates. There are important roles for ovarian steroids (e.g., estradiol and progesterone), adrenal steroids (e.g., glucocorticoids), and neuropeptide hormones (e.g., prolactin, oxytocin, arginine-vasopressin, and corticotropin-releasing factor) released during pregnancy, parturition, and postpartum in the onset and maintenance of caregiving behaviors in a broad range of commonly studied animals including rats, mice, rabbits, sheep, and primates. It is especially remarkable that the same collection of hormones influences caregiving similarly across these diverse animals, although to varying degrees. In addition to the well-known effects of hormones and neuropeptides on motherhood, more recent research indicates that experience-dependent epigenetic effects are also powerful modulators of the same neural substrates that can influence maternal responding.