COMMENTARY
Intersections of Sex and Corticotropin-Releasing Factor Shannon L. Gourley and Jane R. Taylor
S
ince its original identification and characterization in 1981 by Vale et al. (1), corticotropin-releasing factor (CRF)—now also called corticotropin-releasing hormone—has been intimately linked with stress regulation and conditioned fear and anxiety. For example, knockout of the CRF receptor 1 (CRFr1) has anxiolytic effects (2,3), while CRF overexpression increases conditioned fear (4). With the increasing availability of highly selective tools, roles for CRF in discrete cell populations have also been established. For example, Gafford et al. (5) selectively knocked down gamma-aminobutyric acid (GABA) Aα1 receptor subunits in CRF-containing cells within the amygdala. This procedure impaired fear extinction; in other words, mice with this highly selective deficiency are incapable of learning that a previously shock-associated cue is no longer threatening, implicating CRF systems in pathologies such as posttraumatic stress disorder. In the current issue, a new report by Bale and colleagues importantly considers sexually dimorphic sensitivities to CRF. This is critical because women are far more likely to report and seek treatment for stressor-related psychopathologies, but preclinical research overwhelmingly uses male rodents as subjects despite this fact, and rigorous methods for the determination of sex-specific differences in brain functions are widely available [cf. (6–8)]. Starting from the commonly held perspective that stressorrelated disease may emerge through excessive activation of CRFr1, Howerton et al. (9) intensively investigated the behavioral and physiological sensitivities of both male and female rodents to CRFr1 antagonism. Focused on the dorsal raphe, the hub of serotonin synthesis, Howerton et al. (9) hypothesized that differential sensitivity to CRF systems within the dorsal raphe between male and female subjects might account for differential prevalence of stressor-related disease and potentially for the failure of CRFr1 antagonists in clinical trials aimed at treating depression and anxiety (Figure 1). Howerton et al. (9) report for the first time clear behavioral differences between the sexes in response to an infusion of a CRFr1 antagonist directly into the dorsal raphe. For example, CRFr1 antagonism blocks stressor-induced corticosterone secretion, decreases immobility in the tail suspension test, and reduces anxiety-like behavior…but only in male rodents and not in female rodents. At a cellular level, CRF infusion increased the expression of c-Fos within the dorsal raphe in males, but levels were paradoxically decreased in females. This effect was most apparent in the dorsomedial and lateral wings of the dorsal raphe, which are associated with uncontrollable stressor exposure and anxietylike behavior. From the Department of Pediatrics (SLG), Emory University School of Medicine, Yerkes National Primate Research Center, Atlanta, Georgia; and Departments of Psychiatry and Psychology (JRT), Yale University School of Medicine, New Haven, Connecticut. Address correspondence to Shannon L. Gourley, Ph.D., Emory University, Yerkes National Primate Research Center, 954 Gatewood Road NE, Atlanta GA 30329; E-mail: [email protected]. Received Mar 18, 2014; accepted Mar 19, 2014.
0006-3223/$36.00 http://dx.doi.org/10.1016/j.biopsych.2014.03.021
The authors then analyzed sex differences in the expression of CRFr1 on local GABAergic neurons, revealing a surprising finding —reduced, rather than increased, expression in females. Thus, rather than increased CRFr1-mediated GABAergic tone in female rodents, the authors propose that differences in CRF-mediated neuronal excitability might be due to currently unknown sex differences in intracellular mechanisms, e.g., in receptor signaling or trafficking. Additional key findings were that serotoninexpressing neuron excitability was reduced in females relative to males, as well as evidence of sex differences in presynaptic GABAergic input onto serotonin neurons. These fundamental sex differences may contribute to increased risk of stressor-related psychiatric disease in women. And as discussed by the authors, sex differences may account for why no CRFr1 antagonists have completed phase III clinical trials. In addition to these critical new findings, Howerton et al. (9) provide another valuable resource: an up-to-date summary of CRFr1 clinical trials [(9),see Table 3). This table highlights the lack of efficacy of CRFr1 antagonists in trials focused on women. Notably, the only trial currently classified as successful included only male participants, suggesting that CRFr1 antagonists may be effective for men, though not women. Importantly, this outcome is directly in line with basic research using animal models, since the vast majority of this research uses male rodents. What does the future hold for research regarding CRF approaches to treating psychiatric disease? First, additional tools for basic research are still necessary; for example, despite the utility of reporter mice (such as the line used in the present study), antibodies that discern between CRFr1 and CRF receptor 2 are still needed. Further, future studies could identify whether sex hormones influenced the findings reported here, since the mice in this report were gonadally intact (modeling gonadally intact women). But more importantly, the stark differences between male and female rodents reported by Howerton et al. (9) argue strongly for the necessity of neuroscientists to consider female animals/subjects in their studies. In this spirit, recent addictionrelated research in our groups has shown that chromosomal sex is a primary factor in the formation of habitual alcohol seeking (10), and sex determines the habit-inducing effects of cocaine (L. DePoy, B.S., et al., unpublished data, March 29, 2014), adding to an extensive literature on the influence of sex in aspects of addiction. Identification of chromosomal- and gonadal-based sex differences in disease and in sensitivity to novel pharmacotherapies may lead to more effective and specialized treatment approaches. As highlighted in Table 3 of Howerton et al. (9), it may also reveal unappreciated successes of animal research in males in identifying novel approaches to treating psychiatric disease in men. Indeed, rather than just a consideration of the importance of sexually dimorphic factors in disease risk and treatment outcome, it is essential to probe the complex interactions between chromosomal or gonadal sex and the intrauterine environment, epigenetics, and behavioral factors, such as stressors, if we are to BIOL PSYCHIATRY 2014;75:838–839 & 2014 Society of Biological Psychiatry
Commentary
Figure 1. A new report by Howerton et al. (9) identifies neurobiological factors that may explain why corticotrophin-releasing factor receptor 1 antagonists seem to have antidepressant actions in men but not women. (Illustration courtesy of Ms. Amanda Allen, Department of Pediatrics, Emory University School of Medicine).
take advantage of animal models of psychiatric disease to ultimately discover effective—individualized—therapies. The authors report no biomedical financial interests or potential conflicts of interest. 1. Vale W, Spiess J, Rivier C, Rivier J (1981): Characterization of a 41residue ovine hypothalamic peptide that stimulates secretion of corticotropin and beta-endorphin. Science 213:1394–1397.
BIOL PSYCHIATRY 2014;75:838–839 839 2. Timpl P, Spanagel R, Sillaber I, Kresse A, Reul JM, Stalla GK, et al. (1998): Impaired stress response and reduced anxiety in mice lacking a functional corticotropin-releasing hormone receptor 1. Nat Genet 19: 162–166. 3. Smith GW, Aubry JM, Dellu F, Contarino A, Bilezikjian LM, Gold LH, et al. (1998): Corticotropin releasing factor receptor 1-deficient mice display decreased anxiety, impaired stress response, and aberrant neuroendocrine development. Neuron 20:1093–1102. 4. Sink KS, Walker DL, Freeman SM, Flandreau EI, Ressler KJ, Davis M (2013): Effects of continuously enhanced corticotropin releasing factor expression within the bed nucleus of the stria terminalis on conditioned and unconditioned anxiety. Mol Psychiatry 18:308–319. 5. Gafford GM, Guo JD, Flandreau EI, Hazra R, Rainnie DG, Ressler KJ (2012): Cell-type specific deletion of GABA(A)α1 in corticotropinreleasing factor-containing neurons enhances anxiety and disrupts fear extinction. Proc Natl Acad Sci U S A 109:16330–16335. 6. Becker JB, Arnold AP, Berkley KJ, Blaustein JD, Eckel LA, Hampson E, et al. (2005): Strategies and methods for research on sex differences in brain and behavior. Endocrinology 146:1650–1673. 7. Becker JB, Monteggia LM, Perrot-Sinal TS, Romeo RD, Taylor JR, Yehuda R, Bale TL (2007): Stress and disease: Is being female a predisposing factor? J Neurosci 27:11851–11855. 8. McCarthy MM, Arnold AP, Ball GF, Blaustein JD, De Vries GJ (2012): Sex differences in the brain: The not so inconvenient truth. J Neurosci 32: 2241–2247. 9. Howerton AR, Roland AV, Fluharty JM, Marshall A, Chen A, Daniels D, et al. (2013): Sex differences in corticotropin-releasing factor receptor1 action within the dorsal raphe nucleus in stress responsivity. Biol Psychiatry 75:873–883. 10. Barker JM, Torregrossa MM, Arnold AP, Taylor JR (2010): Dissociation of genetic and hormonal influences on sex differences in alcoholismrelated behaviors. J Neurosci 30:9140–9144.
www.sobp.org/journal
Intersections of Sex and Corticotropin-Releasing Factor Shannon L. Gourley and Jane R. Taylor
S
ince its original identification and characterization in 1981 by Vale et al. (1), corticotropin-releasing factor (CRF)—now also called corticotropin-releasing hormone—has been intimately linked with stress regulation and conditioned fear and anxiety. For example, knockout of the CRF receptor 1 (CRFr1) has anxiolytic effects (2,3), while CRF overexpression increases conditioned fear (4). With the increasing availability of highly selective tools, roles for CRF in discrete cell populations have also been established. For example, Gafford et al. (5) selectively knocked down gamma-aminobutyric acid (GABA) Aα1 receptor subunits in CRF-containing cells within the amygdala. This procedure impaired fear extinction; in other words, mice with this highly selective deficiency are incapable of learning that a previously shock-associated cue is no longer threatening, implicating CRF systems in pathologies such as posttraumatic stress disorder. In the current issue, a new report by Bale and colleagues importantly considers sexually dimorphic sensitivities to CRF. This is critical because women are far more likely to report and seek treatment for stressor-related psychopathologies, but preclinical research overwhelmingly uses male rodents as subjects despite this fact, and rigorous methods for the determination of sex-specific differences in brain functions are widely available [cf. (6–8)]. Starting from the commonly held perspective that stressorrelated disease may emerge through excessive activation of CRFr1, Howerton et al. (9) intensively investigated the behavioral and physiological sensitivities of both male and female rodents to CRFr1 antagonism. Focused on the dorsal raphe, the hub of serotonin synthesis, Howerton et al. (9) hypothesized that differential sensitivity to CRF systems within the dorsal raphe between male and female subjects might account for differential prevalence of stressor-related disease and potentially for the failure of CRFr1 antagonists in clinical trials aimed at treating depression and anxiety (Figure 1). Howerton et al. (9) report for the first time clear behavioral differences between the sexes in response to an infusion of a CRFr1 antagonist directly into the dorsal raphe. For example, CRFr1 antagonism blocks stressor-induced corticosterone secretion, decreases immobility in the tail suspension test, and reduces anxiety-like behavior…but only in male rodents and not in female rodents. At a cellular level, CRF infusion increased the expression of c-Fos within the dorsal raphe in males, but levels were paradoxically decreased in females. This effect was most apparent in the dorsomedial and lateral wings of the dorsal raphe, which are associated with uncontrollable stressor exposure and anxietylike behavior. From the Department of Pediatrics (SLG), Emory University School of Medicine, Yerkes National Primate Research Center, Atlanta, Georgia; and Departments of Psychiatry and Psychology (JRT), Yale University School of Medicine, New Haven, Connecticut. Address correspondence to Shannon L. Gourley, Ph.D., Emory University, Yerkes National Primate Research Center, 954 Gatewood Road NE, Atlanta GA 30329; E-mail: [email protected]. Received Mar 18, 2014; accepted Mar 19, 2014.
0006-3223/$36.00 http://dx.doi.org/10.1016/j.biopsych.2014.03.021
The authors then analyzed sex differences in the expression of CRFr1 on local GABAergic neurons, revealing a surprising finding —reduced, rather than increased, expression in females. Thus, rather than increased CRFr1-mediated GABAergic tone in female rodents, the authors propose that differences in CRF-mediated neuronal excitability might be due to currently unknown sex differences in intracellular mechanisms, e.g., in receptor signaling or trafficking. Additional key findings were that serotoninexpressing neuron excitability was reduced in females relative to males, as well as evidence of sex differences in presynaptic GABAergic input onto serotonin neurons. These fundamental sex differences may contribute to increased risk of stressor-related psychiatric disease in women. And as discussed by the authors, sex differences may account for why no CRFr1 antagonists have completed phase III clinical trials. In addition to these critical new findings, Howerton et al. (9) provide another valuable resource: an up-to-date summary of CRFr1 clinical trials [(9),see Table 3). This table highlights the lack of efficacy of CRFr1 antagonists in trials focused on women. Notably, the only trial currently classified as successful included only male participants, suggesting that CRFr1 antagonists may be effective for men, though not women. Importantly, this outcome is directly in line with basic research using animal models, since the vast majority of this research uses male rodents. What does the future hold for research regarding CRF approaches to treating psychiatric disease? First, additional tools for basic research are still necessary; for example, despite the utility of reporter mice (such as the line used in the present study), antibodies that discern between CRFr1 and CRF receptor 2 are still needed. Further, future studies could identify whether sex hormones influenced the findings reported here, since the mice in this report were gonadally intact (modeling gonadally intact women). But more importantly, the stark differences between male and female rodents reported by Howerton et al. (9) argue strongly for the necessity of neuroscientists to consider female animals/subjects in their studies. In this spirit, recent addictionrelated research in our groups has shown that chromosomal sex is a primary factor in the formation of habitual alcohol seeking (10), and sex determines the habit-inducing effects of cocaine (L. DePoy, B.S., et al., unpublished data, March 29, 2014), adding to an extensive literature on the influence of sex in aspects of addiction. Identification of chromosomal- and gonadal-based sex differences in disease and in sensitivity to novel pharmacotherapies may lead to more effective and specialized treatment approaches. As highlighted in Table 3 of Howerton et al. (9), it may also reveal unappreciated successes of animal research in males in identifying novel approaches to treating psychiatric disease in men. Indeed, rather than just a consideration of the importance of sexually dimorphic factors in disease risk and treatment outcome, it is essential to probe the complex interactions between chromosomal or gonadal sex and the intrauterine environment, epigenetics, and behavioral factors, such as stressors, if we are to BIOL PSYCHIATRY 2014;75:838–839 & 2014 Society of Biological Psychiatry
Commentary
Figure 1. A new report by Howerton et al. (9) identifies neurobiological factors that may explain why corticotrophin-releasing factor receptor 1 antagonists seem to have antidepressant actions in men but not women. (Illustration courtesy of Ms. Amanda Allen, Department of Pediatrics, Emory University School of Medicine).
take advantage of animal models of psychiatric disease to ultimately discover effective—individualized—therapies. The authors report no biomedical financial interests or potential conflicts of interest. 1. Vale W, Spiess J, Rivier C, Rivier J (1981): Characterization of a 41residue ovine hypothalamic peptide that stimulates secretion of corticotropin and beta-endorphin. Science 213:1394–1397.
BIOL PSYCHIATRY 2014;75:838–839 839 2. Timpl P, Spanagel R, Sillaber I, Kresse A, Reul JM, Stalla GK, et al. (1998): Impaired stress response and reduced anxiety in mice lacking a functional corticotropin-releasing hormone receptor 1. Nat Genet 19: 162–166. 3. Smith GW, Aubry JM, Dellu F, Contarino A, Bilezikjian LM, Gold LH, et al. (1998): Corticotropin releasing factor receptor 1-deficient mice display decreased anxiety, impaired stress response, and aberrant neuroendocrine development. Neuron 20:1093–1102. 4. Sink KS, Walker DL, Freeman SM, Flandreau EI, Ressler KJ, Davis M (2013): Effects of continuously enhanced corticotropin releasing factor expression within the bed nucleus of the stria terminalis on conditioned and unconditioned anxiety. Mol Psychiatry 18:308–319. 5. Gafford GM, Guo JD, Flandreau EI, Hazra R, Rainnie DG, Ressler KJ (2012): Cell-type specific deletion of GABA(A)α1 in corticotropinreleasing factor-containing neurons enhances anxiety and disrupts fear extinction. Proc Natl Acad Sci U S A 109:16330–16335. 6. Becker JB, Arnold AP, Berkley KJ, Blaustein JD, Eckel LA, Hampson E, et al. (2005): Strategies and methods for research on sex differences in brain and behavior. Endocrinology 146:1650–1673. 7. Becker JB, Monteggia LM, Perrot-Sinal TS, Romeo RD, Taylor JR, Yehuda R, Bale TL (2007): Stress and disease: Is being female a predisposing factor? J Neurosci 27:11851–11855. 8. McCarthy MM, Arnold AP, Ball GF, Blaustein JD, De Vries GJ (2012): Sex differences in the brain: The not so inconvenient truth. J Neurosci 32: 2241–2247. 9. Howerton AR, Roland AV, Fluharty JM, Marshall A, Chen A, Daniels D, et al. (2013): Sex differences in corticotropin-releasing factor receptor1 action within the dorsal raphe nucleus in stress responsivity. Biol Psychiatry 75:873–883. 10. Barker JM, Torregrossa MM, Arnold AP, Taylor JR (2010): Dissociation of genetic and hormonal influences on sex differences in alcoholismrelated behaviors. J Neurosci 30:9140–9144.
www.sobp.org/journal
