Acute and chronic effects of estrogenic compounds on glutamate-stimulated phosphatidylinositol metabolism in primary neuronal cultures

Sex-specific neuroendocrine and behavioral phenotypes in hypomorphic Type II Neuregulin 1 rats

Neuregulin 1 (NRG1) is an important growth factor involved in the development and plasticity of the central nervous system. Since its identification as a susceptibility gene for schizophrenia, several transgenic mouse models have been employed to elucidate the role NRG1 may play in the pathogenesis of psychiatric disease. Unfortunately very few studies have included females, despite the fact that some work suggests that the consequences of disrupted NRG1 expression may be sex-specific. Here, we used Nrg1 hypomorphic (Nrg1(Tn)) Fischer rats to demonstrate sex-specific changes in neuroendocrine and behavioral phenotypes as a consequence of reduced Type II NRG1 expression. We have previously shown that male Nrg1(Tn) rats have increased basal corticosterone levels, and fail to habituate to an open field despite normal overall levels of locomotor activity. The current studies show that, in contrast, female Nrg1(Tn) rats exhibit enhanced suppression of corticosterone levels following an acute stress, reduced locomotor activity, and enhanced habituation to novel environments. Furthermore, we also show that female, but not male, Nrg1(Tn) rats have impaired prepulse inhibition. Finally, we provide evidence that sex-specific changes are not likely attributable to major disruptions in the hypothalamic-pituitary-gonadal axis, as measures of pubertal onset, estrous cyclicity, and reproductive capacity were unaltered in female Nrg1(Tn) rats. Our results provide further support for both the involvement of NRG1 in the control of hypothalamic-pituitary-adrenal axis function and the sex-specific nature of this relationship.

Rapid, nongenomic steroid actions: A new age?

In the traditional theory of steroid action, steroids bind to intracellular receptors and modulate nuclear transcription after translocation of steroid-receptor complexes into the nucleus. Due to similarities of molecular structure, specific receptors for steroids, vitamin D(3) derivatives, and thyroid hormone are considered to represent a superfamily of steroid receptors. While genomic steroid effects characterized by their delayed onset of action and their sensitivity to blockers of transcription and protein synthesis have been known for several decades, rapid actions of steroids have been more widely recognized and characterized in detail only recently. Rapid effects of steroids, thyroid hormones, and the steroid hormone metabolite of vitamin D(3), 1alpha, 25-dihydroxyvitamin D(3), on cellular signaling and function may be transmitted by specific membrane receptors. Binding sites in membranes have been characterized, exposing binding features compatible with an involvement in rapid steroid signaling. Characteristics of putative membrane receptors are completely distinct from intracellular steroid receptors, a fact which is further supported by the inability of classic steroid receptor antagonists to block nongenomic steroid actions. A putative progesterone membrane receptor has been cloned and functionally expressed with regard to progesterone binding. Development of drugs that specifically affect nongenomic action alone or even both modes of action may find applications in various, areas such as in the cardiovascular and central nervous systems and treatment of preterm labor, infertility, and electrolyte abnormalities.

Nongenomic steroid actions: fact or fantasy?

In the common theory of steroid action, steroids bind to intracellular receptors and modulate nuclear transcription after translocation of steroid--receptor complexes into the nucleus. Due to homologies of molecular structure, specific receptors for steroids, vitamin D3, and thyroid hormone are considered to represent a superfamily of steroid receptors. While genomic steroid effects being characterized by their delayed onset of action and their sensitivity to blockers of transcription and protein synthesis have been known for several decades, very rapid actions of steroids have been more widely recognized and characterized in detail only recently. Rapid effects of steroids, vitamin D3, and thyroid hormones on cellular signaling and function may be transmitted by specific membrane receptors. Although no receptor of this kind has been cloned up to now, binding sites in membranes have been characterized exposing binding features compatible with an involvement in rapid steroid signaling. Characteristics of putative membrane receptors were completely different from those of intracellular steroid receptors, which was further supported by the inability of classic steroid receptor antagonists to inhibit nongenomic steroid actions. Development of drugs that specifically affect nongenomic action alone or even both modes of actions may find applications in various areas such as the cardiovascular and central nervous systems and treatment of preterm labor, infertility, and electrolyte homeostasis. To acquaint the reader with major aspects of nongenomic steroid actions, these effects on cellular function will be summarized, potentially related binding sites in membranes discussed, and the physiological or pathophysiological relevance of nonclassic actions exemplified.