Estrogen Regulation of mRNAs in the Brain and Relationship to Lordosis Behavior

Crosstalk between oestrogen receptors and thyroid hormone receptor isoforms results in differential regulation of the preproenkephalin gene

Nuclear receptors are ligand-activated transcription factors, which have the potential to integrate internal metabolic events in an organism, with consequences for control of behaviour. Previous studies from this laboratory have shown that thyroid hormone receptor (TR) isoforms can inhibit oestrogen receptor (ER)alpha-mediated induction of preproenkephalin (PPE) gene expression in the hypothalamus. Also, thyroid hormone administration inhibits lordosis, a behaviour facilitated by PPE expression. We have examined the effect of multiple ligand-binding TR isoforms on the ER-mediated induction of the PPE gene in transient transfection assays in CV-1 cells. On a natural PPE gene promoter fragment containing two putative oestrogen response elements (EREs), both ER alpha and beta isoforms mediate a four to five-fold induction by oestrogen. Cotransfection of TR alpha 1 along with ER alpha inhibited the ER alpha transactivation of PPE by approximately 50%. However, cotransfection with either TR beta 1 or TR beta 2 expression plasmids produced no effect on the ER alpha or ER beta mediated induction of PPE. Therefore, under these experimental conditions, interactions with a single ER isoform are specific to an individual TR isoform. Transfection with a TR alpha 1 DNA-binding mutant could also inhibit ER alpha transactivation, suggesting that competition for binding on the ERE may not be the exclusive mechanism for inhibition. Data with the coactivator, SRC-1, suggested that coactivator squelching may participate in the inhibition. In dramatic contrast, when ER beta is cotransfected, TR alpha 1 stimulated ER beta-mediated transactivation of PPE by approximately eight-fold over control levels. This is the first study revealing specific interactions among nuclear receptor isoforms on a neuroendocrine promoter. These data also suggest that the combinatorics of ER and TR isoforms allow multiple forms of flexible gene regulations in the service of neuroendocrine integration.

Vasopressin-induced antipyresis. Sex- and experience-dependent febrile responses

There is now good evidence that vasopressin (AVP) acts, in the male rat, as a neurotransmitter in the ventral septal area to reduce fever. In light of the well known sexual dimorphism in the AVP innervation of the brain, we asked if female rats would (a) display fevers different from those seen in male rats, (b) respond to AVP with antipyresis, (c) display evidence of endogenous AVP-induced antipyresis during fever, and (d) display altered fevers and AVP involvement as a function of hormonal status. Our experiments indicate that female rats display larger fevers to intracranial prostaglandin E2 (PGE2) but not to systemic lipopolysaccharide or interleukin-1 beta than do male rats. The larger fevers may be due, in part, to a lack of AVP-induced antipyresis, as an AVP antagonist elevates PGE2 fever in male but not in female rats and dialysates of the ventral septal area show increased AVP levels only in male rats during defervescence. Nonetheless, females respond to exogenous AVP with antipyresis. Throughout late pregnancy, parturition, and lactation, PGE2 fevers are reduced, but this appears to be due to a general suppression of autonomic output not involving enhanced AVP antipyresis. Fevers due to lipopolysaccharide and interleukin-1 beta are also suppressed at this time, and in some animals, fevers are dramatically suppressed at about the time of parturition. Our results indicate that female rats may utilize different strategies for antipyresis than do male rats and that hormonal status may influence both peripherally generated and centrally activated fevers.

Estrogen regulation of mu-opioid receptor mRNA in the forebrain of female rats

Previous studies have suggested that opioids play a role in the regulation of reproductive behaviors in the female rat. The present study examined whether estrogen treatment alters mu-opioid receptor mRNA levels in different areas of the forebrain of ovariectomized (OVX) female rats using the in situ hybridization technique. We observed an increase in mu-opioid receptor mRNA levels in the ventromedial nucleus of the hypothalamus (VMH) and arcuate nucleus (ARN) after 48 h of 10 microg of 17-beta-estradiol-3-benzoate treatment when compared to OVX females. No effects of estrogen were observed on mu-opioid receptor mRNA levels in the posterior medial nucleus of the amygdala (MeAmyg), hippocampus, caudate-putamen (CPu) or the medial habenula. Our result suggests that the estrogenic regulation of mu-opioid receptor in the CNS may in part be mediated by de novo synthesis and/or stability of the mu-opioid receptor message.

Estrogen regulation of preproenkephalin messenger RNA in the forebrain of female mice

We studied the effects of 10 micrograms of 17-beta-estradiol-3-benzoate treatment on preproenkephalin (PPE) mRNA expression in female ovariectomized (OVX) Swiss Webster mice after 0, 1, 6, 12, 24, or 48 h, using the in situ hybridization technique. The VMH showed a 1.6- and 3.3-fold increase in PPE mRNA levels after 24 and 48 h of estrogen treatment (respectively) when compared to OVX females. No differences at 1, 6 or 12 h of estrogen treatment groups were observed compared to control groups. PPE mRNA levels were also increased at 24 and 48 h after estrogen treatment in the posterior medial nucleus of the amygdala (MeAmyg) by 3.3- and 2.5-fold, respectively, and in the arcuate nucleus (ARC) by 2- and 1.9-fold, respectively. No effects of estrogen were observed on PPE mRNA levels in the caudate-putamen (CPu) or the posterior lateral cortical nucleus of the amygdala (plCoAmyg). Furthermore, basal levels of PPE mRNA expression in the VMH and MeAmyg of female mice were lower than those observed in rats, although levels in the CPu, plCoAmyg, and ARC were similar between females of the two species. In conclusion, we have found two differences between the species. First, Swiss mice demonstrated a slower time course of estrogen induction of PPE mRNA in the VMH, ARC. and MeAmyg compared to female rats. Second, there are differences in basal levels of PPE in the MeAmyg and VMH.

Steroid regulation of sexual behavior

Investigation into the hormonal control of sexual behavior has a rich and extensive history. For many researchers currently active in the field, the physiological psychologist Frank A. Beach is recognized as the modern father of the study of hormones and behavior. His publication of the seminal book Hormones and Behavior-A Survey of Interrelationships Between Endocrine Secretions and Patterns of Overt Response, published in 1948, was a compilation of the previous 20 years of research establishing that gonadal secretions acted in the brain and modulated behavior. The question of precisely how hormones can alter brain functioning in a coordinated fashion and profoundly influence the patterns of behavioral responsiveness remains unanswered. As with many research areas, application of new techniques and approaches to the problem reveals additional layers of complexity and previously unimagined relationships between hormones, brain, and behavior. In addition, with the increasing understanding that the brain is a target organ for steroids, the implications of the ramifications of this steroid sensitivity have broadened. The hormonal regulation of sexual behavior is not an isolated aspect of steroid action in the brain; rather, it is one component of a host of physiological responses influenced by steroids. These include such diverse responses as anxiety, aggression, feeding, and learning and memory. An appreciation of the diverse effects of steroids has emerged from studies on sexual behavior, and a mutually beneficial relationship between this and other aspects of behavioral neuroscience has flourished and endured. As with all of neuroscience, this research area has been dynamic and progressive and has additionally benefited from a long history of comparative and integrative approaches to animal behavior.

Nuclear matrix acceptor binding sites for steroid hormone receptors: a candidate nuclear matrix acceptor protein

Steroid/nuclear-hormone receptors are ligand-activated transcription factors that have been localized to the nuclear matrix. The classic model of hormone action suggests that, following activation, these receptors bind to specific "steroid response elements" on the DNA, then interact with other factors in the transcription initiation complex. However, evidence demonstrates the existence of specific chromatin proteins that act as accessory factors by facilitating the binding of the steroid receptors to the DNA. One such protein, the "receptor binding factor (RBF)-1", has been purified and shown to confer specific, high-affinity binding of the progesterone receptor to the DNA. Interestingly, the RBF-1 is localized to the nuclear matrix. Further, the RBF-1 binds specifically to a sequence of the c-myc proto-oncogene that has the appearance of a nuclear matrix attached region (MAR). These results, and other findings reviewed here, suggest that the nuclear matrix is involved intimately in steroid hormone-regulated gene expression.

Anesthesia during hormone administration abolishes the estrogen induction of preproenkephalin mRNA in ventromedial hypothalamus of female rats

Estrogen treatment increases preproenkephalin (PPE) mRNA levels in the ventromedial nucleus of the hypothalamus (VMH). Roy et al. (Brain Res., 337 (1985) 163-166) discovered that anesthesia during estrogen priming could reduce female rat sexual receptivity. In the present study we tested whether the action of estrogen to induce PPE gene expression in the VMH could be similarly affected by anesthesia. By quantitative in situ hybridization and slot-blot analysis techniques we found a 1.8-fold increase in PPE mRNA levels in the VMH after 1 hour of estrogen treatment in ovariectomized (OVX) Sprague-Dawley female rats. Anesthetizing the rats with pentobarbital for 1 h during the exposure to estrogen blocked the estrogen induction of PPE mRNA in the VMH. By way of contrast no changes in the PPE mRNA levels were observed in the caudate putamen. A similar trend was seen using chloral hydrate. It appears that neuronal activity is required for the early phase of estrogen induction of PPE mRNA levels in the VMH. This in turn could be correlated with changes in female sociosexual behaviors.