Impaired type II glucocorticoid-receptor function in mice bearing antisense RNA transgene

Glucocorticoid receptor gene expression during rat embryogenesis. An in situ hybridization study

Glucocorticoids play an important role in embryonic development. The existence of sufficient amounts of their receptors during rodent embryogenesis has proved to be an absolute necessity for the physiological growth of the animal. We have analyzed the pattern of glucocorticoid receptor gene expression in the rat embryo through embryonic days 12 to 17, by using in situ hybridization histochemistry. Glucocorticoid receptor mRNA is present in the rat liver on embryonic day (E) 12, and by E13 the signal can also be detected in several other tissues, such as the lung, the heart, the mesonephros, the sclerotomes, the thymus and Rathke's pouch. Glucocorticoid receptor gene expression was quite ubiquitous in tissue derivatives of all three germ layers and appeared to vary in intensity within the same tissue during embryogenesis. These variations in the level of receptor gene expression paralleled the developmental stage of each tissue: Intense labelling was detected just prior to the final differentiation step of a structure. Upon differentiation, cell populations highly expressing glucocorticoid receptor gene in the previous stage were found to have reduced amounts of the receptor mRNA. Our results support a morphogenetic role for glucocorticoids during embryogenesis.

Antidepressants restore hypothalamic-pituitary-adrenal feedback function in aged, cognitively-impaired rats

Aged, cognitively-impaired rats (and humans) show hypothalamic-pituitary-adrenal (HPA) hyperactivity that correlates with hippocampal damage. The resultant increase in plasma glucocorticoid exposure is thought to contribute to impaired hippocampal function and to potentiate hippocampal neuron death. In young, adult rats antidepressant drugs increase corticosteroid receptor expression in brain regions known to regulate the HPA axis, leading to increased negative-feedback control and decreased HPA activity. In the present study we examined basal levels of plasma adrenocorticotropin hormone (ACTH) and corticosterone in aged, cognitively-impaired (AI), aged, cognitively-unimpaired (AU) and young, adult (Yg) rats. Plasma ACTH and corticosterone levels were significantly elevated in the AI rats, but only in samples obtained during the diurnal peak. Five weeks of treatment with desipramine (15 mg/kg) significantly reduced evening levels of both ACTH and corticosterone in all groups, and eliminated the group differences. We then examined delayed, glucocorticoid negative feedback in these animals. Among vehicle-treated animals, a bolus injection of corticosterone (10 mg/kg), administered 3 hours prior to testing, completely inhibited the plasma ACTH response to restraint in AU and Yg, but not AI animals. In contrast, plasma ACTH responses to restraint were completely inhibited in AI rats following chronic treatment with desipramine. These findings indicate that the antidepressant, desipramine, decreases HPA activity and increases glucocorticoid negative-feedback sensitivity in AI rats, suggesting that antidepressant drugs may form a useful therapeutic approach to HPA dysfunction in elderly human populations.

Transgenic Mouse Models: New Tools for Psychiatric Research

The revolution in molecular genetics promises to identify genes that are responsible for susceptibility to psychopathology and to clarify how genes interact with environmental factors. To date, most studies reporting abnormal behavior have disrupted one specific gene and examined changes in emotionality, cognition, and consumption of food or addictive drugs. Although relating the absence of the product of a deleted gene to a specific behavior is tempting, more refined analysis has shown that the phenotype of a mutant may be a combination of a lacking gene product and the organism's attempt to compensate for the loss. Thus, an absent behavioral phenotype in a mouse with targeted gene disruption does not necessarily indicate the irrelevance of a gene product for behavior, and, vice versa, a specific behavioral abnormality in a mutant does not allow for attribution of this alteration to the lacking gene product. With these limitations in mind, it becomes clear that psychiatric research can expect major profit from the more recently developed gene technologies. The possibility of directing a mutation to specific cell types and sites in the CNS avoids the confounds imposed by changed gene function throughout the body. With few exceptions, psychiatric disorders precipitate in adulthood; thus, an animal model is preferred where the gene under study can be site-specifically turned on or off by a drug-driven “genetic switch.” Recent developments suggest that such tempting research tools will become available in the near future. NEUROSCIENTIST 3:328–336, 1997

Mapping of mouse obesity genes: A generic approach to a complex trait

Identification of genes underlying any complex trait such as obesity is an important and difficult problem in genetics. Traditional candidate gene approaches cannot be relied on to identify all of the genes influencing a complex trait, and positional cloning is very laborious. With the advent of new tools and methods, however, comprehensive approaches to the identification of any genes underlying complex traits are now available. Quantitative trait locus (QTL) mapping is a general technique to map Mendelian factors influencing complex traits. The QTL approach involves the crossing of two strains that differ in the trait of interest to produce F2 or back-cross progeny, individually phenotyping and genotyping each progeny, and statistically associating the typed markers and the phenotype. QTL mapping has been used in the last 4 years to map genes for a wide variety of traits, including body weight and growth, obesity, atherosclerosis and susceptibility to cancer in the mouse, and hypertension, hyperactivity and arthritis in the rat. QTL mapping has also been used to map genes in pigs, poultry, cows, fish and plants. Once a trait has been located in a chromosomal subregion, identifying the underlying gene remains a significant problem. A monogenic model must be developed, isolating one gene influencing a trait from other genes affecting the same phenotype. Then the positional candidate strategy, which relies on a combination of mapping to a chromosomal subregion followed by a survey of the interval to see if attractive candidates reside there, becomes practical.

Hypothalamic-pituitary-adrenocortical axis changes in a transgenic mouse with impaired glucocorticoid receptor function

Recently, a transgenic mouse with impaired glucocorticoid receptor (GR) function was created to serve as an animal model for the study of neuroendocrine changes occurring in stress-related disorders, such as major depression. Here, we investigated the hypothalamic-pituitary-adrenocortical (HPA) axis changes in these transgenic mice. There were no significant differences between basal early morning plasma ACTH and corticosterone levels in normal and transgenic mice. When animals were exposed to a mild stressor, an enhanced response in plasma ACTH was observed in the transgenic mice, whereas plasma corticosterone responses were not different. In view of these differences in plasma ACTH and corticosterone responses, we directed our studies toward the regulation of ACTH secretion on the hypothalamic-hypophyseal level in vitro. Therefore, an in vitro model, the pituitary-hypothalamic complex (PHc) was developed and its ACTH release profile was compared with that of the pituitary (PI) alone. The basal ACTH release by PHc and PI from normal and transgenic mice was similar. Regardless of the strain under study, the basal ACTH release by PI was significantly lower than the release by PHc. Stimulation of tissues with either high K+ (56 mM) or CRH (10 or 20 nM) produced an enhanced ACTH release from both PHc and PI, whereas the response in PI was larger than that in PHC. Moreover, the responses to these stimuli were markedly enhanced in tissues from transgenic mice. In tissues of normal mice, corticosterone inhibited both basal and CRH-stimulated ACTH release more potently in PHc than in PI. Furthermore, the feedback capacity of corticosterone to restrain both basal and CRH-stimulated ACTH release was highly impaired in tissues of transgenic mice, whereas the feedback in PHc appeared to be more affected than that in the PI of these animals. In conclusion, the in vitro data on PHc and PI revealed intrahypothalamic mechanisms operating 1) to fine-tune stimulus-evoked ACTH responses; and 2) to facilitate the negative feedback action of glucocorticoids. Moreover, in the transgenic tissues, the impaired GR function was found to cause augmented stimulus-evoked ACTH responses and an impaired glucocorticoid feedback efficacy which appeared to be mainly defective at the hypothalamic level. Thus, in the transgenic mice with life-long central GR dysfunction we found impaired negative feedback combined with "normal" (i.e. noncompensated) in vivo plasma corticosterone responses. This is a condition with potentially grave pathophysiological consequences and, therefore, this transgenic animal may be regarded as a valuable model for the study of functional glucocorticoid insufficiency at the central nervous system level.

Corticotropin-releasing factor and glucocorticoid receptor (GR) gene expression in the paraventricular nucleus of immune-challenged transgenic mice expressing type II GR antisense ribonucleic acid

The purpose of this study was to investigate the effect of the immune activator lipopolysaccharide (LPS) on the expression of corticotropin-releasing factor (CRF) and glucocorticoid receptor (GR) mRNA in the paraventricular nucleus (PVN) of transgenic mice with impaired GR function caused by endogenous expression of GR antisense RNA. At 3 and 8 wk of age, control and transgenic mice were sacrificed 4.5 h after a single ip administration of LPS (100 micrograms/100 g of body wt) or vehicle. Frozen brains were mounted on a microtome and cut in 20-microns sections. mRNAs encoding CRF and GR were assayed by in situ hybridization histochemistry using 35S-labeled riboprobes, and localization of Fos-immunoreactive (Fos-ir) nuclei was determined by immunocytochemistry. Basal expression of CRF mRNA in the PVN, central nucleus of the amygdala (CeA), and geniculate complex (GN) was similar in the control and transgenic mice. LPS induced a comparable neuronal activation in the PVN of control and transgenic mice as revealed by the number of Fos-ir neurons. Moreover, the endotoxin caused a significant increase in the CRF mRNA levels within the PVN and CeA, an effect observed in both animal models. The endotoxin did not notably modulate CRF expression in other regions, such as GN. Although GR mRNA was expressed in the PVN of control mice under basal conditions, this transcript was not detected in this hypothalamic structure in LPS-treated and transgenic animals. This indicated that endogenous Type II GR mRNA is decreased in the PVN of mice expressing Type II GR antisense RNA and that gene is downregulated by LPS. Hybridization signal for CRF and GR transcripts was not notably altered by the age of mice. These results provide evidence that the basal expression of CRF and the increase of neuroendocrine CRF transcription in response to immunogenic challenges are not significantly affected by impairment of the Type II GR function.

Selective suppression of CD44 in keratinocytes of mice bearing an antisense CD44 transgene driven by a tissue-specific promoter disrupts hyaluronate metabolism in the skin and impairs keratinocyte proliferation

CD44 is a broadly distributed polymorphic glycoprotein that serves as the principal cell-surface receptor for hyaluronate. Although CD44-mediated cell interaction with hyaluronate has been implicated in a variety of physiologic events, including cell-cell and cell-substrate adhesion, cell migration, proliferation, and activation, as well as hyaluronate uptake and degradation, the biologic role of CD44 in vivo in various tissues remains to be determined. In the present work we have developed transgenic mice that express an antisense CD44 cDNA driven by the keratin-5 promoter. These mice lack detectable CD44 expression in skin keratinocytes and corneal epithelium and display abnormal hyaluronate accumulation in the superficial dermis and corneal stroma, distinct morphologic alterations of basal keratinocytes and cornea, and defective keratinocyte proliferation in response to mitogen and growth factors. These alterations are reflected by a decrease in skin elasticity, impaired local inflammatory response and tissue repair, delayed hair regrowth, and failure of the epidermis to undergo hyperplasia in response to carcinogen. Our observations indicate that two major functions of CD44 in skin are the regulation of keratinocyte proliferation in response to extracellular stimuli and the maintenance of local hyaluronate homeostasis.

Pediatric obesity. An overview of etiology and treatment

Pediatric obesity is a chronic and growing problem for which new ideas about the biologic basis of obesity offer hope for effective solutions. Prevalence of pediatric and adult obesity is increasing despite a bewildering array of treatment programs and severe psychosocial and economic costs. The definition of obesity as an increase in fat mass, not just an increase in body weight, has profound influence on the understanding and treatment of obesity. In principle, body weight is determined by a balance between energy expenditure and energy intake, but this observation does not by itself explain obesity. There is surprisingly little evidence that the obese overeat and only some evidence that the obese are more sedentary. Understanding of the biologic basis of obesity has grown rapidly in the last few years, especially with the identification of a novel endocrine pathway involving the adipose tissue secreted hormone leptin and the leptin receptor that is expressed in the hypothalamus. Plasma leptin levels are strongly correlated with body fat mass and are regulated by feeding and fasting, insulin, glucocorticoids, and other factors, consistent with the hypothesis that leptin is involved in body weight regulation and may even be a satiety factor (Fig. 2, Table 1). Leptin injections have been shown to reduce body weight of primates, although human clinical trials will not be reported until summer 1997. So many peptides influencing feeding have been described that one or more may have therapeutic potential (Fig. 2, Table 1). Although the complexity of pathways regulating body weight homeostasis slowed the pace of understanding underlying mechanisms, these complexities now offer many possibilities for novel therapeutic interventions (Fig. 2). Obesity is a major risk factor for insulin resistance and diabetes, hypertension, cancer, gallbladder disease, and atherosclerosis. In particular, adults who were obese as children have increased mortality independent of adult weight. Thus, prevention programs for children and adolescents will have long-term benefits. Treatment programs focus on modification of energy intake and expenditure through decreased calorie intake and exercise programs. Behavior-modification programs have been developed to increase effectiveness of these intake and exercise programs. These programs can produce short-term weight loss. Long-term losses are more modest but achieved more successfully in children than in adults. Several drug therapies for obesity treatment recently have been approved for adults that produce sustained 5% to 10% weight losses but experience with their use in children is limited. Identification of the biochemical pathways causing obesity by genetic approaches could provide the theoretic foundation for novel, safe, and effective obesity treatments. The cloning of leptin in 1994 has already led to testing the efficacy of leptin in clinical trials that are now underway. Although novel treatments of obesity are being developed as a result of the new biology of obesity, prevention of obesity remains an important goal.

Considerations on genetic and environmental factors that contribute to resistance or sensitivity of mammals including humans to toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. Part 1: Genetic factors affecting the toxicity of TCDD

The marked species differences in short-term toxicity (30-day LD50) of ca. 10,000 (LD50: guinea pigs ca. 1 microgram/kg body wt and Han/Wistar Kuopio rats more than 9600 micrograms/kg body wt) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is one of the central issues of the controversies that have developed on the validity of risk assessment strategies for TCDD and related compounds. One of the most challenging issues that toxicologists face today is the identification of genes that contribute to or are responsible for increased resistance or sensitivity to TCDD and related compounds. It is assumed that most, if not all, toxic effects of TCDD are mediated more or less through the binding affinity to the Ah receptor. This hypothesis was extended and tries to explain the differences in sensitivity/resistance of animals including humans to TCDD by their total fat (lipid) content. In this respect the gene or genes which is or are responsible for obesity of mammals including humans are of great interest. An obvious linear positive logarithmic relationship between the oral 30-day LD50 (microgram/kg) of TCDD in different species and strains of mammals and their total body fat content (TBF%) was found: log LD50 = 5.30 x log (TBF)-3.22, or LD50 = 0.000603 x (TBF)5.30. By means of this regression the toxicity of TCDD in mammals including humans of different age and/or body weight can be predicted if their total body fat content is known. Examples of single-gene and polygenic disease models in different mammals, such as nonobese diabetic, diabetic, viable yellow, obese, and fat mice, as well as transgenic mice, and other suitable animal models, such as fatty Zucker rats, Han/Wistar (Kuopio) rats, and minipigs, are discussed, and predicted LD50 values of TCDD in these animals and humans are presented.

Downregulation of RARα in Mice by Antisense Transgene Leads to a Compensatory Increase in RARβ and RARγ and Development of Lymphoma

Retinoic acid receptors (RARs) α, β, and γ contain retinoic acid response elements (RAREs) in their promoter regions and respond to their own activation, thus forming an autoregulatory loop. We generated transgenic mice that expressed an antisense construct of the RARα. Homozygous transgenic mice demonstrated 30% to 80% reduction in RARα protein expression in various tissues. Unlike RARα null mice generated by knockout, our antisense mice demonstrated significant compensatory increases in the expression of RARβ and RARγ proteins. Coarse fur, male sterility, and low body weight were other abnormalities observed in these mice. Most importantly, lymphoma developed in 44% of our homozygous transgenic mice at an early stage of life. These data suggest that RARα is necessary for appropriate response of the RARβ and RARγ genes to physiologic changes and deregulation of the RARα in transgenic mice, which resulted in upregulation of RARβ and RARγ, can be associated with lymphomagenesis. Thus, the data support the hypothesis that a balance among the RARs is necessary for appropriate response to various homeostatic needs.

Spatial memory in transgenic mice with impaired glucocorticoid receptor function

Spatial learning and memory function of transgenic mice with impaired glucocorticoid receptor function was assessed in the Morris water maze and the radial arm maze. Transgenic mice took longer to find a submerged and a visual platform in the water maze task than did mice from the parent strain (B6C/3F1), although performance was improved in the visible platform condition relative to the submerged platform task. In the radial arm maze, transgenic mice made significantly more errors than B6C/3F1 mice. In both tasks, the behavioural strategies adopted by transgenic mice were non-optimal for correct performance. It is suggested that the impaired performance displayed by transgenic mice in both tests is largely attributable to these altered behavioural strategies.

Human serum reactivity to porcine endothelial cells after antisense-mediated down-regulation of GpIIIa expression

The hyperacute rejection of vascularized grafts exchanged between discordant species is a result of the binding of preformed natural antibodies to the endothelium of the donor organ, and the subsequent activation of the complement system. Human natural antibodies to pig endothelial cell antigens appear to be predominantly directed at carbohydrate epitopes expressed by a variety of porcine integrins, including GpIIIa. The identification of porcine xenoantigens whose recognition by human natural antibodies results in hyperacute rejection would allow for the development of strategies to genetically modify the xenograft reaction. We have used antisense technology to down-regulate the expression of one of seven recently identified xenoantigens from the surface of pig aortic endothelial cells. Down-regulation of GpIIIa on endothelial cells resulted in a 20.8% decrease in the mean channel shift (MCS) of IgM natural antibody binding from pooled human sera, and a 28-35% decrease in the MCS of IgM binding from two high-titer individuals. The MCS for human IgG natural antibody binding to the surface of pig cells decreased by 27%. Natural antibody-mediated cytotoxicity to pig endothelial cells was not significantly altered, as indicated by a 2.5-6% decline in complement-mediated cytotoxicity. These results indicate that down-regulation of GpIIIa alone may not be sufficient to significantly alter xenograft rejection. Our results also suggest, however, that antisense-mediated regulation of a functionally important target antigen is technically feasible and may represent a strategy to prevent the xenograft reaction.

Transgenic animals as new approaches in pharmacological studies

Transgenic animals are becoming useful tools for pharmacological studies. The use of transgenic technology raises two types of questions, "How are transgenic animals made?" and "What types of pharmacological questions can be answered using transgenic technologies?" Answers to these questions are discussed in this review. The production of animals with specific genetic alteration can be achieved by two strategies. The first involves the simple addition of DNA sequences to the chromosomes. The second strategy is to select particular genetic loci for site-specific changes. There are two well-established procedures for simple introduction of DNA into an animal genome, pronuclear DNA injection and transduction using a retrovirus. In contrast, methods for targeting specific DNA sequences to definite sites in the chromosomes are evolving rapidly. Some of these procedures can be used in combination to make a different variety of gene alterations in animals. Pharmacological studies where transgenic technology has been extensively used are discussed, including studies in the cardiovascular system, the nervous system, the endocrine system, cancer, and toxicology.

Antisense and ribozyme constructs in transgenic animals

Geneticists have long sought the ability to add or subtract individual genes from an organism's genome, or to be able to alter the level of expression of a gene in a targeted, developmentally and tissue-specific manner. The development of transgenic technology realized the possibilities of increasing the expression of a specific gene or the transfer of a new gene into an animal. Homologous recombination techniques allow the deletion or alteration of a gene in vivo. The production of transgenic animals incorporating a gene construct that expresses a complimentary antisense RNA to a targeted gene, or an antisense RNA incorporating a catalytic, ribozyme sequence, have been suggested as a potential mechanism for obtaining the developmentally and tissue-specific down-regulation of expression of a targeted gene in vivo. In this paper we review the current literature with respect to the application of antisense and ribozyme constructs in transgenic animals and conclude that such constructs can effectively downregulate the level of mRNA from a target gene, the amount of protein produced in the cell, and result in phenotypic consequences.

Cross-talk between the T cell antigen receptor and the glucocorticoid receptor regulates thymocyte development

The fate of an immature thymocyte, life or death, is largely determined by the ligand-specificity of its T cell antigen receptor (TCR). The default pathway for thymocytes bearing TCRs with subthreshold avidity for self-antigens is death (death by neglect). Thymocytes bearing TCRs with high avidity for self also undergo apoptosis (negative selection). Those thymocytes with intermediate avidities, or that perhaps recognize self-peptides that have partial agonist or antagonist properties, survive and differentiate into mature immunocompetent T cells (positive selection). How TCR avidity is interpreted as a "rescue" signal or a death signal is unknown. Based upon a T cell hybridoma model, our laboratory proposed that glucocorticoids, which themselves are potent inducers of thymocyte apoptosis, antagonize TCR-mediated thymocyte deletion and allow positive selection to occur. In fact, epithelial cells in the thymus proved to be a source of steroid production, and interference with steroid synthesis in fetal thymic organ culture resulted in a greatly enhanced sensitivity of thymocytes to TCR-mediated apoptosis. Transgenic mice with reduced glucocorticoid receptor (GR) levels were produced by tissue-specific expression of GR antisense. Thymocytes in these mice had high levels of spontaneous apoptosis, and were exquisitely sensitive to deletion induced by cross-linking the TCR. Moreover, there was a very large (> or = 90%) loss of CD4+CD8+ thymocytes, signifying a block at the CD4-CD8- to CD4+CD8+ transition, perhaps due to apoptosis of cells upon engagement of the pre-TCR in the absence of an antagonizing glucocorticoid stimulus. The molecular mechanism of the antagonism is currently being investigated. These data indicate that there is cross-talk in thymocytes between the TCR and glucocorticoid signaling pathways resulting in apoptosis, and that locally produced steroids, in a paracrine fashion, participate in setting the TCR avidity thresholds that determine whether developing thymocytes survive or die, and therefore help to mold the antigen-specific T cell repertoire.

Depression as a spreading neuronal adjustment disorder

The outlines of a theory of the pathophysiology of depression are presented. The classic monoamine theory of depression as well as its more recent elaborations suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity and, concomitantly, exaggerated responses to acute increases in presynaptic firing rate and transmitter release. We propose that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus, which in turn leads to dysregulation of 5-HT-ergic and dopaminergic neurotransmission.

Deficits in memory and hippocampal long-term potentiation in mice with reduced calbindin D28K expression

The influx of calcium into the postsynaptic neuron is likely to be an important event in memory formation. Among the mechanisms that nerve cells may use to alter the time course or size of a spike of intracellular calcium are cytosolic calcium binding or "buffering" proteins. To consider the role in memory formation of one of these proteins, calbindin D28K, which is abundant in many neurons, including the CA1 pyramidal cells of the hippocampus, transgenic mice deficient in calbindin D28K have been created. These mice show selective impairments in spatial learning paradigms and fail to maintain long-term potentiation. These results suggest a role for calbindin D28K protein in temporally extending a neuronal calcium signal, allowing the activation of calcium-dependent intracellular signaling pathways underlying memory function.

Ciliary neurotrophic factor constitutively expressed in the nervous system of transgenic mice protects embryonic dorsal root ganglion neurons from apoptosis

Ciliary neurotrophic factor (CNTF) is a potent survival factor for several neuronal populations. It is expressed postnatally by Schwann cells in the peripheral nervous system and by some glial and neuronal cells in the central nervous system. We used the promoter of the neurofilament light chain gene to produce transgenic mice that express CNTF in neurons from the beginning of neuronal differentiation. These transgenic animals may represent a suitable model to identify neuronal cell types responsive to CNTF in vivo and to study the mechanism of action of this neurotrophic factor. We show that dorsal root ganglion neurons of transgenic mice expressing CNTF in neurons are protected from apoptosis during embryonic development: 40% of these cells undergo apoptosis between embryonic day 12.5 and postnatal day 5 in transgenic mice whereas 60% do so in control animals. However, protection from apoptosis does not result in an increase in the total number of neurons at the end of development. We discuss our results with regard to CNTF potentialities in vivo and the significance of programmed cell death during development.

Morphine-induced locomotor and neurochemical stimulation is enhanced in transgenic mice with impaired glucocorticoid receptor function

It has been suggested that the hypothalamic-pituitary-adrenocortical (HPA) system contributes to individual differences in sensitivity towards drug abuse. Therefore, we studied the effects of the prototypic drug morphine in transgenic mice with impaired glucocorticoid receptor function. This mouse model has a profoundly dysfunctional HPA feedback. Since morphine-induced locomotor stimulation is positively correlated with the rewarding effects of morphine, we examined morphine-induced locomotor activity of transgenic mice and control mice (B6C3F1). Because morphine-induced locomotor activity depends on an intact mesolimbic system, dopaminergic (DAergic) neuronal activity was also estimated within the mesolimbic system. Results indicated that the activity after vehicle injection do not differ between these two mouse lines. Compared to vehicle injections, morphine (7.5 and 15 mg/kg; i.p.) dose-dependently increased motor activity for 3 h in control and transgenic mice. However, morphine-induced locomotion was significantly more pronounced in transgenic mice. Further, morphine-induced mesolimbic DAergic activity was enhanced in transgenic animals as compared to control animals. These results parallel endocrine data that show that the plasma ACTH level of transgenic mice reach higher levels compared to those levels observed in control mice after morphine injections. Altogether, this transgenic mouse line shows an enhanced locomotor-stimulant effect to morphine, a response that is reflected by an enhanced DAergic activity within the mesolimbic system and is also associated with increased HPA activity. We submit that the dysregulation of the HPA system in these transgenic mice influences the enhanced vulnerability to drug-seeking behavior.

Depression-related cognitive impairment: possibilities for its pharmacological treatment

Depression-related cognitive impairment (DRCI) is a condition which despite its initial treatment response, shows a progressive deterioration. No consistent therapeutic strategies have been proposed to combat this condition. This may be due to a reluctance to treat the cognitively impaired, a failure to recognise the deleterious prognosis or a poor understanding of the likely pathogenesis. Increasing evidence implicates the hypothalamo-pituitary-adrenal (HPA) axis as a key neurobiological determinant of the presentation and course of depression-induced cognitive decline. By utilising agents which control central glucocorticoid hyperactivity over a sustained period, whilst avoiding those agents which may compromise cognitive abilities, there exists a pharmacological strategy which may minimise the morbidity of cognitive impairment related to depressive illness.

Neuroendocrineimmunology (NEI) at the turn of the century: towards a molecular understanding of basic mechanisms and implications for reproductive physiopathology

The interactions between the nervous, endocrine and immune systems require a complex communication network. The central nervous system (CNS) affects the immune system through endocrine, paracrine and neuronal mechanisms. Evidence that this bidirectional communication plays a vital role in the regulation of physiological homeostatic mechanisms while a disfunction of the neuroendocrineimmune balance favors the susceptibility to a number of diseases is derived largely by animal models but also by an increasing number of clinical studies in different fields, including endocrinology, reproductive physiology, pediatrics, oncology, neurology and psychiatry. An increasing number of endocrine hormones, neurotransmitters and neuropeptides are expressed in immune tissues and cells and are actively involved in the physiological regulation of immunity. Conversely, the endocrine and nervous systems harbor receptors for a wide variety of immunologically-derived substances, suggesting potential regulatory feedback loops between the three major integrative bodily systems. Major implications for the reproductive endocrinology field are that psychoneuroendocrine processes may alter fertility via immunomodulation, and that events that occur as part of immune responses influence the neuroendocrine axes, which in turn counter-regulate immune function. In the present article, some features of reproductive-immune interactions will be described, and the neuroendocrineimmune dialogue via the chief reproductive hormone, luteinizing hormone-releasing hormone (LHRH), will be summarized as prototype of intersystem crosstalk. A particular emphasis will be given to the cytokine-LHRH interrelationships both at central (i.e. especially with the astroglial compartment) and peripheral levels. The surprisingly similar communication network systems used by the gonads and the thymus will be summarized, and the sexually-driven dimorphisms dictating female versus male reproductive and immunological capacities reviewed. Evidence that neural, endocrine and immune systems work together as a single unit are emphasized in animal models and human pathologies where interruption of NEI feedback loops results in long lasting pathological consequences for the nervous, endocrine and immune functions.

Long-term antidepressant treatment reduces behavioural deficits in transgenic mice with impaired glucocorticoid receptor function

Impaired cognitive function and enhanced activity of the hypothalamic-pituitary-adrenocortical system are among the cardinal symptoms of major depression in humans that resolve after successful antidepressant treatment. We used a transgenic mouse model expressing antisense RNA complementary to that of glucocorticoid receptor (GR) mRNA to test the hypothesis that reduced GR function can cause these clinical disturbances. The transgenic mice show profound behavioural changes in a number of animal tests that are indicative of cognitive impairment. These mice also have elevated plasma corticotropin concentrations in response to stress. After long-term treatment with moclobemide, a reversible inhibitor of monoamine oxidase type A that acts clinically as an antidepressant, both the behavioural deficits and the hormonal alterations disappeared. These observations suggest that a transgenic mouse with GR dysfunction may be a useful model for investigation of drug effects on the cognitive and neuroendocrine aspects of depression.

A targeted glucocorticoid receptor antisense transgene increases thymocyte apoptosis and alters thymocyte development

The exquisite sensitivity of thymocytes to steroid-induced apoptosis, the steroidogenic potential of thymic epithelial cells, and the ability of steroid synthesis inhibitors to enhance antigen-specific deletion of thymocytes in fetal thymic organ cultures suggest a role for glucocorticoids in thymocyte development. To address this further, transgenic mice that express antisense transcripts to the glucocorticoid receptor (GR) specifically in immature thymocytes were generated. The consequent hyporesponsiveness of thymocytes to glucocorticoids was accompanied by a reduction in thymic size, primarily owing to a decrease in the number of CD4+CD8+ cells. While an enhanced susceptibility to T cell receptor (TCR)-mediated apoptosis appeared to be partially responsible for this reduction, thymocyte loss could also be detected before thymocytes progressed to the CD4+CD8+ TCR alpha beta-expressing stage. These results suggest that glucocorticoids are necessary for survival and maturation of thymocytes, and are consistent with a role for steroids in both the transition from CD4-CD8- to CD4+CD8+ cells and the survival of CD4+CD8+ cells stimulated via the TCR.

Use of transgenics, null mutants, and antisense approaches to study ethanol's actions

Behavioral and biochemical responses mediating ethanol's actions have been difficult to study in humans and animals because of their complex polygenic nature. Recent progress in the creation of new animal models using recombinant DNA technology has provided a set of genetic tools by which the role of specific candidate genes in ethanol's actions can be examined. These techniques include the creation of transgenic and null mutant mice, as well as manipulation of protein synthesis with antisense treatments. These techniques are reviewed, and their potential applications to alcohol research are discussed.

Transient inhibition of angiotensinogen production in transgenic mice bearing an antisense angiotensinogen gene

Angiotensinogen is the precursor of the biologically active hormone angiotensin II. Enzyme kinetic parameters suggest that concentrations of plasma angiotensinogen are rate limiting in the renin reaction. It is therefore assumed that a decrease in angiotensinogen synthesis in vivo would result in a decrease in angiotensin II plasma levels and then of blood pressure. To test this hypothesis, we generated a transgenic mouse line that carries an inducible antisense angiotensinogen gene. Transient inhibition of angiotensinogen synthesis could be demonstrated in these transgenic animals. However, the amounts of liver angiotensinogen message and plasma angiotensinogen concentrations were rapidly back to levels observed in control animals.

Individual differences in hypothalamic-pituitary-adrenal activity in later life and hippocampal aging

Variation in magnitude of cognitive decline in later life is a central feature of human aging. The more severe forms of dementias, such as Alzheimer's disease, clearly define one end of the spectrum. However, among those showing no obvious signs of clinical dementia there are considerable individual differences. Thus, although evidence for learning, memory, and language loss appears in some individuals as early as 50-55 years of age, many people continue to function alertly well into their 90s. These individuals exemplify what Rowe and Kahn (1987) have termed "successful" aging. The wide variability in CNS aging, often a nuisance factor in studies, are becoming a major focus for brain aging research (e.g., Gage et al., 1984;Gallager and Pelleymounter, 1988; Aitken and Meaney, 1990; Issa et al., 1990). Our studies over the past few years have added support to the idea that individual differences in hypothalamic-pituitary-adrenal (HPA) activity can account for part of the variation seen in neurological function among the elderly. In this article we discuss the evidence for the idea that adrenal glucocorticoids can compromise hippocampal function and, thus, produce cognitive impairments, as well as the potential mechanisms for these effects.

Glucocorticoid resistance in humans

Generalized inherited glucocorticoid resistance is a rare disorder caused by glucocorticoid receptor mutations and characterized clinically by hypercortisolism. Pituitary and peripheral resistance are balanced so that neither adrenal insufficiency nor Cushingoid features develop. Clinical characteristics reflect overproduction of adrenal androgens and mineralocorticoids, which are caused by excess stimulation of the adrenal gland by ACTH. These clinical characteristics respond to dexamethasone therapy. Localized and/or acquired glucocorticoid resistance may occur in some circumstances.

The genetics of obesity: from genetic epidemiology to molecular markers

Obesity is a highly prevalent disease that carries enormous human and economic costs in western nations. The complexity and diversity of the paths leading to an overweight or an obesity status are enormous. The etiology, causes, associated morbidity, treatment, benefits versus risks of weight loss, prevention, and other aspects of obesity are all highly complex and intimately associated with other diseases, the prevalence of which is augmented by our present way of life. This article gives a brief overview of the current status of knowledge of the genetic basis of human obesity from a genetic epidemiology, experimental genetic and molecular biology perspective. It appears likely that the susceptibility to obesity depends, to a large extent, on several autosomal genes.

Anorexia nervosa viewed as an extreme weight condition: genetic implications

In anorexia nervosa, psychopathological features and reduced body weight are inseparable, suggesting a prominent role of behavioral factors in achievement and maintenance of extreme underweight. Due to the considerably higher prevalence of this eating disorder in females, anorexia nervosa contributes to the left end of the distribution of the body mass index, especially in the female sex. By reviewing the relevant literature we examined whether genetic research in anorexia nervosa can profit from considering this disorder as an extreme weight condition. For this purpose we compared genetic studies pertaining to both anorexia nervosa and the heritability of the body mass index. Whereas previous genetic studies in anorexia nervosa have mostly concentrated on the assessment of the familial psychopathology, further studies are warranted that additionally attempt to analyze the complex phenotype body weight in relatives of affected probands. Further insight into pathogenetic mechanisms underlying anorexia nervosa might be gained by contrasting the epidemiological, psychopathological and prognostic factors with those in severe obesity. Thus, epidemiological studies suggest that females are more likely to develop both extreme underweight and extreme obesity. A possible explanation for this phenomenon is that the, on average, higher percentage of total body weight composed of fat mass might predispose females towards the development of both extreme weight conditions.

Neuropeptide Y, the hypothalamus, and diabetes: insights into the central control of metabolism

Neuropeptide Y (NPY), a major brain neurotransmitter, is expressed in neurons of the hypothalamic arcuate nucleus (ARC) that project mainly to the paraventricular nucleus (PVN), an important site of NPY release. NPY synthesis in the ARC is thought to be regulated by several factors, notably insulin, which may exert an inhibitory action. The effects of NPY injected into the PVN and other sites include hyperphagia, reduced energy expenditure and enhanced weight gain, insulin secretion, and stimulation of corticotropin and corticosterone release. The ARC-PVN projection appears to be overactive in insulin-deficient diabetic rats, and could contribute to the compensatory hyperphagia and reduced energy expenditure, and pituitary dysfunction found in these animals; overactivity of these NPY neurons may be due to reduction of insulin's normal inhibitory effect. The ARC-PVN projection is also stimulated in rat models of obesity +/- non-insulin diabetes, possibly because the hypothalamus is resistant to inhibition by insulin; in these animals, enhanced activity of ARC NPY neurons could cause hyperphagia, reduced energy expenditure, and obesity, and perhaps contribute to hyperinsulinemia and altered pituitary secretion. Overall, these findings suggest that NPY released in the hypothalamuss, especially from the ARC-PVN projection, plays a key role in the hypothalamic regulation of energy balance and metabolism. NPY is also found in the human hypothalamus. Its roles (if any) in human homeostasis and glucoregulation remain enigmatic, but the animal studies have identified it as a potential target for new drugs to treat obesity and perhaps NIDDM.

Do antidepressants stabilize mood through actions on the hypothalamic-pituitary-adrenocortical system?

Patients suffering from severe depression often show an increased activity of the hypothalamic-pituitary-adrenocortical (HPA) system, a premature escape from the cortisol suppressant action of dexamethasone, and a number of other neuroendocrine changes. This might be explained by defective glucocorticoid feedback inhibition. Normalization of the hyperactive HPA system occurs during successful antidepressant pharmacotherapy of depressive illness, and this could be achieved by antidepressant-induced increases in the cellular corticosteroid receptors, rendering the HPA system more susceptible to feedback inhibition by cortisol. Both mineralocorticoid- and glucocorticoid-receptor mRNA levels and hormone-binding activities are found to be increased following treatment of different cell lines or animals with antidepressants. Since the timecourse of antidepressant actions on corticosteroid receptors follows more closely that of clinical improvement of depression, antidepressants might elevate mood in depressives through their long-term effects on HPA regulation.

Evaluation of an antisense RNA transgene for inhibiting growth hormone gene expression in transgenic rats

We compared the levels of growth hormone (GH) mRNA in the pituitary, plasma GH concentration, and altered phenotype in rats heterozygous and homozygous for an antisense RNA transgene targeted to the rat GH gene, with those in nontransgenic rats. We initially investigated whether the transgene promoter, which is connected to four copies of a thyroid hormone response element (TRE) that increases promoter activity, affected in vivo transgene expression in the pituitary of the transgenic rats. Plasma GH concentration correlated negatively with T3 injection in surgically thyroidectomized heterozygous transgenic rats. There was a reduction of about approximately 35-40% in GH mRNA levels in the pituitary of homozygous animals compared with those in non-transgenic rats. Plasma GH concentration was significantly approximately 25-32 and approximately 29-41% lower in heterozygous and homozygous transgenic rats, respectively, compared with that in nontransgenic animals. Furthermore, the growth rates in homozygous transgenic rats were reduced by approximately 72-81 and approximately 51-70% compared with those of their heterozygous and nontransgenic littermates, respectively. The results of these studies suggested that the biological effect of GH in vivo is modulated dose-dependently by the antisense RNA transgene. The rat GH gene can therefore be targeted by antisense RNA produced from a transgene, as reflected in the protein and RNA levels.

Transgenic glutathione peroxidase mouse models for neuroprotection studies

Seleno-glutathione peroxidase (GSHPx) is considered to be the major enzymatic activity in charge of removing excess cytosolic and mitochondrial H2O2 in most tissues including brain. Intracellular GSHPx activity is therefore hypothesized to be one important factor that contributes to minimize hydroxyl radical formation via Fenton-type reactions. An animal model was developed to challenge this hypothesis in vivo and evaluate the role of GSHPx in hydroperoxide metabolism and oxidative stress homeostasis. Three lines of transgenic mice, homozygous for the integration of 1 to 3 GSHPx transgene copies, have been generated. The transgene was placed under transcriptional control of a metallothionein promoter (hMT-IIA). This promoter was chosen because metallothionein expression, normally low in most tissues, can be induced by several inflammatory cytokines, protein kinase C activators, and stress agents including heavy metals. The data reported here provide information on the constitutive expression of GSHPx mRNA and enzyme in various brain regions of healthy untreated adult tg-MT-GPx mice. Northern and/or Western analysis indicated that transgenic GSHPx was expressed constitutively in all brain regions investigated in tg-MT-GPx-6 mice, including the cerebral cortex, brainstem, hippothalamus, cerebellum, substantia nigra, and striatum. Similar results were obtained with the two other transgenic lines, tg-MT-GPx-11 and -13. Depending on the brain region, the GSHPx immunoreactivity detected in tissue extracts with an immunoaffinity-purified polyclonal antibody was about 2- to 5-fold stronger in transgenic extracts than in their non-tg counterparts (western blots). In contrast, the corresponding increase in GSHPx activity measured in these extracts was smaller, for example, about 1.5-fold in transgenic mesencephalon. Immunocytochemical data indicated that GSHPx-like staining was distinctly more intense in transgenic midbrain brain sections than in corresponding non-tg sections. Interestingly, only a subset of the cells displayed higher density staining that most likely reflects increased amounts of GSHPx protein. This observation suggests that the stained cells, not yet identified, may have larger GSHPx activity increments than the cell-average increments measured in tissue extracts. Current work is in progress to determine whether transgenic GSHPx expression may be induced by inflammatory processes or perturbations of heavy metal metabolism.

Paradoxical production of target protein using antisense RNA expression vectors

We used antisense RNA in a protocol designed to reduce estrogen receptor (ER) content in human breast cancer cells and observed paradoxical increases in ER levels. ER protein activity was measured using a highly sensitive reporter gene assay that relies on the ability of functional ER to bind a consensus estrogen response element (ERE) and drive the production of chloramphenicol acetyl-transferase (CAT). Upon transient transfection of ER-positive cell lines with three different vectors containing the full-length ER cDNA cloned in an antisense orientation, we observed unexpected increases in ER-driven CAT activity. To further investigate this phenomenon, expression from the antisense ER vectors was studied in an ER-negative breast tumor cell line, MDA-MB-453. ER activity was observed in these ER-negative cells upon transient transfection with each of three antisense ER vectors, but not from control vectors. Expression of ER from antisense constructs was 30-100-times less efficient than ER expression from isogenic sense constructs. The paradoxical ER activity was consistent with expected ER behavior in that it exhibited characteristic binding to the natural ligand, 17 beta-estradiol (E2), and it was inhibited by the antiestrogens, 4-hydroxy-tamoxifen (OHT) and ICI 164384 (ICI). Control vectors containing a truncated antisense ER cDNA produced no ER activity. Although the mechanism for this ER expression has not been determined, it appears likely that it is due to transcription off the opposite strand of the antisense construct.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and Characterization of Glucocorticoid Receptors in Liver of Nude Mice

Glucocorticoids regulate the expression of many liver-specific genes via glucocorticoid receptors. The presence of glucocorticoid receptors in liver has been reported in many mammalian species but not in nude mice. In the present study, we demonstrate the presence of specific glucocorticoid receptors in nude mouse liver. The binding of ligands to these receptors could be completely inhibited by RU486, and partially blocked by hydrocortisone and progesterone, whereas estrogen and testosterone had no effect. Hydrocortisone downregulated the level of glucocorticoid receptors in livers of nude mice and correspondingly enhanced the activities of tyrosine aminotransferase and gamma-glutamyltransferase. Our results indicate that glucocorticoid receptors in nude mouse liver are specific, fully functional, and present at levels 28.5-fold higher than in the liver of normal inbred mice. We suggest that the nude mouse is a valuable model for studies of hepatic glucocorticoid action and may provide a clue to a putative hepatic-thymic interaction. Copyright 1994 S. Karger AG, Basel

Analysing brain function and dysfunction in transgenic animals

Many neuropsychiatric disorders have a genetic aetiology. In vivo gene modification offers a route to simulating such disorders in transgenic animals, allowing a systematic study of the underlying pathophysiology. However, attempts to mimic diseases such as Alzheimer's disease in transgenic animals have not yet been successful. This principally reflects our lack of knowledge concerning normal brain function, and an understanding of the biochemical mechanisms underlying cognitive processes is a primary objective. We and others have therefore focused on the hippocampus, a brain region involved in learning and memory and an early target for degeneration in Alzheimer's disease. Genetic intervention to date has yielded transgenic animals with apparent functional deficits in the hippocampus, leading the way to a greater understanding of brain function.

Partial rescue of a lethal phenotype of fragile bones in transgenic mice with a chimeric antisense gene directed against a mutated collagen gene

Previously, transgenic mice were prepared that developed a lethal phenotype of fragile bones because they expressed an internally deleted mini-gene for the pro alpha 1(I) chain of human type I procollagen. The shortened pro alpha 1(I) chains synthesized from the human transgene bound to and produced degradation of normal pro alpha 1(I) chains synthesized from the normal mouse alleles. Here we assembled an antisense gene that was similar to the internally deleted COL1A1 minigene but the 3' half of the gene was inverted so as to code for an antisense RNA. Transgenic mice expressing the antisense gene had a normal phenotype, apparently because the antisense gene contained human sequences instead of mouse sequences. Two lines of mice expressing the antisense gene were bred to two lines of transgenic mice expressing the mini-gene. In mice that inherited both genes, the incidence of the lethal fragile bone phenotype was reduced from 92% to 27%. The effects of the antisense gene were directly demonstrated by an increase in the ratio of normal mouse pro alpha 1(I) chains to human mini-pro alpha 1(I) chains in tissues from mice that inherited both genes and had a normal phenotype. The results raise the possibility that chimeric gene constructs that contain intron sequences and in which only the second half of a gene is inverted may be particularly effective as antisense genes.

Animal models of obesity--theories of aetiology

The multiplicity of proposed mechanisms for obesity is confusing and many questions remain to be answered. A review of all the proposed mechanisms for obesity suggests that they can be placed in two groups (Table 3). The first centres on the role of the hypothalamus in the regulation of body weight. With further knowledge it may be possible to find unifying mechanisms originating in the brain for the set-point theory, the autonomic nervous system imbalance hypothesis, the thermogenesis, hyperphagia and the hyperinsulinaemia hypotheses and the gestational undernutrition hypothesis. This group of mechanisms suggests that obesity is due to altered function of central regulatory mechanisms and that the various related hypotheses are merely looking at different aspects of the same problem. The second centres on abnormalities intrinsic to the adipocyte and could link the fat cell and perinatal overnutrition theories. This group of theories suggests that an abnormality at the fat cell level, either genetic or acquired, can result in the excessive accumulation of fat. The two groups are not contradictory. The ability to develop obesity as a result of a fat cell abnormality does not negate the existence of regulatory central mechanisms since there is a finite capacity for these mechanisms to operate.

Reduced beta 2-microglobulin mRNA levels in transgenic mice expressing a designed hammerhead ribozyme

We have generated three artificial hammerhead ribozymes, denoted 'Rz-b', 'Rz-c' and 'Rz-d', with different specificities for exon II of the mouse beta-2-microglobulin (beta 2M) mRNA. In this study we tested for ribozyme mediated reduction of beta 2M mRNA in a cell line and in transgenic mice. Transfections of either of the Rz-b, Rz-c or Rz-d plasmids into a mouse cell-line (NIH/3T3) revealed reductions of beta 2M mRNA substrate in each case. Ribozyme expression in individual transfected clones was accompanied with an up to 80% reduction of beta 2M mRNA levels. Rz-c was selected for a transgenic study. Seven Rz-c transgenic founder animals were identified from which three ribozyme expressing families were established and analysed. Expression of the ribozyme transgene was tested for and detected in lung, kidney and spleen. Expression was accompanied with reduction of the beta 2M mRNA levels of heterozygous (Rz+/-) animals compared to non-transgenic litter mates. The effect was most pronounced in lung with more than 90% beta 2M mRNA reduction in individual mice. In summary, expression of our ribozymes in a cell free system, in a cell-line and in transgenic mice were all accompanied with reductions of beta 2M mRNA levels.

Inhibition of bone resorption in vitro by antisense RNA and DNA molecules targeted against carbonic anhydrase II or two subunits of vacuolar H(+)-ATPase

The bone resorbing cells, osteoclasts, express high levels of carbonic anhydrase II (CA II) and vacuolar H(+)-ATPase (V-ATPase) during bone resorption. We have used antisense RNA and DNA molecules targeted against CA II, and against 16- and 60-kD subunits of vacuolar H(+)-ATPase (V-ATPase), to block the expression of these proteins in vitro. Osteoclastic bone resorption was studied in two in vitro culture systems: release of 45Calcium from prelabeled newborn mouse calvaria cultures, and resorption pit assays performed with rat osteoclasts cultured on bovine bone slices. Both antisense RNA and DNA against CA II and the V-ATPase were used to compare their specificities as regards inhibiting bone resorption in vitro. The antisense molecules inhibited the synthesis of these proteins by decreasing the amounts of mRNA in the cells in a highly specific manner. In osteoclast cultures treated with the 16-kD V-ATPase antisense RNA, acidification of an unknown population of intracellular vesicles was highly stimulated. The acidification of these vesicles was not sensitive to amiloride or bafilomycin A1. This suggests the existence of a back-up system for acidification of intracellular vesicles, when the expression of the V-ATPase is blocked. Our results further indicate that blocking the expression of CA II and V-ATPase with antisense RNA or DNA leads to decreased bone resorption.

Effects of the altered serotonergic signalling by neonatal treatment with 5,7-dihydroxytryptamine, ritanserin or clomipramine on the adrenocortical stress response and the glucocorticoid receptor binding in the hippocampus in adult rats

The aim of the present study is to investigate the effect of neonatal alterations in 5-HT signalling on the regulation of endocrine stress response in adult rats. The neonatal blockade of 5-HT transmission by 5,7-DHT or ritanserin treatment did not alter the density of glucocorticoid receptor (GR) binding sites in the hippocampus, although a 5,7-DHT-induced lesion was clearly shown to decrease in 5-HT content by greater than 80% in the hippocampus. In addition, the animals pretreated with the blockade of 5-HT transmission during early life did not exhibit a hyperresponsiveness of the adrenocortical response to stress. On the other hand, the neonatal administration of the 5-HT uptake inhibitor, clomipramine, was shown to lower the stress responsiveness of the adrenocortical axis in adulthood.

Antisense strategies for the control of aberrant gene expression

Antisense nucleic acids have been shown to be potent and specific inhibitors of gene expression and viral replication in cells from various species, including mammals. Their potential applicability in vivo has been demonstrated by the use of antisense oligonucleotides and antisense RNA transcribed from recombinant antisense genes, respectively. It is conceivable that both classes of antisense nucleic acids can be used to correct pathogenic cellular or viral gene expression, thereby extending the range of therapeutic options from new techniques developed in the field of molecular biology. Possible improvements in the inhibitory potential of antisense nucleic acids and selected points to consider concerning their design, their function, and their application are discussed.

Dexamethasone nonsuppression in transgenic mice expressing antisense RNA to the glucocorticoid receptor

Transgenic mice with impaired glucocorticoid receptor (GR) function produced by partially knocking out GR gene expression with antisense RNA were treated with increasing dosages of dexamethasone. In these mice, ten-fold higher dexamethasone dosages were required to induce full suppression of plasma corticosterone than in normal mice. This relative dexamethasone insensitivity adds to the evidence that these transgenic mice could serve as an appropriate model to study the negative feedback disturbance of the hypothalamic-pituitary-adrenocortical system in affective disorders.

Hormonal control of neural function in the adult brain

Although the mechanisms by which peripheral hormones modulate complex behaviors are far from being well understood, recent advances in deciphering the mechanisms of hormone action in the brain are promising. Current areas of interest include the molecular mechanisms of steroid receptor action, the steroid modulation of synaptic function, and the mediation of steroid-regulated neuronal and glial plasticity by growth factors or proteins associated with brain development.