Dexamethasone and corticosterone receptor sites. Differential topographic distribution in rat hippocampus revealed by high resolution autoradiography

Hippocampal Subfields Volume Reduction in High Schoolers with Previous Verbal Abuse Experiences

Objective

Reduced hippocampal volume and alterations in white matter tracts have been frequently reported in adults having the history of emotional maltreatment. We investigated whether these structural change occur in adolescents with previous verbal abuse (VA) experiences.

Methods

Hippocampal subfield volume and white matter structural connectivity measures were assessed in 31 first year male high school students with various degrees of exposure to parental and peer VA.

Results

The high VA group showed significant volume reduction in the left cornu ammonis (CA) 1 and left subiculum compared to the low VA group (p＜0.05). Volumes of left hippocampal subfields CA1 and subiculum were negatively correlated with previous VA experiences (p＜0.05). Increased mean diffusivity (MD) of the splenium of the corpus callosum was related to high VA score across all subjects (p＜0.05). There was an inverse relationship between volume of the CA1 and subiculum and MD of the splenium (p＜0.05).

Conclusion

Exposure to parental and peer VA may affect development of the left hippocampal subfields and the splenium of corpus callosum. These structural alterations can be discernible during adolescence.

Childhood maltreatment, psychopathology, and the development of hippocampal subregions during adolescence

INTRODUCTION

It is well established that childhood maltreatment has a detrimental impact on the brain, particularly the hippocampus. However, the hippocampus is a functionally and structurally heterogeneous region, and little is known about how maltreatment might affect hippocampal subregion development throughout important periods of plasticity. This study investigated whether childhood maltreatment was associated with the development of hippocampal subregion volumes from early to late adolescence. It also investigated associations between onset of psychiatric disorder and hippocampal subregion volume development.

METHODS

One hundred and sixty-six (85 male) adolescents took part in three magnetic resonance imaging assessments during adolescence (mean age at each assessment: 12.79 [SD 0.43] years, 16.70 [SD 0.52] years, and 19.08 [SD 0.46] years), provided a self-report of childhood maltreatment, and were assessed for Axis I psychopathology.

RESULTS

Childhood maltreatment was associated with the development of right total and left cornu ammonis 4 (CA4-DG) volumes from early to late adolescence. Early and late onset psychopathology was associated with the development of right presubiculum and right cornu ammonis 1 (CA1) volumes, respectively. Maltreatment findings appeared to be specific to males, whereas psychopathology findings appeared to be specific to females.

CONCLUSIONS

These findings provide evidence for possible deleterious effects of childhood maltreatment and early onset psychiatric disorder on the development of different subregions of the hippocampus. Altered development of the right CA1, on the other hand, might precede the development of late-adolescent onset psychopathology. Our results highlight the importance of considering development in research examining associations between stress, mental illness, and hippocampal morphology.

Hippocampal subfield volumetry in patients with subcortical vascular mild cognitive impairment

Memory impairment is a typical characteristic of patients with subcortical vascular mild cognitive impairment (svMCI) or with amnestic mild cognitive impairment (aMCI). The hippocampus, which plays an important role in the consolidation of information from short-term memory to long-term memory, is a heterogeneous structure that consists of several anatomically and functionally distinct subfields. However, whether distinct hippocampal subfields are differentially and selectively affected by svMCI pathology and whether these abnormal changes in hippocampal subfields are different between svMCI and aMCI patients are largely unknown. A total of 26 svMCI patients, 26 aMCI patients and 26 healthy controls matched according to age, gender and years of education were enrolled in this study. We utilized an automated hippocampal subfield segmentation method provided by FreeSurfer to estimate the volume of several hippocampal subfields, including the cornu ammonis (CA) areas, the dentate gyrus (DG), the subiculum and the presubiculum. Compared with controls, the left subiculum and presubiculum and the right CA4/DG displayed significant atrophy in patients with svMCI. Interestingly, we also found significant differences in the volume of the right CA1 between the svMCI and aMCI groups. Taken together, our results reveal region-specific vulnerability of hippocampal subfields to svMCI pathology and identify distinct hippocampal subfield atrophy patterns between svMCI and aMCI patients.

Maternal restraint stress delays maturation of cation-chloride cotransporters and GABAA receptor subunits in the hippocampus of rat pups at puberty

The GABAergic synapse undergoes structural and functional maturation during early brain development. Maternal stress alters GABAergic synapses in the pup's brain that are associated with the pathophysiology of neuropsychiatric disorders in adults; however, the mechanism for this is still unclear. In this study, we examined the effects of maternal restraint stress on the development of Cation-Chloride Cotransporters (CCCs) and the GABA_A receptor α1 and α5 subunits in the hippocampus of rat pups at different postnatal ages. Our results demonstrate that maternal restraint stress induces a transient but significant increase in the level of NKCC1 (Sodium–Potassium Chloride Cotransporter 1) only at P14, followed by a brief, yet significant increase in the level of KCC2 (Potassium-Chloride Cotransporter 2) at P21, which then decreases from P28 until P40. Thus, maternal stress alters NKCC1 and KCC2 ratio in the hippocampus of rat pups, especially during P14 to P28. Maternal restraint stress also caused biphasic changes in the level of GABA_A receptor subunits in the pup's hippocampus. GABA_A receptor α1 subunit gradually increased at P14 then decreased thereafter. On the contrary, GABA_A receptor α5 subunit showed a transient decrease followed by a long-term increase from P21 until P40. Altogether, our study suggested that the maternal restraint stress might delay maturation of the GABAergic system by altering the expression of NKCC1, KCC2 and GABA_A receptor α1 and α5 subunits in the hippocampus of rat pups. These changes demonstrate the dysregulation of inhibitory neurotransmission during early life, which may underlie the pathogenesis of psychiatric diseases at adolescence.

Pharmacological reversion of sphingomyelin-induced dendritic spine anomalies in a Niemann Pick disease type A mouse model

Understanding the role of lipids in synapses and the aberrant molecular mechanisms causing the cognitive deficits that characterize most lipidosis is necessary to develop therapies for these diseases. Here we describe sphingomyelin (SM) as a key modulator of the dendritic spine actin cytoskeleton. We show that increased SM levels in neurons of acid sphingomyelinase knock out mice (ASMko), which mimic Niemann Pick disease type A (NPA), result in reduced spine number and size and low levels of filamentous actin. Mechanistically, SM accumulation decreases the levels of metabotropic glutamate receptors type I (mGluR1/5) at the synaptic membrane impairing membrane attachment and activity of RhoA and its effectors ROCK and ProfilinIIa. Pharmacological enhancement of the neutral sphingomyelinase rescues the aberrant molecular and morphological phenotypes in vitro and in vivo and improves motor and memory deficits in ASMko mice. Altogether, these data demonstrate the influence of SM and its catabolic enzymes in dendritic spine physiology and contribute to our understanding of the cognitive deficits of NPA patients, opening new perspectives for therapeutic interventions.

Subject Categories Genetics, Gene Therapy & Genetic Disease; Neuroscience

Childhood maltreatment is associated with reduced volume in the hippocampal subfields CA3, dentate gyrus, and subiculum

Childhood maltreatment or abuse is a major risk factor for mood, anxiety, substance abuse, psychotic, and personality disorders, and it is associated with reduced adult hippocampal volume, particularly on the left side. Translational studies show that the key consequences of stress exposure on the hippocampus are suppression of neurogenesis in the dentate gyrus (DG) and dendritic remodeling in the cornu ammonis (CA), particularly the CA3 subfield. The hypothesis that maltreatment is associated with volume reductions in 3-T MRI subfields containing the DG and CA3 was assessed and made practical by newly released automatic segmentation routines for FreeSurfer. The sample consisted of 193 unmedicated right-handed subjects (38% male, 21.9 ± 2.1 y of age) selected from the community. Maltreatment was quantified using the Adverse Childhood Experience study and Childhood Trauma Questionnaire scores. The strongest associations between maltreatment and volume were observed in the left CA2-CA3 and CA4-DG subfields, and were not mediated by histories of major depression or posttraumatic stress disorder. Comparing subjects with high vs. low scores on the Childhood Trauma Questionnaire and Adverse Childhood Experience study showed an average volume reduction of 6.3% and 6.1% in the left CA2-CA3 and CA4-DG, respectively. Volume reductions in the CA1 and fimbria were 44% and 60% smaller than in the CA2-CA3. Interestingly, maltreatment was associated with 4.2% and 4.3% reductions in the left presubiculum and subiculum, respectively. These findings support the hypothesis that exposure to early stress in humans, as in other animals, affects hippocampal subfield development.

Opposing roles of glucocorticoid receptor and mineralocorticoid receptor in trimethyltin-induced cytotoxicity in the mouse hippocampus

The organotin trimethyltin (TMT) is known to cause neuronal degeneration in the murine brain. Earlier studies indicate that TMT-induced neuronal degeneration is enhanced by adrenalectomy and prevented by exogenous glucocorticoid. The aim of this study was to investigate the regulation of TMT neuroxicity by corticosterone receptors including type I (mineralocorticoid receptor, MR) and type II (glucocorticoid receptor, GR) in adult mice. The systemic injection of TMT at the dose of 2.0 or 2.8 mg/kg produced a marked elevation in the level of plasma corticosterone that was both dose and time dependent. The MR agonist aldosterone had the ability to exacerbate TMT cytotoxicity in the dentate granule cell layer, whereas its antagonist spironolactone protected neurons from TMT cytotoxicity there. In contrast, the GR antagonist mifepristone exacerbated the TMT cytotoxicity. Taken together, our data suggest TMT cytotoxicity is oppositely regulated by GR and MR signals, being exacerbated by MR activation in adult mice.

Drugs in the brain--cellular imaging with receptor microscopic autoradiography

For cell and tissue localization of drugs, receptor microscopic autoradiography is reviewed, including its development history, multiple testing, extensive applications and significant discoveries. This sensitive high-resolution imaging method is based on the use of radiolabeled compounds (esp. tagged with (3)H or (125)I), preservation through freezing of in vivo localization of tissue constituents, cutting thin frozen sections, and close contact with the recording nuclear emulsion. After extensive testing of the utility of this method, the distribution of radiolabeled compounds has been identified and characterized for estradiol, progestagens, adrenal steroids, thyroid hormone, ecdysteroids, vitamin D, retinoic acid, metabolic indicators glucose and 2-deoxyglucose, as well as extracellular space indicators. Target cells and associated tissues have been characterized with special stains, fluorescing compounds, or combined autoradiography-immunocytochemistry with antibodies to dopamine-beta-hydroxylase, GABA, enkephalin, specific receptor proteins, or other cellular products. Blood-brain barrier and brain entries via capillary endothelium, ependyma, or circumventricular recess organs have been visualized for (3)H-dexamethasone, (210)Pb lead, and (3)H-1,25(OH)(2) vitamin D(3). With this histopharmacologic approach, cellular details and tissue integrative overviews can be assessed in the same preparation. As a result, information has been gained that would have been difficult or impossible otherwise. Maps of brain drug distribution have been developed and relevant target circuits have been recognized. Examples include the stria terminalis that links septal-amygdaloid-thalamic-hypothalamic structures and telencephalic limbic system components which extend as the periventricular autonomic-neuroendocrine ABC (Allocortex-Brainstem-Circuitry) system into the mid- and hindbrain. Discoveries with radiolabeled substances challenged existing paradigms, engendering new concepts and providing seminal incentives for further research toward understanding drug actions. Most notable are discoveries made during the 1980s with vitamin D in the brain together with over 50 target tissues that challenged the century-old doctrine of vitamin D's main role as 'the calcitropic hormone', when the new data made it apparent that the main biological function of this multifunctional sunshine hormone rather is maintenance of life and adapting vital functions to the solar environment. In the brain, vitamin D, in close relation to sex and adrenal steroids, participates in the regulation of the secretion of neuro-endocrines, such as, serotonin, dopamine, nerve growth factor, acetyl choline, with importance in prophylaxis and therapy of neuro-psychiatric disorders. Histochemical imaging with high cellular-subcellular resolution is necessary for obtaining detailed information, as this review indicates. New spectrometric methods, like MALDI-MSI, are unlikely to furnish the same information as receptor microautoradiography does, but can provide important correlative molecular information.

Low doses of dexamethasone can produce a hypocorticosteroid state in the brain

The synthetic glucocorticoid dexamethasone (dex) blocks stress-induced hypothalamic-pituitary-adrenal (HPA) activation primarily at the level of the anterior pituitary because multidrug resistance P-glycoprotein hampers its penetration in the brain. Here, we tested the hypothesis that central components of the HPA axis would escape dex suppression under conditions of potent peripheral glucocorticoid action. We subchronically treated rats with low or high doses of dex. The animals were subjected on the last day of treatment for 30 min to a restraint stressor after which central and peripheral markers of HPA axis activity were measured. Basal and stress-induced corticosterone secretion, body weight gain, adrenal and thymus weight, as well as proopiomelanocortin mRNA in the anterior pituitary were reduced in a dose-dependent manner by dex administered either 5 d sc or 3 wk orally. In the brain, the highest dose dex suppressed CRH mRNA and CRH heteronuclear RNA in the paraventricular nucleus (PVN). However, in the peripherally active low-dose range of dex CRH mRNA and heteronuclear RNA showed resistance to suppression, and CRH mRNA expression in the PVN was in fact enhanced under the long-term treatment condition. In the PVN, c-fos mRNA was suppressed by the highest dose of dex, but this effect showed a degree of resistance after long-term oral treatment. c-fos mRNA responses in the anterior pituitary followed those in PVN and reflect central drive of the HPA axis even if corticosterone responses are strongly reduced. The results support the concept that low doses of dex can create a hypocorticoid state in the brain.

Effects of dexamethasone on declarative memory function in posttraumatic stress disorder

Alterations in the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal-based memory have been associated with posttraumatic stress disorder (PTSD), and the administration of exogenous glucocorticoids has been shown to result in a transient verbal declarative memory impairment in healthy human subjects. The purpose of this study was to assess the effects of the glucocorticoid dexamethasone on verbal declarative memory function in patients with PTSD. Forty-two men and women with (n=14) and without (n=28) PTSD received placebo or dexamethasone (1 and 2 mg on two successive days) in a double-blind, randomized fashion. Declarative memory was assessed with paragraph recall at baseline (day 1) and day 3. There was a significant interaction between diagnosis and drug (dexamethasone vs. placebo) on paragraph recall related to a relative detrimental effect of dexamethasone on memory function in healthy subjects, but not those with PTSD. These findings are consistent with an altered sensitivity of declarative memory function in PTSD to regulation by glucocorticoids, possibly explainable by alterations in glucocorticoid receptors in the hippocampus or other brain regions mediating declarative memory.

Hydrocortisone induced regional cerebral activity changes in schizophrenia: a PET scan study

BACKGROUND

There is evidence that, even during remission, schizophrenia (SZ) patients are especially vulnerable to de-compensate under stress, and that they tend to have a high baseline serum cortisol levels. This study was undertaken to determine whether raising serum cortisol by the infusion of hydrocortisone, in the absence of additional psychological stress, would result in different cerebral activity changes in schizophrenic patients compared to normal controls (CON). We were especially interested in cerebral activity in regions such as the medial temporal lobe and hippocampus, since structural abnormalities in these brain regions were frequent in association with schizophrenia.

METHODS

Serum cortisol levels were raised, by infusing hydrocortisone, in 8 pairwise-matched SZ patients and 8 CONs. The associated regional cerebral activity changes were analyzed using statistical parametric mapping (SPM).

RESULTS

There was increased regional cerebral activity in response to elevated cortisol in the left hippocampal region in the SZ group, while the controls showed evidence of decreased regional cerebral activity in the same anatomical location. For the rest of the brain regions, cerebral activity increases and decreases, in response to raised serum cortisol, in the SZ followed the same regional pattern as in the control group, but with a smaller overall magnitude of change. The blunted response in SZ was most marked in the regions that showed greatest regional cerebral activity changes in normal subjects.

CONCLUSION

Patients with schizophrenia showed an abnormal increased regional cerebral activity response to cortisol infusion in the left hippocampal region, and similar but attenuated regional cerebral activity response in other regions, when compared to matched controls.

Effects of pre- and postnatal corticosterone exposure on the rat hippocampal GABA system

Several lines of evidence have implicated prenatal stress and the hippocampal GABA system in the pathophysiology of schizophrenia, and prenatal stress is believed to increase the risk for schizophrenia through alterations of this neurotransmitter. To explore this hypothesis, we treated male rats pre- and/or postnatally (P48 and P60) with either corticosterone (CORT) or vehicle to establish three study groups: VVV, receiving vehicle at all three time points; VCC, receiving vehicle prenatally and CORT at both postnatal timepoints; and CCC, receiving CORT at all three timepoints. Animals were sacrificed at either 24 h or 5 days after final injection and examined for mRNA levels of GAD65, GAD67, and the GABA(A) receptor subunits alpha2 and gamma2. At 24 h, GAD65 mRNA was decreased in CA1, CA2, CA4, and dentate gyrus (DG) of VCC rats; this effect was either decreased or reversed in CCC-treated animals. No effect was detected in GAD67 mRNA at 24 h. At 5 days, CORT treatment increased GAD67 mRNA levels in CA1, CA3, and DG. Prenatal treatment with CORT was associated with increased responsiveness only in CA3 and DG. For the GABAA receptor, alpha2 subunit mRNA did not show any change in response to CORT treatment, while that for the gamma2 subunit was decreased in CA2 of both VCC- and CCC-treated animals. Consistent with gamma2 subunit mRNA decreases, benzodiazepine (BZ) receptor binding activity was decreased in CA2 with CORT treatment. Prenatal CORT exposure neither increased nor decreased this effect. These results demonstrate that CORT administration is associated with a complex regulation of mRNA expression for pre- and postnatal aspects of the hippocampal GABA system. Under these conditions, prenatal exposure to CORT may sensitize some of these effects, but does not fundamentally alter the nature of this response.

Altered stress-induced anxiety in adenylyl cyclase type VIII-deficient mice

Stress results in alterations in behavior and physiology that can be either adaptive or maladaptive. To define the molecular pathways involved in the response to stress further, we generated mice deficient (KO) in the calcium-stimulated adenylyl cyclase type VIII (AC8) by homologous recombination in embryonic stem cells. AC8 KO mice demonstrate a compromise in calcium-stimulated AC activity in the hippocampus, hypothalamus, thalamus, and brainstem. Hippocampal slices derived from AC8 KO mice fail to demonstrate CA1-region long-term depression after low-frequency stimulation, and AC8 KO mice also fail to activate CRE-binding protein in the CA1 region after restraint stress. To define the behavioral consequences of AC8 deficiency, we evaluated AC8 KO mice in the elevated plus-maze and open field. Although naive AC8 KO mice exhibit indices of anxiety comparable with that of wild-type mice, AC8 KO mice do not show normal increases in behavioral markers of anxiety when subjected to repeated stress such as repetitive testing in the plus-maze or restraint preceding plus-maze testing. These results demonstrate a novel role for AC8 in the modulation of anxiety.

Evidence for altered trisynaptic circuitry in schizophrenic hippocampus

Recent postmortem studies have demonstrated subtle alterations in the hippocampal formation (HIPP) of patients with schizophrenia (SZ). These changes include a decreased density of nonpyramidal neurons (NPs), an increase of the GABAA, but not benzodiazepine receptors and a neuroleptic-dose-related increase of GAD65-IR terminals, particularly in sectors CA3 and CA2. High resolution studies of the GABAA receptor have further suggested that a decrease of disinhibitory GABAergic activity (i.e., GABA-to-GABA) in stratum pyramidale of CA3 may coexist with reduced inhibitory modulation (i.e., GABA-to-excitatory pyramidal neuron) in the stratum oriens of this same sector. These changes could potentially involve excitotoxic damage to interneurons in CA2; but, the precise time frame for the induction of such an injury during pre- versus postnatal life cannot as yet be inferred from the available data. These findings are consistent with reports of abnormal oscillatory rhythms and increased basal metabolic activity in the HIPP of patients with SZ. The fact that patients with manic depression also show a decrease of NPs in CA2 suggests that changes in the GABA system may not be related to a susceptibility gene for SZ. Rather, these alterations could be associated with a nonspecific factor, such as stress, experienced either early in life or much later during adolescence or adulthood. Presumably, there are also changes associated in other transmitter systems that may play a more specific role in establishing the SZ phenotype.

The cellular localization of the L-ornithine decarboxylase/polyamine system in normal and diseased central nervous systems

Natural polyamines, spermidine and spermine, and their precursor putrescine, are of considerable importance for the developing and mature nervous system. They exhibit a number of neurophysiological and metabolic effects in the nervous system, including control of nucleic acid and protein synthesis, modulation of ionic channels and calcium-dependent transmitter release. The polyamine system is also known to be involved in various brain pathologic events (seizures, stroke, Alzheimer's disease and others). While cerebral polyamine concentrations and the activities of polyamine-metabolizing enzymes have been studied in great detail, much less is known about the cells that are responsible for cerebral polyamine synthesis and interconversion. With the present review the attempt is made to show how exact knowledge about the regional distribution and cellular localization of polyamines and the polyamine-synthesizing enzymatic machinery (and especially of L-ornithine decarboxylase) may help to better understand the functional interplay between polyamines and other endogenous agents (transmitters, receptors, growth factors neuroactive drugs etc.). Polyamines have been localized both in neurones and glial cells. However, the main cellular locus of the ODC is the neuron--both in the immature and adult central nervous system. Each period of normal brain development and ageing seems to have its own, characteristic temporo-spatial pattern of neuronal ODC expression. During strong functional activation (kindling, epileptic seizures, neural transplantation) astrocytes and other non-neuronal cells do also express ODC and other polyamine-metabolizing enzymes. Astroglial expression of ODC is accompanied by an increase in glial fibrillary acidic protein in these cells. This shift in the cellular mechanisms of polyamine metabolism is currently far from being understood. In human brain diseases (Alzheimer's disease, schizophrenia) certain neurones show an increased expression of ODC, the first and rate-limiting enzyme of polyamine metabolism. Since polyamines are structurally related to psychoactive drugs (neuroleptics, antidepressants) the polyamine system might be of importance as a putative target for drug intervention in psychiatry.

Plasticity of hippocampal corticosteroid receptors during aging in the rat

Aging is commonly associated with dysregulation of the hypothalamo-pituitary-adrenal axis and cognitive impairment. On the basis of suggestions that these disruptions ensue from changes in the hippocampal complement of corticosteroid (mineralocorticoid and glucocorticoid) receptors (MR and GR), we examined the availability of hippocampal MR and GR by measuring the in vivo uptake of 3H-aldosterone and 3H-dexamethasone (selective MR and GR agonists, respectively); MR and GR mRNA levels were also measured. We observed age-related declines in both the synthesis of MR and GR and the uptake of their respective ligands. Whereas MR mRNA levels and ligand uptake declined in parallel, GR binding declined more steeply than GR mRNA. This latter result, together with our finding that aged rats show impaired corticosteroid receptor mRNA and protein up-regulation after corticosteroid withdrawal, indicates decreased transcription of MR and GR genes and posttranslational modification of GR mRNA during aging. Given that corticosteroids can influence MR and GR synthesis and binding, and based on the finding that aged subjects show reduced basal secretion of corticosterone, we propose that this relative hypocorticalism may be responsible for the changes observed in MR and GR activity, which then leads to disturbances in neuroendocrine regulation and cognitive function in aged subjects.

A reduction of nonpyramidal cells in sector CA2 of schizophrenics and manic depressives

BACKGROUND

Recent studies have suggested that there may be a preferential decrease of "nonpyramidal" neurons (NPs) in several corticolimbic regions of schizophrenic (SZ) brain. The current study was undertaken to determine whether a change in the density of pyramidal neurons (PNs) and NPs might be present in the hippocampal formation (HIPP) of SZ brain.

METHODS

A spatial counting approach in which the location of each and every PN and NP in the stratum pyramidale of sectors CA1-4 was applied to 11 normal control (CONs) and 10 SZs matched for age and postmortem interval, as well as 4 manic depressive (MD) subjects matched for age.

RESULTS

The data indicate that the CONs had approximately 10-20 times as many PNs than NPs in the various HIPP subfields. When the CON data were compared to those for the SZs, both the total number and density of PNs were found to be similar in all four sectors, while NPs were found to be selectively reduced by approximately 40% in CA2 of the SZ group. When the data were broken down according to patients with and without neuroleptic exposure, drug-free SZs showed a significant reduction in the density of NPs in CA2. The 4 MD cases both with and without neuroleptic exposure also showed a similar reduction of NPs in sector CA2.

CONCLUSIONS

Taken together, the results of this study suggest that there may be a highly selective decrease in the number of NPs in sector CA2 that could play a contributory role in the pathophysiology of the major psychoses.

Penetration of dexamethasone into brain glucocorticoid targets is enhanced in mdr1A P-glycoprotein knockout mice

Mice with a genetic disruption of the multiple drug resistance (mdr1a) gene were used to examine the effect of the absence of its drug-transporting P-glycoprotein product from the blood-brain barrier on the distribution and cell nuclear uptake of [3H]-dexamethasone in the brain. [3H]-dexamethasone (4 microg/kg mouse) was administered s.c. to adrenalectomized mdr1a (-/-) and mdr1a (+/+) mice. One hour later, the mice were decapitated, and the radioactivity was measured in homogenates of cerebellum, blood, and liver following extraction of the radioactive steroid. The frontal brain was cut in sections for autoradiography. In the cerebellum of the mdr1a mutants, the amount of [3H]-dexamethasone relative to blood was about 5-fold higher than observed in the controls, whereas the ratio in blood vs. liver was not different. Using autoradiography, it was found that brain areas expressing the glucocorticoid receptor (GR) in high abundance, such as the hippocampal cell fields and the paraventricular nucleus (PVN), showed a 10-fold increase in cell nuclear uptake of radiolabeled steroid. The amount of retained steroid increased toward levels observed in the pituitary, which contains a similar density of GRs. The [3H]-dexamethasone concentration in pituitary was not affected by mdr1a gene disruption. The GR messenger RNA expression pattern in hippocampus was not different between the wild types and mdr1a mutants, which rules out altered receptor expression as a cause of the enhanced dexamethasone uptake. In conclusion, the present study demonstrates that the brain is resistant to penetration by dexamethasone because of mdr1a activity at the level of the blood-brain barrier. The data support the concept of a pituitary site of action of dexamethasone in blockade of stress-induced ACTH release. Dexamethasone poorly substitutes for depletion of the endogenous glucocorticoid from the brain and therefore, in this tissue, may cause a condition resembling that of adrenalectomy.

Sex differences in corticosteroid binding in the rat brain: an in vitro autoradiographic study

Several previous studies have raised the possibility of sex differences in the distribution of corticosteroid receptors in the brain. The direction and magnitude of these differences have, however, remained controversial. In the present study, we have re-examined the concentrations of mineralocorticoid (MR) and glucocorticoid (GR) receptors in the brains of male and female rats at varying times (1 to 6 days) after combined gonadectomy (GDX) and adrenalectomy (ADX). Cytosol binding assays confirmed the presence of higher MR levels in short-term (3-day) GDX-ADX males. This difference disappeared by 6 days after surgery, as receptor levels in females rose to be equivalent to those in males. Using an improved in vitro autoradiographic method, the distribution of MR and GR was studied in males and females 3 days after GDX-ADX. The distribution of MR and GR in the brains of these rats was similar in the two sexes. MR binding in the male, however, was significantly greater than that in the female throughout the principal cell fields of the hippocampus. Measurements of circulating corticosterone levels at the time of GDX-ADX suggest that this sex difference may reflect a more rapid recovery of the MR system in males than in females following the stress-induced rise in corticosterone secretion occurring at the time of surgery.

Synthesis and organ distribution of [18F]fluoro-Org 6141 in the rat: a potential glucocorticoid receptor ligand for positron emission tomography

For the synthesis of [18F]Fluoro-Org 6141 via a nucleophilic substitution reaction with 18F-, the tosyl group was chosen as the leaving group because of its stability and excellent leaving group ability. The biodistribution of the high affinity and moderate lipophilicity (log P = 2.66, calculated value) ligand [18F]Fluoro-Org 6141 (specific activity 8.2 to 37 TBq/mmol, yield 10% at EOB) was examined in sham adrenalectomized (sADX) and adrenalectomized (ADX) male Wistar rats. Two days after ADX or sADX, the animals were anesthetized and 0.37 to 1.85 MBq of [18F]Fluoro-Org 6141 was administered intravenously. Kinetics of 18F activity uptake were monitored for 3 h using a stationary double-headed positron emission tomography (PET) camera, and the biodistribution was assessed by ex vivo determination of radioactivity in several tissues and different brain areas. One hour after injection of the radioligand, the bladder, kidney, liver, trachea, and bone of sADX animals contained more concentration on a wet weight basis than blood. Three hours post injection, radioactivity was retained in bladder, trachea, and bone. The accumulation of radioactivity in brain corresponded to the concentration of activity in the blood within the first hours after injection. ADX animals showed a higher uptake of 18F activity in spleen, testes, and brain areas (hippocampus and brainstem) but a lower uptake in bone than sADX rats. PET scans suggested that 18F activity uptake in the brain had not yet reached a maximum at this interval. Although [18F]Fluoro-Org 6141 is not useful for PET studies of glucocorticoid receptors (GRs), the results obtained with this compound indicate a synthetic strategy suitable for the synthesis of high-affinity radioligands for GRs.

Mineralocorticoid and glucocorticoid receptors in the brain. Implications for ion permeability and transmitter systems

In this review we have argued that corticosteroid hormones represent an endocrine signal that can influence neuronal communication. The steroids bind to intracellular receptors in the brain, resulting in slow effects that involve gene transcription, but they may also evoke rapid effects via membrane receptors. The signal carried by the corticosteroids is therefore divergent with respect to the dimension of space and time. Within the rat brain, at least two intracellular receptor subtypes, i.e. MRs and GRs, bind corticosterone. The affinity, density and localization of the MRs is different from the GRs, although the actual properties may vary somewhat depending on the condition of the animal. In general, due to the difference in affinity, low corticosteroid levels result in a predominant MR occupation, while higher steroid levels additionally occupy GRs. Recent studies indicate that predominant MR occupation is important for the maintenance of ongoing transmission in certain brain regions and for neuroprotection. By contrast, additional GR occupation (for a limited period of time) results in an attenuation of local excitability; yet, prolonged exposure to high steroid levels may become an endangering condition for neurons. Since predominant MR occupation on the one hand and additional GR occupation on the other hand induce different cellular actions, the ratio of MR/GR occupation is an important factor determining the net effect of corticosteroid hormones in the brain. How coordinated MR- and GR-mediated effects control neuronal communication under various physiological and pathological conditions will be a challenge for future research.

Development of mRNAs for glucocorticoid and mineralocorticoid receptors in rat hippocampus

The hippocampus plays an important role in mediating glucocorticoid effects on the brain. Glucocorticoids are also implicated in neurogenesis and age-related neuronal death in the hippocampus. The effects of glucocorticoids in the hippocampus are elicited through two receptors with high-affinity for corticosterone, the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). In this study, we used a sensitive RNase protection assay to quantify the ontogeny of GR mRNA and MR mRNA in hippocampus from embryonic day 18 (E18) to postnatal day 60 (P60). GR mRNA and MR mRNA are expressed at approximately equal levels in the E18 hippocampus. However, by birth, the level of MR mRNA is three-fold that of GR mRNA and remains elevated up to P60. The levels of both mRNAs increase gradually during the period of postnatal neurogenesis after which they markedly increase to adult levels. In addition, the levels of hippocampal MR mRNA are the same in male and female rats, whereas the levels of GR mRNA are significantly higher in the P60 female rat hippocampus, but not in younger female rats. Our data on the development of mRNA levels do not parallel the levels of glucocorticoid and mineralocorticoid receptors as reported in a number of binding studies. Therefore, our studies, when considered together with previous reports, suggest that posttranscriptional mechanisms play a major role in regulating the levels of glucocorticoid-binding sites in the hippocampus.

Dexamethasone target sites in the central nervous system and their potential relevance to mental illness

1. The topical distribution of tritiated dexamethasone (DEX), a potent synthetic glucocorticoid of widespread use in the diagnosis and assessment of mental illness, was studied in rat CNS by autoradiography to obtain information on potential target sites for feedback and other centrally mediated effects of glucocorticoids. 2. The cells of the arcuate nucleus of the hypothalamus and the lateral thalamic nuclei displayed the most concentrated nuclear accumulation of silver grains. 3. Significant accumulation, exceeding that found in the hippocampal formation, also occurred in the cells of the ventromedial, periventricular, and paraventricular nuclei of the hypothalamus, the locus ceruleus, the nucleus tractus solitarii, and the area postrema, none of which are targeted by corticosterone, the native glucocorticoid of the rat. 4. Nuclear accumulation of silver grains was prominent in neural and glial cells of the cerebral cortex, the olfactory nucleus, the dorsolateral septum, the amygdala, the subfornical organ, the lateral parabrachial, medial trapezoid, and dorsal reticular nuclei, the nucleus centralis of the raphe, the cerebellum, and vascular tissues. 5. The localization of DEX in hypothalamic and brain-stem nuclei coincided with that of the glucocorticoid receptor, possibly implicating these sites in direct or modulating effects of glucocorticoids in various forms of mental disturbance, including depression, anxiety, panic disorders, and alcohol withdrawal. 6. The extent to which various CNS regions targeted by DEX feature in negative feedback control of adrenocortical secretion remains to be defined, as does the site of impaired feedback disclosed by the dexamethasone suppression test in psychiatric patients.

Kainic acid-mediated increase of preprotachykinin-A messenger RNA expression in the rat hippocampus and a region-selective attenuation by dexamethasone

The hippocampus contains the highest number of glucocorticoid-sensitive neurons in the rat brain and excessive exposure to glucocorticoids can cause damage to hippocampal neurons and impair the capacity of the hippocampus to survive neuronal insults. In this study in situ hybridization combined with quantitative image analysis was used to study preprotachykinin-A mRNA levels after administration of a toxic dose of kainic acid in animals pretreated with glucocorticoids. Kainic acid was injected into dorsal hippocampus CA3 region in animals pretreated with the synthetic glucocorticoid receptor agonist dexamethasone and in control animals. Preprotachykinin-A mRNA was not detected in the hippocampus of untreated animals or in animals analysed 30 min after a kainic acid injection. However, 4 h after injection of kainic acid, the level of preprotachykinin-A mRNA increased to 20-times above the detection limit both in the dentate gyrus and the CA3 region of the hippocampus. Treatment of kainic acid-injected animals with dexamethasone 30 min before and 2 h after the injection attenuated the increase in the granule cells of the dentate gyrus by 50%. In contrast, dexamethasone pretreatment had no significant effect on the kainic acid-induced increase of preprotachykinin-A mRNA in pyramidal cells in regions CA3 or CA1. These results show that an excitatory stimulus within the hippocampus causes a substantial increase in the level of preprotachykinin-A mRNA in hippocampal granule and pyramidal cells and suggest that in granule cells of the dentate gyrus this increase can be modulated by glucocorticoids.

Distribution of estrogen receptor-immunoreactive cells in the forebrain of the female guinea pig

We mapped the distribution of estrogen receptor-containing cells in the forebrain of the adult female guinea pig. Cellular estrogen receptor content was detected using monoclonal antibody H222, directed against the estrogen receptor, and the avidin-biotin method with nickel-intensified diaminobenzidine as the chromagen. A complete set of deletion, titration, and adsorption controls established the specificity of the staining. The most dense collections of estrogen receptor-immunoreactive cells were found in medial preoptic, medial hypothalamic, and limbic nuclei (amygdala, bed nucleus of the stria terminalis, lateral septum). Numerous estrogen receptor-immunoreactive cells were also found in additional, specific subregions of the remainder of the preoptic area, hypothalamus, and limbic system, and also in the midbrain (central gray). Elsewhere, estrogen receptor-immunoreactive cells were present in smaller numbers or were absent. This map confirms and extends previous maps based on estrogen binding. The majority of estrogen receptor-immunoreactive cells are found in areas known to be involved in some aspect of reproduction. In addition, many estrogen receptor-immunoreactive cells are found in areas not typically considered to have a primary role in reproductive behavior or neuroendocrine function.

Cannabinoid interactions with glucocorticoid receptors in rat hippocampus

Previous studies have found that chronic administration of delta9-tetrahydrocannabinol (THC), a psychoactive cannabinoid, can induce brain aging-like degenerative changes in hippocampal structures (e.g., pyramidal cell loss, glial reactivity). Normal aging changes in the hippocampus appear to be partly corticosteroid-dependent. Because THC is similar in molecular structure to corticosteroids (CORT), therefore, we have suggested that THC may act to induce pathology in the hippocampus through CORT receptors. The possibility of THC interactions with CORT receptors was tested more directly in the present studies. Binding of [3H]dexamethasone (DEX) to hippocampal cytosol, in vitro, was inhibited partially, but not completely, by 100-fold excess unlabeled THC and cannabidiol (CBD), a non-psychoactive cannabinoid. Even at 10,000-fold molar excess, moreover, THC could displace only 50% of radiolabeled DEX binding and CBD could inhibit only 22% of tracer binding. Scatchard plot analyses also pointed to a possible non-competitive site for cannabinoid interaction with glucocorticoid receptors. In addition, several studies utilizing the synthetic steroid RU-28362 indicated that THC interacts primarily with the type II class of glucocorticoid receptors. In a separate study, adrenalectomized rats were treated daily for 14 days with 5-10 mg/kg THC or vehicle, and examined 24 h later for [3H]CORT binding in hippocampal cytosol. In THC-treated animals, the Bmax for type II binding was reduced to a degree almost comparable to the down-regulation seen after chronic stress or high corticosteroid administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosteroids and the brain

Mineralocorticoid (MR) and glucocorticoid receptors (GR) are expressed in the central nervous system. Radioligand binding studies, autoradiography, immunocytochemistry and in situ hybridization have shown that MR and GR are found in abundance in neurons of the limbic system (hippocampus), a structure involved in mood, affect and subtle control of the hypothalamic-pituitary-adrenal (HPA) axis. In the hippocampus MR binds corticosterone (CORT) as well as aldosterone (ALDO) with high affinity. MR seems mainly occupied by CORT in the face of its 2-3 order higher circulating concentration. GR binds CORT with a 6-10-fold lower affinity. MR and GR gene expression, as well as the native receptor proteins, seem to be controlled in a coordinative manner. When GR is down-regulated by excess homologous steroid, MR appears to be increased. Down regulation of MR reduces GR as well. MR and GR display a differential ontogenetic pattern. Ontogeny, particularly that of GR, can be permanently influenced when animals are exposed during the first post-natal week of maternal deprivation, handling, CORT or ACTH1-24 injections. These MR and GR changes persist into senescence and have been proposed to result in altered CORT responsiveness, stress regulation, behavioural adaptation and brain aging.

Steroid hormones and the cardiovascular system: direct actions of estradiol, progesterone, testosterone, gluco- and mineralcorticoids, and soltriol [vitamin D] on central nervous regulatory and peripheral tissues

Knowledge of steroid hormone sites of action and related effects in cardiovascular and neural regulatory tissues is reviewed. Evidence for nuclear receptor sites is derived mainly from autoradiographic studies with relatively intact tissues and some biochemical studies with tissue homogenates. In the heart and in the walls of blood vessels, estradiol, dihydrotestosterone, corticosterone, aldosterone, dexamethasone, and soltriol (vitamin D) show nuclear binding. In the brain and spinal cord, neuronal regions associated with cardiovascular regulation contain nuclear receptors in specific patterns for each steroid hormones, including progesterone and soltriol. These data indicate that all steroid hormones exert direct actions on the cardiovascular system at its different levels of organization, thus enabling adjustment to the changing demands during reproduction (gonadal steroids), stress (adrenal steroids), and solar seasons (vitamin D-soltriol).