A correlative study of RU38486 biopotency and competition with [3H]dexamethasone for receptors in the rat central nervous system

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

Corticosteroid-dependent plasticity mediates compulsive alcohol drinking in rats

Alcoholism is characterized by a compulsion to seek and ingest alcohol, loss of control over intake, and the emergence of a negative emotional state during abstinence. We hypothesized that sustained activation of neuroendocrine stress systems (e.g., corticosteroid release via the hypothalamic-pituitary-adrenal axis) by alcohol intoxication and withdrawal and consequent alterations in glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation drive compulsive alcohol drinking. Our results showed that rats exposed to alcohol vapor to the point of dependence displayed increased alcohol intake, compulsive drinking measured by progressive-ratio responding, and persistent alcohol consumption despite punishment, assessed by adding quinine to the alcohol solution, compared with control rats that were not exposed to alcohol vapor. No group differences were observed in the self-administration of saccharin-sweetened water. Acute alcohol withdrawal was accompanied by downregulated GR mRNA in various stress/reward-related brain regions [i.e., prefrontal cortex, nucleus accumbens (NAc), and bed nucleus of the stria terminalis (BNST)], whereas protracted alcohol abstinence was accompanied by upregulated GR mRNA in the NAc core, ventral BNST, and central nucleus of the amygdala. No significant alterations in MR mRNA levels were found. Chronic GR antagonism with mifepristone (RU38486) prevented the escalation of alcohol intake and compulsive responding induced by chronic, intermittent alcohol vapor exposure. Chronic treatment with mifepristone also blocked escalated alcohol drinking and compulsive responding during protracted abstinence. Thus, the GR system appears to be involved in the development of alcohol dependence and may represent a potential pharmacological target for the treatment of alcoholism.

Effects of the glucocorticoid antagonist, mifepristone, on the consequences of withdrawal from long term alcohol consumption

BACKGROUND

Studies were carried out to test the hypothesis that administration of a glucocorticoid Type II receptor antagonist, mifepristone (RU38486), just prior to withdrawal from chronic alcohol treatment, would prevent the consequences of the alcohol consumption and withdrawal in mice.

MATERIALS AND METHODS

The effects of administration of a single intraperitoneal dose of mifepristone were examined on alcohol withdrawal hyperexcitability. Memory deficits during the abstinence phase were measured using repeat exposure to the elevated plus maze, the object recognition test, and the odor habituation/discrimination test. Neurotoxicity in the hippocampus and prefrontal cortex was examined using NeuN staining.

RESULTS

Mifepristone reduced, though did not prevent, the behavioral hyperexcitability seen in TO strain mice during the acute phase of alcohol withdrawal (4 hours to 8 hours after cessation of alcohol consumption) following chronic alcohol treatment via liquid diet. There were no alterations in anxiety-related behavior in these mice at 1 week into withdrawal, as measured using the elevated plus maze. However, changes in behavior during a second exposure to the elevated plus maze 1 week later were significantly reduced by the administration of mifepristone prior to withdrawal, indicating a reduction in the memory deficits caused by the chronic alcohol treatment and withdrawal. The object recognition test and the odor habituation and discrimination test were then used to measure memory deficits in more detail, at between 1 and 2 weeks after alcohol withdrawal in C57/BL10 strain mice given alcohol chronically via the drinking fluid. A single dose of mifepristone given at the time of alcohol withdrawal significantly reduced the memory deficits in both tests. NeuN staining showed no evidence of neuronal loss in either prefrontal cortex or hippocampus after withdrawal from chronic alcohol treatment.

CONCLUSIONS

The results suggest mifepristone may be of value in the treatment of alcoholics to reduce their cognitive deficits.

Persistent disruption of a traumatic memory by postretrieval inactivation of glucocorticoid receptors in the amygdala

BACKGROUND

Posttraumatic stress disorder (PTSD) is characterized by acute and chronic changes in the stress response, which include alterations in glucocorticoid secretion and critically involve the limbic system, in particular the amygdala. Important symptoms of PTSD manifest as a classical conditioning to fear, which recurs each time trauma-related cues remind the subject of the original insult. Traumatic memories based on fear conditioning can be disrupted if interfering events or pharmacological interventions are applied following their retrieval.

METHODS AND RESULTS

Using an animal model, here we show that a traumatic memory is persistently disrupted if immediately after its retrieval glucocorticoid receptors are inactivated in the amygdala. The disruption of the memory is long lasting and memory retention does not re-emerge following strong reminders of the conditioned fear.

CONCLUSIONS

We propose that a combinatorial approach of psychological and pharmacological intervention targeting the glucocorticoid system following memory retrieval may represent a novel direction for the treatment of PTSD.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Chronic corticosterone treatment maintains synaptic activity of CA1 hippocampal pyramidal cells: acute high corticosterone administration increases action potential number

The hypothalamic-pituitary-adrenocortical (HPA) axis controls the levels of plasma corticosterone (CT) in the rat and the levels of cortisol in man. CT is important in maintaining homeostasis and regulating energy production. Homeostasis is maintained by basal activation of the hippocampal-HPA axis. In response to stress CT secretion is increased. CT activation of receptors in the hippocampus provides feedback inhibition of the HPA axis to return the system to basal activity. There are two types of CT receptors: the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). CT has a 10-fold higher affinity for MR than GR. Normal basal levels of CT occupy the majority of the MR. During the diurnal surge of CT and following the presentation of a stressful stimulus, the MR and GR are both maximally occupied. To begin to understand how CT influences the hippocampal-HPA axis, intracellular recording techniques in the hippocampal brain slice preparation were used to determine how high concentrations of CT may alter cell characteristics and/or evoked synaptic activity. Two treatment groups were used, i.e., adrenalectomized (ADX) and ADX with CT pellet replacement (ADX+CT) that produced plasma blood levels equal to that seen in a normal rat in the morning. Acute administration of 100 nM CT decreased action potential threshold and the number of action potentials elicited by a depolarizing current pulse in cells from both the ADX and ADX+CT treated rats. The amplitude of the evoked excitatory postsynaptic potentials (EPSP) or inhibitory postsynaptic potentials (IPSP) declined in cells recorded from ADX animals and ADX rats acutely treated with high concentrations of CT (ADX/CT).(ABSTRACT TRUNCATED AT 250 WORDS)

Transformation and nuclear translocation of brain type L corticosteroid receptors complexed with the mineralocorticoid antagonist ZK 91587, aldosterone or dexamethasone

Type I corticosteroid receptors were determined in cytosol from hippocampus (HIPPO) and amygdala (AMYG), using [3H]aldosterone (ALDO), [3H]dexamethasone (DEX) or the mineralocorticoid antagonist [3H]ZK 91587 as ligands. Incubations with the first two compounds also contained the pure glucocorticoid RU 28362 to block type II receptors. Binding of the three ligands was comparable in cytosol from HIPPO and it was slightly higher for [3H]DEX in AMYG. However, after heat-induced receptor transformation, binding to DNA-cellulose was observed for [3H]ALDO-receptor complex obtained from HIPPO or AMYG, whereas it was negligible for [3H]ZK 91587. Receptors charged with [3H]DEX or [3H]ALDO showed similar retention on DNA-cellulose columns in the case of the AMYG, while binding to the polynucleotide was higher for [3H]ALDO in the HIPPO. Finally, only [3H]ALDO was taken up to a significant extent in purified cell nuclei prepared from slices of HIPPO and AMYG previously incubated with the three ligands. It is concluded that binding of a natural agonist steroid may be a prerequisite for type I receptor transformation and translocation from the cytoplasm into the nuclear fraction. DEX binding to type I receptors resembles a partial agonist with antagonist properties, whereas antagonists such as ZK 91587 are bound and retained in cytoplasm, without further translocation.

Glucocorticoid type II receptors of the spinal cord show lower affinity than hippocampal type II receptors: binding parameters obtained with different experimental protocols

We have used three experimental protocols to determine binding parameters for type I and type II glucocorticoid receptors in the spinal cord and hippocampus (HIPPO) from adrenalectomized rats. In protocol A, 0.5-20 nM [3H]dexamethasone (DEX) was incubated plus or minus a 1000-fold excess of unlabeled DEX, assuming binding to a two-site model. In protocol B, [3H]DEX competed with a single concentration of RU 28362 (500 nM), whereas in protocol C, we used a concentration of RU 28362 which varied in parallel to that of [3H]DEX, such as 500 x. Results of protocols A and C were qualitatively similar, in that: (1) Bmax for type I receptors favored the HIPPO, while the content of type II sites was comparable in the two tissues; (2) Kd was consistently lower for type I than for type II sites in both tissues; and (3) type II receptors from the spinal cord showed lower affinity than their homologous sites from HIPPO. This last result was also obtained when using protocol B. In contrast, protocol B yielded binding data indicating that type II sites were of similar or higher affinity than type I sites. Computer simulation of the binding protocols demonstrated that protocols A and C were the most theoretically reliable for estimating the Kd and Bmax of type I sites, and the predicted error was smaller for protocol C, in comparison with protocol B. We suggest that the noted differences in the Kd of type II receptors between the spinal cord and HIPPO could account for a difference in sensitivity of the two systems in the physiological adrenal hormone range.

Effects of progesterone, epipregnanolone and RU 38486 on potassium uptake in cultured cortical neurons

It was previously reported that progesterone and its metabolites influence electrical properties of the CNS in many different ways. In the present study we elicited the effects of progesterone, its 5 beta reduced metabolite epipregnanolone and the anti-progestin compound RU 38486 on potassium uptake in cultured cortical neurons. K+ was substituted by the tracer substance 86Rb. When hormone treatment (10(-9)-10(-7) M/l) was performed for 3 days, addition of progesterone and epipregnanolone led to a significant decrease of 86Rb uptake whereas treatment with RU 38486 markedly increased 86Rb uptake. The effect of the anti-progestin could be reversed by the addition of increasing amounts of progesterone. Hormone actions were dose-dependent and most distinct when performed from the very first day of culture. Short-term (15 min) hormone treatment of neurons did not significantly alter 86Rb uptake. These findings suggest a specific receptor mediated progestin action which, in a long-term course, controls potassium uptake across excitable membranes.

Presence of type I and type II/IB receptors for adrenocorticosteroid hormones in the inner ear

Aldosterone-Type I and dexamethasone-Type II/IB receptor complexes were identified in cytosol prepared from both cochlear and vestibular tissue samples. The specific binding capacity of Type I receptors in the cochlear tissues was approximately equal to that in the vestibular tissues. Likewise, the binding capacity of Type II/IB receptors in the cochlea was approximately equal to that in the vestibular endorgans. Based on the total specific binding measured with dexamethasone, the Type II/IB receptors appeared to outnumber the Type I receptors in cochlear and vestibular tissues by a factor of approximately 2.6; however, when adjustments were made for the probable cross-binding of dexamethasone to Type I receptors, these ratios were decreased to approximately 1.6. The existence of protein receptors for adrenocorticosteroid hormones demonstrated in the present study clearly suggests a mechanism whereby such hormones may directly regulate fluid and ionic gradients in the inner ear.

Treatment of mouse brain cytosol with dextran-coated charcoal and high salt does not reveal a new glucocorticoid binder

Incubation of steroid-free whole mouse brain cytosol from adrenalectomized-ovariectomized mice with saturating concentrations of tritiated dexamethasone was found to label all Type I as well as all Type II adrenocorticosteroid receptors. The quantitative and brain regional distribution of residual dexamethasone binding in cytosols pre-treated with dextran-coated charcoal (DCC) and 300 mM KCl was indistinguishable from that for tritiated aldosterone-Type I receptor complexes under the same conditions. We therefore conclude that the dexamethasone binding sites remaining after DCC and KCl treatment of steroid-free brain cytosol are due to the presence of Type I receptors. The differential sensitivity of Type I and Type II receptors to the DCC/KCl treatment paradigm may be useful in the purification of Type I receptors.