Biomedical subjects

R R Sakai

Publications and source records attributed to R R Sakai.

At least 37 records · Page 2Linked to original sources

PubMed1996

Chronic social stress produces reductions in available splenic type II corticosteroid receptor binding and plasma corticosteroid binding globulin levels.

Adult male and female rats were housed for 2 weeks in a Visible Burrow System resulting in the development of strong dominant-subordinate relationships among the male rats. Neuroendocrine measures indicated that the subordinate rats, and to a lesser extent dominant rats, experienced chronic HPA axis hyperstimulation during the 2 week experience. This paper focuses on the consequences of this chronic social stress on cytosolic type II corticosteroid receptor binding in the spleen. In the first study, rats were adrenalectomized 18 h prior to sacrifice in order to measure total cellular receptor protein levels in each animal. In spite of the severity of the social stress, there was no decrease in splenic type II corticosteroid receptor binding levels in these short-term adrenalectomized animals. In the second study, rats were left adrenal-intact. Corticosteroid receptor levels in these adrenal-intact animals reflect the level of receptors (available receptors) that were unoccupied by endogenous hormone at the time of sacrifice. Both subordinate and dominant rats had fewer available splenic type II receptors than control rats, suggesting that a greater proportion of receptors in subordinate and dominant rats were occupied and activated by endogenous hormone at the time of sacrifice than in control rats. The differences in available receptor levels were not a function of total plasma corticosterone levels at the time of sacrifice (mean corticosterone levels were the same for control and subordinate rats). Instead, the differences in available receptor levels may have been a function of plasma corticosteroid binding globulin (CBG) levels which regulate free corticosterone levels. There was a large reduction in plasma CBG levels of subordinate (-70%) and dominant (-40%) rats relative to control rats, and there was a significant correlation between plasma CBG level and available type II receptors in the spleen. These results suggest that a decrease in CBG levels as a result of chronic social stress led to greater access of free corticosterone hormone to type II receptors in the spleen than is typically present in rats under basal or acute stress conditions. This result illustrates one mechanism by which chronic stress may have a greater impact than acute stress on splenic immune function.

Animals↗

PubMed1996

Intracerebral administration of mineralocorticoid receptor antisense oligonucleotides attenuate adrenal steroid-induced salt appetite in rats.

The amygdala contains mineralocorticoid (MR) and glucocorticoid receptors (GR) involved in the arousal of salt appetite. In the present investigation, MR antisense oligonucleotides injected into the amygdala inhibited salt appetite induced by systemic desoxycorticosterone (DOCA) but not adrenalectomy (ADX). In contrast, GR antisense or scrambled oligonucleotides had no effect on stimulated salt intake. MR antisense oligomers also decreased MR but not GR in amygdala, whereas GR antisense oligomers decreased GR but not MR. Immunocytochemical labelling of the biotinylated MR antisense revealed that distribution of the oligomer was restricted to the injection site, with incorporation in neurons and neighboring glial cells. Together, these data demonstrate the utility of receptor antisense oligonucleotides for investigating the central actions of adrenal steroids and the role of amygdala in MR in DOCA-induced sodium intake.

Animals↗

PubMed1995

Intracerebroventricular administration of angiotensin type 1 (AT1) receptor antisense oligonucleotides attenuate thirst in the rat.

The central actions of the peptide hormone angiotensin II (AngII) are importantly involved in body fluid homeostasis. Included amongst these actions is a potent dipsogenic response that has been implicated in the thirst that develops during many forms of extracellular dehydration. The use of highly selective receptor antagonists has revealed that the Type 1 (AT1), and not the Type 2 (AT2), AngII receptor subtype mediates this drinking response. More recently, antisense oligonucleotides specific for the AT1 receptor have been developed and after intracerebroventricular (i.c.v.) administration, they significantly reduce the dipsogenic response elicited by a similar injection of AngII. In the present study AT1 antisense oligonucleotides were used to further investigate their effect on experimentally induced thirst in the rat. In addition, immunohistochemical analysis of biotin-labeled oligonucleotides was performed in order to correlate the behavioral effects of the oligonucleotides with their distribution in the brain. The results demonstrated that the antidipsogenic effects of the oligonucleotides were dose and time-dependent and were limited to those thirst challenges that involve activation of the renin-angiotensin system. Collectively, these results demonstrate the efficacy and behavioral specificity of these oligonucleotides, as well as their utility in investigating the physiological role of cerebral AngII receptor subpopulations in various models of thirst.

Analysis of Variance↗

PubMed1995

Serotonin receptor binding in a colony model of chronic social stress.

Male rats housed in mixed-sex groups quickly established dominance hierarchies in which subordinates appeared severely stressed. Subordinate rats had elevated basal corticosterone (CORT) levels relative to dominants and individually housed controls. Several subordinates had blunted CORT responses to a novel stressor, leading to the classification of subordinates as either stress-responsive or nonresponsive. Binding to 5-HT1A receptors was reduced in stress-responsive subordinates compared to controls throughout hippocampus and dentate gyrus. Decreased binding was observed in nonresponsive subordinates only in CA3 of hippocampus. In addition, 5-HT1A binding was decreased in CA1, CA3, and CA4 in dominants compared to controls. Binding to 5-HT2 receptors was increased in parietal cortex in both responsive and nonresponsive subordinates compared to controls. No changes were observed in binding to 5-HT1B receptors. These results are discussed in the context of regulation of the serotonergic system by stress and glucocorticoids and possible relevance to the pathophysiology of depression.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1995

Effects of chronic social stress on tyrosine hydroxylase mRNA and protein levels.

Males housed in mixed sex groups quickly form dominance hierarchies; subordinates can be further subdivided into stress responsive subordinates (SRS) and non-responsive subordinates (NRS) based on corticosterone responses to a novel stressor. Tyrosine hydroxylase (TH) mRNA levels measured with in situ hybridization were elevated in locus coeruleus (LC) of NRS compared to singly or pair-housed controls; NRS also had higher TH levels than dominants. TH protein levels determined by immunoautoradiography were also higher in LC of NRS and SRS versus pair-housed controls.

Animals↗

PubMed1995

Visible burrow system as a model of chronic social stress: behavioral and neuroendocrine correlates.

In mixed-sex rat groups maintained in visible burrow systems (VBS), consistent asymmetries in offensive and defensive behaviors of male dyads are associated with the development of dominance hierarchies. Subordinate males are characterized by particular wound patterns, severe weight loss, and a variety of behavioral changes, many of them isomorphic to target symptoms of clinical depression. In two VBS studies, subordinate males showed increased basal levels of plasma corticosterone (CORT), and increased adjusted adrenal and spleen weights compared to controls, and often, to dominants as well. Thymus weights and testosterone levels of subordinates were not reliably different in one study using highly aggressive males, but were reduced, along with testes weights, in a second study using unselected males. Glucocorticoid receptor binding levels in hippocampus, hypothalamus, and pituitary were not different, nor were aldosterone levels. When tested in a restraint stress procedure, subordinates had higher basal CORT levels, but about 40% of these animals showed a reduced, or absent, CORT response to restraint. These findings indicate that subordination may be reflected in high magnitude changes consistent with physiological indices of prolonged stress. Dominant rats of such groups may also show physiological changes suggesting stress, particularly when the groups are comprised of highly aggressive males only. The VBS colony model thus appears to enable rat groups to produce natural, stress-engendering, social interactions that constitute a particularly relevant model for investigating the behavioral, neural, and endocrine correlates of chronic stress.

Adrenal Glands↗

PubMed1995

Endocrine consequences of prenatal sodium depletion prepare rats for high need-free NaCl intake in adulthood.

Offspring of dams that were repeatedly sodium depleted during late pregnancy (at days E14, E17, and E20) expressed high need-free 3% NaCl intake in adulthood. Need-free 3% NaCl intake was greater in females, thereby respecting the sexual dimorphism of this behavior, and was increased further by successive sodium depletion in adulthood. Offspring from dams that had been sodium depleted while receiving the angiotensin-converting enzyme inhibitor, captopril, showed a need-free NaCl intake similar to that of control rats nonneonatally sodium depleted. Trunk blood taken from dams at day E18, i.e., 24 h after the second treatment, revealed that sodium depletion produced marked increases in the dam's plasma angiotensin (ANG) II and aldosterone that were not present when dams were treated with captopril during sodium depletion, even though both groups displayed a similar hyponatremia. We therefore propose that, during prenatal sodium depletion, the activation of the angiotensin-aldosterone system rather than the loss of sodium itself is responsible for the modification in need-free NaCl intake behavior. Finally, we suggest that, during pregnancy, ANG II may have an organizational effect on the neural substrate in the fetal brain that subserves subsequent NaCl intake behavior.

Aging↗

PubMed1994

Immunohistochemical mapping of angiotensin type 2 (AT2) receptors in rat brain.

Recently developed antisera selective for angiotensin Type 2 (AT2) receptors were used to localize AT2 receptors in rat brain by immunohistochemistry. While the results from these experiments were largely consistent with previous autoradiographic and radioligand binding analyses of AT2 receptor populations in brain, there were also some notable differences in the distribution of immunoreactivity. More specifically, in agreement with previous studies, AT2 antisera detected apparent receptor populations in the locus coeruleus and the bed nucleus of the accessory olfactory tract, whereas AT2 receptor-immunoreactivity in the cerebellum was primarily associated with the Purkinje cell layer and the deep cerebellar nuclei rather than the molecular layer as has been previously reported in autoradiographic studies. Other regions with prominent immune-staining included all subfields of the hippocampus, which had been previously reported to contain exclusively AT1 receptors. Limbic structures such as the amygdala, thalamic areas such as the rhomboid thalamic nucleus, the paraventricular thalamic nucleus, hypothalamic areas such as the paraventricular hypothalamic nucleus, and the supraoptic nucleus also exhibited prominent AT2-immunoreactivity. In the paraventricular hypothalamic nucleus, AT2 receptor staining appeared to be associated primarily with the magnocellular neurons. In all regions examined, AT2 receptor immunoreactivity was associated with the cytoplasm and cell membrane and was not localized within the nucleus. Collectively, these results confirm and extend the neuroanatomical resolution of previous autoradiographic studies as well as identify new AT2 receptor populations in rat brain.

Angiotensin II↗

PubMed1994

Intracerebroventricular administration of AT1 receptor antisense oligonucleotides inhibits the behavioral actions of angiotensin II.

Antisense oligonucleotides were developed to study the expression and function of angiotensin type 1 (AT1) receptors in cultured cells and brain. In both liver epithelial WB and neuroblastoma N1E-115 cells AT1 antisense oligomers substantially decreased AT1 receptor density, whereas angiotensin type 2 (AT2) receptors remained unchanged. Similarly, repeated intracerebroventricular injections of AT1 antisense oligomers in rats decreased AT1 receptor density in hypothalamic-thalamic-septal tissue, and AT2 receptors were unaffected. Intracerebroventricular antisense oligomers also attenuated drinking elicited by intracerebroventricular angiotensin II but not the cholinomimetic carbachol. Collectively, these results demonstrate that antisense oligonucleotides attenuate angiotensin receptor expression and function in behaving animals.

Angiotensin II↗

PubMed1994

Reciprocal changes in plasma corticosterone and testosterone in stressed male rats maintained in a visible burrow system: evidence for a mediating role of testicular 11 beta-hydroxysteroid dehydrogenase.

The purpose of these studies was to investigate the possible role of rat Leydig cell 11 beta-hydroxysteroid dehydrogenase (11HSD) in mediating the inhibitory effects of corticosterone on testosterone production. In a unique communal environment, the visible burrow system, male Long-Evans rats spontaneously segregated into unstressed dominant and stressed subordinate social relationships. Subordinate animals had elevated plasma corticosterone and diminished circulating testosterone levels relative to the dominant animals. The categories of animals were distinguished by behavioral criteria: weight change, wounds received, offensive and defensive behavior, and freedom of movement. As a result of their persistently elevated corticosterone levels, subordinate animals had smaller thymi and larger adrenals and spleens than dominants. We have postulated that Leydig cells are protected against the inhibitory effects of glucocorticoids on testosterone secretion by the inactivating effects of 11HSD. High corticosterone and low 11HSD are predicted to suppress testosterone production, and normal or diminished corticosterone levels combined with normal or elevated 11HSD should permit undiminished testosterone production. Consistent with these predictions, the testes of subordinate animals contained significantly lower 11HSD activity than those of dominant animals. The 11HSD of livers of subordinate and dominant animals were statistically indistinguishable. The results of this study support the postulated role of 11HSD as a protector of Leydig cell function.

11-beta-Hydroxysteroid Dehydrogenases↗

PubMed1993

Subordination stress: behavioral, brain, and neuroendocrine correlates.

In mixed-sex rat groups consistent asymmetries in offensive and defensive behaviors of male dyads are associated with the development of dominance hierarchies. Subordinate males can be differentiated from dominants on the basis of both agonistic and non-agonistic behaviors, wound patterns, weight changes. Their behavior changes suggest chronic defensiveness and are also broadly isomorphic to many of the symptoms of depression; their voluntary alcohol consumption increases, and their life-spans are shortened. Both subordinate and dominant males tend to show organ change compared to non-grouped controls, with adrenal and spleen enlargement and thymus reduction. However, these changes appear to be more marked in subordinates, and only subordinates show reduced testes weights. Basal corticosterone (CORT) levels were sharply higher, and plasma testosterone (T) sharply lower, in subordinates compared to both dominants and controls, and reduced corticosterone binding globulin further enhanced free CORT for subordinates particularly. Many subordinates failed to show a normal CORT response to restraint stress. Subordinates also appear to show widespread changes in serotonin systems, with increased 5-HIAA/5-HT ratios in a number of brain areas, and alterations of 5-HT1A receptor binding at some sites. These changes suggest that subordination, a common and consistent feature of life for many animals living in social groups, may be a particularly relevant model for investigating the behavioral, neural and endocrine correlates of chronic stress.

Aggression↗

PubMed1993

Stress and antidepressant effects on hippocampal and cortical 5-HT1A and 5-HT2 receptors and transport sites for serotonin.

The interactions between 14 days of repeated restraint stress and daily administration of imipramine or tianeptine (2 h before the beginning of stress) were investigated in rats to assess responses of 5-HT2 and 5-HT1A receptors and serotonin transporter sites labelled by [3H]paroxetine in the cerebral cortex and hippocampus, two brain regions in which adrenal steroid effects on serotonin receptor-binding have been reported. 5-HT2 sites, labelled by [125I]7-amino-8-iodo ketanserin, were decreased in parietal cerebral cortex layers 3 and 5 by imipramine treatment, but not by tianeptine treatment and not by daily restraint stress. Stress, but not antidepressant, depressed 5-HT1A sites labelled with [3H]8-hydroxy-DPAT in hippocampal fields CA3, CA4 and dentate gyrus. [3H]paroxetine-binding to serotonin transporter sites was decreased by tianeptine treatment as well as by imipramine in both hippocampus and cerebral cortex, with some overlap of the fields that were significantly affected, whereas there were no effects of stress per se and no evidence of a stress x drug interaction. These results are discussed in relation to similarities and differences in the effects of different antidepressant drugs on the serotonergic system of the rat brain. Whereas the actions of imipramine and tianeptine on 5-HT2 and 5-HT1A receptors are specific to each drug, the surprising finding of a similar effect of both drugs to reduce serotonin transporter sites labelled by [3H]paroxetine suggest the possibility of a common action for these two drugs in spite of their opposite effects on serotonin re-uptake.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1993

Glucocorticoids facilitate mineralocorticoid-induced sodium intake in the rat.

We confirm and extend the finding that glucocorticoids facilitate mineralocorticoid-induced sodium intake in the rat. First, we report that subcutaneous injections of dexamethasone (DEX) increase deoxycorticosterone-induced sodium intake. Second, we demonstrate that continuous intravenous infusions of either DEX or corticosterone or the TYPE II glucocorticoid receptor agonist RU28362 increases the sodium intake of aldosterone-treated rats. And third, we measured urine sodium loss and found that rats were in positive sodium balance while receiving aldosterone and the glucocorticoid agonist, suggesting that the increased intake of sodium was primary to renal sodium loss. When taken together with the fact that glucocorticoids can increase the TYPE I aldosterone-preferring receptor population in the brain, the results suggests a role for the glucocorticoid hormones in the arousal of sodium appetite in the rat.

Aldosterone↗

PubMed1993

Differential inhibition of 11 beta-hydroxysteroid dehydrogenase by carbenoxolone in rat brain regions and peripheral tissues.

Carbenoxolone (CX), the succinyl ester of glycyrrhetinic acid, causes hypokalemia and hypernatremia. Its pharmacological effects are believed to be due to its inhibition of 11 beta-hydroxysteroid dehydrogenase (11-HSD). There was a marked inhibition of this enzyme in the liver, kidney, pituitary, hippocampus, hypothalamus and amygdala 1 h after intraperitoneal administration of CX (100 mg kg-1) to intact male rats. Intracerebral injection of CX (1.5 mg kg-1) into the 3rd ventricle inhibited the oxidation of corticosterone to 11-dehydrocorticosterone by 11-HSD in the pituitary and hippocampus and produced marked behavioral hyperactivity but had no effect in the liver or kidney. Lower amounts of CX (10-50 micrograms/rat) given intracerebroventricularly (i.c.v) were without significant effect on 11-HSD in the pituitary or amygdala 1 h after infusion but inhibited this enzyme differentially in the hippocampus and hypothalamus. Inhibition of 11-HSD activity in the hippocampus and hypothalamus was observed up to 6 h after i.c.v. administration of CX (50 micrograms/rat) together with some decrease in activity of this enzyme in the pituitary at 3 h. The findings that low doses of CX given i.c.v. can alter the activity of 11-HSD in specific brain regions without affecting its activity in peripheral tissues, and only marginally in the pituitary, provides a method to study the central role of this enzyme independently of systemic effects.

11-beta-Hydroxysteroid Dehydrogenases↗

PubMed1992

Sex and sodium intake in the rat.

Female rats drink more 3% NaCl solution than do males, both when they need sodium (need-induced sodium intake or sodium appetite) and when they do not (need-free sodium intake). The sexual dimorphism of sodium intake is a secondary sexual characteristic because after castration at 1 day of age male rats drank 3% NaCl in adulthood in a manner similar to that of females in both the need-free and need-induced state, and females given long-term, neonatal testosterone drank low, malelike volumes of 3% NaCl on a daily need-free basis, but their response to sodium depletion was unchanged. This sexual dimorphism of sodium intake seems to be governed by testosterone that has been converted in the brain to estrogen because treatment of Day 1 castrated females with a nonaromatizable androgen, dihydrotestosterone, did not change either their need-free or their need-induced 3% NaCl intake. Castration in adulthood of male and female rats did not change their sodium consumption. However, when castrated adults received testosterone, need-free intakes of NaCl were suppressed in both sexes, but the suppression of 3% NaCl intake occurred only while the steroid was present. Exogenous testosterone also lowered the need-induced sodium intake of adult castrated females. Thus, in castrated adults, need-free intake was actively suppressed by exogenous testosterone in both sexes, whereas need-induced intake of NaCl was suppressed only in females. These data indicate that sodium intake in the rat is a sexually dimorphic behavior that is organized neonatally and can be actively suppressed in adulthood by testosterone.

Aggression↗

PubMed1992

The vulnerability of the hippocampus to protective and destructive effects of glucocorticoids in relation to stress.

The pituitary-adrenal axis participates in the diurnal response of the organism to the environment and in its response to stress. Circulating glucocorticoid and mineralocorticoid hormones act on cells in the brain via Type I and Type II receptors, which operate at the level of gene regulation, and mediate various feedback effects of adrenal steroids on brain chemistry and structure, including the operation of second-messenger generating systems, levels of structural proteins of glial cells, and the death and survival of neurons. The hippocampus is prominent in these effects, and it also displays the highest level of Type I receptors of any brain region. New concepts point to a special role of the hippocampus, a nexus of cognition and emotion, in the feedback actions of adrenal steroids during the diurnal rhythm, and in response to stress. The hippocampus is, therefore, a prime target area for investigation of the events which accompany stress, and which may be related to the maladaptive state that results in depressive illness. Initial studies are described which investigate the effects of tianeptine on pituitary-adrenal function, hippocampal morphology and Type I and Type II receptor levels.

Animals↗

PubMed1991

Effects of aldosterone or RU28362 treatment on adrenalectomy-induced cell death in the dentate gyrus of the adult rat.

Previous studies have shown that granule cells of the adult dentate gyrus require adrenal steroids for their survival. In order to investigate whether activation of type I or type II adrenal steroid receptors can mediate granule cell survival, we have analyzed the density of pyknotic cells in the granule cell, CA1 and CA3 pyramidal cell layers in Nissl stained hippocampal sections from adult male rats which were either sham operated, adrenalectomized, or adrenalectomized and treated with aldosterone as a specific type I receptor agonist or RU28362 as a specific type II receptor agonist. Aldosterone treatment completely protected the dentate gyrus from adrenalectomy-induced cell death, while treatment with RU28362 resulted in only a partial protection against cell death in this region. These results indicate that type I adrenal steroid receptor activation is sufficient to protect against adrenalectomy-induced cell death.

Adrenalectomy↗

PubMed1991

Regional distribution of 11 beta-hydroxysteroid dehydrogenase in rat brain.

The activity and distribution of 11 beta-hydroxysteroid dehydrogenase in rat brain is described. Oxidation of corticosterone to 11-dehydrocorticosterone was significantly increased by NADP; the reverse reaction was increased by NADPH. Cortisol was a poor substrate. Both 11-dehydrogenase (11-DH) and 11-oxoreductase (11-OR) activities were found in brains of rats from 6 days to adult, and 11-DH and 11-OR activities were positively correlated with each other. Highest enzyme activities were found in pituitary, cerebellum, hippocampus, and cortex. Lower levels were found in the olfactory region, hypothalamus, brain stem, preoptic nucleus, and amygdala. Two antisera to 11-DH, designated 56-125 and 56-126, reacted with a 34K component corresponding in mass to rat liver 11-DH on Western blots. The dominant species of protein in all brain regions reacting with rat liver 11-DH antibody 56-125, was at 26K mol wt. Antiserum 56-126 did not cross-react with the 26K protein. The 26K component was not a 34K degradation product. In each region of the brain, Western blot analysis showed that the 26K band intensity was directly proportional to enzyme activity. However, the 26K protein was devoid of 11-DH activity. All 11-DH and 11-OR activities were associated with the 34K antigen. The data demonstrate the nonuniform distribution of 11-DH in brain tissue. They are consistent with the notion that 11-DH may confer upon brain the ability to control intracellular levels of active glucocorticoids and in this way mediate steroid function within the cell.

11-beta-Hydroxysteroid Dehydrogenases↗