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G A Saviolakis

Publications and source records attributed to G A Saviolakis.

18 recordsLinked to original sources
PubMed2004

Accelerated Barnes maze test in mice for assessment of stress effects on memory.

Repeated restraint stress in rodents impairs spatial memory in a Y-maze test and induces hippocampal neuronal changes that last up to 5 d after the stressor ends. Our goal was to implement a Barnes maze spatial memory test in mice that could be used to validate our findings of social stress induced Y-maze impairment. We measured performance of mice in 5- and 9-day test paradigms previously used in rats and mice, respectively. Selecting features from each paradigm, we implemented a 5-d test (pre-training, training (4 trials/d/3 d) and probe testing for assessment of spatial memory in mice. Stress consisted of placing each test mouse in a stainless steel perforated box (25.5 cm x 21.5 cm x 16.5 cm) within an aggressor's home cage for 6 h/d for 21 d; direct agonistic encounters occurred randomly throughout stress periods. Barnes maze pre-training (habituation) was on day 21 of the stress exposures. In a preliminary experiment, mice that habituated following their last stressor performed poorly relative to unstressed and to those not habituated prior to the last stressor, as demonstrated by a greater latency to escape and more errors. We conclude that acute stress in a chronic stress paradigm may impair spatial memory acquisition.

Animals↗
PubMed2004

A CRH1 antagonist into the amygdala of mice prevents defeat-induced defensive behavior.

Corticotropin-releasing hormone (CRH) is believed to play an important role in the regulation of behavioral responses to stress. CRH(1) receptor antagonists may reduce stress responsivity. Stress increases CRH in the amygdala, important in memory consolidation. We hypothesized that infusion of a CRH(1) antagonist into the amygdala following social defeat would prevent the development of generalized fear responses. Acute social defeat in mice increases defense towards intruders, even nonaggressive intruders, placed within their home cage. We infused the CRH(1) antagonist antalarmin (0.25 microg/125 nl) bilaterally into the amygdala of mice immediately after defeat and measured their response to a nonaggressive intruder stimulus mouse placed within their home cage 24 h after defeat. Defeated mice that received vehicle displayed high levels of crouch defensive posture and numerous flights from intruders, relative to nondefeated mice that received vehicle. Defeated mice that received antalarmin into the amygdala exhibited significantly less defensive posture than did vehicle-treated defeated mice. Display of defensive posture in antalarmin-treated mice approached that of vehicle-treated nondefeated mice. These findings support a role for CRH in the amygdala to promote consolidation of emotional memory and indicate that antagonism of CRH(1) receptors in the amygdala may prevent the development of exaggerated fear responses in stressed mice.

Aggression↗
PubMed2000

Chronic sustained stress increases levels of anterior pituitary prolactin mRNA.

Our laboratory is investigating the effects of chronic stress on physiological, endocrine and behavioral measures, in order to elucidate the neuronal substrates for the pathophysiological consequences of stress in humans. In these studies, we have employed a rodent model of sustained stress in which rats are exposed to around-the-clock intermittent footshock that can be avoided or escaped by rats in the controllable stress group, but not by rats in the uncontrollable stress group. Each rat in the uncontrollable stress group is paired (yoked) to a rat in the controllable stress group such that the controllable stress group rat avoids or escapes shock for both rats. A third group of rats receives no shock (controls). We have previously reported that in male rats, plasma prolactin levels were elevated after 3 days of stress in both stress groups. In the present experiments we determined whether the increases in plasma prolactin were correlated with increases in anterior pituitary prolactin mRNA. In addition, we measured hormones and mRNA at three time points and we examined these responses in female as well as male rats. Adult male and female Sprague-Dawley rats were exposed to chronic stress for 1, 3 or 14 days. In unstressed control rats, levels of anterior pituitary prolactin mRNA were fivefold higher in female as compared to male rats. However, stress increased levels of anterior pituitary prolactin mRNA over baseline in both genders. After 1 day of stress, anterior pituitary prolactin mRNA levels increased in male and female rats belonging to both stress groups, with no significant difference seen between the uncontrollable vs. controllable stress groups. After 3 days of stress, anterior pituitary prolactin mRNA levels were even more elevated, and rats in the uncontrollable stress group had higher anterior pituitary prolactin mRNA levels than those in the controllable stress group. After 14 days of stress, there were no significant differences in control and stressed groups with respect to anterior pituitary prolactin mRNA. These data suggest that chronic sustained stress increases the synthesis of anterior pituitary prolactin mRNA during the first days of stress, and that levels return to prestress values sometime between 3 and 14 days of stress.

Adrenocorticotropic Hormone↗
PubMed1996

The PC12 rat pheochromocytoma cell line expresses the prodynorphin gene and secretes the 8 kDa dynorphin product.

Most adrenal chromaffin cells synthesize opioids derived from proenkephalin but not from prodynorphin. However, human pheochromocytomas and the PC12 rat pheochromocytoma cell line synthesize dynorphins. The aim of this study was to confirm the presence of the authentic prodynorphin transcript and its dynorphin product in PC12 cells. We have found that the sequence of a 458 bp cDNA fragment derived from RT-PCR amplification of total PC12 RNA was in complete accordance with the published sequence of the equivalent region of the prodynorphin gene. It encodes the potent endogenous kappa opioid agonists alpha-neo-endorphin, dynorphin A and dynorphin B. Furthermore, immunoaffinity-purified PC12 cell extracts were subjected to RP-HPLC. Most of its IR-dynorphin eluted on a peak exhibiting the retention time of similarly treated rat anterior pituitary. The expression of the prodynorphin gene in pheochromocytomas can be explained as either the result of (a) the process of dedifferentiation of chromaffin cells to pheochromocytoma which may thus cause the expression of a previously unexpressed prodynorphin or that (b) those pheochromocytomas expressing the prodynorphin gene derive from the few, centrally located chromaffin cells, which express this gene even under normal conditions.

Adrenal Medulla↗
PubMed1996

Effects of chronic stress on food acquisition, plasma hormones, and the estrous cycle of female rats.

Our laboratory has previously conducted a number of studies to determine the effects of chronic stress on the physiology and behavior of male rats. The present study was performed to extend these investigations to female rats. Female rats were chronically stressed using a behavioral paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock (stress) while another group of rats is yoked to the first group (yoked-stress) and does not have control over shock termination. Control rats were never shocked but all groups lever pressed for food pellets on an FR1 schedule (one pellet per lever press). Daily vaginal samples were obtained for several weeks prior to stress onset and throughout the chronic stress period. After 14 days of stress, the experiment was terminated and morning blood samples were collected for hormonal assays. Stress transiently decreased lever pressing for food pellets and body weights, but both measures returned to prestress levels by day 14 of stress. Plasma adrenocorticotropic hormone (ACTH) concentrations were significantly elevated in the yoked-stress group compared to the other two groups, but there were no significant effects of 14 days of stress treatment on plasma corticosterone, prolactin, estradiol, or progesterone concentrations. There were no significant differences in estrous cycle length among experimental groups.

Adrenocorticotropic Hormone↗
PubMed1986

Human Y-79 retinoblastoma cells exhibit specific insulin receptors.

The presence of insulin receptors was investigated in human Y-79 retinoblastoma cells grown in suspension culture. The binding of [125I] insulin to these cells was time, temperature, and pH dependent, was competed for by insulin and proinsulin but not other peptides, and was inhibited by antibodies against the insulin receptor. The Scatchard plot of insulin competition data was curvilinear and was resolved into a high-affinity (KD approximately 0.5 X 10(-9) M)/low-capacity (approximately 3,000 sites/cell) and a low-affinity (KD approximately 1 X 10(-7) M)/high-capacity (approximately 155,000 sites/cell) component. Negative cooperativity was not found, in agreement with other studies in rodent neural cells. However, in contrast to studies with rodent cells, insulin specifically down-regulated its receptor on human Y-79 cells after prolonged exposure. In conclusion, these data show for the first time the presence of specific insulin receptors in human Y-79 retinoblastoma cells. Because these cells were previously shown to have several characteristics typical of neural cells, we propose their use as a model to study the effects of insulin on neural and retinal tissues of human origin.

Cell Line↗
PubMed1983

Insulin receptor on monocytes from patients with acromegaly and fasting hyperglycemia.

[125I]Insulin binding to insulin receptors on circulating monocytes was studied in 9 patients with acromegaly associated with fasting hyperglycemia and was compared to previously reported studies of 11 patients with acromegaly who had normal or nearly normal glucose tolerance and 29 normal volunteers. In the hyperglycemic acromegalic, as had been found in the normoglycemic acromegalic, the total receptor concentration per cell was decreased in proportion to the hyperinsulinemia, i.e. the receptor concentration was inversely related to the basal level of insulin, similar to what is found in patients with obesity, diabetes, and insulin-secreting tumors. However, the acromegalic patients with hyperglycemia failed to show the increase in affinity of the empty receptor that had previously been found in their normoglycemic counterparts. The failure to increase receptor affinity causes the cells of the hyperglycemic acromegalic patients to bind less insulin at each insulin concentration than do the cells of normoglycemic patients. Again, the abnormalities in the patients correlates very closely with abnormalities at the level of the insulin receptor, though the sequence of the molecular events that produce these changes remains to be determined.

Acromegaly↗
PubMed1982

Mechanism of glucocorticoid-induced increase in insulin receptors of cultured human lymphocytes.

Glucocorticoids increase the number of insulin receptors in cultured human lymphocytes. This effect is specific for the insulin receptor as growth hormone receptor concentration decreases. The effect is time-dependent, dose-dependent over the physiologic concentration range of glucocorticoid, reversible, and appears to be mediated via specific glucocorticoid receptors. Protein synthesis and glycosylation are required as the effect is inhibited by actinomycin D, puromycin, cycloheximide, and tunicamycin. Isolated solubilized plasma membranes, as well as solubilized whole cells from glucocorticoid-treated lymphocytes, show the same increase in insulin receptors as do intact cells. The glucocorticoid-induced receptors are immunologically indistinguishable from control when precipitated by anti-receptor antibody. Glucocorticoids do not stabilize existing receptors since the degradation rate of receptors is actually increased. Regulation of the insulin receptor by insulin is independent of the steroid effect. However, there is a right-ward shift of the dose-response curve for "down regulation" by insulin in the presence of glucocorticoid. We conclude that glucocorticoids increase the number of insulin receptors in cultured human lymphocytes by increasing the synthesis of new receptors. This represents the first induction of insulin receptor synthesis by a pharmacologic agent.

Binding, Competitive↗
PubMed1982

Expression of oncornaviral RNA in mouse uterus during pregnancy.

The expression of oncornaviral-specific RNA was studied in the NIH Swiss mouse uterus during gestation using hybridization with complementary DNAs synthesized from type C viral high molecular weight RNAs. Following conception there was a marked decrease in the relative concentration of viral RNA below the levels in nonpregnant uteri. Thereafter, the level of viral RNA remained low (less than 30% of prepregnancy levels) until Day 14. Following Day 14 there was a progressive increase in levels of viral RNA and peak levels (greater than or equal to pregestation) were reached just before parturition (Day 18). One day after parturition viral RNA levels were still elevated. A similar profile was observed for p30, a viral-coded protein. We suggest that oncornaviral gene expression is under transcriptional control, most likely by ovarian steroid hormones, and that oncornaviruses can be useful tools to study gene expression in the mammalian uterus.

Animals↗
PubMed1981

Heterogeneity of the insulin-receptor interaction in lipoatropic diabetes.

[125] Insulin binding to its receptors was studied on circulating cells from 11 patients (8 females and 3 males) with lipoatropic diabetes. The patients ranged in age from 9-54 yr. All were insulin resistant, as evidenced by fasting hyperinsulinemia and insulin tolerance tests. Nine patients were evaluated by specific [125] insulin binding to monocytes. Three different patterns of receptor abnormalities were observed: 3 patients demonstrated decreased binding due to decreased binding capacity, 2 patients revealed normal tracer binding with decreased receptor affinity,, and 4 patients had normal or increased insulin binding. [125] Insulin binding to erythrocytes in 9 cases demonstrated similar heterogeneities of initial binding. In most cases there was a good correlation between the binding with erythrocytes and monocytes, although decreased affinity was not observed in the red blood cells. There was no obvious correlations between the nature of the receptor defect and the clinical patterns in these patients. Heterogeneity in insulin binding was even observed among affected members of the same family. Antibodies to the insulin receptor were not detected in any of these patients by either binding inhibition or immunoprecipitation assays. These data suggest that the pathogenesis of the insulin resistance in lipoatropic diabetes is heterogeneous and may involve both receptor and postreceptor abnormalities.

Adolescent↗
PubMed1980

Spontaneous adrenal tumors in the aged, ovariectomized NIH swiss mouse without enhanced retrovirus expression.

A high incidence of adrenal tumors was observed in aged female NIH Swiss mice which had been ovariectomized at 2 to 4 weeks of age but not in nonovariectomized controls. Although tumors weighing more than 1 g were not infrequent in the oldest (> 24 months) animals, adrenal glands did not appear macroscopically abnormal before the age of 18 months. Histologically, however, focal or diffuse abnormalities were found in essentially every gland examined from mice over 12 months of age, including glands of normal size. Since the NIH Swiss mouse has been shown to contain an endogenous xenotropic virus whose expression is under hormonal control, the adrenal tumors were examined in detail for evidence of abnormal viral expression. We were unable, by a variety of techniques, to demonstrate elevated expression of type C virus in these adrenal tumors.

Adrenal Gland Neoplasms↗
PubMedDate not supplied

The combined effects of pyridostigmine and chronic stress on brain cortical and blood acetylcholinesterase, corticosterone, prolactin and alternation performance in rats.

Thousands of soldiers who served in the Gulf War have symptoms that have been collectively termed Gulf War Illness (GWI). It has been suggested that a combination of operational stress and pyridostigmine, a drug given as a pretreatment to protect soldiers against the effects of exposure to nerve agents, might have had unexpected adverse health effects causing these symptoms. Our laboratory has previously modeled operational stress in rats using a paradigm of around-the-clock intermittent signalled footshock. In the present studies, this model was used to investigate the potential synergistic effects of chronic stress and pyridostigmine on physiology and behavior. Seventy-two rats were trained to perform an alternation lever pressing task to earn their entire daily food intake. The rats were then implanted with osmotic minipumps containing vehicle, pyridostigmine (25 mg/ml pyridostigmine bromide) or physostigmine (20 mg/ml eserine hemisulfate). The pumps delivered 1 microl/h, which resulted in a cumulative dosing of approximately 1.5 mg/kg/day of pyridostigmine or 1.2 mg/kg/day of physostigmine, equimolar doses of the two drugs. The rats were then returned to their home cages where performance continued to be measured 24 h/day. After 4 days, 24 of the 72 rats were trained to escape signalled footshock (avoidance-escape group) and 24 other rats (yoked-stressed group) were each paired to a rat in the avoidance-escape group. The remaining 24 rats were not subjected to footshock (unstressed group). Shock trials were intermittently presented in the home cage 24 h/day for 3 days, while alternation performance continued to be measured. Since only 12 test cages were available, each condition was repeated to achieve a final n of six rats per group. Pyridostigmine and physostigmine each decreased blood acetylcholinesterase levels by approximately 50%. Physostigmine also decreased brain cortical acetylcholinesterase levels by approximately 50%, while pyridostigmine had no effect on cortical acetylcholinesterase activity. Alternation performance was impaired on the first day of stress and then recovered. Neither pyridostigmine nor physostigmine affected performance in the absence of stress or increased the effects of stress alone. Corticosterone was significantly increased in the yoked stress group compared to unstressed controls. These data suggest that pyridostigmine does not exacerbate the effects of stress on performance or levels of stress hormones. Furthermore, these data do not suggest that stress enables pyridostigmine to cross the blood brain barrier.

Acetylcholinesterase↗
PubMedDate not supplied

Hemorrhagic fever with renal syndrome in Greece: clinical and laboratory characteristics.

The clinical and laboratory characteristics of a severe form of hemorrhagic fever with renal syndrome (HFRS) in Greece are presented. Twenty-seven patients with serologically confirmed HFRS were studied; 10 required renal dialysis, six had hemorrhagic manifestations, and four died. In patients with hemorrhagic manifestations, the platelet counts were generally less than 100,000 cells/microL. In three patients findings were compatible with disseminated intravascular coagulation. Laboratory investigation showed a consistent rise in levels of serum urea nitrogen and creatinine beginning on the fifth or sixth day of illness and reaching a maximum level between the ninth and 12th days of illness. The disease in Greece more closely resembles the Asian form of HFRS (Korean hemorrhagic fever) than the Scandinavian form of the disease (nephropathia epidemica) because of the high mortality rate, the occurrence of hemorrhagic manifestations, and the severity of the clinical disease.

Creatinine↗