Saline-infused Controls Research Articles

Interleukin-10 Administration and Bacterial Endotoxin-Induced Preterm Birth in a Rat Model

In Brief OBJECTIVE To determine whether intrauterine infusion of interleukin-10 prevents preterm delivery in rats treated with endotoxin. METHODS Pregnant rats underwent implantation of uterine catheters and were randomly assigned to receive intrauterine infusion of either normal saline, 50 μg lipopolysaccharide endotoxin, or 50 μg lipopolysaccharide with 500 ng interleukin-10 administered either concurrently or 24 hours later. The interval from infusion to delivery for each group was recorded, along with the number of live born pups and their birth weight. We calculated that to obtain a power of 80%, assuming a 24-hour difference in the treatment to delivery times between the test and control subjects, at least six animals would be needed in each group. RESULTS In females receiving lipopolysaccharide (50 μg) alone, the interval to delivery (P < .05), live birth rate (P < .05), and pup weight (P < .001) were reduced compared with the saline-infused controls. In contrast, females receiving interleukin-10 at the time of the endotoxin challenge or 24 hours after delivered at term with no difference in litter size or live birth weight compared with the controls. CONCLUSION Animals treated with both lipopolysaccharide and interleukin-10, administered concurrently or 24 hours after the endotoxin challenge, delivered normal weight pups at term with a similar litter size as the saline-infused controls. Interleukin-10 appears to be effective in preventing endotoxin-induced preterm birth and fetal wastage in pregnant rats. Interleukin-10 prevents endotoxin-induced preterm birth in a rat model.

Interleukin-10 administration and bacterial endotoxin-induced preterm birth in a rat model

Objective: To determine whether intra-uterine infusion of interleukin-10 prevents preterm delivery in rats treated with endotoxin. Methods: Pregnant rats underwent implantation of uterine catheters and were randomly assigned to receive intrauterine infusion of either normal saline, 50 μg lipopolysaccharide endotoxin, or 50 μg lipopolysaccharide with 500 ng interleukin-10 administered either concurrently or 24 hours later. The interval from infusion to delivery for each group was recorded, along with the number of live born pups and their birth weight. We calculated that to obtain a power of 80%, assuming a 24-hour difference in the treatment to delivery times between the test and control subjects, at least six animals would be needed in each group. Results: In females receiving lipopolysaccharide (50 μg) alone, the interval to delivery ( P < .05), live birth rate ( P < .05), and pup weight ( P < .001) were reduced compared with the saline-infused controls. In contrast, females receiving interleukin-10 at the time of the endotoxin challenge or 24 hours after delivered at term with no difference in litter size or live birth weight compared with the controls. Conclusion: Animals treated with both lipopolysaccharide and interleukin-10, administered concurrently or 24 hours after the endotoxin challenge, delivered normal weight pups at term with a similar litter size as the saline-infused controls. Interleukin-10 appears to be effective in preventing endotoxin-induced preterm birth and fetal wastage in pregnant rats.

Exendin-4 reduces fasting and postprandial glucose and decreases energy intake in healthy volunteers.

Exendin-4 is a long-acting potent agonist of the glucagon-like peptide 1 (GLP-1) receptor and may be useful in the treatment of type 2 diabetes and obesity. We examined the effects of an intravenous infusion of exendin-4 (0.05 pmol. kg(-1). min(-1)) compared with a control saline infusion in healthy volunteers. Exendin-4 reduced fasting plasma glucose levels and reduced the peak change of postprandial glucose from baseline (exendin-4, 1.5 +/- 0.3 vs. saline, 2.2 +/- 0.3 mmol/l, P < 0.05). Gastric emptying was delayed, as measured by the paracetamol absorption method. Volunteers consumed 19% fewer calories at a free-choice buffet lunch with exendin-4 (exendin-4, 867 +/- 79 vs. saline 1,075 +/- 93 kcal, P = 0.012), without reported side effects. Thus our results are in accord with the possibility that exendin-4 may be a potential treatment for type 2 diabetes, particularly for obese patients, because it acts to reduce plasma glucose at least partly by a delay in gastric emptying, as well as by reducing calorie intake.

Direct evidence for tonic sympathetic support of resting metabolic rate in healthy adult humans.

The sympathetic nervous system (SNS) plays an important role in the regulation of energy expenditure. However, whether tonic SNS activity contributes to resting metabolic rate (RMR) in healthy adult humans is controversial, with the majority of studies showing no effect. We hypothesized that an intravenous propranolol infusion designed to achieve complete beta-adrenergic blockade would result in a significant acute decrease in RMR in healthy adults. RMR (ventilated hood, indirect calorimetry) was measured in 29 healthy adults (15 males, 14 females) before and during complete beta-adrenergic blockade documented by plasma propranolol concentrations > or =100 ng/ml, lack of heart rate response to isoproterenol, and a plateau in RMR with increased doses of propranolol. Propranolol infusion evoked an acute decrease in RMR (-71 +/- 11 kcal/day; -5 +/- 0.7%, P < 0.0001), whereas RMR was unchanged from baseline levels during a saline control infusion (P > 0.05). The response to propranolol differed from the response to saline control (P < 0.01). The absolute and percent decreases in RMR with propranolol were modestly related to baseline plasma concentration of norepinephrine (r = 0.38, P = 0.05; r = 0.44, P = 0.02, respectively). These findings provide direct evidence for the concept of tonic sympathetic beta-adrenergic support of RMR in healthy nonobese adults.

Aluminium toxicity in the rat brain: histochemical and immunocytochemical evidence

Although the neurotoxic actions of aluminium (Al) have been well documented, its contribution to neurodegenerative diseases such as Alzheimer’s disease remains controversial. In the present study, we applied histochemical techniques to identify changes induced by intracerebroventricular Al injections (5.4 μg in 5.5 μl, daily over a period of 5 successive days) in the adult rat brain after survival periods of either 1 or 6 weeks. For both Al- and saline-infused controls, no major signs of gross histological changes were evident in cresyl violet-stained sections. Al (as indicated by the fluorescent Morin staining) was concentrated in white matter of the medial striatum, corpus callosum, and cingulate bundle. Immunoreactivity of astrocytes and phagocytic microglia based on glial fibrillary acidic protein and ED1 markers, respectively, revealed a greater inflammatory response in Al-injected animals compared to controls. Damage of the cingulate bundle in Al-treated animals led to a severe anterograde degeneration of cholinergic terminals in cortex and hippocampus, as indicated by acetylcholinesterase labelling. Our data suggest that the enhancement of inflammation and the interference with cholinergic projections may be the modes of action through which Al may cause learning and memory deficits, and contribute to pathological processes in Alzheimer’s disease.

Adaptation of beta-cell mass to substrate oversupply: enhanced function with normal gene expression.

Although type 2 diabetes mellitus is associated with insulin resistance, many individuals compensate by increasing insulin secretion. Putative mechanisms underlying this compensation were assessed in the present study by use of 4-day glucose (GLC; 35% Glc, 2 ml/h) and lipid (LIH; 10% Intralipid + 20 U/ml heparin; 2 ml/h) infusions to rats. Within 2 days of beginning the infusion of either lipid or glucose, plasma glucose profiles were normalized (relative to saline-infused control rats; SAL; 0.45% 2 ml/h). During glucose infusion, plasma glucose was maintained in the normal range by an approximately twofold increase in plasma insulin and an approximately 80% increase in beta-cell mass. During LIH infusion, glucose profiles were also maintained in the normal range. Plasma insulin responses during feeding were doubled, and beta-cell mass increased 54%. For both groups, the increase in beta-cell mass was associated with increased beta-cell proliferation (98% increase during GLC and 125% increase during LIH). At the end of the 4-day infusions, no significant changes were observed in islet-specific gene transcription (i.e., the expression of islet hormone genes, glucose metabolism genes, and insulin transcription factors were unaffected). Two days after termination of the infusions, the glucose-stimulated plasma insulin response was increased approximately 67% in glucose-infused animals. No sustained effect on insulin secretory capacity was observed in the LIH animals. The increase in plasma insulin response after glucose infusion was achieved in the absence of any change in insulin clearance. We conclude that, in rats, an increase in insulin demand after an increase in glucose appearance or free fatty acid leads to an increase in beta-cell mass, mediated in part by an increase in beta-cell proliferation, and that these compensatory changes lead to increased insulin secretion, normal plasma glucose levels, and the maintenance of normal islet gene expression.

GLP-2α accelerates recovery of mucosal absorptive function after intestinal ischemia/reperfusion

Background/Purpose: The authors' previous laboratory results have shown that rats treated for 3 days with intravenous GLP-2α, a synthetic protease-resistant form of glucagonlike peptide-2, showed increased mucosal mass and absorptive function when compared with saline-treated controls after intestinal ischemia/reperfusion (I/R). This study was designed to explore the temporal relationship between injury that occurs secondary to intestinal I/R and recovery of mucosal absorptive function with and without GLP-2α treatment. Methods: Each of 18 male Sprague-Dawley rats (300 to 333 g) was subjected to superior mesenteric artery occlusion for 30 minutes, during which time a jugular venous catheter was placed and connected to a subcutaneous infusion pump. Rats were divided into 4 groups based on the type and duration of infusion as follows: group 1, systemic saline at 1 μL/h for 24 hours (n = 5); group 2, systemic GLP-2α at 100 μg/kg/d for 24 hours (n = 5); group 3, systemic saline at 1 μL/h for 72 hours (n = 4); and group 4, systemic GLP-2α at 100 μg/kg/d for 72 hours (n = 4). Immediately after the infusions, 14C-galactose and 14C-glycine absorption was measured using an in vivo, closed-recirculation technique and expressed as micromoles per square centimeter intestine ± SEM. Statistical analysis was performed using analysis of variance. Results: Twenty-four hours after intestinal I/R injury, there was a decrease in substrate absorption but no significant difference between the saline and GLP-2α—treated groups (galactose absorption, 1.13 ± 0.09 in group 1 v 1.35 ± 0.11 in group 2, P =.15; glycine absorption, 1.18 ± 0.13 in group 1 v 1.34 ± 0.15 in group 2, P =.36). However, after the 72-hour infusion, absorption of galactose and glycine was significantly increased in the rats receiving GLP-2α as compared with the saline-infused control group (galactose absorption, 1.24 ± 0.13 in group 3 v 1.88 ± 0.10 in group 4, P <.01; glycine absorption, 1.64 ± 0.07 in group 3 v 2.05 ± 0.08 in group 4, P <.05). Compared with previously determined levels of absorption in normal, uninjured rat intestine (1.50 ± 0.12 μmol/cm2 for galactose and 1.85 ± 0.17 μmol/cm2 for glycine), after I/R a 72-hour infusion of GLP-2α increased galactose absorption 26% (P <.05) and glycine absorption 11% (P =.29) beyond baseline. Conclusions: When initiated at the time of intestinal I/R, a continuous infusion of GLP-2α accelerated recovery of mucosal absorptive function in rats. Remarkably, carbohydrate absorption at 72 hours was increased to a level significantly greater than that in normal, uninjured rat intestine. J Pediatr Surg 36:570-572. Copyright © 2001 by W.B. Saunders Company.

Inhibitory effects of central neuropeptide Y on the somatotropic and gonadotropic axes in male rats are independent of adrenal hormones

Neuropeptide Y (NPY) in the hypothalamus exerts multiple physiological functions including stimulation of adipogenic pathways such as feeding and insulin secretion as well as inhibition of the somatotropic and gonadotropic axes. Since hypothalamic NPY-ergic activity is increased by negative energy balance, NPY enables coordinated regulation of growth and reproduction in parallel with energy availability. Chronic pathological increases in central NPY-ergic activity contribute to obesity. Many of the adipogenic effects of NPY are specifically dependent on adrenal glucocorticoids. However, in the current study we show that central NPY does not require adrenal hormones to inhibit the somatotropic and gonadotropic axes in rats. Male adrenalectomized and sham-operated normal rats were intracerebroventricularly (ICV) infused with NPY (15 μg/day) or saline for 5–7 days, and plasma leptin, insulin-like growth factor (IGF-1) and testosterone were assayed, and epididymal white adipose tissue (WATe) was weighed. In normal intact rats, WATe weight and leptinemia were significantly increased by NPY, and these effects were prevented by adrenalectomy. In normal rats, NPY markedly reduced plasma IGF-1 levels (470 ± 40 versus 1260 ± 90 ng/ml) and testosterone (0.53 ± 0.28 versus 5.4 ± 0.80 nmol/l in saline-infused controls, p < 0.0001). Adrenalectomy decreased plasma IGF-1 concentrations to 290 ± 30 ( p < 0.0001 versus normal rats), which were significantly reduced further by NPY. However, adrenalectomy had no significant effect on basal nor on NPY-induced plasma testosterone concentrations. In conclusion unlike the stimulatory effects of NPY on fat mass and leptinemia, NPY-induced inhibition of the somatotropic and gonadotropic axes in male rats do not require adrenal hormones.

Plasminogen activator inhibitor-1 expression is regulated by the angiotensin type 1 receptor in vivo

The fibrinolytic system plays an important role in degrading fibrin-rich thrombi and in vascular and tissue remodeling. Elevated levels of plasminogen activator inhibitor-1 (PAI-1) can reduce the efficiency of the endogenous fibrinolytic system. Angiotensin (Ang) has been shown to regulate PAI-1 expression via the Ang type 1 (AT1) receptor in some tissues and via the AT4 receptor in cultured endothelium. The purpose of this study was to examine the tissue-specific pattern of PAI-1 expression in response to infusion of Ang II in vivo. Adult male Sprague-Dawley rats (N = 5 in each group) were treated with four hours of intravenous infusions of Ang II or vehicle control while mean arterial pressure (MAP) was monitored: group 1, 600 ng/kg/min Ang II; group 2, Ang II + 10 mg/kg of the AT1 receptor antagonist (AT1RA) L158-809 q2 hour; group 3, Ang II + 0.01 to 0.1 mg/kg hydralazine as required to maintain normal blood pressure; and group 4, saline-infused controls. After infusion, tissue was harvested for Northern blotting, immunohistochemical analysis, and in situ hybridization. In group 1, Ang II infusion increased MAP from 105 +/- 8 to 160 +/- 9 mm Hg (mean +/- SE, P < 0. 01). Ang II induced increased expression of PAI-1 mRNA in all tissues examined from 5.1-fold in the heart, 9.7-fold in the kidney, 10.0-fold in the aorta, and up to 30.0-fold in the liver (all P < 0. 01 vs. control). While both AT1RA (group 3) and hydralazine (group 4) prevented Ang II-induced elevation in blood pressure, the Ang II-dependent expression of PAI-1 mRNA was reduced by only AT1 receptor blockade. We conclude that in the rat, PAI-1 is induced in a variety of tissues by Ang II directly through the AT1 receptor, independent of its effects on blood pressure.

Nicotine delays arousal during hypoxemia in lambs.

A decreased ability to arouse from sleep in response to arterial hypoxemia may lead to severe asphyxia and has been proposed as a mechanism of sudden infant death syndrome. Based on previous observations that nicotine exposure, a major environmental risk factor for sudden infant death syndrome, may impair hypoxic defense in neonates, we hypothesized that a short-term infusion of nicotine could impair hypoxic arousal through interference with oxygen-sensing mechanisms. Seven chronically instrumented unanesthetized lambs were studied at the age of 4.6 +/- 1.3 d during normoxia and acute hypoxia (0.1 fraction of inspired oxygen) for 5 min. Ventilation, transcutaneous Hb oxygen saturation, blood pressure, heart rate, and time to arousal were compared during a control saline infusion and during a 0.5 microg x kg(-1) x min(-1) nicotine infusion. Activity states, i.e. wakefulness and quiet sleep as well as arousal, were defined by EEG, nuchal electromyogram, and electrooculogram. Each lamb acted as its own control. Arousal from quiet sleep occurred significantly later during nicotine infusion compared with control (177 +/- 93 versus 57 +/- 41 s, p < 0.01) and at a lower transcutaneous Hb oxygen saturation (60 +/- 12 versus 79 +/- 12%, p < 0.01) (paired t test). The ventilatory response to hypoxia in wakefulness was similar during both conditions but was significantly attenuated in quiet sleep during nicotine infusion (p < 0.001, 2-way ANOVA repeated-measures design). Blood pressure and heart rate responses were similar during both conditions. These results suggest that a brief nicotine exposure blunts oxygen sensitivity in young lambs, a finding of potential relevance for sudden infant death syndrome.

Elevation of plasma fatty acids by ten-hour intralipid infusion has no effect on basal or glucose-stimulated insulin secretion in normal man

There is controversy over the effect of free fatty acids (FFAs) on insulin secretion. Previous studies have shown opposite effects of short- and long-term exposure to elevated concentrations of FFAs. We studied 8 normal subjects (mean age, 30 years; mean body mass index, 23.4 kg/m2) on 2 occasions. Each had a 10-hour overnight infusion of Intralipid 20% (Pharmacia, Milton Keynes, UK) with simultaneous infusion of heparin (0.4 U/kg body weight/min) or a control infusion of saline (150 mmol/L). Insulin secretion was assessed immediately after completion of the 10-hour infusion by an intravenous glucose tolerance test. Results were analyzed using paired ttests. Intralipid infusion caused an increase in plasma FFAs of more than 9-fold (P < .01), with a simultaneous increase in glycerol (P < .01) and hydroxybutyrate (P < .01). There was no difference in blood glucose concentrations during the infusion or intravenous glucose tolerance test. Similarly, insulin secretion was not significantly different during Intralipid infusion or in the intravenous glucose tolerance test (peak insulin achieved in glucose tolerance test, P = .51; total insulin secretion during intravenous glucose tolerance test, P = .27). In conclusion, after increasing plasma FFA concentrations over 9-fold during a 10-hour infusion of Intralipid and heparin, we found no difference in basal or glucose-stimulated insulin secretion.

The effects of acute nicotine on the body temperature and striatal dopamine metabolism of mice during chronic nicotine infusion

The effects of acute nicotine administration on body temperature and striatal dopamine metabolism of mice during chronic subcutaneous nicotine infusion were investigated. On the 7th day of nicotine infusion the hypothermic effect of 1 mg/kg nicotine s.c. but not that of 2 mg/kg was weakened suggesting that tolerance developing to nicotine's hypothermic effect during chronic nicotine can be overcome by increasing the dose of nicotine. In saline-infused control mice 1 mg/kg nicotine increased striatal 3,4-dihydroxyphenylacetic acid (DOPAC) but not homovanillic acid (HVA) concentration whereas 2 mg/kg increased both DOPAC and HVA. On the 7th day of nicotine infusion DOPAC and HVA concentrations were similar to control; and acute nicotine did not increase them suggesting that nicotinic acetylcholine receptors (nAChRs) regulating striatal dopamine metabolism were desensitized. The results suggest that the nAChRs mediating nicotine's effects on thermoregulation and brain dopamine metabolism differ.

Hydrophilic bile salts protect bile duct epitheliumduring cold preservation: A scanning electron microscopy study

Prolonged graft preservation is associated with postoperative bile duct strictures after liver transplantation. We previously showed that hydrophilic bile salts mitigate bile duct preservation injury in a pig model. Because this injury occurs at the epithelial level, scanning electron microscopy was performed to further characterize this effect in vitro. Swine livers were harvested after the intravenous infusion of 1 of 3 solutions: saline (n = 7), tauroursodeoxycholate ([TUDC] hydrophilic; n = 4), or taurodeoxycholate ([TDC] hydrophobic; n = 4). Livers were perused with University of Wisconsin solution. The bile ducts were flushed retrograde, and the liver was stored at 0°C to 1°C for 20 hours. Bile duct samples were obtained at the time of harvest and 8, 12, 16, and 20 hours thereafter. In saline-infused controls at time 0, the epithelium was intact and composed of uniform cuboidal cells covered with fine regular microvilli. There were no spaces between individual cells. After 8 to 12 hours of preservation, cells were more irregular in shape, with loss of cell-cell contact. The cell surfaces showed fewer microvilli. Surface erosions suggested loss of cell-wall integrity. TUDC was protective, evidenced by normal-appearing cells with uniform microvilli after 16 hours. In contrast, TDC accelerated the injury process, causing cell-surface erosions, blebs, and loss of microvilli as early as time 0. Scanning electron microscopy is an excellent tool to study injury to bile duct epithelium. This study supports the hypothesis that hydrophilic bile salts protect bile ducts during preservation. To determine whether treatment with hydrophilic bile salts can prevent postoperative stricture, in vivo transplantation studies are needed.

Hydrophilic bile salts protect bile duct epithelium during cold preservation: a scanning electron microscopy study.

Prolonged graft preservation is associated with postoperative bile duct strictures after liver transplantation. We previously showed that hydrophilic bile salts mitigate bile duct preservation injury in a pig model. Because this injury occurs at the epithelial level, scanning electron microscopy was performed to further characterize this effect in vitro. Swine livers were harvested after the intravenous infusion of 1 of 3 solutions: saline (n = 7), tauroursodeoxycholate ([TUDC] hydrophilic; n = 4), or taurodeoxycholate ([TDC] hydrophobic; n = 4). Livers were perfused with University of Wisconsin solution. The bile ducts were flushed retrograde, and the liver was stored at 0 degrees C to 1 degrees C for 20 hours. Bile duct samples were obtained at the time of harvest and 8, 12, 16, and 20 hours thereafter. In saline-infused controls at time 0, the epithelium was intact and composed of uniform cuboidal cells covered with fine regular microvilli. There were no spaces between individual cells. After 8 to 12 hours of preservation, cells were more irregular in shape, with loss of cell-cell contact. The cell surfaces showed fewer microvilli. Surface erosions suggested loss of cell-wall integrity. TUDC was protective, evidenced by normal-appearing cells with uniform microvilli after 16 hours. In contrast, TDC accelerated the injury process, causing cell-surface erosions, blebs, and loss of microvilli as early as time 0. Scanning electron microscopy is an excellent tool to study injury to bile duct epithelium. This study supports the hypothesis that hydrophilic bile salts protect bile ducts during preservation. To determine whether treatment with hydrophilic bile salts can prevent postoperative stricture, in vivo transplantation studies are needed.

A cell-survival factor (N-acetyl-L-cysteine) alters the in vivo fate of constitutively proliferating subependymal cells in the adult forebrain.

The adult mouse brain contains a population of constitutively proliferating subependymal cells that surround the lateral ventricle and are the direct progeny of the neural stem cell. Constitutively proliferating cells divide rapidly; 6 days after labeling, 60% of their progeny undergo cell death, 25% migrate to the olfactory bulbs, and 15% continue to proliferate within the subependyma. We have intraventricularly infused a cell survival factor N-acetyl-L-cysteine (NAC), which is known to have survival effects without concomitant proliferative effects on cells in vitro, and examined the resulting fate of cells spared from the normally occurring cell death. NAC infusion for 5 days results in a five-fold increase in the number of retrovirally labeled subependymal cells compared to saline-infused controls. The increase in the number of subependymal cells is directly proportional to the amount of time during which NAC is present and is not due to increased proliferation. While NAC is able to keep all the normally dying progeny alive, the cells spared from death remain confined to the subependyma lining the lateral ventricles and do not migrate to the olfactory bulbs (one normal fate of constitutively proliferating progeny) or into the surrounding brain parenchyma. When animals survive for an additional 6 days following NAC infusion, the number of retrovirally labeled subependymal cells returns to control values, indicating that the continued presence of NAC is necessary for cell survival. These data suggest that preventing cell death is not sufficient to keep all of the progeny of these cells in a proliferative mode.

N-Proopiomelanocortin (1–77) Suppresses Expression of Steroidogenic Acute Regulatory Protein (Star) mRNA in the Adrenal Gland of the Fetal Sheep

In the sheep, there is a rapid increase in fetal adrenal growth and steroidogenesis during the last 10–15 days gestation. Recently, we have shown that infusion of POMC (1–77) increases fetal adrenal growth and expression of CYP17 mRNA but does not significantly alter fetal plasma cortisol concentrations [1]. We therefore investigated the effects of infusion of bovine POMC (1–77) and its biosynthetic derivative POMC (1–49) on adrenal StAR mRNA expression. At 136d gestation, POMC (1–77) (n=5 fetuses; 2μg/ml/h), POMC (1–49) (n=5 fetuses, 2μg/ml/h) or Saline (n=5 fetuses, 1 ml/h) was infused for 48h. At 138d, fetal adrenal glands were collected and frozen in liquid N2 until RNA was extracted. Northern blot analyses demonstrated a major transcript for StAR mRNA at 3.0kb in fetal adrenal glands from all treatments. The membrane was stripped and re-probed with a 32P-labelled rat 18S rRNA oligo-probe to verify equal RNA loading. Infusion of POMC (1–77), but not POMC (1–49), resulted in a suppression of fetal adrenal StAR mRNA:18S rRNA when compared to adrenal StAR mRNA:18S rRNA from saline-infused controls. Our data suggest POMC (1–77) may act via separate mechanisms to increase fetal adrenal growth and to limit adrenal steroidogenesis through suppression of StAR mRNA.

Excitatory amino acid release in the locus coeruleus during naloxone-precipitated morphine withdrawal in adjuvant arthritic rats.

Excitatory amino acid levels in the locus coeruleus (LC) and the behavioral signs during naloxone-precipitated withdrawal in arthritic rats treated with chronic morphine were investigated by in vivo microdialysis. Increases in glutamate (Glu) and aspartate (Asp) were noted after naloxone (48 nmol/5 microl, LC)-precipitated withdrawal from normal and adjuvant arthritic rats which had been intracerebroventricularly infused for 3 days with morphine (26 nmol/l microl/h). The increases in Glu and Asp levels on morphine withdrawal in normal rats were attenuated following naloxone challenge in the morphine-dependent arthritic rats. Moreover, behavioral signs during morphine withdrawal were detected following the naloxone challenge in both the morphine-dependent normal and adjuvant arthritic rats, but not in the saline-infused controls. These results show that the attenuation of Glu and Asp release from the LC in the adjuvant arthritic rats might explain the anti-inflammatory and analgesic effects of mu-opioids in adjuvant arthritic rats.

Muscle lipid accumulation and protein kinase C activation in the insulin-resistant chronically glucose-infused rat.

Chronic glucose infusion results in hyperinsulinemia and causes lipid accumulation and insulin resistance in rat muscle. To examine possible mechanisms for the insulin resistance, alterations in malonyl-CoA and long-chain acyl-CoA (LCA-CoA) concentration and the distribution of protein kinase C (PKC) isozymes, putative links between muscle lipids and insulin resistance, were determined. Cannulated rats were infused with glucose (40 mg. kg(-1). min(-1)) for 1 or 4 days. This increased red quadriceps muscle LCA-CoA content (sum of 6 species) by 1.3-fold at 1 day and 1.4-fold at 4 days vs. saline-infused controls (both P < 0.001 vs. control). The concentration of malonyl-CoA was also increased (1.7-fold at 1 day, P < 0.01, and 2.2-fold at 4 days, P < 0.001 vs. control), suggesting an even greater increase in cytosolic LCA-CoA. The ratio of membrane to cytosolic PKC-epsilon was increased twofold in the red gastrocnemius after both 1 and 4 days, suggesting chronic activation. No changes were observed for PKC-alpha, -delta, and -theta. We conclude that LCA-CoAs accumulate in muscle during chronic glucose infusion, consistent with a malonyl-CoA-induced inhibition of fatty acid oxidation (reverse glucose-fatty acid cycle). Accumulation of LCA-CoAs could play a role in the generation of muscle insulin resistance by glucose oversupply, either directly or via chronic activation of PKC-epsilon.

GABAergic control of olfactory learning in young rats

Olfactory learning in young rats correlates with neural plasticity in the olfactory bulb, and involves noradrenergic modulation of reciprocal dendrodendritic synapses between mitral cells and GABAergic granule cells. The purpose of this study was to examine, in vivo, the consequences of manipulating bulbar GABA transmission during training. In the first experiment, postnatal day 11 rat pups were trained in an olfactory associative learning task with citral odor and foot shock as the conditioned and unconditioned stimuli, respectively. The pups received continuous infusion of saline or the GABA A receptor agonist muscimol into the olfactory bulbs throughout a 30-min training session. The pups were then tested on postnatal day 12 for a preference for or an aversion to citral odor. Saline-infused control pups developed an aversion to citral odor. The GABA A receptor agonist muscimol impaired this aversive learning in a dose-dependent manner. In the second experiment, pups were exposed to the odor for 30 min while receiving continuous intrabulbar infusion of a low or high dose of the GABA A receptor antagonist bicuculline, without any other reinforcer. Depending on whether a low (0.2 nmol/bulb) or high (1.0 nmol/bulb) dose of bicuculline was infused, the pups showed a preference or an aversion for citral odor after infusion of low and high doses, respectively. These results indicate that disinhibition of mitral cells in the olfactory bulb is critical for olfactory learning in young rats, and suggest that the degree of disinhibition is an important determinant in acquiring either preference or aversion for the conditioned odor.

Acceleration of ageing-related gliopathic changes and hippocampal dysfunction following intracerebroventricular infusion of cysteamine in adult rats

The sulphydryl agent, cysteamine, accelerates the ageing-related accumulation of peroxidase-positive (iron-rich) cytoplasmic inclusions in rat subcortical astroglia and induces their appearance in primary neuroglial cultures. In the present study, infusion of cysteamine into the lateral ventricle of young, adult rats (1 mg/day for three weeks followed by a one-month drug “washout” period) significantly increased numbers of peroxidase-positive astrocytic granules in the stratum oriens of the CA1 hippocampus relative to saline-infused controls. In contrast to the gliopathic changes, no evidence of neuronal or myelin damage was observed in the cysteamine-exposed rats. The cysteamine-treated animals exhibited significant impairment in spatial learning as determined using a three-panel runway task. The working memory deficits were more robust at the end of the drug washout period than immediately following cessation of the cysteamine infusion. Thus, the cysteamine-related memory deficits are of long duration and are not due to any acute neuroactive properties of the drug itself. Using hippocampal slices prepared after the drug washout period, we observed attenuated paired-pulse depression, with no significant effects on basal excitatory synaptic transmission or induction of long-term potentiation, in the cysteamine-infused animals relative to controls. We propose that, in cysteamine-treated rats and in the course of normal ageing, hippocampal dysfunction and associated cognitive deficits may be secondary to fundamental pathological processes originating within the astroglial compartment.