Functional switch from facilitation to inhibition in the control of glutamate release by metabotropic glutamate receptors

We have investigated the role of metabotropic glutamate receptors linked to phosphoinositide hydrolysis in the control of glutamate release in cerebrocortical nerve terminals. The activation of these receptors with the agonist 3,5-dihydroxyphenylglycine enhanced intra-synaptosomal diacylglycerol and facilitated both the depolarization-induced increase in the cytosolic free Ca2+ concentration and the release of glutamate. However, 5 min after receptor activation, a second stimulation of the pathway with the agonist failed to produce diacylglycerol and to facilitate glutamate release. Interestingly, during the period in which the diacylglycerol response was desensitized, a strong agonist-induced inhibition of Ca2+ entry and glutamate release was observed. This change in the presynaptic effects of 3,5-dihydroxyphenylglycine is reversible since 30 min after the first stimulation, the agonist-induced inhibition of release disappeared, whereas both the production of diacylglycerol and the facilitation of glutamate release were recovered. The tonic elevation of the extracellular glutamate concentration from basal levels (0.8 microM) up to 5 microM also produced the switch from facilitation to inhibition in the receptor response. The existence of this activity-dependent switch in the presynaptic control of glutamate release suggests that release facilitation is limited to conditions under which an appropriate clearance of synaptic glutamate exists, probably to prevent the neurotoxic accumulation of glutamate in the synapse.     

Primary human herpesvirus 7 infection: a comparison of human herpesvirus 7 and human herpesvirus 6 infections in children

Atrial fibrillation is an important and independent risk factor for cerebrovascular disease and vascular dementia. There is increasing evidence that atrial fibrillation is associated with an increased risk of asymptomatic or silent cerebral infarction and as a result may confer an increased risk of progressive cognitive impairment on a person. In this study we sought to determine whether this hypothesis could be explored in a prospective case controlled design. Twenty seven patients with non-valvular atrial fibrillation (NVAF) and no history of stroke, transient ischaemic attack, dementia, and thyrotoxicosis were compared with 54 age and sex matched controls in sinus rhythm. All cases underwent clinical examination, ECG, and psychological assessment using a battery of nine neuropsychological tests. Between group analysis and a comparison of mean test scores of paired controls with cases were undertaken. The presence of atrial fibrillation was consistently associated with poorer performances on all the subtests of the neuropsychological battery. There was no association between duration of atrial fibrillation and performance. These results provide evidence to justify further examination of the hypothesis in a larger prospective study to determine whether antithrombotic therapy may protect against cognitive decline in patients at maximal risk of silent cerebral ischaemia and associated cognitive decline.     

A purinergic component of the excitatory postsynaptic current mediated by P2X receptors in the CA1 neurons of the rat hippocampus

The pyramidal neurons in the CA1 area of hippocampal slices from 17- to 19-day-old rats have been investigated by means of patch clamp. Excitatory postsynaptic currents (EPSCs) were elicited by stimulating the Schaffer collateral at a frequency below 0.2 Hz. It was found that inhibition of glutamatergic transmission by 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 100 microM 2-amino-5-phosphonovaleric acid (D-APV) left a small component of the EPSC uninhibited. The amplitude of this residual EPSC (rEPSC) comprised 25 +/- 11% of the total EPSC when measured at a holding potential of -50 mV. The rEPSC was blocked by selective P2 blocker pyridoxal phosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS) 10 microM and bath incubation with non-hydrolysable ATP analogues, ATP-gamma-S and alpha, beta-methylene-ATP at 50 and 20 microM, respectively. The rEPSC was dramatically potentiated by external Zn2+ (10 microM). In another series of experiments exogenous ATP was applied to the CA1 neurons in situ. An inward current evoked by ATP was inhibited by PPADS to the same extent as the rEPSC. It is concluded that, depending on membrane voltage, about one-fifth to one-quarter of the EPSC generated by the excitatory synaptic input to the hippocampal CA1 neurons of rat is due to the activity of P2X receptors.     

Development of orally active oxytocin antagonists: studies on 1-(1-[4-[1-(2-methyl-1-oxidopyridin-3-ylmethyl)piperidin-4-yloxy]-2- methoxybenzoyl]piperidin-4-yl)-1,4-dihydrobenz[d][1,3]oxazin-2-one (L-372,662) and related pyridines

The previously reported oxytocin antagonist L-371,257 (2) has been modified at its acetylpiperidine terminus to incorporate various pyridine N-oxide groups. This modification has led to the identification of compounds with improved pharmacokinetics and excellent oral bioavailability. The pyridine N-oxide series is exemplified by L-372,662 (30), which possessed good potency in vitro (Ki = 4.1 nM, cloned human oxytocin receptor) and in vivo (intravenous AD50 = 0.71 mg/kg in the rat), excellent oral bioavailability (90% in the rat, 96% in the dog), good aqueous solubility (>8.5 mg/mL at pH 5.2) which should facilitate formulation for iv administration, and excellent selectivity against the human arginine vasopressin receptors. Incorporation of a 5-fluoro substituent on the central benzoyl ring of this class of oxytocin antagonists enhanced in vitro and in vivo potency but was detrimental to the pharmacokinetic profiles of these compounds. Although lipophilic substitution around the pyridine ring of compound 30 gave higher affinity in vitro, such substituents were a metabolic liability and caused shortfalls in vivo. Two approaches to prevent this metabolism, addition of a cyclic constraint and incorporation of trifluoromethyl groups, were examined. The former approach was ineffective because of metabolic hydroxylation on the constrained ring system, whereas the latter showed improvement in plasma pharmacokinetics in some cases.     

Thrombolytic therapy in Missouri hospital emergency departments: compliance with the National Heart Attack Alert Program guidelines

Adhesive interactions between leukocytes and endothelium are required for subsequent leukocyte extravasation toward inflammatory sites. Understanding the possible kinetic expression of vascular cell adhesion molecule-1 (VCAM-1) in the middle ear cavity during an inflammatory cascade in vivo may be important for clarifying local immunological responses in otitis media. Two inflammatory models were produced in the rat and involved acute middle ear mucosal and cutaneous inflammation induced after inoculation or intradermal injection of lipopolysaccharide (LPS). After intravenous injection of both 125I-labeled anti-VCAM-1 and 131I-labeled control monoclonal antibody (mAb), the kinetic expression of VCAM-1 in the middle ear and skin was assessed by local radionuclide uptake. The biodistribution of an 125I-labeled anti-VCAM-1 mAb as a potential detector of focal inflammation was examined in normal rats. Both inflammatory lesions were characterized by early and sustained (up to 24 h) expression of VCAM-1, with maximal expression at 4 h after LPS stimulation. The kinetics of VCAM-1 expression was similar among the middle ear mucosa or skin specimens studied and different stimulation methods. A similar biodistribution and clearance of radioactivity between 125I-labeled anti-VCAM-1 mAb and 131I- or 99mTc-labeled control mAb were observed. The present result suggest that functional VCAM-1 induced by LPS is expressed in both middle ear tissue and skin lesions and may play a role in the initial stage of inflammatory response produced. Although VCAM-1 upregulation is a very early event in the inflammatory cascade, 125I-labeled anti-VCAM-1 mAb may be useful for the early detection of focal inflammation in the middle ear.     

Renal changes induced by nitric oxide and prostaglandin synthesis reduction: effects of trandolapril and verapamil

The benefits of the simultaneous administration of low doses of a calcium antagonist and a converting enzyme inhibitor in the treatment of hypertension and renal vasoconstriction are well established. The objective of this study was to evaluate whether the administration of low doses of a calcium antagonist and a converting-enzyme inhibitor have beneficial effects in treating the renal alterations induced by the acute administration of a cyclooxygenase inhibitor when nitric oxide synthesis is reduced. These effects were examined in anesthetized dogs before and during an acute sodium load. It was found that the intrarenal infusion of meclofenamate (5 microg x kg[-1] x min[-1]), simultaneously with a low dose of NG-nitro-L-arginine methyl ester (1 microg x kg[-1] x min[-1]), produced a 40% decrease of renal blood flow and glomerular filtration rate and a reduction in the renal excretory response to the sodium load. In a second group of dogs, intrarenal verapamil (0.5 microg x kg[-1] x min[-1]) was effective in blocking the effects of nitric oxide and prostaglandin synthesis inhibition on sodium excretion and glomerular filtration rate but did not modify the effects on renal blood flow. An intrarenal infusion of trandolapril (0.3 microg x kg[-1] x min[-1]) was effective in a third group of dogs in reducing the renal hemodynamic effects but not in preventing the antinatriuretic effect observed in the first group. Finally, in a fourth group, the simultaneous administration of verapamil and trandolapril was effective in treating all the renal changes induced by the cyclooxygenase inhibitor when nitric oxide synthesis was reduced. These results suggest that the combination of low doses of trandolapril and verapamil has additive effects in treating the renal vasoconstriction and antinatriuresis induced by the acute administration of a cyclooxygenase inhibitor, when nitric oxide synthesis is reduced.     

Diagnosis of pancreatic carcinoma: role of FDG PET

OBJECTIVE: The purpose of this study was to investigate the role of positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) in differentiating benign from malignant disease in patients with possible pancreatic malignancy. SUBJECTS AND METHODS: All patients with a possible diagnosis of pancreatic carcinoma based on CT or ERCP findings were eligible for inclusion in this prospective study. PET imaging of the abdomen was performed in 37 patients and was interpreted as positive if FDG activity in the pancreas exceeded background activity and as negative if activity was less than or equal to background activity. Semiquantitative analysis was performed by calculating a standardized uptake ratio. Studies were reviewed independently by two radiologists, and results were correlated with biopsy results and with CT and ERCP findings. Sensitivity and specificity of FDG PET for revealing pancreatic malignancy was determined. RESULTS: FDG activity in the pancreas was increased in 24 patients, and adenocarcinoma was diagnosed in 22 of these patients (92%). Two patients (8%) with increased activity had benign disease, including one patient with chronic pancreatitis who showed no evidence of tumor at laparotomy and one patient with a mucinous cystic tumor who showed no malignant features at laparotomy. FDG uptake was low or normal in 13 patients, 10 of whom (77%) had benign disease. FDG uptake was also low in three patients with adenocarcinoma, whose tumor size ranged from 2 to 4 cm in diameter. The mean standardized uptake ratio value for malignant disease was 5.1 (range, 1.0-10.1) and for benign disease was 1.9 (range, 0.0-5.8) (p < .001). The sensitivity of FDG PET for revealing malignant disease in the pancreas was 88% and the specificity was 83%. CONCLUSION: FDG PET is a sensitive and specific noninvasive technique for the diagnosis of pancreatic malignancy.     

Long-term effects of perindopril on metabolic parameters and the heart in the spontaneously hypertensive/NIH-corpulent rat with non-insulin-dependent diabetes mellitus and hypertension

The spontaneously hypertensive/NIH-corpulent (SHR/N-cp) rat is a genetic model that exhibits both non-insulin-dependent diabetes mellitus (NIDDM) and hypertension. To determine the impact of long-term treatment with the long-acting angiotensin-converting enzyme (ACE) inhibitor perindopril (PE) on the glucose metabolism, lipid levels, and heart in this model, studies were performed in three groups of SHR/N-cp rats maintained on a diet containing 54% carbohydrate with 18% sucrose and 36% starch. One group of obese rats received PE (0.5 to 1.0 mg/kg body weight/d) for 3 to 4 months, a second group of obese rats received no treatment, and a third group of lean rats were used as controls. The mean systolic blood pressure (SBP) increased gradually in both untreated obese and lean rats, with lean animals showing slightly higher levels compared with untreated obese rats. By contrast, SBP was reduced to normal levels in PE-treated obese rats throughout the treatment period. Compared with lean rats, obese rats showed significantly higher body weight and fasting serum levels of glucose, insulin, total cholesterol (TC), and triglyceride (TG). However, no significant differences were observed in these metabolic parameters between PE-treated and untreated obese rats. Plasma renin activity measured at the end of the treatment period was significantly higher in PE-treated rats compared with untreated obese and untreated lean rats. The mean heart weight and left ventricular weight, expressed in absolute terms or indexed to body weight, were significantly lower in PE-treated versus untreated obese and untreated lean rats. To further determine whether glucose metabolism is directly affected by PE treatment, in vitro glycogen synthesis was evaluated in isolated soleus muscles obtained from three additional groups of animals. The basal rate of muscle glycogen synthesis was significantly lower in obese compared with lean rats (P < .05), but did not differ between PE-treated and untreated obese rats. Maximal insulin-stimulated glycogen synthesis increased threefold in PE-treated obese rats, but this increase did not differ from the increases observed in untreated obese and lean rats. In conclusion, the present study shows that long-term PE treatment in obese SHR/N-cp rats with NIDDM and hypertension effectively controlled systemic arterial pressure and resulted in a significant reduction in left ventricular weight. However, these favorable effects of PE were not associated with significant improvement in glucose tolerance, hyperinsulinemia, and hyperlipidemia in this model. PE also had no direct stimulatory effects on either basal or insulin-mediated glycogen synthesis in the isolated soleus muscle of obese rats, perhaps because of the severe insulin-resistant state of the animals. Our results support the clinical observations that antihypertensive therapy with ACE inhibitors has neutral effects on glucose metabolism and insulin sensitivity in patients with combined hypertension and NIDDM.     

Magnolol decreases body temperature by reducing 5-hydroxytryptamine release in the rat hypothalamus

1. The effects of magnolol, isolated and purified from the cortex of Magnolia officinalis Rehd. et Wils, on thermoregulation and hypothalamic release of 5-hydroxytryptamine (5-HT) by in vivo microdialysis were assessed in normothermic rats and in febrile rats treated with interleukin-1 beta. 2. Intraperitoneal administration of magnolol (25-100 mg/kg) produced a decrease in colon temperature, an increase in foot skin temperature, a decrease in metabolic rate and a decrease in the endogenous release of 5-HT in the rat hypothalamus. 3. Depletion of rat brain 5-HT, produced by intracerebroventricular pretreatment with 5,7-dihydroxytryptamine, attenuated the magnolol-induced hypothermia, cutaneous vasodilation and decreased metabolism. 4. Intracerebroventricular administration of (+/-)-2,5-dimethoxy-4-iodoamphetamine (a 5-HT2 receptor agonist; 5-10 micrograms/5 microL) increased basal colon temperature and reversed the magnolol-induced hypothermia. 5. The increases in both colon temperature and hypothalamic 5-HT release produced by interleukin-1 beta injection were attenuated by treatment with magnolol. 6. The data suggest that magnolol decreases body temperature (due to increased heat loss and decreased heat production) by reducing 5-HT release in rat hypothalamus.     

Excitotoxic neurodegeneration induced by deprivation of oxygen and glucose in isolated retina

PURPOSE: Ischemic neurodegeneration contributes to many retinal diseases. An isolated retina model has been used to examine the neuronal cell death induced by deprivation of oxygen and glucose (simulated ischemia) as a model for ischemic disease. METHODS: Neurodegeneration in the isolated chick embryo retina was induced by simulated ischemia and assessed using biochemical (lactate dehydrogenase release) and morphologic (light microscopy) techniques. RESULTS: Simulated ischemia led to lactate dehydrogenase release gradually in a period of 6 to 24 hours. Light microscopic observations demonstrated morphologic cell degeneration well before lactate dehydrogenase release occurred. N-Methyl-D-aspartate (NMDA) and non-NMDA receptor blockers individually provided partial protection, and the combination was fully protective. No protection was provided if the antagonists were added after simulated ischemia. When NMDA receptors were blocked by MK-801, cyclothiazide, an inhibitor of desensitization at non-NMDA receptors, enhanced lactate dehydrogenase released after 1 or 2 hours of simulated ischemia. Low concentrations of glucose effectively prevented lactate dehydrogenase release, despite anoxic conditions. CONCLUSIONS: The isolated retina provided a convenient system to characterize quantitatively ischemic cell death. Retinal ischemic neurodegeneration is an excitotoxic process that involves overactivation of NMDA and non-NMDA glutamate receptors. Blockade of both of these receptor subtypes was necessary for complete neuroprotection. Receptor desensitization played a protective role. If even low concentrations of glucose were delivered to an ischemic retina in vitro, substantial neuroprotection could be achieved. This may have implications for the management of acute retinal ischemic episodes.