Decrease In Number Of Receptors Research Articles

GABRG2 Deletion Linked to Genetic Epilepsy with Febrile Seizures Plus Affects the Expression of GABAA Receptor Subunits and Other Genes at Different Temperatures

Mutations in γ-aminobutyric acid A receptor (GABAA) subunits and sodium channel genes, especially GABRG2 and SCN1A, have been reported to be associated with febrile seizures (FS) and genetic epilepsy with febrile seizures plus (GEFS+). GEFS+ is a well-known family of epileptic syndrome with autosomal dominant inheritance in children. Its most common phenotypes are febrile seizures often with accessory afebrile generalized tonic-clonic seizures, febrile seizures plus (FS+), severe epileptic encephalopathy, as well as other types of generalized or localization-related seizures. However, the pathogenesis of febrile seizures remains largely unknown. Here, we generated a GABRG2 gene knockout cell line (HT22GABRG2KO) by applying the CRISPR/Cas9-mediated genomic deletion in HT-22 mouse hippocampal neuronal cell line to explore the function of GABRG2 in vitro. With mRNA-seq, we found significant changes in the expression profiles of several epilepsy-related genes when GABRG2 was knockout, some of them showing temperature-induced changes as well. Kyoto Encyclopedia Gene and Genomic (KEGG) analysis revealed a significant alteration in the MAPK and PI3K-Akt signaling pathways. We also observed an up-regulation of the matrix metalloproteinases (MMPs) family after GABRG2 knockout. Furthermore, the significant decrease in expression of GABRA1 and CACNA1A (but not others) with an increase in temperature is a novel finding. In summary, mutations in the GABAA receptor can lead to a decrease in numbers of receptors, which may cause the impairment of GABAergic pathway signaling. This data has been the first time to reveal that GABRG2 mutations would affect the function of other genes, and based on this finding we hope this work would also provide a new direction for the research of GABRG2 in GEFS+. It also may provide a molecular basis for the severity of epilepsy, and guide the clinical medication for the treatment of the epilepsy focused on the function on GABAA receptors, which, might be a new strategy for genetic diagnosis and targeted treatment of epilepsy.

Steroidogenesis and early response gene expression in MA-10 Leydig tumor cells following heterologous receptor down-regulation and cellular desensitization

The Leydig tumor cell line, MA-10, expresses the luteinizing hormone receptor, a G protein-coupled receptor that, when activated with luteinizing hormone or chorionic gonadotropin (CG), stimulates cAMP production and subsequent steroidogenesis, notably progesterone. These cells also respond to epidermal growth factor (EGF) and phorbol esters with increased steroid biosynthesis. In order to probe the intracellular pathways along with heterologous receptor down-regulation and cellular desensitization, cells were preincubated with EGF or phorbol esters and then challenged with CG, EGF, dibutryl-cyclic AMP, and a phorbol ester. Relative receptor numbers, steroid biosynthesis, and expression of the early response genes, JUNB and c-FOS, were measured. It was found that in all cases but one receptor down-regulation and decreased progesterone production were closely coupled under the conditions used; the exception involved preincubation of the cells with EGF followed by addition of CG where the CG-mediated stimulation of steroidogenesis was considerably lower than the level of receptor down-regulation. In a number of instances JUNB and c-FOS expression paralleled the decreases in receptor number and progesterone production, while in some cases these early response genes were affected little if at all by the changes in receptor number. This finding may indicate that even low levels of activated signaling kinases, e.g. protein kinase A, protein kinase C, or receptor tyrosine kinase, may suffice to yield good expression of JUNB and c-FOS, or it may suggest alternative pathways for regulating expression of these two early response genes.

Cholinergic Receptor Alterations in the Brain Stem of Spinal Cord Injured Rats

Cholinergic receptors in upper motor neurons of brain stem control locomotion and coordination. Present study unravels cholinergic alterations in brain stem during spinal cord injury to understand signalling pathway changes which may be associated with spinal cord injury mediated motor deficits. We evaluated cholinergic function in brain stem by studying the expression of choline acetyl transferase and acetylcholine esterase. We quantified metabotropic muscarinic cholinergic receptors by receptor assays for total muscarinic, muscarinic M1 and M3 receptor subunits, gene expression studies using Real Time PCR and confocal imaging using FITC tagged secondary antibodies. The gene expression of ionotropic nicotinic cholinergic receptors and confocal imaging were also studied. The results from our study showed metabolic disturbance in cholinergic pathway as choline acetyl transferase is down regulated and acetylcholine esterase is up regulated in spinal cord injury group. The significant decrease in muscarinic receptors showed by decreased receptor number along with down regulated gene expression and confocal imaging accounts for dysfunction of metabotropic acetylcholine receptors in spinal cord injury group. Ionotropic acetylcholine receptor alterations were evident from the decreased gene expression of alpha 7 nicotinic acetylcholine receptors and confocal imaging. The motor coordination was analysed by Grid walk test which showed an increased foot slips in spinal cord injured rats. The significant reduction in brain stem cholinergic function might have intensified the motor dysfunction and locomotor disabilities.

Disruption of intracardiac flow patterns in the newborn infant.

Consistent patterns of rotational intracardiac flow have been demonstrated in the healthy adult human heart. Intracardiac rotational flow patterns are hypothesized to assist in the maintenance of kinetic energy of inflowing blood, augmenting cardiac function. Newborn cardiac function is known to be suboptimal secondary to decreased receptor number and sympathetic innervation, increased afterload, and increased reliance on atrial contraction to support ventricular filling. Patterns of intracardiac flow in the newborn have not previously been examined. Whereas 5 of the 13 infants studied showed significant evidence of rotational flow within the right atrium, 8 infants showed little or no rotational flow. Presence or absence of rotational flow was not related to gestational age, birth weight, postnatal age, atrial size, or image quality. Despite absence of intra-atrial rotational flow, atrioventricular valve flow into the left and right ventricles later in the cardiac cycle could be seen, suggesting that visualization techniques were adequate. While further study is required to assess its exact consequences on cardiac mechanics and energetics, disruption to intracardiac flow patterns could be another contributor to the multifactorial sequence that produces newborn circulatory failure. We studied 13 newborn infants, using three-dimensional (3D) cardiac magnetic resonance phase-contrast imaging (spatial resolution 0.84 mm, temporal resolution 22.6 ms) performed without sedation/anesthesia.

AT-1001: A High Affinity and Selective α3β4 Nicotinic Acetylcholine Receptor Antagonist Blocks Nicotine Self-Administration in Rats

Genomic and pharmacologic data have suggested the involvement of the α3β4 subtype of nicotinic acetylcholine receptors (nAChRs) in drug seeking to nicotine and other drugs of abuse. In order to better examine this receptor subtype, we have identified and characterized the first high affinity and selective α3β4 nAChR antagonist, AT-1001, both in vitro and in vivo. This is the first reported compound with a Ki below 10 nM at α3β4 nAChR and >90-fold selectivity over the other major subtypes, the α4β2 and α7 nAChR. AT-1001 competes with epibatidine, allowing for [³H]epibatidine binding to be used for structure-activity studies, however, both receptor binding and ligand-induced Ca²⁺ flux are not strictly competitive because increasing ligand concentration produces an apparent decrease in receptor number and maximal Ca²⁺ fluorescence. AT-1001 also potently and reversibly blocks epibatidine-induced inward currents in HEK cells transfected with α3β4 nAChR. Importantly, AT-1001 potently and dose-dependently blocks nicotine self-administration in rats, without affecting food responding. When tested in a nucleus accumbens (NAcs) synaptosomal preparation, AT-1001 inhibits nicotine-induced [³H]dopamine release poorly and at significantly higher concentrations compared with mecamylamine and conotoxin MII. These results suggest that its inhibition of nicotine self-administration in rats is not directly due to a decrease in dopamine release from the NAc, and most likely involves an indirect pathway requiring α3β4 nAChR. In conclusion, our studies provide further evidence for the involvement of α3β4 nAChR in nicotine self-administration. These findings suggest the utility of this receptor as a target for smoking cessation medications, and highlight the potential of AT-1001 and congeners as clinically useful compounds.

Differential Effect of Membrane Cholesterol Removal on μ- and δ-Opioid Receptors: A PARALLEL COMPARISON OF ACUTE AND CHRONIC SIGNALING TO ADENYLYL CYCLASE

According to the lipid raft theory, the plasma membrane contains small domains enriched in cholesterol and sphingolipid, which may serve as platforms to organize membrane proteins. Using methyl-beta-cyclodextrin (MbetaCD) to deplete membrane cholesterol, many G protein-coupled receptors have been shown to depend on putative lipid rafts for proper signaling. Here we examine the hypothesis that treatment of HEK293 cells stably expressing FLAG-tagged mu-opioid receptors (HEK FLAG-mu) or delta-opioid receptors (HEK FLAG-delta) with MbetaCD will reduce opioid receptor signaling to adenylyl cyclase. The ability of the mu-opioid agonist [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin to acutely inhibit adenylyl cyclase or to cause sensitization of adenylyl cyclase following chronic treatment was attenuated with MbetaCD. These effects were due to removal of cholesterol, because replenishment of cholesterol restored [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin responses back to control values, and were confirmed in SH-SY5Y cells endogenously expressing mu-opioid receptors. The effects of MbetaCD may be due to uncoupling of the mu receptor from G proteins but were not because of decreases in receptor number and were not mimicked by cytoskeleton disruption. In contrast to the results in HEK FLAG-mu cells, MbetaCD treatment of HEK FLAG-delta cells had no effect on acute inhibition or sensitization of adenylyl cyclase by delta-opioid agonists. The differential responses of mu- and delta-opioid agonists to cholesterol depletion suggest that mu-opioid receptors are more dependent on cholesterol for efficient signaling than delta receptors and can be partly explained by localization of mu- but not delta-opioid receptors in cholesterol- and caveolin-enriched membrane domains.

Diurnal variation in specific insulin binding to erythrocytes.

We studied the insulin binding to erythrocytes during a 24-h period in 11 normal subjects. Compared with 0800 and 1600 h the specific 125I-insulin binding decreased significantly at midnight. These changes were mainly due to alterations in insulin binding affinity rather than a decrease in receptor number. An inverse finding was obtained concerning the plasma insulin levels. In fact, the highest insulin concentrations were observed at midnight. The results suggest that diurnal variations in insulin receptor function occur in response to fluctuations of plasma insulin levels.

Alterations in D2 dopamine receptor internalization in the presence of the Na+/K+‐ATPase

Using a co‐immunoprecipitation assay for dopamine receptors (DARs) coupled with mass spectrometry (MS) sequencing, we previously identified the Na+/K+‐ATPase (Na+ pump, NKA) as a member of both the D1 and D2 DAR signalplexes. Using fluorescent‐labeled D2 DAR and NKAα1 constructs in confocal microscopy experiments, co‐localization of the two proteins was observed at the plasma membrane. Dopamine stimulation of RFP‐tagged D2 DAR‐expressing cells resulted in marked DAR internalization twenty minutes after drug treatment. Interestingly, when GFP‐tagged NKAα1 was co‐expressed, the D2 DAR internalization twenty minutes after dopamine treatment was diminished. To achieve a more quantitative assessment of receptor expression, cell‐surface binding assays were performed in the presence and absence of over‐expressed NKA. These assays revealed a 45% decrease in cell‐surface D2 DAR number twenty minutes after dopamine treatment, and a 30% decrease in receptor number when the NKA was also present. Longer dopamine incubations enhanced D2 DAR internalization, but co‐expression of NKA prohibited complete internalization as compared to D2 DAR alone. Current studies are underway to determine the impact of the DAR‐NKA complex on receptor recycling, and the role of NKA in lipid rafts on receptor activation and internalization.Support contributed by the NINDS intramural program.

Lipid and Lipoprotein Metabolism in Chronic Kidney Disease

The risk of cardiovascular events and mortality increases as renal function declines although the relative risk of mortality contributed by the standard Framingham risk factors are altered or replaced. Low-density lipoprotein (LDL) cholesterol does not predict mortality but low high-density lipoprotein (HDL) cholesterol and triglycerides remain risk factors. The lipoproteins within each class are shifted to smaller, more dense isoforms. The accumulation of apolipoprotein B-containing lipoproteins, including lipoprotein(a) results primarily from decreased clearance rather than from increased synthesis. Lipoprotein(a) levels are also associated with cardiovascular outcome among dialysis patients. Decreased clearance of very low-density lipoprotein and intermediate-density lipoprotein is a result of decreased lipoprotein lipase, structural alterations in the lipoproteins rendering them poorer substrates, and a decrease in receptor number for these proteins. HDL levels are decreased as a result of an increased fractional catabolic rate both among obese patients with normal renal function and among dialysis patients, but the mechanisms responsible for increased HDL fractional catabolic rate may differ. In patients with advanced kidney disease, HDL fails to mature normally as a result of decreased lecithin cholesterol ester transfer protein, leaving cholesterol ester-poor, triglyceride-rich HDL(3) and pre-beta HDL. HDL in patients with chronic kidney disease is a less effective antioxidative agent than is HDL from normal subjects because of a decrease in paroxonase activity, allowing the accumulation of oxidized LDL.

The PDZ Protein Mupp1 Promotes Gi Coupling and Signaling of the Mt1 Melatonin Receptor

Intracellular signaling events are often organized around PDZ (PSD-95/Drosophila Disc large/ZO-1 homology) domain-containing scaffolding proteins. The ubiquitously expressed multi-PDZ protein MUPP1, which is composed of 13 PDZ domains, has been shown to interact with multiple viral and cellular proteins and to play important roles in receptor targeting and trafficking. In this study, we show that MUPP1 binds to the G protein-coupled MT(1) melatonin receptor and directly regulates its G(i)-dependent signal transduction. Structural determinants involved in this interaction are the PDZ10 domain of MUPP1 and the valine of the canonical class III PDZ domain binding motif DSV of the MT(1) carboxyl terminus. This high affinity interaction (K(d) approximately 4 nm), which is independent of MT(1) activation, occurs in the ovine pars tuberalis of the pituitary expressing both proteins endogenously. Although the disruption of the MT(1)/MUPP1 interaction has no effect on the subcellular localization, trafficking, or degradation of MT(1), it destabilizes the interaction between MT(1) and G(i) and abolishes G(i)-mediated signaling of MT(1). Our findings highlight a previously unappreciated role of PDZ proteins in promoting G protein coupling to receptors.

Altered cholinergic metabolism and muscarinic receptor linked second messenger pathways after chronic exposure to dichlorvos in rat brain

Chronic dichlorvos exposure (6 mg/kg b.wt/day) for a period of 8 weeks resulted in significant reduction in body weight gain of the male Wistar rats. However, the dietary intake remained unchanged in experimental animals following dichlorvos treatment. Activity of the synthesizing enzyme of acetylcholine (ACh) ie, choline acetyltransferase, was found to be significantly increased and the activity of hydrolyzing enzyme, acetyl cholinesterase (AChE), was inhibited in all the three brain regions studied. Chronic dichlorvos treatment also caused significant reduction in both high affinity (HA) and low affinity (LA) choline uptake (CU), with maximal effect being observed in the brain stem followed by cerebellum and cerebrum. Muscarinic receptor binding was significantly decreased in brain stem and cerebellum as reflected in the decreased receptor number (B(max)), without any change in the binding affinity (K(d)) of the receptors. Dichlorvos treatment caused marked inhibition in cAMP synthesis as indicated by decreased adenylate cyclase activity as well as cAMP levels in cerebrum, cerebellum and brain stem. Our study shows that organophosphates may interact with muscarinic receptor-linked second messenger system and this could be a potential mechanism for the neurotoxic effects observed after repeated exposure to low levels of organophosphates, which are unexplainable on the basis of cholinergic hyperactivity.

Measurement and meaning of apolipoprotein AI and apolipoprotein B plasma levels

Apolipoproteins AI and B are structural components of lipoprotein particles, and also determinants of the metabolic fate of the encapsulated lipid, cholesterol and triglyceride. Development of accurate assays for these apolipoproteins has opened the way for their use as predictors of coronary heart disease risk. Interpretation of AI and apo B levels is best undertaken with background knowledge of the metabolic status of an individual, especially the lipolytic capacity as reflected in the triglyceride concentration. Those with raised triglyceride, in general, not only have an elevated apo B/apo AI ratio, but also apo B-containing lipoproteins with a prolonged residence time and hence ample opportunity for modification and damage. Assessment of apolipoprotein levels is an aid to risk prediction and can be useful in tailoring treatment.

Insulin secretion, peripheral insulin sensitivity and insulin-receptor binding in subjects with different degrees of obesity

The aim of the present study was to investigate insulin secretion, insulin-receptor binding and peripheral insulin sensitivity in subjects with different degrees of obesity. 36 obese subjects with normal glucose tolerance and different degrees of obesity and 40 healthy normal-weight subjects participated in the study. Peripheral insulin sensitivity was measured by using the euglycaemic hyperinsulinaemic clamp technique, and insulin-receptor binding-on circulating mononuclear blood cells. Insulin secretion was studied during intravenous tolbutamide test. The subjects with I degree of obesity demonstrated a significant decrease in the number of total (p<0.0001) and high-affinity (p<0.01) insulin receptors per cell, as well as significantly higher insulin receptor affinity (p<0.01) as compared to the normal-weight subjects. The subjects with II degree of obesity also demonstrated a significant decrease in the number of total (p<0.0001) and high-affinity receptors (p<0.001) per cell as well as an increase (p<0.001) in insulin-receptor affinity as compared to the controls. The significantly decreased receptor number in the subjects with I and II degree of obesity was accompanied by an increase in insulin receptor affinity; thus their insulin-receptor binding being maintained similar to the controls. The subjects with III degree obesity presented a significant decrease (p<0.0001) in the number of both the total and high-affinity insulin receptors as well as a reduction in insulin receptor affinity as compared to the controls. Therefore the percentage of specifically bound insulin was significantly lower (p<0.01) as compared to that of the control group. Insulin resistance in the obese subjects is associated with secondary hyperinsulinaemia, which is present in subjects with I and II degree of obesity; while in severely obese subjects exhaustion of beta-cell secretory capacity is observed. We consider that III degree of obesity appears to be a risk factor for type 2 diabetes mellitus as the alterations in insulin sensitivity, insulin-receptor binding and beta-cell secretion are quite similar to the reported in diabetic patients.

Lymphosarcoma-induced alterations in hepatic adrenergic receptors: implications to the hypoglycemia of cancer cachexia.

A highly malignant transplantable rat lymphosarcoma was studied to determine the involvement of hepatic adrenergic receptors in the development of the hypoglycemia of cancer cachexia. Following inoculation of Fischer 344 rats with lymphosarcoma cells, rats were examined at 2 and 4 weeks, at the pre-cachexic stage; 6 weeks, at the transitional stage; and 7 weeks, at the cachexic hypoglycemic stage of lymphosarcoma progression. Death occurred by the 8th week. Blood glucose levels in lymphosarcoma-bearing rats relative to control rats were: unaffected at week 2; significantly reduced 8% at weeks 4 and 6; and reduced 24% at week 7. Alpha1 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 114, 89, 67 and 30% of control at weeks 2, 4, 6, and 7, respectively. Kinetic analysis indicated that the lymphosarcoma-induced decrease at week 7 was due to a decrease in numbers of receptors with no change in affinity: B(max)(control): 1411.1 fmol/mg: Kd(control): 0.44 nm; B(max)(lympho): 345.5 fmol/mg; Kd(lympho): 0.50 nm. Alpha2 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 130, 137, 243 and 212% of control at weeks 2,4, 6, and 7, respectively. The pattern of changes in hepatic alpha1, alpha2 and beta adrenergic receptors at week 6 was comparable to that of 17 day fetal liver: a decrease in alpha1 and beta and an increase in alpha2. Hepatic adrenergic receptor changes occurred in the absence of liver damage and were not due to contamination of the liver plasma membrane fractions with lymphosarcoma cells. Plasma insulin levels displayed modest (10-15%), but not statistically significant, increases post-inoculation after week 4. Plasma glucagon levels fluctuated post-inoculation until week 7 where they were significantly increased: 202% of control. Plasma T3 and T4 levels displayed an early and steady decline after lymphosarcoma inoculation: T3: unchanged at week 2 and significantly decreased 14, 44 and 50% at weeks 4, 6 and 7, respectively. T4 increased 20% at week 1; decreased 9% at week 4 and significantly decreased thereafter: 55 and 49% at weeks 6 and 7, respectively. We propose that the development of the hypoglycemia of cancer cachexia in this lymphosarcoma model is due primarily to an early and progressive thyroid hormone dependent decrease in the number of hepatic alpha1 adrenergic receptors, compounded by an increase and decrease, respectively, in the hepatic beta and alpha2 adrenergic receptors.

Pharmacodynamic and receptor binding changes during chronic lorazepam administration

To assess pharmacodynamic and neurochemical aspects of tolerance, lorazepam (2 mg/kg/day), or vehicle was administered chronically to male Crl: CD-1(ICR)BR mice via implantable osmotic pump. Open-field behavior, benzodiazepine receptor binding in vitro, receptor autoradiography, and muscimol-stimulated chloride uptake were examined at both 1 and 14 days. Open-field activity was depressed in lorazepam-treated animals on Day 1. On Day 14, open-field parameters were indistinguishable from those of vehicle-treated animals, indicating behavioral tolerance. Benzodiazepine binding, as determined by the specific binding of [ 125I]diazepam, was also decreased in cortex on Day 14. Hippocampal binding was unchanged following chronic lorazepam exposure. Apparent affinity in cortical membrane preparations was unchanged, indicating that altered ligand uptake was due to decreased receptor number. Muscimol-stimulated chloride uptake into cortical synaptoneurosomes from lorazepam-treated animals was not significantly different on Day 1 or Day 14 compared to vehicle-treated animals. These results confirm that down-regulation of benzodiazepine receptor binding is closely associated with behavioral tolerance to benzodiazepines. These observed changes in binding are not necessarily associated with robust changes in receptor function.

The Cardiac β -Adrenoceptor-G-protein(s)-adenylyl Cyclase System in Monocrotaline-treated Rats

In rats, injection of the alkaloid monocrotaline (MCT) causes right ventricular hypertrophy and cardiac failure. In order to study whether, in MCT-treated rats, changes in the cardiac β -adrenoceptor-G-protein(s)-adenylyl cyclase system might be comparable to those found in human primary pulmonary hypertension, we assessed in right and left ventricles from MCT-treated rats the components of the β -adrenoceptor system: the receptor number and subtype distribution (by (-)-[125I]iodocyanopindolol binding), the G-proteins (by quantitative Western blotting), and the activity of adenylyl cyclase. A single injection of 60 mg/kg i.p. MCT caused in rats right ventricular hypertrophy (RVH); part of the rats developed cardiac failure (RVF). In these rats the cardiac β -adrenoceptor-G-protein(s)-adenylyl cyclase system was markedly changed β -adrenoceptors were desensitized due to a decrease in receptor number, an uncoupling of the receptor from the Gs-adenylyl cyclase system, a decrease in Gsand a decrease in the activity of the catalytic unit of adenylyl cyclase. In general, these changes were more pronounced in right ventricles v left ventricles, and in rats with RVF v rats with RVH. On the other hand, cardiac muscarinic receptors and Giappeared not to be altered. We conclude that in MCT-treated rats changes in the cardiac β -adrenoceptor-G-protein(s)-adenylyl cyclase system occur that resemble those observed in human primary pulmonary hypertension. Thus, MCT-treated rat appears to be a suitable animal model to study in more detail the pathophysiology of the development of right heart failure, and to identify new therapeutic possibilities.

Reduced contractile response to insulin and IGF-I in ventricular myocytes from genetically obese Zucker rats.

Obesity plays a pivotal role in the pathophysiology of metabolic and cardiovascular diseases. Resistance to insulin is commonly seen in metabolic disorders such as obesity and diabetes. Insulin-like growth factor-I (IGF-I) mimics insulin in many tissues and has been shown to enhance cardiac contractile function and growth. Because IGF-I resistance often accompanies resistance to insulin, we sought to determine whether IGF-I-induced myocardial contractile was elevated and whether heart and kidney size were enlarged in obese compared with lean rats. The myocyte contraction profile in the obese rats showed a decreased peak shortening associated with prolonged relengthening and normal shortening duration, a pattern similar to that observed in diabetes. IGF-I (1-500 ng/ml) caused a dose-dependent increase in peak shortening in lean but not obese animals, but it did not alter the duration of shortening and relengthening. Consistent with contractile data, IGF-I induced a dose-dependent increase in Ca(2+) transients only in myocytes of lean rats. IGF-I receptor mRNA levels were significantly reduced in obese rat hearts. These results suggest that the IGF-I-induced cardiac contractile responses are attenuated in the Zucker model of obesity. The mechanisms underlying this alteration may be related to the decreased receptor number and/or changes in intracellular Ca(2+) handling in these animals.

Neonatal STZ model of type II diabetes mellitus in the Fischer 344 rat: characteristics and assessment of the status of the hepatic adrenergic receptors

The Fischer 344 rat was found to be extremely sensitive to the diabetogenic effects of neonatally injected streptozotocin (STZ): injection of 40–100 mg/kg STZ at 1.5 days postnatal produced in the adult graded levels of hyperglycemia in males but not the females. The optimal dose in the 1.5 day old male was 80 mg/kg: it produced hyperglycemia without affecting growth or thyroid status in the adult. The neonatally STZ-injected adult rat displayed characteristics consistent with type II diabetes: mild hyperglycemia accentuated by fasting or consumption of a high fat diet; little change in insulin levels; slight elevation in glucagon levels; no alterations in ketones. Using radioligand binding techniques to isolated rat liver plasma membranes, compared to the control state, the type II diabetic state was found to have: no effect on either α 2- or β-adrenergic receptor binding; a decrease in the major dominant α 1-adrenergic receptor, reflecting a decrease in receptor numbers but not their affinity; an increase in the plasma membrane calcium transport system, potentially depleting intracellular calcium stores essential for producing an α 1-adrenergic receptor response. Since the α 1-adrenergic receptor–calcium effector system is critical for the actions of catecholamines in the rat, these results suggest that the liver in the type II diabetic state may be refractory to the actions of catecholamines. We propose that the diabetes-evoked decrease in the dominant adrenergic receptor–effector system through which catecholamines act may be the cellular expression of defective glucocounterregulation in the diabetic state.

Characterization of the progestin receptors in the human TE85 and murine MC3T3-E1 osteoblast-like cell lines.

Progestins are believed to exert positive effects on bone density through receptors located in osteoblasts. In the present studies, the binding characteristics and regulation of the progestin receptors in two osteoblast-like cell lines were compared with those in human breast lines. Human TE85 and murine MC3T3-E1 osteoblast-like cells contain a single, high-affinity progestin binding site whose affinity and concentration are lower than in human breast cells. The osteoblastic progestin binding sites showed the expected steroid specificity and associated with the cell nuclei when occupied by ligand. The progestin receptors in osteoblastic cells also had sedimentation coefficients similar to those receptors in breast cells. The regulation of the progestin receptor in the osteoblast-like cells was explored by treating them with estradiol. In contrast to the large, rapid change seen in the breast cells, the progestin receptor levels in the MC3T3-E1 cells showed only a small, delayed up-regulation with estradiol treatment. The progestin receptor number in the TE85 cells was unaffected by estradiol. Down-regulation of the progestin receptors was explored by treating the cells with the progestin, norethindrone (NET). NET administration produced a rapid drop in progestin binding sites in the breast cells and a smaller, more gradual decline in MC3T3-E1 progestin binding. While the maximal decrease in receptor number occurred within 24 h in the breast cells, the receptor number was still continuing to fall after 72 h in the MC3T3-E1 cells. The data presented here demonstrate that both human and murine osteoblast-like cells contain a functional progestin receptor whose binding characteristics and regulation are similar, but not identical, to those receptors in other progestin target tissues such as the breast.

Neurotransmitter alterations in PTSD: catecholamines and serotonin.

In this chapter we review trauma-related studies involving epinephrine (E), norepinephrine (NE), and serotonin (5-HT). Central catecholamine neurons seem to play a critical role in level of alertness, vigilance, orienting, selective attention, memory, fear conditioning, and cardiovascular responses to life-threatening stimuli. Evidence of catecholamine dysregulation in post-traumatic stress disorder (PTSD) includes exaggerated increases in heart rate and blood pressure when exposed to visual and auditory reminders of trauma, elevated 24-hour urine catecholamine excretion, decreased platelet alpha-2 adrenergic receptor number, exaggerated behavioral, cardiovascular, and biochemical responses to IY yohimbine, decreased cortical brain metabolism secondary to IV yohimbine, and clinical efficacy of adrenergic blocking agents. Serotonin seems to play numerous roles in the central nervous system, including regulation of sleep, aggression, appetite, cardiovascular and respiratory activity, motor output, anxiety, mood, neuroendocrine secretion, and analgesia. Evidence of serotonergic dysregulation in PTSD includes frequent symptoms of aggression, impulsivity, depression and suicidality, decreased platelet paroxetine binding, blunted prolactin response to fenfluramine, exaggerated reactivity to m-chloro-phenyl-piperazine, and clinical efficacy of serotonin reuptake inhibitors. It has been suggested that alterations in NE, E, and 5-HT may have relevance for symptoms commonly seen in survivors with PTSD, including hypervigilance, exaggerated startle, irritability, impulsivity, aggression, intrusive memories, depressed mood, and suicidality.