JNK Deficiency Enhances Fatty Acid Utilization and Diverts Glucose From Oxidation to Glycogen Storage in Cultured Myotubes

Although germ‐line deletion of c‐Jun NH₂‐terminal kinase (JNK) improves overall insulin sensitivity in mice, those studies could not reveal the underlying molecular mechanism and the tissue site(s) in which reduced JNK activity elicits the observed phenotype. Given its importance in nonesterified fatty acids (NEFA) and glucose utilization, we hypothesized that the insulin‐sensitive phenotype associated with Jnk deletion originates from loss of JNK function in skeletal muscle. Short hairpin RNA (shRNA)–mediated gene silencing was used to identify the functions of JNK subtypes in regulating energy metabolism and metabolic responses to elevated concentrations of NEFA in C2C12 myotubes, a cellular model of skeletal muscle. We show for the first time that cellular JNK2‐ and JNK1/JNK2‐deficiency divert glucose from oxidation to glycogenesis due to increased glycogen synthase (GS) activity and induction of Pdk4. We further show that JNK2‐ and JNK1/JNK2‐deficiency profoundly increase cellular NEFA oxidation, and their conversion to phospholipids and triglyceride. The increased NEFA utilization was coupled to increased expressions of selective NEFA handling genes including Cd36, Acsl4, and Chka, and enhanced palmitic acid (PA)‐dependent suppression of acetyl‐CoA carboxylase (Acc). In JNK‐intact cells, PA inhibited insulin signaling and glycogenesis. Although silencing Jnk1 and/or Jnk2 prevented PA‐induced inhibition of insulin signaling, it did not completely block decreased insulin‐mediated glycogenesis, thus indicating JNK‐independent pathways in the suppression of glycogenesis by PA. Muscle‐specific inhibition of JNK2 (or total JNK) improves the capacity of NEFA utilization and glycogenesis, and is a potential therapeutic target for improving systemic insulin sensitivity in type 2 diabetes (T2D).     

Whey Protein Hydrolysate Enhances HSP90 but Does Not Alter HSP60 and HSP25 in Skeletal Muscle of Rats

Whey protein hydrolysate (WPH) intake has shown to increase HSP70 expression. The aim of the present study was to investigate whether WPH intake would also influences HSP90, HSP60 and HSP25 expression, as well as associated parameters. Forty-eight male Wistar rats were divided into sedentary (unstressed) and exercised (stressed) groups, and were fed with three different sources of protein: whey protein (WP), whey protein hydrolysate (WPH) and casein (CAS) as a control, based on the AIN93G diet for 3 weeks. WPH intake increased HSP90 expression in both sedentary and exercised animals compared to WP or CAS, however no alteration was found from exercise or diet to HSP60 or HSP25. Co-chaperone Aha1 and p-HSF1 were also increased in the exercised animals fed with WPH in comparison with WP or CAS, consistent with enhanced HSP90 expression. VEGF and p-AKT were increased in the WPH exercised group. No alteration was found in BCKDH, PI3-Kinase (p85), GFAT, OGT or PGC for diet or exercise. The antioxidant system GPx, catalase and SOD showed different responses to diet and exercise. The data indicate that WPH intake enhanced factors related to cell survival, such as HSP90 and VEGF, but does not alter HSP60 or HSP25 in rat skeletal muscle.     

Chemokine-Like Receptor 1 Deficiency Does Not Affect the Development of Insulin Resistance and Nonalcoholic Fatty Liver Disease in Mice

The adipokine chemerin and its receptor, chemokine-like receptor 1 (Cmklr1), are associated with insulin resistance and nonalcoholic fatty liver disease (NAFLD), which covers a broad spectrum of liver diseases, ranging from simple steatosis to nonalcoholic steatohepatitis (NASH). It is possible that chemerin and/or Cmklr1 exert their effects on these disorders through inflammation, but so far the data have been controversial. To gain further insight into this matter, we studied the effect of whole-body Cmklr1 deficiency on insulin resistance and NAFLD. In view of the primary role of macrophages in hepatic inflammation, we also transplanted bone marrow from Cmklr1 knock-out (Cmklr1^-/-) mice and wild type (WT) mice into low-density lipoprotein receptor knock-out (Ldlr^-/-) mice, a mouse model for NASH. All mice were fed a high fat, high cholesterol diet containing 21% fat from milk butter and 0.2% cholesterol for 12 weeks. Insulin resistance was assessed by an oral glucose tolerance test, an insulin tolerance test, and by measurement of plasma glucose and insulin levels. Liver pathology was determined by measuring hepatic inflammation, fibrosis, lipid accumulation and the NAFLD activity score (NAS). Whole-body Cmklr1 deficiency did not affect body weight gain or food intake. In addition, we observed no differences between WT and Cmklr1^-/- mice for hepatic inflammatory and fibrotic gene expression, immune cell infiltration, lipid accumulation or NAS. In line with this, we detected no differences in insulin resistance. In concordance with whole-body Cmklr1 deficiency, the absence of Cmklr1 in bone marrow-derived cells in Ldlr^-/- mice did not affect their insulin resistance or liver pathology. Our results indicate that Cmklr1 is not involved in the pathogenesis of insulin resistance or NAFLD. Thus, we recommend that the associations reported between Cmklr1 and insulin resistance or NAFLD should be interpreted with caution.     

Chronic Treatment of Rats with SCH-23390 or Raclopride Does Not Affect the Concentrations of DARPP-32 or Its mRNA in Dopamine-Innervated Brain Regions

DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein, Mr = 32,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) is a neuronal phosphoprotein that is enriched in neurons which possess dopamine D1 receptors, particularly striatonigral neurons. In rat brain slices, the phosphorylation state of DARPP-32 is regulated by dopamine, acting through the dopamine D1 receptor and the adenylyl cyclase system. This study reports that chronic blockade (21 days) of either dopamine D1 receptors by SCH-23390 or dopamine D2 receptors by raclopride does not affect the concentrations of DARPP-32 in specific rat brain regions (striatum, thalamus, hippocampus, frontal cerebral cortical pole). Northern blot analysis indicates that the steady-state level of DARPP-32 mRNA in striatum is also unchanged by these treatments.     

BDNF Level in the Rat Prefrontal Cortex Increases Following Chronic but Not Acute Treatment with Duloxetine, a Dual Acting Inhibitor of Noradrenaline and Serotonin Re-uptake

Aims Brain-Derived Neurotrophic Factor (BDNF) has a central role in neuronal survival, differentiation, and plasticity. The brain level of BDNF is changed by several mood stabilizers and antidepressant drugs acting on neurotransmitters such as noradrenaline and serotonin. We investigated the effects of acute and chronic treatment with Duloxetine, a new drug blocking the re-uptake of serotonin and noradrenaline (SNRI), on BDNF level in the prefrontal cortex, cerebrospinal fluid, plasma, and serum. Methods Wistar male rats were treated with acute (single treatment) and chronic oral administration (14 days) of different concentrations of Duloxetine (10, 30, and 100 mg/kg/day). At the end of the treatment periods, samples of blood, CSF and the prefrontal cortex were collected. BDNF levels were measured by ELISA. Levels of mature and precursor form of BDNF were measured by Western blot analysis. Results Animals treated with the Duloxetine at all concentrations and examined after 1 and 24 h (single treatment) did not reveal a significant change in the total BDNF level. In animals treated for 14 days with Duloxetine at 30 and 100 mg/kg, the total BDNF level increased significantly in the prefrontal cortex and CSF, but not in the plasma and serum. Using a specific antibody and Western blot we showed that the mature, but not the precursor, form of BDNF was significantly increased in the prefrontal cortex of rats treated for 14 days with Duloxetine at 30 mg/kg/day. Conclusions Our results show a major finding that repeated, but not single, Duloxetine treatment increases the level of BDNF in the prefrontal cortex. Claudio Mannari and Nicola Origlia are contributed equally to this work.     

Flavor Preference Learning Increases Olfactory and Gustatory Convergence onto Single Neurons in the Basolateral Amygdala but Not in the Insular Cortex in Rats

The basolateral amygdala (BLA) and the insular cortex (IC) represent two major areas for odor-taste associations, i.e. flavor integration. This learning may require the development of convergent odor and taste neuronal activation allowing the memory representation of such association. Yet identification of neurons that respond to such coincident input and the effect of flavor experience on odor-taste convergence remain unclear. In the present study we used the compartmental analysis of temporal activity using fluorescence in situ hybridization for Arc (catFISH) to visualize odor-taste convergence onto single neurons in the BLA and in the IC to assess the number of cells that were co-activated by both stimuli after odor-taste association. We used a sucrose conditioned odor preference as a flavor experience in rats, in which 9 odor-sucrose pairings induce a reliable odor-taste association. The results show that flavor experience induced a four-fold increase in the percentage of cells activated by both taste and odor stimulations in the BLA, but not in the IC. Because conditioned odor preference did not modify the number of cells responding selectively to one stimulus, this greater odor-taste convergence into individual BLA neurons suggests the recruitment of a neuronal population that can be activated by both odor and taste only after the association. We conclude that the development of convergent activation in amygdala neurons after odor-taste associative learning may provide a cellular basis of flavor memory.     

Greater Transport Efficiencies of the Membrane Fatty Acid Transporters FAT/CD36 and FATP4 Compared with FABPpm and FATP1 and Differential Effects on Fatty Acid Esterification and Oxidation in Rat Skeletal Muscle

In selected mammalian tissues, long chain fatty acid transporters (FABPpm, FAT/CD36, FATP1, and FATP4) are co-expressed. There is controversy as to whether they all function as membrane-bound transporters and whether they channel fatty acids to oxidation and/or esterification. Among skeletal muscles, the protein expression of FABPpm, FAT/CD36, and FATP4, but not FATP1, correlated highly with the capacities for oxidative metabolism (r ≥ 0.94), fatty acid oxidation (r ≥ 0.88), and triacylglycerol esterification (r ≥ 0.87). We overexpressed independently FABPpm, FAT/CD36, FATP1, and FATP4, within a normal physiologic range, in rat skeletal muscle, to determine the effects on fatty acid transport and metabolism. Independent overexpression of each fatty acid transporter occurred without altering either the expression or plasmalemmal content of other fatty acid transporters. All transporters increased fatty acid transport, but FAT/CD36 and FATP4 were 2.3- and 1.7-fold more effective than FABPpm and FATP1, respectively. Fatty acid transporters failed to alter the rates of fatty acid esterification into triacylglycerols. In contrast, all transporters increased the rates of long chain fatty acid oxidation, but the effects of FABPpm and FAT/CD36 were 3-fold greater than for FATP1 and FATP4. Thus, fatty acid transporters exhibit different capacities for fatty acid transport and metabolism. In vivo, FAT/CD36 and FATP4 are the most effective fatty acid transporters, whereas FABPpm and FAT/CD36 are key for stimulating fatty acid oxidation.Uptake of long chain fatty acids across the plasma membrane had long been considered to occur via passive diffusion. However, in recent years, there has been a fundamental shift in our understanding, and it is now widely recognized that long chain fatty acids cross the plasma membrane via a protein-mediated mechanism (for reviews, see Refs. 1–3). A number of fatty acid transporters have been identified, including fatty acid translocase/CD36 (FAT/CD36), plasma membrane-associated fatty acid binding proteins (FABPpm), and a family of fatty acid transport proteins (FATP1–6)⁵ (for reviews, see Refs. 1 and 4). Selected stimuli (muscle contraction, insulin, and AICAR) induce the translocation of selected fatty acid transporters (FABPpm, FAT/CD36, and FATP1) from an intracellular depot to the plasma membrane, in both heart and skeletal muscle, resulting in concurrently increased rates of fatty acid transport (for a review, see Ref. 1). Some fatty acid transporters have now also been implicated in the dysregulation of fatty acid metabolism in heart and skeletal muscle in models of insulin resistance and type 1 and 2 diabetes, including FAT/CD36 (5–9), FATP1 (10, 11), and possibly FATP4 (11, 12) but not FABPpm (5–7). Thus, in recent years, it has become widely accepted that (a) long chain fatty acids traverse the plasma membrane via a protein-mediated mechanism and (b) some of the fatty acid transporters are central to the dysregulation in skeletal muscle fatty acid metabolism in obesity and type 2 diabetes.In vivo, many of the fatty acid transporters are frequently co-expressed in different tissues. FAT/CD36 and FABPpm are ubiquitously expressed (1), whereas FATP1–6 exhibit a somewhat tissue-specific distribution pattern (13, 14). The reason for the co-expression of different fatty acid transporters within the same tissue remains unclear. It has been speculated that selected fatty acid transporters may need to interact with each other (15, 16). Alternatively, it is also possible that (a) different fatty acid transporters have discrepant transport capacities, and (b) selected transporters may channel fatty acids differentially to fatty acid oxidation and esterification into triacylglycerols in mammalian tissue.Recent evidence has shown that the transport capacities among FATPs can differ substantially, as revealed by overexpression (14, 17, 18) or knockdown studies (19), but there is little agreement as to which FATP is most effective. Extensive studies by DiRusso et al. (17) in yeast revealed that when FATP1–6 were overexpressed to similar levels (qualitative assessment), FATP4 exhibited 1.7- and 3-fold greater fatty acid transport effectiveness compared with FATP1 and FATP2, respectively, whereas no fatty acid transport capacities were attributable to FATP3, -5, and -6 (17). In contrast, in HEK293 cells, the FATP6 transport capacity was 3- and 6.5-fold greater than FATP1 and FATP4, respectively (14), whereas in 3T3-L1 adipocytes, a fatty acid transport role was evident only for FATP1 and not FATP4 (19). Others have also questioned the transport role of FATP4 (20). These discrepant findings with respect to the transport effectiveness of FATPs may reflect, in part, the use of diverse cell types with ill defined metabolic needs and/or machinery for fatty acid uptake and metabolism. Indeed, several recent reports indicate that fatty acid transport cannot be adequately examined in some cells, because these appear to lack accessory proteins that may be involved in fatty acid transport (21, 22). In addition, extrapolation of results from cultured cells to metabolically important tissue in vivo may also be problematic, since cells and mammalian tissues probably have different requirements for fatty acid utilization, and their regulation of fatty acid uptake may also differ. For example, the mechanisms regulating the acute contraction-induced up-regulation of fatty acid transport and oxidation, such as occurs in heart and skeletal muscle, is probably absent in selected cell cultures.Assessment of fatty acid transporter effectiveness, in vivo, cannot be determined in knock-out animals, since compensatory responses in some fatty acid transporters (FATP1 and -4) occur when another fatty acid transporter (FAT/CD36) has been ablated (23, 24). Thus, the relative effectiveness of selected fatty acid transporters on fatty acid transport in vivo remains unknown. In addition, whether fatty acid transporters channel fatty acids to a particular metabolic fate, as has been suggested based on studies in cultured cells (18, 19, 25), may depend on the cell type being examined.It is desirable to discern the effectiveness of selected fatty acid transporters in mammalian tissues that have a well known system for transporting and utilizing fatty acids and in which fatty acid transporters can be independently up-regulated without disturbing the expression of other fatty acid transporters. These criteria can be satisfied in rat skeletal muscle in which genes can be up-regulated under controlled conditions within a physiologically meaningful range (26–28). Therefore, in the present study, we have compared the independent transport effectiveness of fatty acid transporters (FABPpm, FAT/CD36, FATP1, and FATP4) in skeletal muscle, without disturbing the expression and plasmalemmal content of other fatty acid transporters. In addition, we also examined the contributions of these transporters to fatty acid oxidation and esterification into triacylglycerols. These are the first studies to reveal that in vivo (a) the fatty acid transport effectiveness of fatty acid transporters differs considerably, and (b) in skeletal muscle, these transporters serve to channel fatty acids to oxidation, not esterification into triacylglycerols.     

Repetitive Treatment with Volatile Anesthetics Does Not Affect the In Vivo Plasma Concentration and Composition of Extracellular Vesicles in Rats

Background: Anesthetic-induced preconditioning (AIP) with volatile anesthetics is a well-known experimental technique to protect tissues from ischemic injury or oxidative stress. Additionally, plasmatic extracellular vesicle (EV) populations and their cargo are known to be affected by AIP in vitro, and to provide organ protective properties via their cargo. We investigated whether AIP would affect the generation of EVs in an in vivo rat model. Methods: Twenty male Sprague Dawley rats received a repetitive treatment with either isoflurane or with sevoflurane for a duration of 4 or 8 weeks. EVs from blood plasma were characterized by nanoparticle tracking analysis, transmission electron microscopy (TEM) and Western blot. A scratch assay (H9C2 cardiomyoblast cell line) was performed to investigate the protective capabilities of the isolated EVs. Results: TEM images as well as Western blot analysis indicated that EVs were successfully isolated. The AIP changed the flotillin and CD63 expression on the EV surface, but not the EV concentration. The scratch assay did not show increased cell migration and/or proliferation after EV treatment. Conclusion: AIP in rats changed the cargo of EVs but had no effect on EV concentration or cell migration/proliferation. Future studies are needed to investigate the cargo on a miRNA level and to investigate the properties of these EVs in additional functional experiments.     

Fatty Acid Oxidation Changes and the Correlation with Oxidative Stress in Different Preeclampsia-Like Mouse Models

Background

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) expression is decreased in placenta of some cases of preeclampsia (PE) which may result in free fatty acid (FFA) increased. High FFA level will induce oxidative stress, so abnormal long-chain fatty acid-oxidation may participate in the pathogenesis of PE through oxidative stress pathway.

Methods

PE-like groups were ApoC3 transgenic mice with abnormal fatty acid metabolism, classical PE-like models with injection of Nw-nitro-L-arginine-methyl ester (L-NA) or lipopolysaccharide (LPS) and the antiphospholipid syndrome (APS) mouse model with β2GPI injection (ApoC3+NS, ApoC3+L-NA, L-NA, LPS and β2GPI groups). The control group was wild-type mice with normal saline injection. Except for β2GPI mice, the other mice were subdivided into pre-implantation (Pre) and mid-pregnancy (Mid) subgroups by injection time.

Results

All PE-like groups showed hypertension and proteinuria except ApoC3+NS mice only showed hypertension. Serum FFA levels increased significantly except in LPS group compared to controls (P<0.05). LCHAD mRNA and protein expression in the liver and placenta was significantly higher for ApoC3+NS, ApoC3+L-NA and β2GPI mice and lower for L-NA mice than controls (P<0.05) but did not differ between LPS mice and controls. P47phox mRNA and protein expression in the liver significantly increased in all PE-like groups except LPS group, while P47phox expression in the placenta only significantly increased in L-NA and β2GPI groups.

Conclusions

Abnormal long-chain fatty acid-oxidation may play a different role in different PE-like models and in some cases participate in the pathogenesis of PE through oxidative stress pathway.     

Comparative Effects of Dietary Fat Types on Hepatic Enzyme Activities Related to the Synthesis and Oxidation of Fatty Acid and to Lipogenesis in Rats

The effects of different types of dietary fat on the activities of hepatic enzymes related to fatty acid synthesis {glucose-6-phosphate dehydrogenase (G6PDH) and acetyl-CoA carboxylase ACC)}, oxidation {acyl-CoA synthetase (AST), carnitine palmitoyl transferase (CPT), and peroxisomal β-oxidation (P βOX)}, and lipogenesis {phosphatidate phosphohydrolase (PAP), diacylglycerol acyltransferase (DGAT), and phosphocholine diacylglycerol transferase (PCDGT)}, and plasma and liver lipid levels were investigated in male Wistar rats. The animals were 6 weeks old and about 120 g of body weight, and were fed on test diets containing 20% of a mixture of tripalmitin, tristearin and corn oil (SFA), olive oil (OLI), sunflower oil (SUN), linseed oil (LIS), and sardine oil (SAR) for 2 weeks. The concentrations of plasma total cholesterol (T-CHOL), high-density lipoprotein-cholesterol (HDL-CHOL), triacylglycerol (TG) and phospholipid (PL) were generally higher in the rats fed on SEA and OLI than in those given SUN, LIS and SAR. The rats fed on OLI had a higher level of liver T-CHOL than those fed on the other fats. The liver TG content was nearly higher from the intake of SFA and OLI than from SUN, LIS and SAR, although the liver PL level was not affected by the type of dietary fat. The SFA and OLI groups had the highest activities of hepatic G6PDH and ACC, and the SAR group, the lowest activities. The activities of AST and CPT, and peroxisomal P βOX in the liver were higher in the rats fed on the LIS and SAR diets than in those given the other diets. The hepatic PAP activity was higher from the intake of OLI and SUN, and tended to be higher from SFA than from LIS and SAR. The activity of liver DGAT was higher from SFA and inclined to be higher from OLI, SUN, and LIS than from SAR, while the PCDGT activity in the liver was not effected by the type of dietary fat. The concentrations of plasma and liver TG were generally positively correlated with the activities of liver enzymes related to the synthesis of fatty acids and lipids, and negatively with those involved in fatty acid oxidation. Based on these results, it is suggested that the levels of plasma and liver TG were controlled by different types of dietary fat through changes in the hepatic enzyme activities related to fatty acid synthesis, lipogenesis, and fatty acid oxidation.     

高果糖引起的脂肪肝大鼠肾脏脂质合成相关基因和蛋白的表达

大量研究表明,高果糖可引起脂肪肝,但对肾脏脂质代谢的影响尚不清楚。该实验研究给予10％果糖水5周后诱导的脂肪肝大鼠肾脏的脂质代谢情况,并探讨其可能机制。将16只雄性SD大鼠随机分为正常组（con）和果糖组（fru）,果糖组给予10％（W／V）果糖水,第5N末称体重、取血、处死,检测血浆GLU、TG、TC和INSULIN含量。取肾脏、肝脏和白色脂肪称重,采用形态学方法观察肝脏和肾脏脂质沉积情况,酶法测其TG、TC含量,以Real time—PCR检测肾脏、肝脏中脂质合成和脂质氧化相关基因水平,以Westemblot检测肾、肝细胞核脂质合成转录因子的蛋白表达。结果显示,果糖组大鼠血浆TG、INSULIN明显升高,并出现肥胖体征,肝脏脂质沉积严重,其调控脂质合成的两个关键的转录因子ChREBP和SREBPlcmRNA和核蛋白表达都明显升高,并且它们靶向的脂质合成相关酶FAS、ACCl、SCDlmRNA表达也显著增加。但是,在肾脏中,高果糖没有引起TG含量的变化,调控脂质重新合成的基因和蛋白的表达也未发生变化。因此,与果糖致脂肪肝不同,高果糖饮食并没有造成肾脏的脂质沉积和脂质合成相关基因、蛋白的变化。     

Chronic Treatment with the GLP1 Analogue Liraglutide Increases Cell Proliferation and Differentiation into Neurons in an AD Mouse Model

Neurogenesis is a life long process, but the rate of cell proliferation and differentiation decreases with age. In Alzheimer''s patients, along with age, the presence of Aβ in the brain inhibits this process by reducing stem cell proliferation and cell differentiation. GLP-1 is a growth factor that has neuroprotective properties. GLP1 receptors are present on neuronal progenitor cells, and the GLP-1 analogue liraglutide has been shown to increase cell proliferation in an Alzheimer''s disease (AD) mouse model. Here we investigated acute and chronic effects of liraglutide on progenitor cell proliferation, neuroblast differentiation and their subsequent differentiation into neurons in wild type and APP/PS-1 mice at different ages. APP/PS1 and their littermate controls, aged 3, 6, 12, 15 months were injected acutely or chronically with 25 nmol/kg liraglutide. Acute treatment with liraglutide showed an increase in cell proliferation in APP/PS1 mice, but not in controls whereas chronic treatment increased cell proliferation at all ages (BrdU and Ki67 markers). Moreover, numbers of immature neurons (DCX) were increased in both acute and chronic treated animals at all ages. Most newly generated cells differentiated into mature neurons (NeuN marker). A significant increase was observed with chronically treated 6, 12, 15 month APP/PS1 and WT groups. These results demonstrate that liraglutide, which is currently on the market as a treatment for type 2 diabetes (Victoza^TM), increases neurogenesis, which may have beneficial effects in neurodegenerative disorders like AD.     

Time Course and Regional Basis of Pb-Induced Changes in MK-801 Binding: Reversal by Chronic Treatment with the Dopamine Agonist Apomorphine but Not the D1 Agonist SKF-82958

Abstract: In the present study we attempted to further define the time course and regional specificity of lead (Pb)-induced changes in the NMDA receptor complex and the influence of dopaminergic system modulations on these changes. Autoradiographic measurements of alterations in MK-801 binding, as evaluated under four different activation conditions (none, spermidine, glycine, or maximal activation), were performed in medial frontal cortex, dorsal striatum, and nucleus accumbens of male rats after 2 weeks or 8 months of chronic postweaning (from 21 days of age on) exposure to 0, 50, or 150 ppm Pb acetate in drinking water. The 8-month groups also received chronic intermittent intraperitoneal injections of saline, or of the dopamine (DA) agonist apomorphine or the D₁ agonist SKF-82958 2–3 times per week beginning at 60 days of age. Two weeks of 50 ppm Pb exposure resulted in small but significant increases in MK-801 binding under conditions of glycine or spermidine activation, whereas decreases were observed in response to 150 ppm under conditions of no or maximal activation in all regions. After 8 months of Pb, concentration-dependent decreases in MK-801 binding were observed across regions under all activation conditions. These effects were noted at blood Pb concentrations averaging as low as 16 µg/dl. Pb-induced decreases in MK-801 binding were either partially or fully reversed by chronic intermittent treatment with the DA agonist apomorphine but not by the D₁ agonist SKF-82958, implicating D₂-based mechanisms in this reversal. Combined findings from this and previous studies based on this exposure protocol indicate a Pb-induced pattern of widespread hypoglutamatergic function accompanied by increased DA function in mesolimbic systems, a pattern of changes reminiscent of those proposed to underlie schizophrenia. Such findings suggest that Pb exposure, even at current environmental levels, could be a risk factor for behavioral and/or neurological disturbances arising from imbalances of glutamate/dopamine function in mesocorticolimbic systems.     

Expression of Cholinergic,Insulin, Vitamin D Receptors and GLUT 3 in the Brainstem of Streptozotocin Induced Diabetic Rats: Effect of Treatment with Vitamin D3

Complications arising from diabetes mellitus include cognitive deficits, neurophysiological and structural changes in the brain. The current study investigated the expression of cholinergic, insulin, Vitamin D receptor and GLUT 3 in the brainstem of streptozotocin-induced diabetic rats. Radioreceptor binding assays and gene expression were done in the brainstem of male Wistar rats. Our results showed that B_max of total muscarinic, muscarinic M3 receptors was increased and muscarinic M1 receptor was decreased in diabetic rats compared to control. A significant increase in gene expression of muscarinic M3, α7 nicotinic acetylcholine, insulin, Vitamin D₃ receptors, acetylcholine esterase, choline acetyl transferase and GLUT 3 were observed in the brainstem of diabetic rats. Immunohistochemistry studies of muscarinic M1, M3 and α7 nicotinic acetylcholine receptors confirmed the gene expression at protein level. Vitamin D₃ and insulin treatment reversed diabetes-induced alterations to near control. This study provides an evidence that diabetes can alter the expression of cholinergic, insulin, Vitamin D receptors and GLUT 3 in brainstem. We found that Vitamin D₃ treatment could modulate the Vitamin D receptors and plays a pivotal role in maintaining the glucose transport and expressional level of cholinergic receptors in the brainstem of diabetic rats. Thus, our results suggest a therapeutic role of Vitamin D₃ in managing neurological disorders associated with diabetes.