TLCD1 and TLCD2 regulate cellular phosphatidylethanolamine composition and promote the progression of non-alcoholic steatohepatitis.

The fatty acid composition of phosphatidylethanolamine (PE) determines cellular metabolism, oxidative stress, and inflammation. However, our understanding of how cells regulate PE composition is limited. Here, we identify a genetic locus on mouse chromosome 11, containing two poorly characterized genes Tlcd1 and Tlcd2, that strongly influences PE composition. We generated Tlcd1/2 double-knockout (DKO) mice and found that they have reduced levels of hepatic monounsaturated fatty acid (MUFA)-containing PE species. Mechanistically, TLCD1/2 proteins act cell intrinsically to promote the incorporation of MUFAs into PEs. Furthermore, TLCD1/2 interact with the mitochondria in an evolutionarily conserved manner and regulate mitochondrial PE composition. Lastly, we demonstrate the biological relevance of our findings in dietary models of metabolic disease, where Tlcd1/2 DKO mice display attenuated development of non-alcoholic steatohepatitis compared to controls. Overall, we identify TLCD1/2 proteins as key regulators of cellular PE composition, with our findings having broad implications in understanding and treating disease.

Nestin Regulates Neurogenesis in Mice Through Notch Signaling From Astrocytes to Neural Stem Cells.

The intermediate filament (nanofilament) protein nestin is a marker of neural stem cells, but its role in neurogenesis, including adult neurogenesis, remains unclear. Here, we investigated the role of nestin in neurogenesis in adult nestin-deficient (Nes-/-) mice. We found that the proliferation of Nes-/- neural stem cells was not altered, but neurogenesis in the hippocampal dentate gyrus of Nes-/- mice was increased. Surprisingly, the proneurogenic effect of nestin deficiency was mediated by its function in the astrocyte niche. Through its role in Notch signaling from astrocytes to neural stem cells, nestin negatively regulates neuronal differentiation and survival; however, its expression in neural stem cells is not required for normal neurogenesis. In behavioral studies, nestin deficiency in mice did not affect associative learning but was associated with impaired long-term memory.

Lactobacillus rhamnosusGG reduces hepatic fibrosis in a model of chronic liver disease in rats

BACKGROUND: The intestinal dysbiosis is common in chronic liver disease and can induce to inflammatory responses and mediate the collagen deposition in the liver. AIM: To evaluate the probiotic Lactobacillus rhamnosus GG (LGG) for the treatment of liver fibrosis in a model of chronic cholestatic liver disease in rats. METHODS: Male adult Wistar rats (n = 29) were submitted to common bile duct ligation (BDL groups) or manipulation of common bile duct without ligation (Ctrl groups).Two weeks after surgery, each group was randomly divided to receive 1 ml of PBS (Ctrl and BDL) or PBS containing 2.5 x 107 CFU of LGG (Ctrl-P and BDL-P) through gavages for 14 days. Euthanasia occurred 33 days after surgery when samples of blood and liver tissue were collected. RESULTS: The hepatic gene expression of Tlr4, Tnfα, IL-6, Tgfß, and metalloproteinase-2 and -9 were higher in the BDL groups in comparison to Ctrl. The ductular reaction evaluated by immunocontent of cytokeratin-7 (CK7) and the content of collagen were increased in BDL groups. Also, there was an imbalance in the antioxidant defenses (superoxide dismutase and catalase) and an increase in the oxidative stress marker sulfhydryl in BDL groups. The treatment with LGG significantly reduced gene expression of IL-6, collagen deposition, and ductular reaction in hepatic tissue of animals from BDL-P groups. CONCLUSION: The treatment with the probiotic LGG was able to reduce liver fibrosis, ductular reaction, and hepatic gene expression of IL-6 in a model of cholestatic liver disease in rats.

Lactobacillus rhamnosus GG reduces hepatic fibrosis in a model of chronic liver disease in rats / El Lactobacillus rhamnosus GG reduce la fibrosis hepática en un modelo de enfermedad hepática crónica en ratas

Background: The intestinal dysbiosis is common in chronic liver disease and can induce to inflammatory responses and mediate the collagen deposition in the liver. Aim: To evaluate the probiotic Lactobacillus rhamnosus GG (LGG) for the treatment of liver fibrosis in a model of chronic cholestatic liver disease in rats. Methods: Male adult Wistar rats (n = 29) were submitted to common bile duct ligation (BDL groups) or manipulation of common bile duct without ligation (Ctrl groups).Two weeks after surgery, each group was randomly divided to receive 1 ml of PBS (Ctrl and BDL) or PBS containing 2.5 x 107 CFU of LGG (Ctrl-P and BDL-P) through gavages for 14 days. Euthanasia occurred 33 days after surgery when samples of blood and liver tissue were collected. Results: The hepatic gene expression of Tlr4, Tnfα, IL-6, Tgfβ, and metalloproteinase-2 and -9 were higher in the BDL groups in comparison to Ctrl. The ductular reaction evaluated by immunocontent of cytokeratin-7 (CK7) and the content of collagen were increased in BDL groups. Also, there was an imbalance in the antioxidant defenses (superoxide dismutase and catalase) and an increase in the oxidative stress marker sulfhydryl in BDL groups. The treatment with LGG significantly reduced gene expression of IL-6, collagen deposition, and ductular reaction in hepatic tissue of animals from BDL-P groups. Conclusion: The treatment with the probiotic LGG was able to reduce liver fibrosis, ductular reaction, and hepatic gene expression of IL-6 in a model of cholestatic liver disease in rats (AU)

Introducción: la disbiosis intestinal es común en la enfermedad hepática crónica y puede inducir respuestas inflamatorias y mediar la deposición hepática de colágeno. Objetivo: evaluar el efecto del probiótico Lactobacillus rhamnosus GG (LGG) en el tratamiento de la fibrosis hepática en un modelo de enfermedad hepática colestásica en ratas. Métodos: se sometió a ratas Wistar macho adultas (n = 29) a ligadura del conducto biliar común (grupo BDL) o a manipulación del conducto biliar sin ligadura (grupo Ctrl). Dos semanas después, cada grupo se dividió aleatoriamente para recibir 1 ml de PBS (Ctrl y BDL) o PBS con 2,5 x 107 UFC de LGG (Ctrl-P y BDL-P) durante 14 días. Se aplicó la eutanasia 33 días después de la cirugía y se recogieron muestras de sangre y de tejido hepático. Resultados: las expresiones hepáticas de Tlr4, Tnfα, IL-6, Tgfβ, metaloproteinasa-2 y -9 fueron mayores en los grupos BDL. La reacción ductular evaluada por el inmunocontenido de citoqueratina 7 (CK7) y el contenido de colágeno se aumentó en los grupos BDL. Además, hubo un desequilibrio en las defensas antioxidantes (superóxido dismutasa y catalasa) y un aumento en el estrés oxidativo (sulfhidrilo) en los grupos BDL. El tratamiento con LGG redujo la expresión génica de IL-6, la deposición de colágeno y la reacción ductular en el hígado de los animales del grupo BDL-P. Conclusión: el tratamiento con LGG redujo la expresión génica de IL-6 en el hígado, la fibrosis hepática y la reacción ductular en un modelo de enfermedad hepática colestásica en ratas (AU)

The Glutamine Transporters and Their Role in the Glutamate/GABA-Glutamine Cycle.

Glutamine is a key amino acid in the CNS, playing an important role in the glutamate/GABA-glutamine cycle (GGC). In the GGC, glutamine is transferred from astrocytes to neurons, where it will replenish the inhibitory and excitatory neurotransmitter pools. Different transporters participate in this neural communication, i.e., the transporters responsible for glutamine efflux from astrocytes and influx into the neurons, such as the members of the SNAT, LAT, y+LAT, and ASC families of transporters. The SNAT family consists of the transporter isoforms SNAT3 and SNAT5 that are related to efflux from the astrocytic compartment, and SNAT1 and SNAT2 that are associated with glutamine uptake into the neuronal compartment. The isoforms SNAT7 and SNAT8 do not have their role completely understood, but they likely also participate in the GGC. The isoforms LAT2 and y+LAT2 facilitate the exchange of neutral amino acids and cationic amino acids (y+LAT2 isoform) and have been associated with glutamine efflux from astrocytes. ASCT2 is a Na+-dependent antiporter, the participation of which in the GGC also remains to be better characterized. All these isoforms are tightly regulated by transcriptional and translational mechanisms, which are induced by several determinants such as amino acid deprivation, hormones, pH, and the activity of different signaling pathways. Dysfunctional glutamine transporter activity has been associated with the pathophysiological mechanisms of certain neurologic diseases, such as Hepatic Encephalopathy and Manganism. However, there might also be other neuropathological conditions associated with an altered GGC, in which glutamine transporters are dysfunctional. Hence, it appears to be of critical importance that the physiological and pathological aspects of glutamine transporters are thoroughly investigated.

Expression of glutamine transporter isoforms in cerebral cortex of rats with chronic hepatic encephalopathy.

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs due to acute and chronic liver diseases, the hallmark of which is the increased levels of ammonia and subsequent alterations in glutamine synthesis, i.e. conditions associated with the pathophysiology of HE. Under physiological conditions, glutamine is fundamental for replenishment of the neurotransmitter pools of glutamate and GABA. The different isoforms of glutamine transporters play an important role in the transfer of this amino acid between astrocytes and neurons. A disturbance in the GABA biosynthetic pathways has been described in bile duct ligated (BDL) rats, a well characterized model of chronic HE. Considering that glutamine is important for GABA biosynthesis, altered glutamine transport and the subsequent glutamate/GABA-glutamine cycle efficacy might influence these pathways. Given this potential outcome, the aim of the present study was to investigate whether the expression of the glutamine transporters SAT1, SAT2, SN1 and SN2 would be affected in chronic HE. We verified that mRNA expression of the neuronal glutamine transporters SAT1 and SAT2 was found unaltered in the cerebral cortex of BDL rats. Similarly, no changes were found in the mRNA level for the astrocytic transporter SN1, whereas the gene expression of SN2 was increased by two-fold in animals with chronic HE. However, SN2 protein immuno-reactivity did not correspond with the increase in gene transcription since it remained unaltered. These data indicate that the expression of the glutamine transporter isoforms is unchanged during chronic HE, and thus likely not to participate in the pathological mechanisms related to the imbalance in the GABAergic neurotransmitter system observed in this neurologic condition.

Effects of hyperammonemia on brain energy metabolism: controversial findings in vivo and in vitro.

The literature related to the effects of elevated plasma ammonia levels on brain energy metabolism is abundant, but heterogeneous in terms of the conclusions. Thus, some studies claim that ammonia has a direct, inhibitory effect on energy metabolism whereas others find no such correlation. In this review, we discuss both recent and older literature related to this controversial topic. We find that it has been consistently reported that hepatic encephalopathy and concomitant hyperammonemia lead to reduced cerebral oxygen consumption. However, this may not be directly linked to an effect of ammonia but related to the fact that hepatic encephalopathy is always associated with reduced brain activity, a condition clearly characterized by a decreased CMRO2. Whether this may be related to changes in GABAergic function remains to be elucidated.

Expression of Glutamate Decarboxylase (GAD) mRNA in the brain of bile duct ligated rats serving as a model of hepatic encephalopathy.

Hepatic encephalopathy (HE) is a neurologic disorder that involves different pathophysiological mechanisms, including disturbances in the GABAergic neurotransmitter system. Albeit an overall increase in the level of neurotransmitter GABA has not been found in HE, alterations in GABA receptors and metabolism have been described. Moreover, it has been reported that bile duct ligated (BDL) rats, an animal model for the study of HE, exhibited an altered GABA biosynthesis involving preferentially the tricarboxylic (TCA) cycle. In this context it should be noted that the GABA synthesizing enzyme glutamate decarboxylase (GAD) is expressed in the brain in two isoforms GAD67 and GAD65, GAD65 being related to the synthesis of GABA that occurs via the TCA cycle and coupled to the vesicular pool of the neurotransmitter. The aim of the present study was to investigate whether changes in mRNA expression of GAD67 and GAD65 were related to the altered GABA biosynthesis previously observed. To study this, cerebral cortices and hippocampi were dissected from control and BDL rats, total mRNA was isolated and cDNA was synthesized by reverse transcription reaction. Subsequently samples were analyzed for gene expression of GAD67 and GAD65 by qPCR multiplex assay, using GAPDH as endogenous control. No changes in GAD67 and GAD65 mRNA expression between control and BDL rats either in cerebral cortex or in hippocampus were observed indicating that the HE condition did not lead to changes in GAD mRNA expression. However, other regulatory mechanism might be affecting GAD activity and to clarify this additional studies need to be conducted.

Impairment of short term memory in rats with hepatic encephalopathy due to bile duct ligation.

Hepatic encephalopathy (HE) arises from acute or chronic liver diseases and leads to cognitive deficits. Different animal models for the study of HE have demonstrated learning and memory impairment and a number of neurotransmitter systems have been proposed to be involved in this. Recently, it was described that bile duct-ligated (BDL) rats exhibited altered spatio-temporal locomotor and exploratory activities and biosynthesis of neurotransmitter GABA in brain cortices. Therefore, the aim of this study was to evaluate cognition in the same animal model. Male adult Wistar rats underwent common bile duct ligation (BDL rats) or manipulation of common bile duct without ligation (control rats). Six weeks after surgery, control and BDL rats underwent object recognition behavioral task. The BDL rats developed chronic liver failure and exhibited a decreased discrimination index for short term memory (STM) when compared to the control group. There was no difference in long term memory (LTM) as well as in total time of exploration in the training, STM and LTM sessions between the BDL and control rats. Therefore, the BDL rats demonstrated impaired STM for recognition memory, which was not due to decreased exploration.

Impairment of the organization of locomotor and exploratory behaviors in bile duct-ligated rats.

Hepatic encephalopathy (HE) arises from acute or chronic liver diseases and leads to several problems, including motor impairment. Animal models of chronic liver disease have extensively investigated the mechanisms of this disease. Impairment of locomotor activity has been described in different rat models. However, these studies are controversial and the majority has primarily analyzed activity parameters. Therefore, the aim of the present study was to evaluate locomotor and exploratory behavior in bile duct-ligated (BDL) rats to explore the spatial and temporal structure of behavior. Adult female Wistar rats underwent common bile duct ligation (BDL rats) or the manipulation of common bile duct without ligation (control rats). Six weeks after surgery, control and BDL rats underwent open-field, plus-maze and foot-fault behavioral tasks. The BDL rats developed chronic liver failure and exhibited a decrease in total distance traveled, increased total immobility time, smaller number of rearings, longer periods in the home base area and decreased percentage of time in the center zone of the arena, when compared to the control rats. Moreover, the performance of the BDL rats was not different from the control rats for the elevated plus-maze and foot-fault tasks. Therefore, the BDL rats demonstrated disturbed spontaneous locomotor and exploratory activities as a consequence of altered spatio-temporal organization of behavior.

Synthesis of neurotransmitter GABA via the neuronal tricarboxylic acid cycle is elevated in rats with liver cirrhosis consistent with a high GABAergic tone in chronic hepatic encephalopathy.

Hepatic encephalopathy (HE) is a neuropsychiatric complication to liver disease. It is known that ammonia plays a role in the pathogenesis of HE and disturbances in the GABAergic system have been related to HE. Synthesis of GABA occurs by decarboxylation of glutamate formed by deamidation of astrocyte-derived glutamine. It is known that a fraction of glutamate is decarboxylated directly to GABA (referred to as the direct pathway) and that a fraction undergoes transamination with formation of alpha-ketoglutarate. The latter fraction is cycled through the neuronal tricarboxylic acid cycle, an energy-generating pathway, prior to being employed for GABA synthesis (the indirect pathway). We have previously shown that ammonia induces an elevation of the neuronal tricarboxylic acid cycle activity. Thus, the aims of the present study were to determine if increased levels of ammonia increase GABA synthesis via the indirect pathway in a rat model of HE induced by bile-duct ligation and in co-cultures of neurons and astrocytes exposed to ammonia. Employing (13) C-labeled precursors and subsequent analysis by mass spectrometry, we demonstrated that more GABA was synthesized via the indirect pathway in bile duct-ligated rats and in co-cultures subjected to elevated ammonia levels. Since the indirect pathway is associated with synthesis of vesicular GABA, this might explain the increased GABAergic tone in HE.

Inhibition of glutamine synthesis induces glutamate dehydrogenase-dependent ammonia fixation into alanine in co-cultures of astrocytes and neurons.

It has been previously demonstrated that ammonia exposure of neurons and astrocytes in co-culture leads to net synthesis not only of glutamine but also of alanine. The latter process involves the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT). In the present study it was investigated if the glutamine synthetase (GS) inhibitor methionine sulfoximine (MSO) would enhance alanine synthesis by blocking the GS-dependent ammonia scavenging process. Hence, co-cultures of neurons and astrocytes were incubated for 2.5h with [U-(13)C]glucose to monitor de novo synthesis of alanine and glutamine in the absence and presence of 5.0 mM NH(4)Cl and 10 mM MSO. Ammonia exposure led to increased incorporation of label but not to a significant increase in the amount of these amino acids. However, in the presence of MSO, glutamine synthesis was blocked and synthesis of alanine increased leading to an elevated content intra- as well as extracellularly of this amino acid. Treatment with MSO led to a dramatic decrease in glutamine content and increased the intracellular contents of glutamate and aspartate. The large increase in alanine during exposure to MSO underlines the importance of the GDH and ALAT biosynthetic pathway for ammonia fixation, and it points to the use of a GS inhibitor to ameliorate the brain toxicity and edema induced by hyperammonemia, events likely related to glutamine synthesis.

Detoxification of ammonia in mouse cortical GABAergic cell cultures increases neuronal oxidative metabolism and reveals an emerging role for release of glucose-derived alanine.

Cerebral hyperammonemia is believed to play a pivotal role in the development of hepatic encephalopathy (HE), a debilitating condition arising due to acute or chronic liver disease. In the brain, ammonia is thought to be detoxified via the activity of glutamine synthetase, an astrocytic enzyme. Moreover, it has been suggested that cerebral tricarboxylic acid (TCA) cycle metabolism is inhibited and glycolysis enhanced during hyperammonemia. The aim of this study was to characterize the ammonia-detoxifying mechanisms as well as the effects of ammonia on energy-generating metabolic pathways in a mouse neuronal-astrocytic co-culture model of the GABAergic system. We found that 5 mM ammonium chloride affected energy metabolism by increasing the neuronal TCA cycle activity and switching the astrocytic TCA cycle toward synthesis of substrate for glutamine synthesis. Furthermore, ammonia exposure enhanced the synthesis and release of alanine. Collectively, our results demonstrate that (1) formation of glutamine is seminal for detoxification of ammonia; (2) neuronal oxidative metabolism is increased in the presence of ammonia; and (3) synthesis and release of alanine is likely to be important for ammonia detoxification as a supplement to formation of glutamine.

Distinctive effects of unpredictable subchronic stress on memory, serum corticosterone and hippocampal BDNF levels in high and low exploratory mice.

Stress affects learning and memory processes and sensitivity to stress greatly varies between individuals. We studied behavioral and neurobiological effects of unpredictable subchronic stress (USCS) in two behavioral extremes of mice from the same strain (CF1) selected by their exploratory behavior of the central arena of an open field. The top and bottom 25% explorers were classified as low exploratory (LE) and high exploratory (HE) mice, respectively. The open field task, the novel object recognition task (NOR), sucrose intake and tail suspension task were evaluated in LE and HE groups exposed to USCS for two weeks or control conditions. Also serum corticosterone and hippocampal BDNF and S100B levels were analyzed. Both stressed groups exhibited less exploratory activity when submitted to USCS, but their difference in exploratory behavior remained. This short stress protocol did not induce changes in sucrose intake or immobility in the tail suspension task. Also, LE mice exhibited impaired NOR performance after USCS, whereas HE mice changed their pattern of exploration towards less exploration of the familiar object. HE had lower corticosterone levels than LE mice, but corticosterone levels increased after stress only in HE mice. Hippocampal BDNF in LE was lower than in HE but decreased after USCS only in HE mice, whereas S100B levels were not different between groups and did not change with USCS. In conclusion, our results suggest that individual differences in exploratory behavior in rodents from the same strain influence cognitive and biochemical response to stress.

Spinal mechanisms of antinociceptive action caused by guanosine in mice.

It is well known that adenine-based purines exert multiple effects on pain transmission. Recently, we have demonstrated that intracerebroventricular (i.c.v.) administered guanine-based purines are antinociceptive against chemical and thermal pain models in mice. The present study was designed to further investigate the antinociceptive effects of guanosine in mice. Animals received an intrathecal (i.t.) injection of vehicle (0.1 mN NaOH) or guanosine (10 to 400 nmol). Measurements of cerebrospinal fluid (CSF) purine levels and spinal cord glutamate uptake were performed. Guanosine produced dose-dependent antinociceptive effects against tail-flick, hot-plate, intraplantar (i.pl.) capsaicin, and i.pl. glutamate tests. Additionally, i.t. guanosine produced significant inhibition of the biting behavior induced by i.t. injection of glutamate (175 nmol/site), AMPA (135 pmol/site), kainate (110 pmol/site), trans-ACPD (50 nmol/site), and substance P (135 ng/site), with mean ID(50) values of 140 (103-190), 136 (100-185), 162 (133-196), 266 (153-461) and 28 (3-292) nmol, respectively. However, guanosine failed to affect the nociception induced by NMDA (450 pmol/site) and capsaicin (30 ng/site). Intrathecal administration of guanosine (200 nmol) induced an approximately 120-fold increase on CSF guanosine levels. Guanosine prevented the increase on spinal cord glutamate uptake induced by i.pl. capsaicin. This study provides new evidence on the mechanism of action of guanosine presenting antinociceptive effects at spinal sites. This effect seems to be at least partially associated with modulation of glutamatergic pathways by guanosine.

Interleukin-6 serum levels in patients with Parkinson's disease.

Several lines of evidence suggest that neuroimmune mechanisms may be involved in the neurodegenerative process of Parkinson's disease (PD). Interleukin-6 (IL-6) is increased in the nigrostriatal region and in the cerebrospinal fluid of patients with PD. IL-6 serum level was evaluated in PD patients. The effects of levodopa treatment and disease severity on IL-6 were also studied. The IL-6 levels were similar between PD patients (treated and not treated) and controls. However, there was a negative correlation of IL-6 levels and the activities of daily living scale (P < 0.05), indicating that patients with more severe disease have higher levels of this cytokine. No correlation involving levodopa treatment and IL-6 serum level was found. The results suggest that only marginal effects of IL-6 occur on the peripheral immune system, and that the role of IL-6 and others neuroimmune factors needs to be well elucidated on PD.

Antinociceptive effects of intracerebroventricular administration of guanine-based purines in mice: evidences for the mechanism of action.

It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines (GBPs) on pain transmission. The aim of this study was to investigate the effects of intracerebroventricular (i.c.v.) guanosine and GMP on mice pain models. Mice received an i.c.v. injection of vehicle (saline or 10 muM NaOH), guanosine (5 to 400 nmol), or GMP (240 to 960 nmol). Additional groups were also pre-treated with i.c.v. injection of the A(1)/A(2A) antagonist caffeine (15 nmol), the non-selective opioid antagonist naloxone (12.5 nmol), or the 5'-nucleotidase inhibitor AOPCP (1 nmol). Measurements of CSF purine levels and cortical glutamate uptake were performed after treatments. Guanosine and GMP produced dose-dependent antinociceptive effects. Neither caffeine nor naloxone affected guanosine antinociception. Pre-treatment with AOPCP completely prevented GMP antinociception, indicating that conversion of GMP to guanosine is required for its antinociceptive effects. Intracerebroventricular administration of guanosine and GMP induced, respectively, a 180- and 1800-fold increase on CSF guanosine levels. Guanosine was able to prevent the decrease on cortical glutamate uptake induced by intraplantar capsaicin. This study provides new evidence on the mechanism of action of GBPs, with guanosine and GMP presenting antinociceptive effects in mice. This effect seems to be independent of adenosine and opioid receptors; it is, however, at least partially associated with modulation of the glutamatergic system by guanosine.

Demonstration of neuron-glia transfer of precursors for GABA biosynthesis in a co-culture system of dissociated mouse cerebral cortex.

Co-cultures of neurons and astrocytes were prepared from dissociated embryonic mouse cerebral cortex and cultured for 7 days. To investigate if these cultures may serve as a functional model system to study neuron-glia interaction with regard to GABA biosynthesis, the cells were incubated either in media containing [U-(13)C]glutamine (0.1, 0.3 and 0.5 mM) or 1 mM acetate plus 2.5 mM glucose plus 1 mM lactate. In the latter case one of the 3 substrates was uniformly (13)C labeled. Cellular contents and (13)C labeling of glutamate, GABA, aspartate and glutamine were determined in the cells after an incubation period of 2.5 h. The GABA biosynthetic machinery exhibited the expected complexity with regard to metabolic compartmentation and involvement of TCA cycle activity as seen in other culture systems containing GABAergic neurons. Metabolism of acetate clearly demonstrated glial synthesis of glutamine and its transfer to the neuronal compartment. It is concluded that this co-culture system serves as a reliable model in which functional and pharmacological aspects of GABA biosynthesis can be investigated.

Pentylenetetrazol kindling alters adenine and guanine nucleotide catabolism in rat hippocampal slices and cerebrospinal fluid.

Pentylenetetrazol (PTZ) is commonly used as a convulsant drug. The enhanced seizure susceptibility induced by kindling is probably attributable to plastic changes in the synaptic efficacy. Adenosine and guanosine act both as important neuromodulators and neuroprotectors with mostly inhibitory effects on neuronal activity. Adenosine and guanosine can be released per se or generated from released nucleotides (ATP, ADP, AMP, GTP, GDP, and GMP) that are metabolized and rapidly converted to adenosine and guanosine. The aim of this study was to evaluate nucleotide hydrolysis by ecto- and soluble nucleotidases (hippocampal slices and CSF, respectively) after PTZ-kindling (stages 3, 4, or 5 seizures) or saline treatment in rats. Additionally, the levels of purines in rat cerebrospinal fluid (CSF), as well as ecto-NTPDases (1, 2, 3, 5, 6 and 8) and ecto- 5'-nucleotidase expression were determined. Ecto-enzyme assays demonstrated that ATP, AMP, GDP, and GMP hydrolysis enhanced when compared with controls. In addition, there was an increase of ADP, GDP, and GMP hydrolysis by soluble nucleotidases in PTZ-kindling rats compared to control group. The HPLC analysis showed a marked increase in PTZ-kindled CSF concentrations of GTP, ADP, and uric acid, but GDP, AMP, and hypoxanthine concentrations were decreased. Such alterations indicate that the modulatory role of purines in CNS could be affected by PTZ-kindling. However, the physiological significance of these findings remains to be elucidated.

Reduced serum BDNF levels in schizophrenic patients on clozapine or typical antipsychotics.

Neurotrophic factors regulate neuronal development and synaptic plasticity, possibly playing a role in the pathophysiology of schizophrenia and other psychiatric disorders. Decreased brain-derived neurotrophic factor (BDNF) levels have been found in brains and in the serum of schizophrenic patients, but results are inconsistent. Also, clozapine may upregulate brain BDNF expression. In the present study, we assessed serum BDNF immunoreactivity in 44 schizophrenic patients (20 on clozapine and 24 on typical antipsychotics) and in 25 healthy volunteers. Serum BDNF levels were measured using an enzyme immunoassay. Healthy controls showed significantly higher levels of BDNF compared to the whole group of schizophrenic patients (p<0.001) as well as to the subgroups on typical antipsychotics and clozapine (p<0.001). Serum BDNF values for controls were 168.8+/-26.3pg/ml, for the clozapine group were 125.4+/-44.5pg/ml and for the group on typicals were 101.3+/-51.6pg/ml. BDNF values from patients on clozapine were non-significantly higher than values from patients on typical antipsychotics (p=0.09). Serum BDNF was strongly and positively correlated with clozapine dose (r=0.643; p=0.002) but not with other demographic characteristics. These results reinforce previous findings of reduced serum BDNF levels in schizophrenic patients and suggest a differential effect of clozapine compared to typical antipsychotics on such levels.