Jordi Boix

Repeated alcohol administration during adolescence causes changes in the mesolimbic dopaminergic and glutamatergic systems and promotes alcohol intake in the adult rat.

Adolescence is a developmental period which the risk of drug and alcohol abuse increases. Since mesolimbic dopaminergic system undergoes developmental changes during adolescence, and this system is involved in rewarding effects of drugs of abuse, we addressed the hypothesis that ethanol exposure during juvenile/adolescent period over‐activates mesolimbic dopaminergic system inducing adaptations which can trigger long‐term enduring behavioural effects of alcohol abuse. We treated juvenile/adolescent or adult rats with ethanol (3 g/kg) for two‐consecutive days at 48‐h intervals over 14‐day period. Here we show that intermittent ethanol treatment during the juvenile/adolescence period alters subsequent ethanol intake. In vivo microdialysis demonstrates that ethanol elicits a similar prolonged dopamine response in the nucleus accumbens of both adolescent and adult animals pre‐treated with multiple doses of ethanol, although the basal dopamine levels were higher in ethanol‐treated adolescents than in adult‐treated animals. Repeated ethanol administration also down‐regulates the expression of DRD2 and NMDAR2B phosphorylation in prefrontal cortex of adolescent animals, but not of adult rats. Finally, ethanol treatment during adolescence changes the acetylation of histones H3 and H4 in frontal cortex, nucleus accumbens and striatum, suggesting chromatin remodelling changes. In summary, our findings demonstrate the sensitivity of adolescent brain to ethanol effects on dopaminergic and glutamatergic neurotransmission, and suggest that abnormal plasticity in reward‐related processes and epigenetic mechanisms could contribute to the vulnerability of adolescents to alcohol addiction.

Inflammation and hepatic encephalopathy: ibuprofen restores learning ability in rats with portacaval shunts.

One of the neurological alterations in patients with minimal or overt hepatic encephalopathy is cognitive impairment. This impairment is reproduced in rats with chronic liver failure due to portacaval shunt (PCS). These rats show decreased ability to learn a conditional discrimination task in a Y‐maze, likely due to reduced function of the glutamate–nitric oxide (NO)–cyclic guanosine monophosphate (cGMP) pathway in brain. It has been proposed that inflammation exacerbates the neuropsychological alterations induced by hyperammonemia, suggesting that inflammation‐associated alterations may contribute to cognitive impairment in hepatic encephalopathy. This study assessed whether treatment with an anti‐inflammatory drug, ibuprofen, is able to restore the function of the glutamate‐NO‐cGMP pathway in cerebral cortex in brain in vivo and/or learning ability in PCS rats. We show that PCS rats have increased levels of interleukin‐6 and increased activities of cyclooxygenase and of inducible NO synthase in cerebral cortex, indicating the presence of inflammation. Chronic treatment with ibuprofen normalizes cyclooxygenase and inducible NO synthase activities but not interleukin‐6 levels. Moreover, ibuprofen normalizes the function of the glutamate‐NO‐cGMP pathway in cerebral cortex in vivo and completely restores the ability of rats with chronic liver failure to learn the Y‐maze task. This supports that inflammation contributes to the cognitive impairment in hepatic encephalopathy. Conclusion: the results reported point to the possible therapeutic utility of decreasing inflammation in the treatment of the cognitive deficits in patients with minimal or overt hepatic encephalopathy. (HEPATOLOGY 2007.)

Glutamatergic and gabaergic neurotransmission and neuronal circuits in hepatic encephalopathy

Patients with hepatic encephalopathy (HE) may present different neurological alterations including impaired cognitive function and altered motor activity and coordination. HE may lead to coma and death. Many of these neurological alterations are the consequence of altered neurotransmission. Hyperammonemia is a main contributor to the alterations in neurotransmission and in neurological functions in HE. Both glutamatergic and GABAergic neurotransmission are altered in animal models of HE. We review some of these alterations, especially those alterations in glutamatergic neurotransmission responsible for some specific neurological alterations in hyperammonemia and HE: the role 1) of excessive NMDA receptors activation in death induced by acute hyperammonemia; 2) of impaired function of the glutamate-nitric oxide-cGMP pathway, associated to NMDA receptors, in cognitive impairment in chronic HE; 3) of increased extracellular glutamate and activation of metabotropic glutamate receptors in substantia nigra in hypokinesia in chronic HE. The therapeutic implications are discussed. We also review the alterations in the function of the neuronal circuits between basal ganglia-thalamus-cortex modulating motor activity and the role of sequential alterations in glutamatergic and GABAergic neurotransmission in these alterations. HE would be a consequence of altered neuronal communication due to alterations in general neurotransmission involving different neurotransmitter systems in different neurons.

Developmental exposure to polychlorinated biphenyls 52, 138 or 180 affects differentially learning or motor coordination in adult rats. Mechanisms involved.

Exposure to polychlorinated biphenyls (PCBs) during pregnancy and lactation leads to cognitive impairment and motor disorders in children by mechanisms which remain unknown. It also remains unclear whether different non-dioxin-like PCBs have similar or different mechanisms of neurotoxicity. The main aims of this work were: (1) to assess whether developmental exposure to non-dioxin-like-PCBs 52, 138 or 180 affect cognitive function or motor coordination in 3-4 months-old rats; (2) to shed light on the underlying mechanisms. Female rats were treated with PCBs (1 mg/kg day) in food from gestational-day 7 to postnatal-day 21. The ability to learn a Y maze conditional discrimination task was reduced in rats exposed to PCBs 138 or 180, but not in rats exposed to PCB52. The function of the glutamate-nitric oxide-cGMP pathway (NMDA-induced increase in extracellular cGMP) in cerebellum in vivo was reduced by 33-59% in rats exposed to PCBs 138 or 180, but not by PCB52. The amount of NR1 subunit of NMDA receptors was reduced by 41-49% in rats exposed to PCBs 138 or 180, but not by PCB 52. PCB52 but not 138 or 180 increases extracellular GABA in cerebellum and impairs motor coordination. The effects were similar in males and females. Developmental exposure to different non-dioxin-like PCBs induces different behavioural alterations by different mechanisms. PCB52 impairs motor coordination but not learning while PCB138 or 180 impair learning but not motor coordination. These data are consistent with the following possible mechanisms: (1) developmental exposure to PCBs 138 or 180 reduces the amount of NMDA receptors in cerebellum, which would contribute to reduced function of the glutamate-NO-cGMP pathway, which, in turn, would be a main contributor to the impairment of the ability to learn the Y maze task. (2) Developmental exposure to PCB52 increases extracellular GABA in cerebellum, which would contribute to motor coordination impairment.

Brain Region-Selective Mechanisms Contribute to the Progression of Cerebral Alterations in Acute Liver Failure in Rats

BACKGROUND & AIMS Patients with acute liver failure (ALF) often die of intracranial pressure (IP) and cerebral herniation. Main contributors to increased IP are ammonia, glutamine, edema, and blood flow. The sequence of events and underlying mechanisms, as well as the temporal pattern, regional distribution, and contribution of each parameter to the progression of neurologic deterioration and IP, are unclear. We studied rats with ALF to follow the progression of changes in ammonia, glutamine, grade and type (vasogenic or cytotoxic) of edema, blood-brain barrier permeability, cerebral blood flow, and IP. We assessed whether the changes in these parameters were similar between frontal cortex and cerebellum and evaluated the presence, type, and progression of edema in 12 brain areas. METHODS ALF was induced by injection of galactosamine. The grade and type of edema was assessed by measuring the apparent diffusion coefficient by magnetic resonance imaging. Cerebral blood flow was measured by magnetic resonance and blood-brain barrier permeability by Evans blue-albumin extravasation. RESULTS Increased IP arises from an early increase of blood-brain barrier permeability in certain areas (including cerebellum but not frontal cortex) followed by vasogenic edema. Ammonia and glutamine then increase progressively, leading to cytotoxic edema in many areas. Alterations in lactate and cerebral blood flow are later events that further increase IP. CONCLUSIONS Different mechanisms in specific regions of the brain contribute, with different temporal patterns, to the progression of cerebral alterations and IP in ALF.

Differential long-term effects of developmental exposure to polychlorinated biphenyls 52, 138 or 180 on motor activity and neurotransmission. Gender dependence and mechanisms involved

Developmental exposure to polychlorinated biphenyls (PCBs) induces motor alterations in humans by unknown mechanisms. It remains unclear whether: (a) all non-dioxin-like (NDL) PCBs are neurotoxic or it depends on the grade of chlorination; (b) they have different neurotoxicity mechanisms; (c) they affect differently males and females. The aims of this work were to assess: (1) whether perinatal exposure to 3 NDL-PCBs with different grades of chlorination, (PCBs 52, 138 or 180) affects differentially motor activity in adult rats; (2) whether the effects are different in males or females and (3) the mechanisms involved in impaired motor activity. Rats were exposed to PCBs from gestational day 7 to post-natal day 21. Experiments were performed when the rats were 4 months-old. PCB52 did not affect motor activity, PCB180 reduced it in males but not in females and PCB138 reduced activity both in males and females. PCB52 or 138 did not affect extracellular dopamine in nucleus accumbens (NAcc). PCB180 increased it both in males and females. Extracellular glutamate in NAcc was reduced by the three PCBs. Activation of metabotropic glutamate receptors (mGluRs) in NAcc increased extracellular dopamine in control rats and in those exposed to PCB52 and reduced dopamine in rats exposed to PCB180. In rats exposed to PCB138 activation of mGluRs increases dopamine in females and reduces it in males. The opposite changes were observed for glutamate. mGluRs activation reduced extracellular glutamate in control rats and in those exposed to PCB52 and increased glutamate in rats exposed to PCB180. In rats exposed to PCB138 activation of mGluRs reduces glutamate in females and increases it in males. The data support that different NDL-PCBs affect differently motor activity. Increased glutamate release in NAcc following activation of mGluRs would be involved in reduced dopamine release and reduced motor activity in rats exposed to PCB138 or 180.

Role of NMDA receptors in acute liver failure and ammonia toxicity: Therapeutical implications

Acute liver failure (ALF) may lead to rapid death unless the patients receive a liver for transplantation. However, the number of livers available is not enough and a number of patients die before a suitable liver is available for transplantation. The liver has a high capacity for regeneration which may allow complete recovery even in patients with severe liver failure. It would be therefore very useful to have procedures to prevent or delay the mechanisms by which ALF leads to death. These mechanisms are no well understood. Progression of ALF leads to multi-organ failure, systemic inflammatory response, hepatic encephalopathy, cerebral oedema and increased intracranial pressure, which seem the most important immediate causes of mortality in patients with ALF. A main contributor to these events is hyperammonemia, due to impaired ammonia detoxification in the liver. Acute hyperammonemia per se leads to death, which is mediated by activation of the NMDA type of glutamate receptors in brain and may be prevented by antagonists blocking these receptors. Acute liver failure also leads to hyperammonemia and excessive activation of NMDA receptors in brain which contributes to ALF-induced death. Sustained blocking of NMDA receptors by continuous administration of the antagonists MK-801 or memantine increases about twice the survival time of rats with severe ALF due to injection of 2.5g/kg of galactosamine. In rats with milder ALF due to injection of 1.5g/kg of galactosamine, blocking NMDA receptors increases the percentage of surviving rats from 23% to 62% and increases about twice the survival time of the rats which die. These data strongly support that blocking NMDA receptors would improve survival of patients with ALF, either by allowing more time for liver regeneration or to get a liver suitable for transplantation.

Cyclic GMP pathways in hepatic encephalopathy. Neurological and therapeutic implications

Cyclic GMP (cGMP) modulates important cerebral processes including some forms of learning and memory. cGMP pathways are strongly altered in hyperammonemia and hepatic encephalopathy (HE). Patients with liver cirrhosis show reduced intracellular cGMP in lymphocytes, increased cGMP in plasma and increased activation of soluble guanylate cyclase by nitric oxide (NO) in lymphocytes, which correlates with minimal HE assessed by psychometric tests. Activation of soluble guanylate cyclase by NO is also increased in cerebral cortex, but reduced in cerebellum, from patients who died with HE. This opposite alteration is reproduced in vivo in rats with chronic hyperammonemia or HE. A main pathway modulating cGMP levels in brain is the glutamate-NO-cGMP pathway. The function of this pathway is impaired both in cerebellum and cortex of rats with hyperammonemia or HE. Impairment of this pathway is responsible for reduced ability to learn some types of tasks. Restoring the pathway and cGMP levels in brain restores learning ability. This may be achieved by administering phosphodiesterase inhibitors (zaprinast, sildenafil), cGMP, anti-inflammatories (ibuprofen) or antagonists of GABAA receptors (bicuculline). These data support that increasing cGMP by safe pharmacological means may be a new therapeutic approach to improve cognitive function in patients with minimal or clinical HE.

Chronic hyperammonemia induces tonic activation of NMDA receptors in cerebellum

J. Neurochem. (2009) 112, 1005–1014.

Polychlorinated biphenyls PCB 52, PCB 180, and PCB 138 impair the glutamate-nitric oxide-cGMP pathway in cerebellar neurons in culture by different mechanisms.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that accumulate in the food chain and are present in human blood and milk. Children born to mothers exposed to PCBs show cognitive deficits, which are reproduced in rats perinatally exposed to PCBs. It has been proposed that PCB-induced cognitive impairment is due to impairment of the glutamate-nitric oxide (NO)-cGMP pathway. The aim of the present work was to assess whether chronic exposure to the nondioxin-like PCB52, PCB138, or PCB180 alters the function of this pathway in primary cultures of rat cerebellar neurons and to assess whether different PCBs have similar or different mechanisms of action. PCB180 and PCB138 impair the function of the glutamate-NO-cGMP pathway at nanomolar concentrations, and PCB52 impairs the function of the glutamate-NO-cGMP pathway at micromolar concentrations. The mechanisms by which different PCBs impair the function of the glutamate-NO-cGMP pathway are different. Each PCB affects the pathway at more than one step but with different potency and, for some steps, in opposite ways. Exposure to the PCBs alters the basal concentrations of intracellular calcium, NO, and cGMP. The three PCBs increase NO; however, PCB52 and PCB138 increase basal cGMP, while PCB180 decreases it. PCB52 and PCB138 decrease the activation of soluble guanylate cyclase by NO, and PCB180 increases it. Long-term exposure to PCB52, PCB180, or PCB138 reduces the activation of NO synthase and the whole glutamate-NO-cGMP pathway in response to activation of N-methyl-d-aspartate receptors. The EC(50) was 300 nM for PCB52 and 2 nM for PCB138 or PCB180. These results show that chronic exposure to nondioxin like PCBs impairs the function of the glutamate-NO-cGMP pathway in cerebellar neurons by different mechanisms and with different potencies. Impaired function of this pathway would contribute to the cognitive alterations induced by perinatal exposure to PCBs in humans.