The basal ganglia and portal-systemic encephalopathy

Reduced TH expression and α-synuclein accumulation contribute towards nigrostriatal dysfunction in experimental hepatic encephalopathy

PURPOSE

The present work examines α-synuclein expression in the nigrostriatal system of a rat chronic hepatic encephalopathy model induced by portacaval anastomosis (PCA). There is evidence that dopaminergic dysfunction in disease conditions is strongly associated with such expression. Possible relationships among dopaminergic neurons, astroglial cells and α-synuclein expression were sought.

METHODS

Brain tissue samples from rats at 1 and 6 months post-PCA, and controls, were analysed immunohistochemically using antibodies against tyrosine hydroxylase (TH), α-synuclein, glial fibrillary acidic protein (GFAP) and ubiquitin (Ub).

RESULTS

In the control rats, TH immunoreactivity was detected in the neuronal cell bodies and processes in the substantia nigra pars compacta (SNc). A dense TH-positive network of neurons was also seen in the striatum. In the PCA-exposed rats, however, a reduction in TH-positive neurons was seen at both 1 and 6 months in the SNc, as well as a reduction in TH-positive fibres in the striatum. This was coincident with the appearance of α-synuclein-immunoreactive neurons in the SNc; some of the TH-positive neurons also showed α-synuclein immunoreactivity. In addition, α-synuclein accumulation was seen in the SNc and striatum at both 1 and 6 months post-PCA, whereas α-synuclein was only mildly expressed in the nigrostriatal pathway of the controls. Astrogliosis was also seen following PCA, as revealed by increased GFAP expression from 1 month to 6 months post-PCA in both the SN and striatum. The astroglial activation level in the SN paralleled the reduced neuronal expression of TH throughout PCA exposure.

CONCLUSION

α-synuclein accumulation following PCA may induce dopaminergic dysfunction via the downregulation of TH, as well as astroglial activation.

Magnetic resonance imaging of the lentiform nuclei in dogs with portosystemic shunts

OBJECTIVES

To develop and evaluate a method to quantify the T1-weighted magnetic resonance imaging signal intensity of the lentiform nuclei in dogs, and to determine if there is any significant difference in this signal intensity between dogs with portosystemic shunts and a control group.

MATERIALS AND METHODS

A retrospective blinded study was performed to investigate the reliability and use of a quantitative method for assessing the T1-weighted magnetic resonance imaging signal intensity of the lentiform nuclei in dogs with and without portosystemic shunts. The lentiform nuclei index (mean lentiform nucleus signal intensity/mean white matter signal intensity) was calculated for nine dogs with portosystemic shunts and a control group of 14 dogs.

RESULTS

The intra- and inter-observer intraclass correlation coefficients were considered excellent (>0 · 75), suggesting that the lentiform nuclei index is a reliable method. The dogs with portosystemic shunts had a higher lentiform nuclei index than the control group (P = 0 · 0127).

CLINICAL SIGNIFICANCE

This method of quantifying the T1-weighted magnetic resonance imaging signal intensity of the lentiform nuclei was reliable and showed that dogs with portosystemic shunts tend to have increased signal intensity. Further prospective studies are necessary to investigate the clinical significance and applications of these findings.

Disrupted small world networks in patients without overt hepatic encephalopathy: a resting state fMRI study

PURPOSE

To explore changes in functional connectivity and topological organization of brain functional networks in cirrhotic patients with minimal hepatic encephalopathy (MHE) and non hepatic encephalopathy (nonHE) and their relationship with clinical markers.

MATERIALS AND METHODS

Resting-state functional MR imaging was acquired in 22 MHE, 29 nonHE patients and 33 healthy controls. Functional connectivity networks were obtained by computing temporal correlations between any pairs of 90 cortical and subcortical regions. Graph analysis measures were quantitatively assessed for each subject. One-way analysis of covariance was applied to identify statistical differences of functional connectivity and network parameters among three groups. Correlations between clinical markers, such as Child-Pugh scores, venous blood ammonia level, and number connection test type A (NCT-A)/digit symbol test (DST) scores, and connectivity/graph metrics were calculated.

RESULTS

Thirty functional connectivities represented by edges were found to be abnormal (P<0.05, FDR corrected) in cirrhotic patients, in which 16 edges (53.3%) were related with sub-cortical regions. MHE patients showed abnormal small-world attributes in the functional connectivity networks. Cirrhotic patients had significantly reduced nodal degree in 8 cortical regions and increased nodal centrality in 3 cortical regions. Twenty edges were correlated with either NCT-A or DST scores, in which 13 edges were related with sub-cortical regions. No correlation was found between Child-Pugh scores and graph theoretical measures in cirrhotic patients.

CONCLUSION

Disturbances of brain functional connectivity and small world property loss are associated with neurocognitive impairment of cirrhotic patients. Reorganization of brain network occurred during disease progression from nonHE to MHE.

The thalamus in cirrhotic patients with and without hepatic encephalopathy: a volumetric MRI study

BACKGROUND & AIMS

The thalamus is a major relay and filter station in the central neural system. Some previous studies have suggested that the thalamus maybe implicated in the pathogenesis of hepatic encephalopathy. The aim of our study was to investigate changing thalamic volumes in cirrhotic patients with and without hepatic encephalopathy.

METHODS

Neuropsychological tests and structural MR scanning were performed on 24 cirrhotic patients, 23 cirrhotic patients with minimal hepatic encephalopathy, 24 cirrhotic patients during their first episode of overt hepatic encephalopathy, and 33 healthy controls. Voxel-based morphometry analysis was performed to detect gray matter morphological changes. The thalamus and whole brain volume were extrapolated. A receiver operating characteristic curve analysis of thalamic volumes was used to discriminate patients with minimal hepatic encephalopathy from those with hepatic cirrhosis.

RESULTS

Thalamic volume increased in a stepwise manner in patients with progressively worse stages of hepatic encephalopathy compared to healthy subjects. Additionally, a comparison of gray matter morphometry between patients with Child-Pugh grades A, B, or C and controls revealed a progression in thalamic volumes in parallel with the degree of liver failure. Moreover, thalamic volume was significantly correlated with the number connection test A time and digit-symbol test score in cirrhotic patients with minimal hepatic encephalopathy (r=0.659, P=0.001; r=-0.577, P=0.004; respectively). The area under the receiver operating characteristic curve was 0.827 (P=0.001).

CONCLUSIONS

A significantly increased thalamic volume may be provide an objective imaging measure for predicting seizures due to minimal hepatic encephalopathy in cirrhotic patients.

Abnormal chloride homeostasis in the substancia nigra pars reticulata contributes to locomotor deficiency in a model of acute liver injury

BACKGROUND

Altered chloride homeostasis has been thought to be a risk factor for several brain disorders, while less attention has been paid to its role in liver disease. We aimed to analyze the involvement and possible mechanisms of altered chloride homeostasis of GABAergic neurons within the substantia nigra pars reticulata (SNr) in the motor deficit observed in a model of encephalopathy caused by acute liver failure, by using glutamic acid decarboxylase 67 - green fluorescent protein knock-in transgenic mice.

METHODS

Alterations in intracellular chloride concentration in GABAergic neurons within the SNr and changes in the expression of two dominant chloride homeostasis-regulating genes, KCC2 and NKCC1, were evaluated in mice with hypolocomotion due to hepatic encephalopathy (HE). The effects of pharmacological blockade and/or activation of KCC2 and NKCC1 functions with their specific inhibitors and/or activators on the motor activity were assessed.

RESULTS

In our mouse model of acute liver injury, chloride imaging indicated an increase in local intracellular chloride concentration in SNr GABAergic neurons. In addition, the mRNA and protein levels of KCC2 were reduced, particularly on neuronal cell membranes; in contrast, NKCC1 expression remained unaffected. Furthermore, blockage of KCC2 reduced motor activity in the normal mice and led to a further deteriorated hypolocomotion in HE mice. Blockade of NKCC1 was not able to normalize motor activity in mice with liver failure.

CONCLUSION

Our data suggest that altered chloride homeostasis is likely involved in the pathophysiology of hypolocomotion following HE. Drugs aimed at restoring normal chloride homeostasis would be a potential treatment for hepatic failure.

Aberrant resting-state corticostriatal functional connectivity in cirrhotic patients with hyperintense globus pallidus on T1-weighted MR imaging

Neurobiological and neuroimaging studies have emphasized the structural and functional alterations in the striatum of cirrhotic patients, but alterations in the functional connections between the striatum and other brain regions have not yet been explored. Of note, manganese accumulation in the nervous system, frequently reflected by hyperintensity at the bilateral globus pallidus (GP) on T1-weighted imaging, has been considered a factor affecting the striatal and cortical functions in hepatic decompensation. We employed resting-state functional magnetic resonance imaging to analyze the temporal correlation between the striatum and the remaining brain regions using seed-based correlation analyses. The two-sample t-test was conducted to detect the differences in corticostriatal connectivity between 44 cirrhotic patients with hyperintensity at the bilateral GP and 20 healthy controls. Decreased connectivity of the caudate was detected in the anterior/middle cingulate gyrus, and increased connectivity of the caudate was found in the left motor cortex. A reduction in functional connectivity was found between the putamen and several regions, including the anterior cingulate gyrus, right insular lobe, inferior frontal gyrus, left parahippocampal gyrus, and anterior lobe of the right cerebellum; increased connectivity was detected between the putamen and right middle temporal gyrus. There were significant correlations between the corticostriatal connectivity and neuropsychological performances in the patient group, but not between the striatal connectivity and GP signal intensity. These alterations in the corticostriatal functional connectivity suggested the abnormalities in the intrinsic brain functional organiztion among the cirrhotic patients with manganese deposition, and may be associated with development of metabolic encephalopathy. The manganese deposition in nervous system, however, can not be an independent factor predicting the resting-state brain dysfunction in real time.

Altered brain functional connectivity in patients with cirrhosis and minimal hepatic encephalopathy: a functional MR imaging study

PURPOSE

To investigate patterns of whole-brain functional connectivity in patients with minimal hepatic encephalopathy (HE) by using functional magnetic resonance (MR) imaging.

MATERIALS AND METHODS

This study was approved by the local institutional review board and was HIPAA compliant. All participants provided written informed consent. Neuropsychiatric tests including number connection test type A and digit symbol test were used to define minimal HE. Twenty-three patients with minimal HE and 25 age- and sex-matched healthy volunteers were included in this study. Resting-state functional MR imaging was performed by using a 3-T MR imaging unit. Functional connectivities between 90 pairs of cortical and subcortical regions in patients with minimal HE were compared with those in control participants, and significantly different connectivities were chosen as connectivities of interest (COIs). Correlations between neuropsychiatric tests and correlation coefficients of COIs were calculated.

RESULTS

Among the 51 COIs that were significantly different in patients with minimal HE from those in control participants, 44 connectivities were weaker in patients with minimal HE. All 22 COIs related to subcortical regions of interest (bilateral putamen, pallidum, and thalamus) were weaker in patients with minimal HE. Of 29 cortical COIs, 22 connectivities were weaker and seven were stronger in patients with minimal HE. Nearly all COIs with significant differences correlated with digital symbol test scores (P<.05, false discovery rate corrected). No correlation was found among blood ammonia level, Child-Pugh scores, or any COIs in patients with minimal HE (P>.05, false discovery rate corrected).

CONCLUSION

Widespread cortical and subcortical network connectivity changes that correlated with neuropsychologic impairment were found in patients with minimal HE. In particular, impairment in the basal ganglia-thalamocortical circuit could play an important role in mediating neurocognitive dysfunction, especially for psychomotor speed and attention deficits in patients with minimal HE.

Induction of NOS and nitrotyrosine expression in the rat striatum following experimental hepatic encephalopathy

Hepatic encephalopathy (HE) is a neurologic disease associated with hepatic dysfunction. Astroglial and neuronal alterations have been described in the basal ganglia in HE. Our study was performed to determine whether such alterations are mediated by nitric oxide (NO), by using an experimental model of HE (portacaval anastomosis [PCA]). The expression of the NO synthases (nNOS and iNOS) and the production of nitrotyrosine (NT) were evaluated in the striatum of rats exposed to PCA for 1 and 6 months. The expression of nNOS in the striatal neurons of PCA rats was increased compared to controls. nNOS expression was also detectable in astrocytes after 6 months of exposure to PCA. Whereas astroglial cells in the normal striatum showed no iNOS expression, iNOS was expressed in the astrocytes of PCA brains, mainly in perivascular processes at 6 months PCA exposure (demonstrated by colocalization with GFAP). The increased expression of both the nNOS and iNOS isoforms in PCA rats might indicate a critical role for NO in the pathomechanism of HE. To study the potential cell damage caused by NO, the deposition of NT in PCA-rats was analysed. Nitrotyrosine was detected in neurons although it was mainly seen in the astrocytes of PCA brains, in which double immunolabelling showed NT to be colocalized with GFAP. Thus, the present study shows the induction of iNOS and NT in astrocytes, which increases with the duration of PCA exposure. This suggests that the induced astroglial production of NO during PCA might be one of the main factors contributing to HE.

Neurochemical changes in welders revealed by proton magnetic resonance spectroscopy

BACKGROUND

Occupational and environmental exposure to manganese (Mn) is associated with various neurobehavioral and movement dysfunctions. However, few studies have systemically examined the neurochemical effects of Mn exposure.

OBJECTIVES

We examined typical changes in cerebral metabolite ratios in welders chronically exposed to Mn, compared with control individuals, using proton magnetic resonance spectroscopy (MRS), investigated whether an abnormality in brain metabolism is associated with neurobehavioral changes, and assessed possible implications of chronic Mn exposure.

METHODS

Thirty-five welders chronically exposed to Mn and 20 age-matched healthy subjects underwent single-voxel MRS at short echo time to assess the N-acetylaspartate (NAA), myoinositol (mI), total choline (tCho), and glutamine plus glutamate (Glx) levels, each of which was expressed as a ratio to total creatine (tCr). Neurobehavioral tests were also performed to define cognitive status.

RESULTS

NAA/tCr, Glx/tCr, and tCho/tCr ratios in the frontal gray matter (anterior cingulate cortex; ACC) and parietal white matter did not differ significantly between welders and control subjects. These metabolite ratios did not correlate significantly with blood Mn concentration or neurobehavioral parameters. However, mI levels in the ACC, but not in the parietal white matter, were significantly reduced in welders compared with control individuals (P<0.01). Furthermore, in the frontal lobe of the brain, the mI/tCr ratio was significantly correlated with verbal memory scores as well as blood Mn concentration (P<0.05).

CONCLUSIONS

The cognitive decline observed in welders exposed to Mn was associated with a decreased mI/tCr ratio in the ACC. The depletion of mI in welders may reflect possible glial cell swelling and/or detoxification processes associated with long-term exposure to Mn.

Neuroinflammation contributes to hypokinesia in rats with hepatic encephalopathy: ibuprofen restores its motor activity

Patients with hepatic encephalopathy show altered motor function, psychomotor slowing, and hypokinesia, which are reproduced in rats with portacaval shunts (PCS). Increased extracellular glutamate in substantia nigra pars reticulata (SNr) is responsible for hypokinesia in PCS rats. The mechanisms by which liver failure leads to increased extracellular glutamate in SNr remain unclear. Inflammation seems to act synergistically with hyperammonemia to induce neurological alterations in hepatic encephalopathy. It is therefore possible that inflammation-associated alterations may contribute to motor alterations in hepatic encephalopathy. The aim of this work was to assess whether treatment with an antiinflammatory, ibuprofen, is able to normalize extracellular glutamate in SNr and/or to improve hypokinesia in PCS rats. The amounts of the glutamate transporters GLT-1 and EAAC-1 are reduced by 26% and 32%, respectively, in SNr of PCS rats. This reduction is associated with a tenfold increase in extracellular glutamate in SNr and a reduction in motor activity. Chronic treatment with 30 mg/kg ibuprofen completely normalizes the amount of GLT-1 and EAAC-1 and significantly reduces (by 53%) extracellular glutamate in SNr of PCS rats. Moreover, ibuprofen, at 15 or 30 (but not at 5) mg/kg/day, completely eliminates hypokinesia, restoring normal motor activity. This supports the idea that inflammation is a main contributor to the induction of hypokinesia in hepatic encephalopathy. Moreover, these data point to the possible therapeutic utility of decreasing inflammation, by safe procedures, in the treatment of the motor deficits in patients with hepatic encephalopathy.

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.

Selective alterations of brain dopamine D(2) receptor binding in cirrhotic patients: results of a (11)C-N-methylspiperone PET study

Alterations of the brain dopamine system have been implicated in the neurological complications of chronic liver failure. The present study was aimed at the measurement of dopamine D(2) binding sites in cirrhotic patients by positron emission tomography (PET) using (11)C-N-methylspiperone as ligand. The regions of interest (ROI) were designated on a three-dimensional stereotaxic ROI template (3DSRT). The pixel values of twelve ROIs corrected by the pixel value of the cerebellum after 80 min static scanning were used to quantitate changes in binding. D(2) binding sites were significantly decreased in the hippocampus and thalamus of cirrhotic patients and were positively correlated with serum bilirubin levels and Child-Pugh scores and were negatively correlated with prothrombin times (thalamus). Loss of D(2) sites was greater in thalamus and hippocampus of alcoholic cirrhotics compared to non-alcoholics. Statistically significant correlations were also observed between D(2) binding sites in hippocampus, thalamus and lenticular nuclei and history of overt encephalopathy. These findings suggest that D(2) receptor binding in some regions of brain in cirrhotic patients is influenced by factors such as the severity of liver damage and history of alcohol dependency or overt encephalopathy. Alterations of D(2) receptor sites indicative of dopaminergic synaptic dysfunction could play an important role in the pathogenesis of the cognitive and motor disturbances associated with chronic liver failure.

Spatial memory alterations in three models of hepatic encephalopathy

A behavioural evaluation was carried out on three chronic models of hepatic encephalopathy: two models of type B HE, portacaval shunt (PCS) and portal hypertension (PH) and one of type C HE with cirrhosis and portal hypertension from thioacetamide intoxication (TAA). The tasks selected cover a wide range of behaviours related to: locomotion (rotarod-accelerod test), anxiety (open field and elevated plus maze) and memory (Morris water maze). The results indicate that neither locomotor activity nor anxiety was affected in our models, in comparison with their respective controls. However, this is not the case for the mnesic tasks. Hence, the PCS and TAA groups displayed a severe alteration in spatial reference memory and cannot correctly perform the Morris maze task, while this alteration is less severe in the PH group. On the contrary, the PH group revealed a deficit in spatial working memory, like the TAA group, but this does not occur in subjects with PCS. These results reveal a double dissociation in spatial reference memory and spatial working memory between the PCS and PH groups, which would be of great interest to study about cerebral causes and substrates of the alterations accompanying HE.

GABAA-receptor modification in taurine transporter knockout mice causes striatal disinhibition

The Striatum is involved in the regulation of movements and motor skills. We have shown previously, that the osmolyte and neuromodulator taurine plays a role in striatal plasticity. We demonstrate now that hereditary taurine deficiency in taurine-transporter knock-out (TAUT KO) mice results in disinhibition of striatal network activity, which can be corrected by taurine supplementation. Modification of GABAA but not glycine receptors (taurine is a ligand for both receptor types) underlies this disinhibition. Whole-cell recordings from acutely isolated as well as cultured striatal neurons revealed a decreased agonist sensitivity of the GABAA receptor in TAUT KO neurons in the absence of changes in the maximal GABA-evoked current amplitude. The striatal GABA level in TAUT KO mice was unchanged. The amplitude enhancement of spontaneous IPSCs by zolpidem was stronger in TAUT KO than in wild-type (WT) animals. Tonic inhibition was absent in striatal neurons under control conditions but was detected after incubation with the GABA-transaminase inhibitor vigabatrin: bicuculline induced a larger shift of baseline current in WT as compared to TAUT KO neurons. Lack of taurine leads to reduced sensitivity of synaptic and extrasynaptic GABAA receptors and consequently to disinhibition. These findings help in understanding neuropathologies accompanied by the loss of endogenous taurine, for instance in hepatic encephalopathy.

Hyperammonaemia alters the mechanisms by which metabotropic glutamate receptors in nucleus accumbens modulate motor function

Activation of metabotropic glutamate receptors by injecting (S)3,5-dihydroxyphenylglycine (DHPG) in nucleus accumbens (NAcc) increases motor activity by different mechanisms in control rats and in rats with chronic liver failure due to portacaval shunt. In control rats DHPG increases extracellular dopamine in NAcc and induces locomotion by activating the 'normal' circuit: NAcc-->ventral pallidum-->medial-dorsal thalamus-->prefrontal cortex, which is not activated in portacaval shunt rats. In these rats, DHPG activates an 'alternative' circuit: NAcc-->substantia nigra pars reticulata-->ventro-medial thalamus-->prefrontal cortex, which is not activated in control rats. The reasons by which liver failure leads to activation of this 'alternative' circuit remain unclear. The aim of this work was to assess whether hyperammonaemia could be responsible for the alterations found in chronic liver failure. We injected DHPG in NAcc of control or hyperammonaemic rats and analysed, by in vivo brain microdialysis, the neurochemical responses of the 'normal' and 'alternative' circuits. In hyperammonaemic rats DHPG injection in NAcc activates both the 'normal' and 'alternative' circuits. In hyperammonaemia, activation of the 'alternative' circuit and increased motor response following metabotropic glutamate receptors activation in NAcc seem due to an increase in extracellular glutamate which activates AMPA receptors.

Motor activity is modulated via different neuronal circuits in rats with chronic liver failure than in normal rats

The mechanisms by which liver failure alters motor function remain unclear. It has been suggested that liver disease alters the neuronal circuit between basal ganglia and cortex that modulates motor function. Activation of group I metabotropic glutamate receptors in the nucleus accumbens (NAcc) by injecting (S)-3,5-dihydroxyphenylglycine (DHPG) activates this circuit and induces locomotion We analysed by in vivo brain microdialysis the function of the circuits that modulate motor function in rats with liver failure due to portacaval shunt (PCS). We inserted cannulae in the NAcc and microdialysis probes in the NAcc, ventral pallidum (VP), substantia nigra pars reticulata (SNr), medio-dorsal thalamus (MDT), ventro-medial thalamus (VMT) or prefrontal cortex (PFCx). We injected DHPG in the NAcc and analysed extracellular neurotransmitters concentration in these areas. The results indicate that in control rats DHPG induces locomotion by activating the 'normal' neuronal circuit: NAcc --> VP --> MDT --> PFCx. In PCS rats this circuit is not activated. In PCS rats, DHPG injection activates an 'alternative' circuit: NAcc --> SNr --> VMT --> PFCx. This circuit is not activated in control rats. DHPG injection increases dopamine in the NAcc of control but not of PCS rats, and glutamate in PCS but not in control rats. DHPG-induced increase in dopamine would activate the 'normal' neuronal circuit, while an increase in glutamate would activate the 'alternative' circuit. The identification of the mechanisms responsible for altered motor function and coordination in liver disease would allow designing treatments to improve motor function in patients with hepatic encephalopathy.

Bradykinesia in cirrhotic patients with early hepatic encephalopathy is related to a decreased glucose uptake of frontomesial cortical areas relevant for movement initiation

BACKGROUND/AIMS

Bradykinesia is one of the first symptoms of hepatic encephalopathy (HE). Recently it has been suggested that bradykinesia in HE is due to disturbances in movement initiation. Areas involved in self-initiated movement are the motor- and premotor cortex, the supplementary motor cortex, the motor areas of the cingulate gyrus, and part of the frontomesial- and parietal cortex. The present study aimed to test the hypothesis that bradykinesia in HE is due to a functional disturbance of these areas.

METHODS

Fourteen cirrhotics with grade 0-I HE were examined. Patients with alcoholic cirrhosis or concomitant cerebral disorder were excluded. Patients underwent a 3-dimensional computer-assisted movement analysis for forearm pronation and supination, hand tapping and finger tapping and a (18)F-fluorodesoxy-glucose-PET-examination during rest, analysed with statistical parametric mapping (SPM99).

RESULTS

The frequency of finger- and hand tapping was significantly correlated to the glucose metabolism of the motor area of the cingulate gyrus and frontomedial, frontodorsal and parietal cortical areas known to be activated with self-initiated movements. A decrease of movement frequency was associated with a reduction of glucose metabolism within these areas.

CONCLUSIONS

These data support the hypothesis that bradykinesia in cirrhotics with HE is caused by an alteration of movement initiation.

Dopamine transporter SPECT of a liver cirrhotic with atypical parkinsonism

High level of exposure to manganese (Mn) can cause a clinically and pathophysiologically distinct syndrome from idiopathic Parkinson's disease (PD). We describe the clinical features and results of [123I]-fluoropropyl (FP)-CIT SPECT of a liver cirrhotic with atypical parkinsonism. The patient developed atypical parkinsonian features associated with elevated blood Mn from hepatic dysfunction. [123I]-FP-CIT brain SPECT images of dopamine transporter (DAT) demonstrated overall normal range of DAT uptake in the striatum although there were scattered small hypodense regions. The globus pallidum had increased signal on T1-weighted magnetic resonance imaging (MRI). All these findings are compatible with those of manganism, and are remarkably different from that in PD.

Contribution of altered signal transduction associated to glutamate receptors in brain to the neurological alterations of hepatic encephalopathy

Patients with liver disease may present hepatic enceph-alopathy (HE), a complex neuropsychiatric syndrome covering a wide range of neurological alterations, including cognitive and motor disturbances. HE reduces the quality of life of the patients and is associated with poor prognosis. In the worse cases HE may lead to coma or death.

The mechanisms leading to HE which are not well known are being studied using animal models. The neurological alterations in HE are a consequence of impaired cerebral function mainly due to alterations in neurotransmission. We review here some studies indicating that alterations in neurotransmission associated to different types of glutamate receptors are responsible for some of the cognitive and motor alterations present in HE.

These studies show that the function of the signal transduction pathway glutamate-nitric oxide-cGMP associated to the NMDA type of glutamate receptors is impaired in brain in vivo in HE animal models as well as in brain of patients died of HE. Activation of NMDA receptors in brain activates this pathway and increases cGMP. In animal models of HE this increase in cGMP induced by activation of NMDA receptors is reduced, which is responsible for the impairment in learning ability in these animal models. Increasing cGMP by pharmacological means restores learning ability in rats with HE and may be a new therapeutic approach to improve cognitive function in patients with HE. However, it is necessary to previously assess the possible secondary effects.

Patients with HE may present psychomotor slowing, hypokinesia and bradykinesia. Animal models of HE also show hypolocomotion. It has been shown in rats with HE that hypolocomotion is due to excessive activation of metabotropic glutamate receptors (mGluRs) in substantia nigra pars reticulata. Blocking mGluR1 in this brain area normalizes motor activity in the rats, suggesting that a similar treatment for patients with HE could be useful to treat psychomotor slowing and hypokinesia. However, the possible secondary effects of mGluR1 antagonists should be previously evaluated.

These studies are setting the basis for designing therapeutic procedures to specifically treat the individual neurological alterations in patients with HE.

Hypolocomotion in rats with chronic liver failure is due to increased glutamate and activation of metabotropic glutamate receptors in substantia nigra

BACKGROUND/AIMS

Patients with hepatic encephalopathy show altered motor function, psychomotor slowing and hypokinesia. The underlying mechanisms remain unclear. This work's aims were: (1) to analyse in rats with chronic liver failure due to portacaval shunt (PCS) the neurochemical alterations in the basal ganglia-thalamus-cortex circuits; (2) to correlate these alterations with those in motor function and (3) to normalize motor activity of PCS rats by pharmacological means.

METHODS

Extracellular neurotransmitters levels were analysed by in vivo brain microdialysis. Motor activity was determined by counting crossings in open field.

RESULTS

Extracellular glutamate is increased in substantia nigra pars reticulata (SNr) of PCS rats. Blocking metabotropic receptor 1 (mGluR1) in SNr normalizes motor activity in PCS rats. In ventro-medial thalamus of PCS rats GABA is increased and it is normalized by blocking mGluR1 in SNr. Blocking mGluR1 in SNr increases and mGluR1 activation reduces glutamate in motor cortex and motor activity.

CONCLUSIONS

Increased extracellular glutamate and activation of mGluR1 in SNr are responsible for reduced motor activity in rats with chronic liver failure. Blocking mGluR1 in SNr normalizes motor activity in PCS rats, suggesting that, under appropriate conditions, similar treatments could be useful to treat the psychomotor slowing and hypokinesia in patients with hepatic encephalopathy.

Neural synchronization in hepatic encephalopathy

Hepatic encephalopathy (HE) is clinically characterized by a large variety of symptoms including motor symptoms, cognitive deficits, as well as changes in the level of alertness up to hepatic coma. A number of pathological processes affecting glial and neuronal function have been identified, including hyper-ammonia, changes within the excitatory and inhibitory transmitter systems, as well as osmolytic changes with consecutive cell swelling. One explanation how these pathological processes result in neurological deficits in HE is the concept of pathologically synchronized oscillations within and between relevant brain regions. A number of studies suggest that the cognitive deficits and the reduced level of alertness in patients with HE can be attributed to a significantly slowed and pathologically synchronized spontaneous oscillatory brain activity, depending on the grade of HE. Moreover, HE motor symptoms, like postural tremor called"mini asterixis," have recently been shown to be associated with abnormal thalamo-cortical and cortico-muscular synchronization. Indirect evidence exists from studies of processing and recognition of flicker stimuli that in HE slowing of oscillations also occurs in the visual system. Taken together, pathological synchronization of neuronal activity may turn out to be a promising pathophysiological concept for linking neuronal dysfunction to the diversity of clinical deficits in HE.

Altered modulation of motor activity by group I metabotropic glutamate receptors in the nucleus accumbens in hyperammonemic rats

One of the neurological complications in hepatic encephalopathy is the impairment of motor coordination and function. Clinical signs of basal ganglia, cortico-spinal and cerebellar dysfunction have been commonly detected in these patients. We are studying the molecular bases of the alterations in motor coordination and function in hepatic encephalopathy. Hyperammonemia is considered the main factor responsible for the neurological alterations in patients with hepatic encephalopathy. Activation of metabotropic glutamate receptors (mGluRs) in the nucleus accumbens (NAcc) induces locomotion in rats. Asa first step in our studies on the alterations in motor co-ordination and function in hyperammonemia and hepatic encephalopathy we studied whether the control of motor function by mGluRs in the NAcc is altered in hyperammonemic rats. The locomotor activity induced by injection into the nucleus accumbens (NAcc) of DHPG, an agonist of group I mGluRs was significantly increased in hyperammonemic rats. Injection of DHPG increased extracellular dopamine but not glutamate in the NAcc of control rats. In hyperammonemic rats DHPG-induced increase in dopamine was significantly reduced, and extracellular glutamate increased 6-fold. The content of mGluR 1 but not mGluR 5, is increased in the NAcc of hyperammonemic rats. Blockade of mGluR 1 completely prevented motor and neurochemical effects induced by DHPG. These results show that modulation of both motor function and extracellular concentration of neurotransmitters by mGluRs in the NAcc is altered in hyperammonemia. This may contribute to the alterations in motor function in hepatic encephalopathy.

Improvement of regional cerebral blood flow after oral intake of branched-chain amino acids in patients with cirrhosis

AIM: To evaluate the effect of oral intake of branched-chain amino acids (BCAA) on brain perfusion in patients with liver cirrhosis.

METHODS: Single photon emission computed tomography scans were performed in 43 patients with cirrhosis and in 15 age-matched healthy subjects. Twenty-nine out of forty-three patients were randomly treated with either BCAA granules or placebo, and single photon emission computed tomography was performed before and after the treatment. We measured the regional cerebral blood flow values using a three-dimensional stereotaxic region of interest template.

RESULTS: Cirrhotic patients had regions of significant hypoperfusion in the bilateral central (right P = 0.039, P<0.05; left P = 0.006 P<0.01), parietal (right P = 0.018, P<0.05; left P = 0.009, P<0.01), angular (right P = 0.039, P<0.05; left P = 0.008, P<0.01), and left pericallosal segments (P = 0.038 P<0.05) as compared with healthy subjects. A significant increase in cerebral perfusion was observed 70 min after the oral intake of BCAA in the angular (right P = 0.012, P<0.05; left P = 0.049, P<0.05), temporal (right P = 0.012, P<0.05; left P=0.038, P<0.05), pericallosal segments (right P = 0.025, P<0.05; left P = 0.049, P<0.05) and left precentral (P = 0.044, P<0.05), parietal (P = 0.040, P<0.05) and thalamus (P = 0.033, P<0.05). No significant change in perfusion was observed in the placebo group.

CONCLUSION: Administration of BCAA rapidly improves cerebral perfusion.

Neurological and neuropsychiatric syndromes associated with liver disease

The clinical presentation of acute liver failure and hepatic encephalopathy (HE) in patients with cirrhosis differs significantly. The most serious neurological complication of acute liver failure is the development of devastating brain oedema. Therefore, intracranial pressure monitoring is urgently needed in these patients. Brain oedema is amplified by hypoglycemia, hypoxia and seizures, which are also frequent complications of acute liver failure. Therefore, these parameters must also be monitored. In contrast to acute liver failure in which cerebral dysfunction progresses rapidly, cognitive decline may be clinically undetectable for a long time in cirrhotic patients, until clinically overt symptoms such as psychomotor slowing, disorientation, confusion, extrapyramidal and cerebellar symptoms or a decrease in consciousness occur. Clinically, overt HE is preceded by minimal alterations of cerebral function that can only be detected by neuropsychological or neurophysiological measures, but which nevertheless interfere with the patient's daily living. Rapidly progressing spastic paraparesis (hepatic myelopathy) is a rare complication of cirrhosis. In contrast to HE, it does not respond to blood ammonia lowering therapies but must be considered as an indication for urgent liver transplantation. Cognitive dysfunction has recently been detected in hepatitis C virus (HCV)-infected patients with normal liver function. The patients presented with severe fatigue, cognitive dysfunction and mood disorders. Alterations in brain metabolites, as detected by magnetic resonance spectroscopy, indicated central nervous system alteration in these patients. In contrast to patients with HE, HCV-infected patients did not show motor symptoms or deficits in visual perception, but considerable deficits in attention and concentration ability.

Functional imaging of the brain in patients with liver cirrhosis

Brain imaging techniques have provided substantial insight into the pathophysiology of hepatic encephalopathy (HE). Magnetic resonance imaging gave hint to the fact that there is an increased deposition of manganese especially in the basal ganglia. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) showed that the preference of the basal ganglia might be due to differences in regional cerebral blood flow and an additional redistribution of blood flow from the cortex to subcortical regions in cirrhotics. PET studies using ammonia as tracer showed that the cerebral metabolism of ammonia and the permeability of the blood brain barrier for ammonia is increased in cirrhotic patients compared to healthy controls. The regional ammonia supply is in accordance with the regional blood flow. In accordance with these findings fluorodesoxyglucose-PET-studies of the brain in cirrhotics showed characteristic alterations of glucose utilisation in the patients with a relative decrease of the glucose utilisation of the cingulate gyrus, the frontomedial, frontolateral, and parieto-occipital cortex, while the glucose utilisation of the basal ganglia, the hippocampus, and the cerebellum was relatively increased. These findings fit well with the clinical characteristics of early stages of HE such as deficits in attention, visuo-spatial orientation, visuo-constructive abilities, motor speed, and accuracy.

Regional differences in cerebral blood flow and cerebral ammonia metabolism in patients with cirrhosis

Clinical and histopathological findings hint at regional differences in the brain's sensitivity to metabolic changes in cirrhosis. The aim of the present study was to examine regional differences in cerebral ammonia metabolism in patients with cirrhosis and grade 0-to-I hepatic encephalopathy (HE). (13)N-ammonia, (15)O-water positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. Quantitative values of cerebral blood flow (CBF) and the initial cerebral ammonia uptake rate (K1) were derived for several regions of interest from images of the desired parameters after interactive coregistration with the patients' MRI-studies. CBF (mL/mL/min), K1 (mL/mL/min), and the ammonia extraction fraction (K1/CBF) showed marked regional variance with the highest levels in the thalamus, the lenticular nucleus, and the cerebellum. In conclusion, the regional differences in cerebral ammonia uptake correspond to the distribution of histopathological changes in the brain of patients with cirrhosis as well as clinical features of HE, characterized by signs of basal ganglia and cerebellar dysfunction with corresponding signs of functional impairment, especially of the frontal cortex and cingulate gyrus.

Clinical significance of basal ganglia alterations at brain MRI and 1H MRS in cirrhosis and role in the pathogenesis of hepatic encephalopathy

In hepatic encephalopathy, a progressive and diffuse impairment in brain function is associated with gradual alterations that can be detected by magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (1H MRS). In some patients, a variety of movement disorders suggestive of extrapyramidal impairment points toward basal ganglia (BG) alterations. Accordingly, (i) hyperintensities at MRI predominant in the pallidum, an important region of BG involved in the motor control, (ii) redistribution of cerebral blood flow from cortical areas to BG structures observed using positron emission tomography studies, and (iii) the preferential pallidal location of Alzheimer astrocytosis, all support this hypothesis. In most clinical studies, little if any correlations have been found between cerebral hyperintensities and neurological manifestations. The application of a test designed to evaluate patients with Parkinson's disease (where extrapyramidal signs are typical) showed significant clinical correlations both with pallidal hyperintensity and with choline/creatine ratio at 1H MRS in BG structures. Because of complex neuronal connections between BG and many cortical areas, BG dysfunction may influence the neurocognitive manifestations of hepatic encephalopathy. Similarities between chronic Mn intoxication and cirrhosis suggest common pathophysiological mechanisms including altered dopaminergic neurotransmission, although information in chronic liver failure is limited. Clinical observations are presented regarding the evolution of parkinsonian signs in various situations.

Ammonia and Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. Behavioural, cognitive and memory dysfunctions are characteristic symptoms of AD. The formation of amyloid plaques is currently considered as the key event of AD. Other histological hallmarks of the disease are the formation of fibrillary tangles, astrocytosis, and loss of certain neuronal systems in cortical areas of the brain. A great number of possible aetiologic and pathogenetic factors of AD have been published in the course of the last two decades. Among the toxic factors, which have been considered to contribute to the symptoms and progression of AD, ammonia deserves special interest for the following reasons: (a) Ammonia is formed in nearly all tissues and organs of the vertebrate organism; it is the most common endogenous neurotoxic compounds. Its effects on glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures, are known for many years. (b) The impairment of ammonia detoxification invariably leads to severe pathology. Several symptoms and histologic aberrations of hepatic encephalopathy (HE), of which ammonia has been recognised as a pathogenetic factor, resemble those of AD. (c) The excessive formation of ammonia in the brains of AD patients has been demonstrated, and it has been shown that some AD patients exhibit elevated blood ammonia concentrations. (d) There is evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Ammonia is the most important natural modulator of lysosomal protein processing. (e) Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of AD. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia hypothesis of AD has first been suggested in 1993. In the present review old and new observations are discussed, which are in support of the notion that ammonia is a factor able to produce symptoms of AD and to affect the progression of the disease.

Hepatic encephalopathy in liver cirrhosis: pathogenesis, diagnosis and management

The pathogenesis of hepatic encephalopathy (HE) is unknown. Many theories have been proposed. Most established therapies are based on such theories but since no theory has have ever been proved, therapies have to be considered empiric. The spectrum of HE ranges from minimal cerebral functional deficits, which can only be found by sensitive psychometric tests, to coma with signs of decerebration. HE has arbitrarily been divided into stages. A number of precipitating factors are known and the first line of therapy should always be the elimination of these factors. The differential diagnosis includes all states of impaired consciousness and deficits in cerebral function in patients with chronic liver disease, and clinical and biochemical tests to differentiate are indicated. The therapeutic options for HE include: protein restriction only for a limited time in comatous patients; nonabsorbable antibiotics (aminoglycosides), which because of adverse effects are also limited to higher grades of HE: intestinal cleansing which is applicable in all degrees of HE; lactulose, branched chain aminoacids and ornithin aspartate which have been proven to be effective and can be applied long term in patients with lower grades of HE.

Altered striatal dopamine D2 receptor density and dopamine transport in a patient with hepatic encephalopathy

A patient suffering from liver cirrhosis presented with a bradykinetic-rigid syndrome suspected as Parkinson's disease. A detailed work-up of the case revealed hepatic encephalopathy as the cause of the neurological symptomatology. An alteration of striatal dopamine D2 receptor binding and dopamine re-uptake sites was demonstrated by 123I-iodobenzamide (IBZM) and 123I-beta-CIT single photon emission computed tomography (SPECT), respectively. It is suggested that the alteration of the dopamine re-uptake in cirrhotics may be the cause of an increased catabolism of dopamine in HE.

Magnetic resonance imaging and proton spectroscopic alterations correlate with parkinsonian signs in patients with cirrhosis

BACKGROUND & AIMS

The relationship between abnormalities found by magnetic resonance imaging (MRI) and proton spectroscopy (MRS) and the clinical signs of hepatic encephalopathy is not well characterized. Motor disturbances have been described, suggesting that basal ganglia (BG) are altered.

METHODS

We evaluated 19 unselected consecutive patients with biopsy-proven cirrhosis evaluated for liver transplantation for the presence of parkinsonian signs using the Unified Parkinson's Disease Rating Scale (UPDRS) and Purdue Pegboard test, and correlated these neurologic abnormalities with MRI and MRS studies. Brain MRI intensities were expressed as signal-to-noise ratios. MRS findings obtained from one voxel in the BG and one in the occipital white matter (WM) were expressed as metabolite ratios. Six healthy subjects had normal values.

RESULTS

Compared with healthy subjects, patients with subclinical or grade 1 hepatic encephalopathy had hyperintensity in occipital WM and all BG tissues except thalamus and reduced Ino/Cr and Cho/Cr ratios in both voxels. In the BG, MRI intensity was correlated with the UPDRS (P < 0.05, r = 0.56). The Cho/Cr ratio also correlated with both UPDRS (P < 0.02, r = -0.59) and Pegboard scores (P < 0.02, r = 0.61).

CONCLUSIONS

In cirrhosis, parkinsonian signs correlate with BG alterations detected by MRI and MRS.

Partial pressure of ammonia versus ammonia in hepatic encephalopathy

Ammonia is considered the major pathogenetic factor of cerebral dysfunction in hepatic failure. The correlation between total plasma ammonia and the severity of hepatic encephalopathy (HE), however, is variable. Because ammonia that is present in gaseous form readily enters the brain, the correlation with the grade of HE of the pH-dependent partial pressure of gaseous ammonia (pNH(3)) could be better than that of total arterial ammonia levels. To test this hypothesis, 56 cirrhotic patients with acute episodes of clinical HE (median age, 54 years; range, 21-75) were studied by clinical examination and by long-latency median-nerve sensory-evoked potentials (SEPs) N70 peak, an objective and sensitive electrophysiological measure of HE. pNH(3) was calculated from arterial blood according to published methods. The clinical grade of HE correlated (P <.001) with both pNH(3) and total ammonia, but correlation was stronger with pNH(3) (r =.79 vs.69, P =.01). A similar correlation was found for N70 peak latency (r =.71 with pNH(3) vs.64 with total ammonia, respectively, P =.08). In summary, arterial pNH(3) correlates more closely than total ammonia with the degree of clinical and electrophysiological abnormalities in HE. These findings support the ammonia hypothesis of HE and suggest that pNH(3) might be superior to total ammonia in the pathophysiological evaluation of HE.

Ammonia downregulates GLAST mRNA glutamate transporter in rat astrocyte cultures

Abnormalities in glutamate metabolism and glutamatergic neurotransmission appear to play an important role in the pathogenesis of hyperammonemia and hepatic encephalopathy. Previous studies from our laboratory have shown that treatment of cultured astrocytes with NH4Cl result in decreased glutamate uptake. To extend these observations, we performed a Northern blot analysis of the astroglial glutamate transporter GLAST (EAAT1) in NH4Cl-treated primary rat astrocyte cultures. Following treatment with 2, 5, 10 mM NH4Cl for 3 days, cortical astrocytes showed a 22, 29, 36% decrease in GLAST mRNA, respectively. Striatal astrocytes showed 25, 51, 50% reduction, while cerebellar cultures showed decrements of 18, 37, 38%. Similar decreases in GLAST mRNA were also observed after 1 day of ammonia treatment. These findings, together with recent reports on the reduction of the GLT-1 glutamate transporter in in vivo models of acute liver failure and hyperammonemia, strongly suggest that an abnormality in astroglial glutamate uptake constitutes a critical aspect in the pathogenesis of hepatic encephalopathy and other hyperammonemic conditions.

Proton magnetic resonance spectroscopy in portal-systemic encephalopathy

Localized proton magnetic resonance spectroscopy (MRS) with short echo times provides unique information of human cerebral metabolism. Studies on patients with portal-systemic encephalopathy (PSE) have been performed to clarify the pathogenesis of this disease and to find a method which allows an objective diagnosis. Spectra of patients with PSE show typical abnormalities. Regional variations of these spectral changes are observed. The metabolic changes correlate with the grade of encephalopathy but the dependence on the Child-Pugh score is controversial. No causal dependence between MRS findings and abnormalities in magnetic resonance imaging is evident. Differences in magnetic resonance spectra in patients compared to controls vanish after liver transplantation, but increase after TIPS. The results of proton magnetic resonance spectroscopy are important for an understanding of the pathogenesis of PSE, but do not aid in the diagnosis of subclinical hepatic encephalopathy.