Kernicterus: effect on choline acetyltransferase, glutamic acid decarboxylase and tyrosine hydroxylase activities in the brain of the Gunn rat

Precision weighting of cortical unsigned prediction error signals benefits learning, is mediated by dopamine, and is impaired in psychosis

Recent theories of cortical function construe the brain as performing hierarchical Bayesian inference. According to these theories, the precision of prediction errors plays a key role in learning and decision-making, is controlled by dopamine and contributes to the pathogenesis of psychosis. To test these hypotheses, we studied learning with variable outcome-precision in healthy individuals after dopaminergic modulation with a placebo, a dopamine receptor agonist bromocriptine or a dopamine receptor antagonist sulpiride (dopamine study n = 59) and in patients with early psychosis (psychosis study n = 74: 20 participants with first-episode psychosis, 30 healthy controls and 24 participants with at-risk mental state attenuated psychotic symptoms). Behavioural computational modelling indicated that precision weighting of prediction errors benefits learning in health and is impaired in psychosis. FMRI revealed coding of unsigned prediction errors, which signal surprise, relative to their precision in superior frontal cortex (replicated across studies, combined n = 133), which was perturbed by dopaminergic modulation, impaired in psychosis and associated with task performance and schizotypy (schizotypy correlation in 86 healthy volunteers). In contrast to our previous work, we did not observe significant precision-weighting of signed prediction errors, which signal valence, in the midbrain and ventral striatum in the healthy controls (or patients) in the psychosis study. We conclude that healthy people, but not patients with first-episode psychosis, take into account the precision of the environment when updating beliefs. Precision weighting of cortical prediction error signals is a key mechanism through which dopamine modulates inference and contributes to the pathogenesis of psychosis.

Dantrolene exerts protective activity in double and triple combination with nimodipine, ruthenium red and basilene blue in bilirubin-induced neurotoxicity in cell culture of rats

In the present study, dantrolene, nimodipine, basilen blue, and ruthenium red were tested in experimental bilirubin toxicity in cortical cell culture of rats. Neurotoxicity was induced by 10(-4) M bilirubin. Basilen blue in the highest concentration of 10(-4) M was determined as the most protective agent when applied alone. Dantrolene alone was found surprisingly ineffective in all doses tested. But it was found very protective both in double and triple combinations. Nimodipine, basilen blue, and ruthenim red neuroprotective potentials were enhanced by adding dantrolene into the media. Best double combination was determined as dantrolene plus ruthenium red. On the other hand, most useful triple combination was found as dantrolene plus nimodipine plus basilen blue. As a result, dantrolene wasn't found to be effective alone, while it seems most potential compound in combined application in bilirubin-induced neurotoxicity. The importance of calcium intrusion was confirmed in bilirubin-induced neurotoxicity.

Bilirubin induces apoptosis via the mitochondrial pathway in developing rat brain neurons

Increased levels of unconjugated bilirubin, the end-product of heme catabolism, are detrimental to the central nervous system. To examine the role of apoptosis in bilirubin-induced toxicity and to characterize the biochemical pathway of cell death, we exposed developing rat brain neurons to purified unconjugated bilirubin at concentrations below and above saturation of human serum albumin. Isolated neurons treated with bilirubin showed increased levels of apoptosis. Mitochondrial cytochrome c was extensively released and accumulated in cytosol. Consistent with this observation, caspase-3 was activated and the full-length substrate poly(ADP)ribose polymerase (PARP) degraded, even in the presence of very modestly elevated concentrations of bilirubin. In parallel, all events were prevented in cells preincubated with ursodeoxycholate. Further experiments showed that bilirubin diminished mitochondrial transmembrane potential (DeltaPsi(m)) and increased mitochondrial-associated Bax protein levels, while directly disrupting membrane lipid and protein structure. In conclusion, bilirubin induces mitochondrial depolarization and Bax translocation via physical interaction with membranes, mediating the mitochondrial pathway of apoptosis in neurons exposed to bilirubin. These results provide a novel insight into the mechanism of bilirubin-induced toxicity.

Bilirubin directly disrupts membrane lipid polarity and fluidity, protein order, and redox status in rat mitochondria

BACKGROUND/AIMS

Unconjugated bilirubin (UCB) impairs crucial aspects of cell function and induces apoptosis in primary cultured neurones. While mechanisms of cytotoxicity begin to unfold, mitochondria appear as potential primary targets.

METHODS

We used electron paramagnetic resonance spectroscopy analysis of isolated rat mitochondria to test the hypothesis that UCB physically interacts with mitochondria to induce structural membrane perturbation, leading to increased permeability, and subsequent release of apoptotic factors.

RESULTS

Our data demonstrate profound changes on mitochondrial membrane properties during incubation with UCB, including modified membrane lipid polarity and fluidity (P<0.01), as well as disrupted protein mobility (P<0.001). Consistent with increased permeability, cytochrome c was released from the intermembrane space (P<0.01), perhaps uncoupling the respiratory chain and further increasing oxidative stress (P<0.01). Both ursodeoxycholate, a mitochondrial-membrane stabilising agent, and cyclosporine A, an inhibitor of the permeability transition, almost completely abrogated UCB-induced perturbation.

CONCLUSIONS

UCB directly interacts with mitochondria influencing membrane lipid and protein properties, redox status, and cytochrome c content. Thus, apoptosis induced by UCB may be mediated, at least in part, by physical perturbation of the mitochondrial membrane. These novel findings should ultimately prove useful to our evolving understanding of UCB cytotoxicity.

Aging confers different sensitivity to the neurotoxic properties of unconjugated bilirubin

The pathogenesis of bilirubin encephalopathy appears to result from accumulation of unconjugated bilirubin (UCB), which, in turn, may cause mitochondrial perturbation, release of intermembrane proteins, and, ultimately, cell death. Aging imparts to cells a different susceptibility to this toxic stimulus, as neonates are particularly vulnerable to the accumulation of UCB in the CNS. In this paper, we further characterize UCB-induced toxicity in isolated neuronal and glial cells according to age in culture. In addition, we investigate sensitivity of mitochondria derived from young and old rats to UCB-induced membrane permeabilization and, finally, evaluate whether age-dependent changes in UCB toxicity are accompanied by alterations in the mitochondrial content of cytochrome c. The results showed that UCB is more toxic to immature neural cells after 4-5 d in culture (p < 0.001), whereas neurons were more sensitive than astrocytes (p < 0.05). In fact, approximately 40% of cells were apoptotic in immature cultures compared with 20% in mature cultures. Unexpectedly, mitochondrial swelling and subsequent efflux of cytochrome c induced by UCB were 2-fold greater in organelles derived from older rats (p < 0.01). In conclusion, UCB toxicity of isolated rat neuronal and glial cells is modulated by age in culture in that immature cells are more susceptible. Mitochondria derived from younger rats are nevertheless more resistant to membrane permeabilization and cytochrome c release induced by UCB. The data indicate that the cells of young animals are relatively resistant to UCB toxicity, through a protective mechanism at the mitochondrial level; however, this is not sufficient to prevent apoptosis of cells in the young animal. Thus, although playing a role, direct mitochondrial injury may not be the sole mechanism of UCB cytotoxicity.

Bilirubin-induced apoptosis in cultured rat neural cells is aggravated by chenodeoxycholic acid but prevented by ursodeoxycholic acid

BACKGROUND/AIMS

Unconjugated bilirubin (UCB) can be neurotoxic in jaundiced neonates and in patients with Crigler-Najjar syndrome. UCB toxicity may culminate in cell death, however, the occurrence of apoptosis has never been investigated. Ursodeoxycholic acid (UDCA) is a strong modulator of the apoptotic threshold in both hepatic and nonhepatic cells. The aims of this study were to determine whether apoptosis plays a role in neural cell death induced by UCB, and to investigate the ability of UDCA to prevent cell death.

METHODS

Cultured rat astrocytes were incubated with UCB (17 and 86 microM) plus albumin (5.7 and 28.7 microM) for 4-22 h. In addition, astrocytes and neurones were treated with either UCB, 50 microM UDCA, or their combination for 4 h. Cultures were scored for nonviable cells by trypan blue dye exclusion. Apoptosis was assessed by Hoechst staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling assay.

RESULTS

UCB induced a concentration- and time-dependent decrease in astrocyte viability. Apoptosis was 4- and 7-fold increased after 4 h exposure to 17 and 86 microM UCB, respectively (P < 0.01). UDCA reduced apoptosis to <7%, which represents a appoximately 60% protection (P < 0.01). Cholic acid was not protective, and chenodeoxyholic acid aggravated UCB toxicity (P < 0.05). Finally, neurones showed a 1.5-fold greater sensitivity than astrocytes to UCB, while UDCA was still protective.

CONCLUSIONS

UCB is toxic to both astrocytes and neurones, causing cell death through an apoptotic process. Moreover, UDCA inhibits UCB-induced apoptosis in neural cells and this could not be mimicked by other bile acids.

Developmental expression of heme oxygenase-1 (HSP32) in rat brain: an immunocytochemical study

Heme oxygenase (HO) is a microsomal enzyme that oxidatively cleaves heme molecules to produce bile pigments, iron and carbon monoxide. In normal adult rat brain, HO-2 is the most abundant isozyme whereas HO-1 is present at very low levels except in select cell populations. Because its promoter region has NF-kB and AP-1 sites, heat-shock and heme-responsive elements, the HO-1 isozyme can be induced by a variety of stimuli. Since the expression and activity of several transcription factors such as NF-kB, Fos/Jun, and CREB show specific changes during development, we postulated that HO-1 expression may show similar developmental regulation. Using immunocytochemistry and Western blotting, this study demonstrates the development changes of HO-1 protein expression in normal brain from rats at postnatal day 7 (P7), P14, P21, and adult. Brain HO-1 immunoreactivity was highest at P7 in most brain regions including the white matter in areas of myelinogenesis, cerebral cortex, hippocampus, thalamus and hypothalamus and, in the blood vessel endothelial cells throughout the brain. In most regions, the adult pattern was reached by P21 with HO-1 protein localized almost exclusively to the dentate regions of hippocampus, some thalamic and hypothalamic nuclei, with little or no staining of endothelium, white matter and cortex. In a few select areas such as the substantia nigra, globus pallidus, ventromedial hypothalamic nucleus and the lateral preoptic nuclei area, little or no cellular HO-1 staining was observed at P7 whereas increased staining was found with maturation and adulthood. These results show that HO-1 protein expression is regulated in different cell types of specific regions of the rat brain during development.

Methylmercury poisoning of the developing nervous system in the rat: decreased activity of glutamic acid decarboxylase in cerebral cortex and neostriatum

The specific activities of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) were measured in 6 regions of the central nervous system in young rats, following chronic postnatal administration of methylmercuric chloride. These rats exhibited signs of neurological impairment which included visual deficits, ataxia, spasticity and myoclonus. At the onset of neurological impairment, there was a significant reduction in GAD activity in the occipital cortex (43%), frontal cortex (37%) and caudate-putamen (42%). Preceding the onset of neurological impairment, diminished GAD activity was detected only in the occipital cortex. In the cerebellum, thalamus and spinal cord, GAD activities were normal throughout the experiment. No significant differences in ChAT activity were detected in any of the 6 regions. These results are consistent with a preferential involvement of GABAergic neurons in methylmercury-induced lesions of the cerebral cortex and neostriatum.

Kernicterus: enzymatic evidence for difference between the development of cholinergic and GABAergic innervations in the brain of the Gunn rat

The activities of choline acetyltransferase (CAT) and glutamic acid decarboxylase (GAD), markers of cholinergic and GABAergic terminals, were measured in growing and adult Gunn rats, which possess an autosomal recessive gene for jaundice or kernicterus. In the olfactory tubercle, hippocampus, neostriatum, thalamus, and hypothalamus of the animals with kernicterus, the development of the cholinergic pathways was delayed, but by the adult stage it was normal, while there was practically no action on the innervation by GABAergic neurons, at least as indicated by the chemically measured parameters.