Neonatal ethanol exposure alters bcl-2 family mRNA levels in the rat cerebellar vermis

Mitochondrial fusion and Bid-mediated mitochondrial apoptosis are perturbed by alcohol with distinct dependence on its metabolism

Environmental stressors like ethanol (EtOH) commonly target mitochondria to influence the cell’s fate. Recent literature supports that chronic EtOH exposure suppresses mitochondrial dynamics, central to quality control, and sensitizes mitochondrial permeability transition pore opening to promote cell death. EtOH-induced tissue injury is primarily attributed to its toxic metabolic products but alcoholism also impairs tissues that poorly metabolize EtOH. We embarked on studies to determine the respective roles of EtOH and its metabolites in mitochondrial fusion and tBid-induced mitochondrial apoptosis. We used HepG2 cells that do not metabolize EtOH and its engineered clone that expresses EtOH-metabolizing Cytochrome P450 E2 and alcohol dehydrogenase (VL-17A cells). We found that fusion impairment by prolonged EtOH exposure was prominent in VL-17A cells, probably owing to reactive oxygen species increase in the mitochondrial matrix. There was no change in fusion protein abundance, mitochondrial membrane potential or Ca²⁺ uptake. By contrast, prolonged EtOH exposure promoted tBid-induced outer mitochondrial membrane permeabilization and cell death only in HepG2 cells, owing to enhanced Bak oligomerization. Thus, mitochondrial fusion inhibition by EtOH is dependent on its metabolites, whereas sensitization to tBid-induced death is mediated by EtOH itself. This difference is of pathophysiological relevance because of the tissue-specific differences in EtOH metabolism.

Differential effects of ethanol on bid, tBid, and Bax:tBid interactions in postnatal day 4 and postnatal day 7 rat cerebellum

BACKGROUND

Exposure to ethanol (EtOH) during central nervous system (CNS) development can lead to a wide array of neuroanatomical, behavioral, and cognitive abnormalities, broadly subsumed under the fetal alcohol spectrum disorder classification. One mode of EtOH-induced interference in the normal developmental program appears to be through induction of apoptotic processes mediated by the Bcl-2 family of survival-regulatory proteins. The present series of studies investigated the role of the Bcl-2-related, pro-apoptotic Bid protein, and its truncated, apoptotically active fragment, tBid, in developmental EtOH neurotoxicity.

METHODS

Protein analyses were made via enzyme-linked immunosorbent assays (ELISA) in neonatal rat cerebellum, of basal Bid, and of Bid and tBid, following EtOH exposure via vapor inhalation, at an age of peak EtOH sensitivity in this region (postnatal day 4 [P4]) and a later age of relative resistance (P7). ELISA analyses were also made of Bax:tBid heterodimers, a process which activates Bax, essential for its apoptotic functioning. Finally, in vitro assessments of the importance of tBid to EtOH neurotoxicity were made in cultured cerebellar granule cells, using a specific tBid inhibitor.

RESULTS

Basal levels of Bid were higher at P4 compared to P7, possibly contributing to the differential sensitivity. EtOH exposure elicited further increases in cytosolic Bid and mitochondrial tBid when administration was at P4, but not at P7. Bax:tBid heterodimers were markedly increased by EtOH exposure on P4, an increase which persisted even 2 hours after termination of treatment. Similar effects were not seen at P7. The in vitro analyses revealed that tBid inhibition provided complete protection against EtOH-induced cell death and depressed EtOH-mediated cytochrome-c release.

CONCLUSIONS

These results suggest that Bid/tBid may be important elements in EtOH-mediated neurotoxicity during CNS development. The molecular processes and interactions revealed may represent critical points which can be targeted in studies concerned with designing possible therapeutic strategies for minimizing these devastative effects.

Apoptosis and gene expression in the developing mouse brain of fusarenon-X-treated pregnant mice

Fusarenon-X (FX), a type B trichothecene mycotoxin, is mainly produced by Fusarium crookwellense, which occurs naturally in agricultural commodities, such as wheat and barley. FX has been shown to exert a variety of toxic effects on multiple targets in vitro. However, the embryonic toxicity of FX in vivo remains unclear. In the present study, we investigated FX-induced apoptosis and the relationship between the genetic regulatory mechanisms and FX-induced apoptosis in the developing mouse brain of FX-treated pregnant mice. Pregnant mice were orally administered FX (3.5 mg/kg b.w.) and were assessed at 0, 12, 24 and 48 h after treatment (HAT). Apoptosis in the fetal brain was determined using hematoxylin and eosin staining, the TUNEL method, immunohistochemistry for PCNA and electron microscopy. Gene expressions were evaluated using microarray and real time-reverse transcription polymerase chain reaction (qRT-PCR). Histopathological changes showed that the number of apoptotic cells in the telencephalon of the mouse fetus peaked at 12 HAT and decreased at 24 and 48 HAT. FX induced the up-regulation of Bax, Trp53 and Casp9 and down-regulated Bcl2 but the expression levels of Fas and Casp8 mRNA remained unchanged. These data suggested that FX induces apoptosis in the developing mouse brain in FX-treated dams. Moreover, the genetic regulatory mechanisms of FX-induced apoptosis are regulated by Bax, Bcl2, Trp53 and Casp9 or can be defined via an intrinsic apoptotic pathway.

Involvement of sphingolipids in ethanol neurotoxicity in the developing brain

Ethanol-induced neuronal death during a sensitive period of brain development is considered one of the significant causes of fetal alcohol spectrum disorders (FASD). In rodent models, ethanol triggers robust apoptotic neurodegeneration during a period of active synaptogenesis that occurs around the first two postnatal weeks, equivalent to the third trimester in human fetuses. The ethanol-induced apoptosis is mitochondria-dependent, involving Bax and caspase-3 activation. Such apoptotic pathways are often mediated by sphingolipids, a class of bioactive lipids ubiquitously present in eukaryotic cellular membranes. While the central role of lipids in ethanol liver toxicity is well recognized, the involvement of sphingolipids in ethanol neurotoxicity is less explored despite mounting evidence of their importance in neuronal apoptosis. Nevertheless, recent studies indicate that ethanol-induced neuronal apoptosis in animal models of FASD is mediated or regulated by cellular sphingolipids, including via the pro-apoptotic action of ceramide and through the neuroprotective action of GM1 ganglioside. Such sphingolipid involvement in ethanol neurotoxicity in the developing brain may provide unique targets for therapeutic applications against FASD. Here we summarize findings describing the involvement of sphingolipids in ethanol-induced apoptosis and discuss the possibility that the combined action of various sphingolipids in mitochondria may control neuronal cell fate.

Mechanisms of ethanol-induced death of cerebellar granule cells

Maternal ethanol exposure during pregnancy may cause fetal alcohol spectrum disorders (FASD). FASD is the leading cause of mental retardation. The most deleterious effect of fetal alcohol exposure is inducing neuroapoptosis in the developing brain. Ethanol-induced loss of neurons in the central nervous system underlies many of the behavioral deficits observed in FASD. The cerebellum is one of the brain areas that are most susceptible to ethanol during development. Ethanol exposure causes a loss of both cerebellar Purkinje cells and granule cells. This review focuses on the toxic effect of ethanol on cerebellar granule cells (CGC) and the underlying mechanisms. Both in vitro and in vivo studies indicate that ethanol induces apoptotic death of CGC. The vulnerability of CGC to ethanol-induced death diminishes over time as neurons mature. Several mechanisms for ethanol-induced apoptosis of CGC have been suggested. These include inhibition of N-methyl-D-aspartate receptors, interference with signaling by neurotrophic factors, induction of oxidative stress, modulation of retinoid acid signaling, disturbance of potassium channel currents, thiamine deficiency, and disruption of translational regulation. Cultures of CGC provide an excellent system to investigate cellular/molecular mechanisms of ethanol-induced neurodegeneration and to evaluate interventional strategies. This review will also discuss the approaches leading to neuroprotection against ethanol-induced neuroapoptosis.

Ethanol influences on Bax associations with mitochondrial membrane proteins in neonatal rat cerebellum

These studies investigated interactions taking place at the mitochondrial membrane in neonatal rat cerebellum following ethanol exposure and focused on interactions between proapoptotic Bax and proteins of the permeability transition pore (PTP), voltage-dependent anion channel (VDAC) and adenine nucleotide translocator (ANT) of the outer and inner mitochondrial membranes, respectively. Cultured cerebellar granule cells were used to assess the role of these interactions in ethanol neurotoxicity. Analyses were made at the age of maximal cerebellar ethanol vulnerability (P4), compared to the later age of relative resistance (P7), to determine whether differential ethanol sensitivity was mirrored by differences in these molecular interactions. We found that, following ethanol exposure, Bax proapoptotic associations with both VDAC and ANT were increased, particularly at the age of greater ethanol sensitivity, and these interactions were sustained at this age for at least 2 h postexposure. Since Bax:VDAC interactions disrupt protective VDAC interactions with mitochondrial hexokinase (HXK), we also assessed VDAC:HXK associations following ethanol treatment and found such interactions were altered by ethanol treatment, but only at 2 h postexposure and only in the P4, ethanol-sensitive cerebellum. Ethanol neurotoxicity in cultured neuronal preparations was abolished by pharmacological inhibition of both VDAC and ANT interactions with Bax but not by a Bax channel blocker. Therefore, we conclude that, at this age, within the constraints of our experimental model, a primary mode of Bax-induced initiation of the apoptosis cascade following ethanol insult involves interactions with proteins of the PTP complex and not channel formation independent of PTP constituents.

Activity-dependent neurotrophic factor-derived peptide prevents alcohol-induced apoptosis, in part, through Bcl2 and c-Jun N-terminal kinase signaling pathways in fetal brain of C57BL/6 mouse

Fetal alcohol exposure is known to induce alteration in fetal brain development. In this study, we focused on neuroprotection against the effects of alcohol exposure using ADNF-9, a peptide derived from activity-dependent neurotrophic factor. We used a mouse model of fetal alcohol exposure to identify the intracellular mechanisms underlying the neuroprotective effects of ADNF-9. On embryonic day 7 (E7), weight-matched pregnant females were assigned to the following groups: (1) ethanol liquid diet (ALC) of 25% (4.49%, v/v) ethanol-derived calories; (2) pair-fed control (PF); (3) ALC combined with administration (i.p.) of ADNF-9 (ALC/ADNF-9); and (4) pair-fed combined with administration (i.p.) of ADNF-9 (PF/ADNF-9). On E13, fetal brains were collected, weighed, and apoptosis was determined using TdT-mediated dUTP nick-end labeling (TUNEL) assay. Bcl2 protein and phospho-c-Jun N-terminal kinase (JNK) levels were determined using Western blot and enzyme immunometric assay, respectively. ADNF-9 administration significantly prevented alcohol-induced reductions in fetal brain weight. In addition, ADNF-9 prevented an alcohol-induced increase in cell death in the primordium of the cerebral cortex and ganglionic eminence. Western blot analysis of the mitochondrial protein fractions revealed that ADNF-9 administration prevented an alcohol-induced reduction in the Bcl2 level. Moreover, an analysis of the proteins in the upstream signaling pathway revealed that ADNF-9 downregulated the phosphorylation of JNK. These data indicate that the mitochondrial Bcl2 pathway and JNK upstream signaling pathway are the intracellular targets of ADNF-9. The neuroprotective mechanism of action of ADNF-9 provides a direction for potential therapeutics against alcohol-induced neural damage involving mitochondrial dysfunction.

Differential effects of ethanol on c-jun N-terminal kinase, 14-3-3 proteins, and Bax in postnatal day 4 and postnatal day 7 rat cerebellum

These studies investigated ethanol effects on upstream cellular elements and interactions which contribute to Bax-related apoptosis in neonatal rat cerebellum at ages of peak ethanol sensitivity (postnatal day 4 [P4]), compared to later ages of relative resistance (P7). Analyses were made of basal levels of the pro-apoptotic c-jun N-terminal kinase (JNK), Bax, and the 14-3-3 anchoring proteins, as well as the responsiveness of these substances to ethanol at P4 versus P7. Dimerization of Bax with 14-3-3 was also investigated at the two ages following ethanol treatment, a process which sequesters Bax in the cytosol, thus inhibiting its mitochondrial translocation and disruption of the mitochondrial membrane potential. Cultured cerebellar granule cells were used to examine the protective potential of JNK inhibition on ethanol-mediated cell death. Basal levels of JNK were significantly higher at P4 than P7, but no differences in the other proteins were found. Activated JNK, and cytosolic and mitochondrially-translocated Bax were increased in P4 but not P7 animals following ethanol exposure, while protective 14-3-3 proteins were increased only at P7. Ethanol treatment resulted in decreases in Bax:14-3-3 heterodimers at P4, but not at P7. Inhibition of JNK activity in vitro provided partial protection against ethanol neurotoxicity. Thus, differential temporal vulnerability to ethanol in this CNS region correlates with differences in both levels of apoptosis-related substances (e.g., JNK), and differential cellular responsiveness, favoring apoptosis at the most sensitive age and survival at the resistant age. The upstream elements contributing to this vulnerability can be targets for future therapeutic strategies.

Ethanol influences on Bax translocation, mitochondrial membrane potential, and reactive oxygen species generation are modulated by vitamin E and brain-derived neurotrophic factor

BACKGROUND

This study investigated ethanol influences on intracellular events that predispose developing neurons toward apoptosis and the capacity of the antioxidant α-tocopherol (vitamin E) and the neurotrophin brain-derived neurotrophic factor (BDNF) to modulate these effects. Assessments were made of the following: (i) ethanol-induced translocation of the pro-apoptotic Bax protein to the mitochondrial membrane, a key upstream event in the initiation of apoptotic cell death; (ii) disruption of the mitochondrial membrane potential (MMP) as a result of ethanol exposure, an important process in triggering the apoptotic cascade; and (iii) generation of damaging reactive oxygen species (ROS) as a function of ethanol exposure.

METHODS

These interactions were investigated in cultured postnatal day 8 neonatal rat cerebellar granule cells, a population vulnerable to developmental ethanol exposure in vivo and in vitro. Bax mitochondrial translocation was analyzed via subcellular fractionation followed by Western blot, and mitochondrial membrane integrity was determined using the lipophilic dye, JC-1, that exhibits potential-dependent accumulation in the mitochondrial membrane as a function of the MMP.

RESULTS

Brief ethanol exposure in these preparations precipitated Bax translocation, but both vitamin E and BDNF reduced this effect to control levels. Ethanol treatment also resulted in a disturbance of the MMP, and this effect was blunted by the antioxidant and the neurotrophin. ROS generation was enhanced by a short ethanol exposure in these cells, but the production of these harmful free radicals was diminished to control levels by cotreatment with either vitamin E or BDNF.

CONCLUSIONS

These results indicate that both antioxidants and neurotrophic factors have the potential to ameliorate ethanol neurotoxicity and suggest possible interventions that could be implemented in preventing or lessening the severity of the damaging effects of ethanol in the developing central nervous system seen in the fetal alcohol syndrome (FAS).

ER-targeted Bcl-2 and inhibition of ER-associated caspase-12 rescue cultured immortalized cells from ethanol toxicity

Alcohol abuse, known for promoting apoptosis in the liver and nervous system, is a major public health concern. Despite significant morbidity and mortality resulting from ethanol consumption, the precise cellular mechanism of its toxicity remains unknown. Previous work has shown that wild-type Bcl-2 is protective against ethanol. The present study investigated whether protection from ethanol toxicity involves mitochondrial Bcl-2 or endoplasmic reticulum (ER) Bcl-2, and whether mitochondria-associated or ER-associated caspases are involved in ethanol toxicity. Chinese hamster ovary (CHO695) cells were transiently transfected with cDNA constructs encoding wild-type Bcl-2, mitochondria-targeted Bcl-2, or ER-targeted Bcl-2. MTT assay was used to measure cell viability in response to ethanol. Ethanol treatments of 1 and 2.5 M reduced cell viability at 5, 10, and 24 h. Wild-type Bcl-2, localized both to mitochondria and ER, provided significant rescue for CHO695 cells treated with 1M ethanol for 24 h, but did not rescue toxicity at 2.5 M. ER-targeted Bcl-2, however, provided significant and robust rescue following 24 h of 1 and 2.5 M ethanol. Mitochondria-targeted Bcl-2 offered no protection at any ethanol concentration and generally reduced cell viability. To follow up these experiments, we used a peptide inhibitor approach to investigate which caspases were responsible for ethanol-induced apoptosis. Caspase-9 and caspase-12 are known to be downstream of mitochondria and the ER, respectively. CHO695 cells were treated with a pan-caspase inhibitor, a caspase-9 or caspase-12 inhibitor along with 1.5 M ethanol, followed by MTT cell viability assay. Treatment with the pan-caspase inhibitor provided significant rescue from ethanol, whereas inhibition of caspase-9 did not. Inhibition of ER-associated caspase-12, however, conferred significant protection from ethanol toxicity, similar to the pan inhibitor. These findings are consistent with our transfection data and, taken together, suggest a significant role for the ER in ethanol toxicity.

Ethanol impairs activation of retinoic acid receptors in cerebellar granule cells in a rodent model of fetal alcohol spectrum disorders

BACKGROUND

Ethanol is the main addictive and neurotoxic constituent of alcohol. Ethanol exposure during embryonic development causes dysfunction of the central nervous system (CNS) and leads to fetal alcohol spectrum disorders. The cerebellum is one of the CNS regions that are particularly vulnerable to ethanol toxic effects. Retinoic acid (RA) is a physiologically active metabolite of vitamin A that is locally synthesized in the cerebellum. Studies have shown that RA is required for neuronal development, but it remains unknown if ethanol impairs RA signaling and thus induces neuronal malformations. In this study, we tested the hypothesis that ethanol impairs the expression and activation of RA receptors in cerebellum and in cerebellar granule cells.

METHODS

The cerebellum of ethanol unexposed and exposed pups was used to study the expression of retinoic acid receptors (RARs or RXRs) by immunohistochemistry and by Western blot analysis. We also studied the effect of ethanol on expression of RA receptors in the cerebellar granule cells. Activation of RA receptors (DNA-binding activities) in response to high-dose ethanol was determined by electrophoretic mobility shift and supershift assays.

RESULTS

Findings from these studies demonstrated that ethanol exposure reduced the expression of RARalpha/gamma while it increased the expression of RXRalpha/gamma in the cerebellum and in cerebellar granule neurons. Immuno-histological studies further strengthened the expression pattern of RA receptors in response to ethanol. The DNA-binding activity of RARs was reduced, while DNA-binding activity of RXRs was increased in response to ethanol exposure.

CONCLUSION

For the first time, our studies have demonstrated that high-dose ethanol affects the expression and activation of RA receptors, which could impair the signaling events and induce harmful effects on the survival and differentiation of cerebellar granule cells. Taken together, these findings could provide insight into the treatment options for brain defects caused by excessive ethanol exposure, such as in Fetal Alcohol Spectrum Disorders.

Differential expression of proteins in fetal brains of alcohol-treated prenatally C57BL/6 mice: a proteomic investigation

Alcohol is known to impede the growth of the central nervous system and to induce neurodegeneration through cellular apoptosis. We have previously shown that moderate prenatal alcohol exposure results in brain defects at different stages of development. In this study, we further characterize the proteomic architecture underlying ethanol teratogenesis during early fetal brain development using chromatography in conjunction with a LC-MS/MS system. Pregnant C57BL/6 mice were exposed from embryonic day 7 (E7) to E13 with either a 25% ethanol derived calorie or pair-fed liquid diets. At E13, fetal brains were collected from five dams for each group. Individual brains were homogenized and the extracted proteins were then tryptically digested and analyzed by LC-MS/MS. Label-free quantitative proteomic analyses were performed on proteomes extracted from fetal brains of both alcohol-treated (ALC) and pair-fed groups. These analyses demonstrated that prenatal alcohol exposure induced significant downregulation (p<0.001) of the expression of mitochondrial enzymes including ADP/ATP translocase 1, ATP synthase subunit alpha and ubiquinol-cytochrome-c reductases. In addition, mitochondrial carrier homolog 1, which plays a role in apoptosis, was significantly downregulated (p<0.001) in the ALC group. Moreover, among the cytosolic proteins that were significantly downregulated (p<0.001) are Bcl-2, 14-3-3 protein and calmodulin. Significant downregulation (p<0.001) of proteins that are critical for fetal brain development was observed such as prohibitin and neuronal migration protein doublecortin. These findings provide information about possible mechanisms underlying the effects of prenatal alcohol exposure during early embryonic stage.

A novel peptide, colivelin, prevents alcohol-induced apoptosis in fetal brain of C57BL/6 mice: signaling pathway investigations

Fetal alcohol exposure is known to induce cell death through apoptosis. We found that colivelin (CLN), a novel peptide with the sequence SALLRSIPAPAGASRLLLLTGEIDLP, prevents this apoptosis. Our initial experiment revealed that CLN enhanced the viability of primary cortical neurons exposed to alcohol. We then used a mouse model of fetal alcohol exposure to identify the intracellular mechanisms underlying these neuroprotective effects. On embryonic day 7 (E7), weight-matched pregnant females were assigned to the following groups: (1) ethanol liquid diet 25% (4.49% v/v) ethanol derived calories; (2) pair-fed control; (3) normal chow; (4) ethanol liquid diet combined with administration (i.p.) of CLN (20 microg/20 g body weight); and (5) pair-fed combined with administration (i.p.) of CLN (20 microg/20 g body weight). On E13, fetal brains were collected and assayed for TdT-mediated dUTP nick end labeling staining, caspase-3 colorimetric assay, enzyme-linked immunosorbent assay, and Meso scale discovery electrochemiluminescence. CLN blocked the alcohol-induced decline in brain weight and prevented alcohol-induced: apoptosis, activation of caspase-3 and increases of cytosolic cytochrome c, and decreases of mitochondrial cytochrome c Analysis of proteins in the upstream signaling pathway revealed that CLN down-regulated the phosphorylation of the c-Jun N-terminal kinase. Moreover, CLN prevented alcohol-induced reduction in phosphorylation of BAD protein. Thus, CLN appears to act directly on upstream signaling proteins to prevent alcohol-induced apoptosis. Further assessment of these proteins and their signaling mechanisms is likely to enhance development of neuroprotective therapies.

Activity-dependent neuroprotective protein-derived peptide, NAP, preventing alcohol-induced apoptosis in fetal brain of C57BL/6 mouse

Possible prevention of the effects of prenatal alcohol exposure has been investigated using peptides that were previously shown to be involved in neuroprotection both in vitro and in vivo. I focused in this study on investigating the neuroprotective effects of one of these peptides with regard to the determination of the downstream signaling pathways involved in neuroprotection. This peptide with the sequence NAPVSIPQ, known as NAP, a fragment of activity-dependent neuroprotective protein, demonstrated a potent protective effect against oxidative stress associated with alcohol exposure. On embryonic day 7 (E7), weight-matched C57BL/6 pregnant females were assigned the following groups: (1) Ethanol liquid diet group (ALC) 25% (4.49%, v/v) ethano-derived calories, (2) Pair-fed (PF) control group (3) Chow control group, (4) treatment groups with alcohol alongside i.p. injections of d-NAP (ALC/d-NAP, 20 or 30 microg/20 g body weight), (5) PF/d-NAP control group. On E13, fetal brains were collected and assayed for TdT-mediated dUTP nick end labeling (TUNEL) staining, caspase-3 colorimetric assay and ELISA for cytochrome c detection. My results show that NAP significantly prevented alcohol-induced weight reduction of the fetal brain. Apoptosis was determined by TUNEL staining; NAP administration significantly prevented alcohol-induced increases in TUNEL-positive cells in primordium cingulate cortex and basal ganglia eminence. The investigation of downstream signaling pathways involving NAP neuroprotection revealed that this peptide significantly prevented alcohol-induced increase in the concentrations of caspase-3 in E13 fetal brains. Moreover, ELISA for cytochrome c shows that NAP significantly prevented both alcohol-induced increases in the level of cytosolic cytochrome c and alcohol-induced decreases in the level of mitochondrial cytochrome c. These data provide an understanding of NAP intracellular target, and the downstream mechanisms of action that will pave a path toward potential therapeutics against alcohol intoxication during prenatal stages.

Glutathione content as a potential mediator of the vulnerability of cultured fetal cortical neurons to ethanol-induced apoptosis

Ethanol ingestion during pregnancy elicits damage to the developing brain, some of which appears to result from enhanced apoptotic death of neurons. A consistent characteristic of this phenomenon is a highly differing sensitivity to ethanol within specific neuron populations. One possible explanation for this "selective vulnerability" could be cellular variations in glutathione (GSH) homeostasis. Prior studies have illustrated that ethanol elicits apoptotic death of neurons in the developing brain, that oxidative stress may be an underlying mechanism, and that GSH can be neuroprotective. In the present study, both multiphoton microscopy and flow cytometry demonstrate a striking heterogeneity in GSH content within cortical neuron populations. Ethanol differentially elicits apoptotic death and oxidative stress in these neurons. When neuron GSH content is reduced by treatment with butathione sulfoxamine, the ethanol-mediated enhancement of reactive oxygen species is exacerbated. Sorting of cells into high- and low-GSH populations further exemplifies ethanol-mediated oxidative stress whereby apoptotic indices are preferentially elevated in the low-GSH population. Western blot analysis of the low-GSH subpopulations shows higher ethanol-mediated expression of active caspase 3 and 24-kDa PARP-1 fragments compared with the high-GSH subpopulation. In addition, neuronal content of 4-hydroxynonenal adducts is higher in low-GSH neurons in response to ethanol. These studies suggest that GSH content is an important predictor of neuronal sensitivity to ethanol-mediated oxidative stress and subsequent cell death. The data support the proposition that the differences in proapoptotic responses to ethanol within specific neuron populations reflect a heterogeneity of neuron GSH content.

Genetic influence on dysmorphogenesis in embryos from different rat strains exposed to ethanol in vivo and in vitro

BACKGROUND

The aim was to investigate the susceptibility of embryos from 2 rat strains (U and H) to a 48 hours ethanol exposure in early pregnancy, both in vivo and in vitro.

METHODS

The embryos were studied on gestational days 9 to 11. We used 1 ethanol dose in vivo (6 g/kg x 2), 3 different ethanol concentrations in vitro (88 mM, 132 mM, 176 mM) and also attempted to diminish the teratogenic effect in vitro by supplying the antioxidant N-acetylcysteine (NAC, 0.5 mM) to the culture medium.

RESULTS

The U embryos were more damaged by ethanol than the H embryos, both in vivo and in vitro. NAC addition diminished, but failed to completely normalize, the embryonic maldevelopment. Ethanol increased the Bax/Bcl-2 ratio in the U embryos both in vivo and in vitro, but not in the H embryos. Furthermore, ethanol caused increased Caspase-3 immunostaining in U embryos, but not in H embryos. Ethanol exposure in vivo did not alter CuZnSOD and MnSOD mRNA levels in U and H embryos. In vitro, however, the ethanol-exposed U embryos increased their CuZnSOD and MnSOD mRNA levels, whereas the CuZnSOD mRNA was unchanged and MnSOD mRNA decreased in the H embryos, in neither strain did NAC exert any effect. The U embryos increased catalase gene expression in response to ethanol in vivo, but decreased catalase mRNA levels in vitro, changes normalized by NAC. The H embryos did not alter catalase mRNA levels in vivo, but increased gene expression in vitro, with no NAC effect. Ethanol affected the gene expression of the other ROS scavenging enzymes and the developmental genes studied - Bmp-4, Ret, Shh, Pax-6 - similarly in the 2 strains.

CONCLUSIONS

The findings support a role for genetic predisposition, oxidative stress, and apoptosis in ethanol teratogenicity, and suggest that the teratogenic predisposition of the more susceptible U rats may reside, at least in part, in the regulation of the ROS scavenging enzymes in the U embryos.

Embryonic cerebral cortical progenitors are resistant to apoptosis, but increase expression of suicide receptor DISC-complex genes and suppress autophagy following ethanol exposure

BACKGROUND

In utero exposure to ethanol can result in severe fetal brain defects. Previous studies showed that ethanol induces apoptosis in differentiated cortical neurons. However, we know little about ethanol's effects on proliferating embryonic cortical progenitors. This study investigated the impact of ethanol exposure on the Fas/Apo-1/CD95 suicide receptor pathway, and on the survival of proliferating cortical neuroepithelial progenitors.

METHODS

Murine embryonic-derived primary cortical neuroepithelial cells were maintained as neurosphere cultures and exposed to a dose range of ethanol for periods ranging from 1 to 5 days. Programmed cell death was measured by 4 independent means (Annexin-V staining, caspase activation, DNA fragmentation, and autophagic vacuole formation). Surface Fas/Apo-1 suicide receptor expression was measured by flow cytometry. Expression of Fas/Apo-1-associated DISC-complex genes was measured by quantitative polymerase chain reaction.

RESULTS

Ethanol exposure did not substantially increase apoptosis, necrosis, or surface Fas/Apo-1 expression. Moreover, ethanol significantly decreased caspase activation and autophagic activity. Finally, ethanol exposure induced mRNA expression of genes that constitute the death receptor complex.

CONCLUSIONS

This study provides surprising evidence that ethanol does not induce either programmed cell death or necrosis of immature progenitors during neurogenesis, although ethanol may render neural progenitors susceptible to future apoptotic insults. Furthermore, our novel observation that ethanol suppresses autophagy is consistent with a hypothesis that ethanol promotes premature neural progenitor maturation. Taken together with our previous data regarding the role of the Fas/Apo-1 receptor in neural development, we conclude that ethanol disrupts basic proliferation and differentiation machinery rather than initiating cell death per se.

Effects of Acute Ethanol Exposure on Regulatory Mechanisms of Bcl-2-Associated Apoptosis Promoter, Bad, in Neonatal Rat Cerebellum: Differential Effects During Vulnerable and Resistant Developmental Periods

BACKGROUND

Prenatal alcohol exposure produces anatomical and behavioral abnormalities associated with fetal alcohol syndrome (FAS). Animal FAS models have demonstrated temporal windows of vulnerability in the developing cerebellum, with substantial ethanol (EtOH)-mediated apoptotic activation during these periods. In rodents, the cerebellum is most sensitive to EtOH on postnatal days 4 to 6 (P4 to P6). At slightly later ages (P7 and later), this region is less vulnerable to EtOH. The present study investigated EtOH effects on mechanisms related to activities of Bad, a proapoptotic member of the Bcl-2 gene family, to further characterize processes underlying these disparate EtOH sensitivities. In healthy cells, Bad is retained in the cytosol by association with 14-3-3, a primarily cytosolic protein. Bad promotes apoptosis by disassociating from 14-3-3 and sequestering Bcl-xL through heterodimerization. This dimerization prevents the neutralizing association of Bcl-xL with Bax, freeing Bax to perform in a prodeath manner. Caspase-dependent cleavage of Bad to a 15-kDa fragment increases its proapoptogenic capacity.

METHODS

Two hours following EtOH exposure of P4 and P7 animals via inhalation, we determined how exposure affects intracellular localization and proteolytic cleavage of Bad and expression of cerebellar 14-3-3, using subcellular fractionation and Western blot techniques. Ethanol effects on interactions between Bad and 14-3-3 or Bcl-xL at the more vulnerable and less vulnerable ages were determined using an enzyme-linked immunosorbent assay-based technique to detect native protein-protein interactions.

RESULTS

At P4, EtOH increased mitochondrial localization of Bad, expression of a 15-kDa fragment recognized by Bad antibody, and formation of Bad:Bcl-xL complexes. At that more vulnerable age, EtOH also decreased formation of Bad:14-3-3 complexes. At P7, EtOH increased Bad:14-3-3 complexes and reduced Bad:Bcl-xL complexes. Cytosolic 14-3-3 remained unchanged by EtOH at P4 and P7.

CONCLUSIONS

Ethanol-induced alterations of Bad-related mechanisms at P4 favor a prodeath response. EtOH does not influence these same mechanisms in a manner that promotes cell death at P7. Divergent Bad-related responses at these 2 developmental ages likely contribute to their differential EtOH vulnerability.

Alcohol and mitochondria in cardiac apoptosis: mechanisms and visualization

Apoptosis of myocytes is likely to contribute to a variety of heart conditions and could also be important in the development of alcoholic heart disease. A fundamental pathway to apoptosis is through mitochondrial membrane permeabilization and release of proapoptotic factors from the mitochondrial intermembrane space to the cytosol. The authors' results show that prolonged exposure of cultured cardiac cells to ethanol (35 mM for 48 hr) promotes Ca2+-induced activation of the mitochondrial permeability transition pore (PTP). PTP-dependent mitochondrial membrane permeabilization is followed by release of cytochrome c and execution of apoptosis. The authors propose that chronic ethanol exposure, in combination with other stress signals, may allow for activation of the PTP by physiological calcium oscillations, providing a trigger for cardiac apoptosis during chronic alcohol abuse. Coincidence of apoptosis promoting factors occurs in only a small fraction of myocytes, but because of the absence of regeneration, even a modest increase in the rate of cell death may contribute to a decrease in cardiac contractility. Detection of apoptotic changes that are present in only a few myocytes at a certain time in the heart is not feasible with most of the apoptotic assays. Fluorescence imaging is a powerful technology to visualize changes that are confined to a minor fraction of cells in a tissue, and the use of multiphoton excitation permits imaging in situ deep in the wall of the intact heart. This article discusses potential mechanisms of the effect of alcohol on mitochondrial membrane permeabilization and visualization of mitochondria-dependent apoptosis in cardiac muscle.

Functional mechanisms of apoptosis-related proteins in neonatal rat cerebellum are differentially influenced by ethanol at postnatal days 4 and 7

Exposure of the developing nervous system to ethanol (EtOH) produces neurological aberrations associated with fetal alcohol syndrome. During a well-defined period, cerebellar neurons are highly susceptible to EtOH-induced death, primarily through apoptosis. Neonatal rodent cerebellum is exquisitely sensitive to EtOH on postnatal days 4-6 (P4-6); however, at slightly later developmental ages (P7 and later), EtOH effects are minimal. We have previously shown that EtOH differentially influences expression of apoptosis-related proteins of the Bcl-2 survival-regulatory gene family in P4 and P7 cerebellum. In the present study, the effects of EtOH on multiple functional mechanisms of Bcl-2, Bcl-xL, and Bax were investigated to characterize further the processes underlying these disparate EtOH sensitivities. For these analyses, we addressed the following questions, by using P4 and P7 cerebellar tissue following in vivo exposure: 1) Are there differential patterns of expression of antiapoptotic Bcl-2 or proapoptotic Bax in EtOH-vulnerable Purkinje cells that could contribute to the different degrees of temporal EtOH vulnerability? 2) How does EtOH affect intracellular localization of apoptosis-related proteins? 3) Does cleavage of Bax contribute to EtOH sensitivity? 4) Does EtOH differentially modulate cerebellar protein-protein interactions of Bcl-2, Bcl-xL, and Bax at the vulnerable vs. the resistant ages? Overall, we show that, at P4, the EtOH-mediated effects on Bcl-2, Bcl-xL, and Bax favor a prodeath response, whereas most of the intracellular responses to EtOH exposure at P7 promote survival. Such differential responsiveness likely plays a major role in the disparate ethanol vulnerability at these two postnatal ages.

Effect ofbax deletion on ethanol sensitivity in the neonatal rat cerebellum

The developing cerebellum is highly sensitive to ethanol during discrete neonatal periods. This sensitivity has been linked to ethanol-induced alterations in molecules of the Bcl-2 survival-regulatory gene family. Ethanol exposure during peak periods of cerebellar sensitivity, for example, results in increased expression of proapoptotic proteins of this family, while overexpression of the antiapoptotic Bcl-2 protein in the nervous system protects against ethanol neurotoxicity. For the present study, neonatal mice with a targeted deletion of the proapoptotic bax gene were used to determine whether elimination of this protein would mitigate ethanol toxicity. bax knock-out and wild-type mice pups were exposed to ethanol via vapor inhalation during the maximal period of neonatal cerebellar ethanol sensitivity and cerebellar tissue was subsequently assessed for Purkinje and granule cell number and ethanol-mediated generation of reactive oxygen species (ROS). The results revealed that: (1) ethanol exposure during the peak period of cerebellar vulnerability resulted in substantial loss of Purkinje cells in wild-type animals, but not in bax knock-outs; (2) granule cells in the bax gene-deleted animals were not similarly protected from ethanol effects; and (3) levels of ROS following acute ethanol exposure were appreciably enhanced in the wild-type animals but not in the bax knock-outs. These results imply that Bax is important to ethanol-induced Purkinje cell death during critical neonatal periods, but that ethanol effects on granule cells may function at least partially independent of this apoptosis agonist. Amelioration of ethanol-mediated increases in ROS production in the knock-outs may contribute to the observed effects.

Alcohol and gene expression in the central nervous system

AIMS

To describe recent research focusing on the analysis of gene and protein expression relevant to understanding ethanol consumption, dependence and effects, in order to identify common themes.

METHODS

A selective literature search was used to collate the relevant data.

RESULTS

Over 160 genes have been individually assessed before or after ethanol administration, as well as in genetically selected lines. Techniques for studying gene expression include northern blots, differential display, real time reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. More recently, high throughput functional genomic technology, such as DNA microarrays, has been used to examine gene expression. Recent gene expression analyses have dramatically increased the number of candidate genes (nine array papers have illuminated 600 novel gene transcripts that may contribute to alcohol abuse and alcoholism).

CONCLUSIONS

Although functional genomic experiments (transcriptome analysis) have failed to identify a single alcoholism gene, they have illuminated important pathways and gene products that may contribute to the risk of alcohol abuse and alcoholism.

Altered expression of Bcl2, Bad and Bax mRNA occurs in the rat cerebellum within hours after ethanol exposure on postnatal day 4 but not on postnatal day 9

Previous studies have demonstrated that ethanol exposure during the vulnerable postnatal (PN) day 4-6 period results in a dose-dependent loss of Purkinje neurons in rats by apoptosis. Although the mechanism of ethanol action and the reasons for Purkinje cell vulnerability are unknown, we hypothesize that during the PN4-6 vulnerable period Purkinje cells are dependent on active trophic factor suppression of apoptosis. Furthermore, ethanol acts to prevent the reception of this trophic signaling resulting in the execution of the apoptotic pathway that includes specific alterations of proteins in the Bcl2 gene family. Ethanol exposure that occurs after this vulnerable period (i.e. PN9) would not be expected to demonstrate alterations in these apoptotic proteins since the Purkinje cells no longer demonstrate vulnerability to ethanol. The current study was undertaken to identify the alterations in mRNA expression for members of the Bcl2-family within the initial hours following ethanol administration on PN4 or PN9. Semi-quantitative reverse transcriptase with polymerase chain reaction (PCR) techniques were used to determine the expression levels of pro-apoptotic factors Bad and Bax, and anti-apoptotic Bcl(2) mRNA. Ethanol was administered at four different doses (1.5, 3.0, 4.5, and 6.0 g/kg) on PN4 and analyses of whole cerebellar mRNA was conducted at 1, 4, 6, and 8 h after treatment. Doses greater than 1.5 g/kg produced significant decreases in Bcl(2) and significant increases in Bad and Bax mRNA during the 8-h period after treatment. In stark contrast, when ethanol was administered at 3.0 or 6.0 g/kg to PN9 pups, no significant alterations of these apoptotic factors were identified at either 1 or 4 h after treatment. These results are in agreement with and provide further support for our hypothesis that ethanol interrupts the active suppression of apoptosis that is a crucial feature of Purkinje cell vulnerability during this time period.

Ethanol exposure alters neurotrophin receptor expression in the rat central nervous system: Effects of neonatal exposure

The detrimental effects of ethanol exposure during nervous system development have been well established. The cellular mechanisms of ethanol neurotoxicity, however, have not been clearly defined. Recent studies suggest that neurotrophin signaling pathways may be involved in ethanol-mediated neuronal death. The present investigation, therefore, was designed to examine ethanol-induced alterations in neurotrophin receptor protein levels in the developing central nervous system (CNS) following chronic ethanol treatment administered during the early neonatal period. For this study, rats were exposed to ethanol via vapor inhalation from postnatal day 4 (P4) to P10. Brains were then dissected on P10 or P21, and Western blots used to quantify expression of neurotrophin receptors TrkA, TrkB, TrkC, and p75. This early postnatal ethanol treatment produced significant alterations in receptor levels in hippocampus, septum, cerebral cortex, and cerebellum. The alterations seen were variable, with decreases generally found in hippocampus and cerebellum, increases noted in septum, and changes in both directions occurring in cortex. These alterations were generally more prevalent in males than in females. While most of the receptor changes observed were transient, sustained or delayed alterations were occasionally seen in hippocampus, cortex, and cerebellum. These results suggest that developmental ethanol exposure modulates expression of these neurotrophin receptors throughout the CNS, alterations which could have wide-ranging effects on functional CNS development. The possible linkage between such changes and abnormalities encountered in the fetal alcohol syndrome are considered.

Vitamin E amelioration of ethanol neurotoxicity involves modulation of apoptotis-related protein levels in neonatal rat cerebellar granule cells

Developmental ethanol exposure leads to a variety of abnormalities in the central nervous system (CNS). Mechanisms proposed as underlying these effects include alterations of protective antioxidant support, increased generation of harmful free radicals, and altered expression of apoptosis-related proteins. In prior studies, exogenous antioxidant application has been found to reduce ethanol neurotoxicity, but the mechanisms by which this protection is afforded have not been defined. This study was designed to investigate the interactions between ethanol and the antioxidant vitamin E (alpha-tocopherol), with respect to neuronal survival and levels of proteins related to the Bcl-2 survival-regulatory gene family. Neonatal rat cerebellar granule cell cultures were used as a model system. It was found that ethanol significantly impaired neuronal survival in these preparations, and that survival in the presence of ethanol was enhanced by inclusion of vitamin E in the culture medium. This elevated survival was paralleled by increased levels of anti-apoptotic proteins (e.g., Bcl-2, Bcl-xl, activated Akt kinase), and concurrent downregulation of pro-apoptotic proteins (e.g., Bcl-xs). These results suggest that such alterations may represent an important mechanism whereby antioxidants protect against the neurotoxic effects of ethanol in the developing CNS. The possible manner by which these changes are effected are considered.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Ethanol exposure alters neurotrophin receptor expression in the rat central nervous system: Effects of prenatal exposure

Developmental ethanol exposure produces significant central nervous system (CNS) abnormalities. The cellular mechanisms of ethanol neurotoxicity, however, remain elusive. Recent data implicate altered neurotrophin signaling pathways in ethanol-mediated neuronal death. The present study investigated ethanol-induced alterations in neurotrophin receptor proteins in the rat CNS following chronic ethanol treatment during gestation, via liquid diet to pregnant dams. Brains were dissected on P1 and P10, and Western blots for the neurotrophin receptors TrkA, TrkB, TrkC, and p75 were quantified. Such ethanol treatment produced significant changes in neurotrophin receptor levels in the hippocampus, septum, cerebral cortex, and cerebellum. Receptor levels in hippocampus, septum, and cerebellum, tended to be decreased, while levels in cortex were consistently increased. Males were generally more affected than females. While most of these alterations were transient, sustained or delayed changes were present in P10 septum, cortex, and cerebellum. These results indicate that developmental ethanol exposure produces major changes in the normal physiological levels of the neurotrophin receptors throughout the CNS. These changes in the receptor complement during critical prenatal stages could relate to the anomalous development of the CNS seen in the fetal alcohol syndrome. This relationship is discussed, together with the potential biological effects of such dramatic changes in neurotrophin receptor expression.

Ethanol-induced oxidative stress precedes mitochondrially mediated apoptotic death of cultured fetal cortical neurons

In utero ethanol exposure elicits apoptotic cell death in the fetal brain, and this may be mediated by oxidative stress. Our studies utilize cultured fetal rat cortical neurons and illustrate that ethanol elicits a rapid onset of oxidative stress, which culminates in mitochondrially mediated apoptotic cell death. Cells exposed to ethanol (2.5 mg/ml) remained attached to their polylysine matrix during a 24-hr exposure, but they exhibited distinct signs of oxidative stress, decreased viability, and apoptosis. Confocal microscopy of live cortical neurons pretreated with dichlorodihydrofluorescein diacetate demonstrated an increase in reactive oxygen species (ROS) within 5 min of ethanol exposure. The levels of ROS further increased by 58% within 1 hr (P <.05) and by 82% within 2 hr (P <.05), accompanied by increases of mitochondrial 4-hydroxynonenal (HNE). These early events were followed by decreased trypan blue exclusion of 10% to 32% (P <.05) at the 6- to 24-hr time points, respectively. This culminates in apoptotic death, with increases of Annexin V binding of 43%, 89%, 123%, and 238%, at 2, 6, 12, and 24 hr of ethanol treatment, respectively, as well as DNA fragmentation increases of 50% and 65% by 12 and 24 hr, respectively. Release of cytochrome c by mitochondria increased by 53% at 6 hr of exposure (P <.05), concomitant with activation of caspase 3 (52% at 12 hr, P <.05). Pretreatment with N-acetylcysteine increased cellular glutathione and prevented apoptosis. These studies provide a time line illustrating that oxidative stress and formation of a proapoptotic lipid peroxidation product, HNE, precede a cascade of mitochondrially mediated events in cultured fetal cortical neurons, culminating in apoptotic death. The prevention of apoptosis by augmentation of glutathione stores also strongly supports a role for oxidative stress in ethanol-mediated apoptotic death of fetal cortical neurons.

Identity and neuroanatomical localization of messenger RNAs that change expression in the neural tube of mouse embryos within 1 h after ethanol exposure

Changes in the expression of various species of messenger RNA (mRNA) are likely to be one of the initial responses of an embryo to in utero ethanol exposure. However, the identity and range of the initial species of mRNAs that change expression in an embryo after acute prenatal ethanol exposure are unknown. mRNA was isolated from embryos treated on embryonic day 9.5 and examined 1 h after treatment. Ethanol-exposed embryos were compared to similarly treated maltose/dextrin and no injection control embryos. Subtractive hybridization was used to find the species of mRNAs. The identity of the differentially expressed mRNAs was ascertained using standard sequencing techniques while in situ hybridization defined the anatomical localization of each message. Four messages from ethanol-treated embryos were differentially expressed. One message has no homology to any known gene in GenBank while three messages are homologous to known genes: the transmembrane molecule mh19, the heterologous ribonuclear protein hnRNP A3, and the mitochondrial enzyme AK2. One message (the novel gene) was turned on, while mh19, AK2 and hnRNP A3 were up-regulated in ethanol-exposed embryos. All messages were expressed in the developing neural tube of the ethanol-exposed embryos, although there were differences in regional localization and extent of expression. Thus, the initial response of the embryo is rapid with changes in expression of multiple genes observed within 1 h after ethanol exposure. Further, these differentially expressed mRNAs are candidates for modulating the type and extent of ethanol-induced damage in the developing CNS.

Effects of ethanol on neurotrophic factors, apoptosis-related proteins, endogenous antioxidants, and reactive oxygen species in neonatal striatum: relationship to periods of vulnerability

The developing central nervous system is extremely sensitive to ethanol, with well-defined temporal periods of vulnerability. Many brain regions are particularly susceptible to ethanol during the early neonatal period, corresponding to the human third trimester, which represents a dynamic period of growth and differentiation. For this study, neonatal rats were acutely exposed to ethanol or control conditions at a neonatal age when the developing striatum has been shown to be vulnerable to ethanol (postnatal day 3 [P3]), and at a later age (P14), when this developing region is relatively ethanol-resistant. We then analyzed basal levels of neurotrophic factors (NTFs), and ethanol-mediated changes in NTFs, apoptosis-related proteins, antioxidants, and reactive oxygen species (ROS) generation, which may underlie this differential temporal vulnerability. Sequential analyses were made following ethanol exposure on these two postnatal days, with assessments of NTFs nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4); apoptosis-related proteins Bcl-2, Bcl-xl, Bax, Akt and c-jun N-terminal kinase (JNK); antioxidants superoxide dismutase, glutathione reductase and catalase; and ROS. The results indicated that basal levels of BDNF, and to some degree NGF, were greater at the older age, and that ethanol exposure at the earlier age elicited considerably more pro-apoptotic and fewer pro-survival changes than those produced at the later age. Thus, differential temporal vulnerability to ethanol in this CNS region appears to be related to differences in both differential levels of protective substances (e.g. NTFs), and differential cellular responsiveness which favors apoptosis at the most sensitive age and survival at the resistant age.

Time course and manner of Purkinje neuron death following a single ethanol exposure on postnatal day 4 in the developing rat

The present study was designed to evaluate the time course and manner of Purkinje cell death following a single ethanol dose delivered intragastrically on postnatal day (PN) 4 to rat pups. Analysis included immunolabeling of Purkinje cells with antibody specific for calbindin D28k and counting of Purkinje cells in each lobule of a mid-vermal slice. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis and immunodetection for cleaved (activated) caspase-3 enzyme was used to identify apoptosis, with calbindin D28k co-immunolabeling to identify apoptotic Purkinje cells. Finally, immunodetection for cytochrome c, again with co-labeling using calbindin D28k antibody, identified intracellular release of cytochrome c from the mitochondria into the cytoplasm of Purkinje cells. The data demonstrate that a single dose of ethanol results in a significant and extensive, lobular dependent loss of Purkinje cells within 24 h after administration. Extensive loss in the early developing lobules (I-III, VIII-X) and less to no loss in the later developing lobules (IV-VII) is consistent with prior literature reports on the ethanol-induced effects on Purkinje cells at this age. Clear and consistent evidence of apoptotic Purkinje cells was identified and the pattern was transient in nature. Finally, cytochrome c is released from the mitochondria of Purkinje cells in a time course consistent with the activation of the mitochondrial pathway of apoptosis. These data support the hypothesis that ethanol-induced loss of Purkinje cells involves apoptotic mechanisms. Furthermore, the initiation of apoptosis by ethanol is consistent with ethanol-induced interruptions of Purkinje cell neurotrophic support leading to activation of the mitochondrial pathway of apoptosis.

Influence of ethanol on neonatal cerebellum of BDNF gene-deleted animals: analyses of effects on Purkinje cells, apoptosis-related proteins, and endogenous antioxidants

The sensitivity of the developing central nervous system (CNS) to the deleterious effects of ethanol has been well documented, with exposure leading to a wide array of CNS abnormalities. Certain CNS regions are susceptible to ethanol during well-defined critical periods. In the neonatal rodent cerebellum, a profound loss of Purkinje cells is found when ethanol is administered early in the postnatal period [on postnatal days 4 or 5 (P4-5)], while this neuronal population is much less vulnerable to similar ethanol insult slightly later in the postnatal period (P7-9). Prior studies have shown that neurotrophic factors (NTFs) can be altered by ethanol exposure, and both in vitro and in vivo studies have provided evidence that such substances have the potential to protect against ethanol neurotoxicity. In the present study, it was hypothesized that depletion of an NTF shown to be important to cerebellar development would exacerbate ethanol-related effects within this region, when administration was confined to a normally ethanol-resistant ontogenetic period. For this study, brain-derived neurotrophic factor (BDNF) gene-deleted ("knockout") and wild-type mice were exposed to ethanol via vapor inhalation or to control conditions during the normally ethanol-resistant period (P7 and P8). Two hours after termination of exposure on P8, analyses were made of body weight, crown-rump length, and brain weight. In subsequent investigations, the number and density of Purkinje cells and the volume of cerebellar lobule I were determined, and the expression of anti- and pro-apoptotic proteins and the activities of endogenous antioxidants were assessed. It was found that the BDNF knockouts were significantly smaller than the wild-type animals, with smaller brain weights. Purkinje cell number and density was reduced in ethanol-treated knockout, but not wild-type animals, and the volume of lobule I was significantly decreased in the gene-deleted animals compared to wild-types, but was not further affected by ethanol treatment. The loss of Purkinje cells in the BDNF knockouts was accompanied by decreases in anti-apoptotic Bcl-xl and in phosphorylated (and hence inactivated) pro-apoptotic Bad, and reduced activity of the antioxidant glutathione reductase, while the antioxidant catalase was increased by ethanol treatment in this genotype. In the wild-type animals, anti-apoptotic Bcl-2 was decreased by ethanol treatment, but the pro-apoptotic c-Jun N-terminal kinase (JNK) was markedly diminished by ethanol exposure, while the activity of the protective antioxidant superoxide dismutase (SOD) was significantly enhanced. These results suggest that neurotrophic factors have the capacity to protect against ethanol neurotoxicity, perhaps by regulation of expression of molecules critical to neuronal survival such as elements of the apoptosis cascade and protective antioxidants.

Developmental instability of the cerebellum and its relevance to Down syndrome

It has been recognized for many years that cerebellar abnormalities are frequently observed in association with Down syndrome (DS). An important question to be asked about these and other findings in DS is whether their occurrence (i) is attributable to specific loci on the triplicated chromosome or chromosomal segment or (ii) derives from exaggerated responses secondary to the genetic imbalance resulting from trisomy (Ts). Recently, similar cerebellar alterations were observed in subjects with DS and in Ts65Dn mice (Baxter et al., 2000), mice segmentally trisomic for a portion of chromosome 16, which is homologous for loci on the long arm of human chromosome 21. It was concluded by these authors that the occurrence of similar cerebellar changes in DS and in the DS mouse model resulted from triplication of these homologous loci in the two trisomic organisms, i.e. cerebellar development is affected similarly by homologous loci in each species. They wrote that their study of Ts65Dn mice "correctly predicts an analagous pathology in humans". . . and that. . . "The candidate region of genes on chromosome 21 affecting cerebellar development in DS is therefore delimited to the subset of genes whose orthologs are at dosage imbalance in Ts65Dn mice, providing the first localization of genes affecting a neuroanatomical phenotype in DS." Findings described in this review suggest otherwise--that cerebellar findings in DS and in the Ts65Dn mouse are a result of exaggerated vulnerability in general of the cerebellum to disturbing events and that liability to expression of response(s) is exacerbated by trisomy. This conclusion is based on the following: (i) the cerebellum has an extended postnatal development; (ii) numerous genetic, environmental, epigenetic and metabolic conditions express cerebellar changes similar to those observed in Down syndrome; (iii) most if not all chromosomal imbalance syndromes express similar cerebellar abnormalities; (iv) the cerebellum is particularly sensitive to diverse toxic agents which may act prenatally, postnatally and/or in the mature organism; and (v) cerebellar abnormalities similar to those found in Ts65Dn mice have been described in Ts19 mice which have no segments homologous to any segment of human chromosome 21. An unavoidable conclusion from the review is that triplication of specific loci on 21q is an unlikely explanation for the cerebellar findings in DS. A simple positive control, in which the effect of triplication of loci other than those in question on a specific phenotype, should be used in experiments comparing human and experimental trisomies. As pointed out many years ago by Lorke and his coworkers (Lorke et al., 1989; Lorke, 1994; Lorke and Albrecht, 1994) similar phenotypic findings in the presence of different trisomies in the same species would suggest that the trisomic state itself rather than the gene content of a particular trisomy is responsible for the genesis of traits at issue.

Effect of neonatal ethanol exposure on parvalbumin-expressing GABAergic neurons of the rat medial septum and cingulate cortex

This study was performed to determine the long-term effects of ethanol exposure during the brain growth spurt (postnatal days 4-10) on the number of parvalbumin-immunoreactive (PA+) GABAergic neurons in the adult (P60) rat medial septum and anterior cingulate cortex. Significant loss of neurons within each of these populations has previously been demonstrated following prenatal ethanol exposure. In the present study, no significant differences in the number of PA+ neurons were found in either the medial septum or the cingulate cortex when control and ethanol-exposed animals were compared. The cellular densities and volumetric measures in both brain regions were also similar in the two groups. We speculate that compensatory up-regulative mechanisms may have accounted for the protection of the PA neuronal populations in these two areas following the early neonatal exposure.