Ethanol-induced death of postnatal hippocampal neurons

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Blood vessel remodeling in the cerebral cortex induced by binge alcohol intake in mice

Ethanol is toxic to the brain and causes various neurological disorders. Although ethanol can directly exert toxicity on neurons, it also acts on other cell types in the central nervous system. Blood vessel endothelial cells interact with, and are affected by blood ethanol. However, the effects of ethanol on the vascular structures of the brain have not been well documented. In this study, we examined the effects of binge levels of ethanol on brain vasculature. Immunostaining analysis indicated structural alterations of blood vessels in the cerebral cortex, which became more tortuous than those in the control mice after ethanol administration. The interaction between the blood vessels and astrocytes decreased, especially in the upper layers of the cerebral cortex. Messenger RNA expression analysis revealed a unique downregulation of Vegfa mRNA encoding vascular endothelial growth factor (VEGF)-A among VEGF, angiopoietin, endothelin family angiogenic and blood vessel remodeling factors. The expression of three proteoglycan core proteins, glypican-5, neurocan, and serglycin, was also altered after ethanol administration. Thus, binge levels of ethanol affect the expression of VEGF-A and blood vessel-supporting proteoglycans, resulting in changes in the vascular structure of the cerebral cortex.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00164-y.

Blood Vessels as a Key Mediator for Ethanol Toxicity: Implication for Neuronal Damage

Excessive intake of ethanol is associated with severe brain dysfunction, and the subsequent neurological and behavioral abnormalities are well-established social risks. Many research studies have addressed how ethanol induces neurological toxicity. However, the underlying mechanisms with which ethanol induces neurological toxicity are still obscure, perhaps due to the variety and complexity of these mechanisms. Epithelial cells are in direct contact with blood and can thus mediate ethanol neurotoxicity. Ethanol activates the endothelial cells of blood vessels, as well as lymphatic vessels, in a concentration-dependent manner. Among various signaling mediators, nitric oxide plays important roles in response to ethanol. Endothelial and inducible nitric oxide synthases (eNOS and iNOS) are upregulated and activated by ethanol and enhance neuroinflammation. On the other hand, angiogenesis and blood vessel remodeling are both affected by ethanol intake, altering blood supply and releasing angiocrine factors to regulate neuronal functions. Thus, ethanol directly acts on endothelial cells, yet the molecular target(s) on endothelial cells remain unknown. Previous studies on neurons and glial cells have validated the potential contribution of membrane lipids and some specific proteins as ethanol targets, which may also be the case in endothelial cells. Future studies, based on current knowledge, will allow for a greater understanding of the contribution and underlying mechanisms of endothelial cells in ethanol-induced neurological toxicity, protecting neurological health against ethanol toxicity.

Metformin relieves neuropathic pain after spinal nerve ligation via autophagy flux stimulation

Neuropathic pain is a well‐known type of chronic pain caused by damage to the nervous system. Autophagy is involved in the development and/or progression of many diseases, including neuropathic pain. Emerging evidence suggests that metformin relieves neuropathic pain in several neuropathic pain models; however, metformin's cellular and molecular mechanism for pain relief remains unknown. In this study, we investigated the therapeutic effects of metformin on pain relief after spinal nerve ligation (SNL) and its underlying mechanism of autophagy regulation. Behavioural analysis, histological assessment, expression of c‐Fos and molecular biological changes, as well as ultrastructural features, were investigated. Our findings showed that the number of autophagosomes and expression of autophagy markers, such as LC3 and beclin1, were increased, while the autophagy substrate protein p62, as well as the ubiquitinated proteins, were accumulated in the ipsilateral spinal cord. However, metformin enhanced the expression of autophagy markers, while it abrogated the abundance of p62 and ubiquitinated proteins. Blockage of autophagy flux by chloroquine partially abolished the apoptosis inhibition and analgesic effects of metformin on SNL. Taken together, these results illustrated that metformin relieved neuropathic pain through autophagy flux stimulation and provided a new direction for metformin drug development to treat neuropathic pain.

Turnover of histones and histone variants in postnatal rat brain: effects of alcohol exposure

BACKGROUND

Alcohol consumption during pregnancy is a significant public health problem and can result in a continuum of adverse outcomes to the fetus known as fetal alcohol spectrum disorders (FASD). Subjects with FASD show significant neurological deficits, ranging from microencephaly, neurobehavioral, and mental health problems to poor social adjustment and stress tolerance. Neurons are particularly sensitive to alcohol exposure. The neurotoxic action of alcohol, i.e., through ROS production, induces DNA damage and neuronal cell death by apoptosis. In addition, epigenetics, including DNA methylation, histone posttranslational modifications (PTMs), and non-coding RNA, play an important role in the neuropathology of FASD. However, little is known about the temporal dynamics and kinetics of histones and their PTMs in FASD.

RESULTS

We examined the effects of postnatal alcohol exposure (PAE), an animal model of human third-trimester equivalent, on the kinetics of various histone proteins in two distinct brain regions, the frontal cortex, and the hypothalamus, using in vivo ²H₂O-labeling combined with mass spectrometry-based proteomics. We show that histones have long half-lives that are in the order of days. We also show that H3.3 and H2Az histone variants have faster turnovers than canonical histones and that acetylated histones, in general, have a faster turnover than unmodified and methylated histones. Our work is the first to show that PAE induces a differential reduction in turnover rates of histones in both brain regions studied. These alterations in histone turnover were associated with increased DNA damage and decreased cell proliferation in postnatal rat brain.

CONCLUSION

Alterations in histone turnover might interfere with histone deposition and chromatin stability, resulting in deregulated cell-specific gene expression and therefore contribute to the development of the neurological disorders associated with FASD. Using in vivo ²H₂O-labeling and mass spectrometry-based proteomics might help in the understanding of histone turnover following alcohol exposure and could be of great importance in enabling researchers to identify novel targets and/or biomarkers for the prevention and management of fetal alcohol spectrum disorders.

Mystic Acetaldehyde: The Never-Ending Story on Alcoholism

After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.

Lithium protects against glucocorticoid induced neural progenitor cell apoptosis in the developing cerebellum

Respiratory dysfunction is one of the most common causes of death associated with premature birth (Barton et al., 1999). In the United States, 7-10% of pregnant women receive antenatal glucocorticoid (GC) therapy (Matthews et al., 2004), while approximately 19% of very low birth weight infants receive postnatal GC therapy (Jobe, 2009). Clinical research suggests that GC treatment causes permanent neuromotor and cognitive deficits (Yeh et al., 2004) and stunts cerebellar growth (Parikh et al., 2007; Tam et al., 2011). We previously reported that GC-mediated neural progenitor cell (NPC) apoptosis may be responsible for cerebellar neuropathology (Maloney et al., 2011; Noguchi et al., 2008, 2011). The goal of the current study was to determine whether lithium protects NPCs from GC neuroapoptosis in vivo and in vitro. Given that it protects against a range of brain insults, we hypothesized that lithium would significantly attenuate GC induced NPC toxicity. We report that acute lithium pretreatment provides potent, cell-intrinsic neuroprotection against GC induced NPC toxicity in vivo and in vitro.

Effects of tetramethylpyrazine on neuronal apoptosis in the superficial dorsal horn in a rat model of neuropathic pain

The Bennett and Xie (1988) model of chronic constriction injury (CCI) investigated the effects of tetramethylpyrazine (TMP) on neuropathic pain-associated behaviors and neuronal apoptosis in the spinal dorsal horn. Fifty-four male rats were randomly divided into sham (group S), CCI (group C) and TMP groups (group T). Each group was divided into subgroups (n = 6 in each group) according the time of sacrifice: 3 d, 7 d and 14 d. Rat sciatic nerves were unligated (group S), or the right sciatic nerve was loosely ligated (groups C and T) to produce CCI. Mechanical withdrawal thresholds (MWTs) and thermal withdrawal latencies (TWLs) were measured, and the rats were sacrificed at different time points post-operation. The L4-L6 sections of the spinal cord were removed. Apoptotic changes were evaluated using the TUNEL method. Immunohistochemistry assessed Bcl-2 and caspase-3 expression. TMP treatment increased MWT and TWL values and Bcl-2 expression, but it reduced neuronal apoptosis and caspase-3 expression in laminae I-II of the spinal dorsal horn. These results suggested that the inhibition of neuronal apoptosis via the modulation of Bcl-2 and caspase-3 proteins in the rat spinal dorsal horn contributed to TMP-induced analgesia.

Neuroimmune mechanisms in fetal alcohol spectrum disorder

Fetal alcohol spectrum disorder (FASD) is a major health concern worldwide and results from maternal consumption of alcohol during pregnancy. It produces tremendous individual, social, and economic losses. This review will first summarize the structural, functional, and behavior changes seen in FASD. The development of the neuroimmune system will be then be described with particular emphasis on the role of microglial cells in the normal regulation of homeostatic function in the central nervous system (CNS) including synaptic transmission. The impact of alcohol on the neuroimmune system in the developing CNS will be discussed in the context of several key immune molecules and signaling pathways involved in neuroimmune mechanisms that contribute to FASD. This review concludes with a summary of the development of early therapeutic approaches utilizing immunosuppressive drugs to target alcohol-induced pathologies. The significant role played by neuroimmune mechanisms in alcohol addiction and pathology provides a focus for future research aimed at understanding and treating the consequences of FASD.

Overexpression of serum response factor in astrocytes improves neuronal plasticity in a model of early alcohol exposure

Neuronal plasticity deficits underlie many of the cognitive problems seen in fetal alcohol spectrum disorders (FASD). We have developed a ferret model showing that early alcohol exposure leads to a persistent disruption in ocular dominance (OD) plasticity. Recently, we showed that this deficit could be reversed by overexpression of serum response factor (SRF) in the primary visual cortex during the period of monocular deprivation (MD). Surprisingly, this restoration was observed throughout the extent of visual cortex and most of the cells transfected by the virus were positive for the astrocytic marker GFAP rather than the neuronal marker NeuN. Here we test whether overexpression of SRF exclusively in astrocytes is sufficient to restore OD plasticity in alcohol-exposed ferrets. To accomplish that, first we exposed cultured astrocytes to Sindbis viruses carrying either a constitutively active form of SRF (SRF+), a dominant negative (SRF-) or control Green Fluorescent Protein (GFP). After 24h, these astrocytes were implanted in the visual cortex of alcohol-exposed animals or saline controls one day before MD. Optical imaging of intrinsic signals showed that alcohol-exposed animals that were implanted with astrocytes expressing SRF, but not SRF- or GFP, showed robust restoration of OD plasticity in all visual cortex. These findings suggest that overexpression of SRF exclusively in astrocytes can improve neuronal plasticity in FASD.

Effects of early postnatal exposure to ethanol on retinal ganglion cell morphology and numbers of neurons in the dorsolateral geniculate in mice

BACKGROUND

The adverse effects of fetal and early postnatal ethanol intoxication on peripheral organs and the central nervous system are well documented. Ocular defects have also been reported in about 90% of children with fetal alcohol syndrome, including microphthalmia, loss of neurons in the retinal ganglion cell (RGC) layer, optic nerve hypoplasia, and dysmyelination. However, little is known about perinatal ethanol effects on retinal cell morphology. Examination of the potential toxic effects of alcohol on the neuron architecture is important because the changes in dendritic geometry and synapse distribution directly affect the organization and functions of neural circuits. Thus, in the present study, estimations of the numbers of neurons in the ganglion cell layer and dorsolateral geniculate nucleus (dLGN), and a detailed analysis of RGC morphology were carried out in transgenic mice exposed to ethanol during the early postnatal period.

METHODS

The study was carried out in male and female transgenic mice expressing yellow fluorescent protein (YFP) controlled by a Thy-1 (thymus cell antigen 1) regulator on a C57 background. Ethanol (3 g/kg/d) was administered to mouse pups by intragastric intubation throughout postnatal days (PDs) 3 to 20. Intubation control (IC) and untreated control (C) groups were included. Blood alcohol concentration was measured in separate groups of pups on PDs 3, 10, and 20 at 4 different time points, 1, 1.5, 2, and 3 hours after the second intubation. Numbers of neurons in the ganglion cell layer and in the dLGN were quantified on PD20 using unbiased stereological procedures. RGC morphology was imaged by confocal microscopy and analyzed using Neurolucida software.

RESULTS

Binge-like ethanol exposure in mice during the early postnatal period from PDs 3 to 20 altered RGC morphology and resulted in a significant decrease in the numbers of neurons in the ganglion cell layer and in the dLGN. In the alcohol exposure group, out of 13 morphological parameters examined in RGCs, soma area was significantly reduced and dendritic tortuosity significantly increased. After neonatal exposure to ethanol, a decrease in total dendritic field area and an increase in the mean branch angle were also observed. Interestingly, RGC dendrite elongation and a decrease in the spine density were observed in the IC group, as compared to both ethanol-exposed and pure control subjects. There were no significant effects of alcohol exposure on total retinal area.

CONCLUSIONS

Early postnatal ethanol exposure affects development of the visual system, reducing the numbers of neurons in the ganglion cell layer and in the dLGN, and altering RGCs' morphology.

Role of microglia in ethanol's apoptotic action on hypothalamic neuronal cells in primary cultures

BACKGROUND

Microglia are the major inflammatory cells in the central nervous system and play a role in brain injuries as well as brain diseases. In this study, we determined the role of microglia in ethanol's apoptotic action on neuronal cells obtained from the mediobasal hypothalamus and maintained in primary cultures. We also tested the effect of cAMP, a signaling molecule critically involved in hypothalamic neuronal survival, on microglia-mediated ethanol's neurotoxic action.

METHODS

Ethanol's neurotoxic action was determined on enriched fetal mediobasal hypothalamic neuronal cells with or without microglia cells or ethanol-activated microglia-conditioned media. Ethanol's apoptotic action was determined using nucleosome assay. Microglia activation was determined using OX6 histochemistry and by measuring inflammatory cytokines secretion from microglia in cultures using enzyme-linked immunosorbent assay (ELISA). An immunoneutralization study was conducted to identify the role of a cytokine involved in ethanol's apoptotic action.

RESULTS

We show here that ethanol at a dose range of 50 and 100 mM induces neuronal death by an apoptotic process. Ethanol's ability to induce an apoptotic death of neurons is increased by the presence of ethanol-activated microglia-conditioned media. In the presence of ethanol, microglia showed elevated secretion of various inflammatory cytokines, of which TNF-α shows significant apoptotic action on mediobasal hypothalamic neuronal cells. Ethanol's neurotoxic action was completely prevented by cAMP. The cell-signaling molecule also prevented ethanol-activated microglial production of TNF-α. Immunoneutralization of TNF-α prevented the microglia-derived media's ability to induce neuronal death.

CONCLUSIONS

These results suggest that ethanol's apoptotic action on hypothalamic neuronal cells might be mediated via microglia, possibly via increased production of TNF-α. Furthermore, cAMP reduces TNF-α production from microglia to prevent ethanol's neurotoxic action.

Magnesium induces neuronal apoptosis by suppressing excitability

In clinical obstetrics, magnesium sulfate (MgSO(4)) use is widespread, but effects on brain development are unknown. Many agents that depress neuronal excitability increase developmental neuroapoptosis. In this study, we used dissociated cultures of rodent hippocampus to examine the effects of Mg(++) on excitability and survival. Mg(++)-induced caspase-3-associated cell loss at clinically relevant concentrations. Whole-cell patch-clamp techniques measured Mg(++) effects on action potential threshold, action potential peak amplitude, spike number and changes in resting membrane potential. Mg(++) depolarized action potential threshold, presumably from surface charge screening effects on voltage-gated sodium channels. Mg(++) also decreased the number of action potentials in response to fixed current injection without affecting action potential peak amplitude. Surprisingly, Mg(++) also depolarized neuronal resting potential in a concentration-dependent manner with a +5.2 mV shift at 10 mM. Voltage ramps suggested that Mg(++) blocked a potassium conductance contributing to the resting potential. In spite of this depolarizing effect of Mg(++), the net inhibitory effect of Mg(++) nearly completely silenced neuronal network activity measured with multielectrode array recordings. We conclude that although Mg(++) has complex effects on cellular excitability, the overall inhibitory influence of Mg(++) decreases neuronal survival. Taken together with recent in vivo evidence, our results suggest that caution may be warranted in the use of Mg(++) in clinical obstetrics and neonatology.

Excitotoxicity of TNFalpha derived from KA activated microglia on hippocampal neurons in vitro and in vivo

Highly activated microglia and followed excessive expression of inflammatory cytokines are associated with neuroexcitotoxic injuries. We use electrophysiological techniques, ELISA, western-blot, RT-PCR assay and TUNEL method to explore whether over-produced tumor necrosis factor alpha (TNFalpha) released from activated microglia results in neuronal injuries, and further causes apoptosis through increasing excitotoxicity of hippocampal neurons. Our data showed that kainic acid (KA) activated microglia highly expressed TNFalpha, mRNA and protein. KA activated microglia conditioned media ((KA-MCM) significantly enhanced the amplitude of the population spike at rat's hippocampal CA3 region. It also increased the Ca(2+) current amplitude and density in cultured hippocampal neurons, as well as the high expression of NMDAR1, iNOS, and caspase 3 mRNA and protein at both hippocampal neurons and tissues. KA-MCM also increased TUNEL-positive cells in hippocampal neurons, whereas addition of anti-TNFalpha to the KA-MCM before its application significantly reduced those effects. These studies suggest that TNFalpha derived from KA activated microglia increases excitotoxicity of hippocampal neurons, and might induce neuronal apoptosis in vitro and in vivo.

Dimethyl sulfoxide (DMSO) produces widespread apoptosis in the developing central nervous system

Dimethyl sulfoxide (DMSO) is a solvent that is routinely used as a cryopreservative in allogous bone marrow and organ transplantation. We exposed C57Bl/6 mice of varying postnatal ages (P0-P30) to DMSO in order to study whether DMSO could produce apoptotic degeneration in the developing CNS. DMSO produced widespread apoptosis in the developing mouse brain at all ages tested. Damage was greatest at P7. Significant elevations above the background rate of apoptosis occurred at the lowest dose tested, 0.3 ml/kg. In an in vitro rat hippocampal culture preparation, DMSO produced neuronal loss at concentrations of 0.5% and 1.0%. The ability of DMSO to damage neurons in dissociated cultures indicates that the toxicity likely results from a direct cellular effect. Because children, who undergo bone marrow transplantation, are routinely exposed to DMSO at doses higher than 0.3 ml/kg, there is concern that DMSO might be producing similar damage in human children.

Cellular calcium deficiency plays a role in neuronal death caused by proteasome inhibitors

Cytosolic Ca(2+) concentration ([Ca(2+)](i)) is reduced in cultured neurons undergoing neuronal death caused by inhibitors of the ubiquitin proteasome system. Activation of calcium entry via voltage-gated Ca(2+) channels restores cytosolic Ca(2+) levels and reduces this neuronal death (Snider et al. 2002). We now show that this reduction in [Ca(2+)](i) is transient and occurs early in the cell death process, before activation of caspase 3. Agents that increase Ca(2+) influx such as activation of voltage-gated Ca(2+) channels or stimulation of Ca(2+) entry via the plasma membrane Na-Ca exchanger attenuate neuronal death only if applied early in the cell death process. Cultures treated with proteasome inhibitors had reduced current density for voltage-gated Ca(2+) channels and a less robust increase in [Ca(2+)](i) after depolarization. Levels of endoplasmic reticulum Ca(2+) were reduced and capacitative Ca(2+) entry was impaired early in the cell death process. Mitochondrial Ca(2+) was slightly increased. Preventing the transfer of Ca(2+) from mitochondria to cytosol increased neuronal vulnerability to this death while blockade of mitochondrial Ca(2+) uptake via the uniporter had no effect. Programmed cell death induced by proteasome inhibition may be caused in part by an early reduction in cytosolic and endoplasmic reticulum Ca(2+,) possibly mediated by dysfunction of voltage-gated Ca(2+) channels. These findings may have implications for the treatment of disorders associated with protein misfolding in which proteasome impairment and programmed cell death may occur.

Decline in age-dependent, MK801-induced injury coincides with developmental switch in parvalbumin expression: somatosensory and motor cortex

MK801-induced activation of caspase-3 is developmentally regulated, peaking at postnatal day (P) 7 and decreasing with increasing postnatal age thereafter. Further, at P7, cells displaying activation of caspase-3 lack expression of calcium binding proteins (CaBPs). To further explore this relationship, we investigated postnatal expression of calbindin (CB), calretinin (CR) and parvalbumin (PV) in two brain regions susceptible to MK801-induced injury, the somatosensory cortex (S1) and layer II/III of motor cortex (M1/M2). Expression of CB and especially PV was low to absent prior to P7 but substantially increased from P7 through to P21 and adulthood. In contrast, CR expression was more variable at early developmental ages, stabilized to lower levels after P7 and showed a marked decline by P21. The results suggest that not only does calcium buffering capacity increase developmentally but also acquisition of enhanced buffering may be one mechanism by which neurons survive agent-induced alterations in calcium homeostasis.

Antioxidants prevent ethanol-associated apoptosis in fetal rhombencephalic neurons

It is well known that ethanol damages the developing nervous system by augmenting apoptosis. Previously, this laboratory reported that ethanol augments apoptosis in fetal rhombencephalic neurons, and that the increased apoptosis is associated with reduced activity of the phosphatidylinositol 3-kinase pathway and downstream expression of pro-survival genes. Other laboratories have shown that another mechanism by which ethanol induces apoptosis in developing neurons is through the generation of reactive oxygen species (ROS) and the associated oxidative stress. The present study used an in vitro model to investigate the potential neuroprotective effects of several antioxidants against ethanol-associated apoptosis in fetal rhombencephalic neurons. The investigated antioxidants included three phenolics: (-)-epigallocatechin-3-gallate (EGCG), a flavanoid polyphenol found in green tea; curcumin, found in tumeric; and resveratrol (3,5,4'-trihydroxystilbene), a component of red wine. Additional antioxidants, including melatonin, a naturally occurring indole, and alpha-lipoic acid, a naturally occurring dithiol, were also investigated. These studies demonstrated that a 24-hour treatment of fetal rhombencephalic neurons with 75 mM ethanol caused a 3-fold increase in the percentage of apoptotic neurons. However, co-treatment of these cultures with any of the five different antioxidants prevented ethanol-associated apoptosis. Antioxidant treatment did not alter the extent of apoptosis in control neurons, i.e., those cultured in the absence of ethanol. These studies showed that several classes of antioxidants can exert neuroprotection against ethanol-associated apoptosis in fetal rhombencephalic neurons.

Protective effect of acetyl-l-carnitine on the apoptotic pathway of peripheral neuropathy

Peripheral neuropathies are widespread disorders induced by autoimmune diseases, drug or toxin exposure, infections, metabolic insults or trauma. Nerve damage may cause muscle weakness, altered functionalities and sensitivity, and a chronic pain syndrome characterized by allodynia and hyperalgesia. Pathophysiological mechanisms related to neuropathic disease are associated with mitochondrial dysfunctions that lead to the activation of the apoptotic cascade. In a model of peripheral neuropathy, obtained by the loose ligation of the rat sciatic nerve (CCI), we describe a nerve apoptotic state that encompasses the release of cytochrome C in the cytosol, the activation of caspase 3, and the fragmentation of the genome. Animal treatment with acetyl-L-carnitine (ALCAR), but not with L-carnitine (L-Carn) or Gabapentin, prevents apoptosis induction. ALCAR reduces cytosolic cytochrome C and caspase 3 active fragments expression in a significant manner with respect to saline treatment. Accordingly, ALCAR treatment impairs caspase 3 protease activity, as demonstrated by reduced levels of cleaved PARP. Finally, ALCAR decreases the number of piknotic nuclei. This protection correlates with the induction of X-linked inhibitor apoptosis protein (XIAP). Taken together these results show that CCI is a valuable model to investigate neuropathies-related apoptosis phenomena and that ALCAR is able to prevent regulated cell death in the damaged sciatic nerve.

S100B-mediated protection against the pro-apoptotic effects of ethanol on fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol treatment significantly reduces the number of developing serotonin (5-HT) and other fetal rhombencephalic neurons in rats by augmenting apoptosis. Using a 5-HT(1A) agonist we were able to attenuate the ethanol-associated reduction and apoptosis of 5-HT and rhombencephalic neurons. The downstream pro-survival effects of 5-HT(1A) stimulation were associated with the activation of phosphatidylinositol 3'kinase (PI-3K) and its subsequent up-regulation of specific NF-kappaB-dependent pro-survival genes. Using an in vitro model, we investigated the hypothesis that S100B, a protein which is released from astrocytes following 5-HT(1A) agonist stimulation, can reduce apoptosis in ethanol-treated rat fetal rhombencephalic neurons. We also evaluated whether the anti-apoptotic effects of S100B on fetal rhombencephalic neurons were linked to the activation of the PI-3K-->pAkt pro-survival pathway and the expression of two NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Moreover, we determined whether S100B's pro-survival effects were associated with mitogen activated protein kinase kinase (MAPKK)-->p42/p44 MAPK. The results of these investigations demonstrated that S100B treatment prevented ethanol-associated apoptosis of fetal rhombencephalic neurons. In addition, it appears that these neuroprotective effects are linked to activation of the PI-3K pathways, because the PI-3K inhibitor LY294002 blocks the neuroprotective effects of S100B. Moreover, S100B increases the formation of pAkt and the up-regulation of two downstream NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Although the MAPKK inhibitor PD98059 reduced the number of surviving neurons in S100B-treated cultures, S100B did not activate MAPKK.

Loss of calcium and increased apoptosis within the same neuron

Loss of neuronal calcium is associated with later apoptotic injury but observing reduced calcium and increased apoptosis in the same cell would provide more definitive proof of this apparent correlation. Thus, following exposure to vehicle or the calcium chelator, BAPTA (1-20 microM), primary cortical neurons were labeled with Calcium Green-1 which was then cross-linked with EDAC, prior to immuno-staining for various proteins. We found that BAPTA-induced changes in calcium were highly correlated with changes in expression of activated caspase-3 as well as the calcium binding proteins calbindin, calretinin, and parvalbumin. Additionally, in brain slices from P7 neonatal rats, BAPTA induced significant loss of calcium in a brain region we have previously shown to express only moderate levels of calcium binding proteins as well as display robust apoptosis following calcium entry blockade. In contrast, BAPTA had little influence on calcium levels in a brain region we have previously shown to express robust calcium binding proteins as well as display far less apoptosis following calcium entry blockade. These data suggest that the ability of developing neurons to buffer changes in calcium may be critical to their long-term survival.

Widespread Neonatal Brain Damage following Calcium Channel Blockade

An abundance of evidence exists that shows calcium channel blockade promotes injury in cultured neurons. However, few studies have addressed the in vivo toxicity of such agents. We now show that the L-type calcium channel antagonist nimodipine promotes widespread and robust injury throughout the neonatal rat brain, in an age-dependent manner. Using both isolated neuronal as well as brain slice approaches, we address mechanisms behind such injury. These expanded studies show a consistent pattern of injury using a variety of agents that lower intracellular calcium. Collectively, these observations indicate that postnatal brain development represents a transitional period for still developing neurons, from being highly sensitive to reductions in intracellular calcium to being less vulnerable to such changes. These observations directly relate to current therapeutic strategies targeting neonatal brain injury.

Physiological activity depresses synaptic function through an effect on vesicle priming

Neurons engage compensatory, homeostatic synaptic changes to maintain their overall firing rate. We examined the induction and expression of a persistent presynaptic adaptation. We explored the effect of mild extracellular potassium elevation to increase hippocampal pyramidal neuron spiking over a physiological range. With several days of mild depolarization, glutamate release adapted, as revealed by an increased mismatch between the number of active, FM1-43-positive, glutamatergic synapses and the total number of synapses defined by vesicular glutamate transporter-1 antibody staining. Surprisingly, the adaptation of glutamate terminals was all-or-none; recycling vesicle pool size at remaining active synapses was not significantly altered by the adaptation. Tetrodotoxin (TTX), but not postsynaptic receptor blockade, reversed depolarization-induced adaptation, and TTX added to normal incubation medium increased the number of active synapses, suggesting that normal spiking activity sustains a steady-state percentage of inactive terminals. Chronic mild depolarization depressed EPSCs and decreased the size of the readily releasable pool of vesicles (RRP). Several hours of 10 Hz electrical stimulation also depressed the RRP size, confirming that spiking alone induces adaptation and that strong stimulation induces more rapid presynaptic adaptation. Despite the importance of RRP alteration to the adaptation, ultrastructural experiments revealed no changes in docked or total synaptic vesicle numbers. Furthermore, alpha-latrotoxin induced vesicle release at adapted synapses, consistent with the idea that adaptation resulted from changes in vesicle priming. These results show that glutamatergic neurotransmission persistently adapts to changes in electrical activity over a wide physiological range.

The interactive effect of alcohol and nicotine on NGF-treated pheochromocytoma cells

Previous studies have reported that alcohol exposure reduces the number of neuronal-like pheochromocytoma (PC12) cells in culture. In this study, the interactive effect of coexposure of alcohol and nicotine on PC12 cell numbers was examined in comparison with the effect derived from alcohol or nicotine exposure individually. Moreover, the role of apoptosis in mediating changes in PC12 cell numbers was also investigated. It was hypothesized that alcohol would result in cell loss, and the presence of nicotine would attenuate the damaging effects of alcohol. PC12 cells were exposed to alcohol (100 mM), nicotine (10 microM), or both alcohol and nicotine for 24, 48, 72, or 96 h. Caspase-3 activity and DNA fragmentation, markers for apoptotic cell death, were measured to determine the role of apoptosis in mediating decreases in PC12 cell numbers. The findings indicated that both alcohol and nicotine exposure significantly decreased PC12 cell numbers when compared with the control treatment. Furthermore, the coexposure of these two drugs caused a significantly greater decrease in cell numbers when compared with cells exposed to either alcohol or nicotine alone. This additive effect was related to the duration of exposure with a marked reduction in cell numbers following 96 h of coexposure to alcohol and nicotine. Neither alcohol nor nicotine exposure appeared to alter caspase-3 activity or DNA fragmentation levels, suggesting that the reduction in PC12 cell numbers following alcohol and/or nicotine exposure may possibly be due to factors other than apoptosis, such as interference with proliferation rates.

Inhibition of ethanol-induced toxicity by tanshinone IIA in PC12 cells

AIM

To observe the effects of tanshinone IIA (Tan IIA) on the neurotoxicity induced by ethanol in PC12 cells and to explore its protective role.

METHODS

PC12 cell survival was measured by MTT assay. The formation of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) release were detected by 2',7'-dichlorofluorescin (DCF) fluorescence and calorimetric method, respectively. The percentage of cell apoptosis was monitored by flow cytometry. The expression of p53 was detected by immuno-fluorescence and flow cytometry.

RESULTS

Ethanol significantly impaired the survival of PC12 cells as demonstrated by MTT assay. Ethanol also induced significant ROS formation and increased LDH release. Pre-incubation with Tan IIA in the culture medium significantly reversed these changes. Ethanol caused cell apoptosis and the upregulation of p53 protein. The anti-apoptosis effects of Tan IIA on ethanol-induced toxicity were accompanied by the downregulation of pro-apoptotic p53 protein expression.

CONCLUSION

Tan IIA can protect neurons from apoptosis and might serve as a potential therapeutic drug for neurological disorders induced by ethanol.

The effects of ethanol and the serotonin(1A) agonist ipsapirone on the expression of the serotonin(1A) receptor and several antiapoptotic proteins in fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol reduces the number of developing serotonin (5-HT)-containing neurons by increasing apoptosis. We also found that 5-HT(1A) agonists attenuate the proapoptotic effects of ethanol and the ethanol-mediated reduction of fetal 5-HT neurons. These neuroprotective effects are mediated in part by the ability of 5-HT(1A) agonists to activate the phosphatidyl 3'-kinase (PI-3K) prosurvival pathway. NF-kappaB is one of the downstream effectors activated by this pathway. In the present study, we used quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the effects of 50mM ethanol and 100nM of ipsapirone, a 5-HT(1A) agonist, on the expression of several NF-kappaB-dependent antiapoptotic genes: X-linked inhibitor of apoptosis protein (XIAP), cIAP1, cIAP2, Bcl-2, and Bcl-xl. We also investigated the effects of ethanol and ipsapirone on the expression of the gene encoding the 5-HT(1A) receptor. The results demonstrate that ethanol reduces the expression of several prosurvival genes: XIAP, cIAP1, cIAP2, Bcl-2, and Bcl-xl. Importantly, the ethanol-mediated reduction in the expression of XIAP and Bcl-xl was prevented by co-treatment with ipsapirone. Thus, the damaging effects of ethanol are likely to involve a reduction in several prosurvival proteins. Moreover, the protective effects of ipsapirone on ethanol-treated neurons might involve their ability to prevent the reduction of XIAP and Bcl-xl. Although ipsapirone treatment decreased the expression of cIAP1, Bcl-2, and Bcl-xl in control neurons, our prior studies suggest that their survival is not reduced by ipsapirone. We also observed an increased expression of the 5-HT(1A) receptor in ipsapirone-treated control neurons.

Calcium-stimulated adenylyl cyclases modulate ethanol-induced neurodegeneration in the neonatal brain

Fetal alcohol exposure results in cognitive and neurobehavioral deficits, but the effects of modifying genetic loci on the severity of these sequelas have not been well characterized. Although the cAMP signaling pathway has been shown to be an important modulator of ethanol sensitivity in adult mice, its potential role in modulating ethanol-induced neurodegeneration has not been examined. Adenylyl cyclases (ACs) 1 and 8 produce cAMP in response to intracellular calcium elevation and modulate several aspects of neuronal function, including ethanol sensitivity. AC1 and AC8 are expressed widely throughout the brain of neonatal mice, and genetic deletion of both AC1 and AC8 in double-knock-out (DKO) mice enhances ethanol-induced neurodegeneration in the brains of neonatal mice. In addition, ethanol treatment induces significantly greater levels of caspase-3 activation in the brains of DKO mice compared with wild-type (WT) mice, reflecting higher numbers of apoptotic neurons. Administration of the NMDA receptor antagonist MK801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine hydrogen maleate] or the GABA(A) receptor potentiator phenobarbital, which mimics components of the effects of ethanol on neurons, results in significantly greater neurodegeneration in the brains of neonatal DKO mice than WT mice. Furthermore, loss of a single calcium-stimulated AC isoform potentiates neurodegeneration after administration of ethanol, MK801, or phenobarbital. In contrast, the levels of physiological cell death, death after hypoxia/ischemia, and excitotoxic cell death are not increased in the brains of DKO mice. Thus, AC1 and AC8 are critical modulators of neurodegeneration induced by activity blockade in the neonatal brain and represent genetic loci that may potentially modify the severity of fetal alcohol syndrome.

Mk801-induced caspase-3 in the postnatal brain: Inverse relationship with calcium binding proteins

Age-dependent, neuronal apoptosis following N-methyl-D-aspartate receptor blockade has been linked to loss of calcium. To further explore this relationship, we examined expression of activated caspase-3, as well as the calcium binding proteins, calbindin-D 28K, calretinin and parvalbumin, following injection of vehicle or the N-methyl-D-aspartate receptor blocker, MK801, in postnatal day 7 or 21 rats. At postnatal day 7, MK801-induced activated caspase-3 expression was most frequently found in mutually exclusive cell populations to those expressing any of the three calcium binding proteins. For example, in the somatosensory cortex, most immunoreactivity for activated caspase-3 was found in layers IV/V, layered between areas of high calbindin or calretinin expression. Further, in the caudate putamen, activated caspase-3 rarely invaded zones of intense calbindin immunoreactivity. Suggesting expression patterns of these proteins were inversely related, these same brain regions no longer displayed MK801-induced activated caspase-3 at postnatal day 21, but instead robustly expressed calcium binding proteins. This later surge in expression was especially true for parvalbumin in regions such as the somatosensory and retrosplenial cortex, as well as the subicular complex. Calbindin-D 28K was also found to increase in the same regions though not as impressively as parvalbumin. Thus, developmental regulation of calcium binding protein expression may be a critical factor in age-dependent sensitivity to agents that disrupt calcium homeostasis in maturing neurons, providing a possible mechanistic explanation for age-dependent MK801 toxicity.

Apoptotic effect of ethanol is potentiated by caffeine-induced calcium release in rat astrocytes

In this study, we investigated agents that increased intracellular calcium levels and their correlation with apoptotic cell death induction. We used rat astrocytes to investigate the increase in cytosolic Ca2+ (Ca(c)2+) and apoptosis induction by drugs that mobilize Ca2+ from different sources. We observed that thapsigargin (Thap), caffeine (Caff) and FCCP which caused similar increases in Ca(c)2+ levels (30-40%), also induced similar apoptotic rates (30-35%). On the other hand, antimycin (Anti), staurosporine (STS) and ethanol (Eth) promoted higher increases in Ca(c)2+ (55-65 %) and higher apoptotic rates (55-85%). Eth induced cell death in a concentration- and time-dependent manner. After treatment with Eth plus Caff for 6, 12 and 24 h, these effects were strongly potentiated. Results suggest that there might be a correlation between Ca(c)2+ increase and the rate of apoptosis. It is possible that Eth induces cell death by activation of more than one pathway and Ca2+ might be one of the elements involved. The present work indicates that Ca2+ can potentiate death by ethanol in rat astrocytes.

Signaling pathways involved with serotonin1A agonist-mediated neuroprotection against ethanol-induced apoptosis of fetal rhombencephalic neurons

Previously, this laboratory demonstrated that developing serotonin (5-HT) neurons and other fetal rhombencephalic neurons are reduced by in vivo and in vitro exposure to ethanol, effects that are related to ethanol's augmentation of apoptosis. We also found that 5-HT1A agonists diminished the ethanol-associated reduction of 5-HT neurons and other fetal rhombencephalic neurons by attenuating the pro-apoptotic effects of ethanol. Presently, we investigated the hypothesis that the protective/anti-apoptotic effects of a 5-HT1A agonist on fetal rhombencephalic neurons are mediated by activation of the phosphatidylinositol 3' kinase (PI-3K) and/or the mitogen-activated protein kinase kinase (MAPKK) pathway. Apoptotic and non-apoptotic fetal rhombencephalic neurons were quantitated in primary cultures that were treated with 50 mM ethanol and with 100 nM of a 5-HT1A agonist such as 8-OH-DPAT [8-hydroxy 2-(di-n-propylamino)tetralin], ipsapirone, or buspirone. Analysis of neurons stained with Hoechst 33342 demonstrated the anti-apoptotic effects of 5-HT1A agonists and implicated the involvement of the PI-3K pathway and possibly the MAPKK pathway with the protective effects of these drugs. The protective effects were blocked by a 5-HT1A antagonist (WAY 100635), an inhibitor of PI-3K (LY294002), and an inhibitor of MAPKK (PD98059). Western blot analyses showed that ethanol treatment reduces basal pAkt levels. These analyses also provide support for the involvement of the PI-3K pathway; ipsapirone stimulated the phosphorylation of Akt in control and ethanol-treated neurons, and these effects were antagonized by LY294002.

Astrocytes exert a pro-apoptotic effect on neurons in postnatal hippocampal cultures

We investigated conditions that promote basal and activity-dependent neuronal apoptosis in postnatal rat hippocampal cultures. Low-density mixed cultures of astrocytes and neurons exhibited lower sensitivity than high-density cultures to basal neuronal death and activity-sensitive neuronal death, induced with glutamate receptor blockers, sodium channel blockers, or calcium channel blockers. Although elevations of [Ca(2+)](i) protect neurons from apoptosis, low-density microcultures and mass cultures exhibited only minor differences in resting [Ca(2+)](i) and Ca(2+) current density, suggesting that these variables are unlikely to explain differences in susceptibility. Astrocytes, rather than neurons, were implicated in the neuronal loss. Several candidate molecules implicated in other astrocyte-dependent neurotoxicity models were excluded, but heat inactivation experiments suggested that a heat-labile factor is critically involved. In sum, our results suggest the surprising result that astrocytes can be negative modulators of neuronal survival during development and when the immature nervous system is challenged with drugs that dampen electrical excitability.

Ethanol potentiates HIV-1 gp120-induced apoptosis in human neurons via both the death receptor and NMDA receptor pathways

Neuronal loss is a hallmark of AIDS dementia syndromes. Human immunodeficiency virus type I (HIV-1)-specific proteins may induce neuronal apoptosis, but the signal transduction of HIV-1 gp120-induced, direct neuronal apoptosis remains unclear. Ethanol (EtOH) is considered to be an environmental co-factor in AIDS development. However, whether EtOH abuse in patients with AIDS increases neuronal dysfunction is still uncertain. Using pure, differentiated, and post-mitotic NT2.N-derived human neurons, we investigated the mechanisms of HIV-1 and/or EtOH-related direct neuronal injury and the molecular interactions between HIV-1-specific proteins and EtOH. It was demonstrated that NT2.N neurons were susceptible to HIV-1 Bal (R5-tropic strain) gp120-induced direct cell death. Of importance, EtOH induced cell death in human neurons in a clinically-relevant dose range and EtOH strongly potentiated HIV-1 gp120-induced neuronal injury at low and moderate concentrations. Furthermore, this potentiation of neurotoxicity could be blocked by N-methyl-D-aspartate (NMDA) receptor subunit 2B (NR2B) antagonists. We analyzed human genomic profiles in these human neurons, using Affymetrix genomics technology, to elucidate the apoptotic pathways involved in HIV-1- and EtOH-related neurodegeneration. Our findings indicated significant over-expression of selected apoptosis functional genes. Significant up-regulation of TRAF5 gene expression may play an essential role in triggering potentiation by EtOH of HIV-1 gp120-induced neuronal apoptosis at early stages of interaction. These studies suggested that two primary apoptotic pathways, death receptor (extrinsic) and NMDA receptor (intrinsic)-related programmed cell-death pathways, are both involved in the potentiation by EtOH of HIV-1 gp120-induced direct human neuronal death. Thus, these data suggest rationally-designed, molecular targets for potential anti-HIV-1 neuroprotection.

Caspase signalling in neuropathic and inflammatory pain in the rat

Whereas small-fibre sensory neuropathies might ultimately lead to cell death and loss of sensation, they first progress through a phase, which might last for years, characterized by the presence of analgesia-resistant neuropathic dysesthesias and pain. Much previous research has addressed these two phases as separate phenomena mediated by presumably discrete biochemical mechanisms. We hypothesized that activity in signalling pathways that ultimately lead to apoptosis plays a critical role in the generation of neuropathic pain, before death of sensory neurons becomes apparent. We have tested the hypothesis that activator and effector caspases, defining components of programmed cell death (apoptosis) signalling pathways, also contribute to pain-related behaviour in animals with small-fibre peripheral neuropathies and that the death receptor ligand, tumour necrosis factor-alpha, and its downstream second messenger, ceramide, also produce pain-related behaviour via this mechanism. In two models of painful peripheral neuropathy, HIV/AIDS therapy (induced by the nucleoside reverse transcriptase inhibitor, dideoxycytidine), and cancer chemotherapy (induced by vincristine) peripheral neuropathy, and for pain-related behaviour induced by tumour necrosis factor-alpha and its second messenger, ceramide, inhibition of both activator (1, 2, 8 and 9) and effector (3) caspases attenuates neuropathic pain-related behaviour, although has no effect in streptozotocin-diabetic neuropathy and control rats. We conclude that during a latent phase, before apoptotic cell death is manifest, the caspase signalling pathway can contribute to pain in small-fibre peripheral neuropathies, and that inflammatory/immune mediators also activate these pathways. This suggests that these pathways are potential targets for novel pharmacological agents for the treatment of inflammatory as well as neuropathic pain.

Plastic elimination of functional glutamate release sites by depolarization

To examine persisting effects of depolarizing rises in extracellular potassium concentration ([K+](o)) on synapses, we depolarized cells to simulate ischemia-like rises in [K+](o). Elevated [K+](o) for 1-16 hr severely depressed glutamate signaling, while mildly depressing GABA transmission. The glutamate-specific changes were plastic over several hours and involved a decrease in the size of the pool of releasable vesicles. Rather than a reduction of the number of vesicles per release site, the change involved functional elimination of release sites. This change was clearly dissociable from a second effect, depressed probability of transmitter release, which was common to both glutamate and GABA transmission. Thus, while other recent evidence links alteration of the releasable pool size with changes in p(r), our results suggest the two can be independently manipulated. Selective depression of glutamate release may provide an adaptive mechanism by which neurons limit excitotoxicity.

Critically timed ethanol exposure reduces GABAAR function on septal neurons developing in vivo but not in vitro

Six-day 'binge' ethanol intoxication postnatal days (PD) 4-9 delays up-regulation of gamma-aminobutyric acid type A receptors (GABAARs) in developing rat septal neurons [Dev. Brain Res. 130 (2001) 25]. This distortion occurs during synaptogenesis and could contribute to cognitive dysfunction in fetal alcohol syndrome (FAS). Here, we asked two questions concerning requirements for vulnerability to GABAAR blunting by ethanol. First, we asked whether receptor blunting required PD 4-9 ethanol exposure in rat pups and found that just a brief 2-day exposure (PD 8-9) was as effective as all 6 days. However, 2-day exposure on PD 4-5 was ineffective, showing that 'binge' timing was important. We also asked whether 'binge' exposure directly inhibited intrinsic processes of septal neurons and could blunt GABAARs on cells maturing outside the brain. Embryonic septal neurons grown in serum-free dispersed culture developed extensive dendritic arborizations, spontaneous synaptic activity and robust whole-cell GABAAR function, but surprisingly, did not show developmental up-regulation of GABAARs like septal neurons maturing in vivo [Brain Res. 810 (1998) 100]. Furthermore, age-matched 6-day 'binge' ethanol exposure did not blunt GABAAR function in septal neurons in vitro. These results suggest developmental mechanisms driving up-regulation of GABAAR function in septal neurons in vivo briefly becomes vulnerable to ethanol insult in early postnatal life. While septal neurons express comparable functional GABAARs whether maturing in vivo or in vitro, vulnerability to ethanol-induced receptor blunting requires elements of an intact brain environment not replicated in culture.

The serotonin-1A agonist ipsapirone prevents ethanol-associated death of total rhombencephalic neurons and prevents the reduction of fetal serotonin neurons

Previously, this laboratory showed that in utero and in vitro ethanol exposure significantly reduces developing serotonin (5-HT) neurons and that treatment with a 5-HT1A agonist such as buspirone or ipsapirone prevents the ethanol-associated loss. The present study investigated whether ethanol decreases fetal rhombencephalic neurons, including 5-HT neurons, by causing apoptosis. We also investigated whether ipsapirone prevents the ethanol-associated deficit of fetal rhombencephalic neurons by reducing apoptosis. The results of these studies strongly suggest that the ethanol-associated reduction in fetal rhombencephalic neurons that accompanies both in utero and in vitro exposure to physiological concentrations of ethanol is associated with increased apoptosis in these neurons. A physiological concentration of ethanol (i.e., 50 mM) increases apoptosis in fetal rhombencephalic neurons and decreases the number 5-HT neurons. It also appears that the 5-HT1A agonist ipsapirone provides neuroprotection to these neurons by reducing apoptosis. Another mechanism by which ethanol-associated apoptosis can be blocked is by including serum proteins in the media at a concentration of 1% or higher; this concentration of serum proteins is high in comparison to the protein concentration in cerebrospinal fluid.

Cell death in the rat hippocampus in a model of prenatal brain injury: time course and expression of death-related proteins

Survival rates have increased dramatically for very premature (gestational week 24-28) infants. However, many of these infants grow up to have profound cognitive, motor and behavioral impairments due to brain damage. We have developed a novel model of prenatal infant gray matter injury. During the neonatal period, GABA is an excitatory neurotransmitter. GABA(A) receptor activation results in chloride efflux and membrane depolarization sufficient to open L-type voltage sensitive calcium channels. Our model involves excessive GABA(A) receptor activation in the newborn rat, with damage due to the resultant excessive calcium influx, not GABA(A) receptor activation itself. A common feature among numerous insult pathologies in the neonatal brain is an elevation in the intracellular levels of calcium. The goals of the present study were: 1) to document the time course and amount of cell death (both apoptotic and necrotic), and 2) to investigate the effect of GABA(A) receptor activation on the time course and expression of three cell death-related proteins (caspase-9, bax and bcl-2) in our model of prenatal brain injury. The magnitude of cell death, using TdT-mediated dUTP nick end labeling and Cresyl Violet to quantify the incidence of apoptotic and necrotic cells, was region dependent (CA1>CA2/3>dentate gyrus) and persisted for at least 5 days following insult. There was a relative increase in the amount of bax to bcl-2 protein, and increased protein levels of caspase-9, indicative of cell death. These findings are consistent with mechanisms of cell death seen in other types of early brain insult, and highlight a conserved cascade of events leading to cell death in the developing brain.

Homeostatic effects of depolarization on Ca2+ influx, synaptic signaling, and survival

Depolarization promotes neuronal survival through moderate increases in Ca(2+) influx, but the effects of survival-promoting depolarization (vs conventional trophic support) on neuronal signaling are poorly characterized. We found that chronic, survival-promoting depolarization, but not conventional trophic support, selectively decreased the somatic Ca(2+) current density in hippocampal and cerebellar granule neurons. Depolarization rearing depressed multiple classes of high-voltage activated Ca(2+) current. Consistent with the idea that these changes also affected synaptic Ca(2+) channels, chronic depolarization presynaptically depressed hippocampal neurotransmission. Six days of depolarization rearing completely abolished glutamate transmission but altered GABA transmission in a manner consistent with the alterations of Ca(2+) current. The continued survival of depolarization-reared neurons was extremely sensitive to the re-establishment of basal culture conditions and was correlated with the effects on intracellular Ca(2+) concentration. Thus, compared with cells reared on conventional trophic factors, depolarization evokes homeostatic changes in Ca(2+) influx and signaling that render neurons vulnerable to cell death on activity reduction.