Generation of neurons in the rat dentate gyrus and hippocampus: effects of prenatal and postnatal treatment with ethanol

Inhibition of muscarinic receptor-induced proliferation of astroglial cells by ethanol: mechanisms and implications for the fetal alcohol syndrome

In utero exposure to ethanol is deleterious to fetal brain development. Children born with the fetal alcohol syndrome (FAS) display a number of abnormalities, the most significant of which are central nervous system (CNS) dysfunctions, such as microencephaly and mental retardation. An interaction of ethanol with glial cells, particularly astrocytes, has been suggested to contribute to the developmental neurotoxicity of this alcohol. At low concentrations (10-100 mM) ethanol inhibits the proliferation of astroglial cells in vitro, particularly when stimulated by acetycholine through muscarinic M3 receptors. Of the several signal transduction pathways activated by these receptors in astrocytes or astrocytoma cells, which are involved in mitogenic signaling, only some (e.g. protein kinase C (PKC) zeta, p70S6 kinase) appear to be targeted by ethanol at the same low concentrations which effectively inhibit proliferation. Inhibition of astroglial proliferation by ethanol may contribute to the microencephaly seen in FAS.

Second trimester prenatal alcohol exposure alters development of rat corpus callosum

Prenatal alcohol exposure produces many developmental defects of the central nervous system (CNS), such as in the corpus callosum (CC). This study was designed to observe the effect of prenatal alcohol exposure during the second trimester equivalent on the development of dendritic arbors of CC projection neurons (CCpn) in rat visual cortex. In addition, the effect of second trimester equivalent prenatal alcohol exposure on brain weight was determined. Pregnant dams received 1.2-6.0 g/kg ethanol (EtOH) during gestational day (G) 11-20. Controls consisted of normal and nutritionally matched pairfed (PF) dams. Pups were sacrificed on the day of birth, G26, G29 and G33. DiI crystals were placed in the midsagittal CC bundle to retrogradely label CCpn. Images of visual cortex were obtained from tissue slices using a confocal laser scanning microscope. The number and length of apical and basilar dendrite branches were determined. The results show that prenatal alcohol exposure restricted to the second trimester equivalent alters the development of the CCpn dendritic arbor and the brain weight in a blood alcohol concentration (BAC)-dependent manner. The alteration in the EtOH CCpn is manifested as an increase in the number and length of CCpn apical and basilar dendrite branches, while brain weight is reduced compared with Controls.

Developmental neurotoxicity: do similar phenotypes indicate a common mode of action? A comparison of fetal alcohol syndrome, toluene embryopathy and maternal phenylketonuria

Developmental neurotoxicity can be ascribed to in utero exposure to exogenous substances or to exposure of the fetus to endogenous compounds that accumulate because of genetic mutations. One of the best recognized human neuroteratogens is ethanol. The Fetal Alcohol Syndrome (FAS) is characterized by growth deficiency, particular facial features, and central nervous system (CNS) dysfunctions (mental retardation, microencephaly and brain malformations). Abuse of toluene by pregnant women can lead to an embryopathy (fetal solvent syndrome, (FSS)) whose characteristics are similar to FAS. Phenylketonuria (PKU) is a genetic defect in phenylalanine (Phe) metabolism. Offspring of phenylketonuric mothers not under strict dietary control are born with maternal PKU (mPKU), a syndrome with similar characteristics as FAS and FSS. While ethanol has been shown to cause neuronal death, no such evidence is available for toluene or Phe and/or its metabolites. On the other hand, alterations in astrocyte proliferation and maturation have been found, mostly in in vitro studies, which may represent a potential common mode of action for at least some of the CNS effects found in FAS, mPKU, and FSS. Further in vivo and in vitro studies should validate this hypothesis and elucidate possible molecular targets.

Ethanol-induced alterations of neurotrophin receptor expression on Purkinje cells in the neonatal rat cerebellum

Ethanol causes loss of Purkinje cells in the cerebellum during the early stages of differentiation and maturation by a presently unknown mechanism. Neuronal vulnerability in the cerebellum parallels the prominent temporal and anatomical gradients of development (i.e. early to late interlobular and posterior to anterior, respectively). Development of Purkinje cells is known to require binding of the neurotrophins, including brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3), to the tyrosine-kinase (Trk) receptors TrkB and TrkC, respectively. In addition, Purkinje cells are reported to experience a critical switch between BDNF dependence and NT3 dependence during the period of highest ethanol sensitivity between postnatal days (PN) 4-6. To test the hypothesis that ethanol alters neurotrophin signaling leading to Purkinje neuronal death, the immunohistochemical expression of TrkB and TrkC receptors on Purkinje cells of rat pups following a moderate dose of ethanol was determined at various times surrounding the period of postnatal ethanol vulnerability. Ethanol selectively decreased Purkinje cell expression of TrkB and TrkC receptors following exposures within the vulnerable period (PN4-6). These results suggest that ethanol may induce loss of Purkinje cells by alteration of neurotrophic regulation at this critical stage.

Ethanol neurobehavioral teratogenesis and the role of the hippocampal glutamate-N-methyl-D-aspartate receptor-nitric oxide synthase system

The purpose of this review is to evaluate a proposed mechanism for ethanol neurobehavioral teratogenesis in the hippocampus, involving suppression of the glutamate-N-methyl-D-aspartate (NMDA) receptor-nitric oxide synthase (NOS) system. It is postulated that suppression of this signal transduction system in the fetus by chronic maternal consumption of ethanol plays a key role in hippocampal dysmorphology and dysfunction in postnatal life. This mechanism is evaluated critically based on the current literature and our research findings. In view of the apparent time course for loss of CA1 pyramidal cells in the hippocampus produced by chronic prenatal ethanol exposure that manifests in early postnatal life, it is proposed that therapeutic intervention, which targets the glutamate-NMDA receptor-NOS system, may prevent or lessen the magnitude of postnatal hippocampal dysfunction.

Cell cycle kinetics and immunohistochemical characterization of dissociated fetal neocortical cultures: evidence that differentiated neurons have mitotic capacity

Neurons in the neocortex (regardless of their developmental state) are considered to be post-mitotic and incapable of dividing. We used dissociated primary cultures derived from the neocortices of 16-day-old fetuses to test the counter-hypothesis, that is, differentiating neocortical neurons can divide. The cultured cells experienced considerable cell death, yet the number of viable cells remained relatively constant over the first 5 days in vitro. The implication was that the cultures contained proliferating cells. This was confirmed with a [(3)H]thymidine ([3H]dT) incorporation study and cumulative bromodeoxyuridine labeling. In fact, over 1/4 of the cells were cycling and the length of the cell cycle was 20.0 h; kinetics which mirror those of the developing cortex in vivo. This population of proliferating cells was eliminated by 48 h treatment with fluorodeoxyuridine. Immunohistochemical procedures determined that most cultured cells (>/=90%) expressed proteins associated with differentiating or mature neurons, e.g., neurofilament (NF) 200 and isoforms of microtubule-associated protein (MAP) 2. Markers for immature neurons (e.g., nestin) were expressed by 10% of the cells. In contrast, markers for glia and their precursors were expressed by </=2% of the population. Double-labeling with [3H]dT and a neural-specific antibody showed that cells expressing an antigen for immature neurons constituted most of the proliferating cells, however, a considerable number of [3H]dT-labeled cells expressed markers for differentiating neurons (e.g., NF200 and MAP2). Thus, differentiating neocortical neurons can be mitotically active and it appears that differentiating neurons are derived from both the ventricular and subventricular proliferative zones.

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.

Effects of chronic prenatal ethanol exposure on hippocampal glutamate release in the postnatal guinea pig

This study was designed to test the hypothesis that chronic prenatal ethanol exposure decreases basal and stimulated L-glutamate release in the hippocampus of young, postnatal guinea pigs. Timed, pregnant guinea pigs were randomly assigned to one of the following three chronic treatment groups: 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose and pair-feeding to the ethanol group, and water. Each oral treatment was given daily throughout gestation. Spontaneous locomotor activity was increased on postnatal day (PD) 10, and brain and hippocampal weights were decreased on PD 12 in the offspring of the ethanol group compared with the isocaloric-sucrose/pair-fed and water groups. On PD 12, the 45 mM K(+)- and 10 microM veratridine-stimulated release of glutamate in transverse hippocampal slices was decreased in the ethanol group compared with the two control groups. This alteration in glutamate release produced by chronic prenatal ethanol exposure may decrease the efficiency of excitatory synaptic transmission in the hippocampus during postnatal life.

Effects of prenatal alcohol exposure on the hippocampus: spatial behavior, electrophysiology, and neuroanatomy

Prenatal exposure to alcohol can result in fetal alcohol syndrome (FAS), characterized by growth retardation, facial dysmorphologies, and a host of neurobehavioral impairments. Neurobehavioral effects in FAS, and in alcohol-related neurodevelopmental disorder, include poor learning and memory, attentional deficits, and motor dysfunction. Many of these behavioral deficits can be modeled in rodents. This paper reviews the literature suggesting that many fetal alcohol effects result, at least in part, from teratogenic effects of alcohol on the hippocampus. Neurobehavioral studies show that animals exposed prenatally to alcohol are impaired in many of the same spatial learning and memory tasks sensitive to hippocampal damage, including T-mazes, the Morris water maze, and the radial arm maze. Direct evidence for hippocampal involvement is provided by neuroanatomical studies of the hippocampus documenting reduced numbers of neurons, lower dendritic spine density on pyramidal neurons, and decreased morphological plasticity after environmental enrichment in rats exposed prenatally to alcohol. Electrophysiological studies also demonstrate changes in synaptic activity in in vitro hippocampal brain slices isolated from prenatal alcohol-exposed animals. Considered together, these observations demonstrate that prenatal exposure to alcohol can result in abnormal hippocampal development and function. Such studies provide a better understanding of neurological deficits associated with FAS in humans, and may also contribute to the development of strategies to ameliorate the effects of prenatal alcohol exposure on behavior.

Effects of chronic prenatal ethanol exposure on locomotor activity, and hippocampal weight, neurons, and nitric oxide synthase activity of the young postnatal guinea pig

Decreased nitric oxide synthase (NOS)-catalyzed formation of NO from L-arginine may be involved in ethanol teratogenesis involving the hippocampus. This hypothesis was tested by determining the effects of chronic prenatal ethanol exposure on locomotor activity and on hippocampal weight, number of CA1 and CA3 pyramidal cells and dentate gyrus granule cells, and NOS activity of the postnatal guinea pig. Timed, pregnant guinea pigs received one of the following chronic oral regimens throughout gestation: 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose/pair-feeding, or water. At postnatal day (PD) 10, spontaneous locomotor activity was measured. At PD 12, histological analysis was performed on the hippocampal formation, in which hippocampal CA1 and CA3 pyramidal cells and dentate gyrus granule cells were counted; body, brain, and hippocampal weights were measured; and hippocampal NOS enzymatic activity was determined using a radiometric assay. Chronic prenatal ethanol exposure produced hyperactivity, decreased the brain and hippocampal weights with no change in body weight, decreased the number of hippocampal CA1 pyramidal cells by 25-30%, and had no effect on hippocampal NOS activity compared with the two control groups. These data, together with our previous findings in the fetal guinea pig, demonstrate that chronic prenatal ethanol exposure decreases hippocampal NOS activity in near-term fetal life that temporally precedes the selective loss of hippocampal CA1 pyramidal cells in postnatal life.

Transforming growth factor beta1-regulated cell proliferation and expression of neural cell adhesion molecule in B104 neuroblastoma cells: differential effects of ethanol

The expression and activity of factors influencing early neuronal development are altered by ethanol. Such factors include growth factors, for example, platelet-derived growth factor and basic fibroblast growth factor (for cell proliferation), and cell adhesion molecules (for neuronal migration). One agent, transforming growth factor beta1 (TGFbeta1), may affect both events. We tested the hypothesis that ethanol alters myriad TGFbeta1-mediated activities [i.e., cell proliferation and neural cell adhesion molecule (N-CAM) expression] using B104 neuroblastoma cells. TGFbeta1 inhibited the proliferation of B104 cells as evidenced by decreases in cell number and [3H]thymidine ([3H]dT) incorporation. TGFbeta1 induced sustained activation of extracellular signal-regulated kinases (ERKs), which are part of the family of mitogen-activated protein kinases (MAPKs). Treatment with PD98059 (a MAPK kinase blocker) abolished TGFbeta1-regulated inhibition of [3H]dT incorporation. TGFbeta1-mediated growth inhibition was potentiated by ethanol exposure. Ethanol also produced prolonged activation of ERK, an effect that was partially eliminated by treatment with PD98059. On the other hand, TGFbeta1 up-regulated N-CAM expression, and this up-regulation was not affected by treatment with PD98059. Ethanol inhibited the TGFbeta1-induced up-regulation of N-CAM expression in a concentration-dependent manner. Thus, TGFbeta1 affects ERK-dependent cell proliferation and ERK-independent N-CAM expression in B104 cells. Both activities are sensitive to ethanol and may underlie the ethanol-induced alterations in the proliferation and migration of CNS neurons.

Chronic ethanol exposure alters MK-801 binding sites in the cerebral cortex of the near-term fetal guinea pig

The mechanism of ethanol central nervous system (CNS) teratogenesis, resulting from chronic maternal ingestion of high-dose ethanol during pregnancy, is not clearly understood. One of the target sites for ethanol-induced damage in the developing brain is the cerebral cortex. It has been proposed that chronic prenatal ethanol exposure alters NMDA receptors in the developing cerebral cortex. To test this hypothesis, timed pregnant guinea pigs were administered one of the following oral treatments throughout gestation: 4 g ethanol/kg maternal body weight/day; isocaloric sucrose/pair-feeding; water; or no treatment (ad lib). Near-term fetuses were studied at gestational day (GD) 63 (term, about GD 68). This ethanol regimen produced a maternal blood ethanol concentration of 66+/-4 mM (304+/-19 mg/dl) at 1 h after the daily dose on GD 58. The chronic ethanol regimen decreased near-term fetal body weight (12-26% decrease), brain weight (23% decrease), and cerebral cortical weight (21% decrease), compared with the isocaloric sucrose/pair-feeding, and combined water/ad lib experimental groups. Saturation analysis of near-term fetal cerebral cortical membranes using a [3H]MK-801 radioligand binding assay demonstrated a decreased affinity and increased number of MK-801 binding sites for the chronic ethanol regimen compared with the control treatments. These data support the suggestion that upregulation of NMDA receptors in the cerebral cortex after chronic prenatal ethanol exposure could lead to NMDA receptor-mediated excitotoxicity in this brain region.

Muscarinic cholinergic receptor signal transduction as a potential target for the developmental neurotoxicity of ethanol

Central nervous system dysfunctions (most notably mental retardation and microcephaly) are among the most significant effects of in utero exposure to ethanol. Ethanol has been shown to cause alterations of both neuronal and glial cells, including cell loss, and changes in their migration and maturation. Here, we propose that one of the potential targets for the developmental neurotoxicity of ethanol may be represented by the signal transduction systems activated by cholinergic muscarinic receptors. Ethanol has been shown to inhibit second messenger systems activated by various G-protein-coupled receptors, including certain subtypes of muscarinic receptors. Although the roles of muscarinic receptors in brain development have not been fully elucidated, two potentially relevant effects have been discovered in the past few years. By activating muscarinic receptors coupled to phospholipid metabolism, acetylcholine can induce proliferation of glial cells, and act as a trophic factor in developing neurons by preventing apoptotic cell death. Ethanol has been shown to inhibit both actions of acetylcholine in vitro. These effects of ethanol may lead to a decreased number of glial cells and to a loss of neurons, which have been observed following in vivo alcohol exposure. In turn, these may be the basis of microencephaly and cognitive disturbances in children diagnosed with Fetal Alcohol Syndrome.

Expression of p53 and ALZ-50 immunoreactivity in rat cortex: effect of prenatal exposure to ethanol

Neuronal death is an active process that results in the upregulation of antigens recognized by ALZ-50 and p53. Since prenatal exposure to ethanol can induce the postnatal death of cortical neurons, we examined the effects of ethanol on the in vivo expression of both the ALZ-50-positive antigen and p53. Pregnant rats were fed one of three diets, a liquid diet containing ethanol (Et), an isocaloric and isonutritive diet (Ct), or chow and water (Ch). Segments of frontoparietal cortex from fetuses and pups were examined for ethanol-induced changes (a) in the expression of ALZ-50 and p53 immunoreactivity using a quantitative immunoblotting assay and (b) in the distribution of ALZ-50- and p53-positive cells using immunohistochemistry. In control rats, ALZ-50 identified a 56-kDa peptide that was transiently expressed postnatally and peak expression occurred on postnatal day (P) 6 to P12. In Et-treated rats, peak expression was attained earlier (on P3) and was about three times of that achieved in the controls. The anti-p53 antibody identified three proteins (28, 56, and 58 kDa). Peak expression in control rats occurred during the second postnatal week and only the 58-kDa protein was expressed in appreciable amounts in adult cortex. Each p53-positive protein was affected by ethanol exposure. The 28- and 56-kDa p53-positive proteins were affected by ethanol much in the same way as was the ALZ-50-positive antigen. That is, the timing and amount of peak expression were earlier and lower, respectively, in the Et-treated rats. The postnatal expression of the 58-kDa protein was halved following prenatal exposure to ethanol. Both ALZ-50 and anti-p53 immunoprecipitated proteins are p53- and ALZ-50-positive, respectively. Thus, ethanol alters the expression of the ALZ-50- and p53-positive proteins and presumably the timing of neuronal death in the developing cortex. The parallel effects of prenatal ethanol exposure on the 56-kDa ALZ-50-positive antigen and the 28- and 56-kDa p53-positive proteins and the coprecipitation of the proteins are consistent with the notion that ALZ-50 recognizes a form of p53.

Effect of ethanol on neurotrophin-mediated cell survival and receptor expression in cultures of cortical neurons

The interaction of ethanol and neurotrophin-mediated cell survival was examined in primary cultures of cortical neurons. Cells were obtained from rat fetuses on gestational day 16 and maintained in a medium supplemented with either 10% or 1.0% fetal calf serum (FCS). Exogenous nerve growth factor (NGF; 20 ng/ml), brain-derived neurotrophic factor (BDNF; 20 ng/ml) or neurotrophin 3 (NT-3; 20 ng/ml) was added to the cultures alone, or in combination with ethanol (400 mg/dl). The number of viable neurons was determined after a 48 h treatment with a growth factor and/or ethanol. The effects of ethanol on the expression of high affinity neurotrophin receptors (trkA, trkB, and trkC) and the low-affinity receptor (p75), were analyzed using Western immunoblots. In untreated cultures, 22.7% and 26.3% of the cells raised in a medium containing 10% and 1.0% FCS, respectively, were lost. Only NGF prevented the death of the cultured cortical neurons. Ethanol was toxic; it caused a 23.5% and 16.7% loss of cells (for cells grown in a medium containing 10% and 1.0% FCS, respectively) beyond that occurring 'naturally' in an untreated culture. Ethanol completely blocked the NGF-mediated cell survival. In general, BDNF and NT-3 did not offset the toxic effect of ethanol. Immunoblotting studies showed that the expression of p75 was significantly (p < 0.05) lower (40%) in ethanol-treated cultures, but ethanol did not affect trk expression. Thus, ethanol has specific effects upon NGF-mediated cell survival and the effects on the low affinity receptor imply that p75 specifically plays an important role in NGF signaling.

Prenatal effects of drugs of abuse on brain development

Drugs of abuse modify signaling of neurotransmitter systems and intracellular messengers. Recent studies of central nervous system development show that these same neurotransmitters may serve as molecules that regulate specific aspects of cell proliferation, survival, migration, circuit formation and establishment of topography. Moreover, the convergence of neurotransmitter, growth factor and hormone activity on similar intracellular signaling systems suggests the potential for significant interactions among molecular components that regulate development. The application of modern strategies used by developmental and cell biologists to the question of whether prenatal drug exposure alters brain structure and function has led to discoveries of specific, targeted changes. Studies of the mechanisms of drug action that lead to altered neural development are now reality.

Basic fibroblast growth factor- and platelet-derived growth factor-mediated cell proliferation in B104 neuroblastoma cells: effect of ethanol on cell cycle kinetics

In vivo studies show (a) that early exposure to ethanol depletes neurons in the central nervous system (CNS) and (b) that a primary target of ethanol in the developing nervous system is proliferating neuronal precursors. We used a neuronal cell line (B 104 neuroblastoma cells) as an in vitro model for the effects of ethanol on the proliferation of neuronal precursors to test the hypothesis that ethanol interferes with growth factor-regulated proliferation of neuron-like precursors. The effects of ethanol on the mitogenic activity of two growth factors, basic fibroblast growth factor (bFGF) and platelet-derived growth factor AA and BB (PDGF-AA and PDGF-BB), were examined. Cell proliferation was monitored by tracing the change in the numbers of cultured cells over 4-5 days and in the cell cycle kinetics was determined using a cumulative labeling technique with bromodeoxyuridine (BrdU). Western immunoblots and immunohistochemical preparations show that B104 cells expressed the high affinity receptors for bFGF, PDGF-AA and PDGF-BB. The three growth factors were potent mitogens for the B104 cells; they promoted an increase in cell number even when the cells were grown in serum-free medium. Ethanol depressed the bFGF-, PDGF-AA- and PDGF-BB-mediated cell proliferation without altering the incidence of cell death. These changes in proliferation were concentration-dependent; at a concentration of 100 mg/dl, ethanol partially, but significantly inhibited growth factor-stimulated proliferation and higher ethanol concentrations (400 mg/dl or more) completely abolished growth factor-regulated cell proliferation. The effects of ethanol on cell growth were a result of ethanol-induced changes in growth factor-regulated cell cycle kinetics, principally the total length of the cell cycle and the fraction of the population that was actively cycling (the growth fraction). Ethanol completely negated the action of bFGF, but only partially blocked PDGF-promoted cycling activity. Thus, B104 cells are a suitable model for studying the effects of ethanol on neuronal proliferation. The blockage of bFGF- and PDGF-mediated cell proliferation by ethanol supports the hypothesis that growth factors are a target of ethanol neurotoxicity. Furthermore, the differential actions and effects of ethanol on the two growth factors mirror effects observed in vivo.

Effects of prenatal exposure to ethanol on callosal projection neurons in rat somatosensory cortex

The distribution and density of callosal projection neurons in the somatosensory cortex of mature rats was altered by prenatal exposure to ethanol. The density of callosal neurons was significantly greater in ethanol-treated rats than in controls. Ethanol exposure also altered the laminar distribution of callosal projection neurons. Whereas in control rats the cell bodies of callosal projection neurons were in layers II/III and V, in ethanol-treated rats most of these neurons were distributed in layers V and VI. Many of the ectopic neurons were generated toward the end of cortical neuronogenesis (i.e., on gestational day 20). This contrasts with controls wherein co-generated cohorts were distributed in layer II/III. Thus, the connectional phenotype of the callosal projection neurons is retained regardless of its laminar residence. These ethanol-induced abnormalities apparently result from defects in neuronal migration and axonal pruning.

Limited ethanol exposure selectively alters the proliferation of precursor cells in the cerebral cortex

The present in vivo study tests the hypothesis that limited (4-day) exposure to ethanol differentially affects the proliferation of cortical precursors in the two cortical germinal zones [the ventricular zone (VZ) and the subventricular zone (SZ)] and their descendants in the mature brain. The offspring of pregnant rats fed a liquid diet containing 6.7% (v/v) ethanol when prosencephalic stem cells [gestation day (G) 6-69], VZ cells (G12-G15), and SZ cells were proliferating (G18- G21) throughout much of gestation (G6-G21). In addition, the offspring of rats pair-fed a liquid control diet or fed chow were examined. The pregnant dams were administered with bromodeoxyuridine (BrdU) on either G15 or G21. The ratio of the number of cells that incorporated BrdU to the total number (the labeling index) was determined 1-hr postinjection (i.e., on G15 or G21) or on postnatal day 60, Ethanol treatment between G6 and G21 reduced the ratio of cells labeled by an injection of BrdU on G15 in the fetus and in the adult, and increased the ratio of cells labeled on G21. Regardless of when the injection was placed, ethanol treatment between G6 and G9 had no effect upon the ratio of BrdU-labeled cells in the fetus or mature cortex. Exposure from G12 to G15 decreased the number of VZ cells in the fetus and the number of immunolabeled cells in the adult cortex labeled by an injection on G15. This exposure had no effect on the incorporation by SZ cells. In contrast, ethanol exposure from G18 to G21 increased the labeling indices for fetal SZ cells and for cells in the adult, but it had no effect on the ratio of labeled VZ cells. Although ethanol had no apparent effect on the proliferation of stem cells, it did alter the proliferation of cells in the VZ and SZ. These effects are time-dependent and underlie the ethanol-induced changes in the number of cells in the adult.