Growth factors attenuate the cholinotoxic effects of ethanol during early neuroembryogenesis in the chick embryo

Neuroprotective effect of epidermal growth factor plus growth hormone-releasing peptide-6 resembles hypothermia in experimental stroke

BACKGROUND

Combined therapy with epidermal growth factor (EGF) and growth hormone-releasing peptide 6 (GHRP-6) in stroke models has accumulated evidence of neuroprotective effects from several studies, but needs further support before clinical translation. Comparing EGF + GHRP-6 to hypothermia, a gold neuroprotection standard, may contribute to this purpose.

OBJECTIVES

The aims of this study were to compare the neuroprotective effects of a combined therapy based on EGF + GHRP-6 with hypothermia in animal models of (a) global ischemia representing myocardial infarction and (b) focal brain ischemia representing ischemic stroke.

METHODS

(a) Global ischemia was induced in Mongolian gerbils by a 15-min occlusion of both carotid arteries, followed by reperfusion. (b) Focal brain ischemia was achieved by intracerebral injection of endothelin 1 in Wistar rats. In each experiment, three ischemic treatment groups - vehicle, EGF + GHRP-6, and hypothermia - were compared to each other and to a sham-operated control group. End points were survival, neurological scores, and infarct volume.

RESULTS

(a) In global ischemia, neurological score at 48-72 h, infarct volume, and neuronal density of hippocampal CA1 zone in gerbils treated with EGF + GHRP-6 were similar to the hypothermia-treated group. (b) In focal ischemia, the neurologic score and infarct volume of rats receiving EGF + GHRP-6 were also similar to animals in the hypothermia group.

DISCUSSION

With hypothermia being a good standard neuroprotectant reference, these results provide additional proof of principle for EGF and GHRP-6 co-administration as a potentially neuroprotective stroke therapy.

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).

Nerve growth factor prevents cell death and induces hypertrophy of basal forebrain cholinergic neurons in rats withdrawn from prolonged ethanol intake

We have previously reported that the hippocampal cholinergic fiber network is severely damaged in animals withdrawn from ethanol, and that a remarkable recovery in fiber density occurs following hippocampal grafting, a finding that we suggested to be underpinned by the graft production of neurotrophic factors, which are known to be decreased after ethanol exposure. It is widely accepted that nerve growth factor (NGF) signals the neurons of the brain cholinergic system, including those of the medial septum/vertical limb of the diagonal band of Broca (MS/VDB) nuclei, from which the septohippocampal projection arises. Because neurons in these nuclei are vulnerable to ethanol consumption and withdrawal we thought of interest to investigate, in withdrawn rats previously submitted to a prolonged period of ethanol intake, the effects of intraventricular delivery of NGF upon the MS/VDB cholinergic neurons. Stereological methods were applied to estimate neuron numbers and neuronal volumes in choline acetyltransferase (ChAT)-immunostained and Nissl-stained material. We have found that in ethanol-fed rats there was a significant reduction in the total number of Nissl-stained and cholinergic neurons in the MS/VDB, and that the suppression of ethanol intake further decreased neuron numbers. In addition, the somatic size of ChAT-IR neurons was reduced by ethanol intake, and withdrawal further aggravated neuronal atrophy. NGF treatment prevented the withdrawal-associated loss, and induced hypertrophy, of cholinergic neurons. These findings show that exogenous NGF protects the phenotype and prevents the withdrawal-induced degeneration of cholinergic neurons in the MS/VDB. These effects might be due to the trophic action of NGF upon the basal forebrain cholinergic neurons, including the hippocampal fiber network that conveys this neurotrophin retrogradely to the MS/VDB, and/or upon their targets, that is, the hippocampal formation neurons.

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.

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.

What research with animals is telling us about alcohol-related neurodevelopmental disorder

The substantial advances in understanding fetal alcohol syndrome over the past 20 years were made in large part because of research with animals. This review illustrates recent progress in animal research by focusing primarily on the central nervous system effects of prenatal alcohol exposure. Current findings suggest further progress in understanding consequences, risk factors, mechanisms, prevention and treatment will depend on continued research with animals.

Deficiency of essential neurotrophic factors in conditioned media produced by ethanol-exposed cortical astrocytes

Prior research in this laboratory has shown that in utero ethanol exposure adversely affects the development of serotonergic neurons. The current study investigated the hypothesis that cortical astrocytes produce trophic factors which are essential for the development of the fetal precursors of serotonergic and other raphe neurons (e.g. rhombencephalic neurons), and that ethanol exposure impairs the production of these factors by astrocytes. The results of these experiments demonstrated that cultured cortical astrocytes produce trophic factors which are necessary for the development of rhombencephalic neurons. Conditioned media obtained from control astrocytes promoted both general neuronal development (increased cell number, cell survival, DNA content, protein content, and neurite outgrowth) and serotonergic neuronal development (increased number of serotonin (5-HT) immunopositive cells and [3H]5-HT uptake). However, the conditioned media produced by ethanol-treated astrocytes (ECM) lacked essential neurotrophic factors. Neuronal cultures maintained in ECM had reduced DNA and neuronal survival, and altered neurite outgrowth. 5-HT immunopositive neurons and [3H]5-HT uptake were also decreased in ECM cultures. Thus, the damaging effects of in utero ethanol exposure on developing serotonergic neurons may be due to impaired production of astroglial neurotrophic factors.

Effects of nerve growth factor on splenic norepinephrine and pineal N-acetyl-transferase in neonate rats exposed to alcohol in utero: neuroimmune correlates

Prenatal alcohol exposure (FAE) has been associated with multiple anomalies, including a selective developmental delay of sympathetic innervation in lymphoid organs. Sympathetic neurons require nerve growth factor (NGF) for their development and maintenance, and recent evidence has suggested that alcohol impairs the synthesis and/or biological activity of NGF in selected central and peripheral neurons. Thus, the present study examined the hypothesis that NGF administration to FAE rats during early postnatal development would reverse some of the peripheral sympathetic deficits. Neonate rats, FAE and the corresponding control cohorts, received daily treatments of NGF or cytochrome C (0.3 mg/kg; s.c.) for various time intervals, and were killed 24 hr or 10 days after the last treatment. The measured parameters included norepinephrine (NE) concentrations in the spleen and heart, which receive nor-adrenergic innervation from the coeliac ganglion and the superior cervical ganglion (SCG), respectively. In addition, we measured the activity of pineal N-acetyltransferase (NAT), the rate-limiting enzyme of melatonin biosynthesis, which depends on sympathetic innervation from the SCG. The data show that chronic, but not acute, NGF treatments reversed the FAE-related deficits in splenic NE concentrations as well as in pineal NAT activity in a time- and age-dependent manner. Sympathetic neurons play an important role in immune modulation. Thus, the altered splenic NE levels and pineal NAT activity may play a role in immune deficits associated with exposure to alcohol in utero.

Role of GABAA receptors in the GABA attenuation of ethanol neurotoxicity

We have previously reported that GABA reverses the neuronotoxic effects of ethanol in neuroblast-enriched cultures derived from 3-day-old whole chick embryo (E3WE). In the present study, we examined the effects of GABA agonists and antagonists on morphological growth patterns and on cholinergic neuronal phenotypic expression, using choline acetyltransferase (ChAT) activity as a marker. E3WE neuroblast-enriched cultures showed positive immunoreactivity for neurofilament and as previously reported, control cultures exhibited the characteristic pattern of outgrowth of neurites of varying thickness radiating from the aggregates. In contrast, cultures grown in ethanol consisted of neuronal aggregates lacking fasciculation but having a complex network of individual thin neurites. Both GABA and GABAA agonist muscimol enhanced neuritic fasciculation and arborization in control and ethanol-treated cultures, and this growth enhancement was inhibited by GABAA antagonist bicuculline. No effects were noted with GABAB agonist baclofen. GABA increased ChAT activity in E3WE control cultures, as previously reported. A similar effect was seen with GABAA agonist muscimol, but not with GABAB agonist baclofen. However, the GABA effect was not apparent in the presence of GABAB antagonist phaclofen. Thus, it appears that the cholinotrophic effects of GABA are mediated by both GABAA and GABAB receptors. In ethanol-treated cultures the already-reported ChAT decline was reversed by GABA and muscimol, but not by baclofen. Moreover, the GABA effect in ethanol-treated cultures was not antagonized by GABAB antagonist phaclofen, suggesting that the GABA effect was mediated by a GABAA receptor. We conclude from these findings that the cholinotrophic effects of GABA are mediated by GABAA and GABAB receptors, while the rescuing effects of GABA in the ethanol-treated cultures are mediated via GABAA receptors.

Protective effects of maternal buspirone treatment on serotonin reuptake sites in ethanol-exposed offspring

Previous work in this laboratory demonstrated that in utero ethanol exposure is associated with abnormal development of the serotonergic system. Specific abnormalities included deficiencies of serotonin (5-HT) and its metabolites, and cortical 5-HT reuptake sites. The concentration of 5-HT1A receptors was also altered. The serotonin deficit was detected in the fetal ethanol-exposed brain, at an age when 5-HT would normally function as an essential trophic factor. Thus, it was hypothesized that the early 5-HT ethanol-associated deficit of an essential trophic factor (e.g. 5-HT) could contribute to subsequent developmental abnormalities in serotonergic neurons. In the present investigation we used quantitative autoradiography (QAR) to more fully characterize the developmental abnormalities in 5-HT reuptake sites in developing offspring of ethanol-fed rats. In addition, we attempted to overcome the potential negative impact of the ethanol-associated deficit of fetal 5-HT, by administering a 5-HT1A agonist, buspirone, to pregnant rats. These investigations demonstrated that postnatal (PN) 19 and/or 35 day ethanol-exposed offspring had a significant decrease in [3H]citalopram binding to 5-HT reuptake sites in the frontal cortex, parietal cortex, lateral hypothalamus, substantia nigra, medial septum, and striatum. In contrast, [3H]citalopram binding was increased in the dorsal raphe on PN5 and in the median raphe on PN19. No significant ethanol-associated changes were detected in the hippocampus CA3 region or in the amygdala. When [3H]citalopram binding was compared in the offspring of saline- and buspirone-treated dams, it appeared that maternal treatment with buspirone prevented or reversed most of the ethanol-associated developmental abnormalities in 5-HT reuptake sites. Buspirone prevented the decline in binding of [3H]citalopram in the frontal cortex, lateral hypothalamus, substantia nigra and medial septum. Similarly, buspirone treatment prevented the ethanol-associated increase in binding in the dorsal and median raphe. Additional experiments are needed to elucidate the impact of maternal buspirone treatment on the development of other neurotransmitter systems in offspring.

Ethanol neuronotoxicity in the embryonic chick brain in ovo and in culture: interaction of the neural cell adhesion molecule (NCAM)

The present study was undertaken to investigate the involvement of NCAM in the neuroteratogenic effects of ethanol demonstrated by us and others. In the first experiment we examined the effect of in-ovo ethanol exposure on expression of NCAM in various regions of the embryonic CNS throughout development. Chick embryos received ethanol (10 mg/50 microliters/day) or saline (control) at days 1-3 of development (E1-E3), were sacrificed at various embryonic ages and whole brain (WB), cerebral hemispheres (CH) and cerebellum (CE) processed for SDS-polyacrylamide gel electrophoresis. The normal developmental profile of NCAM in the chick brain exhibited the same dynamics as previously reported by others. When compared to age-matched control brains, an increase was observed in expression of high molecular weight forms of NCAM in cerebral hemispheres between E8 and E10. These bands represented highly sialated (> 180 kDa) forms of NCAM. In fact, the NCAM hand from ethanol-treated embryos at E8 migrated at a higher molecular weight than did its control counterpart, indicating an increase in sialic acid content. In contrast, no clear change was observed in NCAM expression in cerebellum from E10 through E20 as a result of ethanol exposure. In the second experiment, we examined the involvement of NCAM in the alterations in neuronal growth patterns observed in ethanol-exposed cultures. Neuroblast-enriched cultures derived from three-day-old whole chick embryos (E3WE) were maintained on poly-L-lysine pre-coated Petri dishes in DMEM+5% fetal bovine serum with or without 50 mM ethanol. Cultures were fixed at 3, 6 or 9 DIV and co-stained for NCAM and neurofilament (160 kDa). E3WE cultures exhibited intense NCAM immunoreactivity at 3 and 6 DIV decreasing by 9 DIV.NCAM positive structures included all neuronal perikarya, neuritic processes and growth cones. Addition of 50 mM ethanol to the medium resulted in profound alterations in growth patterns of developing neurons which continued to exhibit intense NCAM staining. Ethanol-induced changes in the developmental profile of NCAM expression (i.e. increased sialation) in cerebral hemispheres correspond temporally with the shift in neuronal phenotype from cholinergic to catecholaminergic and GABAergic which we have reported previously. Changes in the normal pattern of cellular contact and interaction as a result of altered NCAM expression may influence establishment of neurotransmitter phenotype. Findings from this study support the view that NCAM may be involved both directly and indirectly in shaping of the CNS during development and we speculate that ethanol neuroembryotoxicity uncouples this relationship.

Ethanol neurotoxicity on neuroblast-enriched cultures from three-day-old chick embryo is attenuated by the neuronotrophic action of GABA

In the present study, using neuroblast-enriched cultures derived from three-day-old chick embryos (E3WE), we examined the morphological effects of ethanol and/or GABA, as well as the developmental profile of the cholinergic and GABAergic neuronal phenotypes, as assessed by the activities of choline acetyltranferase (ChAT) and glutamate decarboxylase (GAD). Cultures exposed to ethanol (50 mM) exhibited smaller and fewer aggregates than controls with a neuritic network that lacked fasciculation. In cultures treated with GABA (10(-5) M) alone or ethanol+GABA the size and number of the neuronal aggregates was increased and also neuritic arborization and fasciculation was enhanced. Thus, addition of GABA restored the normal growth pattern in the ethanol-treated cultures. As previously shown, E3WE culture treated with ethanol alone showed a decrease in both ChAT and GAD activities compared to controls. Both cholinergic and GABAergic neuronal phenotypes were enhanced in cultures treated with GABA as assessed by increases in ChAT and GAD activities, respectively, compared to controls. Moreover, in cultures treated concomitantly with ethanol and GABA both ChAT and GAD activities were higher than in ethanol-alone-treated cultures. Thus, the presence of GABA in the ethanol-treated cultures counteracted the decline in ChAT and GAD activities observed in the ethanol-alone-treated cultures. We conclude that GABA through its neuronotrophic actions can rescue neuroblasts from ethanol insult and restore neuronal phenotypes.

Astrocyte differentiation is enhanced in chick embryos treated with ethanol during early neuroembryogenesis

In this study, we examined the effects of ethanol administered to chick embryos, on the maturation of astrocytes, using glutamine synthetase (GS) activity as an astrocyte marker. Ethanol (50 mM) was administered in ovo via the air sac, embryos were sacrificed at various days of embryonic development and GS activity was determined in cerebral hemispheres and cerebellum. We found that in both cerebral hemispheres and cerebellum, GS activity was higher in the ethanol-treated embryos, as compared to controls, during the embryonic periods, E6 to E10 in the cerebral hemispheres and E10 to E14 in the cerebellum. These periods are characterized by increased neuronal differentiation in these CNS areas. The increase in GS activity in the ethanol-treated embryos is speculated to reflect either a transient reactive gliosis and/or an enhancement in the differentiation of radial glia, immature glia, to more mature astrocytes.

Early neuroblasts are pluripotential: colocalization of neurotransmitters and neuropeptides

This study was undertaken in order to establish the presence of pluripotential neuroblasts in the developing chick CNS. This has been suggested by our previous observations that expression of emerging neuronal phenotypes in the chick embryo CNS is affected by exposure to neurotrophic substances (i.e., GHRH, SRIF, NGF, EGF, muscle-derived factors) or neurotoxins such as ethanol. We have proposed that one mechanism whereby these substances elicit their effects is by shifting phenotypic expression in populations of pluripotential neuroblasts. In order to establish the presence of significant populations of pluripotential neuroblasts, cultures obtained from 3-day-old whole chick embryos (E3WE) were double-stained with antibodies to markers specific for four neuronal phenotypes in various permutations. Cultures at 6 DIV were tested for the presence of tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), gamma-aminobutyric acid (GABA), and somatostatin (SRIF) alone, and in various combinations. We observed a colocalization of all phenotypic markers within neuronal perikarya and processes in more than fifty percent of neuronal cells in these cultures. These data suggest that developing neuroblasts at this stage of embryogenesis possess the machinery necessary to adopt multiple neuronal phenotypes. The colocalization of neurotransmitter proteins in early neuroblasts (60 hr of embryogenesis) supports the recent concept that these substances themselves may influence phenotypic expression and also supports our idea that microenvironmental factors (i.e., ethanol, growth factors) provide signals which affect emerging phenotypes.

Reversal of alcohol's effects on neurite extension and on neuronal GAP43/B50, N-myc, and c-myc protein levels by retinoic acid

Alcohol teratogenesis may be due in part to inhibition of neuronal differentiation by ethanol. We showed previously that alcohol decreased neuronal differentiation (neurite extension) and increased N-myc and c-myc neuronal protein levels. Since Growth-Associated Protein 43 (GAP43/B50) levels must increase for neurons to differentiate, alcohol may decrease GAP43/B50. Alcohol dose-dependently (0-0.5%) decreased GAP43/B50 protein levels by up to 92% in immature LA-N-5 cells. Five nM retinoic acid alone induced differentiation and increased GAP43/B50 levels to 230% of control. These retinoic acid-induced increases in GAP43/B50 and neurite outgrowth, and decreases in N-myc and c-myc, were reversed dose-dependently by alcohol (0-0.5%). Conversely, the adverse effects of 0.25% alcohol on neurite extension, GAP43/B50, N-myc, and c-myc were prevented by 15 and 45 nM retinoic acid. These results suggest that inhibition of neuronal differentiation by alcohol and prevention of such effects by retinoic acid are related to changes in GAP43/B50, N-myc and c-myc.

GABA attenuates the neurotoxic effects of ethanol in neuron-enriched cultures from 8-day-old chick embryo cerebral hemispheres

Neuron-enriched cultures were prepared from 8-day-old chick embryo cerebral hemispheres and exposed to ethanol (50 mM), GABA (10(-5) M) and ethanol (50 mM) + GABA (10(-5) M) from day 4 to 8 in culture. At day 8, control, ethanol, GABA and ethanol + GABA-treated cultures were examined morphologically and biochemically. Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities were used as markers for cholinergic and GABAergic neuronal phenotypic expression, respectively. Control cultures showed more numerous and large neuronal aggregates as well as prominent neuritic bundles. Moreover, cultures treated with GABA depicted even more numerous neuronal aggregates with interconnecting neurites as compared to control. In contrast, ethanol-treated cultures exhibited smaller neuronal aggregates with less prominent neuritic bundles than control. However, cultures treated concomitantly with ethanol + GABA exhibited numerous and larger aggregates than cultures treated with ethanol alone. Neuritic bundles which were highly reduced in ethanol-treated cultures became prominent in the presence of GABA. As previously reported, ethanol alone enhanced ChAT and reduced GAD activities. GABA given alone enhanced the expression of both neuronal phenotypes. When GABA was given concomitantly with ethanol the decline in GAD and the rise in ChAT observed in ethanol-treated cultures was restored by GABA to almost control levels. Thus, ethanol-induced alterations in morphology and neuronal phenotypes were counteracted by the neurontrophic effect of GABA.

Ethanol's effect on tissue polyamines and ornithine decarboxylase activity: a concise review

An extraordinarily diverse literature describes the cellular/tissue systems in which the molecular effects of both acute and chronic alcohol exposure seem to be mediated by changes in polyamine levels and/or ornithine decarboxylase (ODC) activity. The single unifying factor that links most of these studies is that they all, in some way, involve tissues that are undergoing relatively rapid cell division. Non-dividing cells expressing the NMDA receptor are a notable exception in that ethanol and the polyamines seem to act via discrete regions of that receptor. Under most cellular conditions, ODC activity is a reflection of the relative tissue polyamine content, and an increase in ODC activity and polyamine content seems to be one of the early events in the progression of quiescent cells toward cell division. Thus, it is not surprising that ethanol, which has been widely reported to delay cell division, should be found to interact with the ODC/polyamine pathway. Perhaps the most unique aspect of these studies is the fact that, with rare exception, both acute and chronic ethanol exposure have been found to slow growth and to lower tissue polyamine (putrescine) content. Furthermore, in most studies, the ethanol-induced suppression of cell division could be overcome by the administration of exogenous putrescine. These data suggest that the ethanol-induced suppression of cell division resulted from the loss of putrescine. In addition, because the cells were able to respond to the exogenous putrescine, the studies suggest that the signaling pathway remained intact beyond the polyamine synthesis step.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol influences on the chick embryo spinal cord motor system: analyses of motoneuron cell death, motility, and target trophic factor activity and in vitro analyses of neurotoxicity and trophic factor neuroprotection

A series of in vivo and in vitro experiments were conducted to determine the influence of prenatally administered ethanol on several aspects of the developing chick embryo spinal cord motor system. Specifically, we examined: (1) the effect of chronic ethanol administration during the natural cell death period on spinal cord motoneuron numbers; (2) the influence of ethanol on ongoing embryonic motility; (3) the effect of ethanol exposure on neurotrophic activity in motoneuron target tissue (limb bud); and (4) the responsiveness of cultured spinal cord neurons to ethanol, and the potential of target-derived neurotrophic factors to ameliorate ethanol neurotoxicity. These studies revealed the following: Chronic prenatal ethanol exposure reduces the number of motoneurons present in the lateral motor column after the cell death period [embryonic day 12 (E12)]. Ethanol tends to inhibit embryonic motility, particularly during the later stages viewed (E9-E11). Chronic ethanol exposure reduces the neurotrophic activity contained in target muscle tissue. Such diminished support could contribute to the observed motoneuron loss. Direct exposure of spinal cord neurons to ethanol decreases neuronal survival and process outgrowth in a dose-dependent manner, but the addition of target muscle extract to ethanol-containing cultures can ameliorate this ethanol neurotoxicity. These studies demonstrate ethanol toxicity in a population not previously viewed in this regard and suggest a mechanism that may be related to this cell loss (i.e., decreased neurotrophic support).

Neuroblast cell death in ovo and in culture: interaction of ethanol and neurotrophic factors

We used two experimental paradigms to examine the influence of the neurotrophins, NGF, EGF, and bFGF on normal neuroblast survival and also after ethanol insult. In the first paradigm, chick embryos received in ovo at embryonic day 1 and 2 (E1 and E2) saline (control) ethanol (10mg/50 microliters/day), NGF (50 ng/50 microliters/day), or EGF (25 ng/50 microliters/day), or ethanol+NGF or EGF. At E3, cultures were prepared from whole embryos separately from each group. At C2, all cultures were labeled with [3H]thymidine and assessed for effects or neuronal survival. In the second paradigm, cultures were prepared from 3-day-old whole embryos and at C0, cultures were treated with either ethanol (50 mM) alone, NGF (50 ng/ml) alone, EGF (25 ng/ml) alone, bFGF (50 ng/ml) alone, or were treated concomitantly with ethanol plus one of the neurotrophins; control had only the culture medium, DMEM + 5% FBS. We obtained the following findings. 1) Cultures derived from embryos treated with either of the three neurotrophins exhibited a higher neuronal survival as compared to controls (1st paradigm). 2) The survival-promoting effect was also observed when the neurotrophins were added directly to the cultures (2nd paradigm). 3) As reported previously, cultures derived from ethanol-treated embryos exhibited a marked decline in neuronal survival as compared to controls. 4) All three neurotrophins attenuated the decline in neuronal survival produced by ethanol. The 'rescuing' effects of the neurotrophins support our early hypothesis that ethanol administration during early neurogenesis interferes with microenvironmental trophic signals essential for neuroblast survival and differentiation.

Responsiveness of cultured septal and hippocampal neurons to ethanol and neurotrophic substances

Dissociated septal and hippocampal neurons from E18 fetal rats were cultured with varying concentrations of ethanol (0.6-2.4 g/dl) and in cultures containing ethanol plus nerve growth factor (NGF) or basic fibroblast growth factor (bFGF). These substances have been shown to provide neurotrophic support for these populations and to afford neuroprotection against certain toxic substances or conditions applied to some neuronal populations. Both the septal and hippocampal neurons responded to ethanol in a dose-dependent manner. Survival of septal neurons was generally unaffected by initial ethanol concentrations of 0.6 and 1.2 g/dl but was considerably impaired by higher concentrations (1.8 and 2.4 g/dl), while neurite outgrowth was compromised by all ethanol concentrations except the lowest one applied. The hippocampal neurons survived ethanol concentrations up to 2.4 g/dl, although process extension was decreased in concentrations of 1.2 g/dl and higher. NGF or bFGF in the culture medium (in cultures without ethanol) did not affect neuronal survival or process outgrowth in either population, probably owing to the relatively high plating densities of the cultures. NGF did tend to have a moderate ameliorative effect on the ethanol neurotoxicity in the septal cultures, however, and was slightly effective in this regard in hippocampal cultures at intermediate ethanol concentrations (1.8 g/dl). High concentrations of ethanol (2.4 g/dl) reduced the proportion of cholinergic cells in the septal preparations by approximately 50%. This neuronal loss could be reversed by inclusion of high concentrations of NGF in the culture medium (100 ng/ml) but not by a lower concentration (20 ng/ml). bFGF provided some protection against ethanol cytotoxicity with respect to both populations. The implications of these results for studies of fetal alcohol effects are discussed, as well as their relation to prior reports of trophic factor neuroprotection.

Prenatal exposure to ethanol induces changes in the nerve growth factor and its receptor in proliferating astrocytes in primary culture

We have analyzed the effect of prenatal exposure to alcohol on the binding, internalization and secretion of NGF as well as on the content of the NGF receptor (NGFr) in cortical rat astrocytes in primary culture. Secretion of NGF was approximately 1.8-fold greater in 6-day control astrocytes than in 13-day cells. Intracellular content of NGF was very low. Astrocytes in 6-day cultures from control fetuses expressed a relatively large number of NGFr on the cell surface with a steady-state constant in the low nanomolar range. NGF was internalized by astrocytes at a slow rate. Prenatal exposure to ethanol induces a moderate increase in the number of NGFr on the cell surface as well as an increase in the intracellular pool of both NGF and NGFr which is accompanied by an important reduction in the secretion of this factor. We speculate that this decrease in NGF secretion could alter the neuronal migration pattern during development, resulting in the presence of ectopic neurons in the cortex.

The critical period for ethanol effects on cholinergic neuronal expression in neuroblast-enriched cultures derived from 3-day-old chick embryo: NGF ameliorates the cholinotoxic effects of ethanol

Studies from our laboratory have established that ethanol exerts morphological and biochemical neurotoxic effects during early neuroembryogenesis in the chick brain both in ovo and in culture. In the present study, we further localized the critical period for ethanol effects on cholinergic neuronal expression using neuroblast-enriched cultures derived from 3-day-old chick embryos. Moreover, we report that NGF attenuated the cholinotoxic effects of ethanol. We used the following experimental paradigms: cultures treated with ethanol alone either C0-C3 or C4-C10; NGF alone C0-C4 or C4-C10; ethanol and NGF given concomitantly; ethanol given first then replaced with NGF in the medium; or NGF given first then replaced with ethanol in the medium. The results revealed: (1) the cholinotoxic effect of ethanol occurs between culture days C0 and C4 with day 3 appearing to be most critical; (2) similarly, the critical period for the cholinotoxic effects of NGF is during early neuroblast differentiation, culture days C0-C4; (3) NGF can prevent the cholinotoxic effects of ethanol only if both ethanol and NGF are given concomitantly or if ethanol is given first, then culture is replaced with NGF-containing medium.

Early in ovo exposure of chick embryos to ethanol prevents the neuronotrophic effects of intracerebral NGF administration on cholinergic phenotypic expression

We have reported that ethanol administration during early neuroembryogenesis significantly alters neuronal phenotypic expression. In addition, previous findings have indicated that ethanol may interfere with the neurotrophic effects of NGF. In this study, we examined the cholinergic neuronal response to NGF given intracerebrally to embryos at embryonic day 8 (E8) which were exposed to ethanol in ovo via the air sac at E1-3. We found that doses of NGF ranging from 0.01 to 1 ng/2 microliters/embryo given intracerebrally to untreated embryos at E8, and sacrificed at E10, significantly increased choline acetyltransferase (ChAT) activity, the marker for cholinergic neuronal expression. This response was most marked in spinal cord as compared with the low response observed in cerebral hemispheres. In control embryos treated with saline at E1-3 and then receiving NGF intracerebrally at E8, ChAT activity in the spinal cord increased with increasing NGF doses; the highest value was obtained with 0.1 ng NGF. In contrast, in ethanol-treated embryos, ChAT activity was not affected by intracerebral administration of NGF and, in fact, the highest dose (0.1 ng) produced a decrease in ChAT activity. We conclude that: (1) intracerebral administration of NGF produces differential cholinotrophic effects in the embryonic chick CNS; and (2) exposure to ethanol during early neuroembryogenesis interferes with the cholinotrophic effects of NGF.

Modulation of ethanol neurotoxicity by nerve growth factor

Dorsal root ganglion (DRG) neurons were cultured with varying concentrations of ethanol and NGF. At low concentrations of NGF (0.1 ng/ml) moderate initial ethanol levels (250 mg/dl) significantly suppressed neurite outgrowth. Higher NGF concentrations (5 ng/ml) protected against this neurotoxicity. At this higher NGF concentration, neuronal survival was not significantly affected by exposure to 0.25-4 g/dl ethanol, although survival was significantly diminished at 5 and 6 g/dl. Neurite outgrowth was a more sensitive indicator of ethanol neurotoxicity in this population, with significant decreases in process extension seen with 1 g/dl ethanol. When cultures were supplemented with 10 ng/ml NGF, however, process elaboration was significantly greater at 1 g/dl ethanol than that measured with 5 ng/ml NGF, and in fact did not differ from NGF controls. These studies indicate that NGF can provide neuroprotective effects against ethanol toxicity under these conditions. The results are discussed in relation to other recent reports of trophic factor neuroprotection.

Ethanol-induced insulin resistance suppresses the expression of embryonic ornithine decarboxylase activity

In utero exposure to ethanol is associated with significant increases in fetal morbidity and mortality as well as with behavioral and learning problems that appear later in life. Growth suppression of the developing child is the most frequent physical effect of ethanol exposure and is correlated with specific molecular changes within the developing organism. The present report suggests that embryonic ethanol exposure suppresses the normal developmental increase in ornithine decarboxylase (ODC) activity. The loss of ODC activity during the early stages of development is dose-dependent and is correlated with the degree of growth suppression. Because ODC is the rate-limiting step for the synthesis of the polyamines and thus appears to be a focal enzyme for the regulation of growth, we have investigated the biochemical consequences of an ethanol-induced inhibition of ODC activity. Using intact chick embryos as well as cultured embryonic tissue, these studies indicate that ethanol-induced changes in tissue putrescine content result in growth suppression because a single dose of exogenous putrescine blocked the growth suppression. In cultured tissue, ethanol exposure inhibited the ability of a known trophic factor (insulin) to induce ODC activity. The loss of insulin-inducible decarboxylase activity as a result of ethanol exposure was specific to ODC, but ethanol per se had no effect on ODC activity in vitro. The data suggest that exposure to ethanol results in a resistance of the embryonic tissue to the action of insulin and thereby disrupts the molecular path by which this mitogenic compound induces the expression of ODC enzymatic activity.

Role of gangliosides in behavioral and biochemical actions of alcohol: cell membrane structure and function

Alcohol exerts its pharmacological effects in adult brain by altering the physicochemical properties of cellular plasma membranes. Although alcohol does induce changes in membrane lipid composition, studies to relate these alterations to the development of behavioral tolerance to alcohol and the withdrawal effects have been unsuccessful. Actions of alcohol on developing brain are even more complex. Some of the reported effects include inhibition of embryogenesis, cell migration, and differentiation, including synaptogenesis. Gangliosides have neuroprotective action against a variety of neural insults (e.g., mechanical injury, drug toxicity, or hypoxic insult). This review addresses the role and significance of gangliosides in the CNS pathophysiology of alcohol exposure, as well as the effect of changes in endogenous gangliosides on membrane structure and function. We also describe the role of exogenous gangliosides in prevention of alcohol (acute and/or chronic)-induced CNS (prenatal and postnatal) neurotoxicity through their action on cellular plasma membranes. We propose that ganglioside's neuroprotective effects against alcohol neurotoxicity involve protection and restoration of plasma membrane structure (proteins and lipids) and thereby its function (ionic homeostasis, neurotransmitter receptor-mediated signal transduction). Thus gangliosides may have potential therapeutic use in treatment of alcohol-related problems.

Effects of ethanol on cultured fetal serotonergic neurons

In utero ethanol exposure impairs the development of several neurotransmitter systems, including the serotonergic system. However, at present the mechanism by which in utero ethanol exposure damages the developing brain is unknown. This research examined the possibility that ethanol directly impairs the development of serotonergic neurons. This hypothesis was assessed by examining the content of serotonin (5-HT), 5-HT uptake, and 5-HT immunopositive neurons in cultures of fetal rhombencephalic neurons that were exposed to ethanol for 4 days in vitro. In addition, the effects of in vitro ethanol exposure on protein and DNA content of cultured rhombencephalic neurons were determined. These studies demonstrated that a 4-day exposure of cultured rhombencephalic neurons to 50 to 300 mg ethanol/dl did not affect 5-HT content, 5-HT uptake, or the proportion of 5-HT immunopositive neurons. In addition, this ethanol exposure had no significant effect on protein or DNA content. Additional studies, using a 4-day exposure to 450 mg ethanol/dl also did not detect significant differences in 5-HT uptake or in protein or DNA content. The marked differences in the findings of the present in vitro and previous in vivo studies may be due to the fact that the ethanol exposure in vivo was longer than that in vitro, and included the period of early development of serotonergic neurons and their progenitors. Alternatively, the differences may be due to ethanol-associated alterations in maternal or fetal factors (e.g., hormones, amino acids, and growth factors) that are necessary for the normal development of the serotonergic system in vivo. Normal concentrations of such factors in the serum-containing media may have protected the cultured neurons from the damaging effects of ethanol.

The effect of chronic ethanol intake on brain NGF level and on NGF-target tissues of adult mice

The effect of ethanol consumption on the forebrain and hypothalamus of adult mice was investigated. A consistent decrease of biological activity and of nerve growth factor (NGF) immunoreactivity was observed in the hippocampus and hypothalamus of alcohol-treated mice. Biochemical studies also indicate that chronic ethanol intake causes a reduction in the level of choline-acetyltransferase in the septum, hippocampus and striatum, but not in the cortex and other brain regions. This study provides evidence that long-term ethanol intake causes impairment of brain NGF level and of the cholinergic enzyme, regulated by NGF, suggesting that NGF synthesis and/or biological activity is affected in alcohol-related brain neuropathology.

Acetyl-L-carnitine has a neuromodulatory influence on neuronal phenotypes during early embryogenesis in the chick embryo

Studies from this laboratory and others have demonstrated that neuroblasts in early embryogenesis exhibit a high degree of plasticity with respect to neurotransmitter phenotype. The critical period within which these neuroblasts are sensitive to the effects of endogenous neurotrophins has been defined as 1-3 days of development in the chick embryo. In this study, we examined the influence of acetyl-L-carnitine (ALCAR) administered in ovo during embryonic days 1-3 (E1-E3) and sacrificed at embryonic day 8 (E8) on cholinergic and GABAergic neuronal phenotypes using as neuronal markers the activities of choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD), respectively. Phenotypic expression was assessed in 3 distinct anatomical regions of the embryonic brain: cerebral hemispheres (CH), optic lobes (OL), and diencephalon-midbrain-brainstem (DMBS). A single administration of ALCAR at embryonic day 1 resulted in a dose-dependent increase in ChAT activity and decrease in GAD activity in CH. ChAT activity was again increased and GAD activity decreased in CH from embryos that were administered ALCAR (100 micrograms/50 microliters/day) daily from embryonic day E1 to E3. No change was observed in either ChAT or GAD activity in OL in response to ALCAR administration during the critical period (E1-E3) at doses ranging from 10 to 500 micrograms/day. In the DMBS, the activity of ChAT exhibited a marked increase at lower doses (10 micrograms) followed by a marked decrease at higher doses (500 micrograms) of ALCAR. The decrease in ChAT activity in DMBS was again observed at an ALCAR dose of 100 micrograms/day when administered from E1 to E3.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol administration during early embryogenesis affects neuronal phenotypes at a time when neuroblasts are pluripotential

Our previous studies have reported that ethanol administration during a critical period of development profoundly affects the expression of neuronal phenotypes in whole brains of chick embryos. The present study examines a) the long-lasting effects of early ethanol treatment on neurotransmitter phenotypic expression and b) its differential effects on anatomically discrete regions of the developing chick CNS. Ethanol (10 mg/50 microliters) was administered to embryos via the air sac from E1 to E3. Embryos were sacrificed on days 4, 8, 10, or 15 of embryonic development (E4, E8, E10, E15) and assayed in specific regions of the CNS for glutamate decarboxylase (GAD) or choline acetyltransferase (ChAT) as markers for GABAergic or cholinergic neurons, respectively. The magnitude of the developmental profile for ChAT was highest in spinal cord (SC), with similar profiles observed for cerebral hemispheres (CH) and optic lobes (OL). In contrast, the developmental profile for GAD was highest in OL and lowest in SC. Thus, neuronal phenotypes inhabit specific CNS areas from early primordial stages of development. Furthermore, cholinergic neuronal populations in discrete CNS areas reached mature levels by E10, whereas GABAergic populations continued to increase throughout the experimental period. We suggest that GABAergic precursor neuroblasts may differentiate at a later embryonic age and that specific regional factors may play a role in neuronal distribution and the rate of maturation. As reported previously, primordial CNS areas exposed to ethanol (E1-E3) exhibited a differential sensitivity. Cholinergic neuronal expression in CH remained retarded throughout the experimental period examined, whereas the early decline observed at E4 in SC cholinergic expression was reversed by E15.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cocaine, ethanol or nicotine on ornithine decarboxylase activity in early chick embryo brain

Fetal drug exposure causes multiple deficits in the developing child. For both humans and animal models, the single most common drug-related problem is fetal growth suppression. This defect is associated with significant perinatal morbidity and mortality and may also be related to significant behavioral problems appearing later in life. Studies focussed on the molecular mechanism of fetal drug effects in placental models are complicated by multiple interactions of the drug with mother, placenta and fetus. Using early (76-168 h) chick embryos as a non-placental model, and three common drugs of abuse (nicotine, ethanol and cocaine) it was found that each drug suppressed the peak in fetal brain ornithine decarboxylase (ODC) activity that normally occurs at 120 h of development. For each drug, the decrease in ODC activity at 120 h was followed by a small but significant increase in ODC. Thus, although the drug-treated embryos were smaller in size, they appeared to be undergoing compensatory growth and, in fact, became equal in weight to the vehicle-treated animals, if allowed to hatch.

Ethanol increases cholinergic and decreases GABAergic neuronal expression in cultures derived from 8-day-old chick embryo cerebral hemispheres: interaction of ethanol and growth factors

We have shown that ethanol exposure during embryogenesis affects a variety of parameters of neuronal growth both in ovo and in vitro. Moreover, we have found that growth factors significantly attenuate the in ovo neurotoxicity produced by ethanol. In this study, we further examined the direct effects of ethanol exposure on neuron-enriched cultures derived from 8-day-old chick embryo cerebral hemispheres consisting primarily of differentiated neurons. In addition, we examined the interaction of ethanol and nerve growth factor (NGF) or epidermal growth factor (EGF) when the growth factors were given concomitantly with ethanol. Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) were used as markers for cholinergic and GABAergic neuronal phenotypic expression, respectively. We found that ethanol alone enhanced ChAT and reduced GAD activities in a dose-dependent manner. NGF and EGF given alone enhanced the expression of both neuronal phenotypes. When NGF was given concomitantly with ethanol at C4-8 the decline in GAD produced by ethanol was reversed. The effects of concomitant administration of ethanol and growth factors on ChAT activity revealed that ethanol interfered with the increases produced by the growth factors and especially with NGF when given alone. We conclude from these findings that ethanol may interfere with neuronal phenotypic expression by altering neuronal responsiveness to neurotrophic signals important for neuronal differentiation.

Nerve growth factor stimulates neurite regeneration but not survival of adult auditory neurons in vitro

Injury to either the peripheral or central nervous system results in the accumulation of growth factors at the wound site. Some of these growth factors have been shown to participate in the neural repair process. Adult auditory neurons grown in dissociated spiral ganglion cell cultures are injured (i.e. bilateral axotomy) as a result of the initial preparation of these cultures. Therefore, cell cultures of dissociated spiral ganglia provide a model for the study of repair processes of adult auditory neurons (e.g. effects of exogenous growth factors on the process of neuritogenesis by injured neurons). Auditory neurons do not survive in these dissociated ganglion cell cultures when only exogenous NGF is added to the defined culture medium. Previous work has identified substrate bound basic fibroblast growth factor (bFGF) as a survival factor for adult auditory neurons in vitro. Auditory neurons cultured on substrate bound bFGF also do not show increased survival in response to the addition of increasing concentrations of nerve growth factor (NGF) to the defined medium. This is in sharp contrast to the pronounced neurite outgrowth-promoting effects (concentration dependent) observed when exogenous NGF is added to adult auditory neurons cultured on substrate bound bFGF. We propose that several neuronotrophic factors (e.g. TGFB1, bFGF, NGF and other neurotrophins) are active in the spiral ganglions' response to injury. Several of these growth factors (i.e. bFGF, NGF) act in cooperation to promote the regeneration or repair of severed or traumatized neuritic processes.

Correlation between morphological and biochemical effects of ethanol on neuroblast-enriched cultures derived from three-day-old chick embryos

We have shown that ethanol exposure during embryogenesis affects a variety of parameters of neuronal growth. In this study we examined the direct effects of ethanol exposure on developing neuroblasts in culture. Neuroblast-enriched cultures derived from 3-day-old whole chick embryos were grown in the presence of ethanol at doses ranging from 12.5 to 50 mM from culture day 3-14. Cholinergic and GABAergic phenotypic expression were both significantly reduced following ethanol exposure as assessed by the activities of choline acetyltransferase and glutamate decarboxylase, respectively. Morphometric analysis of the growth patterns showed significant differences between control and ethanol-treated cultures. Control cultures exhibited the characteristic pattern of growth consisting of neuronal aggregation with neuritic arborization, i.e., neuritic bundles and fasciculation. Cultures grown in ethanol from culture day 3 consisted of aggregates that measured significantly greater in size than those observed in control cultures. In addition, in ethanol-treated cultures, the primary pattern of neuritic bundles was replaced by a complex network of individual neurites radiating from the central aggregate, forming a defined "neuritic field." Morphometric analysis revealed that both neurite number and neurite length were significantly reduced in ethanol-treated cultures. The biochemical data confirm earlier reports from this laboratory suggesting that ethanol exposure during early embryogenesis alters the normal neuronal pattern of phenotypic expression. In addition, we have presented evidence in this study that ethanol alters the morphological growth patterns of developing neurons. Although ethanol does not alter the ability of these cells to aggregate, there is a significant alteration in neuritic outgrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of early in ovo administration of ethanol on expression of the GABAergic neuronal phenotype in the chick embryo

In order to study the influence of ethanol on GABAergic neuronal expression in the chick embryonic brain, activity of glutamate decarboxylase (GAD; a GABAergic neuronal marker) was examined in whole brain derived from embryonic chick following the in ovo administration of ethanol. GAD activity was already detectable by 3 days of embryogenesis and exhibited a logarithmic increase up to embryonic day 16 (E16). By E18, GAD activity began to plateau. Administration of ethanol (10 mg/50 microliters/day) to embryos in ovo on days E1-E3, resulted in increased GAD activity in whole brain when embryos were sacrificed at E8. However, when embryos were administered ethanol on days E4-E7, activity of GAD was unchanged as compared with controls. Similarly, when embryos were administered ethanol chronically from E1-E7 no significant effect was observed in GAD activity. The increase observed in GAD activity after exposure to ethanol during a period of active neuronal proliferation (E1-E3) supports our view that E1-E3 is the critical period of sensitivity to ethanol with respect to the development of neuronal phenotypes during embryogenesis. Furthermore, the absence of any significant effect of ethanol administered from E1 to E7 on GAD activity suggests the existence of a compensatory response to ethanol insult.

Muscle-derived factors enhance cholinergic neuronal expression in the chick embryo--I. In ovo studies

The effects of muscle-derived factors were studied in the chick embryo in ovo, during early neuroembryogenesis. Limb muscle extract (LME) administration during embryonic period E1-E7 produced a significant increase in choline acetyltransferase activity of both spinal cord and brain in 8-day-old chick embryos. Similar treatment failed to induce significant change in the GABAergic phenotypes as assessed by the activity of the enzyme glutamic acid decarboxylase. Administration of limb muscle extract at either embryonic days 1-3 or 4-7 produced a significant increase in choline acetyltransferase activity in the brain, indicating that the critical period of limb muscle extract in the brain to be between embryonic days E1 and E7, a period of neuronal proliferation and differentiation in the brain. On the other hand, LME administration produced no effect on spinal cord choline acetyltransferase activity when given at embryonic days 1-3, whereas it produced a marked increase when given at embryonic days 4-7. Thus, the critical period of limb muscle extract effect in the spinal cord appears to be confined to embryonic days E4-E7, a period of neuronal differentiation and cell death in the spinal cord. These findings indicate that the cholinotrophic activity of muscle-derived factors is not limited to the muscle target tissues but have a general effect on cholinergic neurons in the CNS. Whether these cholinotrophic effects are mediated by a common factor or by different factors is still under investigation.