Fetal Alcohol Exposure Alters GAP-43 Phosphorylation and Protein Kinase C Responses to Contextual Fear Conditioning in the Hippocampus of Adult Rat Offspring

Effects of ethanol and varenicline on female Sprague-Dawley rats in a third trimester model of fetal alcohol syndrome

Perinatal ethanol exposure disrupts a variety of developmental processes in neurons important for establishing a healthy brain. These ethanol-induced impairments known as fetal alcohol spectrum disorder (FASD) are not fully understood, and currently, there is no effective treatment. Further, growing evidence suggests that adult females are more susceptible to ethanol, with the effects of perinatal ethanol exposure also being sexually divergent. Female models have been historically underutilized in neurophysiological investigations, but here, we used a third-trimester binge-ethanol model of FASD to examine changes to basal forebrain (BF) physiology and behavior in female Sprague-Dawley rats. We also tested varenicline as a potential cholinomimetic therapeutic. Rat pups were gavage-treated with binge-like ethanol, varenicline and ethanol, and varenicline alone. Using patch-clamp electrophysiology in BF slices, we observed that binge-ethanol exposure increased spontaneous post-synaptic current (sPSC) frequency. Varenicline exposure alone also enhanced sPSC frequency. Varenicline plus ethanol co-treatment prevented the sPSC frequency increase. Changes in BF synaptic transmission persisted into adolescence after binge-ethanol treatment. Behaviorally, binge-ethanol treated females displayed increased anxiety (thigmotaxis) and demonstrated learning deficits in the water maze. Varenicline/ethanol co-treatment was effective at reducing these behavioral deficits. In the open field, ethanol-treated rats displayed longer distances traveled and spent less time in the center of the open field box. Co-treated rats displayed less anxiety, demonstrating a possible effect of varenicline on this measure. In conclusion, ethanol-induced changes in both BF synaptic transmission and behavior were reduced by varenicline in female rats, supporting a role for cholinergic therapeutics in FASD treatment.

Impact of combined prenatal ethanol and prenatal stress exposures on markers of activity-dependent synaptic plasticity in rat dentate gyrus

Prenatal ethanol exposure and prenatal stress can each cause long-lasting deficits in hippocampal synaptic plasticity and disrupt learning and memory processes. However, the mechanisms underlying these perturbations following a learning event are still poorly understood. We examined the effects of prenatal ethanol exposure and prenatal stress exposure, either alone or in combination, on the cytosolic expression of activity-regulated cytoskeletal (ARC) protein and the synaptosomal expression of AMPA-glutamate receptor subunits (GluA1 and GluA2) in dentate gyrus of female adult offspring under baseline conditions and after 2-trial trace conditioning (TTTC). Surprisingly, baseline cytoplasmic ARC expression was significantly elevated in both prenatal treatment groups. In contrast, synaptosomal GluA1 receptor subunit expression was decreased in both prenatal treatment groups. GluA2 subunit expression was elevated in the prenatal stress group. TTTC did not alter ARC levels compared to an unpaired behavioral control (UPC) group in any of the 4 prenatal treatment groups. In contrast, TTTC significantly elevated both synaptosomal GluA1 and GluA2 subunit expression relative to the UPC group in control offspring, an effect that was not observed in any of the other 3 prenatal treatment groups. Given ARC's role in regulating synaptosomal AMPA receptors, these results suggest that prenatal ethanol-induced or prenatal stress exposure-induced increases in baseline ARC levels could contribute to reductions in both baseline and activity-dependent changes in AMPA receptors in a manner that diminishes the role of AMPA receptors in dentate gyrus synaptic plasticity and hippocampal-sensitive learning.

Novel therapeutic strategies for alcohol and drug addiction: focus on GABA, ion channels and transcranial magnetic stimulation

Drug addiction represents a major social problem where addicts and alcoholics continue to seek and take drugs despite adverse social, personal, emotional, and legal consequences. A number of pharmacological compounds have been tested in human addicts with the goal of reducing the level or frequency of intake, but these pharmacotherapies have often been of only moderate efficacy or act in a sub-population of humans. Thus, there is a tremendous need for new therapeutic interventions to treat addiction. Here, we review recent interesting studies focusing on gamma-aminobutyric acid receptors, voltage-gated ion channels, and transcranial magnetic stimulation. Some of these treatments show considerable promise to reduce addictive behaviors, or the early clinical studies or pre-clinical rationale suggest that a promising avenue could be developed. Thus, it is likely that within a decade or so, we could have important new and effective treatments to achieve the goal of reducing the burden of human addiction and alcoholism.

Opposite effects of acute ethanol exposure on GAP-43 and BDNF expression in the hippocampus versus the cerebellum of juvenile rats

The adolescent brain is particularly vulnerable to the effects of alcohol, with intoxications at this developmental age often producing long-lasting effects. The present study addresses the effects of a single acute ethanol exposure on growth-associated protein-43 (GAP-43) and brain-derived neurotrophic factor (BDNF) gene expression in neurons in the cerebellum and hippocampus of adolescent rats. Male postnatal day 23 (P23) Sprague-Dawley rats were exposed to ethanol vapors for 2h and after a recovery period of 2h, the cerebellum and hippocampus were harvested and samples were taken for blood alcohol concentration (BAC) determinations. We found that this exposure resulted in a mean BAC of 174 mg/dL, which resembles levels in human adolescents after binge drinking. Analyses of total RNA and protein by quantitative reverse transcription PCR and western blotting, respectively, revealed that this single ethanol exposure significantly decreased the levels of GAP-43 mRNA and protein in the cerebellum but increased the levels of mRNA and protein in the hippocampus. BDNF mRNA and protein levels were also increased in the hippocampus but not in the cerebellum of these animals. In situ hybridizations revealed that GAP-43 and BDNF mRNA levels were primarily increased by alcohol exposure in hippocampal dentate granule cells and CA3 neurons. Overall, the reported alterations in the expression of the plasticity-associated genes GAP-43 and BDNF in juvenile rats are consistent with the known deleterious effects of binge drinking on motor coordination and cognitive function.

Umbilical cord-derived mesenchymal stem cells with forced expression of hepatocyte growth factor enhance remyelination and functional recovery in a rat intracerebral hemorrhage model

BACKGROUND

Spontaneous intracerebral hemorrhage (ICH) carries a high mortality rate, with survivors commonly left with permanent neurological deficits. Mesenchymal stem cell (MSC) transplantation promotes functional recovery in experimental ICH, and treatment with hepatocyte growth factor (HGF) is beneficial in ischemic stroke.

OBJECTIVE

We hypothesize that transplantation of MSCs with previous transduction of HGF has an additive effect in promoting neurological recovery through myelin and axonal regeneration.

METHODS

HGF transduction to human umbilical cord-derived MSCs using lentiviral plasmid pWPI-HGF-GFP was prepared. One week after a collagenase-induced ICH, 80 male Sprague-Dawley rats were divided into 3 groups for stereotactic injection of phosphate-buffered saline (group I), MSC transplant (group II), and HGF-transduced MSC transplant (group III), respectively, into the left ventricle. The animals were assessed weekly for 5 weeks using the Rotarod motor function test, at which time they were killed for Luxol fast blue myelin staining and appropriate immunohistochemistry and Western blotting.

RESULTS

Animals receiving transplanted HGF-transduced MSCs (group III) exhibited significantly better motor function recovery than animals treated with MSCs alone (group II), which in turn performed better than the phosphate-buffered saline controls at 2 weeks after transplantation. Luxol fast blue staining of myelin displayed significantly less demyelination and significantly higher reactivity in myelin basic protein and growth-associated protein-43 in immunohistochemistry and Western blotting and significantly reduced myelin-associated glycoprotein activity in group III animals.

CONCLUSION

Animals transplanted with HGF-transduced MSCs 1 week after experimental ICH were shown to achieve a better neurological recovery. This improved neurological recovery from ICH is attributed to nerve fiber remyelination and axonal regeneration.

Molecular mechanisms, biological actions, and neuropharmacology of the growth-associated protein GAP-43

GAP-43 is an intracellular growth-associated protein that appears to assist neuronal pathfinding and branching during development and regeneration, and may contribute to presynaptic membrane changes in the adult, leading to the phenomena of neurotransmitter release, endocytosis and synaptic vesicle recycling, long-term potentiation, spatial memory formation, and learning. GAP-43 becomes bound via palmitoylation and the presence of three basic residues to membranes of the early secretory pathway. It is then sorted onto vesicles at the late secretory pathway for fast axonal transport to the growth cone or presynaptic plasma membrane. The palmitate chains do not serve as permanent membrane anchors for GAP-43, because at steady-state most of the GAP-43 in a cell is membrane-bound but is not palmitoylated. Filopodial extension and branching take place when GAP-43 is phosphorylated at Ser-41 by protein kinase C, and this occurs following neurotrophin binding and the activation of numerous small GTPases. GAP-43 has been proposed to cluster the acidic phospholipid phosphatidylinositol 4,5-bisphosphate in plasma membrane rafts. Following GAP-43 phosphorylation, this phospholipid is released to promote local actin filament-membrane attachment. The phosphorylation also releases GAP-43 from calmodulin. The released GAP-43 may then act as a lateral stabilizer of actin filaments. N-terminal fragments of GAP-43, containing 10-20 amino acids, will activate heterotrimeric G proteins, direct GAP-43 to the membrane and lipid rafts, and cause the formation of filopodia, possibly by causing a change in membrane tension. This review will focus on new information regarding GAP-43, including its binding to membranes and its incorporation into lipid rafts, its mechanism of action, and how it affects and is affected by extracellular agents.

Perinatal exposure to alcohol reduces the expression of complexins I and II

Perinatal exposure to alcohol (PEA) induces general developmental and specific neuropsychiatric disturbances. Ethanol affects amino acid neurotransmission and synaptic plasticity. We were interested in the transcriptional effects of ethanol on the expression of complexins I and II, two synaptic vesicle proteins (SVP) with relevance for cognition and memory. We exposed pregnant Wistar inbred rats (N=4) and their pups until postnatal day 8 (P8) in vapor chambers and performed in situ-hybridizations regarding complexins I and II at P8 as well as neurobehavioral testing in adult animals of the same litters. At P8, serum ethanol levels of 281+/-58 mg/dl were achieved. PEA animals presented a pronounced retardation of postnatal growth. Significantly lower expression levels of complexin I was observed in CA1, together with trends of reductions in other hippocampal and cortical regions. Complexin II was found reduced in anterior cingulate, prefrontal and fronto-parietal cortex. Adult rats of exposed litters showed worse performance in hippocampus-dependent learning (Morris water maze). The observed suppression of complexins I and II reveals disturbed synaptic plasticity and corresponds with long lasting, ethanol-induced deficits of learning and memory. Further investigations should focus on other synaptic vesicle protein genes in order to unravel the molecular basis of ethanol-induced neurocognitive disabilities.

Alterations in mossy fiber physiology and GAP-43 expression and function in transgenic mice overexpressing HuD

HuD is a neuronal RNA-binding protein associated with the stabilization of mRNAs for GAP-43 and other neuronal proteins that are important for nervous system development and learning and memory mechanisms. To better understand the function of this protein, we generated transgenic mice expressing human HuD (HuD-Tg) in adult forebrain neurons. We have previously shown that expression of HuD in adult dentate granule cells results in an abnormal accumulation of GAP-43 mRNA via posttranscriptional mechanisms. Here we show that this mRNA accumulation leads to the ectopic expression of GAP-43 protein in mossy fibers. Electrophysiological analyses of the mossy fiber to CA3 synapse of HuD-Tg mice revealed increases in paired-pulse facilitation (PPF) at short interpulse intervals and no change in long-term potentiation (LTP). Presynaptic calcium transients at the same synapses exhibited faster time constants of decay, suggesting a decrease in the endogenous Ca(2+) buffer capacity of mossy fiber terminals of HuD-Tg mice. Under resting conditions, GAP-43 binds very tightly to calmodulin sequestering it and then releasing it upon PKC-dependent phosphorylation. Therefore, subsequent studies examined the extent of GAP-43 phosphorylation and its association to calmodulin. We found that despite the increased GAP-43 expression in HuD-Tg mice, the levels of PKC-phosphorylated GAP-43 were decreased in these animals. Furthermore, in agreement with the increased proportion of nonphosphorylated GAP-43, HuD-Tg mice showed increased binding of calmodulin to this protein. These results suggest that a significant amount of calmodulin may be trapped in an inactive state, unable to bind free calcium, and activate downstream signaling pathways. In conclusion, we propose that an unregulated expression of HuD disrupts mossy fiber physiology in adult mice in part by altering the expression and phosphorylation of GAP-43 and the amount of free calmodulin available at the synaptic terminal.

Coordinated expression of HuD and GAP-43 in hippocampal dentate granule cells during developmental and adult plasticity

Previous work from our laboratory demonstrated that the RNA-binding protein HuD binds to and stabilizes the GAP-43 mRNA. In this study, we characterized the expression of HuD and GAP-43 mRNA in the hippocampus during two forms of neuronal plasticity. During post-natal development, maximal expression of both molecules was found at P5 and their levels steadily decreased thereafter. At P5, HuD was also present in the subventricular zone, where it co-localized with doublecortin. In the adult hippocampus, the basal levels of HuD and GAP-43 were lower than during development but were significantly increased in the dentate gyrus after seizures. The function of HuD in GAP-43 gene expression was confirmed using HuD-KO mice, in which the GAP-43 mRNA was significantly less stable than in wild type mice. Altogether, these results demonstrate that HuD plays a role in the post-transcriptional control of GAP-43 mRNA in dentate granule cells during developmental and adult plasticity.

Purkinje cell dysfunction and alteration of long-term synaptic plasticity in fetal alcohol syndrome

In cerebellum and other brain regions, neuronal cell death because of ethanol consumption by the mother is thought to be the leading cause of neurological deficits in the offspring. However, little is known about how surviving cells function. We studied cerebellar Purkinje cells in vivo and in vitro to determine whether function of these cells was altered after prenatal ethanol exposure. We observed that Purkinje cells that were prenatally exposed to ethanol presented decreased voltage-gated calcium currents because of a decreased expression of the gamma-isoform of protein kinase C. Long-term depression at the parallel fiber-Purkinje cell synapse in the cerebellum was converted into long-term potentiation. This likely explains the dramatic increase in Purkinje cell firing and the rapid oscillations of local field potential observed in alert fetal alcohol syndrome mice. Our data strongly suggest that reversal of long-term synaptic plasticity and increased firing rates of Purkinje cells in vivo are major contributors to the ataxia and motor learning deficits observed in fetal alcohol syndrome. Our results show that calcium-related neuronal dysfunction is central to the pathogenesis of the neurological manifestations of fetal alcohol syndrome and suggest new methods for treatment of this disorder.

Prenatal ethanol exposure in rats decreases levels of complexin proteins in the frontal cortex

BACKGROUND

Rodents that are prenatally exposed to ethanol have been shown to exhibit a wide range of cognitive deficits, including impairments in memory, attention and executive function. To determine a potential molecular substrate for cognitive dysfunction in adulthood, we measured regional levels of the presynaptic proteins complexin I and II in a rat model of prenatal ethanol exposure, as levels of these proteins are altered in cognitive-related synaptic plasticity.

METHODS

Pregnant female rats received either a liquid ethanol diet (36% ethanol-derived calories) or a liquid control diet (maltose-dextrin isocalorically substituted for ethanol, matched in amount [g/kg body wt/day of gestation] to an ethanol-consuming partner), or were given ad libitum-fed access to standard laboratory chow and water. Levels of complexin I, II and the ubiquitous presynaptic marker synaptophysin were measured in the frontal cortex and hippocampus of adult male offspring, using ELISA.

RESULTS

Prenatal exposure to ethanol did not alter levels of presynaptic proteins in the hippocampus or levels of synaptophysin in the prefrontal cortex. However, rats prenatally exposed to ethanol displayed significantly lower levels of both complexin I and II in the prefrontal cortex compared to control animals.

CONCLUSIONS

These data indicate that prenatal exposure to ethanol is associated with a selective loss of complexin proteins in the frontal cortex. These proteins are known to be important for activity-dependent neurotransmission, and have previously been shown to mediate synaptic plasticity and cognition. These combined findings suggest that further study of complexin proteins as a substrate for cognitive impairment related to prenatal exposure to ethanol is warranted.

Behavioral deficits associated with fetal alcohol exposure are reversed by prenatal thyroid hormone treatment: a role for maternal thyroid hormone deficiency in FAE

Children prenatally exposed to alcohol typically exhibit behavioral abnormalities, including hyperactivity, learning deficits, and an increased prevalence of depression. Similar impairments are found in children of hypothyroid mothers, and we have shown that alcohol-consuming rat dams have suppressed hypothalamic-pituitary-thyroid (HPT) function. Therefore, we hypothesized that suppressed maternal thyroid hormonal milieu may contribute to the deleterious consequences of prenatal alcohol exposure. We aimed first to confirm and then to reverse the behavioral deficits in the fetal alcohol exposed (FAE) rat offspring by administration of thyroxine (T4) to the alcohol-consuming dams. Adult offspring prenatally exposed to ethanol (FAE; 35% ethanol-derived calories), pair-fed (PF) or control (C) diets were tested in the Morris water maze (MWM), the forced swim test (FST), and the open field test (OFT) to assess spatial learning, depressive behavior, and exploratory behavior/anxiety, respectively. Adult FAE offspring took longer to locate a hidden platform in the MWM and showed increased depressive behavior in the FST both of which were reversed by administration of T4 to the alcohol-consuming mother. We found sex and brain region-specific alterations in expression of genes involved in these behaviors in FAE adult offspring. Specifically, decreased hippocampal GAP-43 mRNA levels in adult FAE females and decreased glucocorticoid receptor (GR) expression in the amygdala of male and female FAE offspring were observed. The decreased mRNA levels of GAP-43 and GR were normalized by T4 treatment to the alcohol-consuming mother. Our results suggest that the suppressed HPT function of the alcohol-consuming mother contributes to the behavioral and cognitive dysfunctions observed in the offspring.

Safety and Efficacy of GABAergic Medications for Treating Alcoholism

This article highlights the proceedings of a symposium presented at the 27th Annual Scientific Meeting of the Research Society on Alcoholism in Vancouver, British Columbia, Canada, June 29, 2004. The organizers and co-chairs were Bankole A. Johnson, MD, PhD, and Robert M. Swift, MD, PhD. The presentations included (1) Introduction, by Bankole A. Johnson; (2) Safety, Tolerability, and Efficacy of gamma-Hydroxybutyric Acid and Baclofen in the Treatment of Alcohol Addiction, by Giovanni Addolorato; (3) Safety of Gabapentin in Treating Alcoholism, by Hugh Myrick; (4) New Data on the Safety and Effectiveness of Topiramate in the Treatment of Alcohol Dependence, by Bankole A. Johnson; (5) Evaluating the Risk of Benzodiazepine Prescription to Alcohol-Dependent Individuals, by Domenic A. Ciraulo; and (6) Safety and Efficacy of GABAergic Agents in Treating Alcoholics: Discussion, by Robert M. Swift.

Growth-associated protein 43 (GAP-43) and synaptophysin alterations in the dentate gyrus of patients with schizophrenia

Growth-associated protein 43 (GAP-43) expression is critical for the proper establishment of neural circuitry, a process thought to be disrupted in schizophrenia. Previous work from our laboratory demonstrated decreased GAP-43 levels in post-mortem tissue from the entire hippocampal formation of affected individuals. In the present study, we used immunocytochemical techniques to localize alterations in GAP-43 protein to specific synapses. GAP-43 distribution was compared to that of synaptophysin, another synaptic protein known to be altered in schizophrenia. The levels and distribution of GAP-43 and synaptophysin proteins were measured in the dentate gyrus of subjects with schizophrenia and sex-, age-, and postmortem interval-matched normal controls and subjects with bipolar disorder. Tissue from subjects was provided by the Harvard Brain Tissue Resource Center. In control subjects, GAP-43 immunostaining was prominent in synaptic terminals in the inner molecular layer and hilar region. Subjects with schizophrenia had significant decreases in GAP-43 immunoreactivity in the hilus (p<0.05, paired t-test) and inner molecular layer (p<0.05, paired t-test) but not in the outer molecular layer. In the same tissues, synaptophysin immunoreactivity was significantly reduced in both the inner and outer molecular layers of the dentate gyrus (both p<0.01 by paired t-test), but not in the hilus. In contrast to patients with schizophrenia, GAP-43 and synaptophysin levels in subjects with bipolar disorder did not differ from controls. Given the relationship of GAP-43 and synaptophysin with the development and plasticity of synaptic connections, the observed alterations in the hippocampus of patients with schizophrenia may be related to cognitive deficits associated with this illness.

Prenatal ethanol exposure reduces mGluR5 receptor number and function in the dentate gyrus of adult offspring

BACKGROUND

Previous studies in our laboratory indicated that metabotropic glutamate receptor (mGluR)-stimulated phosphoinositide hydrolysis is markedly reduced in the hippocampal formation of adult rat offspring whose mothers drank moderate amounts of ethanol during pregnancy. In the present study, we extended these observations by measuring the impact of prenatal ethanol exposure on proteins associated with the mGluR5 receptor-effector system along with two mGluR5 agonist-mediated responses in dentate gyrus of adult offspring.

METHODS

Sprague-Dawley rat dams consumed one of three diets throughout gestation: (1) a BioServ liquid diet that contained 5% ethanol (v/v), (2) pair-fed an isocalorically equivalent amount of 0% ethanol liquid diet, or (3) lab chow ad libitum. Microdissected slices of dentate gyrus were prepared from adult female offspring from each diet group and used for (1) Western blot analyses of mGluR5, the G-proteins Galphaq and Galpha11, and phospholipase C-beta1; (2) 2-chloro-5-hydroxyphenylglycine (CHPG)-stimulated growth associated protein 43 (GAP-43) phosphorylation; or (3) CHPG potentiation of electrically evoked [H]-D-aspartate (D-ASP) release from dentate gyrus slices.

RESULTS

In tissue prepared from untreated control rats, CHPG produced a dose-dependent increase in phosphate incorporation into GAP-43, with maximal agonist stimulation occurring at 20 microM of CHPG. CHPG produced a quantitatively similar dose-dependent increase in the potentiation of electrically evoked D-ASP release from dentate gyrus slices from untreated controls. Fetal ethanol exposure reduced the amount of dentate gyrus mGluR5 receptor protein by 36% compared with the diet control groups. There were no significant differences between diet groups in the two G-proteins or phospholipase C-beta1 protein. Fetal ethanol exposure reduced CHPG-stimulated GAP-43 phosphorylation to approximately one half the amount of CHPG stimulation observed in the control diet groups. Prenatal ethanol exposure also reduced CHPG potentiation of D-ASP release to a similar degree compared with control.

CONCLUSIONS

These results indicate that prenatal exposure to moderate quantities of ethanol reduces mGluR5 expression in the dentate gyrus of adult offspring. Although the subcellular site(s) for reduced mGluR5 expression cannot be discerned from Western blot data, the quantitatively similar effects of prenatal ethanol exposure on mGluR5 agonist stimulation of presynaptically localized GAP-43 phosphorylation and CHPG potentiation of evoked D-ASP release suggest that the presynaptic nerve terminal is one site where prenatal ethanol exposure has reduced mGluR5 receptor number and function. Furthermore, these data implicate these neurochemical alterations as one factor contributing to the hippocampal synaptic plasticity and behavioral deficits that we have observed previously in prenatal ethanol-exposed offspring.

Nerve Ending “Signal” Proteins GAP‐43, MARCKS, and BASP1

Mechanisms of growth cone pathfinding in the course of neuronal net formation as well as mechanisms of learning and memory have been under intense investigation for the past 20 years, but many aspects of these phenomena remain unresolved and even mysterious. "Signal" proteins accumulated mainly in the axon endings (growth cones and the presynaptic area of synapses) participate in the main brain processes. These proteins are similar in several essential structural and functional properties. The most prominent similarities are N-terminal fatty acylation and the presence of an "effector domain" (ED) that dynamically binds to the plasma membrane, to calmodulin, and to actin fibrils. Reversible phosphorylation of ED by protein kinase C modulates these interactions. However, together with similarities, there are significant differences among the proteins, such as different conditions (Ca2+ contents) for calmodulin binding and different modes of interaction with the actin cytoskeleton. In light of these facts, we consider GAP-43, MARCKS, and BASP1 both separately and in conjunction. Special attention is devoted to a discussion of apparent inconsistencies in results and opinions of different authors concerning specific questions about the structure of proteins and their interactions.