Polyamine-enhanced NMDA receptor activity: effect of ethanol

Acute Alcohol Withdrawal is Associated with c-Fos Expression in the Basal Ganglia and Associated Circuitry: C57BL/6J and DBA/2J Inbred Mouse Strain Analyses

BACKGROUND

The DBA/2J (D2) and C57BL/6J (B6) mouse strains are the most widely studied genetic models of severe and mild acute alcohol withdrawal, respectively. Previous studies have identified quantitative trait loci and genes involved in risk for acute ethanol withdrawal using mapping populations derived from the D2 and B6 strains, but the brain region(s) and circuit(s) by which these genes and their protein products influence ethanol physiological dependence and associated withdrawal remain to be elucidated.

METHODS

B6 and D2 were administered a sedative-hypnotic dose of ethanol (4 g/kg) or saline (control) and returned to their home cages where they were left undisturbed for 7 hr, which has been shown in previous studies to correspond to peak acute ethanol withdrawal severity. The mice were then euthanized and assessed for their numbers of c-Fos immunoreactive neurons across 26 brain regions. The question addressed was whether or not ethanol-withdrawn D2 and B6 mice differed in c-Fos induction (neural activation) within circuitry that could explain the severe ethanol withdrawal of the D2 strain and the mild ethanol withdrawal in B6 strain mice.

RESULTS

At peak acute ethanol-withdrawal ethanol-withdrawn D2 and B6 mice differed in neural activation within the basal ganglia, including the subthalamic nucleus and the two major output nuclei of the basal ganglia (the medial globus pallidus and the substantia nigra pars reticulata). Genotype-dependent c-Fos induction was also apparent in associated circuitry including the lateral septum, the ventral tegmental area, the nucleus accumbens core, the dorsolateral caudate putamen, the substantia nigra pars compacta, the cingulate and entorhinal cortices, and the ventral pallidum. D2 and B6 mice showed comparable neural activation in the bed nucleus of the stria terminalis, and the nucleus accumbens shell.

CONCLUSIONS

The present studies are the first to use immediate early gene product expression to assess the pattern of neural activation associated with acute ethanol withdrawal. Our results point to the involvement of an extended basal ganglia circuit in genetically determined differences in acute ethanol withdrawal. Based on these data, we suggest that quantitative trait genes (QTGs) involved in acute ethanol withdrawal exert their effects on this phenotype via one or more of the brain regions and circuits identified. As more information becomes available that integrates neural circuit and QTG analyses, the precise mechanisms by which QTGs affect ethanol physiological dependence and associated withdrawal will become apparent.

Phase 1 study of N1-N11-diethylnorspermine (DENSPM) administered TID for 6 days in patients with advanced malignancies

This was a dose escalation Phase 1 trial designed to determine the maximum tolerated dose (MTD) and dose-limiting toxicities (DLT) of DENSPM.

METHODS

Adult patients with refractory solid tumors were treated with DENSPM administered by intravenous infusion in 100 ml of normal saline over 30 minutes. The daily dose of DENSPM was divided into three equal doses administered approximately every eight hours for six days. Courses were repeated every 28 days.

RESULTS

Twenty-eight patients were enrolled in the study. Dose levels of DENSPM explored were 25 mg/m2/day (3 patients), 50 mg/m2/day (9 patients), 60 mg/m2/day (5 patients), 75 mg/m2/day (6 patients), 94 mg/m2/day (3 patients) and 118 mg/m2/day (2 patients). The DLT for DENSPM was central nervous system toxicity characterized by aphasia, ataxia, dizziness, vertigo and slurred speech occurring at dose levels > or = 94 mg/m2/day, which was also the MTD.

SAFETY

The most frequent drug-related adverse events were asthenia (9 patients), injection site reaction (6 patients) and anemia (6 patients). One patient was removed from the study due to CNS toxicity. There were no treatment-related deaths. No trends were observed regarding hematologic toxicities, biochemical changes or changes in vital signs.

EFFICACY

Nineteen of the 28 patients enrolled in the study were assessed for response. No objective responses were observed. Five patients had stable disease as the best response to therapy.

CONCLUSIONS

Because the DLT was CNS and because of the relatively low doses that could be safely administered on this schedule as compared with a once-a-day schedule, this regimen was not recommended for Phase 2.

Glutamate-mediated transmission, alcohol, and alcoholism

Glutamate-mediated neurotransmission may be involved in the range of adaptive changes in brain which occur after ethanol administration in laboratory animals, and in chronic alcoholism in human cases. Excitatory amino acid transmission is modulated by a complex system of receptors and other effectors, the efficacy of which can be profoundly affected by altered gene or protein expression. Local variations in receptor composition may underlie intrinsic regional variations in susceptibility to pathological change. Equally, ethanol use and abuse may bring about alterations in receptor subunit expression as the essence of the adaptive response. Such considerations may underlie the regional localization characteristic of the pathogenesis of alcoholic brain damage, or they may form part of the homeostatic change that constitutes the neural substrate for alcohol dependence.

Glutamate-induced increase of extracellular glutamate through N-methyl-D-aspartate receptors in ethanol withdrawal

Ethanol withdrawal is a physiopathological state associated with increased number and function of N-methyl-D-aspartate glutamate receptors. We assessed the effect of N-methyl-D-aspartate receptor stimulation on the extracellular levels of glutamate in vivo by the focal application of N-methyl-D-aspartate in the striatum of dependent rats following withdrawal from chronic treatment with ethanol. In control, chronic sucrose-treated rats, 800 microM N-methyl-D-aspartate increased glutamate levels to 268% of baseline values. In ethanol-withdrawn animals, 12 h after interruption of the chronic treatment, the application of N-methyl-D-aspartate increased glutamate levels to 598% of baseline values. In ethanol-intoxicated rats N-methyl-D-aspartate was ineffective. Concentration-response curves showed that in ethanol withdrawn animals N-methyl-D-aspartate was five-fold more potent than in controls. In withdrawn animals, the non-competitive N-methyl-D-aspartate receptor antagonist dizocilpine (1.0 mg/kg i.p.) or ethanol (5 g/kg i.g.) markedly reduced the N-methyl-D-aspartate-induced increase in glutamate levels. These results are consistent with the up-regulation of N-methyl-D-aspartate receptors by chronic ethanol and add biochemical evidence for the presence of N-methyl-D-aspartate receptors facilitating glutamate release through a positive feedback mechanism. The glutamate-induced, N-methyl-D-aspartate receptor-mediated elevations of extracellular glutamate may constitute a neurochemical substrate for the neuropathological alterations associated with alcoholism.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

The NMDA/glycine receptor antagonist, L-701,324, produces discriminative stimuli similar to those of ethanol

The ethanol-like discriminative stimulus properties of a novel NMDA glycine receptor antagonist, L-701,324 ((7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2-(1H)-quinolone), a polyamine receptor antagonist, eliprodil, and a non-competitive NMDA receptor antagonist, MK-801 (dizocilpine), were examined in rats trained to discriminate ethanol from vehicle in a two-lever discrimination procedure. In rats trained to discriminate ethanol from vehicle, L-701,324 and MK-801 substituted for ethanol in a dose-dependent fashion with a complete substitution noted following administration of 7.5 mg/kg L-701,324 and 0.2 mg/kg MK-801, respectively. Full substitution for ethanol was achieved with no alteration in the rate of responding. In contrast, administration of eliprodil (in doses up to 5 mg/kg) showed only a partial, but not dose-dependent, substitution for ethanol. These findings indicate that a reduction of NMDA receptor activity, produced either via a blockade of non-competitive NMDA recognition sites or of NMDA/glycine-sensitive regulatory sites, had discriminative stimulus properties that are similar to those produced by ethanol. Furthermore, the observation that the NMDA/glycine receptor antagonist, L-701,324, was a more effective substitute for ethanol than was the polyamine antagonist, eliprodil, suggests that several NMDA receptor subunits, and thus not only NMDAR2B receptor subunits, are of importance for the discriminative stimulus effects of ethanol.

Individual and combined effects of ethanol and cocaine on intracellular signals and gene expression

1. Ethanol and cocaine are drugs of abuse that can produce long-lived changes in behavior, including dependence. 2. A common set of neural pathways appears to mediate the addictive actions of ethanol and cocaine. 3. Many prominent aspects of drug dependence may be the result of alterations in intracellular signals as well as specific patterns of gene expression. 4. For instance, changes in G proteins and cAMP, phosphorylation of proteins and induction of c-fos and zif/268 in specific drug-sensitive brain regions may represent adaptive changes in response to a drug-dependent state. 5. The concurrent use of ethanol and cocaine is the most prevalent pattern of drug abuse in humans. However, the number of studies investigating the behavioral and molecular effects of this combination are few. 6. Emerging evidence indicates a possible antagonistic effect of ethanol and cocaine action on transcription factor function. In addition, cocaethylene (a psychoactive metabolite derived from combined ethanol and cocaine exposure) has significant effects on gene expression as well.

Effects of ethanol on ion channels

Ion channels play critical roles in nervous system function, from initiating rapid synaptic activity to propagation of action potentials. Studies have indicated that many of the effects of ethanol on the nervous system are likely caused by the actions of ethanol on ion channels. Ion channels are multimeric structures that gate ions through subtle changes in tertiary structure. Ethanol readily enters molecular sites within multimeric ion channels, modifying intermolecular forces and bonds that are important for the open-close-inactivation kinetic properties of channels. The diversity of channel composition caused by the multimeric structure results in subtypes of channels that have a spectrum of sensitivity to ethanol that translates into brain regional differences in ethanol sensitivity, in part caused by differences in ion channel subunit composition. Ethanol has been shown to affect both receptor-activated ion channels and voltage-gated ion channels. The acute intoxicating and incoordinating effects of ethanol are probably related to inhibition of subtypes of NMDA-glutamate receptor ion channels and potentiation of certain subtypes of GABAA receptor ion channels. Effects on these channels, as well as glycine, nicotinic cholinergic, serotonergic, and other ion channels, likely contribute to the euphoric, sedative, and other acute actions of ethanol. Changes in ion channel subunit composition, density, and properties probably also contribute to ethanol tolerance, dependence, withdrawal hyperexcitability, and neurotoxicity. A substantial number of studies have implicated glutamate NMDA receptor, GABAA, and L-type voltage-gated calcium channels in the adaptive changes in the brain during chronic ethanol exposure. The diversity of ion channels subunits, their prominent role in brain function, and ethanol action are likely to make them important contributors to alcoholism and alcohol abuse.

In vivo pharmacological study of spermine-induced neurotoxicity

Spermine-induced neurotoxicity and its pharmacological manipulation was studied in the rat striatum in vivo. Spermine (50, 100, 250 nmol) was injected into the striatum and the volume of damage quantified by computer-based image analysis. Spermine produced a dose-dependent increase in the volume of damage. Co-administration of MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate; dizocilpine, 60 nmol), 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (25, 40 nmol) and pretreatment with pentobarbital (40 mg/kg, i.p.) significantly reduced the volume of damage induced by 100 nmol spermine. MK-801 (30 nmol) was also effective in reducing the damage induced by 50 nmol spermine. Treatment with a specific inhibitor of nitric oxide synthase, N omega-nitro-L-arginine methyl ester (50 mg/kg, i.p., twice daily for 10 days) was ineffective. These results suggest an involvement of both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in the cascade of spermine-induced neurotoxicity.

Increased NMDA-induced excitability during ethanol withdrawal: a behavioural and histological study

Intrahippocampal injections of N-methyl-D-aspartic acid (NMDA) leads to neurodegeneration in a dose-dependent manner. Chronic administration of ethanol to animals leads to CNS tolerance and dependence. Hyperexcitability following ethanol withdrawal is thought to be related to increased sensitivity of the NMDA receptors. The purpose of this study was to investigate this predisposition to hyperexcitability by intrahippocampal injection of low dose of NMDA. Using control and ethanol-withdrawn male Wistar rats, behavioural indices were determined immediately after injection and morphological damage was assessed after a period of recovery. There was significantly increased hyperactivity in the ethanol-treated rats immediately after injection. Morphological damage resulting from 5 nmol of NMDA was significantly greater in the CA3 region of the hippocampus in these animals. These data support the hypothesis that ethanol dependence and subsequent withdrawal is associated with increased sensitivity to NMDA which may underlie ethanol withdrawal-associated brain damage.

Acute administration of alcohol blocks cocaine-induced striatal c-fos immunoreactivity protein in the rat

Immediate-early genes, such as c-fos, are induced in the brain by cocaine and other psychotropic drugs. This induction is thought to be mediated via the activation of dopamine D1 and glutamate N-methyl-D-aspartate (NMDA) receptor subtypes. Because alcohol selectively blocks NMDA receptor function, we determined the ability of alcohol to block the expression of c-fos normally induced by systemic cocaine exposure in perikarya of the rat striatum. Acute administration of alcohol (2 g/kg; IP) approximately 30 min prior to a single cocaine (20 mg/kg) injection significantly reduced the patchy appearance of intensely immunoreactive gene signal in dorsal-central quadrants of the caudate putamen. Separate administration of three doses of alcohol alone (1, 2, or 3 g/kg) was ineffectual in inducing FOS-like protein in this or other regions of the rat brain. The blockade of the encoded protein by alcohol was partial in magnitude reminiscent of that produced by MK-801 and related NMDA receptor antagonist drugs. Furthermore, the blockade of cocaine-induced FOS-like protein by alcohol occurred at a dose which produced a blood alcohol concentration of approximately 180 mg/dl (40 mM), comparable to that detected in intoxicating humans. Considering the fact that the concomitant use of alcohol and cocaine is the most common substance abuse pattern found in the addictive population, the present results suggest an antagonist effect exerted by these two drugs at the transcriptional level and further support the consensus that NMDA receptors are the plausible surface-target elements mediating some of the effects of alcohol and cocaine.