Ethanol withdrawal seizure susceptibility is associated with upregulation of L- and P-type Ca2+ channel currents in rat inferior colliculus neurons

Targeted Inhibition of Upregulated Sodium-Calcium Exchanger in Rat Inferior Colliculus Suppresses Alcohol Withdrawal Seizures

The inferior colliculus (IC) is critical in initiating acoustically evoked alcohol withdrawal-induced seizures (AWSs). Recently, we reported that systemic inhibition of Ca2+ entry via the reverse mode activity of the Na+/Ca2+ exchanger (NCXrev) suppressed AWSs, suggesting remodeling of NCX expression and function, at least in the IC, the site of AWS initiation. Here, we probe putative changes in protein expression in the IC of NCX isoforms, including NCX type 1 (NCX1), 2 (NCX2), and 3 (NCX3). We also evaluated the efficacy of targeted inhibition of NCX1rev and NCX3rev activity in the IC on the occurrence and severity of AWSs using SN-6 and KB-R943, respectively. We used our well-characterized alcohol intoxication/withdrawal model associated with enhanced AWS susceptibility. IC tissues from the alcohol-treated group were collected 3 h (before the onset of AWS susceptibility), 24 h (when AWS susceptibility is maximal), and 48 h (when AWS susceptibility is resolved) following alcohol withdrawal; in comparison, IC tissues from the control-treated group were collected at 24 h after the last gavage. Analysis shows that NCX1 protein levels were markedly higher 3 and 24 h following alcohol withdrawal. However, NCX3 protein levels were only higher 3 h following alcohol withdrawal. The analysis also reveals that bilateral microinjections of SN-6 (but not KB-R7943) within the IC markedly suppressed the occurrence and severity of AWSs. Together, these findings indicate that NCX1 is a novel molecular target that may play an essential role in the pathogenesis and pathophysiology of AWSs.

Inhibition of the Sodium Calcium Exchanger Suppresses Alcohol Withdrawal-Induced Seizure Susceptibility

Calcium influx plays important roles in the pathophysiology of seizures, including acoustically evoked alcohol withdrawal-induced seizures (AWSs). One Ca²⁺ influx route of interest is the Na⁺/Ca²⁺ exchanger (NCX) that, when operating in its reverse mode (NCX_rev) activity, can facilitate Ca²⁺ entry into neurons, possibly increasing neuronal excitability that leads to enhanced seizure susceptibility. Here, we probed the involvement of NCX_rev activity on AWS susceptibility by quantifying the effects of SN-6 and KB-R7943, potent blockers of isoform type 1 (NCX1_rev) and 3 (NCX3_rev), respectively. Male, adult Sprague-Dawley rats were used. Acoustically evoked AWSs consisted of wild running seizures (WRSs) that evolved into generalized tonic-clonic seizures (GTCSs). Quantification shows that acute SN-6 treatment at a relatively low dose suppressed the occurrence of the GTCSs (but not WRSs) component of AWSs and markedly reduced the seizure severity. However, administration of KB-R7943 at a relatively high dose only reduced the incidence of GTCSs. These findings demonstrate that inhibition of NCX1_rev activity is a putative mechanism for the suppression of alcohol withdrawal-induced GTCSs.

The Inferior Colliculus in Alcoholism and Beyond

Post-mortem neuropathological and in vivo neuroimaging methods have demonstrated the vulnerability of the inferior colliculus to the sequelae of thiamine deficiency as occurs in Wernicke-Korsakoff Syndrome (WKS). A rich literature in animal models ranging from mice to monkeys-including our neuroimaging studies in rats-has shown involvement of the inferior colliculi in the neural response to thiamine depletion, frequently accomplished with pyrithiamine, an inhibitor of thiamine metabolism. In uncomplicated alcoholism (i.e., absent diagnosable neurological concomitants), the literature citing involvement of the inferior colliculus is scarce, has nearly all been accomplished in preclinical models, and is predominately discussed in the context of ethanol withdrawal. Our recent work using novel, voxel-based analysis of structural Magnetic Resonance Imaging (MRI) has demonstrated significant, persistent shrinkage of the inferior colliculus using acute and chronic ethanol exposure paradigms in two strains of rats. We speculate that these consistent findings should be considered from the perspective of the inferior colliculi having a relatively high CNS metabolic rate. As such, they are especially vulnerable to hypoxic injury and may be provide a common anatomical link among a variety of disparate insults. An argument will be made that the inferior colliculi have functions, possibly related to auditory gating, necessary for awareness of the external environment. Multimodal imaging including diffusion methods to provide more accurate in vivo visualization and quantification of the inferior colliculi may clarify the roles of brain stem nuclei such as the inferior colliculi in alcoholism and other neuropathologies marked by altered metabolism.

Intermittent hypoxia training: Powerful, non-invasive cerebroprotection against ethanol withdrawal excitotoxicity

Ethanol intoxication and withdrawal exact a devastating toll on the central nervous system. Abrupt ethanol withdrawal provokes massive release of the excitatory neurotransmitter glutamate, which over-activates its postsynaptic receptors, causing intense Ca2+ loading, p38 mitogen activated protein kinase activation and oxidative stress, culminating in ATP depletion, mitochondrial injury, amyloid β deposition and neuronal death. Collectively, these mechanisms produce neurocognitive and sensorimotor dysfunction that discourages continued abstinence. Although the brain is heavily dependent on blood-borne O2 to sustain its aerobic ATP production, brief, cyclic episodes of moderate hypoxia and reoxygenation, when judiciously applied over the course of days or weeks, evoke adaptations that protect the brain from ethanol withdrawal-induced glutamate excitotoxicity, mitochondrial damage, oxidative stress and amyloid β accumulation. This review summarizes evidence from ongoing preclinical research that demonstrates intermittent hypoxia training to be a potentially powerful yet non-invasive intervention capable of affording robust, sustained neuroprotection during ethanol withdrawal.

Alcohol withdrawal upregulates mRNA encoding for CaV2.1-α1 subunit in the rat inferior colliculus

We previously reported increased current density through P-type voltage-gated Ca²⁺ channels in inferior colliculus (IC) neurons during alcohol withdrawal. However, the molecular correlate of this increased P-type channel current is currently unknown. Here, we probe changes in mRNA and protein expression of the pore-forming Ca_V2.1-α1 (P/Q-type) subunits in IC neurons during the course of alcohol withdrawal-induced seizures (AWSs). Rats received three daily doses of ethanol or the vehicle every 8 h for 4 consecutive days. The IC was dissected at various time intervals following alcohol withdrawal, and the mRNA and protein levels of the Ca_V2.1-α1 subunits were measured. In separate experiments, rats were tested for acoustically evoked seizure susceptibility 3, 24, and 48 h after alcohol withdrawal. AWSs were observed 24 h after withdrawal; no seizures were observed at 3 or 48 h or in the control-treated rats. Compared to control-treated rats, the mRNA levels of the Ca_V2.1-α1 subunit were increased 1.9-fold and 2.1-fold at 3 and 24 h, respectively; change in mRNA expression was nonsignificant at 48 h following alcohol withdrawal. Western blot analyses revealed that protein levels of the Ca_V2.1-α1 subunits were not altered in IC neurons following alcohol withdrawal. We conclude that expression of the Cacna1a mRNA increased before the onset of AWS susceptibility, suggesting that altered Ca_V2.1 channel expression may play a role in AWS pathogenesis.

Voltage-Sensitive Calcium Channels in the Brain: Relevance to Alcohol Intoxication and Withdrawal

Voltage-sensitive Ca²⁺ (Ca_V) channels are the primary route of depolarization-induced Ca²⁺ entry in neurons and other excitable cells, leading to an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i). The resulting increase in [Ca²⁺]_i activates a wide range of Ca²⁺-dependent processes in neurons, including neurotransmitter release, gene transcription, activation of Ca²⁺-dependent enzymes, and activation of certain K⁺ channels and chloride channels. In addition to their key roles under physiological conditions, Ca_V channels are also an important target of alcohol, and alcohol-induced changes in Ca²⁺ signaling can disturb neuronal homeostasis, Ca²⁺-mediated gene transcription, and the function of neuronal circuits, leading to various neurological and/or neuropsychiatric symptoms and disorders, including alcohol withdrawal induced-seizures and alcoholism.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

Differential Roles for L-Type Calcium Channel Subtypes in Alcohol Dependence

It has previously been shown that the inhibition of L-type calcium channels (LTCCs) decreases alcohol consumption, although the contribution of the central LTCC subtypes Cav1.2 and Cav1.3 remains unknown. Here, we determined changes in Cav1.2 (Cacna1c) and Cav1.3 (Cacna1d) mRNA and protein expression in alcohol-dependent rats during protracted abstinence and naive controls using in situ hybridization and western blot analysis. Functional validation was obtained by electrophysiological recordings of calcium currents in dissociated hippocampal pyramidal neurons. We then measured alcohol self-administration and cue-induced reinstatement of alcohol seeking in dependent and nondependent rats after intracerebroventricular (i.c.v.) injection of the LTCC antagonist verapamil, as well as in mice with an inducible knockout (KO) of Cav1.2 in Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα)-expressing neurons. Our results show that Cacna1c mRNA concentration was increased in the amygdala and hippocampus of alcohol-dependent rats after 21 days of abstinence, with no changes in Cacna1d mRNA. This was associated with increased Cav1.2 protein concentration and L-type calcium current amplitudes. Further analysis of Cacna1c mRNA in the CA1, basolateral amygdala (BLA), and central amygdala (CeA) revealed a dynamic regulation over time during the development of alcohol dependence. The inhibition of central LTCCs via i.c.v. administration of verapamil prevented cue-induced reinstatement of alcohol seeking in alcohol-dependent rats. Further studies in conditional Cav1.2-KO mice showed a lack of dependence-induced increase of alcohol-seeking behavior. Together, our data indicate that central Cav1.2 channels, rather than Cav1.3, mediate alcohol-seeking behavior. This finding may be of interest for the development of new antirelapse medications.

Alcohol Withdrawal Increases Protein Kinase A Activity in the Rat Inferior Colliculus

BACKGROUND

Cyclic AMP-dependent protein kinase A (PKA) signaling is a key target for the action of alcohol and may therefore play a role in the pathophysiology of alcohol withdrawal seizures (AWSs). Here, we investigated the role of PKA activity with respect to increased seizure susceptibility in rats that were subjected to alcohol withdrawal.

METHODS

Adult male Sprague Dawley rats received 3 daily doses of ethanol (EtOH) (or vehicle) for 4 consecutive days. Rats were then tested for susceptibility to acoustically evoked AWSs 3, 24, and 48 hours after the last alcohol dose. In separate experiments, the inferior colliculus (IC) was collected at these same time points from rats subjected to alcohol withdrawal and control rats following alcohol withdrawal. PKA activity, catalytic Cα (PKA_Cα ) protein, regulatory RIIα (PKA_RIIα ) protein, and RIIβ (PKA_RIIβ ) protein were measured in the IC. Lastly, in situ pharmacological studies were performed to evaluate whether inhibiting PKA activity in the IC suppressed AWSs.

RESULTS

In the EtOH-treated group, AWSs were observed at the 24-hour time point, but not at the 3-hour or 48-hour time points. In the IC, PKA activity was significantly higher both 3 hours (i.e., before AWS susceptibility) and 24 hours after the last alcohol dose (when AWS susceptibility peaked) than in control rats. Consistent with these findings, protein levels of the PKA_Cα subunit were significantly increased in the IC both 3 and 24 hours after the last alcohol dose. Lastly, in situ inhibition of PKA activity within the IC suppressed AWSs.

CONCLUSIONS

The increase in PKA activity and PKA_Cα protein expression in the IC preceded the occurrence of AWSs, and inhibiting PKA activity within the IC suppressed acoustically evoked AWSs. Together, these findings suggest that altered PKA activity plays a key role in the pathogenesis of AWSs.

Alcohol Withdrawal and Cerebellar Mitochondria

Cerebellar disorders trigger the symptoms of movement problems, imbalance, incoordination, and frequent fall. Cerebellar disorders are shown in various CNS illnesses including a drinking disorder called alcoholism. Alcoholism is manifested as an inability to control drinking in spite of adverse consequences. Human and animal studies have shown that cerebellar symptoms persist even after complete abstinence from drinking. In particular, the abrupt termination (ethanol withdrawal) of long-term excessive ethanol consumption has shown to provoke a variety of neuronal and mitochondrial damage to the cerebellum. Upon ethanol withdrawal, excitatory neurotransmitter molecules such as glutamate are overly released in brain areas including cerebellum. This is particularly relevant to the cerebellar neuronal network as glutamate signals are projected to Purkinje neurons through granular cells that are the most populated neuronal type in CNS. This excitatory neuronal signal may be elevated by ethanol withdrawal stress, which promotes an increase in intracellular Ca(2+) level and a decrease in a Ca(2+)-binding protein, both of which result in the excessive entry of Ca(2+) to the mitochondria. Subsequently, mitochondria undergo a prolonged opening of mitochondrial permeability transition pore and the overproduction of harmful free radicals, impeding adenosine triphosphate (ATP)-generating function. This in turn provokes the leakage of mitochondrial molecule cytochrome c to the cytosol, which triggers a cascade of adverse cytosol reactions. Upstream to this pathway, cerebellum under the condition of ethanol withdrawal has shown aberrant gene modifications through altered DNA methylation, histone acetylation, or microRNA expression. Interplay between these events and molecules may result in functional damage to cerebellar mitochondria and consequent neuronal degeneration, thereby contributing to motoric deficit. Mitochondria-targeting research may help develop a powerful new therapy to manage cerebellar disorders associated with hyperexcitatory CNS disorders like ethanol withdrawal.

Altered voltage-gated calcium channels in rat inferior colliculus neurons contribute to alcohol withdrawal seizures

We have previously reported that enhanced susceptibility to alcohol withdrawal seizures (AWS) parallels the enhancement of the current density of high-threshold voltage-gated Ca(2+) (CaV) channels in rat inferior colliculus (IC) neurons. However, whether this increased current density is a cause or consequence of AWS is unclear. Here, I report changes in the current density of CaV channels in IC neurons during the course of alcohol withdrawal and the potential anticonvulsant effect of intra-IC infusions of L- and P-type CaV channel antagonists. Whole-cell currents were activated by depolarizing pulses using barium as the charge carrier. Currents and seizure susceptibility were evaluated in control animals 3h after alcohol intoxication, as well as 3h (before AWS), 24h (when AWS susceptibility is maximal), and 48h (when AWS susceptibility is no longer present) after alcohol withdrawal. Nifedipine, nimodipine (L-type antagonists) or ω-agatoxin TK (P-type antagonist) were infused intra-IC to probe the role of CaV channels in the pathogenesis of AWS. CaV current density and conductance in IC neurons were significantly increased 3 and 24h after alcohol withdrawal compared with the control group or the group tested 3h following ethanol intoxication. Blockade of L-type CaV channels within the IC completely suppressed AWS, and inhibition of P-type channels reduced AWS severity. These findings suggest that the enhancement of CaV currents in IC neurons occurs prior to AWS onset and that alterations in L- and P-type CaV channels in these neurons may underlie the pathogenesis of AWS.

Ethosuximide Reduces Mortality and Seizure Severity in Response to Pentylenetetrazole Treatment During Ethanol Withdrawal

AIMS

We recently demonstrated that T-type calcium channels are affected by alcohol abuse and withdrawal. Treatment with ethosuximide, an antiepileptic drug that blocks T-type calcium channels, reduces seizure activity induced by intermittent ethanol exposures and withdrawals. Here, we expand on these findings to test whether ethosuximide can reduce the sensitivity to pentylenetetrazole-induced seizures during ethanol withdrawal.

METHODS

We used an intermittent ethanol exposure model to produce withdrawal-induced hyperexcitability in DBA/2J mice.

RESULTS

Ethosuximide (250 mg/kg) reduced seizure severity in mice undergoing ethanol withdrawal with concurrent PTZ treatment (20 mg/kg). Importantly, ethosuximide did not produce rebound excitability and protected against ethanol withdrawal-induced mortality produced by concurrent PTZ treatment (40 mg/kg).

CONCLUSION

These results, in addition to previous preclinical findings, suggest that ethosuximide should be further evaluated as a safe, effective alternative to benzodiazepines for the treatment of alcohol withdrawal.

Alcohol Withdrawal-Induced Seizure Susceptibility is Associated with an Upregulation of CaV1.3 Channels in the Rat Inferior Colliculus

BACKGROUND

We previously reported increased current density through L-type voltage-gated Ca(2+) (CaV1) channels in inferior colliculus (IC) neurons during alcohol withdrawal. However, the molecular correlate of this increased CaV1 current is currently unknown.

METHODS

Rats received three daily doses of ethanol every 8 hours for 4 consecutive days; control rats received vehicle. The IC was dissected at various time intervals following alcohol withdrawal, and the mRNA and protein levels of the CaV1.3 and CaV1.2 α1 subunits were measured. In separate experiments, rats were tested for their susceptibility to alcohol withdrawal-induced seizures (AWS) 3, 24, and 48 hours after alcohol withdrawal.

RESULTS

In the alcohol-treated group, AWS were observed 24 hours after withdrawal; no seizures were observed at 3 or 48 hours. No seizures were observed at any time in the control-treated rats. Compared to control-treated rats, the mRNA level of the CaV1.3 α1 subunit was increased 1.4-fold, 1.9-fold, and 1.3-fold at 3, 24, and 48 hours, respectively. In contrast, the mRNA level of the CaV1.2 α1 subunit increased 1.5-fold and 1.4-fold at 24 and 48 hours, respectively. At 24 hours, Western blot analyses revealed that the levels of the CaV1.3 and CaV1.2 α1 subunits increased by 52% and 32%, respectively, 24 hours after alcohol withdrawal. In contrast, the CaV1.2 and CaV1.3 α1 subunits were not altered at either 3 or 48 hours during alcohol withdrawal.

CONCLUSIONS

Expression of the CaV1.3 α1 subunit increased in parallel with AWS development, suggesting that altered L-type CaV1.3 channel expression is an important feature of AWS pathogenesis.

Alcohol withdrawal is associated with a downregulation of large-conductance Ca²⁺-activated K⁺ channels in rat inferior colliculus neurons

RATIONALE

Large conductance calcium-activated potassium (BK(Ca) or K(Ca)1.1) channels are well-known molecular targets for the action of alcohol and therefore may play an important role in the pathogenesis of alcohol withdrawal syndrome.

OBJECTIVES

We evaluate the modifications of total outward K⁺ currents and protein expression of BK(Ca) channels α-subunit in inferior colliculus (IC) neurons obtained from controls and rats subjected to alcohol withdrawal associated with enhanced susceptibility to seizures.

METHODS

Outward K⁺ currents and BK(Ca) channel proteins were measured using the whole cell configuration of patch clamp techniques and Western blot analysis, respectively.

RESULTS

Total outward K⁺ current density was significantly reduced in IC neurons at 24 and 48 h during the alcohol withdrawal period when the susceptibility to seizures was maximal and absent, respectively. The iberiotoxin-sensitive (BK(Ca)) current density and conductance also were significantly reduced at 24 h following alcohol withdrawal. Consistent with functional data, the levels of protein expression of α-subunit associated with BK(Ca) channels also was significantly reduced in IC neurons at 24 and 48 h following alcohol withdrawal.

CONCLUSIONS

The downregulation of BK(Ca) channels outlasts the finite period of elevated susceptibility to alcohol withdrawal seizures. These findings indicate that BK(Ca) channels, per se, may not be fundamentally important for the generation of alcohol withdrawal seizures.

Phenolic compounds protect cultured hippocampal neurons against ethanol-withdrawal induced oxidative stress

Ethanol withdrawal is linked to elevated oxidative damage to neurons. Here we report our findings on the contribution of phenolic antioxidants (17beta-estradiol, p-octyl-phenol and 2,6-di-tert-butyl-4-methylphenol) to counterbalance sudden ethanol withdrawal-initiated oxidative events in hippocampus-derived cultured HT-22 cells. We showed that ethanol withdrawal for 4 h after 24-h ethanol treatment provoked greater levels of oxidative damage than the preceding ethanol exposure. Phenolic antioxidant treatment either during ethanol exposure or ethanol withdrawal only, however, dose-dependently reversed cellular oxidative damage, as demonstrated by the significantly enhanced cell viability, reduced malondialdehyde production and protein carbonylation, compared to untreated cells. Interestingly, the antioxidant treatment schedule had no significant impact on the observed neuroprotection. In addition, the efficacy of the three phenolic compounds was practically equipotent in protecting HT-22 cells in spite of predictions based on an in silico study and a cell free assay of lipid peroxidation. This finding implies that free-radical scavenging may not be the sole factor responsible for the observed neuroprotection and warrants further studies to establish, whether the HT-22 line is indeed a suitable model for in vitro screening of antioxidants against EW-related neuronal damage.

Calcium channel dysfunction in inferior colliculus neurons of the genetically epilepsy-prone rat

Voltage-gated calcium (Ca(2+)) channels are thought to play an important role in epileptogenesis and seizure generation. Here, using the whole cell configuration of patch-clamp techniques, we report on the modifications of biophysical and pharmacological properties of high threshold voltage-activated Ca(2+) channel currents in inferior colliculus (IC) neurons of the genetically epilepsy-prone rats (GEPR-3s). Ca(2+) channel currents were measured by depolarizing pulses from a holding potential of - 80 mV using barium (Ba(2+)) as the charge carrier. We found that the current density of high threshold voltage-activated Ca(2+) channels was significantly larger in IC neurons of seizure-naive GEPR-3s compared to control Sprague-Dawley rats, and that seizure episodes further enhanced the current density in the GEPR-3s. The increased current density was reflected by both a - 20 mV shifts in channel activation and a 25% increase in the non-inactivating fraction of channels in seizure-naive GEPR-3s. Such changes were reduced by seizure episodes in the GEPR-3s. Pharmacological analysis of the current density suggests that upregulation of L-, N- and R-type of Ca(2+) channels may contribute to IC neuronal hyperexcitability that leads to seizure susceptibility in the GEPR-3s.

Up-Regulation of Myocardial L-Type Ca2+Channel in Chronic Alcoholic Subjects Without Cardiomyopathy

BACKGROUND

Excessive ethanol intake is one of the most frequent causes of acquired dilated cardiomyopathy in developed countries. L-type Ca(2+) channels, involved in excitation-contraction coupling, are disturbed in animal models of persistent ethanol consumption. This study was designed to evaluate the density and function of myocardial L-type Ca(2+) channel receptors in organ donors with chronic alcoholism and controls.

METHODS

The protein expression of L-type Ca(2+) channels was determined with (3)H-(+)-PN 200-110-binding experiments using a specific antibody against the alpha(1)-subunit in homogenate samples of left-ventricle apex from organ donors: healthy controls (n=11), chronic alcoholic without cardiomyopathy (n=12), and alcoholics with cardiomyopathy (n=11). Morphometric measurements of cardiomyocytes were performed.

RESULTS

Binding experiments proved an up-regulation of L-type Ca(2+) channels expression in alcoholic patients compared with controls (B(max) 2.61 +/- 1.10 vs 1.33 +/- 0.49 fmol/mg, respectively; p<0.001). This up-regulation was present in the group of alcoholic subjects without cardiomyopathy, and was not seen in those with cardiomyopathy (3.39 +/- 2.20 vs 1.77 +/- 0.53 fmol/mg, respectively; p=0.02). The cross-sectional area and perimeter of the cells were greater in alcoholic patients with cardiomyopathy compared with controls and alcoholic patients without cardiomyopathy (500 +/- 87 vs 307 +/- 74 and 255 +/- 25 microm(2), respectively; p<0.001 both) as was the perimeter (78.7 +/- 7.7 vs 61.5 +/- 7.2 and 56.5 +/- 2.8 microm, respectively; p<0.001 both). Binding results did not change after adjusting receptor measurements for cross-sectional area and cell perimeter.

CONCLUSIONS

Chronic alcoholism causes an up-regulation of myocardial L-type Ca(2+) channel receptors, which decreases when cardiomyopathy is present.

Ethanol tolerance caused by slowpoke induction in Drosophila

BACKGROUND

The large-conductance calcium-activated potassium channel encoded by the slowpoke gene has recently been implicated in the ethanol response. Caenorhabditis elegans carrying mutations in this gene have altered ethanol sensitivity and Drosophila mutant for this gene are unable to acquire rapid tolerance to ethanol or anesthetics. In Drosophila, induction of slowpoke expression has been linked to anesthetic resistance.

METHODS

We used Drosophila as a model system to examine the relationship between slowpoke expression and ethanol tolerance. Real-time PCR and a reporter transgene were used to measure slowpoke induction after ethanol sedation. An inducible slowpoke transgene was used to manipulate slowpoke levels in the absence of ethanol sedation.

RESULTS

Ethanol sedation increased transcription from the slowpoke neural promoters but not from the slowpoke muscle/tracheal cell promoters. This neural-specific change was concomitant with the appearance of ethanol tolerance, leading us to suspect linkage between the two. Moreover, induction of slowpoke expression from a transgene produced a phenotype that mimics ethanol tolerance.

CONCLUSIONS

In Drosophila, ethanol sedation induces slowpoke expression in the nervous system and results in ethanol tolerance. The induction of slowpoke expression alone is sufficient to produce a phenotype that is indistinguishable from true ethanol tolerance. Therefore, the regulation of the slowpoke BK-type channel gene must play an integral role in the Drosophila ethanol response.

Ethanol withdrawal is accompanied by downregulation of calcium channel alpha 1B subunit in rat inferior colliculus neurons

Ethanol withdrawal enhances the current density of calcium (Ca(2+)) channels in inferior colliculus (IC) neurons. The present report shows that ethanol withdrawal markedly enhanced the susceptibility to seizures as it decreased significantly the protein levels of alpha(1B) subunit associated with N-type Ca(2+) channel in IC neurons of animals not tested for seizures. Thus, remodeling of N-type Ca(2+) channels may play an important role in neuronal hyperexcitability that leads to ethanol withdrawal seizures.

Update on the neurobiology of alcohol withdrawal seizures

Abrupt cessation of alcohol intake after prolonged heavy drinking may trigger alcohol withdrawal seizures. Generalized tonic-clonic seizures are the most characteristic and severe type of seizure that occur in this setting. Generalized seizures also occur in rodent models of alcohol withdrawal. In these models, the withdrawal seizures are triggered by neuronal networks in the brainstem, including the inferior colliculus; similar brainstem mechanisms may contribute to alcohol withdrawal seizures in humans. Alcohol causes intoxication through effects on diverse ion channels and neurotransmitter receptors, including GABA(A) receptors--particularly those containing delta subunits that are localized extrasynaptically and mediate tonic inhibition--and N-methyl-D-aspartate (NMDA) receptors. Alcohol dependence results from compensatory changes during prolonged alcohol exposure, including internalization of GABA(A) receptors, which allows adaptation to these effects. Withdrawal seizures are believed to reflect unmasking of these changes and may also involve specific withdrawal-induced cellular events, such as rapid increases in alpha4 subunit-containing GABA(A) receptors that confer reduced inhibitory function. Optimizing approaches to the prevention of alcohol withdrawal seizures requires an understanding of the distinct neurobiologic mechanisms that underlie these seizures.

Neuronal responses to lemniscal stimulation in laminar brain slices of the inferior colliculus

The central nucleus of the inferior colliculus (ICC) receives inputs from all parts of the auditory brainstem and transmits the information to the forebrain. Fibrodendritic laminae of the ICC provide a structural basis for a tonotopic organization, and the interaction of inputs within a single layer is important for ICC processing. Transverse slice planes of the ICC sever the layers and many of the ascending axons that enter through the lateral lemniscus. Consequently, the activity initiated within a lamina by a pure lemniscal stimulus is not well characterized. Here, we use a slice plane that maintains the integrity of the laminae in ICC and allows the axons in the lateral lemniscus to be stimulated at a distance from the ICC. We examined both the postsynaptic currents and potentials of the same neurons to lemniscal stimuli in this laminar brain slice. Our main finding is that lemniscal stimulation evokes prolonged synaptic potentials in ICC neurons. Synaptic potential amplitudes and durations increase with lemniscal shock strength. In approximately 50% of ICC neurons, the postsynaptic potential is equal in duration to the postsynaptic current, whereas in the remaining neurons it is three to four times longer. Synaptic responses to single shocks or shock trains exhibit plateau potentials that enable sustained firing in ICC neurons. Plateau potentials are evoked by N-methyl-D-aspartate (NMDA) receptor activation, and their amplitudes and durations are regulated by both NMDA-R and gamma-aminobutyric acid A (GABAA)-R activation. These data suggest that in the intact laminae of the ICC, lemniscal inputs initiate sustained firing through monosynaptic and polysynaptic NMDA-mediated synapses regulated by GABAA synapses.

Ethanol withdrawal reduces cerebellar parvalbumin expression in a manner reversed by estrogens

Parvalbumin (PA) is a calcium-binding protein that has been implicated in neuroprotection. We examined whether the stimulus effect of ethanol withdrawal (EW) alters the expression of PA in a manner that is prevented by 17beta-estradiol (E2). Ovariectomized rats implanted with E2 (EW/E2) or oil (EW/Oil) pellets received chronic ethanol (7.5%, w/v, 5 weeks) or control dextrin diets (Dex/Oil). At 24h of EW, rats were tested for overt EW signs, and the cerebellum was prepared for immunoblotting and immunohistological assessment for PA. The EW/Oil group showed a higher EW sign score, a lower PA expression, and fewer PA-positive Purkinje neurons than the dextrin control group. In the EW/E2 group, EW sign scores, PA expression, and PA-positive Purkinje neurons were not significantly different from those in the control dextrin group. These data suggest that E2 treatment protects against the PA-suppression associated with EW toxicity.

Chronic ethanol consumption reduces delta-and mu-opioid receptor-stimulated G-protein coupling in rat brain

BACKGROUND

Ethanol consumption is thought to enhance the release of endogenous opioids acting at opioid receptors (ORs) in the central nervous system. Prior studies have shown that chronic ethanol consumption in alcohol-preferring rats uncouples mu-ORs from Gi proteins. The purpose of this study was to investigate the potential for uncoupling of the delta- and the mu-OR after chronic ethanol consumption in a nonpreferring rat strain.

METHODS

We used radiohistochemical methods to study mu- and delta-OR-stimulated G-protein coupling in brain tissue of rats ingesting liquid diets containing 6.7% ethanol (v/v) for 16 days, as compared with 0% ethanol pair-fed control rats. Sections of brain from pair-fed and ethanol-treated rats were incubated with guanylyl 5'-[gamma-[35S]-thio]-triphosphate ([35S]-GTPgammaS) in the absence and presence of d-Pen2,d-Pen5 enkephalin (DPDPE), a delta-OR agonist, or Tyr-d-Ala-Gly-N(me)Phe-Gly-ol-enkephalin (DAMGO), a mu-OR agonist.

RESULTS

DPDPE significantly stimulated [35S]-GTPgammaS binding in the hippocampal dentate gyrus (DG), CA1, cerebellum, and inferior colliculus of untreated pair-fed controls. By contrast, DPDPE-stimulated [35S]-GTPgammaS binding was reduced significantly in those brain regions in the ethanol-consuming group. DAMGO stimulated [35S]-GTPgammaS binding in cortex, caudate, nucleus accumbens, DG, CA1, and superior and inferior colliculi, whereas the DG, CA1, and colliculi showed a significant reduction of binding after chronic ethanol. Basal [35S]-GTPgammaS binding was not different between the two diet groups. CONCLUSIONS These data are the first to demonstrate functional uncoupling of delta-ORs from G proteins after chronic ethanol consumption. Uncoupling may result from modulation of receptors, possibly by internalization or phosphorylation. Alterations in functional coupling of both delta- and mu-ORs and subsequent effects may contribute to continued ethanol consumption.