Ethanol Activation of Protein Kinase A Regulates GABA(A) Receptor Subunit Expression in the Cerebral Cortex and Contributes to Ethanol-Induced Hypnosis

Apremilast-induced increases in acute ethanol intoxication and decreases in ethanol drinking in mice involve PKA phosphorylation of GABAA β3 subunits

We previously showed that apremilast, an FDA-approved PDE4 inhibitor, selectively alters behavioral responses to ethanol and certain GABAergic drugs in a PKA-dependent manner in C57BL6/J mice. Here, we investigated if PKA phosphorylation of β3 GABAA receptor subunits is involved in apremilast regulation of ethanol, propofol, or diazepam responses. Apremilast prolonged rotarod ataxia and loss of the righting reflex by ethanol and propofol in wild-type mice, but not in β3-S408A/S409A knock-in mice. In contrast, apremilast hastened recovery from the ataxic and sedative effects of diazepam in both genotypes. These findings suggest that apremilast modulation of ethanol and propofol behaviors in wild-type mice is mediated by β3 subunit phosphorylation, whereas its actions on diazepam responses involve a different mechanism. The PKA inhibitor H-89 prevented apremilast modulation of ethanol-induced ataxia. Apremilast sensitized wild-type males to ethanol-induced ataxia and decreased acute functional tolerance (AFT) in females but had no effect in β3-S408A/S409A mice of either sex. These results could not be attributed to genotype differences in blood ethanol clearance. There were also no baseline genotype differences in ethanol consumption and preference in two different voluntary drinking procedures. However, the ability of apremilast to reduce ethanol consumption was diminished in β3-S408A/S409A mice. Our results provide strong evidence that PKA-dependent phosphorylation of β3 GABAA receptor subunits is an important mechanism by which apremilast increases acute sensitivity to alcohol, decreases AFT, and decreases ethanol drinking.

Alcohol as a Non-UV Social-Environmental Risk Factor for Melanoma

Although cancer mortality has declined among the general population, the incidence of melanoma continues to rise. While identifying high-risk cohorts with genetic risk factors improves public health initiatives and clinical care management, recognizing modifiable risk factors such as social-environmental risk factors would also affect the methods of patient outreach and education. One major modifiable social-environmental risk factor associated with melanoma is ultraviolet (UV) radiation. However, not all forms of melanoma are correlated with sun exposure or occur in sun-exposed areas. Additionally, UV exposure is rarely associated with tumor progression. Another social-environmental factor, pregnancy, does not explain the sharply increased incidence of melanoma. Recent studies have demonstrated that alcohol consumption is positively linked with an increased risk of cancers, including melanoma. This perspective review paper summarizes epidemiological data correlating melanoma incidence with alcohol consumption, describes the biochemical mechanisms of ethanol metabolism, and discusses how ethanol and ethanol metabolites contribute to human cancer, including melanoma.

Regulation of GABAA Receptors Induced by the Activation of L-Type Voltage-Gated Calcium Channels

GABA_A receptors are pentameric ion channels that mediate most synaptic and tonic extrasynaptic inhibitory transmissions in the central nervous system. There are multiple GABA_A receptor subtypes constructed from 19 different subunits in mammals that exhibit different regional and subcellular distributions and distinct pharmacological properties. Dysfunctional alterations of GABA_A receptors are associated with various neuropsychiatric disorders. Short- and long-term plastic changes in GABA_A receptors can be induced by the activation of different intracellular signaling pathways that are triggered, under physiological and pathological conditions, by calcium entering through voltage-gated calcium channels. This review discusses several mechanisms of regulation of GABA_A receptor function that result from the activation of L-type voltage gated calcium channels. Calcium influx via these channels activates different signaling cascades that lead to changes in GABA_A receptor transcription, phosphorylation, trafficking, and synaptic clustering, thus regulating the inhibitory synaptic strength. These plastic mechanisms regulate the interplay of synaptic excitation and inhibition that is crucial for the normal function of neuronal circuits.

Effects of Paternal Preconception Vapor Alcohol Exposure Paradigms on Behavioral Responses in Offspring

We and others previously reported that paternal preconception chronic ethanol exposure leads to molecular, physiological, and behavioral changes in offspring including reduced ethanol consumption and preference relative to controls. The goal of the present study was to further explore the impact of paternal ethanol exposure on a wide variety of basal and drug-induced behavioral responses in first generation offspring. Adult male mice were exposed to chronic intermittent vapor ethanol or control conditions for 5-6 weeks before being mated with ethanol-naïve females to produce ethanol (E)- and control (C)-sired offspring. E-sired male offspring showed stress hyporesponsivity in a stress-induced hyperthermia assay and E-sired female offspring had reduced binge-like ethanol consumption in a drinking in the dark assay compared to C-sired offspring. E-sired offspring also showed altered sensitivity to a sedative/hypnotic dose of the GABAergic drug midazolam, but not ketamine or ethanol, in a loss of the righting response assay. E-sired offspring did not differ from controls in marble burying, novel object location, novel object recognition, social interaction, bottle-brush, novelty suppressed feeding, prepulse inhibition, every-other-day ethanol drinking, or home cage activity assays. This study adds to a growing body of literature suggesting that like in utero alcohol exposure, paternal preconception alcohol exposure can also have effects that persist and impact behavior of offspring.

A possible neuroprotective property of ethanol and/or NeuroAiD on the modulation of cognitive function

Cognitive impairments and poor performance on tasks needing behavioral flexibility are observable in chronic alcohol exposure. NeuroAid decreases cognitive deficits and improves functional outcomes by restoring neuronal circuits. The aim of the current study was to assess the hypothesis that ethanol exposure would induce neurobehavioral defects which may be reversed by the neuroprotective property of NeuroAid. Adult male Wistar rats were treated with saline, ethanol (0.2 g/kg), NeuroAid (0.8 g/kg) and ethanol (0.2 g/kg) + NeuroAid (0.8 g/kg). Then, behavioral tests were performed using the Y-maze apparatus, hot-plate and tail-flick apparatuses, locomotion apparatus as well as the loss of righting reflex (LORR) and hanging protocols (performance in a wire hanging test). Our results indicated that intraperitoneal (i.p.) administration of ethanol alone and administration of ethanol along with NeuroAid for one week reversed ethanol-induced spatial memory deficits in rats (P < 0.01). Interestingly, treatment with ethanol (0.2 g/kg) for one week induced nociception (P < 0.01). Moreover, one week administration of ethanol (0.2 g/kg) along with NeuroAid (0.8 g/kg) increased latency to LORR (P < 0.001) while four weeks administration of ethanol (0.2 g/kg) along with NeuroAid (0.8 g/kg) decreased sleep time (P < 0.01). In addition, a single administration of all drugs did not alter locomotor activity (P > 0.05) and hanging (P > 0.05). Improvement of behavioral tasks after one-week i.p. administration of ethanol and/or NeuroAid in comparison with a single administration of ethanol and/or NeuroAid may be due to the neuroprotective property of ethanol and/or NeuroAiD.

Apremilast regulates acute effects of ethanol and other GABAergic drugs via protein kinase A-dependent signaling

Phosphodiesterase type 4 (PDE4) inhibitors prevent hydrolysis of cyclic adenosine monophosphate and increase protein kinase A (PKA)-mediated phosphorylation. PDE4 inhibitors also regulate responses to ethanol and GABAergic drugs. We investigated mechanisms by which the PDE4 inhibitor, apremilast, regulates acute effects of ethanol and GABAergic drugs in male and female mice. Apremilast prolonged the sedative-hypnotic effects of gaboxadol, zolpidem, and propofol but did not alter etomidate effects, and unexpectedly shortened the sedative-hypnotic effects of diazepam. Apremilast prolonged rotarod ataxia induced by zolpidem, propofol, and loreclezole, shortened recovery from diazepam, but had no effect on ataxia induced by gaboxadol or etomidate. The PKA inhibitor H-89 blocked apremilast's ability to prolong the sedative-hypnotic effects of ethanol, gaboxadol, and propofol and to prolong ethanol- and propofol-induced ataxia. H-89 also blocked apremilast's ability to shorten the sedative-hypnotic and ataxic effects of diazepam. The β1-specific antagonist, salicylidene salicylhydrazide (SCS), produced faster recovery from ethanol- and diazepam-induced ataxia, but did not alter propofol- or etomidate-induced ataxia. SCS shortened the sedative-hypnotic effects of ethanol and diazepam but not of propofol. In Xenopus oocytes, a phosphomimetic (aspartate) mutation at the PKA phosphorylation site in β1 subunits decreased the maximal GABA current in receptors containing α1 or α3, but not α2 subunits. In contrast, phosphomimetic mutations at PKA sites in β3 subunits increased the maximal GABA current in receptors containing α1 or α2, but not α3 subunits. The GABA potency and allosteric modulation by ethanol, propofol, etomidate, zolpidem, flunitrazepam, or diazepam were not altered by these mutations. We propose a model whereby apremilast increases PKA-mediated phosphorylation of β1-and β3-containing GABA_A receptors and selectively alters acute tolerance to ethanol and GABAergic drugs.

Spinal protein kinase A and phosphorylated extracellular signal-regulated kinase signaling are involved in the antinociceptive effect of phytohormone abscisic acid in rats

OBJECTIVE

The phytohormone abscisic acid (ABA) as a signaling molecule exists in various types of organisms from early multicellular to animal cells and tissues. It has been demonstrated that ABA has an antinociceptive effect in rodents. The present study was designed to assess the possible role of PKA and phosphorylated ERK (p-ERK) on the antinociceptive effects of intrathecal (i.t.) ABA in male Wistar rats.

METHODS

The animals were cannulated intrathecally and divided into different experimental groups (n=6‒7): Control (no surgery), vehicle (received ABA vehicle), ABA-treated groups (received ABA in doses of 10 or 20 µg/rat), ABA plus H.89 (PKA inhibitor)-treated group which received the inhibitor 15 min prior to the ABA injection. Tail-flick and hot-plate tests were used as acute nociceptive stimulators to assess ABA analgesic effects. p-ERK was evaluated in the dorsal portion of the spinal cord using immunoblotting.

RESULTS

Data showed that a microinjection of ABA (10 and 20 µg/rat, i.t.) significantly increased the nociceptive threshold in tail flick and hot plate tests. The application of PKA inhibitor (H.89, 100 nM/rat) significantly inhibited ABA-induced analgesic effects. Expression of p-ERK was significantly decreased in ABA-injected animals, which were not observed in the ABA+H.89-treated group.

CONCLUSIONS

Overall, i.t. administration of ABA (10 µg/rat) induced analgesia and p-ERK down-expression likely by involving the PKA-dependent mechanism.

Acute Low Alcohol Disrupts Hippocampus-Striatum Neural Correlate of Learning Strategy by Inhibition of PKA/CREB Pathway in Rats

The hippocampus and striatum guide place-strategy and response-strategy learning, respectively, and they have dissociable roles in memory systems, which could compensate in case of temporary or permanent damage. Although acute alcohol (AA) treatment had been shown to have adverse effects on hippocampal function, whether it causes the functional compensation and the underlying mechanisms is unknown. In this study, rats treated with a low dose of AA avoided a hippocampus-dependent spatial strategy, instead preferring a striatum-dependent response strategy. Consistently, the learning-induced increase in hippocampal, but not striatal, pCREB was rendered less pronounced due to diminished activity of pPKA, but not pERK or pCaMKII. As rats approached the turn-decision area, Sp-cAMP, a PKA activator, was found to mitigate the inhibitory effect of AA on intra- and cross-structure synchronized neuronal oscillations, and rescue response-strategy bias and spatial learning deficits. Our study provides strong evidence of the critical link between neural couplings and strategy selection. Moreover, the PKA/CREB-signaling pathway is involved in the suppressive effect of AA on neural correlates of place-learning strategy. The novel important evidence provided here shows the functional couplings between the hippocampus and striatum in spatial learning processing and suggests possible avenues for therapeutic intervention.

Single Ethanol Withdrawal Regulates Extrasynaptic δ-GABAA Receptors Via PKCδ Activation

Alcohol (ethanol, EtOH) is one of the most widely abused drugs with profound effects on brain function and behavior. GABA_A receptors (GABA_ARs) are one of the major targets for EtOH in the brain. Temporary plastic changes in GABA_ARs after withdrawal from a single EtOH exposure occur both in vivo and in vitro, which may be the basis for chronic EtOH addiction, tolerance and withdrawal symptoms. Extrasynaptic δ-GABA_AR endocytosis is implicated in EtOH-induced GABA_AR plasticity, but the mechanisms by which the relative abundance and localization of specific GABA_ARs are altered by EtOH exposure and withdrawal remain unclear. In this study, we investigated the mechanisms underlying rapid regulation of extrasynaptic δ-GABA_AR by a single EtOH withdrawal in cultured rat hippocampal neurons. Thirty-minutes EtOH (60 mM) exposure increased extrasynaptic tonic current (I_tonic) amplitude without affecting synaptic GABA_AR function in neurons. In contrast, at 30 min after withdrawal, I_tonic amplitude and responsiveness to acute EtOH were both reduced. Similar results occurred in neurons with okadaic acid (OA) or phorbol 12,13-dibutyrate (PDBu) exposure. Protein kinase C (PKC) inhibition prevented the reduction of I_tonic amplitude and the tolerance to acute EtOH, as well as the reduction of GABA_AR-δ subunit abundance induced by a single EtOH withdrawal. Moreover, EtOH withdrawal selectively increased PKCδ level, whereas PKCδ inhibition specifically rescued the EtOH-induced alterations in GABA_AR-δ subunit level and δ-GABA_AR function. Together, we provided strong evidence for the important roles of PKCδ in the rapid regulation of extrasynaptic δ-GABA_AR induced by a single EtOH withdrawal.

Maternal care-related differences in males and females rats' sensitivity to ethanol and the associations between the GABAergic system and steroids in males

This study investigated the effect of maternal care on adolescent ethanol consumption, sensitivity to ethanol-induced hypnosis, as well as gonadal hormones and γ-aminobutyric acid type-A (GABA_A ) systems. Long Evans rat dams were categorized by maternal licking/grooming (LG) frequency into High- and Low-LG mothers. Both female and male offspring from Low-LG rats demonstrated a greater sensitivity to ethanol-induced hypnosis in the loss-of-righting-reflex test at ethanol doses of 3.0 and 3.5 g/kg during late-adolescence (postnatal Day 50) but not at mid-adolescence (postnatal Day 42). However, we found no effect of maternal care on consumption of a 5% ethanol solution in a two-bottle choice test. We further investigated the association between the observed variations in sensitivity to ethanol-induced hypnosis and baseline hormonal levels in males. In male offspring from Low-LG mothers compared to High-LG mothers, baseline plasma corticosterone and progesterone levels were higher. GABA_A α1 and δ subunit expressions were also higher in the cerebral cortex of Low-LG males but lower in the cerebellar synaptosomal fraction. Early environmental influences on adolescent sensitivity to ethanol-induced hypnosis, consumption, and preference may be mediated by gonadal hormones and possibly through GABAergic functions.

Ethanol-induced PGE2 up-regulates Aβ production through PKA/CREB signaling pathway

Ethanol abuse aggravates dementia-associated cognitive defects through the progression of Alzheimer's disease (AD) pathophysiology. Beta-site APP-cleaving enzyme 1 (BACE1) has been considered as a key regulator of AD pathogenesis by controlling amyloid beta peptide (Aβ) accumulation. In addition, previous studies reported that endoplasmic reticulum (ER) stress and neuroinflammation have been proposed in ethanol-induced neurodegeneration. Thus, we investigated the role of ER stress and PGE₂, a neuroinflammation mediator, in the ethanol-stimulated BACE1 expression and Aβ production. Using the human-derived neuroblastoma cell line SK-N-MC, the results show that ethanol up-regulated BACE1 expression in a dose-dependent manner. Ethanol stimulated reactive oxygen species (ROS) production, which induced CHOP expression and eIF2α phosphorylation. PBA (an ER stress inhibitor) attenuated the ethanol-increased cyclooxygenase-2 (COX-2) expression and PGE₂ production. By using salubrinal (an eIF2α dephosphorylation inhibitor) or EIF2A siRNA, we found that eIF2α phosphorylation mediated the ethanol-induced COX-2 expression. In addition, COX-2-induced BACE1 up-regulation was abolished by NS-398 (a selective COX-2 inhibitor). And, PF-04418948 (an EP-2 receptor inhibitor) pretreatment reduced ethanol-induced PKA activation and CREB phosphorylation as well as ethanol-stimulated Aβ production. Furthermore, 14-22 amide (a PKA inhibitor) pretreatment or CREB1 siRNA transfection suppressed the ethanol-induced BACE1 expression. In conclusion, ethanol-induced eIF2α phosphorylation stimulates COX-2 expression and PGE₂ production which induces the BACE1 expression and Aβ production via EP-2 receptor-dependent PKA/CREB pathway.

Inhibitors of Calcium-Activated Anion Channels Modulate Hypnotic Ethanol Responses in Adult Sprague Dawley Rats

BACKGROUND

Ethanol is widely known for its depressant effects; however, the underlying neurobiological mechanisms are not clear. Calcium-activated anion channels (CAACs) contribute to extracellular chloride levels and thus may be involved in regulating inhibitory mechanisms within the central nervous system. Therefore, we hypothesized that CAACs influence ethanol behavioral sensitivity by altering CAAC expression.

METHODS

We assessed the role of CAACs in ethanol-induced loss of righting reflex (LORR) and locomotor activity using intracerebroventricular infusions of several nonselective CAAC blockers. CAAC expression was determined after ethanol exposure.

RESULTS

Ethanol-induced LORR (4.0 g/kg, intraperitoneally [i.p.]) was significantly attenuated by all 4 CAAC blockers. Blocking CAACs did not impact ethanol's low-dose (1.5 g/kg, i.p.) locomotor-impairing effects. Biochemical analysis of CAAC protein expression revealed that cortical Bestrophin1 (Best1) and Tweety1 levels were reduced as early as 30 minutes following a single ethanol injection (3.5 g/kg, intraperitoneally [i.p.]) and remained decreased 24 hours later in P2 fractions. Cortical Best1 levels were also reduced following 1.5 g/kg. However, CAAC expression was unaltered in the striatum following a single ethanol exposure. Ethanol did not affect Tweety2 levels in either brain region.

CONCLUSIONS

These results suggest that CAACs are a major target of ethanol in vivo, and the regulation of these channels contributes to select behavioral actions of ethanol.

Ethanol potentiates both GABAergic and glutamatergic signaling in the lateral habenula

Ethanol's aversive property may limit it's use, but the underlying mechanisms are no well-understood. Emerging evidence suggests a critical role for the lateral habenula (LHb) in the aversive response to various drugs, including ethanol. We previously showed that ethanol enhances glutamatergic transmission and stimulates LHb neurons. GABAergic transmission, a major target of ethanol in many brain regions, also tightly regulates LHb activity. This study assessed the action of ethanol on LHb GABAergic transmission in rat brain slices. Application of ethanol accelerated spontaneous action potential firing of LHb neurons, and LHb activity was increased by the GABA_A receptor antagonist gabazine, and ethanol-induced acceleration of LHb firing was further increased by gabazine. Additionally, ethanol potentiated GABAergic transmission (inhibitory postsynaptic currents, IPSCs) with an EC₅₀ of 1.5 mM. Ethanol-induced potentiation of IPSCs was increased by a GABA_B receptor antagonist; it was mimicked by dopamine, dopamine receptor agonists, and dopamine reuptake blocker, and was completely prevented by reserpine, which depletes store of catecholamine. Moreover, ethanol-induced potentiation of IPSCs involved cAMP signaling. Finally, ethanol enhanced simultaneously glutamatergic and GABAergic transmissions to the majority of LHb neurons: the potentiation of the former being greater than that of the latter, the net effect was increased firing. Since LHb excitation may contribute to aversion, ethanol-induced potentiation of GABAergic inhibition tends to reduce aversion.

Potentiation of Gamma Aminobutyric Acid Receptors (GABAAR) by Ethanol: How Are Inhibitory Receptors Affected?

In recent years there has been an increase in the understanding of ethanol actions on the type A γ-aminobutyric acid chloride channel (GABA_AR), a member of the pentameric ligand gated ion channels (pLGICs). However, the mechanism by which ethanol potentiates the complex is still not fully understood and a number of publications have shown contradictory results. Thus many questions still remain unresolved requiring further studies for a better comprehension of this effect. The present review concentrates on the involvement of GABA_AR in the acute actions of ethanol and specifically focuses on the immediate, direct or indirect, synaptic and extra-synaptic modulatory effects. To elaborate on the immediate, direct modulation of GABA_AR by acute ethanol exposure, electrophysiological studies investigating the importance of different subunits, and data from receptor mutants will be examined. We will also discuss the nature of the putative binding sites for ethanol based on structural data obtained from other members of the pLGICs family. Finally, we will briefly highlight the glycine gated chloride channel (GlyR), another member of the pLGIC family, as a suitable target for the development of new pharmacological tools.

Transgenerational Transmission of the Effect of Gestational Ethanol Exposure on Ethanol Use-Related Behavior

BACKGROUND

Prenatal alcohol exposure (PAE) enhances the risk for alcoholism by increasing the propensity to consume alcohol and altering neurophysiological response to alcohol challenge. Trans-generationally transmittable genetic alterations have been implicated in these behavioral changes. To date, transgenerational transmission of PAE-induced behavioral responses to alcohol has never been experimentally investigated. Therefore, we explored the transgenerational transmission of PAE-induced behavioral effects across 3 generations.

METHODS

Pregnant Sprague Dawley dams received 1 g/kg ethanol (EtOH) or water daily on gestational days 17 through 20 via gavage, or remained untreated in their home cages. To produce second filial (F2) or F3 generations, similarly treated adult F1 or F2 offspring were mated and left undisturbed through gestation. On postnatal day (PND) 14, male and female F1, F2, and F3 offspring were tested for consumption of 5% (w/v) EtOH (in water), or water. Using the loss of righting reflex (LORR) paradigm on PND 42, F1 and F2 adolescent male offspring were tested for sensitivity to acute EtOH-induced sedation-hypnosis at 3.5 or 4.5 g/kg dose. F3 male adolescents were similarly tested at 3.5 g/kg dose. Blood EtOH concentration (BEC) was measured at waking.

RESULTS

EtOH exposure increased EtOH consumption compared to both water and untreated control groups in all generations. EtOH-treated group F1 and F2 adolescents displayed attenuated LORR duration compared to the water group. No attenuated LORR was observed in the F3 generation. BEC at waking corroborated with the significant LORR duration differences while also revealing differences between untreated control and water groups in F1 and F2 generations.

CONCLUSIONS

Our results provide novel behavioral evidence attesting that late gestational moderate EtOH exposure increases EtOH intake across 3 generations and may alter sensitivity to EtOH-induced sedation-hypnosis across 2 generations.

Phosphodiesterase regulation of alcohol drinking in rodents

Alcohol use disorders are chronically relapsing conditions characterized by persistent drinking despite the negative impact on one's life. The difficulty of achieving and maintaining sobriety suggests that current treatments fail to fully address the underlying causes of alcohol use disorders. Identifying additional pathways controlling alcohol consumption may uncover novel targets for medication development to improve treatment options. One family of proteins recently implicated in the regulation of alcohol consumption is the cyclic nucleotide phosphodiesterases (PDEs). As an integral component in the regulation of the second messengers cyclic AMP and cyclic GMP, and thus their cognate signaling pathways, PDEs present intriguing targets for pharmacotherapies to combat alcohol use disorders. As activation of cAMP/cGMP-dependent signaling cascades can dampen alcohol intake, PDE inhibitors may provide a novel target for reducing excessive alcohol consumption, as has been proposed for PDE4 and PDE10A. This review highlights preclinical literature demonstrating the involvement of cyclic nucleotide-dependent signaling in neuronal and behavioral responses to alcohol, as well as detailing the capacity of various PDE inhibitors to modulate alcohol intake. Together these data provide a framework for evaluating the potential utility of PDE inhibitors as novel treatments for alcohol use disorders.

Regulation of Extrasynaptic GABAA α4 Receptors by Ethanol-Induced Protein Kinase A, but Not Protein Kinase C Activation in Cultured Rat Cerebral Cortical Neurons

Ethanol produces changes in GABAA receptor trafficking and function that contribute to ethanol dependence symptomatology. Extrasynaptic γ-aminobutyric acid A receptors (GABAA-R) mediate inhibitory tonic current and are of particular interest because they are potentiated by physiologically relevant doses of ethanol. Here, we isolate GABAA α4δ receptors by western blotting in subsynaptic fractions to investigate protein kinase A (PKA) and protein kinase C (PKC) modulation of ethanol-induced receptor trafficking, while extrasynaptic receptor function is determined by measurement of tonic inhibition and responses evoked by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). Rat cerebral cortical neurons were grown for 18 days in vitro and exposed to ethanol and/or PKA/PKC modulators. Ethanol exposure (1 hour) did not alter GABAA α4 receptor abundance, but it increased tonic current amplitude, an effect that was prevented by inhibiting PKA, but not PKC. Direct activation of PKA, but not PKC, increased the abundance and tonic current of extrasynaptic α4δ receptors. In contrast, prolonged ethanol exposure (4 hours) reduced α4δ receptor abundance as well as tonic current, and this effect was also PKA dependent. Finally, PKC activation by ethanol or phorbol-12,13-dibutyrate (PdBu) had no effect on extrasynaptic α4δ subunit abundance or activity. We conclude that ethanol alters extrasynaptic α4δ receptor function and expression in cortical neurons in a PKA-dependent manner, but ethanol activation of PKC does not influence these receptors. These results could have clinical relevance for therapeutic strategies to restore normal GABAergic functioning for the treatment of alcohol use disorders.

Alcohol binding in the C1 (C1A+C1B) domain of protein kinase C epsilon

BACKGROUND

Alcohol regulates the expression and function of protein kinase C epsilon (PKCε). In a previous study we identified an alcohol binding site in the C1B, one of the twin C1 subdomains of PKCε (Das et al., Biochem. J., 421, 405-13, 2009).

METHODS

In this study, we investigated alcohol binding in the entire C1 domain (combined C1A and C1B) of PKCε. Fluorescent phorbol ester, SAPD and fluorescent diacylglycerol (DAG) analog, dansyl-DAG were used to study the effect of ethanol, butanol, and octanol on the ligand binding using fluorescence resonance energy transfer (FRET). To identify alcohol binding site(s), PKCεC1 was photolabeled with 3-azibutanol and 3-azioctanol, and analyzed by mass spectrometry. The effects of alcohols and the azialcohols on PKCε were studied in NG108-15 cells.

RESULTS

In the presence of alcohol, SAPD and dansyl-DAG showed different extent of FRET, indicating differential effects of alcohol on the C1A and C1B subdomains. Effects of alcohols and azialcohols on PKCε in NG108-15 cells were comparable. Azialcohols labeled Tyr-176 of C1A and Tyr-250 of C1B. Inspection of the model structure of PKCεC1 reveals that these residues are 40Å apart from each other indicating that these residues form two different alcohol binding sites.

CONCLUSIONS

The present results provide evidence for the presence of multiple alcohol-binding sites on PKCε and underscore the importance of targeting this PKC isoform in developing alcohol antagonists.

Adolescent alcohol exposure alters GABAA receptor subunit expression in adult hippocampus

BACKGROUND

The long-term consequences of adolescent alcohol abuse that persist into adulthood are poorly understood and have not been widely investigated. We have shown that intermittent exposure to alcohol during adolescence decreased the amplitude of GABAA receptor (GABAA R)-mediated tonic currents in hippocampal dentate granule cells in adulthood. The aim of this study was to investigate the enduring effects of chronic intermittent alcohol exposure during adolescence or adulthood on the expression of hippocampal GABAA Rs.

METHODS

We used a previously characterized tissue fractionation method to isolate detergent resistant membranes and soluble fractions, followed by Western blots to measure GABAA R protein expression. We also measured mRNA levels of GABAA R subunits using quantitative real-time polymerase chain reaction.

RESULTS

Although the protein levels of α1-, α4-, and δ-GABAA R subunits remained stable between postnatal day (PD) 30 (early adolescence) and PD71 (adulthood), the α5-GABAA R subunit was reduced across that period. In rats that were subjected to adolescent intermittent ethanol (AIE) exposure between PD30 and PD46, there was a significant reduction in the protein levels of the δ-GABAA R, in the absence of any changes in mRNA levels, at 48 hours and 26 days after the last ethanol (EtOH) exposure. Protein levels of the α4-GABAA R subunit were significantly reduced, but mRNA levels were increased, 26 days (but not 48 hours) after the last AIE exposure. Protein levels of α5-GABAA R were not changed by AIE, but mRNA levels were reduced at 48 hours but normalized 26 days after AIE. In contrast to the effects of AIE, chronic intermittent ethanol (CIE) exposure during adulthood had no effect on expression of any of the GABAA R subunits examined.

CONCLUSIONS

AIE produced both short- and long-term alterations of GABAA R subunits mRNA and protein expression in the hippocampus, whereas CIE produced no long-lasting effects on those measures. The observed reduction of protein levels of the δ-GABAA R, specifically, is consistent with previously reported altered hippocampal GABAA R-mediated electrophysiological responses after AIE. The absence of effects of CIE underscores the emerging view of adolescence as a time of distinctive vulnerability to the enduring effects of repeated EtOH exposure.

Cytoplasmic phospholipase A₂ modulation of adolescent rat ethanol-induced protein kinase C translocation and behavior

Ethanol consumption typically begins during adolescence, a developmental period which exhibits many age-dependent differences in ethanol behavioral sensitivity. Protein kinase C (PKC) activity is largely implicated in ethanol-behaviors, and our previous work indicates that regulation of novel PKC isoforms likely contributes to decreased high-dose ethanol sensitivity during adolescence. The cytoplasmic Phospholipase A2 (cPLA2) signaling cascade selectivity modulates novel and atypical PKC isoform activity, as well as adolescent ethanol hypnotic sensitivity. Therefore, the current study was designed to ascertain adolescent cPLA2 activity both basally and in response to ethanol, as well as it's involvement in ethanol-induced PKC isoform translocation patterns. cPLA2 expression was elevated during adolescence, and activity was increased only in adolescents following high-dose ethanol administration. Novel, but not atypical PKC isoforms translocate to cytosolic regions following high-dose ethanol administration. Inhibiting cPLA2 with AACOCF3 blocked ethanol-induced PKC cytosolic translocation. Finally, inhibition of novel, but not atypical, PKC isoforms when cPLA2 activity was elevated, modulated adolescent high-dose ethanol-sensitivity. These data suggest that the cPLA2/PKC pathway contributes to the acute behavioral effects of ethanol during adolescence.

Altered expression of δGABAA receptors in health and disease

γ-Aminobutyric acid type A receptors that contain the δ subunit (δGABAA receptors) are expressed in multiple types of neurons throughout the central nervous system, where they generate a tonic conductance that shapes neuronal excitability and synaptic plasticity. These receptors regulate a variety of important behavioral functions, including memory, nociception and anxiety, and may also modulate neurogenesis. Given their functional significance, δGABAA receptors are considered to be novel therapeutic targets for the treatment of memory dysfunction, pain, insomnia and mood disorders. These receptors are highly responsive to sedative-hypnotic drugs, general anesthetics and neuroactive steroids. A further remarkable feature of δGABAA receptors is that their expression levels are highly dynamic and fluctuate substantially during development and in response to physiological changes including stress and the reproductive cycle. Furthermore, the expression of these receptors varies in pathological conditions such as alcoholism, fragile X syndrome, epilepsy, depression, schizophrenia, mood disorders and traumatic brain injury. Such fluctuations in receptor expression have significant consequences for behavior and may alter responsiveness to therapeutic drugs. This review considers the alterations in the expression of δGABAA receptors associated with various states of health and disease and the implications of these changes.

Adolescent and adult rat cortical protein kinase A display divergent responses to acute ethanol exposure

Adolescent rats display reduced sensitivity to many dysphoria-related effects of alcohol (ethanol) including motor ataxia and sedative hypnosis, but the underlying neurobiological factors that contribute to these differences remain unknown. The cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) pathway, particularly the type II regulatory subunit (RII), has been implicated in ethanol-induced molecular and behavioral responses in adults. Therefore, the current study examined cerebral cortical PKA in adolescent and adult ethanol responses. With the exception of early adolescence, PKA RIIα and RIIβ subunit levels largely did not differ from adult levels in either whole cell lysate or P2 synaptosomal expression. However, following acute ethanol exposure, PKA RIIβ P2 synaptosomal expression and activity were increased in adults, but not in adolescents. Behaviorally, intracerebroventricular administration of the PKA activator Sp-cAMP and inhibitor Rp-cAMP prior to ethanol administration increased adolescent sensitivity to the sedative-hypnotic effects of ethanol compared to controls. Sp-cAMP was ineffective in adults whereas Rp-cAMP suggestively reduced loss of righting reflex (LORR) with paralleled increases in blood ethanol concentrations. Overall, these data suggest that PKA activity modulates the sedative/hypnotic effects of ethanol and may potentially play a wider role in the differential ethanol responses observed between adolescents and adults.

Molecular and behavioral characterization of adolescent protein kinase C following high dose ethanol exposure

RATIONALE

Ethanol is commonly used and abused during adolescence. Although adolescents display differential behavioral responses to ethanol, the mechanisms by which this occurs are not known. The protein kinase C (PKC) pathway has been implicated in mediating many ethanol-related effects in adults, as well as gamma-aminobutyric acid (GABA(A)) receptor regulation.

OBJECTIVES

The present study was designed to characterize cortical PKC isoform and GABA(A) receptor subunit expression during adolescence relative to adults as well as assess PKC involvement in ethanol action.

RESULTS

Novel PKC isoforms were elevated, while PKCγ was lower during mid-adolescence relative to adults. Whole-cell lysate and synaptosomal preparations correlated for all isoforms except PKCδ. In parallel, synaptosomal GABAA receptor subunit expression was also developmentally regulated, with GABA(A)R δ and α4 being lower while α1 and γ2 were higher or similar, respectively, in adolescents compared to adults. Following acute ethanol exposure, synaptosomal novel and atypical PKC isoform expression was decreased only in adolescents. Behaviorally, inhibiting PKC with calphostin C, significantly increased ethanol-induced loss of righting reflex (LORR) in adolescents but not adults, whereas activating PKC with phorbol dibutyrate was ineffective in adolescents but decreased LORR duration in adults. Further investigation revealed that inhibiting the cytosolic phospholipase A2/arachidonic acid (cPLA2/AA) pathway increased LORR duration in adolescents, but was ineffective in adults.

CONCLUSIONS

These data indicate that PKC isoforms are variably regulated during adolescence and may contribute to adolescent ethanol-related behavior. Furthermore, age-related differences in the cPLA2/AA pathway may contribute to ethanol's age-related effects on novel and atypical PKC isoform expression and behavior.

The neurobiology of alcohol consumption and alcoholism: an integrative history

Studies of the neurobiological predisposition to consume alcohol (ethanol) and to transition to uncontrolled drinking behavior (alcoholism), as well as studies of the effects of alcohol on brain function, started a logarithmic growth phase after the repeal of the 18th Amendment to the United States Constitution. Although the early studies were primitive by current technological standards, they clearly demonstrated the effects of alcohol on brain structure and function, and by the end of the 20th century left little doubt that alcoholism is a "disease" of the brain. This review traces the history of developments in the understanding of ethanol's effects on the most prominent inhibitory and excitatory systems of brain (GABA and glutamate neurotransmission). This neurobiological information is integrated with knowledge of ethanol's actions on other neurotransmitter systems to produce an anatomical and functional map of ethanol's properties. Our intent is limited in scope, but is meant to provide context and integration of the actions of ethanol on the major neurobiologic systems which produce reinforcement for alcohol consumption and changes in brain chemistry that lead to addiction. The developmental history of neurobehavioral theories of the transition from alcohol drinking to alcohol addiction is presented and juxtaposed to the neurobiological findings. Depending on one's point of view, we may, at this point in history, know more, or less, than we think we know about the neurobiology of alcoholism.

Altered GABAA receptor expression and seizure threshold following acute ethanol challenge in mice lacking the RIIβ subunit of PKA

Ethanol causes pathological changes in GABAA receptor trafficking and function. These changes are mediated in part by ethanol activation of protein kinase A (PKA). The current study investigated the expression of the GABAA α1 and α4 subunits and the kinase anchoring protein AKAP150, as well as bicuculline-induced seizure threshold, at baseline and following acute injection of ethanol (3.5 g/kg IP) in a mouse line lacking the regulatory RIIβ subunit of PKA. Whole cerebral cortices were harvested at baseline, 1 h, or 46 h following injection of ethanol or saline and subjected to fractionation and western blot analysis. Knockout (RIIβ-/-) mice had similar baseline levels of PKA RIIα and GABAA α1 and α4 subunits compared to wild type (RIIβ+/+) littermates, but had deficits in AKAP150. GABAA α1 subunit levels were decreased in the P2 fraction of RIIβ-/-, but not RIIβ+/+, mice following 1 h ethanol, an effect that was driven by decreased α1 expression in the synaptic fraction. GABAA α4 subunits in the P2 fraction were not affected by 1 h ethanol; however, synaptic α4 subunit expression was increased in RIIβ+/+, but not RIIβ-/- mice, while extrasynaptic α4 and δ subunit expression were decreased in RIIβ-/-, but not RIIβ+/+ mice. Finally, RIIβ knockout was protective against bicuculline-induced seizure susceptibility. Overall, the results suggest that PKA has differential roles in regulating GABAA receptor subunits. PKA may protect against ethanol-induced deficits in synaptic α1 and extrasynaptic α4 receptors, but may facilitate the increase of synaptic α4 receptors.

Ethanol activation of protein kinase A regulates GABAA α1 receptor function and trafficking in cultured cerebral cortical neurons

Ethanol exposure produces alterations in GABAergic signaling that are associated with dependence and withdrawal. Previously, we demonstrated that ethanol-induced protein kinase C (PKC) γ signaling selectively contributes to changes in GABAA α1 synaptic receptor activity and surface expression. Here, we demonstrate that protein kinase A (PKA) exerts opposing effects on GABAA receptor adaptations during brief ethanol exposure. Cerebral cortical neurons from day 0-1 rat pups were tested after 18 days in culture. Receptor trafficking was assessed by Western blot analysis, and functional changes were measured using whole-cell patch-clamp recordings of evoked and miniature inhibitory postsynaptic current (mIPSC) responses. One-hour ethanol exposure increased membrane-associated PKC and PKA, but steady-state GABAA α1 subunit levels were maintained. Activation of PKA by Sp-adenosine 3',5'-cyclic monophosphothioate triethylamine alone increased GABAA α1 subunit surface expression and zolpidem potentiation of GABA responses, whereas coexposure of ethanol with the PKA inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate triethylamine decreased α1 subunit expression and zolpidem responses. Exposure to the PKC inhibitor calphostin-C with ethanol mimicked the effect of direct PKA activation. The effects of PKA modulation on mIPSC decay τ were consistent with its effects on GABA currents evoked in the presence of zolpidem. Overall, the results suggest that PKA acts in opposition to PKC on α1-containing GABAA receptors, mediating the GABAergic effects of ethanol exposure, and may provide an important target for the treatment of alcohol dependence/withdrawal.