Protein kinase Cgamma mediates ethanol withdrawal hyper-responsiveness of NMDA receptor currents in spinal cord motor neurons

Ovariectomy Exacerbates Acute Ethanol-Induced Tachycardia: Role of Nitric Oxide and NMDA Receptors in the Rostral Ventrolateral Medulla

Ethanol consumption influences cardiovascular functions. In humans, acute consumption of ethanol causes dose-dependent tachycardia. Our previous study showed that ethanol-induced tachycardia might involve decreased nitric oxide (NO) signaling in the brain's medulla. NMDA receptors, another important target of ethanol, are one of the upstream signals of nitric oxide. Reports showed the modulation of NMDA receptor function by estrogen or estrogen receptors. The present study aims to examine the hypothesis that depletion of estrogen by ovariectomy (OVX) might modulate ethanol-induced tachycardia by regulating NMDA receptor function and NO signaling in the cardiovascular regulatory nucleus of the brain. Ethanol (3.2 g/kg, 40% v/v, 10 mL/kg) or saline (10 mL/kg) was administered by oral gavage in sham or OVX female Sprague-Dawley (SD) rats. The blood pressure (BP) and heart rate (HR) were measured using the tail-cuff method. The levels of phosphoserine 896 of the GluN1 subunit (pGluN1-serine 896) and NMDA GluN1 subunits (GluN1) were determined by immunohistochemistry. The expressions of nitric oxide synthase (NOS) and estrogen receptors in the tissue were measured by Western blotting. Nitric oxide contents were measured as total nitrate-nitrite by colorimetric assay kit. In a 2-h observation, there was no significant change in BP between the saline and ethanol groups. However, compared with saline, ethanol caused an increase in HR (tachycardia) in sham control or OVX rats. Interestingly, ethanol produced more significant tachycardia in the OVX group than in the sham control group. Nitric oxide levels were lower in the area of the rostral ventrolateral medulla (RVLM) 60 min following ethanol administration in OVX compared with sham control, without significant changes in the expression of NOS and estrogen receptors (ERα and ERβ). In addition, a decrease in the immunoreactivity of pGluN1-serine 896, without significant changes in GluN1, was found in neurons of RVLM 40 min following ethanol administration in OVX compared with sham control. Our results suggest that depletion of estradiol (E2) by OVX might exacerbate the tachycardia following ethanol administration, the underlying mechanism of which might be associated with decreased NMDA receptor function and NO level in the RVLM.

Prevention of glutamate excitotoxicity in lateral habenula alleviates ethanol withdrawal-induced somatic and behavioral effects in ethanol dependent mice

Ethanol withdrawal commonly leads to anxiety-related disorder, a central factor toward negative reinforcement leading to relapse. The lateral habenula (LHb), an epithalamic nucleus, has emerged to be critical for both reward and aversion processing. Recent studies have also implicated the hyperactivity of LHb, adding to the emergence of negative emotional states during withdrawal from addictive drugs. Herein, we have studied the effects of glutamate transporter inhibitor (PDC), GluN2B-containing NMDAR antagonist (Ro25-6981), and intracellular calcium chelator (BAPTA-AM) injection in LHb on ethanol withdrawal symptoms. We found that ethanol 4 g/kg 20 % w/v intragastric (i.g.) for 10 days followed by 24 h of withdrawal showed a significant increase in somatic signs characterized by vocalization, shaking, and scratching. It also increased locomotor activity and anxiety-like behavior, collectively showing expression of ethanol withdrawal symptoms. The intra-LHb administration of PDC (0.5 ng) worsened the effect of ethanol withdrawal, whereas Ro25-6981 (2 and 4 ng) and BAPTA-AM (6.5 and 13 ng) significantly reversed ethanol withdrawal-induced behavior evident by a decrease in somatic signs, locomotor activity, and anxiety-like behavior. Further, pretreatment of Ro25-6981 and BAPTA-AM reduced the neuronal loss, whereas PDC increased it compared to the vehicle-treated group, as evidenced by NeuN staining. Altogether, our results suggest that increased glutamate, GluN2B activation, and likely calcium increase indicative of glutamate excitotoxicity-induced neuronal loss in LHb possibly endorse the emergence of ethanol withdrawal symptoms, while their inhibition might help in alleviating the ethanol withdrawal symptoms.

PKCγ promotes axonal remodeling in the cortico-spinal tract via GSK3β/β-catenin signaling after traumatic brain injury

Traumatic brain injury (TBI) is a common cause of death and disability. Enhancing the midline-crossing of the contralateral corticospinal tract (CST) to the denervated side of spinal cord facilitates functional recovery after TBI. Activation of the gamma isoform of PKC (PKCγ) in contralateral CST implicates its roles in promoting CST remodeling after TBI. In this study, we deployed loss and gain of function strategies in N2a cells and primary cortical neurons in vitro, and demonstrated that PKCγ is not only important but necessary for neuronal differentiation, neurite outgrowth and axonal branching but not for axonal extension. Mechanically, through the phosphorylation of GSK3β, PKCγ stabilizes the expression of cytosolic β-catenin and increase GAP43 expression, thus promoting axonal outgrowth. Further, rAAV2/9-mediated delivery of constitutive PKCγ in the corticospinal tract after unilateral TBI in vivo additionally showed that specifically delivery of active PKCγ mutant to cortical neuron promotes midline crossing of corticospinal fibers from the uninjured side to the denervated cervical spinal cord. This PKCγ-mediated injury response promoted sensorimotor functional recovery. In conclusion, PKCγ mediates stability of β-catenin through the phosphorylation of GSK3β to facilitate neuronal differentiation, neurite outgrowth and axonal branching, and PKCγ maybe a novel therapeutic target for physiological and functional recovery after TBI.

Neonatal ethanol exposure triggers apoptosis in the murine retrosplenial cortex: Role of inhibition of NMDA receptor-driven action potential firing

Exposure to ethanol during the last trimester equivalent of human pregnancy causes apoptotic neurodegeneration in the developing brain, an effect that is thought to be mediated, in part, by inhibition of NMDA receptors. However, NMDA receptors can rapidly adapt to the acute effects of ethanol and are ethanol resistant in some populations of developing neurons. Here, we characterized the effect of ethanol on NMDA and non-NMDA receptor-mediated synaptic transmission in the retrosplenial cortex (RSC), a brain region involved in the integration of different modalities of spatial information that is among the most sensitive regions to ethanol-induced neurodegeneration. A single 4-h exposure to ethanol vapor of 7-day-old transgenic mice that express the Venus fluorescent protein in interneurons triggered extensive apoptosis in the RSC. Slice electrophysiological recordings showed that bath-applied ethanol inhibits NMDA and non-NMDA receptor excitatory postsynaptic currents (EPSCs) in pyramidal neurons and interneurons; however, we found no evidence of acute tolerance development to this effect after the 4-h in-vivo ethanol vapor exposure. Acute bath application of ethanol reduced action potential firing evoked by synaptic stimulation to a greater extent in pyramidal neurons than interneurons. Submaximal inhibition of NMDA EPSCs, but not non-NMDA EPSCs, mimicked the acute effect of ethanol on synaptically-evoked action potential firing. These findings indicate that partial inhibition of NMDA receptors by ethanol has sizable effects on the excitability of glutamatergic and GABAergic neurons in the developing RSC, and suggest that positive allosteric modulators of these receptors could ameliorate ethanol intoxication-induced neurodegeneration during late stages of fetal development.

PKCγ and PKCε are Differentially Activated and Modulate Neurotoxic Signaling Pathways During Oxygen Glucose Deprivation in Rat Cortical Slices

Cerebral ischemia is known to trigger a series of intracellular events such as changes in metabolism, membrane function and intracellular transduction, which eventually leads to cell death. Many of these processes are mediated by intracellular signaling cascades that involve protein kinase activation. Among all the kinases activated, the serine/threonine kinase family, protein kinase C (PKC), particularly, has been implicated in mediating cellular response to cerebral ischemic and reperfusion injury. In this study, using oxygen-glucose deprivation (OGD) in acute cortical slices as an in vitro model of cerebral ischemia, I show that PKC family of isozymes, specifically PKCγ and PKCε are differentially activated during OGD. Detecting the expression and activation levels of these isozymes in response to different durations of OGD insult revealed an early activation of PKCε and delayed activation of PKCγ, signifying their roles in response to different durations and stages of ischemic stress. Specific inhibition of PKCγ and PKCε significantly attenuated OGD induced cytotoxicity, rise in intracellular calcium, membrane depolarization and reactive oxygen species formation, thereby enhancing neuronal viability. This study clearly suggests that PKC family of isozymes; specifically PKCγ and PKCε are involved in OGD induced intracellular responses which lead to neuronal death. Thus isozyme specific modulation of PKC activity may serve as a promising therapeutic route for the treatment of acute cerebral ischemic injury.

Dorsal Horn Parvalbumin Neurons Are Gate-Keepers of Touch-Evoked Pain after Nerve Injury

Neuropathic pain is a chronic debilitating disease that results from nerve damage, persists long after the injury has subsided, and is characterized by spontaneous pain and mechanical hypersensitivity. Although loss of inhibitory tone in the dorsal horn of the spinal cord is a major contributor to neuropathic pain, the molecular and cellular mechanisms underlying this disinhibition are unclear. Here, we combined pharmacogenetic activation and selective ablation approaches in mice to define the contribution of spinal cord parvalbumin (PV)-expressing inhibitory interneurons in naive and neuropathic pain conditions. Ablating PV neurons in naive mice produce neuropathic pain-like mechanical allodynia via disinhibition of PKCγ excitatory interneurons. Conversely, activating PV neurons in nerve-injured mice alleviates mechanical hypersensitivity. These findings indicate that PV interneurons are modality-specific filters that gate mechanical but not thermal inputs to the dorsal horn and that increasing PV inter-neuron activity can ameliorate the mechanical hypersensitivity that develops following nerve injury.

Molecular basis of alcoholism

Acute alcohol intoxication causes cellular changes in the brain that last for hours, while chronic alcohol use induces widespread neuroadaptations in the nervous system that can last a lifetime. Chronic alcohol use and the progression into dependence involve the remodeling of synapses caused by changes in gene expression produced by alcohol. The progression of alcohol use, abuse, and dependence can be divided into stages, which include intoxication, withdrawal, and craving. Each stage is associated with specific changes in gene expression, cellular function, brain circuits, and ultimately behavior. What are the molecular mechanisms underlying the transition from recreational use (acute) to dependence (chronic)? What cellular adaptations result in drug memory retention, leading to the persistence of addictive behaviors, even after prolonged drug abstinence? Research into the neurobiology of alcoholism aims to answer these questions. This chapter will describe the molecular adaptations caused by alcohol use and dependence, and will outline key neurochemical participants in alcoholism at the molecular level, which are also potential targets for therapy.

Nociceptive-induced myocardial remote conditioning is mediated by neuronal gamma protein kinase C

Deciphering the remote conditioning molecular mechanism may provide targets to develop therapeutics that can broaden the clinical application. To further investigate this, we tested whether two protein kinase C (PKC) isozymes, the ubiquitously expressed epsilon PKC (εPKC) and the neuronal-specific gamma PKC (γPKC), mediate nociceptive-induced remote myocardial conditioning. Male Sprague-Dawley rats were used for both in vivo and ex vivo myocardial ischemia-reperfusion protocols. For the in vivo studies, using a surgical abdominal incision for comparison, applying only to the abdomen either bradykinin or the εPKC activator (ψεRACK) reduced myocardial infarct size (45 ± 1, 44 ± 2 %, respectively, vs. incision: 43 ± 2 %, and control: 63 ± 2 %, P < 0.001). Western blot showed only εPKC, and not γPKC, is highly expressed in the myocardium. However, applying a selective γPKC inhibitor (γV5-3) to the abdominal skin blocked remote protection by any of these strategies. Using an ex vivo isolated heart model without an intact nervous system, only selective εPKC activation, unlike a selective classical PKC isozyme activator (activating α, β, βII, and γ), reduced myocardial injury. Importantly, the classical PKC isozyme activator given to the abdomen in vivo (with an intact nervous system including γPKC) during myocardial ischemia reduced infarct size as effectively as an abdominal incision or ψεRACK (45 ± 1 vs. 45 ± 2 and 47 ± 1 %, respectively). The classical PKC activator-induced protection was also blocked by spinal cord surgical transection. These findings identified potential remote conditioning mimetics, with these strategies effective even during myocardial ischemia. A novel mechanism of nociceptive-induced remote conditioning, involving γPKC, was also identified.

Regulation of cardiac excitability by protein kinase C isozymes

Cardiac excitability and electrical activity are determined by the sum of individual ion channels, gap junctions and exchanger activities. Electrophysiological remodeling during heart disease involves changes in membrane properties of cardiomyocytes and is related to higher prevalence of arrhythmia-associated morbidity and mortality. Pharmacological and genetic manipulation of cardiac cells as well as animal models of cardiovascular diseases are used to identity changes in electrophysiological properties and the molecular mechanisms associated with the disease. Protein kinase C (PKC) and several other kinases play a pivotal role in cardiac electrophysiological remodeling. Therefore, identifying specific therapies that regulate these kinases is the main focus of current research. PKC, a family of serine/threonine kinases, has been implicated as potential signaling nodes associated with biochemical and biophysical stress in cardiovascular diseases. In this review, we describe the role of PKC isozymes that are involved in cardiac excitability and discuss both genetic and pharmacological tools that were used, their attributes and limitations. Selective and effective pharmacological interventions to normalize cardiac electrical activities and correct cardiac arrhythmias will be of great clinical benefit.

Regulation of cardiac excitability by protein kinase C isozymes

Cardiac excitability and electrical activity are determined by the sum of individual ion channels, gap junctions and exchanger activities. Electrophysiological remodeling during heart disease involves changes in membrane properties of cardiomyocytes and is related to higher prevalence of arrhythmia-associated morbidity and mortality. Pharmacological and genetic manipulation of cardiac cells as well as animal models of cardiovascular diseases are used to identity changes in electrophysiological properties and the molecular mechanisms associated with the disease. Protein kinase C (PKC) and several other kinases play a pivotal role in cardiac electrophysiological remodeling. Therefore, identifying specific therapies that regulate these kinases is the main focus of current research. PKC, a family of serine/threonine kinases, has been implicated as potential signaling nodes associated with biochemical and biophysical stress in cardiovascular diseases. In this review, we describe the role of PKC isozymes that are involved in cardiac excitability and discuss both genetic and pharmacological tools that were used, their attributes and limitations. Selective and effective pharmacological interventions to normalize cardiac electrical activities and correct cardiac arrhythmias will be of great clinical benefit.

Na(+)/K(+)-ATPase inhibition upregulates NMDA-evoked currents in rat hippocampal CA1 pyramidal neurons

Na(+)/K(+)-ATPase and N-methyl-D-aspartate (NMDA) receptor in hippocampus play very important roles in the regulation of learning and memory. Here, we showed that dihydroouabain (DHO, 10(-5)-10(-3) M), a Na(+)/K(+)-ATPase inhibitor, significantly potentiated NMDA current in rat hippocampal CA1 pyramidal neurons, which was blocked by PP2 (the selective Src tyrosine kinase inhibitor) and PD-98059 [the selective inhibitor of the mitogen-activated protein kinases (MAPK) cascade]. These findings reported here uncover that Src mediates the cross-talk between Na(+)/K(+)-ATPase and NMDA receptor to transduce the signals from Na(+)/K(+)-ATPase to the MAPK cascade and provide new insights into therapeutic target for deeper understanding of the nature of cognitive disorder.

Reduced respiratory neural activity elicits phrenic motor facilitation

We hypothesized that reduced respiratory neural activity elicits compensatory mechanisms of plasticity that enhance respiratory motor output. In urethane-anesthetized and ventilated rats, we reversibly reduced respiratory neural activity for 25-30 min using: hypocapnia (end tidal CO(2)=30 mmHg), isoflurane (~1%) or high frequency ventilation (HFV; ~100 breaths/min). In all cases, increased phrenic burst amplitude was observed following restoration of respiratory neural activity (hypocapnia: 92±22%; isoflurane: 65±22%; HFV: 54±13% baseline), which was significantly greater than time controls receiving the same surgery, but no interruptions in respiratory neural activity (3±5% baseline, p<0.05). Hypocapnia also elicited transient increases in respiratory burst frequency (9±2 versus 1±1bursts/min, p<0.05). Our results suggest that reduced respiratory neural activity elicits a unique form of plasticity in respiratory motor control which we refer to as inactivity-induced phrenic motor facilitation (iPMF). iPMF may prevent catastrophic decreases in respiratory motor output during ventilatory control disorders associated with abnormal respiratory activity.

Long-lasting adaptations of the NR2B-containing NMDA receptors in the dorsomedial striatum play a crucial role in alcohol consumption and relapse

A growing number of studies suggest that the development of compulsive drug seeking and taking depends on dorsostriatal mechanisms. We previously observed that ex vivo acute exposure of the dorsal striatum to, and withdrawal from, alcohol induces long-term facilitation (LTF) of the activity of NR2B-containing NMDA receptors (NR2B-NMDARs) in a mechanism that requires the Src family protein tyrosine kinase (PTK), Fyn (Wang et al., 2007). In the present study, we first compared alcohol's actions in rat dorsomedial (DMS) and the dorsolateral (DLS) subregions of the striatum, which differ in their anatomical connectivity and function. We found that alcohol-mediated induction of LTF of NR2B-NMDAR activity is centered in the DMS. Next, we tested whether in vivo exposure of rats to alcohol leads to long-term adaptations of the NMDAR system in the DMS. We observed that repeated daily administration of alcohol results in a long-lasting increase in the activity of the NR2B-NMDARs in the DMS. The same procedure leads to a prolonged activation of Fyn, increased NR2B phosphorylation, and membrane localization of the subunit. Importantly, similar electrophysiological and biochemical modifications were observed in the DMS of rats that consumed large quantities of alcohol. Finally, we show that inhibition of NR2B-NMDARs or Src family PTKs in the DMS, but not in the DLS, significantly decreases operant self-administration of alcohol and reduces alcohol-priming-induced reinstatement of alcohol seeking. Our results suggest that the upregulation of NR2B-NMDAR activity within the DMS by alcohol contributes to the maladaptive synaptic changes that lead to excessive alcohol intake and relapse.

Ethanol inhibition of recombinant NMDA receptors is not altered by coexpression of CaMKII-alpha or CaMKII-beta

Previous studies have shown that the N-methyl-d-aspartate (NMDA) receptor is an important target for the actions of ethanol in the brain. N-methyl-d-aspartate receptors are glutamate-activated ion channels that are highly expressed in neurons. They are activated during periods of significant glutamatergic synaptic activity and are an important source of the signaling molecule calcium in the postsynaptic spine. Alterations in the function of NMDA receptors by drugs or disease are associated with deficits in motor, sensory and cognitive processes of the brain. Acutely, ethanol inhibits ion flow through NMDA receptors whereas sustained exposure to ethanol can induce compensatory changes in the density and localization of the receptor. Defining factors that govern the acute ethanol sensitivity of NMDA receptors is an important step in understanding how an individual responds to ethanol. In the present study, we investigated the effect of calcium-calmodulin dependent protein kinase II (CaMKII) on the ethanol sensitivity of recombinant NMDA receptors. Calcium-calmodulin dependent protein kinase II is a major constituent of the postsynaptic density and is critically involved in various forms of learning and memory. NMDA receptor subunits were transiently expressed in human embryonic kidney 293 cells along with CaMKII-alpha or CaMKII-beta tagged with the green fluorescent protein. Whole cell currents were elicited by brief exposures to glutamate and were measured using patch-clamp electrophysiology. Neither CaMKII-alpha or CaMKII-beta had any significant effect on the ethanol inhibition of NR1/2A or NR1/2B receptors. Ethanol inhibition was also unaltered by deletion of CaMKII binding domains in NR1 or NR2 subunits or by phospho-site mutants that mimic or occlude CaMKII phosphorylation. Chronic treatment of cortical neurons with ethanol had no significant effect on the expression of CaMKII-alpha or CaMKII-beta. The results of this study suggest that CaMKII is not involved in regulating the acute ethanol sensitivity of NMDA receptors.

Alcohol related changes in regulation of NMDA receptor functions

Long-term alcohol exposure may lead to development of alcohol dependence in consequence of altered neurotransmitter functions. Accumulating evidence suggests that the N-methyl-D-aspartate (NMDA) type of glutamate receptors is a particularly important site of ethanol's action. Several studies showed that ethanol potently inhibits NMDA receptors (NMDARs) and prolonged ethanol exposition leads to a compensatory "up-regulation" of NMDAR mediated functions. Therefore, alterations in NMDAR function are supposed to contribute to the development of ethanol tolerance, dependence as well as to the acute and late signs of ethanol withdrawal.A number of publications report alterations in the expression and phosphorylation states of NMDAR subunits, in their interaction with scaffolding proteins or other receptors in consequence of chronic ethanol treatment. Our knowledge on the regulatory processes, which modulate NMDAR functions including factors altering transcription, protein expression and post-translational modifications of NMDAR subunits, as well as those influencing their interactions with different regulatory proteins or other downstream signaling elements are incessantly increasing. The aim of this review is to summarize the complex chain of events supposedly playing a role in the up-regulation of NMDAR functions in consequence of chronic ethanol exposure.

Glycine inhibitory dysfunction turns touch into pain through PKCgamma interneurons

Dynamic mechanical allodynia is a widespread and intractable symptom of neuropathic pain for which there is a lack of effective therapy. During tactile allodynia, activation of the sensory fibers which normally detect touch elicits pain. Here we provide a new behavioral investigation into the dynamic component of tactile allodynia that developed in rats after segmental removal of glycine inhibition. Using in vivo electrophysiological recordings, we show that in this condition innocuous mechanical stimuli could activate superficial dorsal horn nociceptive specific neurons. These neurons do not normally respond to touch. We anatomically show that the activation was mediated through a local circuit involving neurons expressing the gamma isoform of protein kinase C (PKCγ). Selective inhibition of PKCγ as well as selective blockade of glutamate NMDA receptors in the superficial dorsal horn prevented both activation of the circuit and allodynia. Thus, our data demonstrates that a normally inactive circuit in the dorsal horn can be recruited to convert touch into pain. It also provides evidence that glycine inhibitory dysfunction gates tactile input to nociceptive specific neurons through PKCγ-dependent activation of a local, excitatory, NMDA receptor-dependent, circuit. As a consequence of these findings, we suggest that pharmacological inhibition of PKCγ might provide a new tool for alleviating allodynia in the clinical setting.

The role of protein kinase A in acute ethanol-induced neurobehavioral actions in rats

BACKGROUND

cAMP-dependent protein kinase (PKA) signaling pathways are involved in the regulation of ethanol-induced sedative effects in knockout mouse models. In the present study, we examined the role of PKA on the behavioral action caused by ethanol in Sprague Dawley rats.

METHODS

A loss of righting reflex (LORR) test was used to study the acute sedative effects of intraperitoneally injected ethanol. Rotarod performance was used to study the motor impairment caused by ethanol. Convulsions induced by intracerebroventricular (ICV) N-methyl-d-aspartate (NMDA) were used to evaluate ethanol's effect on NMDA receptors. Western blot analysis was used to assay protein levels for NR1 and phosphoserine 897 on NR1 subnuits.

RESULTS

ICV pretreatment with H-9 (a nonspecific PK inhibitor) or KT 5720 (a specific PKA inhibitor) dose-dependently attenuated ethanol-induced sleeping time as assessed by LORR. ICV KT 5720 did not reduce ketamine or pentobarbital-induced sleeping time. Pretreatment with forskolin (an activator of adenylyl cyclase) or chelerythrine (a selective PKC inhibitor) had no effect on ethanol-induced LORR. Ethanol-induced motor impairment was also attenuated after pretreatment with KT 5720. Ethanol significantly inhibited NMDA-induced convulsions; the inhibitory effects of ethanol were reduced by prior ICV KT 5720, which had no significant effects on the levels of phosphoserine 897 on NMDA NR1 subunits in the several brain areas we examined.

CONCLUSIONS

Our results suggest that the PKA pathway may participate in ethanol-induced neurobehavioral changes and that NMDA receptors may be involved in the PKA regulation of ethanol's actions.

Protein kinase C as a stress sensor

While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information.

Acute ethanol administration rapidly increases phosphorylation of conventional protein kinase C in specific mammalian brain regions in vivo

BACKGROUND

Protein kinase C (PKC) is a family of isoenzymes that regulate a variety of functions in the central nervous system including neurotransmitter release, ion channel activity, and cell differentiation. Growing evidence suggests that specific isoforms of PKC influence a variety of behavioral, biochemical, and physiological effects of ethanol in mammals. The purpose of this study was to determine whether acute ethanol exposure alters phosphorylation of conventional PKC isoforms at a threonine 674 (p-cPKC) site in the hydrophobic domain of the kinase, which is required for its catalytic activity.

METHODS

Male rats were administered a dose range of ethanol (0, 0.5, 1, or 2 g/kg, intragastric) and brain tissue was removed 10 minutes later for evaluation of changes in p-cPKC expression using immunohistochemistry and Western blot methods.

RESULTS

Immunohistochemical data show that the highest dose of ethanol (2 g/kg) rapidly increases p-cPKC immunoreactivity specifically in the nucleus accumbens (core and shell), lateral septum, and hippocampus (CA3 and dentate gyrus). Western blot analysis further showed that ethanol (2 g/kg) increased p-cPKC expression in the P2 membrane fraction of tissue from the nucleus accumbens and hippocampus. Although p-cPKC was expressed in numerous other brain regions, including the caudate nucleus, amygdala, and cortex, no changes were observed in response to acute ethanol. Total PKCgamma immunoreactivity was surveyed throughout the brain and showed no change following acute ethanol injection.

CONCLUSIONS

These results suggest that ethanol rapidly promotes phosphorylation of cPKC in limbic brain regions, which may underlie effects of acute ethanol on the nervous system and behavior.

Ethanol induces long-term facilitation of NR2B-NMDA receptor activity in the dorsal striatum: implications for alcohol drinking behavior

Addiction is characterized by compulsive alcohol or drug taking and seeking, and the dorsal striatum has been implicated in such maladaptive persistent habits. The NMDA receptor (NMDAR), which is a major target of alcohol, is implicated in striatal-based habit learning. We found that, in the dorsal striatum, alcohol (ethanol) exposure produced an increase in the phosphorylation of the NR2B subunit of the NMDAR, and a corresponding increase in the activity of Fyn kinase, which phosphorylates NR2B. We further observed an ethanol-mediated long-term facilitation (LTF) of the activity of NR2B-containing NMDARs (NR2B-NMDARs) in the dorsal striatum. This LTF is Fyn kinase dependent, because it was observed in Fyn wild-type but not in Fyn knock-out mice. Importantly, none of these biochemical and physiological changes was observed in the ventral striatum. Finally, dorsal but not ventral striatum infusion of a Fyn or NR2B-NMDAR inhibitor reduced rat operant self-administration of ethanol. Our results suggest that the Fyn-mediated phosphorylation and LTF of NR2B-NMDAR activity in the dorsal striatum after exposure to ethanol may underlie aberrant plasticity that contributes to mechanisms underlying alcohol drinking behavior.

Peptides Derived from the C2 Domain of Protein Kinase Cϵ (ϵPKC) Modulate ϵPKC Activity and Identify Potential Protein-Protein Interaction Surfaces

Peptides derived from protein kinase C (PKC) modulate its activity by interfering with critical protein-protein interactions within PKC and between PKC and PKC-binding proteins (Souroujon, M. C., and Mochly-Rosen, D. (1998) Nat. Biotechnol. 16, 919-924). We previously demonstrated that the C2 domain of PKC plays a critical role in these interactions. By focusing on epsilonPKC and using a rational approach, we then identified one C2-derived peptide that acts as an isozyme-selective activator and another that acts as a selective inhibitor of epsilonPKC. These peptides were used to identify the role of epsilonPKC in protection from cardiac and brain ischemic damage, in prevention of complications from diabetes, in reducing pain, and in protecting transplanted hearts. The efficacy of these two peptides led us to search for additional C2-derived peptides with PKC-modulating activities. Here we report on the activity of a series of 5-9-residue peptides that are derived from regions that span the length of the C2 domain of epsilonPKC. These peptides were tested for their effect on PKC activity in cells in vivo and in an ex vivo model of acute ischemic heart disease. Most of the peptides acted as activators of PKC, and a few peptides acted as inhibitors. PKC-dependent myristoylated alanine-rich C kinase substrate phosphorylation in epsilonPKC knock-out cells revealed that only a subset of the peptides were selective for epsilonPKC over other PKC isozymes. These epsilonPKC-selective peptides were also protective of the myocardium from ischemic injury, an epsilonPKC-dependent function (Liu, G. S., Cohen, M. V., Mochly-Rosen, D., and Downey, J. M. (1999) J. Mol. Cell. Cardiol. 31, 1937-1948), and caused selective translocation of epsilonPKC over other isozymes when injected systemically into mice. Examination of the structure of the C2 domain from epsilonPKC revealed that peptides with similar activities clustered into discrete regions within the domain. We propose that these regions represent surfaces of protein-protein interactions within epsilonPKC and/or between epsilonPKC and other partner proteins; some of these interactions are unique to epsilonPKC, and others are common to other PKC isozymes.

Differential effects of systemic ethanol administration on protein kinase cepsilon, gamma, and beta isoform expression, membrane translocation, and target phosphorylation: reversal by chronic ethanol exposure

Systemic ethanol administration alters protein kinase C (PKC) activity in brain, but the effects of ethanol on the expression and translocation of specific isoforms are unknown. Rats were administered ethanol (2 g/kg i.p.) or saline and PKC levels were measured in the cytosolic and membrane fractions by Western blot analysis. PKCepsilon expression was increased in the cytosol and decreased in the membrane (P2) fraction of cerebral cortex at 10 min. At 60 min, expression of PKCepsilon in the P2 fraction was increased by 42.2 +/- 12%, but cytosolic levels were unchanged. In contrast, PKCgamma in the P2 fraction was decreased 32.7 +/- 7% at 60 min but not at 10 min post-ethanol administration. PKCgamma levels in the cytosol were reduced at 10 min post-ethanol administration and unchanged at 60 min. PKCbeta expression was increased 36 +/- 10 and 144 +/- 52% in the P2 fraction both at 10 and 60 min post-ethanol administration, whereas cytosolic levels were unchanged. Serine phosphorylation of GABA(A) receptor beta-chain was reduced, and phosphorylation of N-methyl-d-aspartate receptor NR1 subunit was increased 60 min following ethanol administration. There was no effect of acute ethanol administration on PKC isoform levels in the hippocampus. Ethanol challenge did not alter PKC isoform expression in the P2 fraction of cerebral cortex following chronic ethanol administration. These findings suggest that acute ethanol administration alters PKC synthesis and translocation in an isoform and brain region specific manner that leads to alterations in serine phosphorylation of receptors. Furthermore, chronic ethanol administration prevents ethanol-induced alterations in PKC expression in the P2 fraction, where PKC interacts with ethanol-responsive ion channels.

Ketamine attenuates sympathetic activity through mechanisms not mediated by N-methyl-D-aspartate receptors in the isolated spinal cord of neonatal rats

Ketamine is believed to have sympathomimetic effects, although the central mechanism remains unclear. Using an in vitro splanchnic nerve-spinal cord preparation from neonatal rats, our previous investigations have demonstrated that tonic sympathetic activity is spontaneously generated from the thoracic spinal cord. We designed this study to investigate whether applications of ketamine to the cord would augment sympathetic activity and whether this action was dependent on N-methyl-d-aspartate receptors. Bath application of ketamine significantly reduced sympathetic activity in a concentration-dependent manner. Ketamine in 10, 20, 40, 80, and 120 microM reduced the sympathetic activity to 82.6% +/- 4.4% (P < 0.05), 61.7% +/- 5.1%, 42.8% +/- 4.2%, 24.9% +/- 4.4%, and 9.2% +/- 2.7% of the control value, respectively (P < 0.01, n = 8 for each test). The 50% inhibitory concentration of ketamine on sympathetic activity was 32 muM. Pretreatment with DL-2-amino-5-phosphonovaleric acid, a selective competitive N-methyl-d-aspartate receptor antagonist, did not alter ketamine-induced depression of sympathetic activity. These results suggest that ketamine reduces sympathetic activity by mechanisms that are independent of N-methyl-d-aspartate receptor activity.