Protein phosphorylation in neuronal plasticity and gene expression

Short-Term Extremely Low-Frequency Electromagnetic Field Inhibits Synaptic Plasticity of Schaffer Collateral-CA1 Synapses in Rat Hippocampus via the Ca2+/Calcineurin Pathway

In this study, we investigate the intrinsic mechanism by which an extremely low-frequency electromagnetic field (ELF-EMF) influences neurons in the Schaffer collateral-CA1 (SC-CA1) region of rat hippocampus using electrophysiological techniques. ELF-EMF has an interesting effect on synaptic plasticity: it weakens long-term potentiation and enhances long-term depression. Here, the magnetic field effect disappeared after a blockade of voltage-gated calcium channels and calcineurin, which are key components in the Ca²⁺/calcineurin pathway, with two blockers, cadmium chloride and cyclosporin A. This fully establishes that the effect of ELF-EMF on synaptic plasticity is mediated by the Ca²⁺/calcineurin pathway and represents a novel technique for studying the specific mechanisms of action of ELF-EMF on learning and memory.

Oral quetiapine treatment results in time-dependent alterations of recognition memory and brain-derived neurotrophic factor-related signaling molecules in the hippocampus of rats

Antipsychotic drugs (APDs) have a variety of important therapeutic applications for neuropsychiatric disorders. However, they are routinely prescribed off-label across all age categories, a controversial practice given their potential for producing metabolic and extrapyramidal side effects. Evidence also suggests that chronic treatment with some APDs may lead to impairments in cognition and decreases in brain volume, although these findings are controversial. The purpose of the studies described here was to evaluate one of the most commonly prescribed APDs, quetiapine, for chronic effects on recognition memory, brain-derived neurotrophic factor (BDNF), its precursor proBDNF, as well as relevant downstream signaling molecules that are known to influence neuronal plasticity and cognition. Multiple cohorts of adult rats were treated with quetiapine (25.0 mg/kg/day) for 30 or 90 days in their drinking water then evaluated for drug effects on motor function in a catalepsy assessment, recognition memory in a spontaneous novel object recognition (NOR) task, and BDNF-related signaling molecules in the post mortem hippocampus via Western Blot. The results indicated that oral quetiapine at a dose that did not induce catalepsy, led to time-dependent impairments in NOR performance, increases in the proBDNF/BDNF ratio, and decreases in Akt and CREB phosphorylation in the hippocampus. These results indicate that chronic treatment with quetiapine has the potential to adversely affect recognition memory and neurotrophin-related signaling molecules that support synaptic plasticity and cognitive function. Given the widespread use this APD across multiple conditions and patient populations, such long-term effects observed in animals should be considered.

Chronic oral treatment with risperidone impairs recognition memory and alters brain-derived neurotrophic factor and related signaling molecules in rats

Antipsychotic drugs (APDs) are essential for the treatment of schizophrenia and other neuropsychiatric illnesses such as bipolar disease. However, they are also extensively prescribed off-label for many other conditions, a practice that is controversial given their potential for long-term side effects. There is clinical and preclinical evidence that chronic treatment with some APDs may lead to impairments in cognition and decreases in brain volume, although the molecular mechanisms of these effects are unknown. The purpose of the rodent studies described here was to evaluate a commonly prescribed APD, risperidone, for chronic effects on recognition memory, brain-derived neurotrophic factor (BDNF), its precursor proBDNF, as well as relevant downstream signaling molecules that are known to influence neuronal plasticity and cognition. Multiple cohorts of adult rats were treated with risperidone (2.5 mg/kg/day) or vehicle (dilute acetic acid solution) in their drinking water for 30 or 90 days. Subjects were then evaluated for drug effects on recognition memory in a spontaneous novel object recognition task and protein levels of BDNF-related signaling molecules in the hippocampus and prefrontal cortex. The results indicated that depending on the treatment period, a therapeutically relevant daily dose of risperidone impaired recognition memory and increased the proBDNF/BDNF ratio in the hippocampus and prefrontal cortex. Risperidone treatment also led to a decrease in Akt and CREB phosphorylation in the prefrontal cortex. These results indicate that chronic treatment with a commonly prescribed APD, risperidone, has the potential to adversely affect recognition memory and neurotrophin-related signaling molecules that support synaptic plasticity and cognitive function.

Therapeutic efficacy of environmental enrichment for substance use disorders

Addiction to drug and alcohol is regarded as a major health problem worldwide for which available treatments show limited effectiveness. The biggest challenge remains to enhance the capacities of interventions to reduce craving, prevent relapse and promote long-term recovery. New strategies to meet these challenges are being explored. Findings from preclinical work suggest that environmental enrichment (EE) holds therapeutic potential for the treatment of substance use disorders, as demonstrated in a number of animal models of drug abuse. The EE intervention introduced after drug exposure leads to attenuation of compulsive drug taking, attenuation of the rewarding (and reinforcing) effects of drugs, reductions in control of behavior by drug cues, and, very importantly, relapse prevention. Clinical work also suggests that multidimensional EE interventions (involving physical activity, social interaction, vocational training, recreational and community involvement) might produce similar therapeutic effects, if implemented continuously and rigorously. In this review we survey preclinical and clinical studies assessing the efficacy of EE as a behavioral intervention for substance use disorders and address related challenges. We also review work providing empirical evidence for EE-induced neuroplasticity within the mesocorticolimbic system that is believed to contribute to the seemingly therapeutic effects of EE on drug and alcohol-related behaviors.

Effects of exposure to extremely low frequency electromagnetic fields on hippocampal long-term potentiation in hippocampal CA1 region

Exposure to environmental electromagnetic fields, especially to the extremely low-frequency (ELF < 300 Hz) electromagnetic fields (EMFs) might produce modulation effects on neuronal activity. Long-term changes in synaptic plasticity such as long-term potentiation (LTP) involved in learning and memory may have contributions to a number of neurological diseases. However, the modulation effects of ELF-EMFs on LTP are not yet fully understood. In our present study, we aimed to evaluate the effects of exposure to ELF-EMFs on LTP in hippocampal CA1 region in rats. Hippocampal slices were exposed to magnetic fields generated by sXcELF system with different frequencies (15, 50, and 100 Hz [Hz]), intensities (0.5, 1, and 2 mT [mT]), and duration (10 s [s], 20 s, 40 s, 60 s, and 5 min), then the baseline signal recordings for 20 min and the evoked field excitatory postsynaptic potentials (fEPSPs) were recorded. We found that the LTP amplitudes decreased after magnetic field exposure, and the LTP amplitudes decreased in proportion to exposure doses and durations, suggesting ELF-EMFs may have dose and duration-dependent inhibition effects. Among multiple exposure duration and doses combinations, upon 5 min magnetic field exposure, 15 Hz/2 mT maximally inhibited LTP. Under 15 Hz/2 mT ELF-EMFs, LTP amplitude decreases in proportion to the length of exposure durations within 5 min time frame. Our findings illustrated the potential effects of ELF-EMFs on synaptic plasticity and will lead to better understanding of the influence on learning and memory.

PKC and CaMK-II inhibitions coordinately rescue ischemia-induced GABAergic neuron dysfunction

Cerebral ischemia leads to neuronal death for stroke, in which the imbalance between glutamatergic neurons and GABAergic neurons toward neural excitotoxicity is presumably involved. GABAergic neurons are vulnerable to pathological factors and impaired in an early stage of ischemia. The rescue of GABAergic neurons is expected to be the strategy to reserve ischemic neuronal impairment. As protein kinase C (PKC) and calmodulin-dependent protein kinase II (CaMK-II) are activated during ischemia, we have investigated whether the inhibitions of these kinases rescue the ischemic impairment of cortical GABAergic neurons. The functions of GABAergic neurons were analyzed by whole-cell recording in the cortical slices during ischemia and in presence of 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (CaMK-II inhibitor) and chelerythrine chloride (PKC inhibitor). Our results indicate that PKC inhibitor or CaMK-II inhibitor partially prevents ischemia-induced functional deficits of cortical GABAergic neurons. Moreover, the combination of PKC and CaMK-II inhibitors synergistically reverses this ischemia-induced deficit of GABAergic neurons. One of potential therapeutic strategies for ischemic stroke may be to rescue the ischemia-induced deficit of cortical GABAergic neurons by inhibiting PKC and CaMK-II.

The Antidepressant Agomelatine Improves Memory Deterioration and Upregulates CREB and BDNF Gene Expression Levels in Unpredictable Chronic Mild Stress (UCMS)-Exposed Mice

Agomelatine, a novel antidepressant with established clinical efficacy, acts as an agonist of melatonergic MT1 and MT2 receptors and as an antagonist of 5-HT2C receptors. The present study was undertaken to investigate whether chronic treatment with agomelatine would block unpredictable chronic mild stress (UCMS)-induced cognitive deterioration in mice in passive avoidance (PA), modified elevated plus maze (mEPM), novel object recognition (NOR), and Morris water maze (MWM) tests. Moreover, the effects of stress and agomelatine on brain-derived neurotrophic factor (BDNF) and cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) messenger ribonucleic acid (mRNA) levels in the hippocampus was also determined using quantitative real-time polymerase chain reaction (RT-PCR). Male inbred BALB/c mice were treated with agomelatine (10 mg/kg, i.p.), melatonin (10 mg/kg), or vehicle daily for five weeks. The results of this study revealed that UCMS-exposed animals exhibited memory deterioration in the PA, mEPM, NOR, and MWM tests. The chronic administration of melatonin had a positive effect in the PA and +mEPM tests, whereas agomelatine had a partial effect. Both agomelatine and melatonin blocked stress-induced impairment in visual memory in the NOR test and reversed spatial learning and memory impairment in the stressed group in the MWM test. Quantitative RT-PCR revealed that CREB and BDNF gene expression levels were downregulated in UCMS-exposed mice, and these alterations were reversed by chronic agomelatine or melatonin treatment. Thus, agomelatine plays an important role in blocking stress-induced hippocampal memory deterioration and activates molecular mechanisms of memory storage in response to a learning experience.

The effect of PN-1, a Traditional Chinese Prescription, on the Learning and Memory in a Transgenic Mouse Model of Alzheimer's Disease

Traditional Chinese Medicine (TCM) is a complete medical system that has been practiced for more than 3000 years. Prescription number 1 (PN-1) consists of several Chinese medicines and is designed according to TCM theories to treat patients with neuropsychiatric disorders. The evidence of clinical practice suggests the benefit effects of PN-1 on cognitive deficits of dementia patients. We try to prove and explain this by using contemporary methodology and transgenic animal models of Alzheimer's disease (AD). The behavioral studies were developed to evaluate the memory of transgenic animals after intragastric administration of PN-1 for 3 months. Amyloid beta-protein (A β ) neuropathology was quantified using immunohistochemistry and ELISA. The western blotting was used to detect the levels of plasticity associated proteins. The safety of PN-1 on mice was also assessed through multiple parameters. Results showed that PN-1 could effectively relieve learning and memory impairment of transgenic animals. Possible mechanisms showed that PN-1 could significantly reduce plaque burden and A β levels and boost synaptic plasticity. Our observations showed that PN-1 could improve learning and memory ability through multiple mechanisms without detectable side effects on mice. We propose that PN-1 is a promising alternative treatment for AD in the future.

Chronic psychosocial stress accelerates impairment of long-term memory and late-phase long-term potentiation in an at-risk model of Alzheimer's disease

Although it is generally agreed that Aβ contributes to the pathogenesis of AD, its precise role in AD and the reason for the varying intensity and time of onset of the disease have not been elucidated. In addition to genetic factors, environmental issues such as stress may also play a critical role in the etiology of AD. This study examined the effect of chronic psychosocial stress in an at-risk (treatment with a subpathogenic dose of Aβ; "subAβ") rat model of AD on long-term memory by three techniques: memory tests in the radial arm water maze, electrophysiological recordings of synaptic plasticity in anesthetized rats, and immunoblot analysis of learning- and long-term memory-related signaling molecules. Chronic psychosocial stress was induced using a rat intruder model. The subAβ rat model of AD was induced by continuous infusion of 160 pmol/day Aβ(1-42) via a 14-day i.c.v. osmotic pump. All tests showed that subAβ rats were not different from control rats. Result from behavioral tests and electrophysiological recordings showed that infusion of subAβ in chronically stressed rats (stress/subAβ group) caused significant impairment of cognitive functions and late-phase long-term potentiation (L-LTP). Molecular analysis of various signaling molecules after expression of L-LTP, revealed an increase in the levels of p-CREB in control, stress, and subAβ rats, but not in the stress/subAβ rats. These findings suggest that the chronic stress-induced molecular alteration may accelerate the impairment of cognition and synaptic plasticity in individuals "at-risk" for AD.

Maladaptive striatal plasticity in L-DOPA-induced dyskinesia

Dopamine (DA) replacement therapy with l-DOPA remains the most effective treatment for Parkinson's disease, but causes dyskinesia (abnormal involuntary movements) in the vast majority of the patients. The basic mechanisms of l-DOPA-induced dyskinesia (LID) have become the object of intense research focusing on neurochemical and molecular adaptations in the striatum. Here we review this vast literature and highlight trends that converge into a unifying pathophysiological interpretation. We propose that the core molecular alteration of striatal neurons in LID consists in an inability to turn down supersensitive signaling responses downstream of DA D1 receptors (where supersensitivity is primarily caused by DA denervation). The sustained activation of intracellular signaling pathways induced by each dose of l-DOPA leads to abnormal cellular plasticity and high bioenergetic expenditure. The over-exploitation of signaling pathways and energy reserves during treatment impairs the ability of striatal neurons to dynamically gate cortically driven motor commands. LID thus exemplifies a disorder where 'too much' molecular plasticity leads to plasticity failure in the striatum.

Changes in the proteome after neuronal zif268 overexpression

Long-lasting forms of brain plasticity are a cellular basis for long-term memory, and their disturbance underlies pathological conditions such as dementia and cognitive impairment. Neuronal plasticity is a complex process that utilizes molecular cascades in the cytoplasm and the nucleus and involves numerous transcription factors, in particular, immediate early genes (IEGs). The signaling cascades that control IEGs are fairly well described, but the downstream transcriptional response is poorly understood, especially its late components. Here, we investigated the response induced by the IEG Zif268 in the adult brain in relation to long-term memory. Using a mouse model with increased neuronal expression of Zif268 that leads to improved memory, we identified an ensemble of proteins regulated by Zif268 expression and differentiated between direct and indirect targets based on the presence of a consensus binding motif in their promoter. We show that Zif268 regulates numerous substrates with diverse biological functions including protein modification and degradation (proteasome-core complex), phosphorylation, cell division, sensory perception, metabolism, and metal ion transport. The results provide a comprehensive and quantitative data set characterizing the Zif268-dependent proteome in the adult mouse brain and offers biologically important new insight into activity-dependent pathways downstream of IEGs.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Repeated amphetamine treatment increases phosphorylation of extracellular signal-regulated kinase, protein kinase B, and cyclase response element-binding protein in the rat striatum

Extracellular signal-regulated kinases, protein kinase B/Akt and cyclase response element-binding protein play important roles in drug-induced neuroadaptations. Acute psychostimulant exposure rapidly alters the phosphorylation of these proteins in the striatum but less is known about their responses to repeated stimulant administration. In this study the phosphorylated state of these proteins in rat striatum was analyzed by immunoblotting 15 min and 2 h after amphetamine (AMPH)-induced behavioral sensitization. Two weeks after the last dose of 5 mg/kg, i.p. AMPH once daily for 5 days, rats were challenged with 1 mg/kg, i.p. AMPH or saline and sacrificed 15 min or 2 h later. Sensitization to AMPH-induced behavioral activity was observed in AMPH pre-treated rats after AMPH on the challenge day. Phosphorylation of all three proteins was significantly greater 15 min after AMPH in AMPH-pre-treated than in saline-pre-treated rats. Two hours after AMPH challenge in AMPH-pre-treated rats, phospho-extracellular signal-regulated kinase and phospho-cAMP response element-binding protein immunoreactivity was still significantly elevated but not after AMPH injection in saline-pre-treated rats. In contrast, phospho-Akt was down-regulated to the same extent 2 h after acute AMPH or repeated AMPH with an AMPH challenge. These data implicate differential regulation of phospho-extracellular signal-regulated kinase, phospho-cAMP response element-binding protein versus phospho-Akt in sensitized responses to AMPH.

Post-training intrahippocampal infusion of nicotine-bucladesine combination causes a synergistic enhancement effect on spatial memory retention in rats

We previously had shown that bilateral intrahippocampal infusion of 1 microg nicotine (but not 0.5 microg dose) led to an improvement in spatial memory retention in the Morris water maze task in male rats. We also reported that a similar type of bilateral infusion of H89, a protein kinase AII (PKA II) inhibitor, caused a deficit in spatial memory retention. In the present study, we wished to test the hypothesis that intrahippocampal infusion of dibutyryl cyclic AMP (DB-cAMP also called bucladesine), a membrane permeable selective activator of PKA, into the CA1 region can cause an improvement in spatial memory in this maze task. Indeed, bilateral infusion of 10 and 100 microM bucladesine (but not 1 and 5 microM doses) led to a significant reduction in escape latency and travel distance (showing an improvement in spatial memory) compared to the control. Also, bilateral infusion of 0.5 microg nicotine or 1 microM bucladesine alone did not lead to an improvement in spatial memory. However, such bilateral infusion of bucladesine at 1 and 5 microM concentrations infused within minutes after 0.5 microg nicotine infusion improved spatial memory retention. Taken together, our data suggest that intrahippocampal bucladesine infusions improve spatial memory retention in male rats and that bucladesine can interact synergistically with nicotine to improve spatial memory.

Bidirectional regulation of cytoplasmic polyadenylation element-binding protein phosphorylation by Ca2+/calmodulin-dependent protein kinase II and protein phosphatase 1 during hippocampal long-term potentiation

Induction of hippocampal long-term potentiation (LTP) requires activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), whereas maintenance of LTP additionally requires protein synthesis. We recently reported that CaMKII stimulates protein synthesis in depolarized hippocampal neurons through phosphorylation of the mRNA translation factor cytoplasmic polyadenylation element-binding protein (CPEB), and this phosphorylation is rapidly reversed by protein phosphatase 1 (PP1). Protein synthesis-dependent late-phase LTP (L-LTP) in the hippocampus requires calcium influx through the NMDA-type glutamate receptor (NMDA-R) to activate CaMKII as well as concomitant inhibition of PP1 mediated by protein kinase A. Therefore, we investigated the regulation of CPEB phosphorylation during L-LTP. Pharmacological stimulation of the NMDA-R in hippocampal slices to produce chemical long-term depression induced a brief dephosphorylation of CPEB. Modest LTP induction (once at 100 Hz), which induces a protein synthesis-independent early-phase LTP (E-LTP), resulted in a transient phosphorylation of CPEB. However, stronger stimulation (four times at 100 Hz), known to induce protein synthesis-dependent L-LTP, elicited a prolonged phosphorylation of CPEB. Furthermore, CPEB phosphorylation correlated with phosphorylation of PP1 inhibitor dopamine- and cAMP-regulated phosphoprotein, a known substrate for protein kinase A. These results evoke the hypothesis that bidirectional regulation of CPEB phosphorylation by CaMKII and protein phosphatases may serve as a mechanism to convert E-LTP into protein synthesis-dependent L-LTP by stimulating protein synthesis and thereby stabilizing synaptic enhancement.

Regulation of hippocampal gene expression is conserved in two species subjected to different stressors and antidepressant treatments

BACKGROUND

Chronic stress has significant effects on hippocampal structure and function. We have previously identified nerve growth factor (NGF), membrane glycoprotein 6a (M6a), the guanine nucleotide binding protein (G protein) alpha q polypeptide (GNAQ), and CDC-like kinase 1 (CLK-1) as genes regulated by psychosocial stress and clomipramine treatment in the hippocampus of tree shrews. These genes encode proteins involved in neurite outgrowth.

METHODS

To analyze whether regulation of the above-mentioned genes is conserved between different species, stressors, and antidepressant drugs, we subjected mice to repeated restraint stress and tianeptine treatment and measured hippocampal messenger RNA (mRNA) levels by real time reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Chronically stressed mice displayed a reduction in transcript levels for NGF, M6a, GNAQ, and CLK-1. In addition, other genes implicated in neuronal plasticity, such as brain-derived neurotrophic factor (BDNF), cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), protein kinase C (PKC), neural cell adhesion molecule (NCAM), and synapsin I were downregulated in stressed mice. Tianeptine treatment reversed the stress effects for the genes analyzed. Alterations in gene expression were dependent on the duration of the stress treatment and, in some cases, were only observed in male mice.

CONCLUSIONS

These results suggest that genes involved in neurite remodeling are one of the main targets for regulation by chronic stress. The finding that this regulation is conserved in different stress models and antidepressant treatments highlights the biological relevance of the genes analyzed and suggests that they might be involved in stress-related disorders.

Targeting prefrontal cortical dopamine D1 and N-methyl-D-aspartate receptor interactions in schizophrenia treatment

The prefrontal cortex plays a principal role in higher cognition and particularly in the fast online manipulation of appropriate information to guide forthcoming behavior. Dysfunction of this process represents a main feature in the pathophysiology of schizophrenia. Both dopamine D1 and N-methyl-D-aspartate (NMDA) receptors in the prefrontal cortex play a critical role in synaptic plasticity, memory mechanisms, and cognition. Recent data have shown that D1 and NMDA receptors interact bidirectionally and may greatly influence the output of the prefrontal cortex. Hypofunction of these receptor systems in the prefrontal cortex is found in schizophrenia. This review attempts to summarize some of the latest findings on the cellular mechanisms that underlie D1-NMDA receptor interactions. These findings have provided potential therapeutic strategies that aim to functionally up-regulate D1 and/or NMDA receptor safely via selective activation of D1 receptors or coagonist activation of NMDA receptors through blockade of the glycine transporter-1.

Alzheimer's disease as a disorder of dynamic brain self-organization

Mental function is based on the dynamic organization of neuronal networks. In particular, phylogenetically young brain areas (e.g., cortical associative circuits), involved in the realization of "higher brain functions" such as learning, memory, perception, self-awareness, and consciousness, are continuously re-adjusted even after development is completed. By this life-long self-optimization process, epigenetic information remodels the cognitive, behavioral and emotional reactivity of an individual to meet the environmental demands. To organize brain structures of increasing complexity during evolution, the process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. The mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodeling according to experience, are accompanied, however, by an increasing inherent potential of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time may provide the basis for selective neuronal vulnerability. The mechanisms of synaptic plasticity, i.e., of modifiable interneuronal connectivity, are largely based on external morphoregulatory cues and internal signaling pathways that nonneuronal cells have phylogenetically acquired to sense their relationship to the local neighborhood and to control proliferation and differentiation in the process of tissue repair and regeneration after development is completed. Differentiated neurons that have withdrawn from the cell cycle use these molecular machinery alternatively to control synaptic plasticity. The existence of these alternative effector pathways within a neuron puts it on the risk to erroneously convert signals derived from plastic synaptic changes into positional cues that will activate the cell cycle. This cell cycle activation potentially links synaptic plasticity to cell death. Preventing cell cycle activation by locking neurons in a differentiated but still highly plastic phenotype will, thus, be crucial to prevent neurodegeneration.

Open Tubular Immobilized Metal Ion Affinity Chromatography Combined with MALDI MS and MS/MS for Identification of Protein Phosphorylation Sites

Protein phosphorylation is one of the most important known posttranslational modifications. Tandem mass spectrometry has become an important tool for mapping out the phosphorylation sites. However, when a peptide generated from the enzymatic or chemical digestion of a phosphoprotein is highly phosphorylated or contains many potential phosphorylation residues, phosphorylation site assignment becomes difficult. Separation and enrichment of phosphopeptides from a digest mixture is desirable and often a critical step for MS/MS-based site determination. In this work, we present a novel open tubular immobilized metal ion affinity chromatography (OT-IMAC) method, which is found to be more effective and reproducible for phosphopeptide enrichment, compared to a commonly used commercial product, Ziptip from Millipore. A strategy based on a combination of OT-IMAC, sequential dual-enzyme digestion, and matrix-assisted laser desorption/ionization (MALDI) quadrupole time-of-flight tandem mass spectrometry for phosphoprotein characterization is presented. It is shown that MALDI MS/MS with collision-induced dissociation can be very effective in generating fragment ion spectra containing rich structural information, which enables the identification of phosphorylation sites even from highly phosphorylated peptides. The applicability of this method for real world applications is demonstrated in the characterization and identification of phosphorylation sites of a Na(+)/H(+) exchanger fusion protein, His182, which was phosphorylated in vitro using the kinase Erk2.

From monoamines to genomic targets: a paradigm shift for drug discovery in depression

Depression, a complex psychiatric disorder that affects approximately 15% of the population, has an enormous social cost. Although the disorder is thought to be the outcome of gene-environmental interactions, the causative genes and environmental factors underlying depression remain to be identified. All the antidepressant drugs now in use--the forerunner of which was discovered serendipitously 50 years ago--modulate monoamine neurotransmission, and take six to eight weeks to exert their effects, but each drug is efficacious in only 60-70% of patients. A conceptually novel antidepressant that acted rapidly and safely in a high proportion of patients would almost certainly become the world's bestselling drug. Yet such a drug is not on the horizon. Here, we cover the different phases of antidepressant drug discovery in the past, present and future, and comment on the challenges and opportunities for antidepressant research.

Regulation of hippocampal synaptic plasticity by cyclic AMP-dependent protein kinases

Protein kinases critically regulate synaptic plasticity in the mammalian hippocampus. Cyclic-AMP dependent protein kinase (PKA) is a serine-threonine kinase that has been strongly implicated in the expression of specific forms of long-term potentiation (LTP), long-term depression (LTD), and hippocampal long-term memory. We review the roles of PKA in activity-dependent forms of hippocampal synaptic plasticity by highlighting particular themes that have emerged in ongoing research. These include the participation of distinct isoforms of PKA in specific types of synaptic plasticity, modification of the PKA-dependence of LTP by multiple factors such as distinct patterns of imposed activity, environmental enrichment, and genetic manipulation of signalling molecules, and presynaptic versus postsynaptic mechanisms for PKA-dependent LTP. We also discuss many of the substrates that have been implicated as targets for PKA's actions in hippocampal synaptic plasticity, including CREB, protein phosphatases, and glutamatergic receptors. Future prospects for shedding light on the roles of PKA are also described from the perspective of specific aspects of synaptic physiology and brain function that are ripe for investigation using incisive genetic, cell biological, and electrophysiological approaches.

Phosphorylated cyclic AMP response element binding protein expression induced in the periaqueductal gray by predator stress: its relationship to the stress experience, behavior and limbic neural plasticity

Electrophysiological studies in cats and recently in rats implicate neuroplasticity in the periaqueductal gray (PAG) and its afferents in stressor-induced increases in fearful behavior and anxiety-like behavior (ALB). Such increases may model aspects of affective changes following traumatic stress in humans. The present study explored the role of neuroplasticity in PAG and its connection with the central nucleus of the amygdala (ACE) in male rodent anxiety-like response to predator stress. In the first of two studies, the effects of predator stress on the induction of phosphorylated cyclic AMP response element binding protein (pCREB) were investigated. pCREB expression in the PAG and ventromedial hypothalamus (VMH) was examined immunohistochemically. Predator stress increased the degree of pCREB expression in PAG cells (measured densitometrically) but did not increase the number of cells expressing pCREB (measured stereologically). Moreover, predator stress-specific increase in pCREB-like immunoreactivity (lir) was restricted to the right lateral column of the PAG. In addition, pCREB lir in the right lateral column likely reflects aspects of the stress experience because the stressor (cat behavior) and the response to the stressor (rat defensive behavior) are highly predictive of degree of pCREB expression. There was no effect of predator stress on pCREB lir in the VMH. Because pCREB expression has been associated with long-lasting potentiation (LLP) of neural transmission, we examined the effects of predator stress on transmission in the ACE-PAG pathway in a second study. Predator stress elevated evoked potential measures of ACE-PAG transmission in the right hemisphere but not in the left hemisphere 11-12 days after predator stress. This finding is consistent with the longer-lived effects of pharmacological stress on amygdalo-PAG transmission in the right hemisphere but not in the left hemisphere in cats. Of interest is the fact that the same aspects of the stressor experience and reaction to it, which are predictive of the degree of pCREB expression, are also highly predictive of the degree of potentiation of measures of ACE-PAG transmission. Behavioral analyses revealed that the most consistent effects of predator stress are on behavior in the plus maze (open arm exploration and risk assessment) and on startle. In addition, covariance analysis suggests that ACE-PAG potentiation mediates some but not all of the changes in ALB produced by predator stress. Because pCREB expression may be a precursor to neuroplastic changes in certain forms of memory and LLP, the present findings complement studies in the cat, showing that neuroplastic changes in the PAG underlie changes in affect following stress. Furthermore, these findings suggest that neuroplastic changes in PAG may be important mediators of predator stress-induced changes in affective behavior in rodents. Finally, consistent with cat and human studies, the right hemisphere appears particularly important in long-term response to stress.

Molecular correlates of impaired prefrontal plasticity in response to chronic stress

Disturbed adaptations at the molecular and cellular levels following stress could represent compromised neural plasticity that contributes to the pathophysiology of stress-induced disorders. Evidence illustrates atrophy and cell death of stress-vulnerable neurones in the prefrontal cortex. Reduced plasticity may be realized through the destabilized function of selective proteins involved in organizing the neuronal skeleton and translating neurotrophic signals. To elucidate the mechanisms underlying these effects, rats were exposed to chronic footshock stress. Patterns of c-fos, phospho-extracellular-regulated protein kinases 1/2 (ERK1/2), calcineurin and phospho-cyclic-AMP response-element binding protein (CREB) expression were subsequently investigated. The results indicate chronic stress-induced impairments in prefrontal and cingulate signal transduction cascades underlying neuronal plasticity. The medial prefrontal cortex, demonstrated functional hyperactivity and dendritic phospho-ERK1/2 hyperphosphorylation, while reduced c-fos and calcineurin immunoreactivity occurred in the cingulate cortex. Significantly reduced phospho-CREB expression in both cortical regions, considering its implication in brain-derived neurotrophic factor (BDNF) transcription, suggests reduced synaptic plasticity. This data confirms the damaging effect of stress on cortical activity, on a molecular level. Due to the association of these markers in the regulation of BDNF signalling, these findings suggest a central role for intracellular neurotrophin transduction members in the pathways underlying cellular actions of stress in the brain.

Ca(2+)-dependent prodynorphin transcriptional derepression in neuroblastoma cells is exerted through DREAM protein activity in a kinase-independent manner

Prodynorphin transcription has been postulated as an important molecular mechanism involved in adaptation/repair processes. Expression of prodynorphin is modulated according to the levels of the second messengers cAMP and Ca(2+). In the neuroblastoma cell lines, the increase of prodynorphin mRNA levels is coupled to an elevation of intracellular cAMP levels. Promoter analyses have revealed that the DRE site, a silencer element present in the prodynorphin promoter, is involved in PKA-dependent prodynorphin derepression. In this way, DREAM, a calcium-dependent repressor, plays an outstanding role. In this study, Ca(2+) release from internal stores has been found to promote an increase of prodynorphin mRNA levels in NB69 cells. Surprisingly, Ca(2+)-dependent prodynorphin gene transcription was insensitive to the broad-spectrum kinase inhibitors and sensitive to agents that alter internal Ca(2+) accumulation. Moreover, we demonstrate that in NB69 cells, the Ca(2+) signaling pathway uses DREAM as an effector to evoke prodynorphin transcription derepression in a kinase-independent manner.

Molecular aspects of glutamate dysregulation: implications for schizophrenia and its treatment

The glutamate system is involved in many aspects of neuronal synaptic strength and function during development and throughout life. Synapse formation in early brain development, synapse maintenance, and synaptic plasticity are all influenced by the glutamate system. The number of neurons and the number of their connections are determined by the activity of the glutamate system and its receptors. Malfunctions of the glutamate system affect neuroplasticity and can cause neuronal toxicity. In schizophrenia, many glutamate-regulated processes seem to be perturbed. Abnormal neuronal development, abnormal synaptic plasticity, and neurodegeneration have been proposed to be causal or contributing factors in schizophrenia. Interestingly, it seems that the glutamate system is dysregulated and that N-methyl-D-aspartate receptors operate at reduced activity. Here we discuss how the molecular aspects of glutamate malfunction can explain some of the neuropathology observed in schizophrenia, and how the available treatment intervenes through the glutamate system.

Calcium/calmodulin-dependent protein kinase IIdelta 2 and gamma isoforms regulate potassium currents of rat brain capillary endothelial cells under hypoxic conditions

Endothelial K+ and Ca2+ homeostasis plays an important role in the regulation of tissue supply and metabolism under normal and pathological conditions. However, the exact molecular mechanism of how Ca2+ is involved in the regulation of K+ homeostasis in capillary endothelial cells, especially under oxidative stress, is not clear. To reveal Ca2+-triggered pathways, which modulate K+ homeostasis, Ca2+/calmodulin-dependent protein kinase II and voltage-gated outward K+ currents were studied in rat brain capillary endothelial cells under hypoxia. Whole cell voltage-clamp measurements showed voltage-gated outward K+ current with transient and sustained components. mRNA and protein of Ca2+/calmodulin-dependent protein kinase II delta2 and two gamma isoenzymes were identified. Activation of the isoforms (autophosphorylation) was typically achieved by the Ca2+ ionophore ionomycin, which was prevented by the Ca2+/calmodulin-dependent protein kinase II-specific inhibitor KN-93. Hypoxia resulted in autophosphorylation of the delta2 and gammaB isoforms, augmented the current amplitude, increased the inactivation time constant, and decreased the extent of inactivation of the transient current. KN-93 prevented both the activation of the isoforms and the alterations in the K+ current characteristics. It is concluded that the activation of Ca2+/calmodulin-dependent protein kinase II decreases inactivation of the voltage-gated outward K+ current, thereby counteracting depolarization of the hypoxic endothelium.

cGMP-induced presynaptic depression and postsynaptic facilitation at glutamatergic synapses in visual cortex

The mechanisms by which the intracellular messenger cGMP can modulate synaptic efficacy remain poorly understood. Here we report that cGMP, acting through cGMP-dependent protein kinase (PKG), has multiple rapid and reversible effects on synaptic transmission in slices and cultures of rodent visual cortex. Extracellular application of the membrane permeable cGMP analog 8-bromoguanosine-3',5'-cyclic monophosphate (8-Br-cGMP) and the PKG specific activator beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate sp-isomer (Sp-8-Br-PET-cGMPS) reduced stimulus-evoked EPSPs in slices. In cortical cultures, both analogs reduced the frequency of spontaneous EPSCs, but not their amplitude. In both slices and cultures, intracellular perfusion of the postsynaptic neurons with a pseudosubstrate inhibitory peptide specific for PKG had no effect on the reduction in EPSPs and EPSCs, indicating that the inhibition occurred at presynaptic sites. Whole-cell calcium currents in cultured cortical neurons were also reduced by both analogs, which may account for the effect on synaptic release. To determine whether cGMP was also acting at postsynaptic sites, we applied exogenous kainate/AMPA and NMDA to the recorded cells directly. cGMP and its analogs showed little effect on the postsynaptic kainate/AMPA responses but produced a dramatic enhancement of NMDA responses. cGMP-induced NMDA potentiation was prevented by the specific PKG inhibitory peptide infused into the postsynaptic cell. In summary, cGMP, acting through PKG, had depressive presynaptic and facilitatory postsynaptic actions at excitatory synapses in the visual cortex. We suggest that these opposing actions may be useful for altering the balance of synaptic inputs to cortical neurons in ways that enhance signals important for synaptic facilitation and neuronal plasticity.

Antipsychotic drugs and neuroplasticity: insights into the treatment and neurobiology of schizophrenia

This paper reviews the evidence that antipsychotic drugs induce neuroplasticity. We outline how the synaptic changes induced by the antipsychotic drug haloperidol may help our understanding of the mechanism of action of antipsychotic drugs in general, and how they may help to elucidate the neurobiology of schizophrenia. Studies have provided compelling evidence that haloperidol induces anatomical and molecular changes in the striatum. Anatomical changes have been documented at the level of regional brain volume, synapse morphology, and synapse number. At the molecular level, haloperidol has been shown to cause phosphorylation of proteins and to induce gene expression. The molecular responses to conventional antipsychotic drugs are predominantly observed in the striatum and nucleus accumbens, whereas atypical antipsychotic drugs have a subtler and more widespread impact. We conclude that the ability of antipsychotic drugs to induce anatomical and molecular changes in the brain may be relevant for their antipsychotic properties. The delayed therapeutic action of antipsychotic drugs, together with their promotion of neuroplasticity suggests that modification of synaptic connections by antipsychotic drugs is important for their mode of action. The concept of schizophrenia as a disorder of synaptic organization will benefit from a better understanding of the synaptic changes induced by antipsychotic drugs.

Developmental regulation and specific brain distribution of phosphorabphilin

Protein kinases and phosphatases play an important role in modulating synaptic transmission. The synaptic protein rabphilin associates with synaptic vesicles through the small GTPase Rab3A, binds Ca(2+) and phospholipids, and interacts with cytoskeletal elements, yet its function remains controversial. In this study, we have generated phosphospecific antibodies and studied the developmental, subcellular, and brain distribution of rabphilin phosphorylated at serine-234 and serine-274. Our results show that phosphorabphilin is present in vivo under basal conditions in a specific subset of synapses. The phosphorylated rabphilin is abundant in the cerebellum, midbrain, and medulla; phosphorabphilin is specifically enriched in the climbing fiber synapses of the cerebellar cortex. Its developmental profile reveals a sharp and transient increase at approximately postnatal day 16, a period critical for the activity-dependent pruning of supernumerary climbing fibers in the cerebellum. We propose that the phosphorylation of rabphilin regulates neuronal activity through development and in a synapse-specific manner.

Environmental enrichment: effects on spatial memory and hippocampal CREB immunoreactivity

Environmental enrichment has been shown to improve performance in tests of spatial memory, induce neurogenesis in the hippocampus, enhance survival of newly formed granule cells, and inhibit spontaneous apoptosis. Although neuroplasticity of the mammalian brain declines with age, recent evidence suggests that the adult brain exhibits significant plasticity in response to environmental stimulation. The present study was designed to evaluate the effect of environmental enrichment on spatial memory and on immunoreactivity to cAMP response element binding protein (CREB) from the hippocampus. C57/BL/6 mice were trained in a Morris water maze after exposure to an enriched environment, either from 35 to 94 days or from 100 to 159 days of age. Hippocampal tissue from representative animals was later analyzed by Western blot for CREB immunoreactivity. Results indicate that environmental enrichment (particularly during the earlier period) improved performance on the Morris water maze and tended to increase immunoreactivity to CREB in the hippocampus. Social interaction by itself did not result in significant differences in navigational performance. Results with regard to social interaction and CREB immunoreactivity were mixed. Results are discussed in terms of evaluating the construct of enrichment, the correlation of CREB transcription and behavior change, and the importance of the developmental period for enrichment.

Disturbance of neuronal plasticity is a critical pathogenetic event in Alzheimer's disease

Brain areas affected by AD pathology are primarily those structures that are invovled in the regulation of "higher brain functions". The functions these areas subserve such as learning, memory, perception, self-awareness, and consciousness require a life-long re-fittng of synaptic contacts that allows for the acquistion of new epigenetic information, a process based on a particularly high degree of structural plasticity. Here, we outline a hypothesis that it is the "labile state fo differentiation" of a subset of neurons in the adult brain that allows for ongoing neuroplastic processes after development is completed but at the same time renders these neurons particularly vulnerable. Mechanisms of molecular and cellular control of neuronal differentiation and proliferation might, thus, not only play a role during development but critically involved in the pathogenesis of neurodegeneration.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Protein synthesis in entorhinal cortex and long-term potentiation in dentate gyrus

Despite the concentration of effort in recent years, the mechanisms underlying the expression of long-term potentiation (LTP) in the hippocampus remain elusive, but amidst the uncertainty and sometimes controversy, one consistent finding is emerging; this is that late-phase LTP requires synthesis of proteins. This hypothesis was first proposed by a number of groups who reported that the more persistent components of LTP were blocked by protein synthesis inhibitors, and was supported by a significant literature which indicated that morphological changes accompanied LTP. Recent evidence indicated that the increase in protein synthesis may be cAMP-dependent and that subsequent activation of the transcription factor, CREB, represented one step in the cascade of events leading to protein synthesis. Whether protein synthesis occurs in presynaptic or postsynaptic neurons, or both, is still a subject of debate. Here we present evidence which suggests that LTP in perforant path-granule cell synapses is accompanied by protein synthesis, specifically synthesis of synaptic vesicle proteins, in the entorhinal cortex. We also show that protein synthesis is decreased in the entorhinal cortex of aged rats and a strain of rat which is genetically hypertensive, both of which exhibited impaired LTP. We propose that that the observed increase in protein synthesis in the entorhinal cortex, which accompanied LTP in the dentate gyrus, contributes to the reported changes in morphology in the presynaptic terminal.

Protein phosphatase-mediated regulation of protein kinase C during long-term depression in the adult hippocampus in vivo

The neural substrates of learning and memory are thought to involve use-dependent long-term changes in synaptic function, including long-term depression (LTD) of synaptic strength. One biochemical event hypothesized to contribute to the maintenance and expression of LTD is decreased protein phosphorylation, caused by a decrease in protein kinase activity and/or an increase in protein phosphatase activity. We tested whether the activity of protein kinase C (PKC) decreases after the induction of LTD in area CA1 of the adult hippocampus in vivo, and then investigated the mechanism responsible for the LTD-associated alteration in PKC activity. We found that LTD was associated with a significant decrease in both autonomous and cofactor-dependent PKC activity. The decrease in PKC activity was prevented by NMDA receptor blockade and was not accompanied by a decrease in the level of either PKCalpha, beta, gamma, or zeta. Western blot analysis with phosphospecific antibodies revealed that phosphorylation of Ser-657 on the catalytic domain of PKCalpha (Ser-660 on PKCbetaII) was decreased significantly after the induction of LTD, and that this dephosphorylation was prevented by the protein phosphatase inhibitor okadaic acid. The decrease in autonomous and cofactor-dependent PKC activity likewise was prevented by okadaic acid. These findings suggest that LTD in the adult hippocampus in vivo involves a decrease in PKC activity that is mediated, at least in part, by dephosphorylation of the catalytic domain of PKC by protein phosphatases activated after LTD-inducing stimulation. Our findings are consistent with the idea that protein dephosphorylation contributes to the expression of LTD.

The calmodulin multigene family as a unique case of genetic redundancy: multiple levels of regulation to provide spatial and temporal control of calmodulin pools?

Calmodulin (CaM) is a ubiquitous, highly conserved calcium sensor protein involved in the regulation of a wide variety of cellular events. In vertebrates, an identical CaM protein is encoded by a family of non-allelic genes, raising questions concerning the evolutionary pressure responsible for the maintenance of this apparently redundant family. Here we review the evidence that the control of the spatial and temporal availability of CaM may require multiple regulatory levels to ensure the proper localization, maintenance and size of intracellular CaM pools. Differential transcription of the CaM genes provides one level of regulation to meet tissue-specific, developmental and cell-specific needs for altered CaM levels. Post-transcriptional regulation occurs at the level of mRNA stability, perhaps dependent on alternative polyadenylation and differences in the untranslated sequences of the multiple gene transcripts. Recent evidence indicates that trafficking of specific CaM mRNAs may occur to specialized cellular locales such as the dendrites of neurons. This could allow local CaM synthesis and thereby help generate local pools of CaM. Local CaM activity may be further regulated by post-translational mechanisms such as phosphorylation or storage of CaM in a 'masked' form. The spatial resolution of CaM activity is enhanced by the limited free diffusion of CaM combined with differential affinity for and availability of target proteins. Preserving multiple CaM genes with divergent noncoding sequences may be necessary in complex organisms to ensure that the many CaM-dependent processes occur with the requisite spatial and temporal resolution. Transgenic mouse models and studies on mice carrying single and double gene 'knockouts' promise to shed further light on the role of specificity versus redundancy in the evolutionary maintenance of the vertebrate CaM multigene family.

The inhibitory effects of interleukin-6 on synaptic plasticity in the rat hippocampus are associated with an inhibition of mitogen-activated protein kinase ERK

Several cytokines have short-term effects on synaptic transmission and plasticity that are thought to be mediated by the activation of intracellular protein kinases. We have studied the effects of interleukin-6 (IL-6) on the expression of paired pulse facilitation (PPF), posttetanic potentiation (PTP), and long-term potentiation (LTP) in the CA1 region of the hippocampus as well as on the activation of the signal transducer and activator of transcription-3 (STAT3), the mitogen-activated protein kinase ERK (MAPK/ERK), and the stress-activated protein kinase/c-Jun NH(2)-terminal kinase (SAPK/JNK). IL-6 induced a marked and dose-dependent decrease in the expression of PTP and LTP that could be counteracted by the simultaneous treatment with the tyrosine kinase inhibitor lavendustin A (LavA) but did not significantly affect PPF. The IL-6-induced inhibition of PTP and LTP was accompanied by a simulation of STAT3 tyrosine phosphorylation and an inhibition of MAPK/ERK dual phosphorylation, in the absence of changes in the state of activation of SAPK/JNK. Both effects of IL-6 on STAT3 and MAPK/ERK activation were effectively counteracted by LavA treatment. The results indicate the tyrosine kinases and MAPK/ERK are involved in hippocampal synaptic plasticity and may represent preferential intracellular targets for the actions of IL-6 in the adult nervous system.

NMDA-Dependent modulation of hippocampal kainate receptors by calcineurin and Ca(2+)/calmodulin-dependent protein kinase

Neurotransmitter receptor function can be influenced by the phosphorylation state of the receptor or of associated proteins. Here we show that kainate receptors expressed in cultured hippocampal neurons can be modulated by Ca(2+)/calmodulin-dependent phosphatase (calcineurin) and Ca(2+)/calmodulin-dependent kinase (CaMK). Ca(2+) influx through NMDA receptor or voltage-sensitive calcium channels resulted in a transient depression of the kainate receptor current. This calcium-induced depression of the kainate receptor current depended on the activation of the phosphatase calcineurin. The amplitude of the kainate receptor currents returned to the baseline level in approximately 9 sec (tau = 3.6 sec), and the recovery of the current amplitude depended on CaMK activity. The effect on kainate receptor currents was dependent on the frequency of NMDA receptor activation. Although low-frequency (0.1 Hz) NMDA application induced depression followed by recovery of the kainate receptor currents, higher frequency (1 Hz) NMDA applications induced a more prolonged depression. Kainate receptors have been shown to modulate synaptic transmission by both presynaptic and postsynaptic mechanisms. Our results suggest that synaptic activity mediated by NMDA receptors, or other routes of Ca(2+) influx, may, in turn, modulate the function of kainate receptors.

High-frequency synaptic stimulation induces association of fyn and c-src to distinct phosphorylated components

Signaling via tyrosine kinases appears necessary for regulation of synaptic efficacy. Interactions of the src-family kinases with phosphorylated proteins were studied in area CAI of rat hippocampal slices 10 min after induction of long-term potentiation (LTP) by 100 Hz/l s stimulation (HFS). HFS enhanced association of the src-family kinases fyn and c-src with an approximately 120 kDa tyrosine phosphorylated component containing the focal adhesion kinase (FAK) and its homologue PYK2. Association of fyn with FAK and of c-src with PYK2 was increased following the HFS. Further, increase in tyrosine phosphorylation of PYK2 was detected following the HFS. These results suggest that fyn and c-src are involved in distinct signaling pathways and provide evidence for activation of FAK and PYK2 following synaptic stimulation inducing LTP in vitro.

Neuropsin regulates an early phase of schaffer-collateral long-term potentiation in the murine hippocampus

We found that neuropsin, an extracellular matrix serine protease, has a regulatory effect on Schaffer-collateral long-term potentiation (LTP) in the mouse hippocampus. Bath application of 1-170 nM recombinant neuropsin modulated early phase LTP in the Schaffer-collateral pathway with a 'bell-shape' dose-response curve. The maximum enhancing activity (134% of control LTP) was found at approximately 2.5 nM. Bath application of a neutralizing antibody against neuropsin in the hippocampal slice resulted in a marked inhibition of the tetanus-induced early phase of LTP. The in vivo continuous intraventricular infusion of an antisense oligonucleotide against neuropsin significantly reduced the amplitude of the tetanus-induced early phase of LTP in vitro. Neuropsin did not directly change the N-methyl D-aspartate (NMDA) current. Thus, neuropsin appears to act as a regulatory molecule in the early phase of LTP via its proteolytic function on extracellular matrix rather than affecting NMDA receptor-mediated calcium increase.

Identification of two persistently activated neurotrophin-regulated pathways in rat hippocampus

Brain-derived neurotrophic factor contributes profoundly to modulate activity-dependent synaptic plasticity in adult brain areas such as the hippocampus, but the mechanisms underlying this important role still remain unclear. Recently, we have shown that two serine/threonine kinases, calcium/calmodulin-dependent protein kinase-2 and casein kinase-2, are capable of mediating brain-derived neurotrophic factor responses in adult rat hippocampus. In the present study, using hippocampal slices from adult rat, we show that phospholipase C-regulated calcium signals couple the brain-derived neurotrophic factor receptor to two distinct pathways: a pathway in which calcium/calmodulin-dependent protein kinase-2 stimulates a signalling module involving the p38 subfamily of mitogen-activated protein kinases and its downstream target, usually named mitogen-activated protein kinase-activated protein kinase-2; and a pathway in which the extracellular signal-regulated kinase subfamily of mitogen-activated protein kinases activates casein kinase-2. Our results suggest that: (i) extracellular signal-regulated kinase is activated by B-Raf in response to a calcium-sensitive adenylate cyclase; and (ii) extracellular signal-regulated kinase activates casein kinase-2 via a protein phosphatase(s) that may be of the PP1 and/or PP2A type. Interestingly, we also show that neurotrophin-induced activation of the two signalling cascades promotes a sustained activation of mitogen-activated protein kinase-activated protein kinase-2 and casein kinase-2 in slices. Considering the ability of these two kinases to be persistently activated, and that most of the protein kinases which lie in these pathways are believed to be important for multiple events underlying neuronal plasticity, it is suggested that the mechanisms described here might contribute both to rapid synaptic changes through local effects and to long-lasting synaptic responses through new gene transcription in the hippocampus.

The D1 dopamine receptor agonist SKF-38393 stimulates the release of glutamate in the hippocampus

The present study was undertaken to better assess the role of dopamine on exocytosis. Since direct activation of adenylate cyclase (e.g., with forskolin) enhances neurotransmitter release it was of interest to see whether the activation of D1-type dopamine receptors, which are positively coupled to adenylate cyclase, could also modulate the molecular machinery underlying the fusion of synaptic vesicles and the release of neurotransmitter. To answer this question we have looked at the effect of the D1-type dopamine receptor agonist SKF-38393 on the spontaneous release of glutamate from cultured rat hippocampal neurons. SKF-38393 enhanced the frequency but not the amplitude of tetrodotoxin-resistant excitatory postsynaptic currents which argues for a presynaptic locus of D1 action. This effect was blocked by the D1-dopaminergic receptor antagonist SCH-23390 and the protein kinase A inhibitors H-7 and Rp-cAMP whereas pertussis toxin failed to affect the dopaminergic response. In addition, carbachol and Ruthenium Red also stimulated exocytosis but did not occlude the SKF-38393-induced modulation. These results indicate that SKF-38393 presynaptically enhances the release of glutamate via a pertussis toxin-insensitive and protein kinase A-dependent mechanism, which most likely involves D1-type dopamine receptors. Our results underline the importance of protein kinase A as potent modulator of synaptic transmission and suggest that high concentrations of dopamine can greatly enhance the release of glutamate in the hippocampus.

Casein kinase 2 as a potentially important enzyme in the nervous system

Protein kinase CK2 is a ubiquitous and pleiotropic seryl/threonyl protein kinase which is highly conserved in evolution indicating a vital cellular role for this kinase. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. Special attention has been devoted to phosphorylation status and structure of these enzymic molecules, however, their regulation and roles remain intriguing. Until recently, CK2 was believed to represent a kinase especially required for cell cycle progression in non-neural cells. At present, with respect to recent findings, four essential features suggest potentially important roles for this enzyme in specific neural functions: (1) CK2 is much more abundant in brain than in any other tissue; (2) there appear to be a myriad of substrates for CK2 in both synaptic and nuclear compartments that have clear implications in development, neuritogenesis, synaptic transmission, synaptic plasticity, information storage and survival; (3) CK2 seems to be associated with mechanisms underlying long-term potentiation in hippocampus; and (4) neurotrophins stimulate activity of CK2 in hippocampus. In addition, some data are suggestive that CK2 might play a role in processes underlying progressive disorders due to Alzheimer's disease, ischemia, chronic alcohol exposure or immunodeficiency virus HIV. The present review focuses mainly on the latest data concerning the regulatory mechanisms and the possible neurophysiological functions of this enzyme.

Developmental regulation and effect of early undernutrition on phosphorylation of rat cortical synaptic membrane proteins

Undernutrition during early postnatal life was employed in rats by restricting the feeding time. The synaptic membrane fraction from cerebral cortex of normal and undernourished rats of various ages was prepared and endogenous protein phosphorylation studied. Many of the synaptic membrane proteins were found to be phosphorylated in an age-dependent manner. Early undernutrition affects the phosphorylation of various proteins in a complex way; most affected were 48-, 52-, 61- and 74-kDa proteins. These proteins were found to have phosphorylations mainly at tyrosine residues. This finding indicates that tyrosine phosphorylations may be affected most by early undernutrition. Adequate nutrition after early undernutrition removes most of the effects of undernutrition on synaptic protein phosphorylation. To address the question of how undernutrition may affect protein phosphorylation, we studied the lipid content of synaptic membrane fraction as it can affect membrane properties, including the fluidity. We found that undernutrition affects phosphorylation of most of the synaptic membrane proteins in the same manner in which it affects the cholesterol-phospholipid ratio of synaptic membrane and, hence, the fluidity of the membrane. This indicates that lipid biosynthesis is one of the ways by which undernutrition can affect synaptic membrane protein phosphorylation.

Protein phosphorylation and the regulation of synaptic membrane traffic

It is well established that protein phosphorylation has an important role in synaptic plasticity. This is achieved, in part, via the presynaptic modulation of neurotransmitter release by protein kinases and protein phosphatases. In recent years, the increase in information available about proteins that are involved in synaptic exocytosis and endocytosis has been exploited in order to study the effects of protein phosphorylation on synaptic-vesicle cycling at the molecular level. The best-characterized protein in this respect is synapsin, whose function in the release of synaptic vesicles from the reserve pool is regulated by phosphorylation. More recently, it has emerged that proteins that function at other stages of the synaptic-vesicle cycle, which include priming of vesicles for docking-fusion and endocytic recycling, are also controlled by phosphorylation. Furthermore, recent work suggests that this regulation of membrane traffic by phosphorylation also occurs postsynaptically, where it contributes to synaptic plasticity.

Calcium as a versatile second messenger in the control of gene expression

The elevation of intracellular calcium is a major effector of stimulus-induced physiological change in a variety of cell types. Such change is invariably complex and frequently involves the activation of gene expression. Calcium signals are often able to activate different subsets of genes within the same cell, the basis for which has been unclear. Recent studies have revealed that a number of differing properties of the calcium signal are responsible for distinct cellular responses.