Effects of Zinc, Mercury, or Lead on [3H]MK-801 and [3H]Fluorowillardiine Binding to Rat Synaptic Membranes

Glutamate (Glu) is considered the most important excitatory amino acid neurotransmitter in the mammalian Central Nervous System. Zinc (Zn) is co-released with Glu during synaptic transmission and interacts with Glutamate receptors and transporters. We performed binding experiments using [³H]MK-801 (NMDA), and [³H]Fluorowillardine (AMPA) as ligands to study Zn-Glutamate interactions in rat cortical synaptic membranes. We also examined the effects of mercury and lead on NMDA or AMPA receptors. Zinc at 1 nM, significantly potentiates [³H]MK-801 binding. Lead inhibits [³H]MK-801 binding at micromolar concentrations. At millimolar concentrations, Hg also has a significant inhibitory effect. These effects are not reversed by Zn (1 nM). Zinc displaces the [³H]FW binding curve to the right. Lead (nM) and Hg (μM) inhibit [³H]FW binding. At certain concentrations, Zn reverses the effects of these metals on [³H]FW binding. These specific interactions serve to clarify the role of Zn, Hg, and Pb in physiological and pathological conditions.

Depolarization-dependent Induction of Site-specific Changes in Sialylation on N-linked Glycoproteins in Rat Nerve Terminals

Synaptic transmission leading to release of neurotransmitters in the nervous system is a fast and highly dynamic process. Previously, protein interaction and phosphorylation have been thought to be the main regulators of synaptic transmission. Here we show that sialylation of N-linked glycosylation is a novel potential modulator of neurotransmitter release mechanisms by investigating depolarization-dependent changes of formerly sialylated N-linked glycopeptides. We suggest that negatively charged sialic acids can be modulated, similarly to phosphorylation, by the action of sialyltransferases and sialidases thereby changing local structure and function of membrane glycoproteins. We characterized site-specific alteration in sialylation on N-linked glycoproteins in isolated rat nerve terminals after brief depolarization using quantitative sialiomics. We identified 1965 formerly sialylated N-linked glycosites in synaptic proteins and found that the abundances of 430 glycosites changed after 5 s depolarization. We observed changes on essential synaptic proteins such as synaptic vesicle proteins, ion channels and transporters, neurotransmitter receptors and cell adhesion molecules. This study is to our knowledge the first to describe ultra-fast site-specific modulation of the sialiome after brief stimulation of a biological system.

Input from the medial geniculate nucleus modulates amygdala encoding of fear memory discrimination

Generalization of fear can involve abnormal responding to cues that signal safety and is common in people diagnosed with post-traumatic stress disorder. Differential auditory fear conditioning can be used as a tool to measure changes in fear discrimination and generalization. Most prior work in this area has focused on elevated amygdala activity as a critical component underlying generalization. The amygdala receives input from auditory cortex as well as the medial geniculate nucleus (MgN) of the thalamus, and these synapses undergo plastic changes in response to fear conditioning and are major contributors to the formation of memory related to both safe and threatening cues. The requirement for MgN protein synthesis during auditory discrimination and generalization, as well as the role of MgN plasticity in amygdala encoding of discrimination or generalization, have not been directly tested. GluR1 and GluR2 containing AMPA receptors are found at synapses throughout the amygdala and their expression is persistently up-regulated after learning. Some of these receptors are postsynaptic to terminals from MgN neurons. We found that protein synthesis-dependent plasticity in MgN is necessary for elevated freezing to both aversive and safe auditory cues, and that this is accompanied by changes in the expressions of AMPA receptor and synaptic scaffolding proteins (e.g., SHANK) at amygdala synapses. This work contributes to understanding the neural mechanisms underlying increased fear to safety signals after stress.

Hippocampal Aromatization Modulates Spatial Memory and Characteristics of the Synaptic Membrane in the Male Zebra Finch

The estrogen-synthesizing enzyme aromatase is abundant at the synapse in the zebra finch hippocampus (HP), and its inhibition impairs spatial memory function. To more fully test the role of local estradiol (E2) synthesis in memory, the HP of adult male zebra finches was exposed to either control pellets or those containing the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD), ATD and E2, ATD and the G protein-coupled estrogen receptor (GPER) agonist G1, or the antagonist G15 alone. Birds were tested for spatial memory acquisition and performance, and HP levels of the postsynaptic protein PSD95 were measured. ATD-treated birds took longer to reach criterion than control birds, whereas acquisition in ATD+E2 and ATD+G1 birds was indistinguishable from control and ATD treatments. Interestingly, all G15 birds failed to acquire the task. Following a retention interval, ATD birds took the longest to reach the (formerly) baited cup and made the most mistakes. ATD+E2 animals displayed the lowest retention latencies and made fewer mistakes than ATD-treated birds, and ATD+G1 birds did not significantly differ from controls in retention latencies. The amount of PSD95 in the HP was lowest in ATD-treated animals compared with birds with silicone-only-implanted craniotomies, ATD+E2, and ATD+G1 birds, who did not differ in this expression. Thus, spatial memory acquisition and performance appear aromatase and E2 dependent, an effect more reliably revealed after consolidation and/or recall compared to acquisition. E2 may exert this effect via GPERs, resulting in an increase in PSD95 levels that may modify receptor activity or intracellular signaling pathways to increase synaptic strength.

Endocannabinoids and Synaptic Function in the CNS

Marijuana affects neural functions through the binding of its active component (Δ9-THC) to cannabinoid receptors in the CNS. Recent studies have elucidated that endogenous ligands for cannabinoid receptors, endocannabinoids, serve as retrograde messengers at central synapses. Endocannabinoids are produced on demand in activity-dependent manners and released from postsynaptic neurons. The released endocannabinoids travel backward across the synapse, activate presynaptic CB1 cannabinoid receptors, and modulate presynaptic functions. Retrograde endocannabinoid signaling is crucial for certain forms of short-term and long-term synaptic plasticity at excitatory or inhibitory synapses in many brain regions, and thereby contributes to various aspects of brain function including learning and memory. Molecular identities of the CB1 receptor and enzymes involved in production and degradation of endocannabinoids have been elucidated. Anatomical studies have demonstrated unique distributions of these molecules around synapses, which provide morphological bases for the roles of endocannabinoids as retrograde messengers. CB1-knockout mice exhibit various behavioral abnormalities and multiple defects in synaptic plasticity, supporting the notion that endocannabinoid signaling is involved in various aspects of neural function. In this review article, the authors describe molecular mechanisms of the endocannabinoid-mediated synaptic modulation and its possible physiological significance. NEUROSCIENTIST 13(2):127—137, 2007.

Postsynaptic adenosine A2A receptors modulate intrinsic excitability of pyramidal cells in the rat basolateral amygdala

BACKGROUND

The basolateral amygdala plays a critical role in the etiology of anxiety disorders and addiction. Pyramidal neurons, the primary output cells of this region, display increased firing following exposure to stressors, and it is thought that this increase in excitability contributes to stress responsivity and the expression of anxiety-like behaviors. However, much remains unknown about the underlying mechanisms that regulate the intrinsic excitability of basolateral amygdala pyramidal neurons.

METHODS

Ex vivo gramicidin perforated patch recordings were conducted in current clamp mode where hyper- and depolarizing current steps were applied to basolateral amygdala pyramidal neurons to assess the effects of adenosine A(2A) receptor modulation on intrinsic excitability.

RESULTS

Activation of adenosine A(2A) receptors with the selective A(2A) receptor agonist CGS-21680 significantly increased the firing rate of basolateral amygdala pyramidal neurons in rat amygdala brain slices, likely via inhibition of the slow afterhyperpolarization potential. Both of these A(2A) receptor-mediated effects were blocked by preapplication of a selective A(2A) receptor antagonist (ZM-241385) or by intra-pipette infusion of a protein kinase A inhibitor, suggesting a postsynaptic locus of A(2A) receptors on basolateral amygdala pyramidal neurons. Interestingly, bath application of the A(2A) receptor antagonist alone significantly attenuated basolateral amygdala pyramidal cell firing, consistent with a role for tonic adenosine in the regulation of the intrinsic excitability of these neurons.

CONCLUSIONS

Collectively, these data suggest that adenosine, via activation of A(2A) receptors, may directly facilitate basolateral amygdala pyramidal cell output, providing a possible balance for the recently described inhibitory effects of adenosine A1 receptor activation on glutamatergic excitation of basolateral amygdala pyramidal cells.

[Studying the effect of Dimebon and NT-1505 on microviscosity of mice brain synaptosomal membranes in vivo by EPR spin labeling method]

In this work membrane fluidity alterations in synaptosomes, isolated from mice brain tissue, at chronic administration of neuroprotectors Dimebon and NT-1505 in vivo were studied. Membrane microviscosity was measured by electron paramagnetic resonance spin labeling of 2,2,6,6-tetramet-hyl-4-capryloyl-oxylpiperidine-l-oxyl (lipid probe) and 5,6-benzo-2,2,6,6-tetramethyl-1,2,3,4-tetrahydro-gamma-carboline-3-oxyl (near protein probe). It was shown that the neuroprotectors Dimebon and NT-1505 affect a membrane structure. Despite the difference in membrane structures, fluidity of the lipid bilayer in time returned to control values.

Increased susceptibility of brain acetylcholinesterase activity to methylmalonate in young rats with renal failure

Tissue methylmalonic acid (MMA) accumulation is the biochemical hallmark of methylmalonic acidemia. Clinically, the disease is characterized by progressive neurological deterioration and renal failure, whose pathophysiology is still undefined. In the present study we investigated the effect of acute MMA administration on some important parameters of brain neurotransmission in cerebral cortex of rats, namely Na(+), K(+)-ATPase, ouabain-insensitive ATPases and acetylcholinesterase activities, in the presence or absence of kidney injury induced by gentamicin administration. Initially, thirty-day old Wistar rats received one intraperitoneal injection of saline or gentamicin (70 mg/kg). One hour after, the animals received three consecutive subcutaneous injections of MMA (1.67 μmol/g) or saline, with an 11 h interval between each injection. One hour after the last injection the animals were killed and the cerebral cortex isolated. MMA administration by itself was not able to modify Na(+), K(+)-ATPase, ATPases ouabain-insensitive or acetylcholinesterase activities in cerebral cortex of young rats. In rats receiving gentamicin simultaneously with MMA, it was observed an increase in the activity of acetylcholinesterase activity in cerebral cortex, without any alteration in the activity of the other studied enzymes. Therefore, it may be speculated that cholinergic imbalance may play a role in the pathogenesis of the brain damage. Furthermore, the pathophysiology of tissue damage cannot be exclusively attributed to MMA toxicity, and control of kidney function should be considered as a priority in the management of these patients, specifically during episodes of metabolic decompensation when MMA levels are higher.

Simvastatin alters membrane cholesterol distribution and beta-amyloid levels in brains of female APP751SL mice

Statins (HMG-CoA reductase or CSE-inhibitors) strongly reduce the cellular amyloid-beta protein production by modulating the processing of amyloid precursor protein (APP) in vitro. Several in vivo studies have addressed this important issue in transgenic mouse models with inconsistent results. Recently, we showed that simvastatin alters cholesterol distribution in synaptosomal membranes (SPM) in vivo. In the present study, we tested whether these changes in cholesterol membrane distribution affect APP-processing in vivo. Female APP751SL mice were force-fed with simvastatin (50 mg/kg b.wt.) by oral gavage over a time period of 3 weeks. Our data show that chronic simvastatin treatment decreased cholesterol levels in the brain and affected cholesterol distribution within SPM. Simvastatin significantly increased the levels of insoluble Abeta1-40 and Abeta1-42 but reduced levels of soluble Abeta1-40 in the brain. The reduction of soluble Abeta1-40 levels in the brain was associated with an increase of plasma-levels of AP31.40 in simvastatin-treated animals that may indicate enhanced Abeta1-40-clearance from the brain. Although the observed alteration in transbilayer cholesterol is likely to be involved in changes of APP processing by alpha-, beta- and gamma-secretase, we cannot exclude other potential mechanisms of statins such as lipid and non-lipid related, pleiotropic effects. Our data were evaluated in reference to published studies and a possible gender effect was identified.

Botulinum neurotoxins: mechanism of action

Botulinum neurotoxins are used clinically for conditions characterized by hyperexcitability of peripheral nerve terminals and hypersecretory syndromes. These neurotoxins are synthesized as precursor proteins with low activity, but their effects are mediated by the active form of the neurotoxin through a multistep mechanism. Following a high-affinity interaction with a protein receptor and polysialogangliosides on the synaptic membrane, botulinum neurotoxins enter the neuron and causes a sustained inhibition of synaptic transmission. The active neurotoxin is part of a high-molecular-weight complex that protects the neurotoxin from proteolytic degradation. Although complexing proteins do not affect diffusion of therapeutic neurotoxin, they may lead to the development of neutralizing antibodies that block responsiveness to it. Nerve terminal intoxication is reversible and its duration varies for different BoNT serotypes. Although it was previously assumed that botulinum neurotoxins exert effects only on the peripheral synapses, such as the neuromuscular junction, there is now substantial evidence that these neurotoxins affect neurotransmission at distal central nervous system sites as well.

[Brucine chitosan thermosensitive hydrogel for intra-articular injection]

The aim of this study was to develop a sustained release converse thermosensitive hydrogel for intra-articular injection using chitosan-glycerol-borax as matrix, its physical properties and biocompatibility were investigated. Taking gelation time and gelation condition as index, the influence of concentration of chitosan, ratio of chitosan to glycerol, pH on physical properties of hydrogel were investigated. And then the in vitro drug release, rheological properties and biocompatibility were studied. The thermosensitive hydrogel flows easily at room temperature and turns to gelation at body temperature, which can certainly prolong the release of drug and has good biocompatibility.

Role of antioxidants on Na(+),K (+)-ATPase activity and gene expression in cerebral cortex of hyperprolinemic rats

Considering that Na(+),K(+)-ATPase is an embedded-membrane enzyme and that experimental chronic hyperprolinemia decreases the activity of this enzyme in brain synaptic plasma membranes, the present study investigated the effect of chronic proline administration on thiobarbituric acid-reactive substances, as well as the influence of antioxidant vitamins E plus C on the effects mediated by proline on Na(+),K(+)-ATPase activity in cerebral cortex of rats. The expression of Na(+),K(+)-ATPase catalytic subunits was also evaluated. Results showed that proline increased thiobarbituric acid-reactive substances, suggesting an increase of lipid peroxidation. Furthermore, concomitant administration of vitamins E plus C significantly prevented the increase of lipid peroxidation, as well as the inhibition of Na(+),K(+)-ATPase activity caused by proline. We did not observe any change in levels of Na(+),K(+)-ATPase mRNA transcripts after chronic exposure to proline and vitamins E plus C. These findings provide insights into the mechanisms through which proline exerts its effects on brain function and suggest that treatment with antioxidants may be beneficial to treat neurological dysfunctions present in hyperprolinemic patients.

Characterization of three "Birtoxin-like" toxins from the Androctonus amoreuxi scorpion venom

The venom of the North African scorpion Androctonus amoreuxi (Aam) was analyzed using a combination of gel filtration, C18 reverse phase HPLC together with mass spectrometry analysis and bioassays. Three novel Birtoxin-like (BTX-L) peptides of 58 amino acid residues comprising three disulfide bridges were isolated and chemically characterized. One peptide, AamBTX-L3, induced serious toxic symptoms in mice and was lethal at nanogram quantities using intracerebroventricular injection. The three BTX-L peptides were tested in competition experiments on rat brain synaptosomes against the (125)I-labeled "classical" α- and β-toxins of reference, as well as with the (125)I-KTX, a voltage-gated potassium channel blocker. Only AamBTX-L3 was able to prevent the equilibrium binding of the β-toxin (125)I-Css IV to its receptor site 4 with a IC(50) value of 189 nM. Even if previous electrophysiological data allowed the classification of other BTX-L peptides among the β-type toxins, this report clearly shows that AamBTX-L3 is pharmacologically a β-toxin, which recognizes the voltage-gated Na(+) (Na(v)) channels from central mammalian neurons. In order to uncover the residues functionally essential for interaction between the AamBTX-L3 with the putative receptor site of (125)I-Css IV on Na(v)1.2, molecular models of the three novel Aam BTX-L molecules were made and their surfaces were compared to the already described Css IV biologically interactive surfaces. A hypothesis is given that in BTX-L3, three residues found in the α-helix play a key role during target binding.

Effects of fluoride on synaptic membrane fluidity and PSD-95 expression level in rat hippocampus

The objective of this study is to investigate the neurotoxicity of drinking water fluorosis on rat hippocampus. Just weaning male Sprague-Dawley rats were randomly divided into four groups and given 15, 30, and 60 mg/L NaF solution and distilled water, respectively, for 9 months. The fluidity of brain synaptic membrane and expression level of postsynaptic density 95 (PSD-95) were tested. Results showed that the fluidity of brain synaptic membrane decreased gradually with increasing of fluoride concentration, and it was significantly decreased (P < 0.05) in moderate-fluoride group compared with control group, and expression level of PSD-95 was significantly decreased (P < 0.01) in moderate-fluoride group when compared with that of control group. These results indicate that decrease of synaptic membrane fluidity and PSD-95 expression level may be the molecular basis of central nervous system damage caused by fluoride intoxication; PSD-95 in CA3 region of hippocampus is probably a target molecule for fluoride.

Lycopodium alkaloids from Huperzia serrata

A new lycopodane-type Lycopodium alkaloid, 6α-hydroxy-5,15-oxide-lycopodane (1), and seven known alkaloids were isolated from the whole plants of Huperzia serrata. Their structures were elucidated by means of spectroscopic methods. 12-Deoxyhuperzine O (2) was reported as a naturally occurring alkaloid for the first time, and showed an antagonist effect on the N-methyl-d-aspartate receptor with an IC(50) value of 0.92 μM.

Measuring and modelling mixture toxicity of imidacloprid and thiacloprid on Caenorhabditis elegans and Eisenia fetida

While the standard models of concentration addition and independent action predict overall toxicity of multicomponent mixtures reasonably, interactions may limit the predictive capability when a few compounds dominate a mixture. This study was conducted to test if statistically significant systematic deviations from concentration addition (i.e. synergism/antagonism, dose ratio- or dose level-dependency) occur when two taxonomically unrelated species, the earthworm Eisenia fetida and the nematode Caenorhabditis elegans were exposed to a full range of mixtures of the similar acting neonicotinoid pesticides imidacloprid and thiacloprid. The effect of the mixtures on C. elegans was described significantly better (p<0.01) by a dose level-dependent deviation from the concentration addition model than by the reference model alone, while the reference model description of the effects on E. fetida could not be significantly improved. These results highlight that deviations from concentration addition are possible even with similar acting compounds, but that the nature of such deviations are species dependent. For improving ecological risk assessment of simple mixtures, this implies that the concentration addition model may need to be used in a probabilistic context, rather than in its traditional deterministic manner.

Role of muscarinic signal transduction and CREB phosphorylation in dichlorvos-induced memory deficits in rats: an acetylcholine independent mechanism

The present study was designed to explore the alternative mechanism (other than AChE inhibition) for chronic, low-level exposure to dichlorvos, an organophosphate, in vivo. Dichlorvos, at a dose of 1.0 and 6.0 mg/kg body weight (b.wt.) for 12 weeks, showed impairment in neurobehavioral indices viz. rota rod, passive avoidance and water maze tests. Though high dose of dichlorvos had a detrimental effect on acetylcholinesterase activity, no significant inhibition was seen with low dose of dichlorvos. Western blot analysis and immunofluorescence studies showed a significant reduction in the expression of M(1), M(2) and M(3) muscarinic receptor subtypes in high dose group animals, whereas in low dose group animals only the M(2) receptor subtype was reduced significantly. Further, the signal transduction cascade linked to these receptor subtypes was affected in high dose group animals whereas in low dose group only adenylyl cyclase-linked signaling pathway was impaired. Finally, the phosphorylation of CREB, a memory enhancing transcription factor, was significantly reduced in both low dose and high dose group animals. Thus, the present study reveals the significance of M(2) muscarinic receptor linked adenylyl cyclase signaling pathway and phosphorylation of CREB in the development of neurobehavioral impairments after chronic low-level exposure to dichlorvos.

Cl- conduction of GABA(A)-receptor complex of synaptic membranes of rat brain cortex after development of chronic epileptization of the brain (pharmacological kindling)

Experiments on Wistar rats showed that basal and muscimol-induced 36Cl- entry into synaptoneurosomes isolated from the brain cortex decreased after kindling (30 mg/kg pentylenetetrazole intraperitoneally for 30 days) in animals with seizure severity score 4-5. Changes in Cl- conduction during kindling are discussed.

Regulation of the neuronal norepinephrine transporter by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

We previously reported that endothelin-1 and endothelin-3 modulate norepinephrine neuronal release and tyrosine hydroxylase activity and expression in the hypothalamus. In the present study we sought to establish the role of endothelin-1 and -3 in the regulation of norepinephrine uptake in the anterior and posterior hypothalamus. Results showed that in the anterior hypothalamus endothelin-3 increased neuronal norepinephrine uptake whereas endothelin-1 decreased it. Conversely, in the posterior hypothalamic region both endothelins diminished the neuronal uptake of the amine. Endothelins response was concentration dependent and maintained at all studied times. Endothelins also modified the kinetic and internalization of the NE neuronal transporter. In the anterior hypothalamic region endothelin-3 increased the V(max) and the B(max) whereas endothelin-1 decreased them. However, in the posterior hypothalamic region both endothelins diminished the V(max) as well as B(max). Neither endothelin-1 nor endothelin-3 modified neuronal norepinephrine transporter K(d) in the studied hypothalamic regions. These findings support that in the posterior hypothalamic region both endothelins diminished neuronal norepinephrine transporter activity by reducing the amine transporter expression on the plasmatic membrane. Conversely, in the anterior hypothalamic region endothelin-3 enhanced neuronal norepinephrine transporter activity by increasing the expression of the transporter on the presynaptic membrane, whereas endothelin-1 induced the opposite effect. Present results permit us to conclude that both endothelins play an important role in the regulation of norepinephrine neurotransmission at the presynaptic nerve endings in the hypothalamus.

Cocaine withdrawal-induced trafficking of delta-opioid receptors in rat nucleus accumbens

Interactions between the opioidergic and dopaminergic systems in the nucleus accumbens (NAcb) play a critical role in mediating cocaine withdrawal-induced effects on cell signaling and behavior. In support of this, increased activation of striatal dopamine-D1 receptors (D1R) results in desensitization of delta-opioid receptor (DOR) signaling through adenylyl cyclase during early cocaine withdrawal. A potential cellular substrate underlying receptor desensitization is receptor internalization. The present study examined the effect of cocaine withdrawal on subcellular localization of DOR in dendrites of the NAcb core (NAcbC) and shell (NAcbS) using immunoelectron microscopy. Female and male rats received binge-pattern cocaine or saline for 14 days and subsequently underwent 48 h withdrawal. Animals were transcardially perfused and tissue sections were processed for immunogold-silver localization of DOR. Semi-quantitative analysis revealed that cocaine withdrawal caused an increase in the percentage of DOR localized intracellularly in the NAcbS of male and female rats and the NAcbC of male rats compared to saline controls. In contrast, in the NAcbC of female rats, there was an increase in DOR associated with the plasma membrane following cocaine withdrawal. To determine whether modulation of D1R could directly impact DOR containing neurons, the hypothesis that DOR and D1R co-exist in common neurons of the NAcb was examined in naïve rats. Semi-quantitative analysis revealed a subset of profiles containing both DOR and D1R immunoreactivities. The present findings demonstrate a redistribution of DOR in the NAcb following cocaine withdrawal and provide anatomical evidence supporting D1R regulation of DOR function in a subset of NAcb neurons.

Sulfite increases lipoperoxidation and decreases the activity of catalase in brain of rats

The main objective of this study was to investigate the in vitro effects of sulfite, a metabolite accumulated in isolated sulfite oxidase deficiency, on Na (+), K (+)-ATPase activity and on some parameters of oxidative stress, namely thiobarbituric acid-reactive substances (TBARS) and catalase activity (antioxidant enzyme) in cerebral cortex, striatum and hippocampus from 10- and 60-day-old rats. Results showed that 500 microM sulfite significantly increased TBARS and reduced catalase activity in the cerebral structures studied from neonates and adults rats; in contrast, sulfite did not alter Na(+), K(+)-ATPase activity. Our present findings show that sulfite increases lipid peroxidation and decreases antioxidant enzyme defenses in rat brain, suggesting an induction of oxidative stress. We presumed that oxidative stress might be, at least in part, associated with the neuronal dysfunction of patients affected by isolated sulfite oxidase deficiency.

Synaptic accumulation of PSD-95 and synaptic function regulated by phosphorylation of serine-295 of PSD-95

The scaffold protein PSD-95 promotes the maturation and strengthening of excitatory synapses, functions that require proper localization of PSD-95 in the postsynaptic density (PSD). Here we report that phosphorylation of ser-295 enhances the synaptic accumulation of PSD-95 and the ability of PSD-95 to recruit surface AMPA receptors and potentiate excitatory postsynaptic currents. We present evidence that a Rac1-JNK1 signaling pathway mediates ser-295 phosphorylation and regulates synaptic content of PSD-95. Ser-295 phosphorylation is suppressed by chronic elevation, and increased by chronic silencing, of synaptic activity. Rapid dephosphorylation of ser-295 occurs in response to NMDA treatment that causes chemical long-term depression (LTD). Overexpression of a phosphomimicking mutant (S295D) of PSD-95 inhibited NMDA-induced AMPA receptor internalization and blocked the induction of LTD. The data suggest that synaptic strength can be regulated by phosphorylation-dephosphorylation of ser-295 of PSD-95 and that synaptic depression requires the dephosphorylation of ser-295.

Involvement of hyperpolarization-activated cation channels in synaptic modulation

The frequency of miniature excitatory postsynaptic currents (mEPSCs) in cultured hippocampal neurons increases under the action of drugs that trigger a rise in the intracellular concentration of cyclicAMP. It is generally believed that this type of effect is mediated by protein kinase A. Here, we show that it largely depends on the activation of hyperpolarization-activated cation channels (Ih) by cyclicAMP. In mammals, Ih channels control membrane excitability, thanks to their function as ionic channels. Here, we show that the effect of Ih channels on glutamate release is not mediated by the depolarization induced by their activation and thus is not linked to the ionic channel aspect of Ih channels. This suggests that the Ih channel could be a bifunctional protein.

Fluctuations in brain concentrations of neurosteroids are not associated to changes in gephyrin levels

Fluctuations in the brain concentrations of neurosteroids are accompanied by changes in the expression of GABA(A) receptor subunits in the cerebral cortex and hippocampus. Here, we investigated the expression of the postsynaptic molecule gephyrin in the cerebral cortex and hippocampus of pregnant rats, as well as in rats treated chronically with contraceptive drugs. The amounts of gephyrin mRNA and protein did not change during pregnancy and after delivery, as well as in rats treated with ethynylestradiol (EE) and levonorgestrel (LNG) for 4 weeks. Similarly, using immunofluorescence and laser scanning confocal microscopy, we did not detect significant changes in the number and size of gephyrin-immunopositive clusters, which likely represent inhibitory postsynaptic sites. These findings indicate that the expression of gephyrin and the density of cortical inhibitory synapses are not influenced by endogenous neurosteroids.

Rapsyn interaction with calpain stabilizes AChR clusters at the neuromuscular junction

Agrin induces, whereas acetylcholine (ACh) disperses, ACh receptor (AChR) clusters during neuromuscular synaptogenesis. Such counteractive interaction leads to eventual dispersal of nonsynaptic AChR-rich sites and formation of receptor clusters at the postjunctional membrane. However, the underlying mechanisms are not well understood. Here we show that calpain, a calcium-dependent protease, is activated by the cholinergic stimulation and is required for induced dispersion of AChR clusters. Interestingly, the AChR-associated protein rapsyn interacted with calpain in an agrin-dependent manner, and this interaction inhibited the protease activity of calpain. Disrupting the endogenous rapsyn/calpain interaction enhanced CCh-induced dispersion of AChR clusters. Moreover, the loss of AChR clusters in agrin mutant mice was partially rescued by the inhibition of calpain via overexpressing calpastatin, an endogenous calpain inhibitor, or injecting calpeptin, a cell-permeable calpain inhibitor. These results demonstrate that calpain participates in ACh-induced dispersion of AChR clusters, and rapsyn stabilizes AChR clusters by suppressing calpain activity.

Reduction of gangliosides, phospholipids and cholesterol content in cerebral cortex of rats caused by chronic hypermethioninemia

Neurological dysfunction is observed in patients with severe hypermethioninemia, whose physiopathology is still poorly understood. In the current study we investigated the effect of chronic administration of methionine on the content and species of gangliosides and phospholipids, as well as on the concentration of cholesterol in rat cerebral cortex. Wistar rats received subcutaneous injections of methionine (1.34-2.68 micromol/g of body weight), twice a day, from the 6th to the 28th day of age and controls received saline. Animals were killed 12h after the last injection. Results showed that methionine administration significantly decreased the total content of lipids in cerebral cortex of rats. We also observed that this amino acid significantly reduced the absolute quantity of the major brain gangliosides (GM1, GD1a, GD1b and GT1b) and phospholipids (sphingomyelin, phosphatidylcholine and phosphatidylethanolamine). We also showed that Na+,K+-ATPase activity and TBARS were changed in cerebral cortex of rats subjected to hypermethioninemia. If confirmed in human beings, these data could suggest that the alteration in lipid composition, Na+,K+-ATPase activity and TBARS caused by methionine might contribute to the neurophysiopathology observed in hypermethioninemic patients.

[The interaction between glycine and GABA postsynaptic effects in the spinal cord neurons of frog Rana temporaria]

Patch-clamp study in the whole multipolar cell (presumably motoneuron) was performed, the cells having been mechanically isolated from the spinal cord of the frog Rana ridibunda. It was shown that GABA and glycine, when applied simultaneously, produced a transmembrane current. Its amplitude was lower than the summed amplitude of currents produced in the same neuron by separate applications of GABA and glycine. The investigation of this occlusion showed that the superfusion of the neurons with solution containing 0.2 mM of glycine totally blocked the responses to GABA (5 mM) application, and vice versa. The crossinhibition can lie in the basis of this phenomenon. It could be due to either the existence of a common receptor complex sensitive to both GABA and glycine or to interaction between GABA and glycine receptors.

Reversal of synaptic memory by Ca2+/calmodulin-dependent protein kinase II inhibitor

Long-term potentiation (LTP) is an activity-dependent strengthening of synapses that is thought to underlie memory storage. Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been a leading candidate as a memory molecule because it is persistently activated after LTP induction and can enhance transmission. Furthermore, a mutation that blocks persistent activation blocks LTP and forms of learning. However, direct evidence for a role of the kinase in maintaining synaptic strength has been lacking. Here, we show that a newly developed noncompetitive inhibitor of CaMKII strongly reduces synaptic transmission in the CA1 region of the hippocampal slice. This occurs through both presynaptic and postsynaptic action. To study the role of CaMKII in the maintenance of LTP, inhibitor was applied after LTP induction and then removed. Inhibition occurred in both LTP and control pathways but only partially recovered. The nonrecovering component was attributable primarily to a postsynaptic change. To test whether nonrecovery was attributable to a persistent reversal of LTP, we first saturated LTP and then transiently applied inhibitor. This procedure allowed additional LTP to be induced, indicating a reversal of an LTP maintenance mechanism. This is the first procedure that can reverse LTP by chemical means and suggests that a component of synaptic memory is attributable to CaMKII. The procedure also enhanced the LTP that could be induced in the control pathway, consistent with the idea that CaMKII is involved in controlling basal synaptic strength, perhaps as a result of LTP that occurred in vivo.

Rapid synapse elimination after postsynaptic protein synthesis inhibition in vivo

To examine the role of retrograde signals on synaptic maintenance, we inhibited protein synthesis in individual postsynaptic cells in vivo while monitoring presynaptic terminals. Within 12 h, axon terminals begin to atrophy and withdraw from normal postsynaptic sites. Structural similarities between this process and naturally occurring synapse elimination suggest that short-lived target derived factors not only participate in synaptic maintenance in adults, but also regulate elimination of connections during development.

Caffeine facilitation of glutamate release from rat cerebral cortex nerve terminals (synaptosomes) through activation protein kinase C pathway: an interaction with presynaptic adenosine A1 receptors

The present study used nerve terminals (synaptosomes) isolated from rat cerebral cortex to investigate the relationship between caffeine and 4-aminopyridine (4AP)-evoked endogenous excitatory neurotransmitter glutamate release. Micromolar concentrations of caffeine facilitated 4AP, but not KCl or ionomycin-evoked glutamate release from synaptosomes. This release facilitation resulted from an enhancement of vesicular and nonvesicular release and associated with an increase both in 4AP-evoked depolarization of the synaptosomal plasma membrane potential and in 4AP-evoked increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](C)). In addition, the release facilitation by caffeine was significantly reduced in synaptosomes pretreated with a wide spectrum blocker of N- and P/Q-type Ca(2+) channels, omega-conotoxin MVIIC. Furthermore, protein kinase C (PKC) activator and inhibitor, respectively, superseding or suppressing the caffeine-mediated facilitation of glutamate release. These results concluded that caffeine exerts their presynaptic facilitatory effect, likely through the activation of PKC pathway, which subsequently enhances terminal excitability and Ca(2+) entry to cause an increase in evoked glutamate release from rat cerebrocortical nerve terminals. Additionally, this release facilitation may involve an interaction of caffeine with presynaptic adenosine A1 receptors as adenosine A1 receptor inhibition abolished the caffeine-mediated facilitation of evoked glutamate release.

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 5: 2'-Substituted 6-nitroquipazines

Five C2'-substituted 6-nitroquipazine (6-NQ) derivatives were prepared and evaluated in terms of their biological abilities (K(i)) to displace [(3)H]citalopram binding to serotonin transporter. The relationship between their structure and biological activities revealed that shorter alkyl groups tend to possess higher binding affinity. Both compounds 12a and 12c were found to have the equally highest binding affinity (K(i)=0.43+/-0.02 nM).

GM1-ganglioside-induced Aβ assembly on synaptic membranes of cultured neurons

The cell-surface expression of GM1 ganglioside was studied using various cultured cells, including brain-derived endothelial cells, astrocytes, neuroblastoma cells (SH-SY5Y), and pheochromocytoma cells (PC12). GM1 ganglioside was detected only on the surface of native and nerve-growth-factor (NGF)-treated PC12 cells. We investigated whether GM1 ganglioside on the surface of these cells is sufficiently potent to induce the assembly of an exogenous soluble amyloid beta-protein (Abeta). A marked Abeta assembly was observed in the culture of NGF-treated PC12 cells. Notably, immunocytochemical study revealed that, despite the ubiquitous surface expression of GM1 ganglioside throughout cell bodies and neurites, Abeta assembly initially occurred at the terminals of SNAP25-immunopositive neurites. Abeta assembly in the culture was completely suppressed by the coincubation of Abeta with the subunit B of cholera toxin, a natural ligand for GM1 ganglioside, or 4396C, a monoclonal antibody specific to GM1-ganglioside-bound Abeta (GAbeta). In primary neuronal cultures, Abeta assembly initially occurred at synaptophysin-positive sites. These results suggest that the cell-surface expression of GM1 ganglioside is strictly cell-type-specific, and that expression of GM1 ganglioside on synaptic membranes is unique in terms of its high potency to induce Abeta assembly through the generation of GAbeta, which is an endogenous seed for Abeta assembly in Alzheimer brain.

[Methyl-beta-cyclodextrin influences glutamate transport in the rat brain nerve terminals by depletion of membrane cholesterol]

Role of membrane cholesterol in direct and reversed function of Na+ -dependent glutamate transporters and exocytosis was investigated. The depletion of membrane cholesterol by methyl-beta-cyclodextrin (MebetaCD) resulted in a dose-dependent significant reduction of the L-[14C]glutamate uptake by synaptosomes. Treatment of synaptosomes with 15 mM MebetaCD caused a decrease in the velocity of L-[14C]glutamate uptake by 49 +/- 4% (P < or = 0.05). The depolarization stimulated Ca2+ -dependent glutamate release that occurred via reverse functioning of glutamate transporters decreased insignificantly for 1 min from 8.0 +/- 0.4% to 6.7 +/- 0.4% of total accumulated synaptosomal label after MebetaCD treatment. The depletion of membrane cholesterol resulted in a reduction of the depolarization evoked exocytotic release from 8.0 +/- 1.0% to 4.2 +/- 1.0% of total synaptosomal label. Thus, cholesterol depletion was found to decrease significantly the Na+ -dependent uptake and exocytotic release of glutamate.

Brain-derived neurotrophic factor regulates AMPA receptor trafficking to post-synaptic densities via IP3R and TRPC calcium signaling

The change in the number of post-synaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamatergic receptors (AMPARs) by neuronal activity is recognized as a molecular basis of synaptic plasticity. Here, we show that Ca(2+) transients evoked by brain-derived neurotrophic factor (BDNF) induce translocation of a subunit of AMPAR, GluR1, but not NMDAR, to the post-synaptic membrane in cultured cortical pyramidal neurons. Among BDNF-induced Ca(2+) transients, that dependent on IP3R was fully required, while store-operated calcium influx through the non-selective cation channel TRPC (transient receptor potential canonical) was partially required for the GluR1 up-regulation, suggesting that spatial and temporal calcium signaling regulate translocation of GluR1 to the polarized membrane domain.

Isovaleric acid reduces Na+, K+-ATPase activity in synaptic membranes from cerebral cortex of young rats

1. Patients affected by isovaleric acidemia (IVAcidemia) suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. The objective of the present study was to investigate the in vitro effects of the metabolites that predominantly accumulate in IVAcidemia, namely isovaleric acid (IVA), 3-hydroxyisovaleric acid (3-OHIVA) and isovalerylglycine (IVG), on important parameters of energy metabolism, such as (14)CO(2) production from acetate and the activities of the respiratory chain complexes I-IV, creatine kinase and Na(+), K(+)-ATPase in synaptic plasma membranes from cerebral cortex homogenates of 30-day-old rats. 2. We observed that 3-OHIVA acid and IVG did not affect all the parameters analyzed. Similarly, (14)CO(2) production from acetate (Krebs cycle activity), the activities of creatine kinase, and of the respiratory chain complexes was not modified by IVA. In contrast, IVA exposition to cortical homogenates provoked a marked inhibition of Na(+), K(+)-ATPase activity. However, this activity was not changed when IVA was directly exposed to purified synaptic plasma membranes, suggesting an indirect effect of this organic acid on the enzyme. Furthermore, pretreatment of cortical homogenates with alpha-tocopherol and creatine totally prevented IVA-induced inhibition on Na(+), K(+)-ATPase activity from synaptic plasma membranes, whereas glutathione (GSH) and the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) did not alter this inhibition. 3. These data indicate that peroxide radicals were probably involved in this inhibitory effect. Since Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning and necessary to maintain neuronal excitability, it is presumed that the inhibitory effect of IVA on this activity may be involved in the pathophysiology of the neurological dysfunction of isovaleric acidemic patients.

Amphiphilic effects of dibucaine·HCl on rotational mobility of n-(9-anthroyloxy)stearic acid in neuronal and model membranes

We studied dibucaine's effects on specific locations of n-(9-anthroyloxy)palmitic acid or stearic acid (n-AS) within phospholipids of synaptosomal plasma membrane vesicles isolated from bovine cerebral cortex (SPMV) and model membranes. Giant unilamellar vesicles (GUVs) were prepared with total lipids (SPMVTL) and mixture of several phospholipids (SPMVPL) extracted from SPMV. Dibucaine.HCl increased rotational mobility (increased disordering) of hydrocarbon interior, but it decreased mobility (increased ordering) of membrane interface, in both native and model membranes. The degree of rotational mobility in accordance with the carbon atom numbers of phospholipids comprising neuronal and model membranes was in the order at the 16, 12, 9, 6 and 2 position of aliphatic chain present in phospholipids. The sensitivity of increasing or decreasing effect of rotational mobility of hydrocarbon interior or surface region by dibucaine.HCl differed depending on the neuronal and model membranes in the descending order of SPMV, SPMVPL and SPMVTL.

Dynorphin displaces binding at the glycine site of the NMDA receptor in the rat striatum

Binding of dynorphin A (1-17 and 2-17) to NMDA receptors in the rat striatum was studied by displacing radioactive ligands for the receptor's polyamine ([3H]-Ifenprodil), glutamate ([3H]-CGP-39653), dizocilpine ([3H]-MK-801) and glycine ([3H]-MDL105,519) sites with the neuropeptide. Dynorphin A selectively displaced [3H]-MDL105,519 and none of the other ligands. Opioid antagonists did not affect displacement. Thus, in the striatum dynorphin may regulate NMDA receptor function via the glycineB site through non-opioid mechanisms. This may contribute to the long-term changes in behavioral responsiveness seen after dopamine depletion and treatment with dopaminomimetics which are associated with substantial changes in striatal dynorphin metabolism.

Mechanisms underlying the rapid induction and sustained expression of synaptic homeostasis

Homeostatic signaling systems are thought to interface with the mechanisms of neural plasticity to achieve stable yet flexible neural circuitry. However, the time course, molecular design, and implementation of homeostatic signaling remain poorly defined. Here we demonstrate that a homeostatic increase in presynaptic neurotransmitter release can be induced within minutes following postsynaptic glutamate receptor blockade. The rapid induction of synaptic homeostasis is independent of new protein synthesis and does not require evoked neurotransmission, indicating that a change in the efficacy of spontaneous quantal release events is sufficient to trigger the induction of synaptic homeostasis. Finally, both the rapid induction and the sustained expression of synaptic homeostasis are blocked by mutations that disrupt the pore-forming subunit of the presynaptic Ca(V)2.1 calcium channel encoded by cacophony. These data confirm the presynaptic expression of synaptic homeostasis and implicate presynaptic Ca(V)2.1 in a homeostatic retrograde signaling system.

State-dependent mechanisms of LTP expression revealed by optical quantal analysis

The expression mechanism of long-term potentiation (LTP) remains controversial. Here we combine electrophysiology and Ca(2+) imaging to examine the role of silent synapses in LTP expression. Induction of LTP fails to change p(r) at these synapses but instead mediates an unmasking process that is sensitive to the inhibition of postsynaptic membrane fusion. Once unmasked, however, further potentiation of formerly silent synapses leads to an increase in p(r). The state of the synapse thus determines how LTP is expressed.

Neuroprotective effect of the surfactant poloxamer 188 in a model of intracranial hemorrhage in rats

OBJECT

Neuronal injury remains a leading cause of morbidity in both neonates and adults with injuries induced by intracranial hemorrhage, ischemia-reperfusion, and excitotoxicity. To date, a number of neuroprotective strategies have been evaluated, but they have shown little benefit. Poloxamer 188 (P-188), a membrane-active triblock copolymer, has been studied extensively as a cell-membrane sealant. The authors used an animal model to study the neuroprotectant effects of P-188 administered by intracisternal (IC) injection after experimentally induced intraparenchymal hemorrhage.

METHODS

Sprague-Dawley rats received an IC injection of either P-188 or vehicle (artificial cerebrospinal fluid) 10 minutes after striatal infusion of 50 microl of autologous blood. Animals from both treatment groups were killed either 2 or 7 days later. In a second experiment, after striatal blood infusion and early IC injection of either P-188 or vehicle, animals received daily IC injections of either P- 188 or vehicle for 5 days, and were killed 7 days after induction of the experimental hemorrhage. Striatal tissues were histologically analyzed for neuronal loss, and lesion volumes were determined. Lesion volumes in the animals that received a single dose of P-188 were significantly smaller (mean+/-standard deviation 18.3+/-4.3 mm(3), six rats; p = 0.04) than those in the control group (31.4+/-4.3 mm(3), seven rats) when measured 2 days postinjection; however, no difference in lesion volumes was present 7 days postinjection. Lesion volumes in the animals who received 5 days of daily P-188 injections were significantly smaller (1.50+/-0.58 mm(3), 10 rats; p = 0.04) than those in the corresponding control group (5.04+/-1.85 mm(3), eight rats) when measured at 7 days.

CONCLUSIONS

A single dose of P- 188 protects against early neuronal loss after hemorrhage but has no effect on long-term hemorrhage-induced neuronal loss. However, repeated daily P-188 treatment appears to produce effective long-term neuronal protection.

Effects of GABAA and GABAB agonists on interhemispheric inhibition in man

OBJECTIVE

Animal studies on neurotransmitter systems that mediate interhemispheric inhibition (IHI) suggest that, (i) callosal transmission is regulated by presynaptic GABA(B) receptors, and (ii) GABA(A)-ergic neurones mediate early IHI, whereas GABA(B)-ergic neurones mediate later IHI. In humans the mechanism is unclear. Interactions between cortical inhibitory circuits suggest a postsynaptic GABA(B)-ergic mechanism. We will here test this hypothesis.

METHODS

Short-latency IHI (s-IHI) and long-latency IHI (l-IHI) were evaluated using the paired pulse paradigm before and under medication with (i) a GABA(B)-agonist (baclofen) in 17 subjects, and (ii) a GABA(A)-agonist (midazolam) in 10 subjects participating twice.

RESULTS

Baclofen did not significantly enhance s-IHI. L-IHI between 20 and 50ms was significantly strengthened, and obtained also at ISIs between 100 and 200ms. Midazolam had no effect on s-IHI, whereas l-IHI was attenuated.

CONCLUSIONS

Our results support the hypothesis, that l-IHI in humans is mediated by postsynaptic GABA(B) receptors. GABA(A)-ergic medication resulted in attenuation of l-IHI. Regarding s-IHI, our results are inconclusive and require further investigation.

SIGNIFICANCE

This is the first human study evaluating the effect of baclofen on IHI, indicating that l-IHI is mediated by GABA(B)-ergic neurones. Because interhemispheric interaction is now also been used as a therapeutic approach, understanding the underlying neurotransmitter systems will be increasingly relevant.

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.

17-Beta-estradiol-mediated activation of extracellular-signal regulated kinase, phosphatidylinositol 3-kinase/protein kinase B-Akt and N-methyl-D-aspartate receptor phosphorylation in cortical synaptoneurosomes

In addition to its well-known activational mechanism, the steroid hormone 17-beta-estradiol (E2) has been shown to rapidly activate various signal transduction pathways that could participate in estrogen-mediated regulation of synaptic plasticity. Although the mechanisms underlying these effects are not clearly understood, it has been repeatedly suggested that they involve a plasma membrane receptor which has direct links to several intracellular signaling cascades. To further address the question of whether E2 acts directly at the synapse and through membrane-bound receptors, we studied the effects of E2 and of ligands of estrogen receptors on various signaling pathways in cortical synaptoneurosomes. Our results demonstrate that E2 elicits N-methyl-D-aspartate receptor phosphorylation and activates the extracellular signal-regulated kinase and the phosphatidylinositol 3-kinase/Akt signal transduction pathways in this cortical membrane preparation. Furthermore, we provide evidence for the presence of a membrane-bound estrogen receptor responsible for these effects in cortical synaptoneurosomes. Our study demonstrates that E2 directly acts at cortical synapses, and that synaptoneurosomes provide a useful system to investigate the mechanisms by which E2 regulates synaptic transmission and plasticity.

Evaluation of neuronal phosphoproteins as effectors of caffeine and mediators of striatal adenosine A2A receptor signaling

Adenosine A(2A) receptors are predominantly expressed in the dendrites of enkephalin-positive gamma-aminobutyric acidergic medium spiny neurons in the striatum. Evidence indicates that these receptors modulate striatal dopaminergic neurotransmission and regulate motor control, vigilance, alertness, and arousal. Although the physiological and behavioral correlates of adenosine A(2A) receptor signaling have been extensively studied using a combination of pharmacological and genetic tools, relatively little is known about the signal transduction pathways that mediate the diverse biological functions attributed to this adenosine receptor subtype. Using a candidate approach based on the coupling of these receptors to adenylate cyclase-activating G proteins, a number of membranal, cytosolic, and nuclear phosphoproteins regulated by PKA were evaluated as potential mediators of adenosine A(2A) receptor signaling in the striatum. Specifically, the adenosine A(2A) receptor agonist, CGS 21680, was used to determine whether the phosphorylation state of each of the following PKA targets is responsive to adenosine A(2A) receptor stimulation in this tissue: Ser40 of tyrosine hydroxylase, Ser9 of synapsin, Ser897 of the NR1 subunit of the N-methyl-d-aspartate-type glutamate receptor, Ser845 of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-type glutamate receptor, Ser94 of spinophilin, Thr34 of the dopamine- and cAMP-regulated phosphoprotein, M(r) 32,000, Ser133 of the cAMP-response element-binding protein, Thr286 of Ca(2+)/calmodulin-dependent protein kinase II, and Thr202/Tyr204 and Thr183/Tyr185 of the p44 and p42 isoforms, respectively, of mitogen-activated protein kinase. Although the substrates studied differed considerably in their responsiveness to selective adenosine A(2A) receptor activation, the phosphorylation state of all postsynaptic PKA targets was up-regulated in a time- and dose-dependent manner by treatment with CGS 21680, whereas presynaptic PKA substrates were unresponsive to this agent, consistent with the postsynaptic localization of adenosine A(2A) receptors. Finally, the phosphorylation state of these proteins was further assessed in vivo by systemic administration of caffeine.

Chronic treatment with mood stabilizers increases membrane GRK3 in rat frontal cortex

BACKGROUND

G-protein receptor kinases (GRKs) are a family of serine/threonine kinases involved in the homologous desensitization of agonist activated G-protein coupled receptors (GPCRs). G-protein coupled receptor supersensitivity, possibly as a result of decreased GRK, has been suggested in affective disorders.

METHODS

We used immunobloting to determine if chronic, therapeutically relevant doses of lithium (Li+), carbamazepine (CBZ), and valproate (VPA), would increase GRK2/3 protein levels in rat frontal cortex.

RESULTS

Chronic Li+ (24%) and CBZ (44%) significantly increased GRK3 in the membrane but not cytosol fractions. Chronic VPA had no effect on GRK3. G-protein receptor kinase 2 protein levels were unchanged by all treatments. The GRK3 membrane to cytosol ratio was increased significantly in Li+ and CBZ treated rats.

CONCLUSIONS

These results show that chronically administered Li+ and CBZ, but not VPA, increase the translocation of GRK3 from cytosol to membrane, possibly correcting supersensitivity of GPCRs in bipolar disorder.

Synaptic vesicles recycling spontaneously and during activity belong to the same vesicle pool

Recently, it has been claimed that vesicles recycling spontaneously and during activity belong to different pools. Here we simultaneously measured, using spectrally separable styryl dyes, the release kinetics of vesicles recycled spontaneously or upon stimulation and the effects of the v-ATPase blocker folimycin on the frequency of miniature postsynaptic currents in rat hippocampal neurons. Our results provide evidence as to the identities of the vesicle pools recycling at rest and during stimulation.

AMPA and NMDA receptors in P2 fractions of cocaine and cocaine-prazosin-treated rats

Cocaine sensitization results in the development of increased locomotion and stereotypy. It is accompanied by changes in glutamatergic trasmission that appear to be region-specific. The purpose of this article was to determine the effect(s) of cocaine and prazosin plus cocaine treatments on ionotropic glutamate receptors in rat cerebral cortex (CTX) and prefrontal cortex (PFC). Cocaine-sensitized rats (15 mg/kg, i.p. once for 5 days), withdrawn (7 days) and later challenged with a single cocaine dose, showed region-specific in NMDA-2A and Glu-R2 in the CTX and PFC membranes in cocaine- and prazosin-treated rats when compared to the saline controls. Co-administration of prazosin inhibits sensitization and changes in NMDA 2A and Glu-R2. Furthermore, prazosin inhibits the effect of cocaine in CTX and PFC on [(3)H]FW (AMPA agonist) binding when compared to controls. In cortex, cocaine treatment causes a marked increase in total binding, while in PFC there is a significant decrease. In both regions, cocaine-prazosin treatment attenuates the effects of cocaine. These results suggest that cocaine affects ionotropic glutamate receptors (NMDA and AMPA) and that prazosin inhibits such effects in a region-specific form in rat brain.