Presynaptic inhibition of glutamate transmission by α2 receptors in the VTA

The ventral tegmental area (VTA) forms part of the mesocorticolimbic system and plays a pivotal role in reward and reinforcing actions of drugs of abuse. Glutamate transmission within the VTA controls important aspects of goal-directed behavior and motivation. Noradrenergic receptors also present in the VTA have important functions in the modulation of neuronal activity. Here we studied the effects of α2 noradrenergic receptor activation in the alteration of glutamate neurotransmission in VTA dopaminergic neurons from male Sprague-Dawley rats. We used whole-cell patch-clamp recordings from putative VTA dopaminergic neurons and measured excitatory postsynaptic currents. Clonidine (40 μm) and UK 14,304 (40 μm), both α2 receptor agonists, reduced (approximately 40%) the amplitude of glutamate-induced excitatory postsynaptic currents. After clonidine administration, there was a dose-dependent reduction over the concentration range of 15-40 μm. Using yohimbine (20 μm) and two other α2 adrenergic receptor antagonists, idaxozan (40 μm) and atipemazole (20 μm), we demonstrated that the inhibitory action is specifically mediated by α2 receptors. Moreover, by inhibiting protein kinases with H-7 (75 μm), Rp-adenosine 3',5'-cyclic (11 μm) and chelerythrine (1 μm) it was shown that the clonidine-induced inhibition seems to involve a selective activation of the protein kinase C intracellular pathway. Increased paired-pulse ratios and changes in spontaneous and miniature excitatory postsynaptic current frequencies but not amplitudes indicated that the effect of the α2 agonist was presynaptically mediated. It is suggested that the suppression of glutamate excitatory inputs onto VTA dopaminergic neurons might be relevant in the regulation of reward and drug-seeking behaviors.     

Involvement of group Ⅲ metabotropic glutamate receptors in the modulation of spinal nociceptive signals

BACKGROUND： Previous morphological studies have demonstrated that group Ⅲ metabotropic glutamate receptors （mGluRs） are commonly found in nociceptive pathways, particularly in the terminals of primary afferent fibers in the spinal dorsal horn. OBJECTIVE： To investigate the role of group Ⅲ mGluRs in a rat model of spinal nociception by intrathecal administration of a selective agonist, L-Serine-O-phosphate （L-SOP）. DESIGN, TIME AND SETTING： A randomized, controlled, animal experiment. The study was performed at the Department of Physiology and Neurobiology, Shanxi Medical University, between March 2007 and May 2008. MATERIALS： L-SOP of group Ⅲ mGluRs （Tocris Cookson Ltd, UK）, formalin （Sigma, USA）, rabbit anti-c-Fos polyclonal antibody and biotin-labeled goat anti-rabbit IgG （Cell Signaling Technology, USA） were used in this study. METHODS： A total of 26 healthy Wistar rats, aged 1 month and weighing 100-120 g, were subjected to intrathecal catheter implantation. After 5-8 days, 10 rats were selected according to experimental requirements. L-SOP 250 nmol in 10 μL, or the equivalent volume of normal saline, was administered by intrathecal injection into the L3-5 region of the spinal cord in the experimental and control groups, respectively. After 15 minutes, formalin （5%, 50 μL） was subcutaneously injected into the plantar of the left hindpaw of each rat to establish formalin-induced pain models. MAIN OUTCOME MEASURES： Nociceptive behavioral responses and immunohistochemical examination of Fos expression. RESULTS： Intrathecal injection of L-SOP significantly attenuated the second phase nociceptive response compared with the control group （P 〈 0.05）, and Fos expression in the spinal dorsal horn was significantly decreased along with the number of Fos-like immunoreactive neurons （P 〈 0.05）. CONCLUSION： Group Ⅲ mGluRs are involved in the modulation of nociceptive signals, and their activation suppresses the transmission of nociceptive signals.     

Is activation of the metabotropic glutamate receptors impaired in the hippocampal CA1 area of the aged rat?

The effects of aging on activation of metabotropic glutamate (mGlu) receptors were studied in the CA1 field of hippocampal slices from young (3- to 4-month-old) and aged (24- to 27-month-old) Sprague-Dawley rats with the use of ex vivo electrophysiological recording techniques. The depolarization of membrane potential, the increase in input resistance, and the blockade of the afterhyperpolarization induced in pyramidal cells of young rats by bath application of the mGlu receptor agonist (±)-trans-1-aminocyclopentate-1,3-dicarboxylic acid were not altered in aged animals. No age-related changes of the depressive effects of the mGlu receptor agonist were found on either the excitatory glutamatergic postsynaptic potential or the GABA-mediated inhibitory postsynaptic potentials induced by the stimulation of the stratum radiatum. The magnitude of synaptic plasticity involving mGlu receptor activation, although weaker, was not significantly altered in aged rats. This absence of age-related effects on activation of mGlu receptors may be important in understanding the possible origins of the alterations in neuronal plasticity which occur in brain aging. Hippocampus 1997;7:455–459. © 1997 Wiley-Liss, Inc.     

Therapeutic potential of targeting glutamate receptors in Parkinson’s disease

Glutamate plays a complex role in many aspects of Parkinson’s disease including the loss of dopaminergic neurons, the classical motor symptoms as well as associated non-motor symptoms and the treatment-related side effect, l-DOPA-induced dyskinesia. This widespread involvement opens up possibilities for glutamate-based therapies to provide a more rounded approach to treatment than is afforded by current dopamine replacement therapies. Beneficial effects of blocking postsynaptic glutamate transmission have already been noted in a range of preclinical studies using antagonists of NMDA receptors or negative allosteric modulators of metabotropic glutamate receptor 5 (mGlu5), while positive allosteric modulators of mGlu4 in particular, although at an earlier stage of investigation, also look promising. This review addresses each of the key features of Parkinson’s disease in turn, summarising the contribution glutamate makes to that feature and presenting an up-to-date account of the potential for drugs acting at ionotropic or metabotropic glutamate receptors to provide relief. Whilst only a handful of these have progressed to clinical trials to date, notably NMDA and NR2B antagonists against motor symptoms and l-DOPA-induced dyskinesia, with mGlu5 negative allosteric modulators also against l-DOPA-induced dyskinesia, the mainly positive outcomes of these trials, coupled with supportive preclinical data for other strategies in animal models of Parkinson’s disease and l-DOPA-induced dyskinesia, raise cautious optimism that a glutamate-based therapeutic approach will have significant impact on the treatment of Parkinson’s disease.     

Functional polymorphisms in the human β4 subunit of nicotinic acetylcholine receptors

Human nicotinic acetylcholine receptor (nAChR) polymorphisms occur in different ethnic populations and may result in differences in nAChR ion channel properties. We have identified four nAChR beta 4 subunit (4) nucleotide variants: 392CT, 526CT, 538AG, and 1519AG. Their corresponding amino acid substitutions are: Thr to Ile at codon 91 (T91I), Arg to Trp at codon 136 (R136W), Ser to Gly at codon 140 (S140G), and Met to Val at codon 467 (M467V), respectively. The nAChR ion channel properties of these variants were studied and compared with the more-common (wild-type) allele as wild-types. The nAChRs (44 channels) were expressed heterologously in Xenopus oocytes and studied using the two-electrode voltage clamp technique to reveal functional differences between the wild-type and the variants. The receptors containing the R136W and M467V mutations (or variants) had a higher sensitivity to acetylcholine and lower EC₅₀ than the wild-type. The T91I mutation had lower sensitivity to acetylcholine and the EC₅₀ was larger than in wild-type nAChRs. The S140G mutation had a dose-response relationship that was similar to the wild-type. The T91I, R136W, and M467V mutations (or variants) also showed a slightly greater degree of steady-state desensitization than the wild-type in response to a 30-min exposure to one tenth of their EC₅₀. The present results demonstrate that human 4 nAChR DNA polymorphisms result in functional changes, and suggest that certain individuals with those variants may be more or less sensitive to cholinergic drugs or to dysfunctions associated with nicotinic cholinergic systems.     

The potential role of kynurenines in Alzheimer’s disease: pathomechanism and therapeutic possibilities by influencing the glutamate receptors

The pathomechanism of neurodegenerative disorders still poses a challenge to neuroscientists, and continuous research is under way with the aim of attaining an understanding of the exact background of these devastating diseases. The pathomechanism of Alzheimer’s disease (AD) is associated with characteristic neuropathological features such as extracellular amyloid-β and intracellular tau deposition. Glutamate excitotoxicity and neuroinflammation are also factors that are known to contribute to the neurodegenerative process, but a cerebrovascular dysfunction has recently also been implicated in AD. Current therapeutic tools offer moderate symptomatic treatment, but fail to reduce disease progression. The kynurenine pathway (KP) has been implicated in the development of neurodegenerative processes, and alterations in the KP have been demonstrated in both acute and chronic neurological disorders. Kynurenines have been suggested to be involved in the regulation of neurotransmission and in immunological processes. Targeting the KP, therefore, offers a valuable strategic option for the attenuation of glutamatergic excitotoxicity, and for neuroprotection.     

Presenilins, β-amyloid precursor protein and the molecular basis of Alzheimer's disease

Progressive cerebral deposition of the 40- and 42-residue amyloid β-proteins is an early and invariant event in all forms of Alzheimer's disease (AD). Aβ proteins are generated from the β-amyloid precursor protein (APP) via two sequential cleavages by proteases designated β-secretase and γ-secretase and are constitutively secreted by essentially all cells throughout life. APP can undergo these cleavages during its secretory trafficking to the cell surface, yet much of Aβ appears to be generated after APP reaches the surface, i.e. in the endosomal pathway. Presenilin (PS) 1 and 2, homologous proteins with eight transmembrane (TM) domains, play a critical role in the γ-secretase cleavage of APP. Deletion of presenilin 1 (PS1) in mice markedly decreases Aβ production, whereas AD-causing PS1 mutations selectively increase Aβ₄₂ production, thereby markedly accelerating amyloid plaque formation, both in humans and transgenic mice. Small amounts of APP and PS can be co-immunoprecipitated from cells, suggesting a direct role of PS1 in the cleavage of APP by γ-secretase. We recently observed and mutated two unusual intramembranous aspartate residues in TM6 and TM7 of each presenilin, resulting in complete blockage of the γ-secretase cleavage of APP, with no detectable Aβ production by cells. Because our protease inhibitor studies suggest that γ-secretase is an aspartyl protease, we hypothesize that these two key aspartates serve as the active site of an unprecedented intramembranous aspartyl protease (i.e. γ-secretase). The recent discovery that Notch, a protein critical for cell fate determination during development, also undergoes an intramembranous cleavage mediated by PS suggests that presenilin may be a key regulatory enzyme for several vital proteolytic events. Thought of in this context, AD may arise late in the post-reproductive life of humans as an ancillary metabolic consequence of a proteolytic mechanism which confers strong evolutionary advantage. Specific and potent inhibitors of γ-secretase/presenilin or of the recently cloned β-secretase may well prove useful for the treatment and the prevention of AD.     

Effects of reboxetine and sertraline treatments alone and in combination on the binding properties of cortical NMDA and β1-adrenergic receptors in an animal model of depression

Summary. Changes to the binding properties of cortical N-methyl-D-aspartic acid (NMDA) and beta-adrenergic receptors have both been reported as potential indicators of antidepressant activity. In the present investigation we examined the effects of the noradrenaline reuptake inhibitor, reboxetine, the serotonin reuptake inhibitor, sertraline, alone and in combination on the binding properties of cortical NMDA receptors and cortical β₁-adrenoceptors following 14 days of treatment in the olfactory bulbectomized rat model of depression. A decrease in the potency of glycine to displace the strychnine insensitive glycine antagonist [³H] 5,7 dichlorokynurenic acid (5,7 DCKA) was observed in cortical homogenates of OB rats when compared to sham-operated controls. Similarly, treatment with the combination of reboxetine and sertraline for 14 days produced a decrease in the potency of glycine when compared to vehicle treated controls. By contrast neither olfactory bulbectomy or drug treatment significantly altered basal or glycine enhanced binding of the non-competitive NMDA antagonist [³H] MK-801 in cortical homogenates. Reboxetine alone, and in combination with sertraline, down-regulated [³H]-CGP 12177 (a selective β-adrenoceptor antagonist) binding in both OB and sham-operated animals. The lack of a bulbectomy effect in the [³H] CGP-12177 binding assay, and the fact that olfactory bulbectomy and antidepressant treatments produce a similar change to the potency of glycine at the NMDA receptor, suggests that these tests do not provide a neurochemical marker for either the behavioral hyperactivity deficit or antidepressant response in the model. Received February 6, 2000; accepted March 6, 2000     

Respiratory responses evoked by blockades of ionotropic glutamate receptors within the Bötzinger complex and the pre-Bötzinger complex of the rabbit

The respiratory role of excitatory amino acid (EAA) receptors within the Bötzinger complex (BötC) and the pre‐Bötzinger complex (pre‐BötC) was investigated in α‐chloralose–urethane anaesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30–50 nL) of EAA receptor antagonists. Blockade of both N‐methyl‐d ‐aspartic acid (NMDA) and non‐NMDA receptors by 50 mm kynurenic acid (KYN) within the BötC induced a pattern of breathing characterized by low‐amplitude, high‐frequency irregular oscillations superimposed on tonic phrenic activity and successively the disappearance of respiratory rhythmicity in the presence of intense tonic inspiratory discharges (tonic apnea). KYN microinjections into the pre‐BötC caused similar respiratory responses that, however, never led to tonic apnea. Blockade of NMDA receptors by D(–)‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5; 1, 10 and 20 mm ) within the BötC induced increases in respiratory frequency and decreases in peak phrenic amplitude; the highest concentrations caused tonic apnea insensitive to chemical stimuli. Blockade of non‐NMDA receptors by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; 1, 10 and 20 mm ) within the BötC produced only less pronounced increases in respiratory frequency. Responses to D‐AP5 in the pre‐BötC were similar, although less pronounced than those elicited in the BötC and never characterized by tonic apnea. In the same region, CNQX provoked increases in respiratory frequency similar to those elicited in the BötC, associated with slight reductions in peak phrenic activity. The results show that EAA receptors within the investigated medullary subregions mediate a potent control on both the intensity and frequency of inspiratory activity, with a major role played by NMDA receptors.     

Functional expression of adrenergic and opioid receptors in Xenopus oocytes: interaction between α2- and β2-adrenergic receptors

We functionally expressed α₂-adrenergic, β₂-adrenergic, and δ-opioid receptors in Xenopus laevis oocytes. We detected receptor function as changes in currents carried by adenosine 3′,5′-cyclic monophosphate (cAMP)-regulated chloride channels provided by the cystic fibrosis transmembrane conductance regulator (CFTR) and recorded by two-electrode voltage clamp. Co-application of forskolin and isobutylmethylxanthine (IBMX) or IBMX alone produced currents with a reversal potential indicative of chloride ions only in oocytes previously injected with mRNA encoding CFTR. Isoproterenol produced concentration-dependent responses in oocytes injected with mRNA encoding β₂-adrenergic receptors and CFTR, and co-administration of propranolol antagonized these responses. Similarly, the α₂-adrenergic agonist UK14304 increased IBMX-induced currents only in oocytes injected with mRNA encoding α₂-adrenergic receptors and CFTR, and idazoxan antagonized these enhancements. The δ-opioid agonist DADLE produced concentration-related, naloxonc-reversible increases in IBMX- and forskolin-induced currents only in oocytes injected with mRNA encoding δ-opioid receptors and CFTR. In oocytes co-injected with α₂, β₂, and CFTR mRNAs, isobolographic analysis revealed an additive interaction between α₂ - and β₂-adrenergic receptors. These studies establish the oocyte as a cell system for studying the interactions among cAMP-modulating G protein-coupled receptors and provide another example of alternative coupling of α₂-adrenergic and δ-opioid receptors to G proteins, possibly G_s proteins, other than G_i proteins.     

In vitro and in vivo characterization of the bifunctional μ- and δ- opioid receptors ligand MCRT on mouse gastrointestinal motility

BackgroundChimeric opioid MCRT was a novel multi-target ligand based on morphiceptin and PFRTic-NH₂, and produced potent analgesia (ED₅₀ = 0.03 nmol/mouse) with less upper gastrointestinal dysmotility. In this study, we sought to perform the tests to evaluate the pharmacological effects of MCRT on distal colon motility and defecation function. Moreover, opioid receptor antagonists and neuropeptide FF (NPFF) receptor antagonists were utilized to explore the mechanisms.MethodsIsolated mouse colon bioassay and colonic bead expulsion were to characterize MCRT-induced inhibition of colonic motility in vitro and in vivo, respectively. Fecal pellet output was to evaluate the defecation function.Results(1) In vitro, MCRT increased colonic contraction via μ- and δ- opioid receptors (MOR and DOR). (2) In vivo, MCRT delayed colonic bead expulsion (ED₅₀ = 1.1 nmol/mouse) independent of opioid and NPFF receptors. (3) In vivo, MCRT inhibited fecal number (ED₅₀ = 1.43 nmol/mouse) and dry weight (ED₅₀ = 1.63 nmol/mouse), which was mediated by DOR partially but not MOR.Conclusions(1) Data indicated that MCRT was less prone to induce gastrointestinal dysmotility at analgesic doses, and provided a possibility for safer opioid analgesic. (2) Based on the mechanism explorations, we speculated on the existence of such an opioid receptor subtype or MOR/DOR heterodimer, which was involved in the central analgesia and the in vitro colonic contractions but not the central colonic dysmotility.     

α- and β-Adrenergic receptors differentially modulate the emission of spontaneous and amphetamine-induced 50-kHz ultrasonic vocalizations in adult rats

Amphetamine (AMPH) increases adult rat 50-kHz ultrasonic vocalizations, preferentially promoting frequency-modulated (FM) calls that have been proposed to reflect positive affect. The main objective of this study was to investigate a possible noradrenergic contribution to AMPH-induced calling. Adult male Long-Evans rats were tested with AMPH (1?mg/kg intraperitoneal) or saline combined with various systemic pretreatments: clonidine (α2 adrenergic agonist), prazosin (α1 antagonist), atipamezole (α2 antagonist), propranolol, betaxolol, and/or ICI 118,551 (β1/β2, β1, and β2 antagonists, respectively), nadolol (β1/β2 antagonist, peripheral only), or NAD-299 (5HT(1A) antagonist). In addition, effects of cirazoline (α1 adrenergic agonist) and cocaine (0.25-1.5?mg/kg intravenous) were studied alone. AMPH-induced calling was suppressed by low-dose clonidine and prazosin. Cirazoline and atipamezole did not significantly affect calling rate. Propranolol, without affecting the call rate, dose dependently promoted 'flat' calls under AMPH while suppressing 'trills,' thus reversing the effects of AMPH on the 'call subtype profile.' This effect of propranolol seemed to be mediated by simultaneous inhibition of CNS β1 and β2 rather than by 5HT(1A) receptors. Finally, cocaine elicited fewer calls than did AMPH, but produced the same shift in the call subtype profile. Taken together, these results reveal differential drug effects on flat vs trill vs other FM 50-kHz calls. These findings highlight the value of detailed call subtype analyses, and show that 50-kHz calls are associated with adrenergic α1- and β-receptor mechanisms. These preclinical findings suggest that noradrenergic contributions to psychostimulant subjective effects may warrant further investigation.     

The role of group I metabotropic glutamate receptors in neuronal excitotoxicity in alzheimer’s disease

Neurodegenerative diseases such as Huntington's disease, ischemia, and Alzheimer's disease (AD) are major causes of death. Recently, metabotropic glutamate receptors (mGluRs), a group of seven-transmembrane-domain proteins that couple to G-proteins, have become of interest for studies of pathogenesis. Group I mGluRs control the levels of second messengers such as inositol 1,4,5-triphosphate (IP3), Ca2+ ions and cAMP. They elicit the release of arachidonic acid via intracellular Ca2+ mobilization from intracellular stores such as mitochondria and endoplasmic reticulum. This facilitates the release of glutamate and could trigger the formation of neurofibrillary tangles, a pathological hallmark of AD. mGluRs regulate neuronal injury and survival, possibly through a series of downstream protein kinase and cysteine protease signaling pathways that affect mitochondrially mediated programmed cell death. They may also play a role in glutamate-induced neuronal death by facilitating Ca(II) mobilization. Hence, mGluRs have become a target for neuroprotective drug development. They represent a pharmacological path to a relatively subtle amelioration of neurotoxicity because they serve a modulatory rather than a direct role in excitatory glutamatergic transmission.     

Vesicular glutamate transporter-immunoreactivities in the vestibular nuclear complex of rat

1 Introduction Glutamate neurotransmission in life state involves glutamate uptake-exocytosis cycle at the locus of pre- synaptic compartment[1]. It has been well established that glutamate within the neuronal terminal should be firstly packaged into the synaptic vesicles before its release into the synaptic cleft, this process is fulfilled through the action of proton-driven carriers located to the synaptic vesicle membrane[1,2]. Recently, three isoforms of vesicular glutamate transporter (V…     

Antibodies to the rat β3 subunit of the γ-aminobutyric acidA receptors

Polymerase chain reaction was used to amplify the cDNA region that codes for the large intracellular loop of the β₃ subunit of the γ-aminobutyric acid_A/benzodiazepine receptors (GABA_AR/BZDR) from rat brain. The amplified cDNA was inserted into the prokaryotic expression vector pGEX-3X and a fusion protein containing glut athione-S-transferase and β₃ intracellular loop moieties was expressed in bacteria. The fusion protein was affinity-purified and it was used to raise a rabbit anti-β₃ antiserum. The anti-β₃ antiserum immunoprecipitated the γ-aminobutyric acid_A receptor from rat and bovine brain. Immunoblots of the affinity-purified GABA_AR/BZDR from bovine brain revealed that the anti-β₃ antiserum reacted with a 57 kDa peptide, whereas the monoclonal antibody 62-3G1 that recognized both β₂ and β₃ reacted with 55 and 57 kDa peptides. The anti-β₃ antiserum showed specificity for the β₃ subunit vs β₂ and β₁.     

Increased [³H]D-aspartate release and changes in glutamate receptor expression in the hippocampus of the mnd mouse

Neuronal ceroid lipofuscinoses (NCLs) are a group of hereditary childhood diseases characterized mainly by lipopigment accumulation and a multisystemic pattern of symptoms including mental retardation, seizures, motor impairment, and blindness. The mnd mouse, carrying a mutation in the Cln8 gene, has been proposed as a model of epilepsy with mental retardation (EPMR, ornorthern epilepsy). We recently showed neuronal hyperexcitability and seizure hypersusceptibility in mnd mice. To elucidate the cellular mechanisms related to hippocampal hyperexcitability, the glutamatergic transmission and the expression of postsynaptic glutamate receptors were investigated in hippocampus. A significant increase in either spontaneous or KCl‐stimulated overflow of [³H]D‐aspartate was found in mnd mice compared with controls. This increase was maintained after DL ‐threo‐β‐benzyloxyaspartic acid (TBOA) treatment, suggesting a nonrelevant role for transporter‐mediated release and supporting the involvement of exocytotic [³H]D‐aspartate release. Accordingly, Ca²⁺‐dependent overflow induced by ionomycin was also increased in mnd mice. Levels of glutamate 1–3 AMPA receptor subunits were increased, and levels of the NR2A NMDA receptor subunit were decreased in the hippocampus of mnd mice, suggesting an adaptive response to glutamate overstimulation. © 2012 Wiley Periodicals, Inc.     

In vivo and in vitro imaging of I₂ imidazoline receptors in the monkey brain

I₂ imidazoline receptors (I₂Rs) are associated with depression, Alzheimer's disease, and Huntington's disease. However, in vivo imaging of I₂Rs in the monkey brain has not been reported until now. We performed in vitro and in vivo imaging of (I₂Rs) in the monkey brain using ¹¹C‐labeled 2‐(3‐fluoro‐4‐tolyl)‐4,5‐dihydro‐1H‐imidazole ([¹¹C]FTIMD) which has high and selective affinity of I₂Rs. In an auto‐radiography (ARG) study, the distribution pattern of [¹¹C]FTIMD in the monkey brain was similar to that of [³H]idazoxan binging to I₂Rs in the human brain, which was previously described. The specific binding of [¹¹C]FTIMD accounted for >97% of total binding in brain regions existing I₂Rs. In positron emission tomography (PET) studies, the radioactivity was accumulated in brain regions existing I₂Rs ligand BU224, the accumulated radioactivity was decreased to approximately 66%–75% of the baseline measurement at 15–45 min after injection of [¹¹C]FTIMD. These results suggest that [¹¹C]FTIMD shows the specific‐binging to I₂Rs in the monkey brain as depicted by PET and ARG. We performed the first in vivo imaging of I₂Rs using [¹¹C]FTIMD in the monkey brain. Synapse, 2011. © 2010 Wiley‐Liss, Inc.     

Effects of blockade of ionotropic glutamate receptors on blood–brain barrier disruption in focal cerebral ischemia

To determine whether blockade of ionotropic glutamate receptors such as NMDA or AMPA receptors would attenuate blood–brain barrier (BBB) disruption in focal cerebral ischemia, 15 min before middle cerebral artery (MCA) occlusion, CGS-19755 or NBQX was injected intraperitoneally in rats. At 1 h after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (K _i ) of ¹⁴C-α-aminoisobutyric acid and the volume of dextran distribution. With MCA occlusion, K _i was increased in the ischemic cortex (IC) (316%). CGS-19755 attenuated the increase in K _i in the IC (−46%), but NBQX did not significantly decrease it. The difference in the volume of dextran distribution between the IC and the contralateral cortex became insignificant with the blockade of NMDA or AMPA receptors. Our data demonstrated that blockade of NMDA or AMPA receptors could attenuate the BBB disruption in focal cerebral ischemia and suggest that ionotropic glutamate receptors are involved in part in BBB disruption.     

Oxidative stress in the production and expression of neurotoxic β-amyloid

Although there is not yet any in vivo evidence of the neurotoxic action of β-amyloid in humans, it is well established that the insoluble form of full length β-amyloid 1-40, and the fragment comprised of amino acids 25-35, are both toxic in vitro to neurons in tissue culture. β-amyloid 25-35 increases cytosolic calcium in rat PC12 cells and in rat cortical neurons in primary culture by facilitating the entry of extracellular calcium into the cell. This effect is not altered by calcium channel blocking drugs but is prevented by U-83836E, one of the lazaroid anti-oxidant drugs, and by vitamin E. Similarly, the neurotoxic actions of β-amyloid 25-35 are also prevented by U-83836E and by vitamin E. These observations indicate that the actions of β-amyloid 25-35 are mediated by free radicals. In vivo, β-amyloid 1-40 is cleaved from a precursor protein that appears to be synthesized and inserted into cellular membranes following damage to cells. To form neurotoxic β -amyloid, the precursor protein must be cleaved within the transmembrane portion of its structure. In spite of extensive world-wide effort, an enzyme capable of doing this has not been found. However, a peroxidation cascade propagated through the lipid bilayer of the cellular membrane would cleave the precursor protein at a site needed to form β-amyloid. If this is the case, then free radicals would play a role both in the formation of β-amyloid and in its neurotoxic actions.