Synthesis and pharmacology of new enantiopure delta(3)-4-arylkainoids

Seven delta(3)-4-arylkainoids possessing various 4-position aromatic and heteroaromatic groups were synthesized and their apparent affinities were measured in order to explore the influences of 4-position electron density and stereochemistry on receptor affinity and specificity. Kainoids 1a-f were shown to be selective agonists at the NMDA receptor and the electron rich furanyl and thienyl analogues exhibited the highest affinities. Naphthylkainoid 1g proved to be a nonselective antagonist at the iGluRs.

Methionine sulfoximine shows excitotoxic actions in rat cortical slices

Methionine sulfoximine (MSO) is a rare amino acid. It occurs in nature or as a by-product of some forms of food processing. A notable example of the latter was a former method for bleaching wheat flour, using nitrogen trichloride, the "agene process," in use for most of the first 50 years of this century. "Agenized" flour was found to be responsible for various neurological disorders in animals, and MSO was identified as the toxic factor. The agene process was subsequently discontinued in the United States and the United Kingdom circa 1950. MSO inhibits the synthesis of both glutathione and glutamine, and it is possible that its actions on the nervous system arise from alterations in the amount or distribution of these molecules. Structurally, MSO resembles glutamate, an observation that has also raised the possibility that it might have more direct glutamate-like actions on neurons. In the present investigation, we report excitatory and toxic actions of MSO in an in vitro preparation of adult rat cortex. Field potential recordings in this preparation show that MSO application evokes a sustained depolarization, which can be blocked by the N-methyl-D-aspartate (NMDA) antagonist L-(+)-2-amino-5-phosphonovalerate (AP5). However, competition assays using MSO on [3H]CGP-39653 (DL-(E)-2-amino-4-propyl-1-phosphono-3-pentenoate) binding in rat cortical homogenates show only 20% displacement of total binding, suggesting that MSO is acting indirectly, perhaps by releasing glutamate. To investigate this possibility, we measured glutamate release during MSO application. Time course and dose-response experiments with MSO showed significant [3H]glutamate release, which was partially attenuated by AP5. To assess cellular toxicity, we measured lactate dehydrogenase (LDH) release from cortical sections exposed to MSO. MSO treatment led to a rapid increase in LDH activity, which could be blocked by AP5. These data suggest that MSO acts by increasing glutamate release, which then activates NMDA receptors, leading to excitotoxic cell death. These data suggest the possibility that MSO in processed flour had excitotoxic actions that may have been contributing factors to some human neuronal disorders.

A novel fluorescent GSH-adduct binds to the NMDA receptor

In an attempt to develop various fluorescent probes to label glutathione (GSH) receptors, we have serendipitously synthesized a probe that binds to and antagonizes the NMDA receptor. Probe 1, a GSH adduct, displaces the competitive NMDA antagonist [3H]-CGP 39653 with a higher affinity than NMDA or cysteine in rat synaptic membranes. In recording experiments from a rat cortical 'wedge' preparation, Probe 1 reversibly blocks both NMDA- and cysteine-induced depolarization. In mixed astrocyte-neuron tissue culture preparations, Probe 1 labels parts of both cell bodies as well as processes. The present data suggest that Probe 1 binds to the NMDA receptor and antagonizes channel function.

Methionine sulfoximine shows excitotoxic actions in rat cortical slices

Methionine sulfoximine (MSO) is a rare amino acid. It occurs in nature or as a by-product of some forms of food processing. A notable example of the latter was a former method for bleaching wheat flour, using nitrogen trichloride, the "agene process," in use for most of the first 50 years of this century. "Agenized" flour was found to be responsible for various neurological disorders in animals, and MSO was identified as the toxic factor. The agene process was subsequently discontinued in the United States and the United Kingdom circa 1950. MSO inhibits the synthesis of both glutathione and glutamine, and it is possible that its actions on the nervous system arise from alterations in the amount or distribution of these molecules. Structurally, MSO resembles glutamate, an observation that has also raised the possibility that it might have more direct glutamate-like actions on neurons. In the present investigation, we report excitatory and toxic actions of MSO in an in vitro preparation of adult rat cortex. Field potential recordings in this preparation show that MSO application evokes a sustained depolarization, which can be blocked by the N-methyl-D-aspartate (NMDA) antagonist L-(+)-2-amino-5-phosphonovalerate (AP5). However, competition assays using MSO on [3H]CGP-39653 (DL-(E)-2-amino-4-propyl-1-phosphono-3-pentenoate) binding in rat cortical homogenates show only 20% displacement of total binding, suggesting that MSO is acting indirectly, perhaps by releasing glutamate. To investigate this possibility, we measured glutamate release during MSO application. Time course and dose-response experiments with MSO showed significant [3H]glutamate release, which was partially attenuated by AP5. To assess cellular toxicity, we measured lactate dehydrogenase (LDH) release from cortical sections exposed to MSO. MSO treatment led to a rapid increase in LDH activity, which could be blocked by AP5. These data suggest that MSO acts by increasing glutamate release, which then activates NMDA receptors, leading to excitotoxic cell death. These data suggest the possibility that MSO in processed flour had excitotoxic actions that may have been contributing factors to some human neuronal disorders.Key words: agene process, glutamate release, lactate dehydrogenase, methionine sulfoximine, N-methyl-D-aspartate (NMDA) receptor, neurological disorders.

Pharmacological profile of the isomers of the GluR-specific agonist ATPA

We have synthesized the (R)- and (S)-isomers of 2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoate (ATPA) by stereochemically certain routes. Our studies in the rat cortical wedge preparation indicate that (R)-ATPA has no observable excitatory effect, while (S)-ATPA has an apparent K(D) of 16 microM. This excitatory response is unaffected by the specific N-methyl-D-aspartate (NMDA) antagonist, D-2-amino-5-phosphonopentanoic acid (DAP5) but is partially blocked by 6-nitro-sulfamoyl[f]quinoxalinedione (NBQX) at concentrations that attenuate the effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA), the effects are however reduced by the nonspecific antagonist kynurenate (KYN), indicating an interaction with a class of kainate receptor.

New analogues of ACPD with selective activity for group II metabotropic glutamate receptors

In this study we have determined the pharmacology of a series of 1-aminocyclopentane-1,3-dicarboxylic acid (1,3-ACPD) analogues at cloned metabotropic glutamic acid (mGlu) receptors. The new analogues comprise the four possible stereoisomers of 1-amino-1-carboxycyclopentane-3-acetic acid (1,3-homo-ACPD) and the racemic mixture of (1RS,2RS)-1-amino-1-carboxycyclopentane-2-acetic acid (1RS,2RS-homo-ACPD), (1RS,2RS)-Homo-ACPD was shown to be a competitive mGlu2 receptor antagonist with a KB of 391 microM. (1S,3R)-Homo-ACPD and (1R,3R)-homo-ACPD were both shown to be mGlu2 receptor agonists with EC50 values of 122 and 105 microM, respectively. Compared to (S)-Glu both compounds displayed partial agonism with intrinsic activities of 79% and 47%, respectively. (1S,3S)-Homo-ACPD was also found to be a partial mGlu2 receptor agonist with an intrinsic activity of 27% compared to (S)-Glu. None of the compounds tested showed any activity at mGlu1a or mGlu4a receptors. These homo-ACPD's show a higher degree of subtype selectivity than the parent compound (1SR,3RS)-ACPD. In addition none of the compounds demonstrated any activity at ionotropic Glu receptors.

Glutathione-induced sodium currents in neocortex

The present report demonstrates that glutathione (GSH), a tripeptide composed of glutamate, glycine and cysteine (gamma-L-glutamyl-L-cysteinyl-glycine) and best known as a free radical scavenger, elicits a large fast depolarizing potential when applied to cortical slices. This potential is maximally larger than that produced by either NMDA or AMPA. Like AMPA, the GSH current appears to be carried by sodium ions, but cannot be blocked by the glutamate receptor antagonists AP5 or DNQX. In addition, removal of external calcium or blockade of potassium currents by TEA does not diminish the GSH-induced potential. Together, these results suggest that GSH acts through its own receptor-mediated channels, independently of the known EAA receptors, and that its receptors may be a key, and previously unknown, component of cortical excitatory neurotransmission.

Molecular, functional, and pharmacological characterization of the metabotropic glutamate receptor type 5 splice variants: comparison with mGluR1

The main excitatory neurotransmitter in the brain, glutamate (Glu), activates not only receptor-channels, but also receptors coupled to G-protein called metabotropic Glu receptors (mGluRs). Eight genes coding for mGluRs have been characterized to date giving rise to even more proteins due to alternative splicing phenomena. Here we characterized a splice variant of mGluR5, called mGluR5b which contains a 32 amino acid fragment inserted in the cytoplasmic tail, 50 residues after the 7th transmembrane domain. mGluR5b mRNAs are present in different regions of the adult rat brain and are expressed at a higher level than mGluR5a mRNA. Functional analysis of mGluR5a and mGluR5b revealed that they share all the properties of mGluR1a, but not those of mGluR1b or 1c. Like mGluR1a, both mGluR5a and mGluR5b activate a rapid and transient current in Xenopus oocytes. When expressed in LLC-PK1 cells, they show the same subcellular distribution as mGluR1a, and stimulate both inositol phosphate (IP) and cAMP production. Moreover, cells expressing mGluR5a or mGluR5b, like those expressing mGluR1a have a higher basal PLC activity that is not inhibited by glutamate-pyruvate transaminase (GPT), suggesting that these receptors have an intrinsic activity. Interestingly, the pharmacological profiles of mGluR5a and b are identical, but different from that of mGluR1a. Most agonists, except glutamate, are more potent on mGluR5a/b than on mGluR1a. Interestingly, the mGluR1a antagonists MCPG and 4CPG have no effect on mGluR5a/b; 4C3HPG which is a full antagonist at mGluR1a is a partial agonist at mGluR5a/b. These results indicate that the long C-terminal intracellular domain present only in mGluR1a and mGluR5a/b, although not well conserved, is likely to be involved in the specific functional properties of these receptors. Although the ligand recognition sites of mGluR5a/b and mGluR1a are highly conserved, these receptors have different pharmacology.

Pharmacological characterization of metabotropic glutamate receptors in several types of brain cells in primary cultures

Several cDNAs coding for metabotropic glutamate receptors (mGluR1-7) have now been isolated. mGluR1 and -5 are positively coupled to phospholipase C, whereas mGluR2, -3, -4, -6, and -7 are negatively coupled to adenylyl cyclase (AC) when they are expressed in Chinese hamster ovary or baby hamster kidney cells. However, the exact transduction mechanisms of these receptors in their natural environment remain to be determined. In a previous work, we demonstrated that striatal neurons in primary culture expressed a mGluR that is negatively coupled to AC and that has a pharmacology different from that of mGluR2. In the present study, the pharmacology of mGluRs negatively coupled to AC in several neuronal types and in glial cells was compared with the pharmacology of mGluR2, -3, and -4. Like striatal neurons, cerebral cortical neurons express a mGluR that is able to inhibit AC both in intact cells and in membrane preparations, via a pertussis toxin-sensitive G protein. This mGluR has a pharmacological profile similar to that of mGluR3, because quisqualate is active at relatively low concentrations (EC50 < 100 microM). Similar experiments revealed that cerebellar granule cells expressed mGluR2-like and mGluR4-like receptors. Striatal glial cells also expressed a mGluR negatively coupled to AC via a pertussis toxin-sensitive G protein. However, only glutamate and aspartate, and not quisqualate, 2-(carboxycyclopropyl)glycine, trans-1-aminocyclopentane-1,3-dicarboxylate, or L-2-amino-4-phosphonobutyrate, were agonists for this glial mGluR. This pharmacology is different from that of any cloned mGluR. Reverse transcription associated with polymerase chain reaction revealed that mGluR2 and mGluR3 mRNAs are present in striatal, cortical, and cerebellar neurons but not in striatal glial cells. Interestingly, mGluR4 mRNA was found at a high level in cerebellar granule cells and at a lower level in cortical neurons and glial cells. However, the mGluR4-specific agonist L-2-amino-4-phosphonobutyrate was found to inhibit AC very slightly in granule cells only. In conclusion, our data show that mGluR2- and mGluR3-like receptors can directly inhibit AC in neurons, and they raise the question of whether mGluR4 is really negatively coupled to AC in its normal environment. We also present evidence for a new mGluR subtype expressed in glial cells.

Managing an outbreak of Staphylococcus aureus in a rehabilitation center

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen. This article describes the management of an out-break of MRSA in a comprehensive rehabilitation center affiliated with a major referral hospital in the Southeast. Collective efforts involving quality assurance measures, restricted admissions, staff education, and infection control surveillance were employed in managing this outbreak. An effective management program that included standardized isolation precautions was developed and implemented. An algorithm for managing infected or colonized patients is featured.

Characterization of a metabotropic glutamate receptor: direct negative coupling to adenylyl cyclase and involvement of a pertussis toxin-sensitive G protein

We have characterized a G-protein-coupled glutamate receptor in primary cultures of striatal neurons. Glutamate, quisqualate, or trans-1-aminocyclopentane-1,3-dicarboxylate inhibited by 30-40% either forskolin-stimulated cAMP production in intact cells or forskolin plus vasoactive intestinal peptide-activated adenylyl cyclase assayed in neuronal membrane preparations. These inhibitory effects were suppressed after treatment of striatal neurons with Bordetella pertussis toxin, suggesting the involvement of a heterotrimeric guanine nucleotide-binding protein (G protein) of the G(i)/G(o) subtype. The pharmacological profile of this glutamate receptor negatively coupled to adenylyl cyclase was different from that of the metabotropic Qp glutamate receptor coupled to phospholipase C in striatal neurons and from that of the recently cloned "mGluR2" glutamate receptor, which is negatively coupled to adenylyl cyclase when expressed in non-neuronal cells.

Both enantiomers of 1-aminocyclopentyl-1,3-dicarboxylate are full agonists of metabotropic glutamate receptors coupled to phospholipase C

We tested the effects of two enantiomers of a glutamate analogue, (trans)-1-aminocyclopentyl-1,3-dicarboxylate (t-ACPD), in striatal and cerebellar neurons in primary culture, as well as in Xenopus oocytes injected with cerebellar rat RNA. In the presence of MK-801, to avoid N-methyl-D-aspartate receptor activation, and 3 microM tetrodotoxin, both enantiomers [(1R,3S)- and (1S,3R)-t-ACPD] stimulated inositol phosphate (InsP) formation both in striatal neurons after 9-11 days in vitro [EC50, 3.7 +/- 1.1 microM, three experiments, and 33 +/- 7.5 microM, three experiments; maximal stimulatory effects, 252 +/- 15%, 13 experiments, and 269 +/- 15% of basal InsP formation, 14 experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively] and in cerebellar granule cells after 9-11 days in vitro [EC50, 50 +/- 18 microM, four experiments, and 307 +/- 92 microM, four experiments; maximal stimulatory effects, 401 +/- 71%, eight experiments, and 423 +/- 75% of basal InsP formation, eight experiments, for (1R,3S)- and (1S,3R)-t-ACPD, respectively]. These effects were not additive, indicating that both enantiomers acted at the same receptor molecule. When we monitored t-ACPD-induced increases in intracellular Ca2+ concentration ([Ca2+]i) with fura-2 ratio-imaging, we found that both enantiomers could elicit similar increase in [Ca2+]i, in the presence of 1 microM MK-801 and 3 microM tetrodotoxin; these effects were also observed in the absence of external Ca2+. Moreover, in Xenopus oocytes injected with adult rat cerebellar RNA, both drugs elicited oscillatory increases of a Ca(2+)-dependent chloride conductance, with similar efficacy, with (1R,3S)-t-ACPD being the more potent isomer. These data are in contradiction to previous reports showing that, in "immature" cerebellar neurons and adult hippocampal slices, (1S,3R)-t-ACPD was either the only active enantiomer or a full agonist of metabotropic receptors, with (1R,3S)-t-ACPD being ineffective or a partial agonist. However, performing these experiments in immature (2-3 days in vitro) striatal or cerebellar neurons, we found that only (1S,3R)-t-ACPD was active in stimulating [Ca2+]i.

The relationship between extended periods of immobility and decubitus ulcer formation in the acutely spinal cord-injured individual

Several variables may influence the development of decubitus ulcers during the acute treatment phase following spinal cord injury. Three independent variables were studied: level of injury, completeness of injury and length of time immobilized. Of these, length of immobilization exceeding 6 hours was associated with subsequent development of a sacral or occipital decubitus at a statistically significant level (p = .0094). The presence of a complete injury was associated with decubitus formation at a noticeable but statistically insignificant level (p = .0759). Cervical injuries were not associated with an increased rate of decubitus formation. Results suggested that initial treatment of acute spinal cord injuries should include the use of pressure relieving maneuvers or devices as soon as possible, especially in patients with anticipated extensive immobilization. Recognizing that risk of decubitus formation increases with immobilization time, the period of time involved in initial diagnosis and intervention should be kept to a minimum. This is particularly true in patients with complete spinal cord injuries.

The actions of a conformationally restricted analogue of aspartic acid on mammalian spinal neurones

The effects of the 4 stereoisomers of 1-aminocyclopentane-1,2-dicarboxylic acid (CPA), a conformationally restricted analogue of aspartic acid, have been examined on spinal dorsal horn neurones of the rat in vivo. Unlike the corresponding 1,3-dicarboxylate compounds which are glutamate analogues and markedly excitatory, the CPA isomers had no evident excitatory actions of their own. Three were weak and non-specific antagonists of other amino acid-induced excitations, while the (+)-trans isomer had a slight potentiating effect.

Rigid analogues as probes of excitatory amino acid receptors

The classes of compounds to be discussed are based on rigid analogues of glutamic and aspartic acids. The glutamate analogue 1-amino-1,3-cyclopentane dicarboxylic acid (1,3-ACPD) exists as two enantiomeric pairs of geometric isomers. The absolute configurations were assigned and the compounds were found to differentiate between the kainic acid (KA) and N-methyl-D-aspartic acid (NMDA) receptor subtypes when applied iontophoretically to hippocampal CA1 pyramidal neurones. The results indicate a high degree of specificity for the interaction of D-cis-1,3-ACPD with the NMDA receptor, while the remaining three isomers of 1,3-ACPD were KA-like in their action. The results are augmented with binding studies and patch clamp analysis. The second class of compound is the closely related aspartate analogue 1-amino-1,2-cyclopentane dicarboxylic acid (1,2-ACPD). The geometric isomers have been examined and found to be somewhat less active than their 1,3-ACPD counterparts; however, the cis isomer does have antagonistic properties against quisqualate (QA) evoked excitation. The results indicate that while the three-dimensional arrangement of functional groups is important for the activation of receptor subtypes, other considerations must be made, including stereochemistry and receptor affinity for sterically hindered analogues of excitatory amino acids.

Contingent reinforcement effects on movement responses of prison inmates to the Holtzman Inkblot Technique

Prison inmates were administered the Holtzman Inkblot Technique (HIT) under conditions of either verbal or nonverbal reinforcement of movement responses. Overall, there were no differences among the verbal, nonverbal, and control groups. Inmates charged with violent crimes were found to give the fewest movement responses. With crime category controlled, more movement responses were given under nonverbal conditions. There were no sex differences for movement responses but testing time increased significantly when administered by the female examiner.

Quinolinate activation of N-methyl-D-aspartate ion channels in rat hippocampal neurons

The cell attached configuration of the patch clamp method has been used to determine the single channel properties of the ion channel coupled to activation of the N-methyl-D-aspartate (NMDA) receptor by the endogenous NMDA agonist quinolinate. Openings of the NMDA channel were recorded from cultured CA1 hippocampal neurons over a hyperpolarizing potential range from cell resting potential. The slope conductance of the channel was 39 pS with 75 microM quinolinate, 1.8 mM Ca2+ and no Mg2+ in the patch pipette. The mean channel open times were decreased with hyperpolarization in an exponential manner with a mean slope of 0.6 ms/20 mV. Addition of Mg2+ to the pipette (at 30 microM) caused the mean open time, at a potential of -100 mV, to be decreased to a value about one-third that of control. The mean open times with quinolinate as the agonist were shorter for all potentials studied compared with activation of the NMDA receptor with NMDA or D-cis-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD). Both the mean open times and the channel amplitudes were significantly altered when the bath temperature was decreased; the Q10 values for both quantities were in excess of 2.8.

Single channel properties of the N-methyl-D-aspartate receptor channel using NMDA and NMDA agonists: on-cell recordings

The cell-attached patch-clamp mode has been applied in cultured rat hippocampal neurons to record single channel currents through the ion channel which is coupled to activation of the N-methyl-D-aspartate (NMDA) receptor. A channel, with a conductance of 37 pS, was studied with either NMDA or D-cis-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD) in the patch pipette. The mean open time of the channels with NMDA in the pipette was near 5 ms at -80 mV and was diminished about 0.7 ms for each 20 mV of hyperpolarization. The mean open times with ACPD in the pipette were longer at all voltages studied and for both agonists the mean open times showed an exponential dependence on patch potential. Distributions for the channel open times were generally well-fit with single exponentials, whereas distributions for closed times required two-component fits. In some instances, the open distributions also showed a second, rapid time component. When Mg2+ was included in the pipette (40 or 100 microM), the mean open times were significantly diminished with the effect increasing with the magnitude of the hyperpolarization. Both the amplitudes and mean open times of the NMDA channel were strongly modulated by temperature with Q10 values in excess of 2.5.

Executive roundup. Surviving the cash flow crunch

With today's dual pressures demanding quality health care at more affordable prices, it's little wonder many hospital executives are worried about their institutions' financial health--and even their jobs. Still, many of these officials are trying to keep a positive face on things. In part, they express the hope that creative product supply systems and better overall communication with vendors will generate efficiencies and help offset dwindling reserves. The following excerpts from a discussion among hospital authorities shed some light on the thought processes behind those beliefs and attitudes. The views, offered at a recent meeting sponsored in part by Medline Industries, are edited here as a round-up of selected opinion on issues affecting suppliers.

Structural requirements for activation of excitatory amino acid receptors in the rat spinal cord in vitro

The conformational requirements for activation of N-methyl-D-aspartate (NMDA) and quisqualate (QUIS) excitatory amino acid receptors on rat spinal neurones in vitro have been examined using a number of conformationally restricted compounds related to L-glutamate (L-GLU). The excitants were assigned to a receptor type on the basis of their susceptibility to blockade by D (-)-2-amino-5-phosphonvalerate (DAPV) and kynurenate (KYNA). When iontophoretically applied to unidentified neurones in the dorsal horn of spinal cord slices maintained in vitro, three of the isomers of 1-amino-1,3-cyclopentane dicarboxylate (ACPD) evoked excitations which were DAPV-sensitive and therefore were probably elicited via NMDA receptors. The fourth isomer (D-trans-(1R,3S)-ACPD) resembled quinolinate (QUIN) in its actions, and differed from both NMDA and QUIS. Several pyridine derivatives in addition to QUIN were tested, and both the 2,5- and 2,6-pyridine dicarboxylates evoked excitations which, like those produced by QUIS and L-GLU, were largely unaffected by both DAPV and KYNA and thus appeared due to activation of the QUIS receptor. 2,4-Pyridine dicarboxylate acted as a weak and unselective antagonist of amino acid-induced excitations. The results support an earlier conclusion that compounds reacting with the NMDA receptor do so in an extended configuration whereas the QUIS receptor has a more folded template. The possibility that QUIN reacts with a receptor different from those activated by other amino acids is considered.

Validation study of gas chromatographic determination of pentachlorophenol in animal liver

A validation study was conducted of a gas chromatographic procedure for the determination of pentachlorophenol (PCP) in chicken, pork, and beef liver. Five analysts representing 5 laboratories analyzed randomly numbered blind duplicates at 3 fortified tissue concentrations and one incurred tissue on 2 consecutive days. The PCP concentrations ranged from approximately 40 to 400 parts per billion (ppb). All data were reported to 3 significant figures in ppb. The coefficients of variation for repeatability were between 2.8 and 8.5%, except for the beef liver, at a mean value of 80 ppb PCP, where the CV was 11.3%. The CVs for reproducibility were in the range of 9.7-16.5% with little significant difference by species. The CV asymptotically approached 10% as the PCP level increased.

The actions of cyclopentane analogues of glutamic acid at binding sites for kainic and glutamic acids

The actions of the four isomers of 1-amino-1, 3-cyclopentane dicarboxylate (ACPD), a conformationally restricted analogue of glutamate, have been examined for their ability to displace radiolabelled kainate and glutamate from their binding sites on membranes prepared from rat brain. All four of the isomers reduced specific kainate binding, and all enhanced that of glutamate although one (D-(-)-cis-(1R,3R)-ACPD) was significantly more active in this respect than were the other three. The results are discussed in terms of the pharmacological effects of the isomers of ACPD on single neurones and the possible structural requirements of the NMDA and kainate receptors.

Synthesis, resolution, and absolute configuration of the isomers of the neuronal excitant 1-amino-1,3-cyclopentanedicarboxylic acid

The endogenous amino acids glutamate and aspartate depolarize mammalian neurons to produce excitation, and the rigid glutamate analogue 1-amino-1,3-cyclopentanedicarboxylic acid also has this effect. This compound exists as two pairs of geometric isomers, and in the present study the absolute configuration of the four isomers is assigned. The known (+)-S and (-)-R isomers of 3-oxocyclopentanecarboxylic acid were used as the basis for the synthesis. The cis and trans amino acids were obtained by fractional crystallization. Spectral data, including optical rotation, circular dichroism, and 13C nuclear magnetic resonance, are presented. The compounds were evaluated as excitants by microiontophoretic ejection into the dendritic region of impaled CA1 pyramidal neurons of rat hippocampal slices. One isomer, cis-1R,3R, mimicked completely the actions elicited by N-methyl-D-aspartic acid; the other three isomers were alpha-kainic acid like.

The action of quinolinate in the rat spinal cord in vitro

The responses of dorsal horn neurones to the excitatory amino acids quisqualate, kainate, N-methyl-D-aspartate (NMDA), and quinolinate have been examined in an in vitro preparation of the rat spinal cord. The antagonism of these responses by iontophoretically applied D-(-)-2-amino-5-phosphonovalerate (DAPV), kynurenate, and acridinate was tested, and the results were compared with data obtained from the spinal cord in vivo. The pattern of antagonism was similar in both preparations, although the potencies of agonists and antagonists were found to be significantly greater in vitro. The antagonism of amino acid induced firing of neurones was also recorded during the application of DAPV and kynurenate in the bathing medium. Dose-response curves and IC50 values were determined for these antagonists against all four agonists. The responses to quinolinate were antagonized differently from those to NMDA, quisqualate, or kainate, suggesting that quinolinate does not act specifically through the NMDA receptor as it does in other regions, nor does it appear to act via two or more of the three archetypal amino acid receptors. These findings suggest that a fourth amino acid receptor responsible for quinolinate's action in the spinal cord may exist.

Excitation of rat hippocampal neurones by the stereoisomers of cis- and trans-1-amino-1,3-cyclopentane dicarboxylate

Intracellular recordings were obtained from rat hippocampal neurons during the microiontophoretic ejection of the stereoisomers of cis- and trans-1-amino-1,3-cyclopentane dicarboxylate into the dendritic region (stratum radiatum) of the impaled cells. L-(+)-cis-1-Amino-1,3-cyclopentane dicarboxylate, D(+)-trans-1-amino-1,3-cyclopentane dicarboxylate, and L-(-)-trans-1-amino-1,3-cyclopentane dicarboxylate all evoked patterns of excitation resembling that elicited by kainate. All of these responses were unaffected by D-(-)-2-amino-5-phosphonovalerate but were antagonized at comparable currents by kynurenate. The excitation produced by D-(-)-cis-1-amino-1,3-cyclopentane dicarboxylate was similar to that evoked by N-methyl-D-aspartate. At low ejection currents a slow depolarization triggered rhythmic burst firing, each burst consisting of a depolarizing shift in membrane potential upon which were superimposed four to five action potentials. These responses were antagonized both by D-(-)-2-amino-5-phosphonovalerate and by kynurenate. The results are discussed with respect to the conformational requirements considered to be necessary for interaction at the kainate and N-methyl-D-aspartate receptors on CA1 pyramidal neurones. It is important to note that the isopropylene side chain of kainate is absent from the 1-amino-1-3-cyclopentane dicarboxylate molecule.

The N-methyl-D-aspartate receptor and burst firing of CA1 hippocampal pyramidal neurons

Previous intracellular investigations in the rat hippocampus have demonstrated that N-methyl-D-aspartate, ibotenate and 2,3-pyridine dicarboxylate (quinolinate) all evoke burst firing of CA1 pyramidal neurons, whereas kainate and quisqualate, which are thought to react with different receptors, do not. The purpose of the present study has been to investigate the ability of a series of compounds either to trigger burst firing or to antagonize this pattern of excitation. We report here that N-methyl-L-aspartate, 1,2-benzene dicarboxylate (phthalate) and methylene succinate (itaconate) are also capable of evoking burst firing. The results of this investigation suggest that since both quinolinate and phthalate are rigid planar molecules and only the 2 and 3 positioning of the carboxylates of pyridine was active, a cis configuration of the carboxyls with respect to the 2,3 carbon bond appears to be necessary for excitation. While a nitrogen atom is not necessary for activity (this is absent in phthalate and itaconate) a third functional group, bearing at least a partial positive charge, and in a position alpha to one of the carboxyl groups is required. The requirements for pyridine derivatives to trigger burst firing is similar to that reported as necessary for evoking convulsions and neurotoxicity after intrahippocampal infusion and a correlation between N-methyl-D-aspartate-like burst firing and depolarization and this neuropathology is considered. An important observation has been that the addition of a benzene ring to either quinolinate or phthalate to yield 2,3-quinoline dicarboxylate and 2,3-napthalene dicarboxylate, respectively, converted these excitants into antagonists of burst firing.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel spinal cord slice preparation from the rat

A spinal cord slice preparation is described. The lumbar enlargement of weanling rats is exposed by laminectomy, the dorsal and ventral roots cut and a portion of cord consisting of about 4 segments removed and chilled to 3 degrees C. A modified tissue chopper is used to produce 400 micron dorsoventral longitudinal slices. The slices are maintained in a low-volume, continuously perfused tissue chamber at the interface between warm moist 95% O2/5% CO2 and oxygenated artificial cerebrospinal fluid, and remain viable for over 8 h. An extracellular recording of excitatory amino acid-induced activity of a dorsal horn lamina IV cell is shown. Excitatory amino acid antagonists applied iontophoretically and in the perfusate have actions similar to those in the adult spinal cord in vivo. This in vitro preparation of the cord has permitted stable extracellular recordings from single cells of 2 h or more, and has the potential for intracellular investigation of spinal cord neurones.

Acridinic acid: a new antagonist of amino acid-induced excitations of central neurones

The actions of acridinic acid (2,3-quinoline dicarboxylic acid), a new derivative of quinolinic acid, as an antagonist of amino acid-induced excitations are described. Acridinate, like kynurenate, in the cerebral cortex reduced the effects of all amino acids equally, but in the spinal cord was significantly less active against quisqualate.

Ca2+-dependent depolarization and burst firing of rat CA1 pyramidal neurones induced by N-methyl-D-aspartic acid and quinolinic acid: antagonism by 2-amino-5-phosphonovaleric and kynurenic acids

The excitatory effects of microiontophoretically applied quisqualic (QUIS), N-methyl-D-aspartic (NMDA), and quinolinic (QUIN) acids were investigated using intracellular recording from CAl pyramidal neurones in slices of rat hippocampus. QUIS evoked only simple action potentials superimposed upon a depolarization which attained a clear plateau. When this level had been reached, increased ejecting currents did not produce further depolarization. By contrast, with low currents NMDA and QUIN elicited small membrane depolarizations which triggered bursts of action potentials superimposed upon rhythmically occurring depolarizing shifts. Larger currents caused depolarization which if sufficiently large completely blocked spike activity. Tetrodotoxin (TTX) prevented the spikes evoked by QUIS and the bursts of action potentials seen with NMDA and QUIN, and the rhythmic depolarizing shifts then appeared as broad spikes of up to 50 mV in amplitude. These and the underlying membrane depolarization were blocked by Co2+, by the NMDA antagonist D(-)-2-amino-5-phosphonovaleric acid (DAPV), and by kynurenic acid (KYNU). It thus appears that the depolarization and burst firing of rat CAl pyramidal neurones elicited by NMDA and QUIN are Ca2+ dependent while the actions of QUIS are not.

D-aminophosphonovalerate is 100-fold more powerful than D-alpha-aminoadipate in blocking N-methylaspartate neurotoxicity

Here we report that the D-isomers of 2-amino-5-phosphonovalerate (D-APV) and alpha-amino-adipate (D-alpha AA) protect arcuate hypothalamic neurons from the potent excitotoxic activity of N-methylaspartate (NMA). Consistent with evidence that APV is much more powerful than alpha AA in antagonizing the neuroexcitatory activity of NMA, we found D-APV nearly 100 times more powerful than D-alpha AA in preventing NMA from destroying arcuate neurons.

Phosphonate analogues of carboxylic acids as aminoacid antagonists on rat cortical neurones

Phosphonate analogues of carboxylic acids have been tested as antagonists of excitatory aminoacids in rat cerebral cortex. (+/-)--2-Amino-7-phosphono-heptanoic acid and the (-)-D-isomer of the pentanoate derivative were more potent and selective antagonists of N-methyl-D-aspartate (NMDA) than compounds tested previously. The results support the view that a distinct population of receptors exists which are preferentially activated by NMDA.