Repression of the genes for lysine biosynthesis in Saccharomyces cerevisiae is caused by limitation of Lys14-dependent transcriptional activation

The product of the LYS14 gene of Saccharomyces cerevisiae activates the transcription of at least four genes involved in lysine biosynthesis. Physiological and genetic studies indicate that this activation is dependent on the inducer alpha-aminoadipate semialdehyde, an intermediate of the pathway. The gene LYS14 was sequenced and, from its nucleotide sequence, predicted to encode a 790-amino-acid protein carrying a cysteine-rich DNA-binding motif of the Zn(II)2Cys6 type in its N-terminal portion. Deletion of this N-terminal portion including the cysteine-rich domain resulted in the loss of LYS14 function. To test the function of Lys14 as a transcriptional activator, this protein without its DNA-binding motif was fused to the DNA-binding domain of the Escherichia coli LexA protein. The resulting LexA-Lys14 hybrid protein was capable of activating transcription from a promoter containing a lexA operator, thus confirming the transcriptional activation function of Lys14. Furthermore, evidence that this function, which is dependent on the presence of alpha-aminoadipate semialdehyde, is antagonized by lysine was obtained. Such findings suggest that activation by alpha-aminoadipate semialdehyde and the apparent repression by lysine are related mechanisms. Lysine possibly acts by limiting the supply of the coinducer, alpha-aminoadipate semialdehyde.

Inhibition of the glutamate transporter and glial enzymes in rat striatum by the gliotoxin, alpha aminoadipate

1. The effect of the gliotoxic analogue of glutamate, alpha aminoadipate, on the high affinity transport of D-[3H]-aspartate into a crude striatal P2 preparation, and on the activity of two enzymes of which glutamate is the substrate has been examined. 2. The L-isomer of alpha aminoadipate competitively inhibited the transport protein, with a Ki value of 192 microM, whereas the D-isomer of alpha aminoadipate was ineffective. The potent convulsant, L-methionine-S-sulphoximine, was also without effect on the activity of the glutamate transport protein. 3. L-alpha Aminoadipate was a competitive inhibitor of both glutamine synthetase, and gamma-glutamylcysteine synthetase, with Ki values of 209 microM and 7 mM respectively. Once again, the D-isomer of alpha aminoadipate was a far weaker inhibitor of either enzyme. 4. The results are discussed in terms of the mechanism of action of alpha aminoadipate in causing toxicity of glial cells.

The synthesis and thymidylate synthase inhibitory activity of L-gamma-L-linked dipeptide and L-gamma-amide analogues of 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI 198583)

Sixteen gamma-linked dipeptide and four L-Glu-gamma-amide analogues of 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (ICI 198583) have been synthesized and evaluated as inhibitors of thymidylate synthase (TS). Z-blocked L-Glu-gamma-L-linked dipeptides and L-Glu-gamma-amides were prepared by condensing alpha-tert-butyl-N-(benzyloxycarbonyl)-L-glutamic acid with the appropriate tert-butyl-protected L-amino acid or amine. The Z group was removed by catalytic hydrogenolysis, and the resulting dipeptides or L-Glu-gamma-amides were condensed with the appropriate pteroic acid analogue trifluoroacetate salt using diethyl cyanophosphoridate as coupling reagent. Deprotection with trifluoroacetic acid in the final step gave the desired quinazoline gamma-linked dipeptides and L-Glu-gamma-amides as their trifluoroacetate salts. Nearly all the dipeptide analogues were potent inhibitors of TS, the best being ICI 198583-gamma-L-2-aminoadipate (IC50 = 2 nM). Several of these dipeptides were found to be susceptible to enzymatic hydrolysis in mice. The quinazoline monocarboxylate L-Glu-gamma-amides, lacking an alpha'-carboxyl group, are less active against TS and L1210 cell growth but are also not susceptible to enzymatic hydrolysis in mice.

Effects of excitatory amino acid transmitters on hypothalamic corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP) release in vitro: implications in pituitary-adrenal regulation

The effect of excitatory amino acid (EAA) on the release of CRH and AVP--two major neurohumoral activators of the hypothalamic-pituitary-adrenal axis--was studied by in vitro perifusion of hypothalamic organ explants with various concentrations of EAA receptor agonists and antagonists. The agonists L-glutamate (GLU), kainic acid (KAIN) and L-aspartate (ASP) significantly decreased CRH release, while N-methyl-D-aspartate (NMDA) and quisqualic acid (QUIS) did not affect this parameter. AVP release was significantly stimulated by ASP and NMDA, decreased by KAIN and QUIS, and not influenced by GLU. Co-perifusion with equimolar concentrations of ASP and the selective NMDA receptor antagonist D-alpha-aminoadipic acid (aAA) partially diminished the effect of ASP on AVP release, but failed to affect ASP-induced suppression of CRH secretion. The broad-spectrum EAA receptor antagonist kynurenic acid (KYN) completely abolished ASP effects on CRH and AVP release in vitro. The results suggest that EAA transmitters might participate in the regulation of hypothalamic-pituitary-adrenal axis by differentially affecting the release of the two major ACTH secretagogues. In addition, EAA effects on hypothalamic CRH and AVP secretion appear to employ more than one subtype of amino acid receptors.

Induction of c-fos by excitatory amino acids in developing chick retina is affected by changes in cellular interactions

Cell contact is important for normal maturation of chicken retinal Müller cells. In order to gain a better understanding as to how this occurs, we examined the ability of retinal cells with altered cell contacts to respond to an environmental stimulus. The response of Müller cells cultured under conditions which alter cell contacts was measured by activating intracellular signaling systems leading to induction of the early-inducible gene c-fos. Chicken retinal cells were cultured as explants, reaggregates, and monolayers and exposed to extracellular stimuli in the form of the excitatory amino acids D,L-alpha aminoadipic acid (AAA) and N-methyl-D,L-aspartic acid (NMDA). Each culture was exposed to 1.25 mM AAA, 2.5 mM AAA, 50 microM NMDA, or 100 microM NMDA. Toxicity was assessed histologically and by immunocytochemical labeling of Müller cells after 2 days of exposure. Activation of c-fos was determined by Western blot analysis for Fos protein after 30, 60, and 120 minutes of exposure. Exposure to AAA led to a loss of Müller cells in explant and reaggregate cultures; however, Müller cells in monolayer culture were not susceptible to AAA at either dose. NMDA was toxic to a specific population of neurons under all three culture conditions. Fos protein expression paralleled the histologic findings. Fos protein was significantly elevated after exposure to either dose of AAA in explant and reaggregate cultures but not in monolayer cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Quisqualic acid induced sensitization and the active uptake of L-quisqualic acid by hippocampal slices

Hippocampal CA1 pyramidal cell neurons are sensitized to depolarization by L-2-amino-4-phosphonobutanoic acid (L-AP4) following exposure to L-quisqualic acid (QUIS). It has been proposed that induction of this 'QUIS-effect' involves uptake of L-QUIS by hippocampal cells. We have used o-phthaldialdehyde (OPA) derivatization and high performance liquid chromatographic (HPLC) separation of extracts from hippocampal slices which have been exposed to varied concentrations of L-QUIS to investigate L-QUIS uptake into hippocampal slices. We observe uptake rates such that the internal concentration of L-QUIS exceeds the bath concentration within 7 min. The fact that this uptake is concentrative indicates that it is mediated by an active transport system. In addition, uptake of L-QUIS may be linked to the induction of the QUIS-effect. At low concentrations of L-QUIS (< 4 microM), the QUIS-effect is only partially induced within the 4 min incubation time which maximally induces the effect when 16 microM L-QUIS is used. However, repeated 4 min exposure periods of slices to low L-QUIS concentrations will eventually induce the QUIS-effect even when each exposure is separated by extensive washout periods. Hence induction is dependent on both concentration and total exposure time. We also examined the effects of L-alpha-aminoadipic acid and L-serine-O-sulfate on the rate of L-QUIS uptake. Exposure of slices to these compounds prior to treatment with L-QUIS will block the physiological effects of L-QUIS. We found that these 'pre-blocking' compounds did not decrease the rate of L-QUIS uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of glutamate and NMDA sensitivity of neurons within the cochlear nuclear complex of kittens

1. The effects of glutamate, N-methyl-D-aspartate (NMDA), and NMDA receptor antagonists, D-alpha-aminoadipate (D alpha AA) and 2-amino-5-phosphonovalerate (APV), microionophoretically applied onto neurons in the caudal divisions (posteroventral and dorsal subnuclei) of the cochlear nuclear complex (CN), were investigated during postnatal development in kittens with the use of extracellular techniques. From birth through postnatal day 7, microionophoretically applied glutamate elevated the acoustically evoked discharge rates of nearly 80% of neurons studied. Although fewer neurons were studied with the use of NMDA, approximately 65% of these responded to this glutamatergic agonist, and no developmental changes in the percentage of responsive neurons were observed. The actions of NMDA antagonists were studied in a relatively small number of neurons, and results support the supposition that glutamate, or a glutamate-like substance, acts as a CN neurotransmitter throughout postnatal life. 2. Approximately 64% of CN neurons encountered among neonatal animals were unresponsive to acoustic stimulation, even at the highest output levels available (> 120 dB SPL). That percentage declined monotonically during the next three postnatal days, such that approximately 23% of neurons encountered were unresponsive to acoustic stimulation on the third day. Essentially all encountered neurons were responsive to acoustic stimulation by the middle of the second postnatal week. Under conditions of simultaneous glutamate and acoustic stimulation, neurons in this general class of "acoustically unresponsive" neurons segregated into two groups. Glutamate increased spontaneous discharge rate in 45% of the neurons studied, however, these units remained acoustically unresponsive during combined sound and excitatory amino acid stimulation (group A1). In the second group (A2), 55% of the neurons that were acoustically unresponsive under control (sound alone) conditions responded to the acoustic component of the combined acoustic and glutamate stimulation (the experimental condition) in a frequency-dependent manner. A2 neurons exhibited temporal firing patterns characteristic of acoustically responsive neurons of corresponding age, suggesting that these neurons are functionally connected to the auditory periphery, whereas A1 neurons are not. 3. Dose-response curves were either sigmoidal or linear over the range that measurements were made, and maximum discharge rates evoked by high doses of glutamate in the youngest animals studied tended to be lower than those produced by acoustic stimulation alone in older animals. These results suggest that intrinsic properties contribute to the mechanism(s) that limits neuronal responsiveness. Average dose-response curve slopes were higher for neurons recorded from older animals, also indicating that intrinsic properties regulating dynamic response range are acquired postnatally in the kitten CN.(ABSTRACT TRUNCATED AT 400 WORDS)

The time course of glutamate in the synaptic cleft

The peak concentration and rate of clearance of neurotransmitter from the synaptic cleft are important determinants of synaptic function, yet the neurotransmitter concentration time course is unknown at synapses in the brain. The time course of free glutamate in the cleft was estimated by kinetic analysis of the displacement of a rapidly dissociating competitive antagonist from N-methyl-D-aspartate (NMDA) receptors during synaptic transmission. Glutamate peaked at 1.1 millimolar and decayed with a time constant of 1.2 milliseconds at cultured hippocampal synapses. This time course implies that transmitter saturates postsynaptic NMDA receptors. However, glutamate dissociates much more rapidly from alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Thus, the time course of free glutamate predicts that dissociation contributes to the decay of the AMPA receptor-mediated postsynaptic current.

Evidence that non-NMDA receptors are involved in the excitatory pathway from the pedunculopontine region to nigrostriatal dopaminergic neurons

Extracellular single-neuron recordings were obtained from electrophysiologically identified nigrostriatal neurons in chloral hydrate anesthetized rats, in order to test the hypothesis that excitatory amino acid receptors are involved in responses of these neurons to electrical stimulation of the pontine region where the pedunculopontine nucleus (PPN) is located. The effects of iontophoretic application of excitatory amino acids and their antagonists as well as of cholinergic antagonists were tested on the fast orthodromic excitation of nigrostriatal neurons evoked by stimulation of the PPN region. The N-methyl-D-aspartate (NMDA) receptor antagonist D-alpha-aminoadipic acid as well as the cholinergic receptor antagonists mecamylamine and atropine failed to suppress the synaptic excitation of nigral neurons. The NMDA receptor antagonist DL-2-amino-5-phosphonovalerate exerted a weak depressant action on the synaptic response in a few neurons only. On the contrary, the broad spectrum antagonists of excitatory amino acid receptors kynurenic acid and gamma-D-glutamyl-amino-methyl-sulphonate were found to block simultaneously both the synaptic excitation and the neuronal responses to iontophoretic pulses of glutamate while leaving unaffected the neuronal responses to local application of acetylcholine or carbachol. The competitive antagonist of non-NMDA receptors 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline suppressed the synaptic excitation at ejection currents which antagonized neuronal responses to quisqualate and kainate. These results suggest that PPN excitatory fibers synapsing onto pars compacta nigrostriatal neurons utilize an excitatory amino acid as a synaptic transmitter acting preferentially on non-NMDA receptors.

Rapid increase of intracellular Ca2+ concentration caused by aminoadipic acid enantiomers in retinal Müller cells and neurons in vitro

The ability of the gliotoxic compounds D,L-, D- or L-2-aminoadipic acid (AAA) to increase selectively the intracellular concentration of free calcium ion ([Ca2+]i) was examined in Müller cells cultured with or without retinal neurons. The monitoring of [Ca2+]i following exposure to 0.06 to 6 mM AAA was performed by a microfluorometry using a fluorescent Ca2+ indicator, Fura-2 acetoxymethyl ester. A rapid increase of [Ca2+]i occurred in the Müller cells following exposure to a relatively low concentration of the L-isomer. This is compatible with the known strong gliotoxicity of this isomer. The D,L- and D-forms of AAA activated neurons at low concentrations and activated the Müller cells at higher concentrations. The D-isomer appears to act selectively on retinal neurons and may be an agonist of an excitatory amino acid receptor. These results indicate that the ability of AAA to elevate cytosolic [Ca2+]i depends on the stereospecificity of the AAA and on cell type.

Synthesis, absolute configuration and activity at N-methyl-D-aspartic acid (NMDA) receptor of the four D-2-amino-4,5-methano-adipate diastereoisomers

The four D-2-amino-4,5-methano-adipates 26, 27, 32, 33 were synthesized and their biological activity at the N-methyl-D-aspartate (NMDA) receptor was assessed. The synthesis involved as a key step a rhodium acetate dimer catalyzed addition of ethyl diazoacetate to the protected D-allylglycine (17). In vitro receptor binding using L-[3H]glutamate as the radioligand provided affinity data, while modulation of [3H]TCP binding was used as a functional assay. The analogues were also evaluated in [3H]kainate and [3H]AMPA binding to assess selectivity over non-NMDA glutamate receptors. Three of the four diastereoisomer, D-CAA B (27), C (32) and D (33) were shown to have agonist properties at the NMDA-site, while the fourth, (2R,4R,5R) D-CAA A (26) was characterized as an NMDA-site atypic antagonist.

Reversion of L-lysine inhibition of penicillin G biosynthesis by 6-oxopiperidine-2-carboxylic acid in Penicillium chrysogenum PQ-96

6-Oxopiperidine-2-carboxylic acid (OCA; cyclic alpha-aminoadipic acid) reverses the L-lysine inhibition of penicillin G production by Penicillium chrysogenum PQ-96. The reaction probably depends on the recovery of L-alpha-aminoadipic acid for penicillin G production from OCA.

Pharmacological characterization of the quisqualate receptor coupled to phospholipase C (Qp) in striatal neurons

A detailed pharmacological characterization of the quisqualate (QA) receptor coupled to phospholipase C (Qp) was performed in striatal neurons. The experiments were carried out in the presence of the ionotropic antagonists MK-801 (1 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), concentrations that block N-methyl-D-aspartate (NMDA) or alpha-amino-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in these cells. QA, ibotenate and trans-1-aminocyclopentyl-1,3-dicarboxylate (ACPD) evoked dose-dependent inositol phosphate formations with EC50 values of 0.3, 6.7 and 29 microM, respectively. QA and ibotenate had the same maximal effect (295.7 +/- 17.9% of basal, n = 6) whereas the efficacy of ACPD was somewhat lower (70.2 +/- 8.9% of the maximal quisqualate effect, n = 4). The QA-, ibotenate- and ACPD-induced maximal effects were not additive, and the inositol phosphate formations induced by high concentrations of L-aspartate (L-ASP), AMPA, kainate (KA) and domoate (DO) (100 microM or higher) were also not additive. The inositol phosphate responses induced by all these agonists were totally blocked by the phorbol ester phorbol 12,13-dibutyrate (PdBu), but not by atropine or prazosin suggesting that all these substances were able to stimulate the Qp excitatory amino acid receptor in striatal neurons. Of the excitatory amino acid receptor antagonists tested, only D,L-2-amino-3-phosphonopropionate (D,L-AP3) inhibited QA-induced InsP formation in a competitive manner (mean pKi = 4.45 +/- 0.43, n = 4). However, this drug was also a partial agonist of the Qp receptor since it stimulated the inositol phosphate formation. We found that D,L-AP3 also inhibited NMDA-induced calcium increase, in a competitive manner (mean pIC50 = 4.34 +/- 0.22, n = 8, and mean pKi = 3.7 +/- 0.11, n = 5). The Qp excitatory amino acid receptor in striatal neurons therefore closely resembles Qp receptors with high potency for agonists as described in striatal and retinal slices and synaptoneurosomes, and has several pharmacological differences compared to the Qp receptors which have low potency for agonists described in hippocampal and cortical slices, cerebellar granule cells, astrocytes and rat brain mRNA-injected oocytes.

Terminal excitability of the corticostriatal pathway. II. Regulation by glutamate receptor stimulation

The influence of impulse activity and glutamate receptor stimulation on the electrical excitability of the corticostriatal terminal field was explored. Antidromic responses were recorded from prefrontal cortical neurons the electrical stimulation of their terminal field in the contralateral striatum. Terminal excitability was assessed by determining the percentage of subthreshold current stimulus presentations eliciting an antidromic response. Terminal excitability was found to be positively correlated with variations in spontaneous firing rate: increases and decreases in firing rate were accompanied by corresponding changes in the percentage of antidromic responses elicited by a subthreshold stimulus. Drugs were applied to the striatal stimulation site in a volume of 312 nl delivered over 5 min. Striatal administration of either the competitive NMDA antagonist D-alpha-aminoadipate (DAA) or D-2-amino-7-phosphonoheptanoate (AP-7) or the competitive non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) blocked the correlation between excitability and firing rate. Further examination revealed that the terminal field was rendered more excitable for a period of 20-80 ms following the arrival of an action potential. This post-impulse facilitation of terminal excitability was attenuated after local application of AP-7 (10 microM) or CNQX (20 microM). At half these doses, AP-7 or CNQX produced a non-significant effect, however when administered simultaneously a significant attenuation was observed. The participation of interneurons in these excitability effects was ruled out since they were still seen following kainic acid lesions. We propose that this impulse-dependent enhancement in terminal excitability results from the release of glutamate induced by the action potential in the terminal field and the subsequent stimulation of glutamate autoreceptors on the terminals.

Effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata

1. The effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata were studied. 2. At concentrations of 10(-3) to 10(-6) M. L-glutamic acid diethylester (GDEE) and L-glutamic acid dimethylester (GDME) decreased the resting afferent discharge frequency as well as the electrically evoked activities and depressed the responses to application of excitatory amino acids. 3. D-alpha-Aminoadipic acid (AA) and 2-amino-4 phosphonobutyric acid (APB) had practically no effect either on resting afferent discharge or on evoked afferent activity. 4. 2-Amino-5-phosphonovaleric acid (APV) reduced the resting afferent discharge and electrically evoked activity in the afferent fibres. APV blocked N-methyl-D-aspartate (NMDA) induced responses at a lower concentration than those induced by aspartate,. 5. Responses caused by NMDA were Mg 1(2+)-dependent; those to quisqualate (Q) application depended to a lesser degree on the Mg2+ concentration. 6. Cis-2,-3-piperidinedicarboxylic acid (PDA) blocked both the resting afferent discharge and the electrically evoked activity; it also reversibly blocked the postsynaptic, amino acid-induced responses. The L-glutamate (L-GLU) response was more resistant to the blockade than the L-aspartate (L-ASP) response. 7. Both kynurenic acid (KEN) and gamma-D-glutamylglycine (DGG) reduced the resting and evoked activities in the afferent fibres. L-ASP was more resistant to blockade by KEN than L-GLU. 8. These observations suggest a prominent physiological role of quisqualate-, kainate- and NMDA-preferring receptors in the ampullae of Lorenzini of Raja clavata.

Comparison of three forward mutation systems in Saccharomyces cerevisiae for sensitivity to polycyclic and heterocyclic compounds

Forward mutation to cycloheximide resistance, L-canavanine resistance and DL-alpha-aminoadipic acid resistance in Saccharomyces cerevisiae wild-type strain S7a was tested for sensitivity to nine mutagens in treat-and-plate assays. Eight of these agents, 2-aminofluorene, 2-acetylaminofluorene, benzo[a]pyrene, benzidine, cyclophosphamide, acriflavine, 7,12-dimethylbenz[a]anthracene and 2-aminoanthracene were known or suspected to be difficult to detect whilst one, methyl methanesulphonate, was known to be very active in yeast. Forward mutation to cycloheximide resistance was, overall, the most sensitive system, detecting all nine agents under optimal conditions, although neither benzidine nor benzo[a]pyrene were consistently positive. Mutation to adipic acid resistance occasionally gave responses superior to those at the cycloheximide loci, but mutation to canavanine resistance was never more sensitive than the cycloheximide resistance system. We conclude that forward mutation in strain S7a using both cycloheximide and adipic acid resistance loci is capable of detecting the genetic effects of a range of polycyclic and heterocyclic compounds with greater sensitivity than is seen in other published gene mutation assays with yeast. Although sensitivity is much lower than in bacterial assays, such yeast assays provide a reasonable alternative to bacterial genotoxicity screening for agents such as potent bactericides.

Injury of Müller cells increases the incidence of experimental autoimmune uveoretinitis

Müller cells have been shown to have a dual effect in vitro on autoimmune T helper lymphocytes. In a coculture system, Müller cells have a primary inhibitory effect on the proliferation of T lymphocytes. In conditions where their inhibitory action is suppressed, Müller cells can, however, stimulate T cells. In the present study we evaluated the in vivo effect of Müller cells on actively induced experimental autoimmune uveoretinitis (EAU). Ten millimoles of L-alpha-aminoadipic acid (L-AAA), a specific gliotoxic agent, was injected into the vitreous of one eye of Wistar-Furth (WF) rats (a low EAU responder) on the day of immunization. Control rats were injected similarly with phosphate-buffered saline alone. The rats were immunized with S-antigen in CFA or in CFA alone. The results demonstrate that the incidence of EAU increases twofold in the eyes receiving an intravitreal injection of L-AAA in comparison to the contralateral eyes not receiving an injection. No such difference in EAU incidence was observed in control animals. Some rats that had been immunized with CFA alone after an intravitreal injection of L-AAA demonstrated a small amount of retinal perivascular inflammatory cell infiltrate but did not develop typical EAU lesions. The retinal vasculature was normal on examination by fluorescein angiography after injection of L-AAA. These data suggest that Müller cells can influence the course of uveoretinitis through their interaction with T cells.

GABA and glutamate interact in the substantia innominata/lateral preoptic area to modulate locomotor activity

Previous studies have shown that excitatory amino acid agonists or GABAergic antagonists injected into the substantia innominata/lateral preoptic area (SI/LPO) can produce the stimulation of coordinated locomotor activity. The purpose of the present study was to determine whether GABAergic and glutamatergic mechanisms in the SI/LPO interact to regulate locomotor activity. The stimulation of locomotor activity produced by the bilateral injection into the SI/LPO of 0.5 microgram of AMPA, a potent quisqualic acid receptor agonist, was antagonized by the coinjection of muscimol (25 ng). Similarly, the stimulation of locomotor activity produced by picrotoxin, an inhibitor of the effects of GABA, was antagonized by the coinjection of DNQX, which has been shown to inhibit the behavioral effects of both kainic acid and quisqualic acid, or a high dose of GAMS (25 micrograms), which has been shown to inhibit the behavioral effects of both AMPA and N-methyl-D-aspartic acid. In contrast, a lower dose of GAMS (5 micrograms), which selectively inhibited the locomotor stimulation produced by AMPA, or D-alpha-aminoadipic acid, at a dose (10 micrograms) which selectively inhibited the locomotor stimulation produced by N-methyl-D-aspartic acid, did not inhibit the effects of picrotoxin. However, the combination of both GAMS (5 micrograms) and D-alpha-aminoadipic acid (10 micrograms) produced a marked inhibition of the response to picrotoxin. These results suggest that the hypermotility response elicited by picrotoxin can only be antagonized when more than one subtype of excitatory amino acid receptor is antagonized and support the concept that excitatory amino acid receptors and GABAergic receptors in the SI/LPO interact to regulate locomotor activity.

Pharmacological modification of eye growth in normally reared and visually deprived chicks

Regular injections of the gliotoxins D-alpha-aminoadipic acid and L-alpha-aminoadipic acid were made into the vitreous chamber of the eyes of newly-hatched chicks reared either in a normal visual environment or under conditions of monocular occlusion. Striking differences in the growth rates of the eyes from the different groups were observed. Injection of D-alpha-aminoadipic acid, which causes the Müller glial cells to swell and diminishes the retinal OFF-response, resulted in a marked increase in the rate of axial growth of the eye compared with normal eyes. However, injection of D-alpha-aminoadipic acid into occluded eyes caused a lesser growth rate than was observed in occluded control eyes. By contrast, injection of L-alpha-aminoadipic acid, which also causes severe glial swelling and abolishes the retinal ON-response, caused reduced eye growth in non-occluded eyes. However, injection of L-alpha-aminoadipic acid into occluded eyes caused eye growth in excess of that recorded in the occluded controls. We concluded that the different growth rates observed is more likely a result of the disruption of the neural ON and OFF mechanisms than of the indisposition of the Müller cells.

Attenuation of febrile seizures in epileptic chicks by N-methyl-D-aspartate receptor antagonists

Experimental febrile seizures can be evoked in epileptic chicks by elevation of their body temperature. Both competitive N-methyl-D-aspartate (NMDA) receptor antagonists [(3-(+/- )2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), DL-2-amino-7-phosphosphonoheptanoic acid (APH), DL-2-amino-5-phosphonovaleric acid (APV), D-alpha-aminoadipic acid (AAA), and DL-alpha, epsilon-diaminopimelic acid (DAP)] and the noncompetitive NMDA antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5, 10-imine maleate (MK-801) produced dose-dependent increases in latency to the onset of seizures. Of the drugs tested, MK-801 had the highest potency followed in order by CPP = APH greater than APV much greater than AAA greater than DAP. There was a high correlation (r = 0.995) between the dose capable of doubling seizure latency and the affinity of the competitive NMDA antagonists for the NMDA receptor as determined by in vitro binding assays. These data suggest that NMDA receptor mediated mechanisms may be involved in the production of seizures in response to hyperthermia.

Intrastriatal injection of DL-alpha-aminoadipate reduces kainate toxicity in vitro

Intrastriatal injection of the excitatory amino acid analogue DL-alpha-aminoadipate (100 micrograms in 2 microliters saline, pH 7.4) into anesthetized rats caused a significant reduction in striatal glutamine synthetase activity in the ipsilateral compared to the contralateral striatum 6 h after the injection. Striatal neurons were unaffected by this treatment, and by 24 h after the injection, glutamine synthetase activity had returned to normal. In contrast to the situation in vivo, incubation of coronal slices (which included the striatum) in vitro with DL-alpha-aminoadipate (1-3 mM) for periods of up to 1 h caused no change in glutamine synthetase activity. Increased doses of DL-alpha-aminoadipate coupled with longer incubation times led to widespread neuronal degeneration within the striatum. Preparation of coronal slices from striata which had been injected 6 h previously with DL-alpha-aminoadipate, and subsequently incubated with 300 microM kainate, showed a marked survival of some neurons particularly those ordering the injection tract. The toxicity of 500 microM N-methyl-D-aspartate in similar slices was unchanged. Conversely, co-incubation of DL-alpha-aminoadipate with excitotoxins in vitro provided protection of striatal cells against degeneration by N-methyl-D-aspartate, but not kainate. These findings suggest that, in vivo, DL-alpha-aminoadipate has a specific effect on glial cell metabolism which, in contrast to incubation of coronal slices with the compound in vitro, is not related to the amino acid antagonist properties associated with the D-isomer. Thus, the reduced toxicity of kainate observed in striatal slices following DL-alpha-aminoadipate injection in vivo may indicate a non-neuronal site of action of kainate.

AMPA, kainic acid, and N-methyl-D-aspartic acid stimulate locomotor activity after injection into the substantia innominata/lateral preoptic area

The substantia innominata/lateral preoptic area (SI/LPO) is a subpallidal region which has been shown to regulate the hypermotility produced by drugs acting in the nucleus accumbens. Evidence has been presented that the SI/LPO contains glutamatergic nerve terminals and receptors for excitatory amino acids. The purpose of this study was to determine the effects of the activation of excitatory amino acid receptors in the SI/LPO on locomotor activity following the direct injection of excitatory amino acids into this brain site. It was found that the bilateral injection of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), kainic acid, and N-methyl-D-aspartic acid into the SI/LPO produced marked dose-dependent stimulations of locomotor activity which resembled the effects of these agents after their injection into the nucleus accumbens. The effect, however, was bell-shaped in that at high doses, the locomotor activity values decreased from their peak values. The coinjection of gamma-glutamylaminomethylsulfonate (GAMS) with AMPA into the SI/LPO was found to inhibit the hypermotility response to AMPA at doses that were unable to produce a significant inhibition of the hypermotility responses to kainic acid or N-methyl-D-aspartic acid. The injection of 6,7-dinitroquinoxaline-2,3-dione (DNQX) into the SI/LPO inhibited the hypermotility responses to AMPA or kainic acid while having no significant inhibitory effect on N-methyl-D-aspartic acid stimulated locomotor activity. The injection of D-alpha-aminoadipic acid into the SI/LPO produced a significant inhibition of the hypermotility response produced by N-methyl-D-aspartic acid at a dose that did not produce a significant inhibition of the hypermotility response produced by AMPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of quisqualic acid receptors in the hypermotility response produced by the injection of AMPA into the nucleus accumbens

alpha-Amino-3-hydroxy-5- methylisoxazole-4-propionate (AMPA) is an excitatory amino acid which on the basis of electrophysiological and binding studies appears to act as a quisqualic acid receptor agonist. AMPA and other excitatory amino acids, such as quisqualic acid, kainic acid, and N-methyl-D-aspartic acid, as well as picrotoxin, an inhibitor of endogenous GABA, produce a marked stimulation of locomotor activity after bilateral injection into the nucleus accumbens. The intraacumbens injection of gamma-D-glutamylaminomethylsulphonate (GAMS) was found to inhibit the hypermotility responses produced by AMPA and quisqualic acid at doses that were unable to inhibit the hypermotility responses produced by kainic acid, N-methyl-D-aspartic acid, and picrotoxin. These results suggest that GAMS is able to selectively inhibit quisqualic acid receptors in the nucleus accumbens. The intraacumbens injection of D-alpha-aminoadipic acid at a dose that significantly inhibited N-methyl-D-aspartic acid-stimulated locomotor activity did not produce a significant inhibition of AMPA-stimulated locomotor activity, suggesting that AMPA is not acting at N-methyl-D-aspartic acid receptors. Thus, these results suggest that the activation of quisqualic acid receptors in the nucleus accumbens produces a hypermotility response.