Biomedical subjects

F C Tortella

Publications and source records attributed to F C Tortella.

At least 19 recordsLinked to original sources

PubMed2001

Selective mGluR5 receptor antagonist or agonist provides neuroprotection in a rat model of focal cerebral ischemia.

Activation of group I metabotropic glutamate receptors (mGluR) has been implicated in the pathophysiology of acute central nervous system injury. However, the relative roles of the two group I subtypes, mGluR1 or mGluR5, in such injury has not been well examined. We compared the effects of treatment with the newly developed, selective mGluR5 antagonist 2-methyl-6-phenylethynylpyridine (MPEP) and the selective mGluR5 agonist (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG) in a rat intraluminal filament model of temporary middle cerebral artery occlusion (MCAo). Rats were administered MPEP or CHPG i.c.v. beginning 15 or 135 min after induction of ischemia for 2 h. Infarct size was measured after either 22 or 70 h of reperfusion, and neurological function was quantified at 2, 24, 48 and 72 h. Treatment with MPEP or CHPG at 15 min reduced 24 h infarct volume by 61 and 44%, respectively. The neuroprotective effects were dose dependent. Delaying MPEP treatment until 135 min eliminated the neuroprotective effects. In other studies, using early MPEP treatment (15 min) at optimal doses, infarct volume was reduced by 44% at 72 h and this was correlated with significant neurological recovery. These data suggest that both MPEP and CHPG are neuroprotective when administered after focal cerebral ischemia. In separate, recent studies we found that although MPEP does act as an mGluR5 antagonist and blocks agonist induced phosphoinositide hydrolysis, it also serves as a non-competitive NMDA antagonist; in contrast, other results indicate that CHPG mediated neuroprotection may reflect anti-apoptotic activity. Therefore, both types of compounds may prove to have therapeutic potential for the treatment of stroke.

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PubMed2001

Electroencephalogram analysis and neuroprotective profile of the N-acetylated-alpha-linked acidic dipeptidase inhibitor, GPI5232, in normal and brain-injured rats.

We have evaluated the effects of the N-acetylated-alpha-linked acidic dipeptidase (NAALADase) inhibitor, GPI5232 [2-[(pentafluorophenylmethyl)hydroxyphosphinyl]methyl)-pentanedioic acid], to not only decrease brain injury but also to alter the inherent electroencephalographic (EEG) changes observed in a rat model of transient middle cerebral artery occlusion (MCAo). Continuous i.v. infusion of GPI5232 starting 1 h after injury resulted in more than a 50% reduction in brain infarct volume caused by 2 h of MCAo. This effect was dose-dependent and significant even when first treatment was delayed for 2 h post-MCAo. At 24 h post-MCAo, EEG spectral analysis of the injured hemisphere revealed functional improvement in GPI5232-treated rats. Significant recovery in high-frequency EEG power (8-30 Hz) was measured in GPI5232-treated animals in both parietal and temporal brain regions but not in vehicle-treated animals. MCAo-injured rats were also predisposed to developing cortical brain seizures, and GPI5232-treated rats had significantly fewer brain seizures than vehicle-treated animals. In separate experiments, acute high doses of GPI5232 in normal rats did not significantly alter EEG brain activity as evaluated by spectral analysis and did not produce any signs of seizure activity or behavioral abnormalities. These results show GPI5232 to be an effective neuroprotective treatment when given postinjury by reducing brain infarction and ameliorating the pathological EEG associated with focal brain ischemia.

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PubMed2000

Neuroprotection produced by the NAALADase inhibitor 2-PMPA in rat cerebellar neurons.

The present study examined the neuroprotective actions of the N-acetylated-alpha-linked-acidic dipeptidase (NAALADase) inhibitor 2-(phosphonomethyl)pentanedioic acid (2-PMPA) in four in vitro models of neurotoxicity. Using neuron-enriched primary cultures derived from rat embryo (E15) cerebellum, 2-PMPA afforded 100% neuroprotection from injuries induced by hypoxia (EC(50)=8.4 microM). In contrast, against glutamate or N-methyl-D-aspartate (NMDA) injury, 2-PMPA was less potent and its efficacy limited to a maximum of 46% and 16%, respectively. 2-PMPA was not effective against veratridine-induced injury. Also, the less potent analog of 2-PMPA, 2-[phosphonomethyl]succinic acid (2-PMSA), was ineffective. Unlike 2-PMPA, the endogenous NAALADase substrate and mGlu(3) receptor agonist N-acetyl-aspartyl-glutamate (NAAG) was neuroprotective against all four injury mechanisms and compared to 2-PMPA, exhibited a different "phosphate effect" on neuroprotection. These results confirm the superior efficacy of 2-PMPA to protect against injury caused by cellular anoxia, and are discussed relative to upstream modulation of hyperglutamatergic activity vs. downstream modulation of metabotropic receptors as possible targets for ischemia/stroke therapy.

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PubMed2000

Proteasome inhibitor PS519 reduces infarction and attenuates leukocyte infiltration in a rat model of focal cerebral ischemia.

BACKGROUND AND PURPOSE: Reperfusion brain injury after cerebral ischemia is associated with a developing inflammatory response at the site of infarction. Proteasome inhibitors block nuclear factor-kappaB activation and provide anti-inflammatory effects in several animal models of peripheral inflammation. We tested the novel proteasome inhibitor PS519 in a rat model of transient focal ischemia to establish its pharmacodynamics as a neuroprotection treatment and related effects on leukocyte infiltration. METHODS: Rats were subjected to 2 hours of focal cerebral ischemia by means of the filament method of middle cerebral artery occlusion (MCAo). After either 22 or 70 hours of reperfusion, infarct size was measured and neurological function, electroencephalographic (EEG) activity, and/or neutrophil and macrophage infiltration was quantified. PS519 was administered in a single intravenous bolus at 2 hours after MCAo. In addition, the therapeutic window for PS519 was estimated by delaying treatment for 4 or 6 hours after MCAo. RESULTS: Dose-response analysis of infarct volume at 24 hours revealed that PS519 neuroprotection approached 60%, and clinical evaluations showed significant improvements in neurological function and EEG activity. Neutrophil infiltration at 24 hours was also significantly decreased in cortical and striatal infarcted tissue of PS519-treated rats. Delaying the PS519 treatment up to 4 hours continued to result in significant neuroprotection. In the 72-hour injury model, infarction was reduced 40% by PS519, and significant improvements in neurological function and EEG recovery were again measured. Considerable reductions in both neutrophil and macrophage infiltration were evident. CONCLUSIONS: PS519 mitigates infarction and improves neurological recovery in brain-injured rats, an effect in part caused by a reduction in the leukocyte inflammatory response.

Acetylcysteine↗

PubMed2000

Neuroprotective efficacy and therapeutic window of the high-affinity N-methyl-D-aspartate antagonist conantokin-G: in vitro (primary cerebellar neurons) and in vivo (rat model of transient focal brain ischemia) studies.

Conantokin-G (Con-G), a 17-amino-acid peptide derived from marine snails and a potent N-methyl-D-aspartate (NMDA) antagonist, was evaluated for its neuroprotective properties in vitro and in vivo. In primary cerebellar neurons, Con-G was shown to decrease excitotoxic calcium responses to NMDA and to exhibit differential neuroprotection potencies against hypoxia/hypoglycemia-, NMDA-, glutamate-, or veratridine-induced injury. Using the intraluminal filament method of middle cerebral artery occlusion as an in vivo rat model of transient focal brain ischemia, the neuroprotective dose-response effect of Con-G administration beginning 30 min postocclusion was evaluated after 2 h of ischemia and 22 h of reperfusion. In the core region of injury, an 89% reduction in brain infarction was measured with significant neurological and electroencephalographic recovery at the maximal dose tested (2 nmol), although mild sedation was noted. Lower doses of Con-G (0.001-0.5 nmol) were significantly neuroprotective without causing sedation. Postinjury time course experiments demonstrated a therapeutic window out to at least 4 to 8 h from the start of the injury, providing a 47% reduction in core injury. The neuroprotective effect of Con-G (0. 5 nmol) was also evaluated after 72 h of injury, where a 54% reduction in core brain infarction was measured. Critically, in both recovery models (i.e., 24 and 72 h), the reduction in brain infarction was associated with significant improvements in neurological and electroencephalographic recovery. These data provide evidence for the potent and highly efficacious effect of Con-G as a neuroprotective agent, with an excellent therapeutic window for the potential intervention against ischemic/excitotoxic brain injury.

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PubMed1999

Selective inhibition of NAALADase, which converts NAAG to glutamate, reduces ischemic brain injury.

We describe here a new strategy for the treatment of stroke, through the inhibition of NAALADase (N-acetylated-alpha-linked-acidic dipeptidase), an enzyme responsible for the hydrolysis of the neuropeptide NAAG (N-acetyl-aspartyl-glutamate) to N-acetyl-aspartate and glutamate. We demonstrate that the newly described NAALADase inhibitor 2-PMPA (2-(phosphonomethyl)pentanedioic acid) robustly protects against ischemic injury in a neuronal culture model of stroke and in rats after transient middle cerebral artery occlusion. Consistent with inhibition of NAALADase, we show that 2-PMPA increases NAAG and attenuates the ischemia-induced rise in glutamate. Both effects could contribute to neuroprotection. These data indicate that NAALADase inhibition may have use in neurological disorders in which excessive excitatory amino acid transmission is pathogenic.

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PubMed1999

Anticonvulsant efficacy of N-methyl-D-aspartate antagonists against convulsions induced by cocaine.

Convulsions associated with cocaine abuse can be life threatening and resistant to standard emergency treatment. Cocaine (75 mg/kg, i. p.) produced clonic convulsions in approximately 90% of male, Swiss-Webster mice. A variety of clinically used antiepileptic agents did not significantly protect against cocaine convulsions (e. g., diazepam and phenobarbital). Anticonvulsants in clinical practice that did significantly protect against convulsion did so only at doses with significant sedative/ataxic effects (e.g., clonazepam and valproic acid). In contrast, functional N-methyl-D-aspartate (NMDA) antagonists all produced dose-dependent and significant protection against the convulsant effects of cocaine. Anticonvulsant efficacy was achieved by blockade of both competitive and noncompetitive modulatory sites on the NMDA receptor complex. Thus, competitive antagonists, ion-channel blockers, polyamine antagonists, and functional blockers of the strychnine-insensitive glycine modulatory site all prevented cocaine seizures. The role of NMDA receptors in the control of cocaine-induced convulsions was further strengthened by the positive correlation between the potencies of noncompetititve antagonists or competitive antagonists to block convulsions and their respective affinities for their specific binding sites on the NMDA receptor complex. Although some NMDA blockers produced profound behavioral side effects at efficacious doses (e.g., noncompetitive antagonists), others (e.g., some low-affinity channel blockers, some competitive antagonists, and glycine antagonists) demonstrated significant and favorable separation between their anticonvulsant and side effect profiles. The present results provide the most extensive evidence to date identifying NMDA receptor blockade as a potential strategy for the discovery of agents for clinical use in averting toxic sequelae from cocaine overdose. Given the literature suggesting a role for these drugs in other areas of drug abuse treatments, NMDA receptor antagonists sit in a unique position as potential therapeutic candidates.

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PubMed1999

Neuroprotection (focal ischemia) and neurotoxicity (electroencephalographic) studies in rats with AHN649, a 3-amino analog of dextromethorphan and low-affinity N-methyl-D-aspartate antagonist.

AHN649, an analog of dextromethorphan (DM) and a relatively selective low-affinity N-methyl-D-aspartate antagonist, was evaluated for neuroprotective effects using the rat intraluminal filament model of temporary middle cerebral artery occlusion. Rats were subjected to 2 h of focal ischemia followed by 72 h of reperfusion. In vehicle-treated rats, middle cerebral artery occlusion resulted in neurological deficits and severe infarction measuring 232 +/- 25 mm(3), representing approximately 25% contralateral hemispheric infarction. Post-treatment with AHN649 (0.156-20 mg/kg i.v.) or DM (0.156-10 mg/kg i.v.) significantly reduced cortical infarct volume by 40 to 60% compared with vehicle-control treatments. AHN649 neuroprotection was linear and dose dependent (ED(50) = 0.80 mg/kg), whereas DM neuroprotection (ED(50) = 1.25 mg/kg) was nonlinear and less effective at the higher doses (2.5-10 mg/kg). Although impaired neurological function scores improved in all groups by 24 to 72 h, the most dramatic improvement was associated with AHN649 treatments. In a rat electroencephalographic model of brain function, separate neurotoxicity experiments revealed that acute i.v. doses of DM caused seizures (ED(50) = 19 mg/kg) and death (LD(50) = 27 mg/kg). In contrast, AHN649 failed to induce seizure activity at doses up to 100 mg/kg (LD(50) = 79 mg/kg). Collectively, AHN649 is described as a potent, efficacious neuroprotective agent devoid of serious central nervous system neurotoxicity and possessing potential therapeutic value as antistroke treatment. Furthermore, the feasibility of targeting low-affinity N-methyl-D-aspartate-site ligands as postinjury therapy for ischemic brain injury has been confirmed.

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PubMed1997

Neuroprotective role of c-fos antisense oligonucleotide: in vitro and in vivo studies.

We investigated the dose-response and time-course of c-fos antisense oligodeoxynucleotide (ASO) treatment against excitatory amino acid (EAA)-induced neurotoxicity in rat hippocampal neurons. Glutamate (in vitro) or NMDA (in vivo) produced significant neuronal degeneration. Neuroprotection produced by 30 min or 4 h pretreatment with c-fos ASO in cultured hippocampal neurons was dose-dependent. In vivo, bilateral intrahippocampal injections of c-fos ASO (0.025 nmol/site) was neuroprotective when administered 30 min before or after NMDA treatment. However, 4 h pretreatment was ineffective. A higher dose (0.125 nmol) of c-fos ASO was neurotoxic and failed to afford neuroprotection regardless of the treatment schedule. Collectively, these results demonstrate a neuroprotective effect of c-fos ASO against EAA-induced neuronal injury supporting a causative role of c-fos expression in EAA neurotoxicity.

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PubMed1997

Neuroprotective sigma ligands attenuate NMDA and trans-ACPD-induced calcium signaling in rat primary neurons.

The effect of neuroprotective sigma ligands possessing a range of relative selectivity for sigma and phencyclidine (PCP) binding sites on N-methyl-D-aspartate (NMDA) and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated calcium flux was studied in 12-15-day-old primary cultures of rat cortical neurons. In approximately 80% of the neurons tested, NMDA (80 microM) caused a sustained increase in intracellular calcium ([Ca2+]i). With the exception of R-(+)-3-(3-hydroxyphenyl)-N-propylpiperidine hydrochloride ((+)-3-PPP) (previously shown not to be neuroprotective) all of the sigma ligands studied significantly altered NMDA-induced calcium dynamics. The primary effect of dextromethorphan, (+)-pentazocine, (+)-cyclazocine, (+)-SKF10047, carbetapentane, 1,3-di(2-tolyl) guanidine (DTG), and haloperidol was to shift the NMDA response from a sustained, to either a biphasic or a transient, calcium event. In contrast to NMDA, the primary response observed in 62% of the neurons treated with trans-ACPD (100 microM) was a transient elevation in [Ca2+]i. Here, however, only the highly selective neuroprotective sigma ligands (i.e., those lacking substantial PCP binding affinity) significantly decreased the number of transient responses elicited by trans-ACPD whereas the PCP-related sigma ligands such as dextromethorphan, (+)-SKF10047 and (+)-cyclazocine were ineffective. Unexpectedly, (+)-3-PPP potentiated trans-ACPD activity. These results demonstrating attenuating effects of sigma ligands on NMDA-stimulated neuronal calcium responses agree with earlier studies using glutamate and KCl and identify a sigma receptor modulation of functional NMDA responsiveness. Furthermore, the ability of sigma ligands to attenuate NMDA-, trans-ACPD- and KCl-evoked neuronal calcium dynamics indicates that the receptor mechanisms mediating sigma neuroprotection comprise complex interactions involving ionotropic, metabotropic, and even voltage-gated calcium signaling processes.

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PubMed1997

Dextromethorphan protects against cerebral injury following transient, but not permanent, focal ischemia in rats.

Dextromethorphan (DM) has been observed to afford neuroprotection in a variety of in vitro and in vivo experimental models of CNS injury. We have evaluated the neuroprotective activity of DM following both transient (2 h) and permanent focal cerebral ischemia in the rat. Middle cerebral artery occlusion (MCAO) was produced in male Sprague-Dawley rats using the intraluminal filament technique. Animals were dosed s.c with 20 mg/kg DM at 0.5, 1, 2, 4, and 6 hours post occlusion. Analysis of brain injury was performed 24 hours after permanent occlusion or reperfusion. Following transient MCAO, vehicle treated rats exhibited a total infarct volume of 203 +/- 33 mm3. DM produced a 61% reduction in infarct volume to 79 +/- 13 mm3. Permanent MCAO produced a larger infarct volume (406 +/- 44 mm3) which was not significantly reduced in size by treatment with DM (313 +/- 58 mm3). Infarcted hemispheric oedema was not different in vehicle treated rats following transient or permanent MCAO and was not reduced by DM in either group. Following transient MCAO, rectal temperature was elevated 1,2 and 5 hours post occlusion. While not inducing hypothermia or altering physiological parameters such as blood pressure and blood gases, DM attenuated this injury-related increase in temperature, an effect which appeared to correlate with its ability to protect neurons in temperature regulating hypothalamic centres. The DM-induced reduction in infarction demonstrated in our model of transient focal cerebral ischemia provides further support for the in vivo neuroprotective activity of this compound. Importantly, these data demonstrate the limited neuroprotective efficacy of DM when attempting to combat more severe focal ischemic injuries and imply that drug-induced hypothermia is not ultimately responsible for its protective action.

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PubMed1997

An autoradiographic study of dextromethorphan high-affinity binding sites in rat brain: sodium-dependency and colocalization with paroxetine.

1. The distribution and some pharmacological properties of centrally located dextromethorphan high-affinity binding sites were investigated by in vitro autoradiography. 2. Sodium chloride (50 mM) induced a 7 to 12 fold increase in dextromethorphan binding to rat brain in all areas tested. The effect of sodium was concentration-dependent with a higher dose (120 mM) exerting a smaller effect on binding. 3. [3H]-dextromethorphan binding in the presence of sodium was inhibited in the presence of the anticonvulsant phenytoin at a concentration of 100 microM, while the sigma ligand (+)-3-(-3-hydroxyphenyl)-N-(1-propyl)pipendine ((+)-PPP) had no effect on the binding, suggesting an interaction with the DM2 site. 4. The distribution of the sodium-dependent binding identified in this study correlated significantly with the distribution of the selective 5-HT uptake inhibitor [3H]-paroxetine, and paroxetine and dextromethorphan mutually displaced their binding at concentrations in the low nanomolar range. 5. These data show that dextromethorphan and paroxetine share a sodium-dependent high affinity binding site in rat brain, and suggest that dextromethorphan might interact, in the presence of sodium, with the 5-HT uptake mechanism in rat brain.

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PubMed1997

EEG spectral analysis of the neuroprotective kappa opioids enadoline and PD117302.

The present study characterized the electroencephalographic (EEG) effects of the neuroprotective kappa opioids enadoline and PD117302 in conscious, freely moving rats with the use of computer-assisted spectral analysis (CASA). Enadoline (25-100 microg/kg) or PD117302 (1.25-5.0 mg/kg) was administered intravenously to rats implanted with cortical EEG electrodes. Although both drugs produced an immediate, mild sedation, there were no signs of head-weaving or ataxia, and there was little visual evidence of opioid-like EEG slow-wave bursts or seizures. Both drugs produced only modest increases in total EEG power that were not dose dependent. In contrast, CASA revealed significant dose-dependent frequency shifts in relative power distributions, thereby identifying distinct kappa opioid alterations in awake EEG activity; EEG power decreased in the 0- to 4-Hz frequency band with concomitant increases in power measured in the 4- to 8-Hz frequency range. The kappa opioids produced a dose-dependent consolidation of the EEG waveform centered about a peak frequency of 5.0 Hz (for enadoline) or 4.8 Hz (for PD117302) and a significant shift in the mean EEG frequency from 6.6 Hz (predrug) to 6.2 Hz (postdrug). Further CASA revealed significant postdrug decreases in the edge frequency, mobility and complexity of the EEG. Both drugs produced moderate increases in the latency to slow-wave sleep (SWS). Overall, enadoline (ED50 = 18 microg/kg) was approximately 94 times more potent than PD117302 (ED50 = 1690 microg/kg) in producing the kappa EEG profile. Because the kappa-induced EEG changes were stereospecific for the (-)-enantiomers and inhibited by norbinaltorphimine (nor-BNI), the EEG "fingerprint" described in this study could be attributed to specific activation of brain kappa opioid receptors.

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PubMed1996

EEG seizure activity and behavioral neurotoxicity produced by (+)-MK801, but not the glycine site antagonist L-687,414, in the rat.

The objective of the present study was to compare the in vivo effects of the anticonvulsant/neuroprotective glycine-site partial agonists L-687,414 (3R-amino-1-hydroxy-4R-methylpyrrolidin-2-one) and (+)-HA966 (3-Amino-1-hydroxypyrrolidin-2-one) and the non-competitive N-methyl-D-aspartate (NMDA) antagonist (+)-MK801 on spontaneous cortical EEG activity and behavior in the unanesthetized rat. Comprehensive dose-response assessments demonstrated that acute i.v. injections of (+)-MK801 induced a behavioral neurotoxic syndrome comprised of head-weaving, ataxia, hyperlocomotion and myoclonic/clonic behaviors and associated with disruptions in normal EEG rhythms including paroxysmal EEG spike/wave complexes. Injections of (+)-HA966 produced behavioral sedation associated with high-amplitude, slow-wave synchronized EEG patterns; signs of ictal EEG activity were minimal (33% incidence) and only seen at the highest dose tested (100 mg/kg). Both (+)-MK801 and (+)-HA966 severely delayed the latency to slow-wave sleep (SWS). In contrast, the EEG dynamics and overt behavior associated with L687,414 were essentially indistinguishable from controls. There was no disruption in the latency to SWS and mild ataxia was evident only upon awakening. The calculated protective indices (EEG seizure ED50/anticonvulsant ED50) for (+)-MK801 and L-687,414 were 1.2 and > 4.5, respectively. The results of this study confirm that valuable pharmacological actions mediated via glycine site modulation of the NMDA receptor are possible without the clinical manifestation of unwanted neurotoxic side-effects.

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PubMed1995

Role of calcium in sigma-mediated neuroprotection in rat primary cortical neurons.

Since unique calcium dynamics have been reported for toxic (40-80 M) and non-toxic (5-10 microM) concentrations of glutamate, we evaluated the effect of neuroprotective sigma ligands on glutamate and potassium chloride (KCl)-stimulated changes in [Ca2+]i using 12-15 day old primary rat neuronal cortical cultures. In approximately 80% of the neurons tested, 80 microM glutamate caused a sustained calcium flux previously shown to be associated with neurotoxicity. The majority of sigma ligands that were evaluated altered glutamate-induced calcium flux. For example, the primary effect of maximally neuroprotective concentrations of the sigma ligands dextromethorphan, (+)-pentazocine, (+)-cyclazocine, (+)-SKF 10047, carbetapentane and haloperidol was a shift from a sustained, to either a biphasic or a monophasic transient calcium response indicative of neuroprotection. (+)-3-PPP, previously shown not to be neuroprotective in this model system, failed to alter glutamate-induced calcium flux. In contrast to glutamate, KCl (50 mM) produced changes in [Ca2+]i which were not neurotoxic to the neurons as measured by LDH release. The primary response observed in 59% of the neurons treated with 50 mM KCl alone was an initial spike in [Ca2+]i which abruptly declined then plateaued above basal levels throughout the 12 min of analysis (modified sustained response). The highly selective sigma ligands produced a shift from the modified sustained response to a monophasic transient calcium response. Again, (+)-3-PPP had no effect on KCl-induced calcium dynamics. Of the PCP-related sigma ligands only (+)-SKF-10047 consistently attenuated the KCl-induced calcium flux. Collectively, these results indicate that modulation of [Ca2+]i through receptor and voltage-gated calcium channels contributes significantly to sigma mediated neuroprotection.

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PubMed1995

Dextromethorphan analogs are neuroprotective in vitro and block glutamate-induced excitotoxic calcium signals in neurons.

Consistent with the neuroprotective effects of the non-opioid antitussive dextromethorphan (DM) described in several models of CNS injury, micromolar concentrations of three novel analogs of DM markedly attenuated the injury produced by glutamate in cultured rat cortical neurons. Furthermore, the neuroprotective actions of the DM analogs correlated with their effects to block glutamate-induced excitotoxic calcium signals and were unrelated to metabolism to the phencyclidine (PCP)-like drug dextrorphan (DX). These observations establish a new class of compounds related to DM which, by virtue of their efficacy to protect neurons against a severe glutamate insult, may possess therapeutic potential as treatment modalities for a number of neurodegenerative diseases.

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PubMed1995

Phospholipase A2-induced neurotoxicity in vitro and in vivo in rats.

The present study evaluated the neurotoxic potential of phospholipase A2 (PLA2) in in vitro (primary neuronal cultures) and in vivo (EEG and behavior) rat models of CNS excitability. In vitro, PLA2 (0.0038-5.8 nM) or melittin (a potent activator of endogenous PLA2; 100-5000 nM), were highly neurotoxic, causing approximately 500 units/ml LDH release. The neurotoxic EC50s for PLA2 and melittin were 1.8 (1.4-2.3) and 848 (501-1280) nM, respectively. Neurotoxic concentrations of PLA2 stimulated neuronal release of [3H]AA. Preliminary in vitro experiments evaluating changes in neuronal calcium flux indicated that PLA2 caused transient, and melittin sustained, increases in [Ca2+]i. In vivo, PLA2 (0.5-5 micrograms i.c.v.) or melittin (2.5-20 micrograms i.c.v.) produced nonconvulsive EEG seizures, which generalized to status epilepticus. While the onset of seizure development was markedly delayed for PLA2 (1.5-4.5 h), the seizure inducing effects of melittin were evident within 3.5 +/- 0.2 min and more severe. Both PLA2 and melittin were lethal, exhibiting LD50s of 0.62 micrograms and 8.4 micrograms, respectively. Pretreatment with (+)-MK801 (5 micrograms, i.c.v.) significantly attenuated melittin, but not PLA2, in vivo neurotoxicity. PLA2 induced neuropathology in surviving rats revealed extensive cortical and subcortical injury to forebrain neurons and fibre pathways. Collectively, these results demonstrate the potent neurotoxic potential of PLA2, the delayed clinical nature of its in vivo neurotoxicity and the applicability of these model systems to future studies on mechanisms of PLA2 neurotoxicity and the development of potential PLA2 antagonists.

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PubMed1995

Sigma receptor-mediated neuroprotection against glutamate toxicity in primary rat neuronal cultures.

The role of the putative sigma receptor in mediating neuroprotection against glutamate-induced neuronal injury was examined in mature cultured rat cortical neurons. With the exception of the selective sigma 1 ligand (+)-3-PPP, all of the sigma ligands tested were neuroprotective, preventing glutamate-induced morphological changes and increases in LDH release. Their rank order of neuroprotective potency (and EC50 values) was as follows: (+)-SKF 10,047 (0.81 microM) > (+)- cyclazocine (2.3 microM) > dextromethorphan (3.1 microM) = haloperidol (3.7 microM) > (+)-pentazocine (8.5 microM) > DTG (42.7 microM) = carbetapentane (46.3 microM). When corrected for relative sigma versus PCP binding affinity, it appears that a positive correlation exists between neuroprotective potency and sigma 1 site affinity. However, there does not appear to be a significant correlation between neuroprotective potency and the sigma 2 site. Critically, none of the sigma ligands were neurotoxic when tested alone at concentrations at least 5-30 times their respective neuroprotective EC50 values. Results from preliminary experiments with the selective sigma 1 ligand (+)-pentazocine indicated that sigma-mediated neuroprotection may involve the buffering of glutamate-induced calcium flux. Collectively, the results of these in vitro experiments demonstrate that sigma ligands are neuroprotective and therefore deserve further exploration as potential therapeutic agents in in vivo models of CNS injury and neurodegenerative disorders.

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