Effects of lubeluzole on the methamphetamine-induced increase in extracellular glutamate and the long-term depletion of striatal dopamine

Inhibition of Glutamate Release from Rat Cortical Nerve Terminals by Dehydrocorydaline, an Alkaloid from Corydalis yanhusuo

Excessive release of glutamate induces excitotoxicity and causes neuronal damage in several neurodegenerative diseases. Natural products have emerged as potential neuroprotective agents for preventing and treating neurological disorders. Dehydrocorydaline (DHC), an active alkaloid compound isolated from Corydalis yanhusuo, possesses neuroprotective capacity. The present study investigated the effect of DHC on glutamate release using a rat brain cortical synaptosome model. Our results indicate that DHC inhibited 4-aminopyridine (4-AP)-evoked glutamate release and elevated intrasynaptosomal calcium levels. The inhibitory effect of DHC on 4-AP-evoked glutamate release was prevented in the presence of the vesicular transporter inhibitor bafilomycin A1 and the N- and P/Q-type Ca²⁺ channel blocker ω-conotoxin MVIIC but not the intracellular inhibitor of Ca²⁺ release dantrolene or the mitochondrial Na⁺/Ca²⁺ exchanger inhibitor CGP37157. Moreover, the inhibitory effect of DHC on evoked glutamate release was prevented by the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) inhibitor PD98059. Western blotting data in synaptosomes also showed that DHC significantly decreased the level of ERK1/2 phosphorylation and synaptic vesicle-associated protein synapsin I, the main presynaptic target of ERK. Together, these results suggest that DHC inhibits presynaptic glutamate release from cerebrocortical synaptosomes by suppressing presynaptic voltage-dependent Ca²⁺ entry and the MAPK/ERK/synapsin I signaling pathway.

Evidence for involvement of nitric oxide and GABA(B) receptors in MK-801- stimulated release of glutamate in rat prefrontal cortex

Systemic administration of NMDA receptor antagonists elevates extracellular glutamate within prefrontal cortex. The cognitive and behavioral effects of NMDA receptor blockade have direct relevance to symptoms of schizophrenia, and recent studies demonstrate an important role for nitric oxide and GABA(B) receptors in mediating the effects of NMDA receptor blockade on these behaviors. We sought to extend those observations by directly measuring the effects of nitric oxide and GABA(B) receptor mechanisms on MK-801-induced glutamate release in the prefrontal cortex. Systemic MK-801 injection (0.3 mg/kg) to male Sprague-Dawley rats significantly increased extracellular glutamate levels in prefrontal cortex, as determined by microdialysis. This effect was blocked by pre-treatment with the nitric oxide synthase inhibitor L-NAME (60 mg/kg). Reverse dialysis of the nitric oxide donor SNAP (0.5-5 mM) directly into prefrontal cortex mimicked the effect of systemic MK-801, dose-dependently elevating cortical extracellular glutamate. The effect of MK-801 was also blocked by systemic treatment with the GABA(B) receptor agonist baclofen (5 mg/kg). In combination, these data suggest increased nitric oxide formation is necessary for NMDA antagonist-induced elevations of extracellular glutamate in the prefrontal cortex. Additionally, the data suggest GABA(B) receptor activation can modulate the NMDA antagonist-induced increase in cortical glutamate release.

Effect of paliperidone and risperidone on extracellular glutamate in the prefrontal cortex of rats exposed to prenatal immune activation or MK-801

The NMDA glutamate hypofunction model of schizophrenia is based in part upon acute effects of NMDA receptor blockade in humans and rodents. Several laboratories have reported glutamate system abnormalities following prenatal exposure to immune challenge, a known environmental risk factor for schizophrenia. Here we report indices of NMDA glutamate receptor hypofunction following prenatal immune activation, as well as the effects of treatment during periadolescence with the atypical antipsychotic medications risperidone and paliperidone. Pregnant Sprague-Dawley rats were injected with polyinosinic:polycytidylic acid (poly I:C) or saline on gestational day 14. Male offspring were treated orally via drinking water with vehicle, risperidone (0.01mg/kg/day), or paliperidone (0.01mg/kg/day) between postnatal days 35 and 56 (periadolescence) and extracellular glutamate levels in the prefrontal cortex were determined by microdialysis at PD 56. Consistent with decreased NMDA receptor function, MK-801-induced increases in extracellular glutamate concentration were markedly blunted following prenatal immune activation. Further suggesting NMDA receptor hypofunction, prefrontal cortex basal extracellular glutamate was significantly elevated (p<0.05) in offspring of poly I:C treated dams. Pretreatment with low dose paliperidone or risperidone (0.01mg/kg/day postnatal days 35-56) normalized prefrontal cortical basal extracellular glutamate (p<0.05 vs. poly I:C vehicle-treatment). Pretreatment with paliperidone and risperidone also prevented the acute MK-801-induced increase in extracellular glutamate. These observations demonstrate decreased NMDA receptor function and elevated extracellular glutamate, two key features of the NMDA glutamate receptor hypofunction model of schizophrenia, during periadolescence following prenatal immune activation. Treatment with the atypical antipsychotic medications paliperidone and risperidone normalized basal extracellular glutamate. Demonstration of glutamatergic abnormalities consistent with the NMDA glutamate receptor hypofunction model of schizophrenia as an early developmental consequence of prenatal immune action provides a model to identify novel early interventions targeting glutamatergic systems which play an important role in both positive and negative symptoms of schizophrenia.

Mice with partial deficiency of c-Jun show attenuation of methamphetamine-induced neuronal apoptosis

The regional distribution of c-Jun expression and of the number of apoptotic cells was compared in various brain areas after methamphetamine administration to mice. Our results showed that there was methamphetamine-induced overexpression of c-Jun in the cortex and striatum but not in the cerebellar cortex. There was an almost totally similar regional appearance of methamphetamine-induced apoptotic cells in the mouse brain; no apoptosis was present in the cerebellum. Additionally, in the neocortical area, more positive signals for c-Jun immunoreactivity were observed in the piriform cortex, an area that also showed more positive terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) signals than the frontal and parietal cortices. These observations suggested that c-Jun might be involved in methamphetamine-induced apoptosis. This idea was confirmed by using heterozygous c-Jun knockout mice that showed much less apoptosis than wild-type controls. In addition, we found that the majority of TUNEL-positive cells were also positive for c-Jun-like immunoreactivity in both genotypes. Moreover, methamphetamine-induced caspase-3 activity and PARP cleavage were also reduced in c-Jun heterozygous knockout mice. In contrast, methamphetamine-induced hyperthermia was essentially identical in the two genotypes. When taken together, our data support the hypothesis that c-Jun is involved in methamphetamine-induced apoptosis.

3,4-Methylenedioxymethamphetamine produces glycogenolysis and increases the extracellular concentration of glucose in the rat brain

Oxidative and/or bioenergetic stress is thought to contribute to the mechanism of neurotoxicity of amphetamine derivatives, e.g., 3,4-methylenedioxymethamphetamine (MDMA). In the present study, the effect of MDMA on brain energy regulation was investigated by examining the effect of MDMA on brain glycogen and glucose. A single injection of MDMA (10-40 mg/kg, s.c.) produced a dose-dependent decrease (40%) in brain glycogen, which persisted for at least 1 h. MDMA (10 and 40 mg/kg, s.c.) also produced a significant and sustained increase in the extracellular concentration of glucose in the striatum. Subjecting rats to a cool ambient temperature of 17 degrees C significantly attenuated MDMA-induced hyperthermia and glycogenolysis. MDMA-induced glycogenolysis also was prevented by treatment of rats with the 5-hydroxytryptamine(2) (5-HT(2)) antagonists 6-methyl-1-(1-methylethyl)-ergoline-8 beta-carboxylic acid 2-hydroxy-1 methylprophyl ester maleate (LY-53,857; 3 mg/kg i.p.), desipramine (10 mg/kg i.p.), and iprindole (10 mg/kg i.p.). LY-53,857 also attenuated the MDMA-induced increase in the extracellular concentration of glucose as well as MDMA-induced hyperthermia. Amphetamine analogs (e.g., methamphetamine and parachloroamphetamine) that produce hyperthermia also produced glycogenolysis, whereas fenfluramine, which does not produce hyperthermia, did not alter brain glycogen content. These results support the conclusion that MDMA induces glycogenolysis and that the process involves 5-HT(2) receptor activation. These results are supportive of the view that MDMA promotes energy dysregulation and that hyperthermia may play an important role in MDMA-induced alterations in cellular energetics.

Plasma and brain methamphetamine concentrations in neonatal rats

D-Methamphetamine (D-MA) treatment during the neonatal period has been shown to induce acoustic startle hyperreactivity and Morris maze spatial learning deficits, but not to significantly affect Cincinnati maze sequential learning. In order to characterize the internal dose in these experiments, MA was measured in plasma and brain of neonatal rats at one of two ages, and using one of three dose schedules, two of which were selected to be representative of those used in previously published neurobehavioral studies. Plasma parameters showed few age and dose-frequency effects; however, brain concentrations showed more consistent age-dependent effects. Brain area under the concentration (AUC) values were consistently higher, regardless of dosing schedule, in offspring treated on postnatal day (P) 1 compared to those treated on P11. Previous results with the multiple-dose schedules have shown that Morris maze spatial learning deficits only occur in those exposed beginning on P11, whereas acoustic startle hyperreactivity is associated with exposure beginning on either P1 or P11. The pharmacokinetic parameters did not predict the long-term spatial learning and memory effects of neonatal MA administration, nor are they well correlated to the acoustic startle effects. The plasma concentrations obtained in rats are within the range for human MA abusers based on extrapolations from human low-dose values to those expected for heavy users.