Levels Of Amino Acid Neurotransmitters Research Articles

Development of a PDMS‐based microchip electrophoresis device for continuous online in vivo monitoring of microdialysis samples

A PDMS-based microfluidic system for online coupling of microdialysis sampling to microchip electrophoresis with fluorescence detection for in vivo analysis of amino acid neurotransmitters using naphthalene-2,3-dicarboxaldehyde and sodium cyanide as the derivatization reagents is described. Fabricating chips from PDMS rather than glass was found to be simpler and more reproducible, especially for chips with complex designs. The microchip incorporated a 20-cm serpentine channel in which sample plugs were introduced using a "simple" injection scheme; this made fluid handling and injection on-chip easier for the online system compared with gated or valve-based injection. The microchip was evaluated offline for the analysis of amino acid standards and rat brain microdialysis samples. Next, precolumn derivatization was incorporated into the chip and in vivo online microdialysis-microchip electrophoresis studies were performed. The system was employed for the continuous monitoring of amino acid neurotransmitters in the extracellular fluid of the brain of an anesthetized rat. Fluorescein was dosed intravenously and monitored simultaneously online as a marker of in vivo blood-brain barrier permeability. The microdialysis-microchip electrophoresis system described here will be employed in the future for simultaneous monitoring of changes in blood-brain barrier permeability and levels of amino acid neurotransmitters in the rat stroke model.

Benzo[a]pyrene-induced neurobehavioral function and neurotransmitter alterations in coke oven workers

ObjectiveTo study alterations in neurobehavioral function and neurotransmitter levels in coke oven workers occupationally exposed to benzo[a]pyrene (B[a]P) and explore possible biomarkers of B[a]P neurotoxicity.Methods176 coke oven workers occupationally exposed...

Role of Prostanoid Production and Receptors in the Regulation of Retinal Endogenous Amino Acid Neurotransmitters by 8-Isoprostaglandin E2, Ex Vivo

The role of enzymes and receptors of the prostanoid pathway in the inhibitory effect of 8-isoprostaglandin E2 (8-isoPGE2) on endogenous amino acid neurotransmitter levels was examined, ex vivo. Freshly isolated bovine eyeballs were injected intravitreally with IsoPs, incubated in Krebs buffer for 30 min and retina prepared for HPLC-ECD detection of amino acids. 8-isoPGE2 attenuated retinal glutamate and its metabolite, glutamine and glycine in a concentration-dependent manner. The nonselective cyclooxygenase (COX)-inhibitor, flurbiprofen, COX-2 selective inhibitor, NS-398 and thromboxane (Tx) synthase inhibitor, furegrelate had no effect on both basal amino acid levels and the inhibitory effects of 8-isoPGE2 (1-100 μM) on the retinal amino acids. Whereas the TP-receptor antagonist SQ-29548(10 μM) exhibited no effect, SC-19220(EP1; 30 μM), AH-6809(EP(1-3); 30 μM) and AH-23848(EP4; 30 μM) reversed the inhibitory effects of 8-isoPGE2 (0.01-100 μM) on glutamate, glutamine and glycine levels. We conclude that prostanoid EP-receptors regulate the inhibitory effect of 8-isoPGE2 on basal levels of endogenous amino acids in bovine retina, ex vivo.

Effect of Infrared Laser Irradiation on Amino Acid Neurotransmitters in an Epileptic Animal Model Induced by Pilocarpine

The aim of the present study was to investigate the effect of daily laser irradiation on the levels of amino acid neurotransmitters in the cortex and hippocampus in an epileptic animal model induced by pilocarpine. It has been claimed that at specific wavelengths and energy densities, laser irradiation is a novel and useful tool for the treatment of peripheral and central nervous system injuries and disorders. Adult male albino rats were divided into three groups: control rats, pilocarpinized rats (epileptic animal model), and pilocarpinized rats treated daily with laser irradiation (90 mW at 830 nm) for 7 d. The following parameters were assayed in cortex and hippocampus: amino acid neurotransmitters (excitatory: glutamic acid and aspartate; and inhibitory: gamma-aminobutyric acid [GABA], glycine, and taurine) by high-performance liquid chromatography (HPLC), glucose content, and the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), using a spectrophotometer. Significant increases in the concentrations of glutamic acid, glutamine, glycine, and taurine were recorded in the cortices of pilocarpinized rats, and they returned to initial levels after laser treatment. In the hippocampus, a moderate increase in aspartate accompanied by a significant increase in glycine were observed in the epileptic animal model, and these dropped to near-control values after laser treatment. In addition, a significant increase in cortical AST activity and a significant decrease in ALT activity and glucose content were obtained in the pilocarpinized animals and pilocarpinized rats treated with laser irradiation. In the hippocampus, significant decreases in the activity of AST and ALT and glucose content were recorded in the epileptic animals and in the epileptic animals treated with laser irradiation. Based on the results obtained in this study, it may be suggested that nearinfrared laser irradiation may reverse the neurochemical changes in amino acid neurotransmitters induced by pilocarpine.

Regulatory effect of prostaglandin E2 on protein expression in bovine retinae, ex vivo

We have evidence that prostaglandin (PG)E2 reduces endogenous bovine retinal amino acid neurotransmitter levels, ex vivo [Zhao et al, Methods and Findings, In press]. It is, however, unclear if these changes in neurotransmitter levels involve an effect on protein expression. Freshly isolated bovine eyeballs were injected, intravitreally with PGE2 and retinae were isolated and prepared for determination of protein expression using the 2DE‐DIGE approach. Protein spots exhibiting statistically significant changes (P<0.05) were selected and identified using LC‐MS/MS and analyzed by bioinformatics. PGE2 (10 uM) increased the expression of three proteins while five were decreased. The structural proteins, albumin and tubulin alpha‐1D chain and the cellular defense protein, heat shock 70 kDa protein 1B were up‐regulated. In contrast, peroxiredoxin 2 (a scavenger for peroxides) and aldehyde dehydrogenase 9 family, member A1 (an enzyme that breaks down alcohol) were down‐regulated. Furthermore, the GDP dissociation inhibitor 2, a signal transduction protein, recoverin, a calcium‐binding protein in photoreceptor cells and CNDP dipeptidase 2 were also down‐regulated. In conclusion, PGE2 altered the expression of both structural proteins and those involved in cellular defense and signal transduction pathways in bovine retina, ex vivo.

Strain Differences in Extracellular Amino Acid Neurotransmitter Levels in the Hippocampi of Major Histocompatibility Complex Congenic Mice in Response to Toluene Exposure

Objective: The aim of the present study was to investigate the possible role of the major histocompatibility complex locus in neurotransmitter systems in the mouse hippocampus following toluene exposure. Methods: We compared the changes in toluene-induced extracellular amino acid neurotransmitter levels in the hippocampi of 2 strains of male congenic mice, C57BL/10 (H-2^b) and B10.BR/Sg (H-2^k). In vivo microdialysis was performed in each freely moving mouse after a single intraperitoneal injection of toluene (300 mg/kg), and neurotransmitters in the hippocampal microdialysates were measured using high-performance liquid chromatography. Results: The basal extracelluar glutamate and glycine levels in the hippocampi of the C57BL mice were significantly higher than those in the B10.BR mice. However, the basal extracellular taurine levels in the hippocampi of the C57BL mice were significantly lower than those in the B10.BR mice. Although no changes in the glutamate levels were observed after toluene injection in either strain, the glycine levels increased significantly after toluene injection in the C57BL mice. On the other hand, significantly lower taurine levels were observed after toluene injection in both strains of mice. Conclusions: Our data demonstrate the existence of a relationship between H-2 haplotypes and hippocampal neurotransmitter levels in mice.

Excitatory Neurotransmitters in Brain Regions in Interictal Migraine Patients

ObjectiveTo examine biochemical differences in the anterior cingulate cortex (ACC) and insula during the interictal phase of migraine patients. We hypothesized that there may be differences in levels of excitatory amino acid neurotransmitters and/or their derivatives in migraine group based on their increased sensitivity to pain.Methods2D J-resolved proton magnetic resonance spectroscopy (1H-MRS) data were acquired at 4.0 Tesla (T) from the ACC and insula in 10 migraine patients (7 women, 3 men, age 43 ± 11 years) and 8 age gender matched controls (7 women, 3 men, age 41 ± 9 years).ResultsStandard statistical analyses including analysis of variance (ANOVA) showed no significant metabolite differences between the two subject cohorts in the ACC nor the insula. However, linear discriminant analysis (LDA) introduced a clear separation between subject cohorts based on N-acetyl aspartylglutamate (NAAG) and glutamine (Gln) in the ACC and insula.ConclusionThese results are consistent with glutamatergic abnormalities in the ACC and insula in migraine patients during their interictal period compared to healthy controls. An alteration in excitatory amino acid neurotransmitters and their derivatives may be a contributing factor for migraineurs for a decrease in sensitivity for migraine or a consequence of the chronic migraine state. Such findings, if extrapolated to other regions of the brain would offer new opportunities to modulate central system as interictal or preemptive medications in these patients.

Effect of Three Different Intensities of Infrared Laser Energy on the Levels of Amino Acid Neurotransmitters in the Cortex and Hippocampus of Rat Brain

The aim of this study is to investigate the effects of three different intensities of infrared diode laser radiation on amino acid neurotransmitters in the cortex and hippocampus of rat brain. Lasers are known to induce different neurological effects such as pain relief, anesthesia, and neurosuppressive effects; however, the precise mechanisms of these effects are not clearly elucidated. Amino acid neurotransmitters (glutamate, aspartate, glutamine, gamma-aminobutyric acid [GABA], glycine, and taurine) play vital roles in the central nervous system (CNS). The shaved scalp of each rat was exposed to different intensities of infrared laser energy (500, 190, and 90 mW) and then the rats were sacrificed after 1 h, 7 d, and 14 d of daily laser irradiation. The control groups were exposed to the same conditions but without exposure to laser. The concentrations of amino acid neurotransmitters were measured by high-performance liquid chromatography (HPLC). The rats subjected to 500 mW of laser irradiation had a significant decrease in glutamate, aspartate, and taurine in the cortex, and a significant decrease in hippocampal GABA. In the cortices of rats exposed to 190 mW of laser irradiation, an increase in aspartate accompanied by a decrease in glutamine were observed. In the hippocampus, other changes were seen. The rats irradiated with 90 mW showed a decrease in cortical glutamate, aspartate, and glutamine, and an increase in glycine, while in the hippocampus an increase in glutamate, aspartate, and GABA were recorded. We conclude that daily laser irradiation at 90 mW produced the most pronounced inhibitory effect in the cortex after 7 d. This finding may explain the reported neurosuppressive effect of infrared laser energy on axonal conduction of hippocampal and cortical tissues of rat brain.

Kir6.2 knockout alters neurotransmitter release in mouse striatum: An in vivo microdialysis study

ATP-sensitive potassium (K-ATP) channels have been demonstrated to play important roles in the brain. In the present study, Kir6.2 knockout (Kir6.2-/-) mice were used to examine the contribution of Kir6.2-containing K-ATP channels to the regulation of neurotransmitter release via in vivo microdialysis studies. The results showed that the extracellular levels of monoamine and amino acid neurotransmitters in Kir6.2-/- mouse striatum were similar to those in Kir6.2+/+ mice under basal conditions. After high K+ (100mM) perfusion, the extracellular levels of DA and amino acids were increased in both genotypes. These increases, however, were significantly lower in Kir6.2-/- mice than those in Kir6.2+/+ mice. Extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC), a major metabolite of DA, were increased in Kir6.2-/- mice but decreased in Kir6.2+/+ mice in response to high K+ stimulus. The releases of 4-hydroxy-3-methoxy-phenylacetic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were attenuated to a similar extent in both mouse genotypes. Taken together, this study provides direct in vivo evidence that Kir6.2-containing K-ATP channels play regulatory roles in neurotransmitter release in the striatum.

Acute effects of N-(2-propylpentanoyl)urea on hippocampal amino acid neurotransmitters in pilocarpine-induced seizure in rats

The present study aimed to investigate the anticonvulsant activity as well as the effects on the level of hippocampal amino acid neurotransmitters (glutamate, aspartate, glycine and GABA) of N-(2-propylpentanoyl)urea (VPU) in comparison to its parent compound, valproic acid (VPA). VPU was more potent than VPA, exhibiting the median effective dose (ED(50)) of 49 mg/kg in protecting rats against pilocarpine-induced seizure whereas the corresponding value for VPA was 322 mg/kg. In vivo microdialysis demonstrated that an intraperitoneal administration of pilocarpine induced a pronounced increment of hippocampal glutamate and aspartate whereas no significant change was observed on the level of glycine and GABA. Pretreatment with either VPU (50 and 100 mg/kg) or VPA (300 and 600 mg/kg) completely abolished pilocarpine-evoked increases in extracellular glutamate and aspartate. In addition, a statistically significant reduction was also observed on the level of GABA and glycine but less than a drastic reduction of glutamate and aspartate level. Based on the finding that VPU and VPA could protect the animals against pilocarpine-induced seizure it is suggested that the reduction of inhibitory amino acid neurotransmitters was comparatively minor and offset by a pronounced reduction of glutamate and aspartate. Therefore, like VPA, the finding that VPU could drastically reduce pilocarpine-induced increases in glutamate and aspartate should account, at least partly, for its anticonvulsant activity observed in pilocarpine-induced seizure in experimental animals. Some other mechanism than those being reported herein should be further investigated.

Centrally Administered Tryptophan Suppresses Food Intake in Free Fed Chicks through the Serotonergic System

The effects of intracerebroventricular injection of L-tryptophan on feeding behavior and the levels of brain neurotransmitters (amino acids or monoamines) were investigated in ad libitum chicks. The tryptophan treatment (3 or 6μmol) significantly inhibited food intake in chicks at 30min postinjection. The levels of serotonin (5-HT) and its metabolite, 5-dihydroxyindolacetic acid, in chicks treated with tryptophan were significantly higher than those with saline at 15min postinjection. However, there were no differences in the levels of catecholamines (adrenaline, noradrenaline and dopamine) and amino acid neurotransmitters (e.g., γ-aminobutyric acid, glycine and glutamic acid). The tryptophan-induced anorexia tended to be attenuated by the 5-HT2A receptor antagonist ketanserin (10μg). These results suggest that the administration of tryptophan into the chick brain produces the anorexic effect, and that the change in brain 5-HT content may be involved in this anorexia.

Changes in neurotransmitter levels and proinflammatory cytokine mRNA expressions in the mice olfactory bulb following nanoparticle exposure

Recently, there have been increasing reports that nano-sized component of particulate matter can reach the brain and may be associated with neurodegenerative diseases. Previously, our laboratory has studied the effect of intranasal instillation of nano-sized carbon black (CB) (14 nm and 95 nm) on brain cytokine and chemokine mRNA expressions and found that 14-nm CB increased IL-1β, TNF-α, CCL2 and CCL3 mRNA expressions in the olfactory bulb, not in the hippocampus of mice. To investigate the effect of a single administration of nanoparticles on neurotransmitters and proinflammatory cytokines in a mouse olfactory bulb, we performed in vivo microdialysis and real-time PCR methods. Ten-week-old male BALB/c mice were implanted with guide cannula in the right olfactory bulb and, 1 week later, were instilled vehicle or CB (14 nm, 250 μg) intranasally. Six hours after the nanoparticle instillation, the mice were intraperitoneally injected with normal saline or 50 μg of bacteria cell wall component lipoteichoic acid (LTA), which may potentiate CB-induced neurologic effect. Extracellular glutamate and glycine levels were significantly increased in the olfactory bulb of CB-instilled mice when compared with vehicle-instilled control mice. Moreover, we found that LTA further increased glutamate and glycine levels. However, no alteration of taurine and GABA levels was observed in the olfactory bulb of the same mice. We also detected immunological changes in the olfactory bulb 11 h after vehicle or CB instillation and found that IL-1β mRNA expression was significantly increased in CB- and LTA-treated mice when compared with control group. However, TNF-α mRNA expression was increased significantly in CB- and saline-treated mice when compared with control group. These findings suggest that nanoparticle CB may modulate the extracellular amino acid neurotransmitter levels and proinflammatory cytokine IL-1 β mRNA expressions synergistically with LTA in the mice olfactory bulb.

The essential oil of bergamot enhances the levels of amino acid neurotransmitters in the hippocampus of rat: Implication of monoterpene hydrocarbons

The effects of bergamot essential oil (BEO) on the release of amino acid neurotransmitters in rat hippocampus have been studied by in vivo microdialysis and by in vitro superfusion of isolated nerve terminals. Intraperitoneal administration of BEO (100 μl/kg) significantly elevated the extracellular concentration of aspartate, glycine and taurine in a Ca 2+-dependent manner. A dose-relation study generated a bell-shaped curve. When perfused into the hippocampus via the dialysis probe (20 μl/20 min), BEO produced a significant increase of extracellular aspartate, glycine, taurine as well as of GABA and glutamate. The augmentation of all amino acids was Ca 2+-independent. Focally injected 1:1 diluted BEO preferentially caused extracellular increase of glutamate. Interestingly, this release appeared to be strictly Ca 2+-dependent. BEO concentration-dependently enhanced the release of [ 3H] d-aspartate from superfused hippocampal synaptosomes. Similar results were obtained by monitoring the BEO-evoked release of endogenous glutamate. At relatively high concentrations, the BEO-induced [ 3H] d-aspartate release was almost entirely prevented by the glutamate transporter blocker dl-threo-β-benzyloxyaspartic acid ( dl-TBOA) and was Ca 2+-independent. At relatively low concentrations the release of [ 3H] d-aspartate was only in part (∼50%) dl-TBOA-sensitive and Ca 2+-independent; the remaining portion of release was dependent on extracellular Ca 2+. Interestingly, the monoterpene hydrocarbon-free fraction of the essential oil appeared to be inactive while the bergapten-free fraction superimposed the releasing effect of BEO supporting the deduction that psoralens may not be implicated. To conclude, BEO contains into its volatile fraction still unidentified monoterpene hydrocarbons able to stimulate glutamate release by transporter reversal and/or by exocytosis, depending on the dose administered.

Toluene induces rapid and reversible rise of hippocampal glutamate and taurine neurotransmitter levels in mice

Toluene, a widely used aromatic organic solvent, has been well characterized as a neurotoxic chemical. Although the neurobehavioral effects of toluene have been studied substantially, the mechanisms involved are not clearly understood. Hippocampus, which is one of the limbic areas of brain associated with neuronal plasticity, and learning and memory functions, may be a principal target of toluene. In the present study, to establish a mouse model for investigating the effects of acute toluene exposure on the amino acid neurotransmitter levels in the hippocampus, in vivo microdialysis study was performed in freely moving mice after a single intraperitoneal administration of toluene (150 and 300 mg/kg). Amino acid neurotransmitters in microdialysates were measured by a high performance liquid chromatography system. The extracellular levels of glutamate and taurine were rapidly and reversibly increased within 30 min after the toluene administration in a dose-dependent manner and returned to the basal level by 1 h. Conversely, the extracellular level of glycine and GABA were stable, and no significant change was observed after the toluene administration. To further investigate the brain toluene level in the hippocampus of toluene-administered mice, we used a solid-phase microextraction (SPME) method and examined the time course changes of toluene in the hippocampus of living mice. The brain toluene level reached the peak at 30 min after injection and returned to the basal level after 2 h. In the present study, we observed the relationship between brain toluene levels and amino acid neurotransmitter glutamate and taurine levels in the hippocampus. Therefore, we suggest that toluene may mediate its action through the glutamatergic and taurinergic neurotransmission in the hippocampus of freely moving mice.

Impaired formalin-evoked changes of spinal amino acid levels in diabetic rats

To investigate mechanisms by which diabetes alters sensory processing, we measured levels of amino acid neurotransmitters in spinal dialysates from awake, unrestrained control and diabetic rats under resting conditions and following hind paw formalin injection. Under resting conditions, glutamate concentrations in spinal dialysates were significantly ( P < 0.05) decreased in diabetic rats compared to those of control rats whereas aspartate, taurine, glycine and citrulline remained unchanged and GABA was significantly ( P < 0.05) increased. Noxious stimulation of the hind paw by subcutaneous injection of 0.5% formalin into the dorsum caused a defined flinching behavior in the afflicted paw, and the amount of flinching was significantly ( P < 0.05) greater in diabetic rats than in controls. Paw formalin injection significantly ( P < 0.05) increased dialysate levels of glutamate, aspartate, taurine, glycine and citrulline by 3- to 4-fold above basal in both control and diabetic rats. The concentration of glutamate in dialysate samples collected immediately after paw formalin injection remained significantly ( P < 0.05) lower in diabetic rats compared to those in controls. Formalin injection did not alter dialysate GABA concentrations in control rats, whereas in diabetic rats there was an increase of 151 ± 15% above basal levels. These findings indicate that the selective depression of basal and stimulus-evoked glutamate levels in the spinal cord of diabetic rats occurs in parallel with elevated spinal GABA levels. Because increased pain-associated behavior is accompanied by an attenuated spinal glutamate spike following paw formalin injection, hyperalgesia in diabetic rats does not appear to be secondary to enhanced glutamatergic input to the spinal cord.

NAAG peptidase inhibitor increases dialysate NAAG and reduces glutamate, aspartate and GABA levels in the dorsal hippocampus following fluid percussion injury in the rat

Traumatic brain injury (TBI) produces a rapid and excessive elevation in extracellular glutamate that induces excitotoxic brain cell death. The peptide neurotransmitter N-acetylaspartylglutamate (NAAG) is reported to suppress neurotransmitter release through selective activation of presynaptic group II metabotropic glutamate receptors. Therefore, strategies to elevate levels of NAAG following brain injury could reduce excessive glutamate release associated with TBI. We hypothesized that the NAAG peptidase inhibitor, ZJ-43 would elevate extracellular NAAG levels and reduce extracellular levels of amino acid neurotransmitters following TBI by a group II metabotropic glutamate receptor (mGluR)-mediated mechanism. Dialysate levels of NAAG, glutamate, aspartate and GABA from the dorsal hippocampus were elevated after TBI as measured by in vivo microdialysis. Dialysate levels of NAAG were higher and remained elevated in the ZJ-43 treated group (50 mg/kg, i.p.) compared with control. ZJ-43 treatment also reduced the rise of dialysate glutamate, aspartate, and GABA levels. Co-administration of the group II mGluR antagonist, LY341495 (1 mg/kg, i.p.) partially blocked the effects of ZJ-43 on dialysate glutamate and GABA, suggesting that NAAG effects are mediated through mGluR activation. The results are consistent with the hypothesis that inhibition of NAAG peptidase may reduce excitotoxic events associated with TBI.

Increased glutamate levels in the vitreous of patients with retinal detachment

Experimental models have implicated glutamate in the irreversible damage to retinal cells following retinal detachment. In this retrospective study we investigated a possible role for glutamate and other amino acid neurotransmitters during clinical rhegmatogenous retinal detachment (RRD). Undiluted vitreous samples were obtained from 176 patients undergoing pars plana vitrectomy. The study group consisted of 114 patients (114 eyes) with a rhegmatogenous retinal detachment. Controls included 52 eyes with an idiopathic macular hole or idiopathic epiretinal membrane and 10 eyes with a traction retinal detachment due to proliferative diabetic retinopathy. Vitreous concentrations of glutamate, gamma-aminobutyric acid (GABA), taurine, glycine, and aspartate were determined by high-pressure liquid chromatography (HPLC). Multivariate analysis was used to examine a possible association between amino acid neurotransmitter levels and several clinical variables including visual acuity. The mean vitreous concentration of glutamate in eyes with a rhegmatogenous retinal detachment (16.6 ± 5.6 μM) was significantly higher as compared to the controls (13.1 ± 5.2 μM) ( P = 0.001). Taurine levels were also increased in RRD, whereas no significant difference could be observed in glycine, aspartate and GABA levels when comparing RRD with controls. A correlation was found between increased vitreous glutamate and a lower pre-operative visual acuity. No association was, however, observed between post-operative visual acuity and the level of any of the five amino acid neurotransmitters. RRD was associated with a significantly increased vitreous glutamate concentration. Using visual acuity as a functional parameter in this study, we could not demonstrate a correlation between vitreous glutamate, or any of the other tested amino acid neurotransmitters and visual outcome.

Effects of prenatal paraquat and mancozeb exposure on amino acid synaptic transmission in developing mouse cerebellar cortex

The goal of this study was to analyze the effects of prenatal exposure to the pesticides paraquat (PQ) and mancozeb (MZ) on the development of synaptic transmission in mouse cerebellar cortex. Pregnant NMRI mice were treated with either saline, 10 mg/kg PQ, 30 mg/kg MZ or the combination of PQ + MZ, between gestational days 12 (E12) and E20. Variation in the levels of amino acid neurotransmitters was determined by HPLC, between postnatal day 1 (P1) and P30. Motor coordination was assessed by locomotor activity evaluation of control and experimental pups at P14, P21 and P30. Significant reductions in the levels of excitatory neurotransmitters, aspartate and glutamate, were observed in PQ-, MZ- or combined PQ + MZ-exposed pups, with respect to control, during peak periods of excitatory innervation of Purkinje cells: between P2–P5 and P11–P15. However, at P30, lower aspartate contents, in contrast with increased glutamate levels, were detected in all experimental groups. During the first two postnatal weeks, delays in GABA and glycine ontogenesis were observed in PQ- and PQ + MZ-exposed pups, whereas notable decrements in GABA and glycine levels were seen in PQ + MZ-exposed animals. Decreased taurine contents were detected at P3 and P11 in PQ- and PQ + MZ-exposed mice. Pups in different experimental groups all showed hyperactivity at P14 and then exhibited reduced locomotor activity at P30. Taken together, our results indicate that prenatal exposure to either PQ or MZ or the combination of both could alter the chronology and magnitude of synaptic transmission in developing mouse cerebellar cortex.

Susceptibility to audiogenic seizure and neurotransmitter amino acid levels in different brain areas of IL-6-deficient mice

Interleukin-6-deficient (IL-6 −/−) mice and their normal littermate (WT) were studied to evaluate their susceptibility to seizures induced by electroshock and audiogenic stimuli at different ages. No significant changes in maximal electroshock susceptibility were evidenced between the two strains, while audiogenic seizures (AGS) can be induced only in IL-6 −/− mice. The effects of age and genetic condition on AGSs were evaluated. The behavioural and electrocortical changes during audiogenic stimulus were observed. In addition, the levels of neurotransmitter amino acids in five brain areas (of both strains) were measured at 60 days of age. Aspartate level significantly increased in the brain stem (BS) and hippocampus (HI), while it decreased in the diencephalon (DE) of IL-6 −/− mice. Glutamate content significantly decreased in the cerebellum (CB), DE and HI. GABA levels significantly decreased in all the areas studied. Glycine significantly decreased in the BS, CB and DE, while taurine decreased only in the DE. The levels of glutamine significantly decreased in all the areas examined, except in the cortex (CX). The changes of neuroactive amino acid levels, particularly in the BS, might explain the characteristic of high propensity to AGS of IL-6 −/− mice. The present data support the validity of IL-6 −/− mice as a novel epileptic model for the study of the pathophysiology and pharmacology of epilepsy.

Relationship between cerebral interstitial levels of amino acids and phosphorylation potential during secondary energy failure in hypoxic-ischemic newborn piglets.

The aim of this study was to determine the validity of the hypothesis that excitatory amino acids are related to phosphorylation potential during primary and secondary cerebral energy failure observed in asphyxiated infants. We report here the results of experiments using newborn piglets subjected to severe transient cerebral hypoxia-ischemia followed by resuscitation. We examined cerebral energy metabolism by phosphorus nuclear magnetic resonance spectroscopy and changes in levels of amino acid neurotransmitters in the cortex by microdialysis before, during, and up to 24 h after the hypoxic-ischemic insult. The concentrations of aspartate, glutamate, taurine, and gamma-aminobutyric acid were significantly elevated during the hypoxic-ischemic insult compared with prebaseline values. Shortly after resuscitation, glutamate, taurine, and gamma-aminobutyric acid concentrations decreased but then began to increase again. These secondary elevations were greater than the primary elevations. A negative linear correlation was found between primary interstitial levels of glutamate and taurine and minimum values of phosphocreatine/inorganic phosphate during the secondary energy failure. The cerebral energy state depended on the time course of changes in excitatory amino acids, suggesting that amino acids play distinct roles during the early and delayed phases of injury.