Glutamate Levels In Rats Research Articles

The Role of Hypothermia in the Regulation of Blood Glutamate Levels in Naive Rats

The exact mechanism of hypothermia-induced neuroprotection has not been determined yet; however, we hypothesized that it may be mediated by a blood glutamate-scavenging effect. Here, we examine the effect of hypothermic conditions (mild, moderate, and deep) on blood glutamate levels in naive rats. To identify the mechanism of hypothermia-induced glutamate reduction, we also measured concentrations of glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT), the primary regulators of glutamate concentration in blood. Rats were anesthetized with isoflurane, and their rectal temperature was maintained for 6 hours at 36 to 37°C, 33 to 36°C, 30 to 32°C, 18 to 22°C, or was not maintained artificially. At 6 hours, active cooling was discontinued and rats were allowed to rewarm. There were 12 rats in each group for a total of 60 rats. Blood samples were drawn at 0, 3, 6, 12, 24, and 48 hours for the determination of blood glutamate, GOT, and GPT levels. A strong correlation between body temperature and blood glutamate levels was observed (P<0.001). Mild (33 to 36°C) and moderate (30 to 32°C) hypothermia led to reduced blood glutamate levels (P<0.001). Deep hypothermia (18 to 22°C) was associated with significant elevations in blood glutamate levels (P<0.001). Hypothermia, irrespective of the degree, led to elevations in GOT in plasma (P<0.001). Mild and moderate hypothermia led to a reduction in blood glutamate levels in rats, whereas deep hypothermia was associated with a significant elevation in blood glutamate levels. We further demonstrated an elevation of GOT and GPT levels, supporting their involvement in reducing blood glutamate by the conversion of glutamate to 2-ketoglutarate. We suggest that the neuroprotective properties of hypothermia may be partially because of a blood glutamate-scavenging mechanism.

Effect of estrogens on blood glutamate levels in relation to neurological outcome after TBI in male rats

Estrogen has been shown to possess neuroprotective properties both in vitro and in vivo. Traumatic brain injury (TBI) in ovulating females results in favorable neurological outcomes when compared to males with similar insults. The brain-to-blood glutamate gradient removes excess glutamate from brain extracellular fluids (ECF). Enhancing this gradient leads to improved neurological outcomes following TBI. In this study we investigate the effect of female gonadal steroids on blood glutamate levels and neurological outcomes. Forty male Sprague-Dawley rats were assigned to one of five groups: (1) sham, (2) Premarin treatment, (3) TBI, (4) TBI + Premarin treatment, and (5) TBI + Premarin pretreatment. TBI was induced, and estrogen and glutamate levels were determined at 0, 60, 120, 135, and 150 min. Neurological recovery was evaluated using the Neurological Severity Score (NSS) at 1 h and reassessed at 24 h post TBI. Premarin treatment groups demonstrated a decline in blood glutamate levels by 60 min. This decline was found to be more pronounced in the TBI + Premarin group, which maintained the decline throughout the experiment. At 120 min, the difference between groups was most pronounced (TBI + Premarin 99 ± 36 μM/l vs. control 200 ± 46 μM/l, p < 0.01). Neurological recovery was significantly better in the Premarin treatment group (NSS at 24 h 6 ± 1 vs. control 11 ± 1). Premarin injected into male rats significantly decreases blood glutamate levels in rats suffering TBI. This decrease is associated with improved neurological outcomes, thus implicating the role of estrogen in neuroprotection.

P.2.b.015 Extracellular glutamate levels in rats with high or low exploratory behaviour

P.2.b.015 Extracellular glutamate levels in rats with high or low exploratory behaviour

Rapid microelectrode measurements and the origin and regulation of extracellular glutamate in rat prefrontal cortex

Glutamate in the prefrontal cortex (PFC) plays a significant role in several mental illnesses, including schizophrenia, addiction and anxiety. Previous studies on PFC glutamate-mediated function have used techniques that raise questions on the neuronal versus astrocytic origin of glutamate. The present studies used enzyme-based microelectrode arrays to monitor second-by-second resting glutamate levels in the PFC of awake rats. Locally applied drugs were employed in an attempt to discriminate between the neuronal or glial components of the resting glutamate signal. Local application of tetrodotoxin (sodium channel blocker), produced a significant (∼ 40%) decline in resting glutamate levels. In addition significant reductions in extracellular glutamate were seen with locally applied ω-conotoxin (MVIIC; ∼ 50%; calcium channel blocker), and the mGluR(2/3) agonist, LY379268 (∼ 20%), and a significant increase with the mGluR(2/3) antagonist LY341495 (∼ 40%), effects all consistent with a large neuronal contribution to the resting glutamate levels. Local administration of D,L-threo-β-benzyloxyaspartate (glutamate transporter inhibitor) produced an ∼ 120% increase in extracellular glutamate levels, supporting that excitatory amino acid transporters, which are largely located on glia, modulate clearance of extracellular glutamate. Interestingly, local application of (S)-4-carboxyphenylglycine (cystine/glutamate antiporter inhibitor), produced small, non-significant bi-phasic changes in extracellular glutamate versus vehicle control. Finally, pre-administration of tetrodotoxin completely blocked the glutamate response to tail pinch stress. Taken together, these results support that PFC resting glutamate levels in rats as measured by the microelectrode array technology are at least 40-50% derived from neurons. Furthermore, these data support that the impulse flow-dependent glutamate release from a physiologically -evoked event is entirely neuronally derived.

Episodic Dural Stimulation in Awake Rats: A Model for Recurrent Headache

To model, in rats, the development of chronic trigeminal nociceptive hypersensitivity seen in patients with recurrent headache. Pathophysiology studies suggest that patients with recurrent migraine headache experience repeated bouts of dural nociceptor activation. In some patients, the severity and frequency of headache attacks increase over time. Patients with recurrent headache are hypersensitive to nitric oxide donors, such as glyceryl trinitrate (GTN). Current trigeminal pain models do not reflect the repeated episodic nature of dural nociceptor activation in patients with recurrent headache. Repeated nociceptor activation creates long-lasting changes in the periphery and brain due to activity-dependent neuronal plasticity. An animal model of repeated activation of dural nociceptors will facilitate the study of the physiological changes caused by repeated, episodic pain and the factors important for the transition of episodic to chronic migraine. We induced dural inflammation by infusing an inflammatory soup (IS) through a cannula on the dura in awake behaving rats. This was repeated 3 times per week for up to 4 weeks. Periorbital pressure sensory testing was used to monitor the change in trigeminal sensitivity. Rats were challenged with GTN to test the hypothesis that many dural stimulations are required to model the hypersensitivity of migraine patients. Quantitative trigeminal sensory testing and microdialysis in the trigeminal nucleus caudalis (TNC) were used to measure GTN hypersensitivity. Multiple infusions of IS (>8), over weeks, induced a long-lasting decrease in periorbital pressure thresholds that lasted >3 weeks after the last infusion. In contrast, IS infusion in IS-naive rats and those that received 3 IS infusions produced only short-lasting decreases in periorbital pressure thresholds. Rats that received more than 8 IS infusions showed a marked increase in their neurochemical and behavioral responses to GTN. In these rats, GTN induced a decrease in periorbital von Frey thresholds that lasted >5 hours. In contrast, in rats that received only 3 IS infusions, GTN caused a threshold decrease for 1.5 hour. In vivo microdialysis in the TNC showed that GTN increased extracellular glutamate levels in rats with more than 8 IS infusions to 7.7 times the basal levels. In IS-naive rats and those that received only 3 IS infusions, the extracellular glutamate levels rose to only 1.7 and 1.9 times the basal level, respectively. Repeated IS stimulation of the dura produces a chronic state of trigeminal hypersensitivity and potentiates the response to GTN. This hyperresponsiveness outlasts the last IS infusion and is the basis of our rat model of recurrent headache. This model can be used to study the changes in the brain and periphery induced by repeated trigeminovascular nociceptor activation and has the potential to elucidate the mechanisms for the transition of episodic to chronic headache.

Alterations of plasma and cerebrospinal fluid glutamate levels in rats treated with the N‐methyl‐D‐aspartate receptor antagonist, ketamine

It has been reported that the repeated administration of a sub-anesthetic dose of an N-methyl-D-aspartate receptor antagonist, ketamine, can produce an animal model of schizophrenia. Since no information is available on the alterations of the amino acid levels in ketamine-treated rats, we investigated the amino acid composition in the plasma and cerebrospinal fluid of rats that were repeatedly administered with ketamine for 5 consecutive days (30 mg/kg/day). The plasma and cerebrospinal fluid amino acid compositions in the fifth week after cessation of repeated ketamine administration were determined by highperformance liquid chromatography with fluorescence detection using a pre-column fluorescence reagent, i.e. 4-fluoro-7nitro-2,1,3-benzoxadiazole. Among the amino acids investigated in the present study, the level of plasma glutamic acid increased significantly (p < 0.05), while that of the cerebrospinal fluid glutamic acid decreased significantly in the ketamine-treated rats as compared with these levels in control rats injected with saline (p < 0.05, n = 7). These alterations in the glutamic acid level in the plasma and cerebrospinal fluid resemble those in schizophrenic patients, suggesting that ketamine-treated rats may be a useful model for performing research on the pathophysiology of schizophrenia.

In vivo modulation of ventral tegmental area dopamine and glutamate efflux by local GABA B receptors is altered after repeated amphetamine treatment

The activity of dopamine neurons in the ventral tegmental area is modulated by excitatory (glutamatergic) and inhibitory (GABAergic) afferents. GABA, released by intrinsic neurons and by projection neurons originating in the nucleus accumbens and other regions, inhibits dopamine neurons via activation of GABA A and GABA B receptor subtypes. Using in vivo microdialysis in freely moving rats, we investigated the role of ventral tegmental area GABA B receptors in modulating levels of dopamine and glutamate within the ventral tegmental area, both in naive rats and in rats treated repeatedly with saline or amphetamine (5 mg/kg i.p., for 5 days). In naive rats, administration of a potent and selective GABA B receptor antagonist (CGP 55845A) into the ventral tegmental area elicited a concentration-dependent increase in dopamine levels, but did not alter glutamate levels. In rats tested 3 days after discontinuing repeated amphetamine administration, 50 μM CGP 55845A increased dopamine levels to a greater extent than in saline controls. This difference was no longer present in rats tested 10–14 days after discontinuing repeated amphetamine injections. CGP 55845A (50 μM) had no effect on glutamate levels in the ventral tegmental area of saline-treated rats. However, it produced a robust increase in glutamate levels in rats tested 3 days, but not 10–14 days, after discontinuing repeated amphetamine injections. These results suggest that somatodendritic dopamine release is normally under strong tonic inhibitory control by GABA B receptors. Repeated amphetamine administration enhances GABA B receptor transmission in the ventral tegmental area during the early withdrawal period, increasing inhibitory tone on both dopamine and glutamate levels. This is the first demonstration, in an intact animal, that drugs of abuse alter GABA B receptor transmission in the ventral tegmental area.

Amphetamine-Induced Plasticity of AMPA Receptors in the Ventral Tegmental Area: Effects on Extracellular Levels of Dopamine and Glutamate in Freely Moving Rats

Previous electrophysiological studies suggested that the initiation of behavioral sensitization to cocaine and amphetamine involves a transient increase in AMPA receptor responsiveness in the ventral tegmental area (VTA). To test this, we used in vivo microdialysis to examine the effects of intra-VTA administration of AMPA (10 microm) and NMDA (100 microm) on dopamine (DA) and glutamate efflux in the VTA and the nucleus accumbens (NAC), an important target of VTA DA neurons. We compared rats treated for 5 d with saline or 5 mg/kg amphetamine and withdrawn for 3 or 10-14 d. After 3 d of withdrawal, intra-VTA AMPA increased both NAC and VTA DA levels to a greater extent in the amphetamine group, whereas NMDA produced similar effects in the saline and amphetamine groups. This enhanced responsiveness to AMPA was no longer evident in rats tested 10-14 d after the last injection. In addition, intra-VTA AMPA but not NMDA increased both VTA and NAC glutamate levels in rats tested 3 d after the last injection of amphetamine but not in saline controls. After 10-14 d, the responsiveness of glutamate levels to AMPA was no longer evident in the NAC but persisted in the VTA. Additional studies indicated that the glutamate effect in the NAC may involve increased responsiveness of DA receptors within the NAC. These findings establish an in vivo animal model with which to explore the consequences of repeated drug administration for AMPA receptor plasticity in the VTA. They also indicate that repeated amphetamine leads to potentiated interactions between DA and glutamate transmission.

Experimental studies of agents with potential neuroprotective properties

Acta Ophthalmologica ScandinavicaVolume 77, Issue S229 p. 27-28 Free Access Experimental studies of agents with potential neuroprotective properties Larry A. Wheeler, Larry A. Wheeler Allergan, Inc., Department of Biological Sciences, 2525 Dupont Drive, Irvine, CA 92612, USASearch for more papers by this author Larry A. Wheeler, Larry A. Wheeler Allergan, Inc., Department of Biological Sciences, 2525 Dupont Drive, Irvine, CA 92612, USASearch for more papers by this author First published: 13 November 2014 https://doi.org/10.1111/j.1600-0420.1999.tb01133.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References Quigley HA, Nickells RW, Kerrigan LA et al. (1995): Retinal ganglion cell death in experimental glaucoma and after axotomy occurs by apoptosis. Invest Ophth Vis Sci 36: 774– 786. Kerrigan LA, Zack DJ, Quigley HA, Smith SD & Pease ME (1997): TUNEL-positive ganglion cells in human open-angle Glaucoma. Arch Ophthamol 115: 1031– 1035. Nickells RW (1996): Retinal ganglion cell death in glaucoma: The how, the why and the maybe. J Glaucoma 5: 345– 356. Vorwerk CK, Lipton SA, Zurakowski D et al. (1996): Chronic low-dose glutamate is toxic to retinal ganglion cells. Invest Ophth Vis Sci 37(8): 1618– 1624. Dryer EB, Zurakowski D, Schumer RA, Podos SM & Lipton SA (1996): Elevated glutamate in the vitreous body of humans and monkeys with glaucoma. Arch Ophthalmol 114: 299– 305. Duvdevani R, Rosner M, Belkin M, Sautter J, Sabel BA & Schwartz M (1990): Graded crush of the rat optic nerve as a brain injury model: combining electrophysiological and behavioral outcome. Restor Neurol Neurosci 2: 31– 38. Yoles E & Schwartz M (1998): Elevation of intraocular glutamate levels in rats with partial lesion of the optic nerve. Arch Ophthalmol 116: 906– 910. Garcia-Valenzuela E, Shareef S, Walsh J & Sharma SC (1995): Programmed cell death of retinal ganglion cells during experimental glaucoma. Exp Eye Res 61(1): 33– 44. Yoles E, Wheeler LA & Schwartz M (1999): Aipha-2-adrenoreceptor agonists are neuroprotective in a rat model of optic nerve degeneration. Invest Ophthal V15 Sci; in press. Hicks D, Heidinger V, Mohand-Said S, Sahel J & Dreyfus H (1998): Growth factors and gangliosides as neuroprotective agents in excitotoxicity and ischemia. Gen Pharmacol 30(30): 265– 273. Sievers J, Hausmann B, Unsicker K & Berry M (1987): Fibroblast growth factors promote the survival or adult rat retinal cells after transection of the optic nerve. 76: 157– 162. Peinado-Ramon P, Salvador M, Villegas-Perez MP & Vidat-Sanz M (1996): Effects of axotomy and intraocular administration of NT-4, NT-3, and brain-derived neurotrophic factor on the survival of adult rat retinal ganglion cells. Invest Ophthalmol Vis Sci 37: 489– 500. Zhang C, Takahasi K, Lam TT & Tso MO (1994): Effects of basic fibroblast growth factor in retinal ischemia. Invest Ophthalmol Vis Sci 35(8): 3163– 3168. Wen R, Cheng T, Li Y, Cao W & Steinberg RH (1996): Alpha 2-adrenergic agonists induce basic fibroblast growth factor expression in photoreceptors in vivo and ameliorate light damage. J Neurosci 16(19): 5986– 5992. Peng M, Yiwen L, Zhijun L, Liu C, Latties A & Wen R (1998): Alpha-2-adrenergic agonists selectively activate extracellular signal-regulated kinases in Mueller cells in vivo. Invest Ophthal Vis Sci 39: 721– 1726. Hasson D, Lai RK, Chun T & Wheeler LA (1997): Functional protection of rat retina ischemic injury by brimonidine, Soc Neuroscience 23: 72– 74. Chao DT & Korsmeyer SJ (1998): Bcl-2 family: regulators of cell death. Ann Rev Immunol 16: 395– 419. Volume77, IssueS229December 1999Pages 27-28 ReferencesRelatedInformation

Elevation of intraocular glutamate levels in rats with partial lesion of the optic nerve.

Acute partial lesion of the rat optic nerve, although not a model for glaucoma, mimics some of the features of the disease. To learn whether degeneration of rat optic nerve fibers and death of their retinal ganglion cells induced by an acute partial lesion are associated with elevated levels of glutamate, known to occur in the eyes of humans and monkeys with glaucoma. Rat optic nerve was subjected to a partial crush injury. Aqueous humor samples were aspirated from the anterior and posterior aqueous chambers at specified times and their amino acid contents were determined by means of high-performance liquid chromatography. Three and 7 days after injury, intraocular glutamate and aspartate levels were found to be significantly higher than in normal or sham-operated-on eyes, and returned to normal by day 14. Degeneration of the optic nerve, induced by a mechanical injury of the axons, leads to intraocular elevation of glutamate and aspartate levels. These results illustrate that the model of the partial optic nerve lesion exhibits another feature typical of a long-term optic neuropathy, such as glaucoma.