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The progressive pathogenesis and prevention of Parkinson’s disease (PD) remains unknown at present. Therefore, the present study aimed to investigate the possible progressive pathogenesis and prevention of PD. Our study investigated the content of glutamate, mitochondria calcium, calmodulin, malonaldehyde and trace elements in striatum, cerebral cortex and hippocampus tissues; and the expression of bcl-2, bax and neuronal nitric oxide synthase (nNOS) in substantia nigra and striatum; and the change of apomorphine induced rotation behavior; and the treatmental effect of monosialotetrahexosylganglioside (GM1) intraperitoneal administration for 14 days in a PD rat model induced by 6-hydroxydopamine. The results revealed that the content of glutamate significantly decreased, and that of mitochondria calcium, calmodulin, malonaldehyde and ferrum significantly increased in striatum, cerebral cortex and hippocampus tissues; the content of magnesium significantly decreased, and that of cuprum and zinc significantly increased in cerebral cortex; the expression of bcl-2 significantly decreased, and that of bax and nNOS significantly increased in substantia nigra and striatum in PD rat. GM1 can partially improve the apomorphine induced rotation behavior and changes of glutamate, mitochondria calcium, calmodulin content in striatum of PD rat. Data suggested that dysfunction of excitatory amino acids neurotransmitter, calcium homeostasis disorder, abnormal metabolism of oxygen free radicals, abnormal trace elements distribution and/or deposition and excessive apoptosis participated in the progressive process of PD, and that GM1 could partially prevent the progressive damage. [ABSTRACT FROM AUTHOR]

Abstract: There is an accumulating evidence for a transmitter role of l-aspartate (l-Asp) in various brain regions. Recent studies from our laboratory have indicated that l-Asp is present in excitatory synapses of the striatum/nucl. accumbens of domestic chicks where it is co-released with l-glutamate (l-Glu) from axon terminals. Here we provide data on the postsynaptic effects of l-Asp alongside with l-Glu in striatal slices from chicken (1- to 10-day-old) using visually guided patch-clamp technique. l-Asp and l-Glu produced similar dose-dependent inward currents and an increase in spontaneous synaptic activity in all of the recorded striatal neurons. In the presence of TTX both the NMDA receptor antagonist D-AP5 and the AMPA/kainate receptor antagonist CNQX reduced and the co-application of these two antagonists almost abolished the postsynaptic effects of l-Asp and l-Glu in a reversible manner. Testing the interactions of l-Asp and l-Glu in these striatal neurons we found that co-application of l-Asp and l-Glut produced significantly larger inward currents than l-Asp or l-Glut alone. Our data are the first to demonstrate that l-Asp can induce postsynaptic effects on the chicken striatal neurons. These effects are mediated by both NMDA and non-NMDA type ionotropic glutamate receptors and are similar to those evoked by l-Glu. In addition our results show that co-application of l-Asp and l-Glut facilitates each other''s effect, which is at least in part an excitatory amino acid (EAA) transporter dependent process. This phenomenon may explain the biological importance of the two EAAs with apparently similar postsynaptic activities in the same brain region. [Copyright &y& Elsevier]

Abstract: Previous work had demonstrated that there was elevated regional cerebral O2 consumption in the brains of a tuberous sclerosis model (Eker rat). We tested the hypothesis that the increased cerebral O2 consumption was related to an increased contribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors to the control of cerebral metabolism. Young (4weeks) male control Long Evans (N =14) and Eker (N =14) rats (70–100g) were divided into control and NBQX (50mg/kg, AMPA antagonist) treated animals. Cerebral regional blood flow (14C-iodoantipyrine) and O2 consumption (cryomicrospectrophotometry) were determined in isoflurane anesthetized rats. We found significantly increased basal O2 consumption (+85%) in the cortex, hippocampus, cerebellum and pons of the Eker rats. Regional cerebral blood flow was also elevated in Eker rats at baseline (+53%) as was cerebral O2 extraction (+22%). NBQX significantly lowered O2 consumption in all regions of the Long Evans rats (−41%). Cerebral O2 consumption was lowered in the cortex to a lesser extent (−24%) and there were no changes in other regions of the Eker rats after NBQX. Cerebral blood flow was reduced in the Long Evans, but not the Eker rats, after NBQX. In conclusion, Eker rats had significantly elevated cerebral O2 consumption, O2 extraction and blood flow, but this was not related to AMPA receptor activation. In fact, the importance of AMPA receptors in the control of basal cerebral O2 consumption was reduced. [Copyright &y& Elsevier]

Abstract: We examined the effect of the peripheral application of glutamate and capsaicin to the temporomandibular joint (TMJ) in influencing the activation and central sensitization of TMJ-responsive nociceptive neurons in the trigeminal subnucleus caudalis/upper cervical cord (Vc/UCC). The activity of single neurons activated by noxious mechanical stimulation of the TMJ was recorded in the Vc/UCC of 49 halothane-anesthetized male rats. Cutaneous mechanoreceptive field (RF), cutaneous mechanical activation threshold (MAT), and TMJ MAT of each neuron were assessed before and after injection of 0.5 M glutamate (or vehicle) and 1% capsaicin (or vehicle) into the TMJ. A total of 49 nociceptive neurons (37 nociceptive-specific, 12 wide-dynamic-range) that could be activated by blunt noxious mechanical stimulation of the TMJ were studied. When injected alone, glutamate and capsaicin activated and induced central sensitization (reflected in cutaneous RF expansion and cutaneous and/or TMJ MAT reduction) in most Vc/UCC neurons. Following glutamate injection, capsaicin evoked greater activity and less cutaneous/TMJ MAT reduction compared with capsaicin alone, whereas capsaicin abolished all subsequent glutamate-evoked activity and depressed cutaneous RF expansion in most neurons. Glutamate effects on deep afferents and Vc/UCC neurons were analogous since glutamate sensitized afferent and neuronal responses to capsaicin but the desensitizing effects of capsaicin on glutamate-evoked excitability of Vc/UCC neurons contrast with the lack of capsaicin-induced modulation of glutamate-evoked afferent excitability [], suggesting that peripheral and central sensitization may be differentially involved in the nociceptive effects of glutamate and capsaicin applied to deep craniofacial tissues. [Copyright &y& Elsevier]

Abstract: We have examined the effect of the peripheral application of glutamate and capsaicin to deep craniofacial tissues in influencing the activation and peripheral sensitization of deep craniofacial nociceptive afferents. The activity of single trigeminal nociceptive afferents with receptive fields in deep craniofacial tissues were recorded extracellularly in 55 halothane-anesthetized rats. The mechanical activation threshold (MAT) of each afferent was assessed before and after injection of 0.5 M glutamate (or vehicle) and 1% capsaicin (or vehicle) into the receptive field. A total of 68 afferents that could be activated by blunt noxious mechanical stimulation of the deep craniofacial tissues (23 masseter, 5 temporalis, 40 temporomandibular joint) were studied. When injected alone, glutamate and capsaicin activated and induced peripheral sensitization reflected as MAT reduction in many afferents. Following glutamate injection, capsaicin-evoked activity was greater than that evoked by capsaicin alone, whereas following capsaicin injection, glutamate-evoked responses were similar to glutamate alone. These findings indicate that peripheral application of glutamate or capsaicin may activate or induce peripheral sensitization in a subpopulation of trigeminal nociceptive afferents innervating deep craniofacial tissues, as reflected in changes in MAT and other afferent response properties. The data further suggest that peripheral glutamate and capsaicin receptor mechanisms may interact to modulate the activation and peripheral sensitization in some deep craniofacial nociceptive afferents. [Copyright &y& Elsevier]

Abstract: This study was designed to investigate the effect of acute intrathecal (i.t.) injection of amitriptyline (AMI) on the antinociceptive effect of morphine in rats treated with pertussis toxin (PTX). Male Wistar rats were implanted with an i.t. catheter for drug injection and some were implanted with an additional microdialysis probe used for CSF dialysate collection and measurement of excitatory amino acids (EAAs). The expression of glutamate transporters (GTs) in the spinal cord dorsal horn was also measured. A tail-flick test was performed and CSF dialysate was collected as the baseline-B value (day 0) before PTX (1 μg, i.t.) injection and at 4 days after PTX injection, but before drug challenge as the baseline-P value (day 4), and at 30, 60, 90, and 120 min after drug challenge on day 4. The baseline-P tail-flick latencies were significantly lower than the baseline-B values. In PTX-treated rats (day 4), morphine (10 μg, i.t.) did not produce an antinociceptive effect, but this was retained by acute AMI (15 μg, i.t.) pretreatment 30 min before morphine injection. In addition, concentrations of glutamate and aspartate were higher in baseline-P dialysates than in baseline-B dialysates, and the expression of the GTs (GLT-1, GLAST, and EAAC1) was downregulated by PTX treatment. Acute injection of PTX-treated rats with either AMI (15 μg, i.t.) or morphine (10 μg, i.t.) alone had no significant effect on CSF EAA concentrations and GT expression. In contrast, AMI (15 μg, i.t.) pretreatment followed 30 min later by morphine (10 μg, i.t.) injection inhibited the increase in EAA concentrations and reversed the downregulation of all three GTs. Our results show that AMI preserves the antinociceptive effect of morphine in PTX-treated rats. The mechanisms involve suppression of the increase in EAA concentrations in spinal CSF dialysates and reversion of GT expression in PTX-treated rats. [Copyright &y& Elsevier]

Abstract: The receptor localization of metabotropic glutamate receptors (mGlu) 2 and 3 was examined by using in situ hybridization and a well-characterized mGlu2-selective antibody in the rat forebrain. mGlu2 was highly and discretely expressed in cell bodies in almost all of the key regions of the limbic system in the forebrain, including the midline and intralaminar structures of the thalamus, the association cortices, the dentate gyrus of the hippocampus, the medial mammillary nucleus, and the lateral and basolateral nuclei of the amygdala. Moreover, presynaptic mGlu2 terminals were found in most of the forebrain structures, especially in the lateral part of the central nucleus of the amygdala, and the CA1 region of the hippocampus. Although some overlaps exist, such as in the hippocampus and the amygdala, the expression of mGlu3 mRNA, however, appeared to be more disperse, compared with that of mGlu2 mRNA. These distribution results support previous behavioral studies that the mGlu2 and 3 receptors may play important roles in emotional responses. In addition to its expression in glia, mGlu3 was distinctively expressed in cells in the GABAergic reticular nucleus of the thalamus. Local infusion of a non-selective mGlu2/3 agonist, LY379268, in the reticular nucleus of the thalamus, significantly reduced GABA release, suggesting that mGlu3 may also play a role in central disinhibition. [Copyright &y& Elsevier]

Abstract: The nucleus of the solitary tract (NTS) is the site of the first synapse of cardiovascular afferent fibers in the central nervous system. Important mechanisms for cardiovascular regulation are also present in the caudal pressor area (CPA) localized at the caudal end of the ventrolateral medulla. In the present study we sought to investigate the role of the commissural subnucleus of the NTS (commNTS) on pressor and tachycardic responses induced by l-glutamate injected into the CPA. Male Holtzman rats (n =8 rats/group) anesthetized with urethane (1.2 g/kg of body weight, iv) received injections of the GABAA receptor agonist muscimol into the commNTS. Unilateral injection of l-glutamate (10 nmol/100 nL) into the CPA increased mean arterial pressure (MAP, 31±4 mm Hg, vs. saline: 3±2 mm Hg) and heart rate (HR, 44±8 bpm, vs. saline: 10 ±7 bpm). Inhibition of commNTS neurons with muscimol (120 pmol/60 nL) abolished the increase in MAP (9±4 mm Hg) and HR (17±7 bpm) produced by l-glutamate into the CPA. The present results suggest that the pressor and tachycardic responses to CPA activation are dependent on commNTS mechanisms. [Copyright &y& Elsevier]

Abstract: Synapses onto dendritic spines in the lateral amygdala formed by afferents from the auditory thalamus represent a site of plasticity in Pavlovian fear conditioning. Previous work has demonstrated that thalamic afferents synapse onto LA spines expressing glutamate receptor (GluR) subunits, but the GluR subunit distribution at the synapse and within the cytoplasm has not been characterized. Therefore, we performed a quantitative analysis for α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits GluR2 and GluR3 and N-methyl-d-aspartate (NMDA) receptor subunits NR1 and NR2B by combining anterograde labeling of thalamo-amygdaloid afferents with postembedding immunoelectron microscopy for the GluRs in adult rats. A high percentage of thalamo-amygdaloid spines was immunoreactive for GluR2 (80%), GluR3 (83%), and NR1 (83%), while a smaller proportion of spines expressed NR2B (59%). To compare across the various subunits, the cytoplasmic to synaptic ratios of GluRs were measured within thalamo-amygdaloid spines. Analyses revealed that the cytoplasmic pool of GluR2 receptors was twice as large compared to the GluR3, NR1, and NR2B subunits. Our data also show that in the adult brain, the NR2B subunit is expressed in the majority of in thalamo-amygdaloid spines and that within these spines, the various GluRs are differentially distributed between synaptic and non-synaptic sites. The prevalence of the NR2B subunit in thalamo-amygdaloid spines provides morphological evidence supporting its role in the fear conditioning circuit while the differential distribution of the GluR subtypes may reflect distinct roles for their involvement in this circuitry and synaptic plasticity. [Copyright &y& Elsevier]

Abstract: β-N-oxalyl-amino-l-alanine, (l-BOAA), an excitatory amino acid, acts as an agonist of the AMPA subtype of glutamate receptors. It inhibits mitochondrial complex I in motor cortex and lumbosacral cord of male mice through oxidation of critical thiol groups, and glutaredoxin, a thiol disulfide oxido-reductase, helps maintain integrity of complex I. Since incidence of neurolathyrism is less common in women, we examined the mechanisms underlying the gender-related effects. Inhibition of complex I activity by l-BOAA was seen in male but not female mice. Pretreatment of female mice with estrogen receptor antagonist ICI 182,780 or tamoxifen sensitizes them to l-BOAA toxicity, indicating that the neuroprotection is mediated by estrogen receptors. l-BOAA triggers glutathione (GSH) loss in male mice but not in female mice, and only a small but significant increase in oxidized glutathione (GSSG) was seen in females. As a consequence, up-regulation of γ-glutamyl cysteinyl synthase (the rate-limiting enzyme in glutathione synthesis) was seen only in male mouse CNS but not in females. Both glutathione reductase and glutaredoxin that reduce oxidized glutathione and protein glutathione mixed disulfides, respectively, were constitutively expressed at higher levels in females. Furthermore, glutaredoxin activity in female mice was down-regulated by estrogen antagonist indicating its regulation by estrogen receptor. The higher constitutive expression of glutathione reductase and glutaredoxin could potentially confer neuroprotection to female mice. [Copyright &y& Elsevier]

Abstract: This study was designed to investigate the effect of acute and chronic intrathecal (i.t.) injection of gabapentin (GBP) on the antinociceptive effect of morphine and tolerance development using a tail-flick latency test. Levels of excitatory amino acids (EAA) in i.t. CSF dialysates were also measured by high performance liquid chromatography. Male Wistar rats were implanted with either one or two i.t. catheters for drug injection or pump infusion and with a microdialysis probe for CSF dialysate collection. The effect of acute GBP (10 μg i.t.) injection on the morphine dose response was examined in both naïve rats and rats made tolerant by continuous infusion of morphine (15 μg/h i.t.) for 5 days. At such a low dose (10 μg i.t.), GBP did not enhance morphine''s antinociception in naïve rats. In morphine-tolerant rats, however, acute GBP (10 μg i.t.) injection potentiated morphine''s antinociception and yielded a 14.6-fold shift in morphine''s dose–response curve. When GBP (10 μg/h i.t.) was co-infused with morphine (15 μg/h i.t.) to examine its effect on the development of morphine tolerance, GBP attenuated the development of morphine tolerance. The effect of GBP and morphine on CSF glutamate and aspartate levels was examined in naïve rats, and the effect of morphine challenge on CSF glutamate and aspartate levels was examined in rats previously infused for 5 days with morphine alone or morphine plus GBP. Acute injection of GBP (10 μg i.t.), morphine (50 μg i.t.), or GBP (10 μg i.t.) followed by morphine (50 μg i.t.) 30 min later had no significant effect on CSF EAA concentration in naïve rats; however, in tolerant rats, morphine challenge (50 μg i.t.) increased aspartate and glutamate levels to 221 ± 22% and 296 ± 43%, respectively, of those before morphine challenge, and this phenomenon was inhibited by GBP co-infusion. Our results show that GBP, at a dose without enhanced effect on morphine''s antinociception in naïve rats, not only potentiates morphine''s antinociceptive effect in morphine-tolerant rats but also attenuates the development of morphine tolerance. The mechanism of the effect of GBP on morphine tolerance might be via suppression of the EAA concentration in spinal CSF dialysate. [Copyright &y& Elsevier]

Abstract: Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia, Parkinson''s disease, autism, cognitive disorders) that are linked with abnormalities in these systems. Since the kainate receptor plays an essential role in mesolimbic neuronal development and excitability, we examined the effects of physiologically relevant concentrations of IL-2 on kainate-activated current (I KA) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA) of 3- to 14-day-old rats. IL-2 (0.01–10 ng/ml) alone had no effect on membrane conductance. When co-applied with kainate, IL-2 significantly decreased I KA. IL-2 (2 ng/ml) shifted the kainate concentration–response curve to the right in a parallel manner, significantly increasing the EC50 without changing the maximal I KA. IL-2 inhibition of I KA was voltage-dependent, being greater at negative potentials. IL-2 did not alter the reversal potential. These findings suggest that IL-2 potently modulates kainate receptors of developing mesolimbic neurons. We suggest that IL-2 plays a role in the excitability of developing neurons in the mesolimbic system. Inasmuch as increased I KA is associated with excitotoxicity, coupled with the present observation that IL-2 inhibits I KA, we suggest an adaptive role for IL-2 in limiting excitotoxicity in the developing brain. IL-2 might thus be required for normal cell development in the mesolimbic and mesostriatal systems. [Copyright &y& Elsevier]

Volatile hydrocarbon based CNS depressants including short chain alcohols and anesthetics act, in part, by inhibition of the excitatory effect of glutamate at the NMDA receptor. While effects of several of these volatile agents on NMDA-gated currents have been demonstrated, there has been no direct comparison of different chemical classes of CNS depressant drugs on NMDA-gated currents. Here, whole-cell voltage clamp measurements of currents gated by 100 μM NMDA from cultured cerebrocortical neurons were examined in the presence of varying concentrations of the alcohols ethanol and hexanol, the halogenated alcohol trichloroethanol, the halogenated alkane halothane and the halogenated ethers isoflurane and sevoflurane. All drugs tested showed concentration-dependent inhibition of NMDA-gated currents with anesthetic concentrations of each agent producing approximately 30% inhibition of the NMDA-gated current. A rapid-translation perfusion system was used to study the onset and offset kinetics of each of the volatile agents. Onset kinetics for the CNS depressants was similar with τ values near 100 ms. Offset kinetics was more variable with τ ranging from 88.2 ms for ethanol to 221.4 ms for trichloroethanol. These data indicate that a wide variety of volatile hydrocarbon based CNS depressants produce a similar inhibition of NMDA-gated currents and that the kinetics for these agents are inconsistent with an open channel block. [Copyright &y& Elsevier]

Numerous data indicate that nonsynaptic release of glutamate occurs both in normal and pathophysiological conditions. When reaching receptors in the postsynaptic density (PSD), glutamate (Glu) could affect the synaptic transmission. We have tested this possibility in the hippocampal CA1 synapses of rats, either by applying exogenous Glu to the CA1 neurons or by disruption of Glu transporter activity. l-Glu (400 μM) was directly applied to the hippocampal slices acutely isolated from the rats. It produced a strong inhibition of both ortho- and antidromically elicited action potentials fired by CA1 neurons while the excitatory postsynaptic current (EPSC) measured in these neurons remained totally unaffected. The optical isomer D-Glu which is not transported by the systems of Glu uptake inhibited not only orthodromic and antidromic spikes, but also EPSC. Non-specific glutamate transporter inhibitor DL-threo-β-hydroxyaspartic acid (THA, 400 μM) mimicked the effects of exogenous Glu and produced strong inhibition of both orthodromic and antidromic spikes, without any influence on the amplitude of EPSCs. Dihydrokainate (DHK, 300 μM), selective inhibitor of GLT-1 subtype of glutamate transporter, exerted a significant inhibitory action on the orthodromically evoked spikes and also on the EPSC. Our results indicate that extrasynaptic and PSD membranes of CA1 neurons form separate compartments differing in the mechanisms and efficiency of external Glu processing: the protection of PSD markedly prevails. [Copyright &y& Elsevier]

A calcium imaging technique combined with a confocal laser scanning microscope (CLSM) was applied to investigate the effects of phencyclidine (PCP) on glutamate-induced calcium increases in same group of primary cultured neocortical neurons. Non-N-methyl-d-aspartate (NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) alone did not significantly alter glutamate-induced changes of fluorescence (89.6%), while addition of PCP greatly blocked increases in fluorescence to 32.6% of the glutamate response. Competitive NMDA receptor antagonist dl-2-amino-5-phosphonovaleric acid (APV) alone and the addition of PCP reduced glutamate responses to 30.5% and 21.2%, respectively. These data clearly demonstrate that the neuropharmacological properties of PCP may function through its blockade of the NMDA receptor. [Copyright &y& Elsevier]

Previous studies in piglets have shown that the generation of oxygen free radicals (O−2) following traumatic brain injury and hypoxia/ischemia contribute to the reversal of N-methyl-d-aspartate (NMDA)-induced pial artery dilation to vasoconstriction. This study determined the contribution of protein tyrosine kinase (PTK) and mitogen-activated protein (MAPK) activation to impairment of NMDA cerebrovasodilation by O−2 in piglets equipped with a closed window. Exposure of the cerebral cortex to a xanthine oxidase O−2 generating system (OX) reversed NMDA (10−8, 10−6 M) dilation to vasoconstriction but such impairment was partially prevented by the PTK inhibitor, genistein, the MAPK (ERK isoform) inhibitor, U0126, and the MAPK (p38 isoform) inhibitor, SB203580 (9±1 and 15±1 vs. −1±1 and −1±1 vs. 5±1 and 9±1% for sham control, OX and OX in the presence of genistein, respectively). However, the p38 MAPK inhibitor, SB203580, prevented NMDA dilator impairment significantly less than the ERK MAPK inhibitor, U0126. Similar results were obtained for glutamate. These data show that PTK and MAPK activation by the presence of O−2 contributes to the impairment of NMDA dilation. Furthermore, these data indicate a differential role for ERK and p38 MAPK activation in impairment of NMDA dilation by O−2 in the brain. [Copyright &y& Elsevier]

N-Methyl-d-aspartate (NMDA) may affect dopaminergic cells, which contain tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. To clarify the involvement of TH in the neuroprotective effects of nitric oxide (NO), we investigated whether NMDA alters TH mRNA and TH protein levels and whether NO inhibits NMDA-induced changes in the rat retina. Dopamine levels in the retina were measured by high-performance liquid chromatography (HPLC). Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR showed that intravitreal injection of NMDA caused a significant reduction in TH mRNA levels in the retina. Similarly, Western blot analysis showed that NMDA decreased the production of TH protein. These reductions in TH mRNA and TH protein levels were attenuated by concomitant injection of NOC 18, an NO donor. HPLC analysis showed that NMDA reduced dopamine levels in the retina and that NO attenuated this reduction. Furthermore, morphological analysis showed that NO prevents NMDA-induced neurotoxicity through dopamine D1 receptors. These results suggest that the neuroprotective effect of NO may be associated with the induction of TH expression and increased levels of dopamine. [Copyright &y& Elsevier]

The effects of 17β-estradiol (17βE2) on spontaneous and excitatory amino acid (EAA) induced nucleus tractus solitarius (NTS) neuronal activity were investigated by electrophysiological and immunohistochemical experiments in ovariectomized female Sprague–Dawley rats. Out of 62 NTS neurons tested, 42 were inhibited (68%) following iontophoretic application of 17βE2 in a current-dependent manner. The averaged firing rate decreased from 3.06±0.40 to 0.78±0.17 Hz. The inhibitory responses were rapid in onset (within 1 min) and variable in duration (2–4 min). The inhibitory effects of 17βE2 were blocked by simultaneously applied 17βE2 antagonist ICI182,780, but not by GABA antagonist, bicuculline and phaclofen. l-Glutamate, AMPA or NMDA enhanced the activity of 71, 73 or 69% of NTS cells tested, respectively. The excitatory effects of EAA were significantly inhibited in the presence of 17βE2. Fluorescent immunohistochemistry revealed that all subnuclei of the NTS contained high levels of estrogen receptors (ERs) immunoreactivity. These results suggest that 17βE2 inhibits spontaneous and EAA-induced NTS neuronal activity through 17βE2 activation of ERs. [Copyright &y& Elsevier]

In this report we show that dextromethorphan, a non-opioid cough suppressant, prevents the neurodegeneration of dopaminergic neurons in the substantia nigra of mice treated with diethyldithiocarbamate (DDC) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). This effect is further substantiated by the assessment of dopamine (DA) content in the striatum of these animals. Dextromethorphan does not attenuate the striatal DA fall induced by MPTP alone but completely prevents DDC-induced enhancement after the combined treatment. Moreover, a study of DA metabolites has confirmed this neuroprotective property. The striatal levels of serotonin, which were studied as a control neuronal marker, did not change with any of the treatments administered. Furthermore, we show that dextromethorphan reduces the toxicity of glutamate against dopamine neurons in mesencephalic cell cultures. In line with previous data suggesting that dextromethorphan can prevent neuronal damage, our observations supply new evidence regarding the possibility of this compound being of therapeutic use in neurodegenerative diseases. [Copyright &y& Elsevier]

Excitatory amino acids acting at non-NMDA receptors contribute to transmission of nociceptive information. SYM 2081 ((2S,4R)-4-methyl glutamic acid) desensitizes kainate receptors, one subtype of non-NMDA receptors, to subsequent release of excitatory amino acids and thus may attenuate transmission of nociceptive information. To determine if SYM 2081 can prevent development of hyperalgesia, SYM 2081 (10, 50 or 100 mg/kg, i.p.) was administered prior to injection of capsaicin into the hindpaw of rats, which produces mechanical and heat hyperalgesia. To determine if SYM 2081 can reduce ongoing inflammatory hyperalgesia, SYM 2081 (10 or 100 mg/kg, i.p.) was administered after development of carrageenan-evoked hyperalgesia. Intraplantar injection of capsaicin produced an increase in hindpaw withdrawal frequency to mechanical stimuli (from 4±2 to 41±7%; mean±S.E.M.) and a decrease in withdrawal latency to heat (from 12.3±0.3 to 5.9±0.4 s) in rats that received vehicle. In contrast, rats that received SYM 2081 (100 mg/kg) prior to injection of capsaicin exhibited a lower hindpaw withdrawal frequency (18±4%) and a longer withdrawal latency (7.7±0.5 s). Intrathecal (1–100 μg/5 μl), but not intraplantar (10 or 100 μg/50 μl), injection of SYM 2081 attenuated the development of capsaicin-evoked heat hyperalgesia suggesting that SYM 2081’s antihyperalgesic effects were due to its central effects. Furthermore, SYM 2081 completely reversed ongoing carrageenan-evoked mechanical hyperalgesia and partially (∼50%) reversed ongoing heat hyperalgesia. The present study demonstrates that administration of a high-potency ligand that selectively desensitizes kainate receptors attenuates the development of mechanical and heat hyperalgesia and attenuates ongoing inflammatory hyperalgesia. [Copyright &y& Elsevier]

Injection of glutamate into the rat temporomandibular joint (TMJ) evoked a concentration-dependent increase in jaw muscle activity. We investigated whether there are sex-related differences in glutamate-evoked jaw muscle activity that are mediated by sex hormones and whether prior injection of glutamate into the TMJ alters the magnitude of jaw muscle activity evoked by a subsequent injection of the algesic and inflammatory compound mustard oil (MO) into the TMJ. The magnitude of glutamate-evoked digastric and masseter muscle activity was significantly greater in female than male rats when 1000 mM glutamate was injected into the TMJ. Gonadectomy significantly reduced the magnitude of glutamate-evoked digastric muscle activity in female rats. Treatment of gonadectomized female rats with estrogen (20 μg/day) increased the magnitude of glutamate-evoked digastric muscle activity. Glutamate-evoked jaw muscle activity in gonadectomized and estrogen-treated gonadectomized males was not significantly different from intact males. Prior injection of glutamate over a concentration range of 10–1000 mM significantly increased digastric muscle activity evoked by MO injection into the TMJ 30 min later. In contrast, MO-evoked masseter muscle activity was significantly increased by prior injection of 250 mM glutamate only. There were, however, no sex-related differences in the enhancement of MO-evoked jaw muscle activity by prior injection of glutamate. These findings indicate that there are sex-related differences in glutamate-evoked jaw muscle activity that are dependent on female sex hormones, and increased glutamate concentrations sensitize the TMJ to noxious chemical stimuli. [Copyright &y& Elsevier]

Mammals exhibit circadian rhythms in behavior generated by the suprachiasmatic nucleus (SCN). Exposure to light synchronizes the circadian clock to the environmental light:dark cycle through the release of glutamate into the SCN. In nocturnal animals such as Syrian hamsters, direct application of NMDA to the SCN results in phase shifts similar to those produced by exposure to light. This study was designed to determine if light phase shifts the circadian pacemaker of diurnal Nile grass rats (Arvicanthis niloticus) housed in constant darkness by acting on NMDA-type glutamate receptors in the suprachiasmatic nucleus (SCN). N-Methyl-d-aspartate (NMDA; 0, 1, 10, 50, and 100 mM) was administered through guide cannulae aimed at the SCN at circadian times when light induces phase shifts. Maximal phase delays were attained with 50 mM NMDA, and maximal phase advances were seen after 100 mM NMDA. A phase–response curve (PRC) for NMDA, determined by administering NMDA at each hour over the circadian cycle, resembled the PRC to light in this species. These data support the hypothesis that NMDA-type glutamate receptors play a critical role in mediating the phase shifting effects of light in diurnal, as well as nocturnal, animals. In addition, these data suggest that diurnal grass rats may be less sensitive to the phase shifting properties of NMDA than nocturnal rodents. [Copyright &y& Elsevier]

The subretrofacial nucleus (SRF) has been known to play a crucial role in the expression of the exercise pressor reflex. Previously, we have reported that the release of glutamate (Glu) in the SRF was increased during muscle contraction in anesthetized cats. In this study, static muscle contraction of the triceps surae for 4 min was induced by electrical stimulation of L7 and S1 ventral roots. Endogenous release of Glu and citrulline (Cit) from the SRF was recovered by microdialysis and measured by HPLC. The microdialysis probes were also used to deliver l-arginine and l-NAME to test the effect of nitric oxide (NO) on release of Glu in the SRF and on the cardiovascular responses during muscle contraction. During control, muscle contraction significantly increased mean arterial pressure (MAP) from 98±8 to 151±9 mmHg, and the extracellular concentration of Glu from 610±120 to 1280±290 nM. Dialyzing 2 mM l-arginine into the SRF increased basal Cit concentration from 260±50 to 760±210 nM (P<0.05). During contraction after l-arginine, the increases in MAP and Glu concentration were significantly attenuated (86±3–124±6 mmHg and 300±60–460±100 nM, respectively). Dialysis of 0.5 mM l-NAME into the SRF decreased Cit concentration from 340±40 to 180±20 nM (P<0.05). During contraction after dialyzing l-NAME, the increases in MAP and Glu concentration were significantly potentiated (93±6–154±9 mmHg and 520±80–1290±380 nM, respectively). These results suggest that endogenous NO modulates the cardiovascular responses to static muscle contraction by affecting the release of Glu in the SRF. [Copyright &y& Elsevier]

Activation of κ-opioid receptors (KOR) in the medial prefrontal cortex (mPFC) modulates excitatory transmission, which may involve interactions with N-methyl-d-aspartate (NMDA) glutamate receptors. We investigated possible anatomical correlates of this modulation by using dual labeling electron microscopy to examine the cellular distributions of antibodies raised against KOR and the R1 subunit of the NMDA receptor (NR1). KOR immunoreactivity primarily was localized to plasma and vesicular membranes of axons and axon terminals that were morphologically heterogeneous. A small proportion of KOR immunoreactivity was associated with cytosolic compartments of dendrites and membranes of glial processes. NR1 labeling was mainly postsynaptic, associated most often with membranes of cytoplasmic organelles in cell bodies and large dendrites and plasmalemmal surfaces of distal dendrites. The remaining NR1-labeled profiles were axonal profiles and glial processes. Of all cellular associations between labeled profiles, the majority were KOR-labeled axons that contacted NR1-immunoreactive dendrites or cell bodies. Occasionally the two antigens were colocalized in axon terminals that formed either asymmetric synapses or displayed varicose morphology. KOR and NR1 also were colocalized within dendrites, and rarely were observed in the same cell bodies. Occasionally glial processes coursing adjacent to axo-spinous appositions expressed both KOR and NR1 immunoreactivity. These results indicate that ligand activation of KOR or NMDA receptors differentially modulates excitatory transmission in the mPFC through pre- and postsynaptic mechanisms, respectively. The data also suggest more minor roles for colocalized KOR and NMDA receptors in shared regulation of presynaptic transmitter release, postsynaptic responsivity, and glial function. [Copyright &y& Elsevier]