Distribution of ferritin in the rat hippocampus after kainate-induced neuronal injury

A gradual increase in iron occurs in the lesioned hippocampus after neuronal injury induced by the excitotoxin kainate, and the present study was carried out to investigate whether this increase in iron might be associated with changes in expression of the iron binding protein, ferritin. An increase in ferritin immunoreactivity was observed in glial cells of the hippocampus, as early as three days after intracerebroventricular injections of kainate. The number of ferritin positive cells peaked four weeks after the kainate injection, and decreased eight and twelve weeks after injection. They were found to be mostly microglia and oligodendrocytes by double immunofluorescence labeling with glial markers. A number of ferritin-labeled endothelial cells were also observed via electron microscopy. The decline in ferritin immunoreactivity four weeks after the injection of kainate is accompanied by an increase in the number of ferric and ferrous iron positive cells in the lesioned tissue. A substantial non-overlap between ferritin and iron-containing cells was observed. In particular, spherical ferric or ferrous iron-laden cells in the degenerating hippocampus were unlabeled for ferritin for long time periods after the kainate injection. An increase in iron, together with a reduced expression of iron binding proteins such as ferritin at long time intervals after kainate lesions, could result in a relative decrease in ferritin-induced ferroxidase activity and the presence of some of the iron in the ferrous form. It is postulated that this may contribute to chronic neuronal injury, following acute kainate-induced neurodegeneration.     

Lead-induced blockade of kainate-sensitive receptor channels

The effects of bivalent lead on ion channels activated by kainate and -amino-3-hydroxy-5-methyl-4-isoxazolpropionate (AMPA) were studied using Xenopus oocytes microinjected with mRNA from rat brain. Lead reduced kainate-induced membrane currents in a reversible and dose-dependent manner, without affecting membrane currents induced by AMPA. Lead decreased the kainate currents with a concentration of 0.1 mol/l to 0.93 ± 0.01 and with a concentration of 100 mol/l to 0.41 ± 0.04 of the control values. The blocking effect of lead on kainate responses was voltage dependent. The inhibition was strongest at - 90 mV to - 70 mV and became weaker at more positive membrane potentials. The effect of lead on the kainate-induced membrane currents remained unchanged when the concentration of kainate was increased. Hence lead probably represents a noncompetitive channel-blocking agent for non-N-methyl-d-aspartate (NMDA) receptor channels activated by kainate.     

Kainate activates Ca2+-permeable glutamate receptors and blocks voltage-gated K+ currents in glial cells of mouse hippocampal slices

Glial cells in the CA1 stratum radiatum of the hippocampus of 9- to 12-day-old mice show intrinsic responses to glutamate due to the activation of -amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/ kainate receptors. In the present study we have focused on a subpopulation of the hippocampal glial cells, the complex cells, characterized by voltage-gated Na⁺ and K⁺ channels. Activation of glutamate receptors in these cells led to two types of responses, the activation of a cationic conductance, and a longer-lasting blockade of voltage-gated K⁺ channels. In particular, the transient (inactivating) component of the outwardly rectifying K⁺ current was diminished by kainate. Concomitantly, as described in Bergmann glial cells, kainate also elevated cytosolic Ca²⁺. This increase was due to an influx via the glutamate receptor itself. In contrast to Bergmann glial cells, the cytosolic Ca²⁺ increase was not a link to the K⁺ channel blockade, since the blockade occurred in the absence of the Ca²⁺ signal and, vice versa, an increase in cytosolic Ca²⁺ induced by ionomycin did not block the transient K⁺ current. We conclude that glutamate receptor activation leads to complex and variable changes in different types of glial cells; the functional importance of these changes is as yet unresolved.     

红藻氨酸受体与神经退行性变疾病相关性研究进展

研究表明,红藻氨酸受体（ KARs）在神经退行性变疾病中起着重要作用。兴奋性神经递质的过度活化KARs可引起该受体的过度表达,从而使神经细胞死亡。研究KARs的作用机制,可为临床治疗神经退行性变疾病提供治疗的靶点。     

Role of glutamatergic receptors located in the nucleus raphe magnus on antinociceptive effect of morphine microinjected into the nucleus cuneiformis of rat

Neurons in the nucleus cuneiformis (CnF), located just ventrolateral to the periaqueductal gray, project to medullary nucleus raphe magnus (NRM), which is a key medullary relay for descending pain modulation and is critically involved in opioid-induced analgesia. Previous studies have shown that antinociceptive response of CnF-microinjected morphine can be modulated by the specific subtypes of glutamatergic receptors within the CnF. In this study, we evaluated the role of NMDA and kainate/AMPA receptors that are widely distributed within the NRM on morphine-induced antinociception elicited from the CnF. Hundred and five male Wistar rats weighing 250-300 g were used. Morphine (10, 20 and 40 microg) and NMDA receptor antagonist, MK-801 (10 microg) or kainate/AMPA receptor antagonist, DNQX (0.5 microg) in 0.5 microl saline were stereotaxically microinjected into the CnF and NRM, respectively. The latency of tail-flick response was measured at set intervals (2, 7, 12, 17, 22, 27 min after microinjection) by using an automated tail-flick analgesiometer. The results showed that morphine microinjection into the CnF dose-dependently causes increase in tail-flick latency (TFL). MK-801 microinjected into the NRM, just 1 min before morphine injection into the CnF, significantly attenuated antinociceptive effects of morphine. On the other hand, DNQX microinjected into the NRM, significantly increased TFL after local application of morphine into the CnF. We suggest that morphine related antinociceptive effect elicited from the CnF is mediated, in part, by NMDA receptor at the level of the NRM whereas kainite/AMPA receptor has a net inhibitory influence at the same pathway.     

Association Between Polymorphisms in GRIK2 Gene and Obsessive‐Compulsive Disorder: A Family‐Based Study

Several studies support a genetic influence on obsessive‐compulsive disorder (OCD) etiology. The role of glutamate as an important neurotransmitter affecting OCD pathophysiology has been supported by neuroimaging, animal model, medication, and initial candidate gene studies. Genes involved in glutamatergic pathways, such as the glutamate receptor, ionotropic, kainate 2 (GRIK2), have been associated with OCD in previous studies. This study examines GRIK2 as a candidate gene for OCD susceptibility in a family‐based approach. Probands had full DSM‐IV diagnostic criteria for OCD. Forty‐seven OCD probands and their parents were recruited from tertiary care OCD specialty clinics from France and USA. Genotypes of single nucleotide polymorphism (SNP) markers and related haplotypes were analyzed using Haploview and FBAT software. The polymorphism at rs1556995 (P= 0.0027; permuted P‐value = 0.03) was significantly associated with the presence of OCD. Also, the two marker haplotype rs1556995/rs1417182, was significantly associated with OCD (P= 0.0019, permuted P‐value = 0.01). This study supports previously reported findings of association between proximal GRIK2 SNPs and OCD in a comprehensive evaluation of the gene. Further study with independent samples and larger sample sizes is required.     

Chronic prenatal ethanol exposure alters ionotropic glutamate receptor subunit protein levels in the adult guinea pig cerebral cortex

BACKGROUND: The superfamily of glutamate-gated ion channels mediates fast excitatory synaptic transmission in the central nervous system and is composed of the NMDA, AMPA, and kainate receptors. Binding studies have shown that chronic prenatal and/or neonatal ethanol exposure produces persistent effects on the numbers of some of these channels. However, whether or not this chronic ethanol exposure produces long-lasting effects on the expression of specific ionotropic receptor subunits remains an open question. METHODS: Timed pregnant Dunkin-Hartley strain guinea pigs received oral administration of one of the following regimens between gestational days 2 and 67: (1) 4 g of ethanol per kilogram of maternal body weight per day with ad libitum access to pellet food and water (ethanol group), (2) isocaloric sucrose- and pair-feeding with ad libitum access to water (sucrose group), or (3) isovolumetric water with ad libitum access to food and water (water group). The maternal blood ethanol concentration produced by the ethanol regimen was 71 +/- 12 mM. Adult offspring were killed on postnatal day 61, and cerebral cortical tissue was analyzed for ionotropic glutamate receptor subunit expression by Western immunoblotting. RESULTS: There was a statistically significant decrease in NR2B subunit protein expression and an increase in GluR2/3 subunit protein expression in the ethanol group. Expression of NR1, NR2A, NR2C, GluR1, GluR6/7, and KA2 subunit proteins was not affected. CONCLUSIONS: These results demonstrate that chronic prenatal ethanol exposure produces long-lasting effects on the subunit composition of NMDA and AMPA receptors in the cerebral cortex of the adult guinea pig.     

Modification of glutamate binding sites in newborn brain during hypoglycemia

We have shown that acute insulin-induced hypoglycemia leads to specific changes in the cerebral NMDA receptor-associated ion channel in the newborn piglet. The present study tests the hypothesis that exposure to acute hypoglycemia in the newborn will alter the glutamate binding site of both NMDA and kainate receptors. Studies were performed in 3-6 days-old piglets randomized to control (n=6) or hypoglycemic (n=6) groups. Hypoglycemia was maintained for 120 min using insulin infusion. Saturation binding assays were performed in cerebral cell membranes using (3)H-glutamate or (3)H-kainate to determine the characteristics of the glutamate binding sites of the NMDA and kainate receptors, respectively. The concentration of glucose in cerebral cortex was 10-fold less in hypoglycemic piglets than in controls (P<0.05). Brain ATP was not significantly decreased during hypoglycemia, but phosphocreatine decreased from control of 6.6 +/- 1.3 micromoles/g brain to 3.2 +/- 1.9 micromoles/g brain in hypoglycemic piglets. The B(max) for NMDA-displaceable (3)H-glutamate binding was 992 +/- 64 fmol/mg protein in hypoglycemic animals, significantly higher than the control value of 746 +/- 42 fmol/mg protein. However, the dissociation constant for glutamate was unchanged during hypoglycemia. The (3)H-kainate binding studies demonstrated no change in B(max) of high-affinity kainate receptors during hypoglycemia. In contrast, the affinity of the kainate receptor glutamate binding site significantly increased compared to control. Thus, acute hypoglycemia in the newborn piglet had specific effects on the glutamate binding sites of the NMDA and kainate receptors that could be due to alterations in cell membrane lipids or modification of receptor proteins.