Kainate Receptor Binding Research Articles

3-Hydroxy-1H-quinazoline-2,4-dione derivatives as new antagonists at ionotropic glutamate receptors: Molecular modeling and pharmacological studies

Based on our 3-hydroxy-7-chloroquinazoline-2,4-dione derivatives, previously reported as antagonists at ionotropic glutamate receptors, we synthesized new 3-hydroxyquinazoline-2,4-diones bearing a trifluoromethyl group at the 7-position and different groups at position 6. Glycine/NMDA, AMPA and kainate receptor binding data showed that the 7-trifluoromethyl residue increased AMPA and kainate receptor affinity and selectivity, with respect to the 7-chlorine atom. Among the probed 6-substituents, the 6-(1,2,4-triazol-4-yl) group (compound 8) was the most advantageous for AMPA receptor affinity and selectivity. Derivative 8 demonstrated to be effective in decreasing neuronal damage produced by oxygen and glucose deprivation in organotypic rat hippocampal slices and also showed anticonvulsant effects in pentylenetetrazole-induced convulsions. The previously reported kainate receptor antagonist 6-(2-carboxybenzoyl)-amino-7-chloro-3-hydroxyquinazoline-2,4-dione 3 prevented the failure of neurotransmission induced by oxygen and glucose deprivation in the CA1 region of rat hippocampal slices.

Patterns of neurotransmitter receptor distributions following cortical spreading depression

Spreading depression (SD), a self-propagating depolarization of neurons and glia, is believed to play a role in different neurological disorders including migraine aura and acute brain ischaemia. Initiation and propagation of SD modulate excitability of neuronal network. A brief period of excitation heralds SD which is immediately followed first by prolonged nerve cell depression and later by an excitatory phase. The aim of the present study was to characterize local and remote transmitter receptor changes after propagation of cortical SD. Quantitative receptor autoradiography was used to asses 16 transmitter receptor types in combined striatum-hippocampus–cortex slices of the rat 1 h after induction of cortical SD. In neocortical tissues, local increases of glutamate NMDA, AMPA, and kainate receptor binding sites were observed. In addition to up-regulation of ionotropic glutamate receptors, receptor binding sites of GABAA, muscarinic M1 and M2, adrenergic α1 and α2, and serotonergic 5-HT2 receptors were increased in the hippocampus. Cortical SD also upregulated NMDA, AMPA, kainate, GABAA, serotonergic 5-HT2, adrenergic α2 and dopaminergic D1 receptor binding sites in the striatum. These findings indicate selective changes in several receptors binding sites both in cortical and subcortical regions by SD which may explain delayed excitatory phase after SD. Mapping of receptor changes by cortical SD increases our understanding of the mechanism of SD action in associated neurological disorders.

Effects of chronic haloperidol and clozapine treatment on AMPA and kainate receptor binding in rat brain.

Alterations in AMPA and kainate receptor binding have been revealed in post-mortem schizophrenic brains. As most patients had been treated with antipsychotics, medication effects cannot be excluded as a possible explanation for these results. Within the framework of this animal study, we investigated [3H]AMPA and [3H]kainate receptor binding in different rat brain regions following 6 months of oral treatment with either haloperidol (1.5 mg/kg/day) or clozapine (45 mg/kg/day). AMPA receptor binding was increased after haloperidol treatment in the striatum, nucleus accumbens, cingulate cortex, and insular cortex. Clozapine showed increased AMPA receptor binding only in the anterior cingulate cortex. Kainate receptor binding was increased by both drugs in all hippocampal subfields. This altered receptor binding may be related to beneficial neuroleptic effects and side effects. Furthermore, neuroleptic therapy may contribute to some of the post-mortem findings in the striatum in schizophrenia.

Distribution of glutamate receptor subunits in experimentally induced cortical malformations

Electrophysiological studies in humans and animal models have revealed an intrinsic epileptogenicity of cortical dysplasias which are a frequent cause of drug-resistant epilepsy. An imbalance of inhibition and excitation has been causative related. Receptor-binding studies in rodents demonstrated reduced binding to GABA and increased binding to glutamate receptors within cortical dysplasias and increments of AMPA- and kainate-receptor binding in its surround. Immunohistochemically a differential downregulation of GABA A receptor subunits could be demonstrated in widespread areas within and around dysplasias. As receptor binding critically depends on receptor subunit composition the observed changes in binding properties might be related to this. Here, we immunohistochemically analyzed the regional expression of four NMDA receptor subunits and two major AMPA- and kainate-receptor complexes in adult rats after neonatal freeze lesions. These lesions are characterized by a three- to four-layered cortex and a microsulcus which mimic human polymicrogyria. Using antibodies against NR1, NR2A, NR2B, NR2D, GluR2,3, and GluR5,6,7 receptor subunits we demonstrated a pronounced disturbance of cortical immunostaining pattern in the cortical malformation. These changes reflected the structural disorganization of the microgyrus with some distortion of the apical dendrites of paramicrogyral pyramidal cells, a decrease and disorganization of cells at the bottom of the microsulcus, and an inflection of apical dendrites toward the microsulcus. The neuronal staining pattern of large pyramidal cells in the neighborhood of the dysplasia did not differ for any subunit investigated. No remote or widespread changes of glutamate-receptor subunit distribution could be detected. The lack of gross and/or widespread alterations of glutamate-receptor subunit distribution in the surround of focal cortical dysplasia suggests the presence of other or additional mechanisms underlying the increased excitatory neurotransmitter binding and excitability in cortical malformations.

Benzodiazepine and kainate receptor binding sites in the RCS rat retina.

The effect of age and photoreceptor degeneration on the kainate subtype of glutamate receptors and on the benzodiazepine-sensitive gamma-aminobutyric acid-A receptors (GABA(A)) in normal and RCS (Royal College of Surgeons) rats were investigated. [(3)H]Kainate and [(3)H]flunitrazepam were used as radioligands for kainate and GABA(A)/benzodiazepine()receptors, respectively, using the quantitative receptor autoradiography technique. In both normal and RCS rat retina we observed that [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were several times higher in inner plexiform layer (IPL) than in outer plexiform layer (OPL) at all four ages studied (P17, P35, P60 and P180). Age-related changes in receptor binding were observed in normal rat retina: [(3)Eta]flunitrazepam binding showed a significant decrease of 25% between P17 and P60 in IPL,and [(3)Eta]kainate binding showed significant decreases between P17 and P35 in both synaptic layers (71% in IPL and 63% in OPL). Degeneration-related changes in benzodiazepine and kainate receptor binding were observed in RCS rat retina. In IPL, [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were higher than in normal retina at P35 (by 24% and 86%, respectively). In OPL, [(3)Eta]flunitrazepam binding was higher in RCS than in normal retina on P35 (74%) and also on P60 (62%). The results indicate that postnatal changes occur in kainate and benzodiazepine receptor binding sites in OPL and IPL of the rat retina up to 6 months of age. The data also suggest that the receptor binding changes observed in the RCS retina could be a consequence of the primary photoreceptor degeneration.

Downregulation of kainate receptors in the hippocampus following repeated seizures in immature rats

There are significant differences in seizure-induced sequelae between the immature and mature brain. We have previously demonstrated that repeated doses of the chemoconvulsant kainic acid is associated with a progressive increase in severity of seizures in adult animals while in immature rats the opposite occurs; seizure intensity decreases with subsequent doses of kainic acid. Likewise, repeated kainic acid seizures causes severe hippocampal damage in mature rats while in the immature brain serial administration of kainic acid causes no demonstrable cell loss. Here we show that recurrent kainic acid seizures in immature rats are associated with a downregulation of kainate receptor binding. No histological damage was noted in any of the rats exposed to recurrent seizures. Furthermore, when tested for visual–spatial memory immature rats with recurrent kainate seizures did not differ from controls. The downregulation of KA receptors following repeated exposure to KA suggests that the decrease in glutamate receptor density might account in part for the observed lack of neuronal loss and decrease in seizure intensity in these animals.

Maturational Aspects of Epilepsy Mechanisms and Consequences for the Immature Brain

Maturational Aspects of Epilepsy Mechanisms and Consequences for the Immature Brain

Abnormal kainate receptor expression in prefrontal cortex in schizophrenia.

Abnormalities of molecules associated with the glutamate synapse have been implicated in the pathophysiology of schizophrenia. Of the many glutamate receptors, those most commonly suggested to be involved in schizophrenia are the ionotropic subtypes, the NMDA, AMPA, and kainate receptors. Both the NMDA and AMPA subtypes have been extensively studied in postmortem brains of individuals with schizophrenia, but relatively little is known about the expression of the kainate subtype of glutamate receptor. In this study, we have determined cortical and striatal kainate receptor expression in brains from persons with schizophrenia and a comparison group, using both in situ hybridization and receptor autoradiography. At the level of subunit mRNA expression, a shift in subunit stoichiometry was evident in multiple regions of the prefrontal cortex, with increased expression of gluR7 mRNA and decreased expression of KA2 mRNA. Decreased kainate receptor binding was also observed in the subjects with schizophrenia, but was restricted to infragranular laminae of the prefrontal cortex. No differences in kainate receptor binding or subunit mRNA levels were found in striatum or occipital cortex, suggesting that these findings may be restricted to association cortex. These data add to the growing literature implicating ionotropic glutamate receptor disturbances in schizophrenia, and indicate that in addition to AMPA and NMDA receptors, the kainate receptors are also abnormally expressed in this illness.

Decreased serotonergic receptor binding in rhombic lip-derived regions of the medulla oblongata in the sudden infant death syndrome.

The sudden infant death syndrome (SIDS) is postulated to result from a failure of homeostatic responses to life-threatening challenges (e.g. asphyxia, hypercapnia) during sleep. The ventral medulla participates in sleep-related homeostatic responses, including chemoreception, arousal, airway reflex control, thermoregulation, respiratory drive, and blood pressure regulation, in part via serotonin and its receptors. The ventral medulla in humans contains the arcuate nucleus, in which we have shown isolated defects in muscarinic and kainate receptor binding in SIDS victims. We also have demonstrated that the arcuate nucleus is anatomically linked to the nucleus raphé obscurus, a medullary region with serotonergic neurons. We tested the hypothesis that serotonergic receptor binding is decreased in both the arcuate nucleus and nucleus raphé obscurus in SIDS victims. Using quantitative autoradiography, 3H-lysergic acid diethylamide (3H-LSD binding) to serotonergic receptors (5-HT1A-D and 5-HT2 subtypes) was measured blinded in 19 brainstem nuclei. Cases were classified as SIDS (n = 52), acute controls (infants who died suddenly and in whom a complete autopsy established a cause of death) (n = 15), or chronic cases with oxygenation disorders (n = 17). Serotonergic binding was significantly lowered in the SIDS victims compared with controls in the arcuate nucleus (SIDS, 6 +/- 1 fmol/mg tissue; acutes, 19 +/- 1; and chronics, 16 +/- 1; p = 0.0001) and n. raphé obscurus (SIDS, 28 +/- 3 fmol/mg tissue; acutes, 66 +/- 6; and chronics, 59 +/- 1; p = 0.0001). Binding, however, was also significantly lower (p < 0.05) in 4 other regions that are integral parts of the medullary raphé/serotonergic system, and/or are derived, like the arcuate nucleus and nucleus raphé obscurus, from the same embryonic anlage (rhombic lip). These data suggest that a larger neuronal network than the arcuate nucleus alone is involved in the pathogenesis of SIDS, that is, a network composed of inter-related serotonergic nuclei of the ventral medulla that are involved in homeostatic mechanisms, and/or are derived from a common embryonic anlage.

Pertussis toxin prevents presynaptic inhibition by kainate receptors of rat hippocampal [ 3H]GABA release

Kainate receptors are ionotropic receptors, also reported to couple to G i/G o proteins, increasing neuronal excitability through disinhibition of neuronal circuits. We directly tested in hippocampal synaptosomes if kainate receptor-mediated inhibition of GABA release involved a metabotropic action. The kainate analogue, domoate (3 μM), inhibited by 24% [ 3H]GABA-evoked release, an effect reduced by 76% in synaptosomes pre-treated with pertussis toxin. Protein kinase C inhibition attenuated by 82% domoate-induced inhibition of GABA release whereas protein kinase C activation did not change kainate receptor binding. Thus, domoate inhibition of GABA release recruits G i/G o proteins and a protein kinase C pathway.

Localization of ionotropic glutamate receptors in caudate‐putamen and nucleus accumbens septi of rat brain: Comparison of NMDA, AMPA, and kainate receptors

Changes in binding of selective radioligands at NMDA ([3H]MK-801), AMPA ([3H]CNQX), and kainate ([3H]kainic acid) glutamate (GLU) ionotropic receptors in rat caudate-putamen (CPu) and nucleus accumbens (NAc) were examined by quantitative autoradiography following: 1) unilateral surgical ablation of frontal cerebral cortex to remove descending corticostriatal GLU projections, 2) unilateral injection of kainic acid (KA) into CPu or NAc to degenerate local intrinsic neurons, or 3) unilateral injections of 6-hydroxydopamine (6-OH-DA) into substantia nigra to degenerate ascending nigrostriatal dopamine (DA) projections. Cortical ablation significantly decreased NMDA receptor binding in ipsilateral medial CPu (20%), and NAc (16%), similar to previously reported losses of DA D4 receptors. KA lesions produced large losses of NMDA receptor labeling in CPu and NAc (both by 52%), AMPA (41% and 45%, respectively), and kainate receptors (40% and 45%, respectively) that were similar to the loss of D2 receptors in CPu and NAc after KA injections. Nigral 6-OH-DA lesions yielded smaller but significant losses in NMDA (17%), AMPA (12%), and kainate (11%) receptor binding in CPu. The results indicate that most NMDA, AMPA, and kainate receptors in rat CPu and NAc occur on intrinsic postsynaptic neurons. Also, some NMDA, but not AMPA or kainate, receptors are also found on corticostriatal projections in association with D4 receptors; these may, respectively, represent excitatory presynaptic NMDA autoreceptors and inhibitory D4 heteroceptors that regulate GLU release from corticostriatal axons in medial CPu and NAc. Conversely, the loss of all three GLU receptor subtypes after lesioning DA neurons supports their role as excitatory heteroceptors promoting DA release from nigrostriatal neurons. Synapse 30:227–235, 1998. © 1998 Wiley-Liss, Inc.

Excitatory Amino Acid Receptors and Puberty

Glutamate is an important excitatory signal in the hypothalamus for the steroid-mediated preovulatory gonadotropin surge. Steroids may exert this action by regulating glutamate receptor levels or glutamate release, or both. Work in our laboratory found no changes in NMDA and kainate receptor binding in the hypothalamus of castrated or castrated plus steroid-replaced male and female rats. Likewise, we found that NMDA and kainate binding did not change over the onset of puberty in the female rat. A competitive quantitative RT-PCR assay using exogenous internal standards was used to measure NMDAR1, GluR1, and β-actin mRNAs levels. NMDAR1 and GluR1 expression was examined in the preoptic hypothalamic area and in the medial basal hypothalamus at Postnatal Days 10, 15, 20, 25, 30, 32, 34, 36, 40, and 63. A transient increase in GluR1 mRNA levels in the preoptic hypothalamic area was observed on Day 20, with all other time points showing comparable levels. NMDAR1 levels in the POA and medial basal hypothalamus did not change significantly at any of the time points; in contrast, however, AMPA receptor binding levels were increased in the hypothalamus at the time of puberty in the female rat. Thus, in addition to the previously reported elevation of glutamate release rates in the hypothalamus at the time of puberty, AMPA receptors may also be elevated and play a role in mediating glutamate regulatory effects on the timing of puberty in the female rat.

Kainate and AMPA receptor binding in seizure-prone and seizure-resistant inbred mouse strains

Glutamate and its receptors represent the major excitatory neurotransmission system in the mammalian brain and are considered important in the pathogenesis of many neurological diseases. The present study describes saturation binding experiments performed to measure the affinity ( K d) and density ( B max) of kainate and AMPA receptors in striatum, cortex and hippocampus from mature DBA/2J (DBA) and C57BL/6J (C57) mice. Previous studies have documented that these two strains differ significantly in seizure susceptibility, with DBA mice exhibiting greater sensitivity in various convulsant tests compared to C57 mice. Non-linear regression analysis of binding data together with Student's t-test and ANOVA revealed significantly higher densities of kainate receptors in striatum and of AMPA receptors in cortex of DBA mice. C57 mice exhibited higher striatal [ 3H]AMPA binding. There were no significant differences between the mouse strains in binding sites prepared from hippocampus and no differences in affinity for either receptor in any brain region studied. The results support a role for kainate and AMPA receptors in seizure sensitivity, possibly by influencing glutamate transmission in specific pathways. It is unlikely, however, that these receptors account for the generation of seizures alone but rather cooperate with other glutamatergic and non-glutamatergic neurotransmitter systems.

Pentylenetetrazol kindling decreases N-methyl- d-aspartate and kainate but increases gamma-aminobutyric acid-A receptor binding in discrete rat brain areas

Pentylenetetrazol is a convulsive drug acting on gamma-aminobutyric acid-A (GABA A) gated-chloride receptors. In this study we used a subconvulsive dose (30 mg/kg) of pentylenetetrazol to induce a fully kindled state in rats. Glutamate receptors were evaluated using [ 3H]-[1(2-thienylcyclohexyl)]-piperidin (TCP) and [ 3H]kainate receptor autoradiography and [ 3H]muscimol autoradiography was used to study GABA A receptors. In fully kindled rats decreased N-methyl- d-aspartate receptor binding was found in parietal cortex, area CA2 of hippocampus and piriform cortex. Decreased kainate receptor binding was observed in all areas of the hippocampus, the medial amygdala and in the piriform cortex in the kindled rats. In contrast, GABA A receptor binding increased in the dentate gyrus. It is concluded that modulatory neuronal plasticity events are induced in fully pentylenetetrazol kindled rats, which appears to lead to decreased glutamatergic excitation and increased GABAergic inhibition in brain regions implicated in the development of seizure activity.

Decreased kainate receptor binding in the arcuate nucleus of the sudden infant death syndrome.

The human arcuate nucleus is postulated to be homologous to ventral medullary surface cells in animals that participate in ventilatory and blood pressure responses to hypercarbia and asphyxia. Recently, we reported a significant decrease in muscarinic cholinergic receptor binding in the arcuate nucleus in victims of the sudden infant death syndrome compared with control patients that died of acute causes. To test the specificity of the deficit to muscarinic cholinergic binding, we examined kainate binding in the arcuate nucleus in the same database. We assessed 3H-kainate binding to kainate receptors with tissue receptor autoradiography in 17 brainstem nuclei. Analysis of covariance was used to examine differences in binding by diagnosis, adjusted for postconceptional age (the covariate). Cases were classified as SIDS, 47; acute control, 15; and chronic group with oxygenation disorder, 17. (Acute controls are infants who died suddenly and unexpectedly and in whom a complete autopsy established a cause of death). The arcuate nucleus was the only region in which there was a significant difference in the age-adjusted mean kainate binding between the SIDS group (37+/-2 fmol/mg tissue) and both the acute controls (77+/-4 fmol/mg tissue) (p < 0.0001) and the chronic group (69+/-4 fmol/mg tissue) (p < 0.0001). There was a positive correlation between the density of muscarinic cholinergic and kainate binding in the SIDS cases only (R = 0.460; p = 0.003). The neurotransmitter deficit in the arcuate nucleus in SIDS victims involves more than one receptor type relevant to carbon dioxide and blood pressure responses at the ventral medullary surface.

Nitric oxide does not modulate kainate receptor binding in human brain

The ability of three nitric oxide (NO) donor compounds to modify ligand binding to kainate receptors was studied in tissue from human adult autopsy brains. Binding of [ 3H]kainic acid (5 nM) was measured in frontal cortex membranes made from Brodmann area 8 (BA 8) and autoradiographically using sections of frontal cortex (BA 8 and 9). None of the three donors, S-nitroso- N-acetyl- d, l-penicillamine (SNAP), S-nitrosocysteine (Cys-NO) and 3-morpholinosydnonimine chloride (SIN-1) altered the specific binding of [ 3H]kainic acid. Nitrite accumulation assays confirmed that adequate amounts of NO were released by the donors under the ligand binding conditions used. The findings show that binding to the kainate receptor, in contrast to the other ionotropic glutamate receptors, is not affected by NO and strongly suggest that endogenous NO produced by NO synthase (NOS) does not modulate kainate receptors in vivo. Mechanisms whereby NOS inhibitors potentiate kainic acid-induced seizures in animal models may include altered modulation of glutamate N-methyl- d-aspartate (NMDA) receptors.

Unilateral eyeball enucleation differentially alters AMPA-, NMDA- and kainate glutamate receptor binding in the newborn rat brain

The aim of the present work was to evaluate the neurochemical effects of early unilateral visual deprivation as a model of impaired visual maturation. For this purpose, binding to the different ionotropic glutamate receptor subtypes was quantified in vision-related and vision-unrelated brain structures of control and unilaterally deprived newborn rats. At post-natal (PN) day 10, male Sprague-Dawley rats underwent either unilateral eyeball enucleation (enucleation group, n = 12) or sham operation (control group, n = 12). In each group, brains were obtained either post-natal day 20 ( n = 6) or post-natal day 30 ( n = 6) and processed for quantitative in vitro autoradiography selective for NMDA, kainate, and AMPA glutamate-binding sites, as well as for the presynaptic adenosine A1 receptor as a control of the deafferentation efficacy. In control animals, quantitative autoradiography revealed an increase in NMDA (e.g. +45% in superior colliculus) and kainate receptor binding (e.g. +55% in visual cortex, layer IV) from post-natal day 20 to post-natal day 30, associated with stable levels of AMPA receptor binding, in the vision-related structures. In the deafferented visual structures, monocular enucleation induces a marked decrease in A1 site density (e.g. −38 to − 52%, in the superficial layer of superior colliculi, at PN day 20 and PN day 30, respectively) in parallel with a mild increase in both NMDA (e.g. + 8 to 9%, in superior colliculi and visual cortex, layer IV at PN day 30, respectively) and AMPA (e.g. +16%, in layer IV of the visual cortex at PN day 30). Superimposed on marked bilateral decreases at PN day 30 in the enucleated rats, kainate receptor binding also revealed a slight but significant decrease (−5%) in the deafferented superior colliculus as compared to the non-deafferented side. The present findings (different time-courses of, and differential effects of deafferentation on, the NMDA, kainate and AMPA glutamate receptor subtypes throughout the visual brain structures) further support the involvement of these receptors in distinctive roles during maturation of the visual system.

S-30-3 - Temporal lobe cytoarchitectural pathology in schizophrenia

Electrophysiological studies in humans and animal models have revealed an intrinsic epileptogenicity of cortical dysplasias which are a frequent cause of drug-resistant epilepsy. An imbalance of inhibition and excitation has been causative related. Receptor-binding studies in rodents demonstrated reduced binding to GABA and increased binding to glutamate receptors within cortical dysplasias and increments of AMPA- and kainate-receptor binding in its surround. Immunohistochemically a differential downregulation of GABAA receptor subunits could be demonstrated in widespread areas within and around dysplasias. As receptor binding critically depends on receptor subunit composition the observed changes in binding properties might be related to this. Here, we immunohistochemically analyzed the regional expression of four NMDA receptor subunits and two major AMPA- and kainate-receptor complexes in adult rats after neonatal freeze lesions. These lesions are characterized by a three- to four-layered cortex and a microsulcus which mimic human polymicrogyria. Using antibodies against NR1, NR2A, NR2B, NR2D, GluR2,3, and GluR5,6,7 receptor subunits we demonstrated a pronounced disturbance of cortical immunostaining pattern in the cortical malformation. These changes reflected the structural disorganization of the microgyrus with some distortion of the apical dendrites of paramicrogyral pyramidal cells, a decrease and disorganization of cells at the bottom of the microsulcus, and an inflection of apical dendrites toward the microsulcus. The neuronal staining pattern of large pyramidal cells in the neighborhood of the dysplasia did not differ for any subunit investigated. No remote or widespread changes of glutamate-receptor subunit distribution could be detected. The lack of gross and/or widespread alterations of glutamate-receptor subunit distribution in the surround of focal cortical dysplasia suggests the presence of other or additional mechanisms underlying the increased excitatory neurotransmitter binding and excitability in cortical malformations.

Developmental changes in [3H]kainate binding in human brainstem sites vulnerable to perinatal hypoxia-ischemia.

The human brainstem is especially susceptible to hypoxia-ischemia in early life. To test the hypothesis that the period of vulnerability of the developing human brainstem to hypoxia-ischemia correlates with a transient elevation in kainate receptor binding, we compared the quantitative distribution of [3H]kainate binding in brainstem nuclei between four fetuses (19-26 gestational weeks), four infants (one to nine months), and three "mature" individuals (one child and two adults) without neurological disease. Quantitative tissues autoradiography was used. [3H]Kainate binding decreased in all brainstem regions from early life to maturity with the most significant decreases occurring in nuclei thought to be especially vulnerable to perinatal hypoxia-ischemia (e.g. principal inferior olive, griseum pontis, inferior colliculus and reticular core). The highest binding in the fetal and infant period was found primarily in the major cerebellar-relay nuclei. In the inferior olive and arcuate nucleus, binding increased from the fetal to the infant period, and then fell 50-61% to low mature levels. In the griseum pontis, binding decreased 60% between the fetal and mature periods. In the reticular formation, binding fell 67-78% from the fetal to mature period. These data support a correlation between the period of brainstem vulnerability to hypoxia-ischemia in early life to transient elevation in kainate binding, and are particularly relevant to the topographic brainstem patterns in perinatal hypoxia-ischemia of infantile olivary gliosis, pontosubicular necrosis and reticular core damage. Striking localization of [3H]kainate binding to rhombic lip derivatives further suggests that kainate receptors may be involved in the development and function of human brainstem-cerebellar circuitry.

Effects of adrenal steroid manipulations and repeated restraint stress on dynorphin mRNA levels and excitatory amino acid receptor binding in hippocampus

Adrenal steroid and stress effects were determined in hippocampus on levels of dynorphin (DYN) mRNA, expressed in dentate gyrus, and excitatory amino acid receptors, measured in Ammon's horn and dentate gyrus. Adrenalectomy (ADX) decreased DYN mRNA levels in dentate gyrus and replacement with aldosterone (ALDO), a specific type I adrenal steroid receptor agonist, prevented the decrease. Ru28362, a specific type II receptor agonist, had no effect. Likewise, kainate receptor binding to the stratum lucidum and hilus region of dorsal hippocampus was decreased after ADX and this decrease was prevented by ALDO but not by Ru28362 treatment. Similar though smaller effects were found for CNQX binding to AMPA receptors but only in the dentate gyrus molecular or infra- and supragranular layers. Although corticosterone (CORT) treatment of intact rats (40 mg/kg for 3 weeks) elevated DYN mRNA levels in dentate gyrus, up to 14 days of daily restraint stress (1 or 6 h/day) had no significant effect. Neither CORT treatment nor repeated restraint stress altered NMDA and non-NMDA glutamate receptors in hippocampus. The results of this study showing ADX-induced decreases of DYN mRNA and CNQX binding in dentate gyrus and decreased kainate binding in mossy fiber terminal regions are consistent with morphological evidence showing that adrenal steroids maintain normal integrity and structure of dentate gyrus neurons and do so via type I adrenal steroid receptors. These same parameters are apparently not sensitive to chronic restraint stress although the effects of other stressors must be examined.