Distribution of NMDA and AMPA receptors in the cerebellar cortex of rhesus macaques

Localization of AMPA, kainate, and NMDA receptor mRNAs in the pigeon cerebellum

In the present study, we investigated the location of mRNAs for three types of ionotropic glutamate receptors (iGluRs) in the pigeon cerebellum and then compared the results with those of mammals. The following nine iGluRs subunits were analyzed by in situ hybridization: AMPA receptors (GluA1, GluA2, GluA3, and GluA4), kainate receptors (GluK1, GluK2, and GluK4), and NMDA receptors (GluN1 and GluN2A). Subunit hybridization revealed expression in different cell types of the cerebellar cortex: Purkinje cells expressed most subunits, including AMPA receptors (GluA1, GluA2, and GluA3), kainate receptors (GluK1 and GluK4), and NMDA receptors (GluN1); granule cells expressed four subunits of kainate (GluK1 and GluK2) and NMDA receptors (GluN1 and GluN2A); stellate and basket cells expressed GluK1, GluK2, and GluN1; Golgi cells expressed GluA1, GluA3, and GluN1; and Bergmann glial cells expressed only AMPA receptors (GluA2 and GluA4). Cerebellar nuclei showed no AMPA subunit signals, whereas kainate and NMDA receptors were observed in the five cerebellar nuclei divisions (CbL, CbMic, CbMim, CbMin, and CbMvm). The five divisions showed weak expression of GluK1, GluK2, and GluN2A; moderate to intense expression of GluK4; and intense expression of GluN1. These results demonstrate that in pigeons the cerebellar cortex expresses AMPA, kainate, and NMDA receptors, while the cerebellar nuclei express kainate and NMDA receptors. Taken together, these findings provide anatomical data for further analysis of the functions of iGluR-expressing neurons in glutamatergic circuits of the avian cerebellum.

Gene expression profiling in the rhesus macaque: methodology, annotation and data interpretation

Gene microarray analyses represent potentially effective means for high-throughput gene expression profiling in non-human primates. In the companion article, we emphasize effective experimental design based on the in vivo physiology of the rhesus macaque, whereas this article emphasizes considerations for gene annotation and data interpretation using gene microarray platforms from Affymetrix. Initial annotation of the rhesus genome array was based on Affymetrix human GeneChips. However, annotation revisions improve the precision with which rhesus transcripts are identified. Annotation of the rhesus GeneChip is under continuous revision with large percentages of probesets under multiple annotation systems having undergone multiple reassignments between March 2007 and November 2008. It is also important to consider that quantitation and comparison of gene expression levels across multiple chips requires appropriate normalization. External corroboration of microarray results using PCR-based methodology also requires validation of appropriate internal reference genes for normalization of expression values. Many tools are now freely available to aid investigators with microarray normalization and selection of internal reference genes to be used for independent corroboration of microarray results.

Glutamate receptor subunit expression in the rhesus macaque locus coeruleus

The locus coeruleus (LC) is a major noradrenergic brain nucleus that regulates states of arousal, optimizes task-oriented decision making, and may also play an important role in modulating the activity of the reproductive neuroendocrine axis. Rodent studies have shown that the LC is responsive to glutamate receptor agonists, and that it expresses various glutamate receptor subunits. However, glutamate receptor subunit expression has not been extensively examined in the primate LC. We previously demonstrated expression of the NR1 NMDA glutamate receptor subunit in the rhesus macaque LC and now extend this work by also examining the expression of non-NMDA (AMPA and kainate) ionotropic glutamate receptor subunits. Using in situ hybridization histochemistry and immunohistochemistry, we confirmed the presence of the obligatory NR1 subunit in the LC. In addition, we demonstrated expression of the AMPA glutamate receptor subunits GluR1, GluR2, and GluR3. More extensive receptor profiling, using rhesus monkey gene microarrays (Affymetrix GeneChip), further corroborated the histological findings and showed expression of mRNA encoding ionotropic glutamate receptor subunits NR2A, NR2D, GluR4, and GluR6, as well as the metabotropic glutamate receptor subunits mGluR1, mGluR3, mGluR4, mGluR5, and mGluR7. These data provide a foundation for future examination of how changes in glutamate receptor composition contribute to the control of primate physiology.

The new 2,3-benzodiazepine derivative EGIS-8332 inhibits AMPA/kainate ion channels and cell death

We observed in vitro neuroprotective and AMPA/kainate receptor antagonist effects of the new 2,3-benzodiazepine derivative EGIS-8332 (R,S-1-(4-aminophenyl)-7,8-methylenedioxy-4-cyano-4-methyl-3-N-acetyl-5H-3,4-dihydro-2,3-benzodiazepine) using the lactate dehydrogenase (LDH) release assay and patch clamp recordings on primary cultures of rat embryonic telencephalon neurons exposed to AMPA/kainate receptor agonists. EGIS-8332 potently decreased alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and quisqualate induced LDH release (IC(50)=5.2+/-0.4 and 7.4+/-1.3 microM, respectively) from the cells. Whole-cell patch clamp studies carried out on the ionotropic glutamate receptors N-methyl D-aspartate (NMDA), as well as AMPA (and kainate) in cultured telencephalon neurons verified that EGIS-8332 blocked steady state responses to AMPA and kainate (IC(50)=1.7+/-0.4 and 6.2+/-1.6 microM, respectively), but hardly influenced currents evoked by NMDA. EGIS-8332 also inhibited kainate-evoked response in CHO cells expressing the flop variant of GluR1 receptor and, in cerebellar Purkinje cells at similar efficiency. The stereoselectivity of the inhibitory site is established by the clearly dissimilar inhibitory potency of the enantiomer components of EGIS-8332 differing in the configuration of methyl and cyano substituents on carbon C(4): the R(-) enantiomer was found to be the efficient species. This finding suggests that the inhibitory interaction between the channel protein and drug is promoted by presence of the C(4) methyl group. The inhibition of the AMPA/kainate ion channels by EGIS-8332 is non-competitive, not use dependent, and depends neither on the closed/open state of the channel, nor the membrane potential. These findings suggest an allosteric mechanism for the inhibition. These in vitro observations suggest that the compound might be useful in the treatments of certain acute and chronic neurological syndromes initiated by derangements of ionotropic glutamate receptor function.

Localization of endogenous biotin-containing proteins in mouse Bergmann glial cells

A peroxidase-conjugated avidin-biotin complex was used to detect endogenous biotin-containing proteins in mouse cerebellum. By this method, Bergmann glial cells were found to be strongly labelled in the adult mouse cerebellum. Developmentally, cells in the granular layer, probably astrocytes, appeared to be labelled around postnatal 10-day (P10). Their labelling decreased after P20, although the positive-labelling remained in the Bergmann glial cells up to the adult stage. The findings were confirmed by using a Alexa Fluor 488-conjugated streptavidin technique. The labelling was not affected by routine hydrogen peroxide treatment, but it was eliminated by avidin-biotin blocking. By another transblot method, the reactive proteins in the mouse cerebellum were found to be 120 kDa (the strongest one) and 75 kDa. For electron microscopy, a gold-conjugated anti-biotin antibody was immunoreacted to the mitochondria of Bergmann glial cells. These results suggest that endogenous biotin-containing proteins are abundant in the Bergmann glial cells. Therefore, the avidin-biotin complex method is useful for detecting Bergmann glial cells, probably because of the difference of biotin metabolism in the cerebellar glial cells.

Expression of transcripts encoding AMPA receptor subunits and associated postsynaptic proteins in the macaque brain

Glutamate is the primary excitatory neurotransmitter in the central nervous system, regulating numerous cellular signaling pathways and controlling the excitability of central synapses both pre- and postsynaptically. Localization, cell surface expression, and activity-dependent regulation of glutamate receptors in both neurons and glia are performed and maintained by a complex network of protein-protein interactions associated with targeting, anchoring, and spatially organizing synaptic proteins at the cell membrane. Using in situ hybridization, we examined the expression of transcripts encoding the AMPA receptor subunits (GluR1-GluR4) and a family of AMPA-related intracellular proteins. We focused on PDZ-proteins that are involved in the regulated pool and anchoring AMPA subunits to the cell membrane (PICK1, syntenin), and those maintaining the constitutive pool of AMPA receptors at the glutamatergic synapse (NSF, stargazin). In addition, we studied a fifth protein, KIAA1719, with high homology to the rat PDZ protein ABP, associated with the clustering of AMPA receptors at the glutamate synapse. The AMPA subunits showed significant differences in regional expression, especially in the neocortex, thalamus, striatum, and cerebellum. The expression of other proteins, even those related to a specific AMPA subunit (such as ABP and PICK1 to GluR2 and GluR3), often had different distributions, whereas others (like NSF) are ubiquitously distributed in the brain. These results suggest that AMPA subunits and related intracellular proteins are differentially distributed in the macaque brain, and in numerous structures there are significant mismatches, suggesting additional functional properties of the associated intracellular proteins..

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Gonadotropin-releasing hormone neurons, NMDA receptors, and their regulation by steroid hormones across the reproductive life cycle

The effects of ovarian steroid hormones on gonadotropin-releasing hormone (GnRH) neurons have been studied for many years. In addition to their regulation by sex steroids, GnRH neurons are affected by inputs from neurotransmitters such as glutamate, acting via the NMDA receptor (NMDAR). Moreover, the NMDAR itself is subject to estrogen regulation. Thus, effects of ovarian steroids on GnRH neurons and the NMDAR, and their interactions, are under intense investigation. Messenger RNA and protein levels of GnRH and NMDAR subunits were measured in neuroendocrine brain regions in response to estrogen treatment, or across the reproductive cycle. Stimulatory effects of ovarian steroids on GnRH gene expression occur during the preovulatory LH surge in young adult rats, and this is abolished in middle-aged rats that have an attenuated LH surge. Effects of estrogen on GnRH neurons have also been studied in the ovariectomized, estrogen-primed rat, and while results vary between laboratories, there appear to be age-related changes in the sensitivity of GnRH neurons to estrogen. Estrogen also has effects on NMDAR mRNA levels. In intact rats, mRNA levels of NMDAR decrease during reproductive aging in the preoptic area, the site of GnRH perikarya, while in the medial basal hypothalamus-median eminence, the site of GnRH neuroterminals, levels of NMDAR subunit mRNAs increase with aging. Thus, glutamatergic inputs to GnRH perikarya and neuroterminals and other neuroendocrine cells may change during reproductive aging in intact rats. In ovariectomized rats, NMDAR subunit mRNA levels also undergo age-related changes, and respond to estrogen replacement in a subunit- and age-specific manner. Notably, there are major differences in NMDAR gene expression during aging between intact and ovariectomized rats, suggesting that ovarian factors other than estrogen play a role in the regulation of this receptor.

Two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed by two separate populations of cells in the rhesus macaque hypothalamus

Gonadotropin-releasing hormone represents the primary neuroendocrine link between the brain and the reproductive axis, and at least two distinct molecular forms of this decapeptide (GnRH-I and GnRH-II) are known to be expressed in the forebrain of rhesus macaques (Macaca mulatta). Although the distribution pattern of the two corresponding mRNAs is largely dissimilar, their expression appears to show some overlap in specific regions of the hypothalamus; this raises the possibility that some cells express both molecular forms of GnRH. To resolve this issue, double-label histochemistry was performed on hypothalamic sections from six male rhesus macaques, using a monoclonal antibody to GnRH-I and a riboprobe to monkey GnRH-II mRNA. In total, more than 2000 GnRH neurons were examined but in no instance were GnRH-I peptide and GnRH-II mRNA found to be coexpressed. This finding emphasizes that GnRH-I and GnRH-II are synthesized by two distinct populations of hypothalamic neurons, and suggests that they may be regulated by different neuroendocrine pathways.

Differential expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor subunits by calretinin-immunoreactive neurons in the human striatum

We recently reported the existence of medium and large intemeurons immunoreactive for the calcium-binding protein calretinin in the human striatum. We also showed a selective sparing of all medium, but not all large, calretinin-immunoreactive striatal neurons in Huntington's disease striatum. Because glutamate receptor-mediated excitotoxicity has been implicated in the massive loss of striatal projection neurons that characterizes Huntington's disease, we have applied a double-antigen localization procedure to post mortem tissue from eight normal human subjects to determine the expression of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate glutamate receptor subunits 1/2/4 by the calretinin-immunoreactive interneurons. The two types of calretinin-immunoreactive neurons were found to display various patterns of glutamate receptor subunit expression and a specific regionalization was also noted in the expression of these glutamate receptor subunits. Approximately half of the large calretinin-immunoreactive neurons displayed immunoreactivity for glutamate receptor subunits 1 and 2, and about the same proportion of medium calretinin-immunoreactive neurons expressed glutamate receptor subunits 1 and 4. These double-labeled neurons were rather uniformly distributed in the caudate nucleus and putamen. In contrast, as much as 70.1% of the large calretinin-immunoreactive neurons displayed glutamate receptor subunit 4 immunoreactivity in the postcommissural portion of the putamen, an area that corresponds to the sensorimotor striatal territory. For their part, the medium calretinin-immunoreactive neurons were markedly enriched with glutamate receptor subunit 2, 76% of them being double labeled in the caudate nucleus, which corresponds to the striatal associative territory, compared with 85.5% in the postcommissural putamen. Receptor subunit composition plays a key role in determining the functional properties of glutamate receptors, including their permeability to calcium and susceptibility to excitotoxic insults. Thus, the differential expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate glutamate receptor subunits reported here may help to explain the selective sparing of certain types of calretinin-immunoreactive striatal interneurons in Huntington's disease, although other factors, such as post-transcriptional editing, are also likely to be involved.

Regional distribution of glutamic acid decarboxylase (GAD65 and GAD67) mRNA in the hypothalamus of male rhesus macaques before and after puberty

Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme in the gamma-aminobutyric acid (GABA) biosynthetic pathway, and is coded for by two mRNAs, GAD65 and GAD67. Using in situ hybridization, we examine the distribution pattern of both GAD mRNAs in the hypothalamus and thalamus of prepubertal and adult male rhesus macaques. Qualitatively, GAD65 and GAD67 mRNAs showed a similar wide, but highly specific distribution pattern, supporting the view that GABAergic neurons play an important role in modulating neuroendocrine function. However, no quantitative difference in the intensity of hybridization signal was detected between prepubertal and adult animals in any of the hypothalamic or thalamic nuclei. Therefore, although GABAergic neurons are anatomically well-placed to control the secretion of gonadotropin-releasing hormone (GnRH) in primates, it is unlikely that the onset of puberty and the associated increase in GnRH secretion is triggered by a change in GAD gene transcription.

Regional distribution of glutamate receptor mRNA in the monkey hippocampus and temporal cortex: influence of estradiol

The distribution of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor subunits was examined in the hippocampus and temporal cortex of adult ovariectomized female rhesus macaques, some of which received estradiol replacement. In situ hybridization revealed a generalized overlap of NR1, GluR1, and GluR2 subunit mRNAs, but no effect due to estradiol treatment. However, regional differences in expression were noted for each subunit.

Modulation of AMPA receptor subunits GluR1 and GluR2/3 in the rat cerebellum in an experimental hepatic encephalopathy model

The immunohistochemical expression and distribution of the AMPA-selective receptor subunits GluR1 and GluR2/3 were investigated in the rat cerebellum following portocaval anastomosis (PCA) at 1 and 6 months. With respect to controls, GluR1 and GluR2/3 immunoreactivities increased over 1 to 6 months following PCA, although immunolabelling patterns for both antibodies were different at the two analysed times. GluR1 immunoreactivity was expressed by Bergmann glial cells, which showed immunoreactive glial processes crossing the molecular layer at 6 months following PCA. The GluR2/3 subunit was expressed by Purkinje neurons and moderately expressed by neurons of the granule cell layer. Immunoreactivity for GluR2/3 was detectable in cell bodies and dendrites of Purkinje cells in young control cerebella, whereas GluR2/3 immunoreactivity was scarce 1 month post PCA. However, despite a lack of immunoreactivity in the Purkinje somata and main processes of adult control rats, GluR2/3 immunoreactivity was strongly enhanced in Purkinje neurons following long-term PCA. These findings suggest that the localization of the GluR2/3 subunit in Purkinje cells undergoes an alteration and/or reorganization as a consequence of long-term PCA. The combination of enhanced GluR immunoreactivity in long-term PCA, both in Bergmann glial cells and in Purkinje neurons, suggests some degree of neuro-glial interaction, possibly through glutamate receptors, in this type of encephalopathy.

Distribution of glutamate receptors GluR 2/3 and NR1 in the developing rat cerebellum

The distribution of glutamate receptors GluR2/3 and NR1 was analysed immunohistochemically during development of the rat cerebellum. GluR2/3 immunoreactivity appeared by postnatal day P0 in somata of Purkinje cells. Throughout P7, P15, P20 and adulthood, GluR2/3 immunoreactivity was found in the entire Purkinje cell dendritic arbor reaching to the external granular layer and, by P15, the surface of the cerebellum. By P7, the granular layer revealed scattered, mildly reactive, cells. NR-1 immunoreactivity first gained prominence about P7 in the region of the multi-layered Purkinje cell somata. By P15, NR1 was prominent in Purkinje cell somata and Golgi cells. The reaction product extended into the primary main dendrite of Purkinje cells. By P21, stellate and basket cells had intense reactivity throughout the molecular layer and reactive large-diameter dendrites of Golgi cells projected toward the molecular layer. Granule cells remained very weak among strongly reactive Golgi cell somata and dendrites. Ultrastructural immunohistochemistry revealed NR1 reaction product in Purkinje cell somata, in stellate cell somata and dendrites and on postsynaptic membranes of scattered spines throughout the molecular layer. The later appearance and restricted location of NR1 in somata and proximal dendrites of Purkinje cells contrasted markedly with GluR2/3 which appeared before birth and remained prominent throughout Purkinje cell dendritic arbors of adults. The time of NR1 expression correlated with the generation of granule cells, their synaptogenesis on Purkinje cells, the formation of stellate/baske cells and the shift of climbing fibre synapses from distal to proximal dendrites. The developmental appearance of stellate/basket cells and Golgi cells as well as their high reactivity remaining into adulthood suggest that these inhibitory molecular and granular layer interneurons are the principal targets of glutamate axons serving NR1 synaptic properties while Purkinje cells and brush type granule cells are targets for glutamate connections with GluR2/3 characteristics.

Excitatory amino acid receptors coupled to the phosphoinositide pathway in Bergmann glia

Glutamate (L-glu) receptors coupled to phosphoinositide hydrolysis in primary cultures of Bergmann cells from chick cerebellum were characterized biochemically and pharmacologically. Both ionotropic and metabotropic receptor agonists stimulated [3H] inositol phosphates accumulation in the following order of potency: QA > NMDA > L-glu > KA approximately QA > AMPA > > t-ACPD. QA showed a biphasic dose-response curve (EC50 = 0.07 and 53 microM), suggesting interaction with two populations of receptors; L-glu was the most efficient agonist. Stimulation by NMDA was blocked by CPP, AP5 and MK-801; that by AMPA and KA was inhibited 100% by CNQX and DNQX, whereas the effect of QA was decreased both by CNQX and the metabotropic antagonist 4-CPG. Stimulation of PIP2 hydrolysis induced by metabotropic L-glu receptor agonist t-ACPD was blocked by 4-CPG but was only moderately inhibited by MCPG. EAA-induced [3H]IPs accumulation was dependent on external Ca2+ and was not affected by nifedipine verapamil, or dantrolene; thapsigargin increased the effect. Results suggest that EAA activate the PI pathway in Bergmann glia through ionotropic (NMDA and AMPA/KA) as well as metabotropic receptor subtypes (t-ACPD) which could act jointly influencing neurotransmission at the parallel fiber-Purkinje cell synapses in the cerebellum.

Alpha-adrenergic receptor antagonism and N-methyl-D-aspartate (NMDA) induced luteinizing hormone release in female rhesus macaques

The stimulatory influence of N-methyl-D-aspartate (NMDA), a glutamate receptor agonist, on LH secretion is well established in several mammalian species including the rhesus macaque. Although the mechanism of excitation appears to involve enhanced GnRH secretion, it is unclear whether the GnRH neurons respond directly to this excitation or whether stimulatory inter-neurons are involved. This study investigated the possibility that noradrenergic afferents play a major role in mediating the response of the primate hypothalamo-pituitary reproductive axis to NMDA. In situ hybridization histochemistry, using a cRNA probe coding for the NMDAR1 receptor subunit, revealed abundant mRNA in the locus coeruleus, a brain area rich in noradrenergic neurons. Furthermore, using double-label fluorescence immunocytochemistry, the tyrosine hydroxylase immunopositive neurons of the locus coeruleus showed immunoreactivity for the NMDAR1 receptor subunit protein. A second experiment examined whether prazosin, an alpha 1-adrenergic receptor antagonist, could attenuate NMDA-induced stimulation of LH release. Prazosin (either 1 or 5 mg/kg b.wt., i.v.) was administered to female rhesus macaques during the luteal phase of the menstrual cycle, 40 min before administration of NMDA (10 mg/kg b.wt., i.v.). Regardless of the prazosin pre-treatment, plasma LH concentrations showed a significant increase (P < 0.01) within 10 min of the administration of NMDA. Therefore, in spite of the evidence that at least some of the noradrenergic neurons of the primate hindbrain express the NMDAR1 receptor subunit, it is unlikely that noradrenergic inter-neuronal pathways alone play a major role in mediating the stimulatory action of NMDA on GnRH/LH secretion in primates. Indeed, because the GnRH neurons of the rhesus macaque are located diffusely in various regions of the hypothalamus and medial-septal/preoptic area, their net response to excitatory amino acids is likely to be more complicated, involving a combination of both stimulatory and inhibitory inter-neurons, and possibly also a direct interaction.