Assessment of a prepulse inhibition deficit in a mutant mouse lacking mGlu5 receptors.

The glutamate hypothesis of schizophrenia derived from evidence that phencyclidine, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist, produces schizophrenia-like symptoms in healthy humans. Sensorimotor gating, measured by prepulse inhibition (PPI), is a fundamental form of information processing that is deficient in schizophrenia patients and rodents treated with NMDA antagonists. Hence, PPI is widely used to study the neurobiology of schizophrenia. As the use of PPI as a model of gating deficits in schizophrenia has become more widespread, it has become increasingly important to assess such deficits accurately. Here we identify a possible role of mGluR5 in PPI by using wild type (WT) and mGluR5 knockout (KO) mice of two different background strains, 129SvPasIco and C57BL/6. In both strains, PPI was disrupted dramatically in the mGluR5 KO mice throughout a range of interstimulus intervals and sensory modalities. The present findings further support the glutamate hypothesis of schizophrenia and identify a functional role for mGluR5 in sensorimotor gating.

Effect of antipsychotic treatment on the prepulse inhibition deficit of mGluR5 knockout mice.

RATIONALE: Prepulse inhibition of the startle response (PPI), a model of sensorimotor gating, is deficient in persons with schizophrenia. In rodents, the reversal of induced deficits in PPI demonstrates predictive validity for identifying antipsychotic treatments. Metabotropic glutamate receptor 5 (mGluR5) has been implicated in schizophrenia, in part because mGluR5 knockout (KO) mice exhibit PPI deficits. OBJECTIVE: We examined whether mGluR5 KO mice might serve as a novel model for detecting antipsychotic treatments. METHODS: Using C57BL/6J or 129SvPasIco mice, we first determined doses of the typical antipsychotic raclopride or the atypical antipsychotic clozapine that were effective in blocking the PPI-disruptive effects of amphetamine or ketamine, respectively. We then examined the effects of these doses on the deficit in PPI in mGluR5 KO mice. RESULTS: Administration of raclopride or clozapine reversed either an amphetamine or a ketamine-induced PPI deficit, as had the novel mood stabilizer lamotrigine in previous studies. In contrast, the PPI deficit of the mGluR5 KO mice was not altered by administration of raclopride, clozapine, or lamotrigine. The serotonin(2A) antagonist M100,907 was also ineffective in reversing the mGluR5 KO deficit in PPI. CONCLUSIONS: Most of the compounds examined ameliorated at least a subset of pharmacologically induced PPI deficits. That none of the antipsychotic treatments attenuated the PPI deficit in the mGluR5 KO mice indicates that this model is not predictive of known treatments for schizophrenia, but does not preclude a role for the mGluR5 receptor in schizophrenia or other psychiatric disorders.

Disruption of prepulse inhibition in mice lacking mGluR1.

Sensorimotor gating, measured by prepulse inhibition of the startle response (PPI), is a cross-species form of information processing that is deficient in patients with schizophrenia and is widely used as a model to study the neurobiology of this disorder. The eight known metabotropic glutamate receptors (mGluRs) are divided into three groups on the basis of sequence homology and pharmacological properties. Group I consists of mGluR5 and mGluR1, both of which are coupled positively to phospholipase C. Mice lacking mGluR5 exhibit a deficit in PPI. Like mGluR5, mGluR1 is located in regions that are involved in the modulation of PPI. To test the hypothesis that mGluR1 is involved in the modulation of PPI we assessed PPI in mGluR1 knockout (KO) mice. Littermate mGluR1 wild-type and KO mice were tested at multiple ages in a standard PPI paradigm containing a 65 dB background, 120 dB pulses and prepulses of 69, 73 and 77 dB. At all ages tested, mGluR1 KO mice exhibited a significant PPI deficit. The PPI deficit of the mGluR1 KO mice was not further exaggerated by administration of the N-methyl-d-aspartate antagonist phencyclidine nor was it reversed by administration of the dopamine antagonist raclopride (3.0 mg/kg). The PPI deficit of the mGluR1 KO mice was, however, ameliorated by administration of the mood stabilizer lamotrigine (27 mg/kg base equivalent weight), though increases in PPI were also seen with lamotrigine in the wild-type mice. Thus, both group I metabotropic glutamate receptors are involved in the regulation of PPI in mice.

Determination of group I metabotropic glutamate receptor subtypes involved in the frequency of epileptiform activity in vitro using mGluR1 and mGluR5 mutant mice.

In mouse hippocampal slices, bicuculline elicited spontaneous epileptiform bursts with a duration of 200-300 ms and with a frequency of five to six events per minute. Application of group I metabotropic glutamate receptor agonist (RS)-3,5-dihydroxyphenylglycine ((RS)-DHPG) increased the burst frequency up to 300% at concentrations of 50 to 100 microM, while it decreased the burst duration below 100 ms. In slices of subtype I mGluR1 or subtype I mGluR5 knockout mice, bicuculline elicited spontaneous epileptiform bursts with similar duration and frequency as those measured in wild-type mice but without the previous effects seen following application of DHPG at concentrations up to 100 microM. Likewise, in slices of wild-type mice, preincubation with mGluR1 antagonist, 1-aminoindan-1,5-dicarboxylic acid (AIDA) or mGluR5 receptor antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) blocked in both cases completely the increase in frequency following DHPG application. These findings suggest an interactive mechanism between mGluR1 and mGluR5 receptors in the modulation of epileptiform bursting activity by DHPG that could indicate a common intracellular signaling mechanism or possibly direct interaction between these two receptors.

Corticostriatal LTP requires combined mGluR1 and mGluR5 activation.

Metabotropic glutamate receptors (mGluRs) have been demonstrated to play a role in synaptic plasticity. It has been recently shown that mGluR1 is involved in corticostriatal long-term depression, by means of pharmacological approach and by using mGluR1-knockout mice. Here, we report that both mGluR1 and mGluR5 are involved in corticostriatal long-term potentiation (LTP). In particular, the mGluR1 antagonist LY 367385, as well as the mGluR5 antagonist MPEP, reduce LTP amplitude. Moreover, blockade of both mGluR1 and mGluR5 by LY 367385 and MPEP co-administration fully suppresses LTP. Accordingly, group II and group III mGluRs antagonists fail to affect LTP induction. Interestingly, LTP amplitude is also significantly reduced in both mGluR1- and mGluR5-knockout mice. The differential function of mGluR1 and mGluR5 in corticostriatal synaptic plasticity may play a role in the modulation of the motor activity mediated by the basal ganglia, thus providing a substrate for the pharmacological treatment of motor disorders involving the striatum.

Metabotropic glutamate receptor 5 mediates the potentiation of N-methyl-D-aspartate responses in medium spiny striatal neurons.

Medium spiny neurons were recorded from striatal slices obtained from mice lacking the group I metabotropic glutamate receptor (mGluR) subtype 1 or subtype 5. In wild-type animals, N-methyl-D-aspartate (NMDA)-induced membrane depolarization/inward currents were potentiated in the presence of both the group I mGluR agonist 3,5-dihydroxyphenylglycine (3,5-DHPG) and the mGluR5 selective agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG). Likewise, in mGluR1 knockout mice, both 3,5-DHPG and CHPG were able to potentiate NMDA responses. Conversely, in neurons recorded from mGluR5-deficient mice, the enhancement of NMDA responses by both 3,5-DHPG and CHPG was absent. Pharmacological analysis performed from rat slices confirmed the data obtained with mice. In the presence of the competitive mGluR1 antagonist LY367385, the NMDA responses were potentiated in the presence of CHPG, whereas the CHPG-induced enhancement was not observed in slices treated with the non-competitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine. As in wild-type mice, in neither of the mGluR1- and mGluR5-deficient mice did (2S,1'R,2'R,3'R)-2-(2,3-dicarboxylcyclopropyl)-glycine (1 microM), nor L-serine-O-phosphate (30 microM) (agonists for group II and III mGluRs, respectively) affect the NMDA-evoked responses. In striatal medium spiny neurons, NMDA responses are potentiated by endogenous acetylcholine via M1-like muscarinic receptors. Since the enhancement of NMDA responses by 3,5-DHPG and by M1-like muscarinic agonists was shown to share common post-receptor mechanisms, we verified whether the muscarinic potentiation of NMDA responses was affected in these group I mGluR-deficient mice. Both in mGluR1 and mGluR5 knockout animals, in the presence of either muscarine or the M1-like muscarinic receptor agonist McN-A-343, the positive modulation of the NMDA-induced membrane depolarization persisted.These results confirm the permissive role of group I mGluRs on NMDA responses in striatal neurons and reveal that this functional interplay occurs exclusively through the mGluR5 subtype. The NMDA-mGluR5 interaction might play an important modulatory role in the final excitatory drive from corticostriatal afferents and suggests that drugs acting at mGluR5 might prove useful for the treatment of movement disorders involving the striatum.

Augmented motor activity and reduced striatal preprodynorphin mRNA induction in response to acute amphetamine administration in metabotropic glutamate receptor 1 knockout mice.

Metabotropic glutamate receptor 1 (mGluR1) is a G-protein-coupled receptor and is expressed in the medium spiny projection neurons of mouse striatum. To define the role of mGluR1 in actions of psychostimulant, we compared both motor behavior and striatal neuropeptide mRNA expression between mGluR1 mutant and wild-type control mice after a single injection of amphetamine. We found that acute amphetamine injection increased motor activity in both mutant and control mice in a dose-dependent manner (1, 4, and 12 mg/kg, i.p.). However, the overall motor responses of mGluR1 -/- mice to all three doses of amphetamine were significantly greater than those of wild-type +/+ mice. Amphetamine also induced a dose-dependent elevation of preprodynorphin mRNA in the dorsal and ventral striatum of mutant and wild-type mice as revealed by quantitative in situ hybridization. In contrast to behavioral responses, the induction of dynorphin mRNA in both the dorsal and ventral striatum of mutant mice was significantly less than that of wild-type mice in response to the two higher doses of amphetamine. In addition, amphetamine elevated basal levels of substance P mRNA in the dorsal and ventral striatum of mGluR1 mutant mice to a similar level as that of wild-type mice. There were no differences in basal levels and distribution patterns of the two mRNAs between the two genotypes of mice treated with saline. These results demonstrate a clear augmented behavioral response of mGluR1 knockout mice to acute amphetamine exposure that is closely correlated with reduced dynorphin mRNA induction in the same mice. It appears that an intact mGluR1 is specifically critical for full dynorphin induction, and impaired mobilization of inhibitory dynorphin system as a result of lacking mGluR1 may contribute to an augmentation of motor stimulation in response to acute administration of psychostimulant.

Activation of metabotropic glutamate receptor subtype 1/protein kinase C/mitogen-activated protein kinase pathway is required for postischemic long-term potentiation in the striatum.

Excessive stimulation of glutamate receptors is believed to contribute substantially in determining neuronal vulnerability to ischemia. However, how this pathological event predisposes neurons to excitotoxic insults is still largely unknown. By using electrophysiological recordings from single striatal neurons, we demonstrate in a corticostriatal brain-slice preparation that in vitro ischemia (glucose and oxygen deprivation) activates a complex chain of intracellular events responsible for a dramatic and irreversible increase in the sensitivity of striatal neurons to synaptically released glutamate. This process follows the stimulation of both N-methyl-D-aspartate and metabotropic glutamate receptors and involves the activation of the mitogen-activated protein kinase ERK via protein kinase C. This pathological form of synaptic plasticity might play a role in the cell type-specific neuronal vulnerability in the striatum, because it is selectively expressed in neuronal subtypes that are highly sensitive to both acute and chronic disorders involving this brain area.

Reinforcing and locomotor stimulant effects of cocaine are absent in mGluR5 null mutant mice.

Both ionotropic and metabotropic glutamate receptors (mGluRs) are involved in the behavioral effects of pyschostimulants; however, the specific contributions of individual mGluR subtypes remain unknown. Here we show that mice lacking the mGluR5 gene do not self-administer cocaine, and show no increased locomotor activity following cocaine treatment, despite showing cocaine-induced increases in nucleus accumbens (NAcc) dopamine (DA) levels similar to wild-type (WT) mice. These results demonstrate a significant contribution of mGlu5 receptors to the behavioral effects of cocaine, and suggest that they may be involved in cocaine addiction.

Selective involvement of mGlu1 receptors in corticostriatal LTD.

Although metabotropic glutamate receptors (mGluRs) have been proposed to play a role in corticostriatal long-term depression (LTD), the specific receptor subtype required for this form of synaptic plasticity has not been characterized yet. Thus, we utilized a corticostriatal brain slice preparation and intracellular recordings from striatal spiny neurons to address this issue. We observed that both AIDA (100 microM) and LY 367385 (30 microM), two blockers of mGluR1s, were able to fully prevent the induction of this form of synaptic plasticity, whereas MPEP (30 microM), a selective antagonist of the mGluR5 subtype, did not significantly affect the amplitude and time-course of corticostriatal LTD. Both AIDA and LY 367385 were ineffective on LTD when applied after its induction. The critical role of mGluR1s in the formation of corticostriatal LTD was confirmed in experiments performed on mice lacking mGluR1s. In these mice, in fact, a significant reduction of the LTD amplitude was observed in comparison to the normal LTD measured in their wild-type counterparts. We found that neither acute pharmacological blockade of mGluR1s nor the genetic disruption of these receptors affected the presynaptic modulation of corticostriatal excitatory postsynapic potentials (EPSPs) exerted by DCG-IV and L-SOP, selective agonists of group II and III mGluRs, respectively. Our data show that the induction of corticostriatal LTD requires the activation of mGluR1 but not mGluR5. mGluR1-mediated control of this form of synaptic plasticity may play a role in the modulatory effect exerted by mGluRs in the basal ganglia-related motor activity.

A key role for CC chemokine receptor 4 in lipopolysaccharide-induced endotoxic shock.

CC chemokine receptor (CCR)4, a high affinity receptor for the CC chemokines thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC), is expressed in the thymus and spleen, and also by peripheral blood T cells, macrophages, platelets, and basophils. Recent studies have shown that CCR4 is the major chemokine receptor expressed by T helper type 2 (Th2) polarized cells. To study the in vivo role of CCR4, we have generated CCR4-deficient (CCR4(-/-)) mice by gene targeting. CCR4(-/-) mice developed normally. Splenocytes and thymocytes isolated from the CCR4(-/-) mice failed to respond to the CCR4 ligands TARC and MDC, as expected, but also surprisingly did not undergo chemotaxis in vitro in response to macrophage inflammatory protein (MIP)-1alpha. The CCR4 deletion had no effect on Th2 differentiation in vitro or in a Th2-dependent model of allergic airway inflammation. However, CCR4(-/-) mice exhibited significantly decreased mortality on administration of high or low dose bacterial lipopolysaccharide (LPS) compared with CCR4(+/+) mice. After high dose LPS treatment, serum levels of tumor necrosis factor alpha, interleukin 1beta, and MIP-1alpha were reduced in CCR4(-/-) mice, and decreased expression of MDC and MIP-2 mRNA was detected in peritoneal exudate cells. Analysis of peritoneal lavage cells from CCR4(-/)- mice by flow cytometry also revealed a significant decrease in the F4/80(+) cell population. This may reflect a defect in the ability of the CCR4(-/-) macrophages to be retained in the peritoneal cavity. Taken together, our data reveal an unexpected role for CCR4 in the inflammatory response leading to LPS-induced lethality.

Immunolocalization of the mGluR1b splice variant of the metabotropic glutamate receptor 1 at parallel fiber-Purkinje cell synapses in the rat cerebellar cortex.

Several metabotropic glutamate receptor (mGluR) subtypes have been identified in the cerebellar cortex that are targeted to different compartments in cerebellar cells. In this study, preembedding immunocytochemical methods for electron microscopy were used to investigate the subcellular distribution of the mGluR1b splice variant in the rat cerebellar cortex. Dendritic spines of Purkinje cells receiving parallel fiber synaptic terminals were immunoreactive for mGluR1b. With a preembedding immunogold method, approximately 25% of the mGluR1b immunolabeling was observed perisynaptically within 60 nm from the edge of the postsynaptic densities. Values of extrasynaptic gold particles beyond the first 60 nm were maintained at between 10 and 18% along the whole intracellular surface of the dendritic spine membranes of Purkinje cells. For comparison, the distribution of mGluR1a was studied. A predominant (approximately 37%) perisynaptic localization of mGluR1a was seen in dendritic spines of Purkinje cells, dropping the extrasynaptic labeling to 15% in the 60-120-nm bin from the edge of the postsynaptic specialization. Our results reveal that mGluR1b and mGluR1a are localized to the same subcellular compartments in Purkinje cells but that the densities of the perisynaptic and extrasynaptic pools were different for both isoforms. The compartmentalization of mGluR1b and mGluR1a might serve distinct requirements in cerebellar neurotransmission.

Synaptic depression induced by pharmacological activation of metabotropic glutamate receptors in the perirhinal cortex in vitro.

The perirhinal cortex is crucially involved in various forms of learning and memory. Decrements in neuronal responsiveness occur in the perirhinal cortex with stimulus repetition during visual recognition performance. However, very little is known concerning the underlying mechanisms of synaptic transmission and plasticity in this cortical region. In this study, we provide evidence demonstrating the presence of functional group I, II and III metabotropic glutamate receptors in the rat perirhinal cortex in vitro. Furthermore, the results demonstrate long-lasting synaptic depression in the perirhinal cortex. Extracellular synaptic responses were recorded from superficial layers of the perirhinal cortex directly below the rhinal sulcus, in response to electrical stimuli delivered in the superficial or intermediate layers to the entorhinal or temporal cortex sides of the rhinal sulcus. Evoked synaptic potentials were depressed during bath perfusion of each of the following: the broad-spectrum metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid, the selective group I agonist (R,S)-3,5-dihydroxyphenylglycine, the group II agonist (2S,1'R,2'R,3'R)-(2',3'-dicarboxycyclopropyl)glycine and the group III agonist (S)-2-amino-4-phosphonobutanoate. Furthermore, there was a long-lasting depression of synaptic transmission following washout of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid, (R,S)-3,5-dihydroxyphenylglycine or (2S,1'R,2'R,3'R)-(2',3'-dicarboxy-cyclopropyl)glycine. Activation of group III metabotropic glutamate receptors by (S)-2-amino-4-phosphonobutanoate did not result in long-lasting changes in synaptic transmission. Thus, the pharmacological activation of metabotropic glutamate receptors can produce short- or long-term changes in synaptic transmission in the perirhinal cortex. It is possible therefore, that metabotropic glutamate receptors are involved in the decrement in neuronal responsiveness associated with visual recognition in the perirhinal cortex.

Circadian expression of the steroid 15 alpha-hydroxylase (Cyp2a4) and coumarin 7-hydroxylase (Cyp2a5) genes in mouse liver is regulated by the PAR leucine zipper transcription factor DBP.

To study the molecular mechanisms of circadian gene expression, we have sought to identify genes whose expression in mouse liver is regulated by the transcription factor DBP (albumin D-site-binding protein). This PAR basic leucine zipper protein accumulates according to a robust circadian rhythm in nuclei of hepatocytes and other cell types. Here, we report that the Cyp2a4 gene, encoding the cytochrome P450 steroid 15alpha-hydroxylase, is a novel circadian expression gene. This enzyme catalyzes one of the hydroxylation reactions leading to further metabolism of the sex hormones testosterone and estradiol in the liver. Accumulation of CYP2A4 mRNA in mouse liver displays circadian kinetics indistinguishable from those of the highly related CYP2A5 gene. Proteins encoded by both the Cyp2a4 and Cyp2a5 genes also display daily variation in accumulation, though this is more dramatic for CYP2A4 than for CYP2A5. Biochemical evidence, including in vitro DNase I footprinting on the Cyp2a4 and Cyp2a5 promoters and cotransfection experiments with the human hepatoma cell line HepG2, suggests that the Cyp2a4 and Cyp2a5 genes are indeed regulated by DBP. These conclusions are corroborated by genetic studies, in which the circadian amplitude of CYP2A4 and CYP2A5 mRNAs and protein expression in the liver was significantly impaired in a mutant mouse strain homozygous for a dbp null allele. These experiments strongly suggest that DBP is a major factor controlling circadian expression of the Cyp2a4 and Cyp2a5 genes in the mouse liver.

Inositol-1,4,5-trisphosphate-mediated rescue of cerebellar long-term depression in subtype 1 metabotropic glutamate receptor mutant mouse.

Recent reports have outlined that cerebellar long-term depression requires the activation of subtype 1 metabotropic glutamate receptors, since long-term depression is impaired in subtype 1 metabotropic glutamate receptor (mGluR1) knockout mice. In order to better define the role of mGluR1-activated signal transduction pathways, we attempted to rescue cerebellar long-term depression in mGluR1 knockout mice by direct activation of subsequent intracellular cascades. The present results demonstrate that the inositol-1,4,5-trisphosphate signal transduction pathway remains functional in mGluR1 knockout mice, that calcium release from internal stores evoked by the combined photolytic release of inositol- 1,4,5-trisphosphate/pairing protocol is sufficient to rescue long-term depression in these mutants, and that this long-term depression is sensitive to a protein kinase C inhibitor. Therefore, our results provide compelling evidence that the impairment of long-term depression observed in mGluR1 knockout mice is not a consequence of developmental abnormalities, but is directly due to mGluR1 gene inactivation.

Immunohistochemical localization of the mGluR1beta metabotropic glutamate receptor in the adult rodent forebrain: evidence for a differential distribution of mGluR1 splice variants.

Alternative splicing has been shown to occur at the metabotropic glutamate receptor 1 (mGluR1) gene. Three main isoforms that differ in their carboxy-termini have been described so far and named mGluR1alpha, mGluR1beta and mGluR1c. These variants when expressed in recombinant systems all activate phospholipase C, although the [Ca2+] signals generated have different kinetics. Tissue distribution studies of specific mGluR1 splice variants are limited to the mGluR1alpha isoform. In the present work, we examined the localization of mGluR1beta in the adult rat and mouse forebrain by using a specific antipeptide antibody. Furthermore, the mGluR1beta immunostaining was compared with that obtained with antibodies specific for mGluR1alpha or with a pan-mGluR1 antibody which recognizes all isoforms. mGluR1beta-like immunoreactivity (LI) was found confined to the neuropil and neuronal perikarya and appeared discretely distributed in the rodent forebrain. Differential cellular distribution between mGluR1alpha and mGluR1beta was observed. In the hippocampus, mGluR1alpha-LI was restricted to non-principal neurons in all fields, whereas mGluR1beta-LI was strongest in principal cells of the CA3 field and dentate granule cells but absent in CA1. We have also shown that the vast majority of neurons in the striatum express mGluR1. The predominant form appeared to be mGluR1beta, with a distribution pattern reflecting the patch-matrix organization of the striatum. The specificity of the immunoreactivity described for mGluR1 splice variants was confirmed in mGluR1-deficient mice. The observation of a different cellular and regional distribution of mGluR1 splice variants, in particular in the hippocampus, suggests that they may mediate different roles in synaptic transmission.

Disruption of retinoid-related orphan receptor beta changes circadian behavior, causes retinal degeneration and leads to vacillans phenotype in mice.

The orphan nuclear receptor RORbeta is expressed in areas of the central nervous system which are involved in the processing of sensory information, including spinal cord, thalamus and sensory cerebellar cortices. Additionally, RORbeta localizes to the three principal anatomical components of the mammalian timing system, the suprachiasmatic nuclei, the retina and the pineal gland. RORbeta mRNA levels oscillate in retina and pineal gland with a circadian rhythm that persists in constant darkness. RORbeta-/- mice display a duck-like gait, transient male incapability to sexually reproduce, and a severely disorganized retina that suffers from postnatal degeneration. Consequently, adult RORbeta-/- mice are blind, yet their circadian activity rhythm is still entrained by light-dark cycles. Interestingly, under conditions of constant darkness, RORbeta-/- mice display an extended period of free-running rhythmicity. The overall behavioral phenotype of RORbeta-/- mice, together with the chromosomal localization of the RORbeta gene, suggests a close relationship to the spontaneous mouse mutation vacillans described >40 years ago.

staggerer phenotype in retinoid-related orphan receptor alpha-deficient mice.

Retinoid-related orphan receptor alpha (RORalpha) is a member of the nuclear receptor superfamily. To study its physiological role we generated null-mutant mice by targeted insertion of a lacZ reporter gene encoding the enzyme beta-galactosidase. In heterozygous RORalpha+/- mice we found beta-galactosidase activity, indicative of RORalpha protein expression, confined to the central nervous system, skin and testis. In the central nervous system, the RORalpha gene is expressed in cerebellar Purkinje cells, the thalamus, the suprachiasmatic nuclei, and retinal ganglion cells. In skin, RORalpha is strongly expressed in the hair follicle, the epidermis, and the sebaceous gland. Finally, the peritubular cells of the testis and the epithelial cells of the epididymis also strongly express RORalpha. Recently, it was reported that the ataxic mouse mutant staggerer (sg/sg) is caused by a deletion in the RORalpha gene. The analysis of the cerebellar and the behavioral phenotype of homozygous RORalpha-/- mice proves identity to sg/sg mice. Although the absence of RORalpha causes dramatic developmental effects in the cerebellum, it has no apparent morphological effect on thalamus, hypothalamus, and retina. Similarly, testis and skin of RORalpha-/- mice display a normal phenotype. However, the pelage hair of both sg/sg and RORalpha-/- is significantly less dense and when shaved shows reluctance to regrow.

Immunocytochemical localization of the mGluR1b metabotropic glutamate receptor in the rat hypothalamus.

The mGluR1 metabotropic glutamate receptor is a G-protein-coupled receptor that exists as different C-terminal splice variants. When expressed in mammalian cells, the mGluR1 splice variants exhibit diverse transduction mechanisms and also slightly differ in their apparent agonist affinities. In the present study, we used an affinity-purified antiserum, specifically reactive to the mGluRlb splice variant, in combination with a highly sensitive preembedding immunocytochemical method for light microscopy to investigate the distribution of this receptor in the rat hypothalamus. An intense immunoreactivity for mGluRlb was observed in distinct hypothalamic nuclei. Thus, neuronal cell bodies and dendrites were stained in the preoptic area, suprachiasmatic nucleus, dorsal hypothalamus, lateral hypothalamus, dorsomedial nucleus, tuberomammilary nucleus, and lateral mammilary body. The ventromedial nucleus exhibited neuropil immunostaining but neuronal cell bodies were not labeled. Strong mGluRlb immunoreactivity was observed in magnocellular neurons of the neuroendocrine supraoptic, paraventricular, and arcuate nuclei. Also, neuronal cell bodies were heavily labeled in the retrochiasmatic nucleus, anterior commissural nucleus, and periventricular nucleus. These immunocytochemical observations, together with previous studies, suggest that mGluRlb is coexpressed with other class I mGluRs in some nuclei throughout the hypothalamus. However, mGluRlb is so far the only receptor of this class strongly expressed in the supraoptic, paraventricular, and arcuate nuclei, which might have relevant implications in the physiological control of the neuroendocrine hypothalamic-pituitary system.

The metabotropic glutamate receptor 1 is not involved in the facilitation of glutamate release in cerebrocortical nerve terminals.

In this study we have addressed the identification of the metabotropic glutamate receptor (mGluR) involved in the facilitation of glutamate release in nerve terminals from the cerebral cortex. mGluR1 and 5 are coupled to phosphoinositide hydrolysis and the activation of these receptors with the specific agonist 3,5-dihydroxyphenylglycine (DHPG) enhances the release of glutamate. We have examined whether mGluR1 is responsible for this modulatory effect by preparing nerve terminals from mGluR 1 deficient mice. The Ca2+-dependent glutamate release evoked by a submaximal depolarization is enhanced by the agonist DHPG in nerve terminals from both wild and mutant mice. This result is consistent with the finding that the mGluR agonist also induces a similar increase in the levels of diacylglycerol (DAG) in the nerve terminals from wild and mutant mice. Moreover, the activity-dependent switch from facilitation to inhibition of release, observed when a second stimulation of the receptor is applied shortly after (5 min) the first pulse, was also observed in the mutant mice. These results indicate therefore, that the facilitation of glutamate release is unlikely to be due to the activation of mGluR1 but related to another phosphoinositide coupled mGluR.