Bidirectional regulation of neurite elaboration by alternatively spliced metabotropic glutamate receptor 5 (mGluR5) isoforms.

Alternative splicing in the mGluR5 gene generates two different receptor isoforms, of which expression is developmentally regulated. However, little is known about the functional significance of mGluR5 splice variants. We have examined the functional coupling, subcellular targeting, and effect on neuronal differentiation of epitope-tagged mGluR5 isoforms by expression in neuroblastoma NG108-15 cells. We found that both mGluR5 splice variants give rise to comparable [Ca2+]i transients and have similar pharmacological profile. Tagged receptors were shown by immunofluorescence to be inserted in the plasma membrane. In undifferentiated cells the subcellular localization of the two mGluR5 isoforms was partially segregated, whereas in differentiated cells the labeling largely redistributed to the newly formed neurites. Interestingly, we demonstrate that mGluR5 splice variants dramatically influence the formation and maturation of neurites; mGluR5a hinders the acquisition of mature neuronal traits and mGluR5b fosters the elaboration and extension of neurites. These effects are partly inhibited by MPEP.

Competitive interaction of seven in absentia homolog-1A and Ca2+/calmodulin with the cytoplasmic tail of group 1 metabotropic glutamate receptors.

BACKGROUND: Group 1 metabotropic glutamate receptors (mGluR1 and mGluR5) are coupled to inositol trisphosphate/Ca2+ signaling via G proteins and play an important role in excitatory synaptic transmission. To explore the regulation of group 1 mGluR function, we applied the yeast two-hybrid system using the intracellular carboxy-terminal domain of group 1 mGluRs (group 1 ct-mGluRs) and attempted to identify novel protein-protein interactions of group 1 mGluRs. RESULTS: The two-hybrid screening revealed a specific interaction between group 1 ct-mGluRs and Siah-1A, the mammalian homolog of Drosophila seven in absentia which is involved in photoreceptor cell differentiation via the ubiquitin/proteasome-dependent mechanism. This interaction occurs within a homologous 27-28 amino acid stretch within group 1 ct-mGluRs and requires the latter two-thirds of Siah-1A. Following coexpression in COS-7 cells, myc-tagged Siah-1A was coimmunoprecipitated with the flag-tagged ct-mGluR1 by anti-flag antibody. Furthermore, in vitro binding revealed that Siah-1A and Ca2+/calmodulin (CaM) binding sites overlap, such that Siah-1A binding is competitively inhibited by CaM in a Ca2+-dependent manner. CONCLUSIONS: The results demonstrate a direct interaction between group 1 mGluRs and Siah-1A and suggest a novel modulatory mechanism mediated by a competitive interaction between Ca2+/CaM and Siah-1A.

SHORT-TERM EFFECT OF CAPTOPRIL ON INTRAOCULAR PRESSURE.

The angiotensin converting enzyme (ACE), which is responsible for the conversion of angiotensin-I to angiotensin-II, and metabolism of bradykinin is found to be present in human ocular tissue and it manifests a variety of physiological and pharmacological effects. Angiotensin increased the intraocular pressure (IOP) in animals. Even, the topical instillation of ACE inhibitors have been reported to reduce the IOP in rabbits. We, therefore performed this randomized, double masked, parallel groups-design and placebo controlled study, to investigate the acute effect of captopril (6.25 mg, 12.50 mg, and 25.00 mg) and placebo on IOP, systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate in healthy human volunteers. These parameters were monitored for 4.0 h after the administration of drugs. Captopril 12.50 mg and 25.00 mg significantly reduced the IOP and SBP (P < 0.05). Captopril 6.25 mg also had a tendency to lower the IOP and significantly decreased the SBP (P < 0.05). The mechanism involved in the decrease of IOP and blood pressure with captopril could be due to inhibition in the formation of angiotensin-II and sparing of bradykinin.

Distribution of a metabotropic glutamate receptor, mGluR2, in the central nervous system of the rat and mouse: an immunohistochemical study with a monoclonal antibody.

The distribution of a metabotropic glutamate receptor mGluR2 in the central nervous system was immunohistochemically examined in the rat and mouse with a monoclonal antibody raised against an N-terminal sequence of rat mGluR2 (amino acid residues 87-134). Neuronal cell bodies with mGluR2-like immunoreactivity (mGluR2-LI) were clearly shown in the horizontal cells of Cajal in the cerebral cortex, neurons in the triangular septal nucleus and medial mammillary nucleus, Golgi cells and the unipolar brush cells in the cerebellar cortex, and Golgi-like and unipolar brush-like cells in the cochlear nucleus. Neuropil was intensely immunostained in the accessory olfactory bulb, bed nucleus of the accessory olfactory tract, neocortex, cingulate cortex, retrosplenial cortex, subicular and entorhinal cortices, stratum lacunosum-moleculare of CA1 and CA3, molecular layer of the dentate gyrus, periamygdaloid cortex, basolateral amygdaloid nucleus, bed nucleus of the anterior commissure, caudate-putamen, accumbens nucleus, thalamic reticular nucleus, anteroventral and paraventricular thalamic nuclei, granular layer of the cerebellar cortex, anterior and ventral tegmental nuclei, granular layer of the cochlear nucleus, and parvicellular part of the lateral reticular nucleus. Many axons in the white matter and fiber bundles were also immunostained. No glial cells with mGluR2-LI were found. No particular species differences were found in the distribution pattern of mGluR2-LI between the rat and mouse. The results indicate that mGluR2 is expressed not only in somato-dendritic domain, but also in axonal domain of excitatory and inhibitory neurons.

Differential presynaptic localization of metabotropic glutamate receptor subtypes in the rat hippocampus.

Neurotransmission in the hippocampus is modulated variously through presynaptic metabotropic glutamate receptors (mGluRs). To establish the precise localization of presynaptic mGluRs in the rat hippocampus, we used subtype-specific antibodies for eight mGluRs (mGluR1-mGluR8) for immunohistochemistry combined with lesioning of the three major hippocampal pathways: the perforant path, mossy fiber, and Schaffer collateral. Immunoreactivity for group II (mGluR2) and group III (mGluR4a, mGluR7a, mGluR7b, and mGluR8) mGluRs was predominantly localized to presynaptic elements, whereas that for group I mGluRs (mGluR1 and mGluR5) was localized to postsynaptic elements. The medial perforant path was strongly immunoreactive for mGluR2 and mGluR7a throughout the hippocampus, and the lateral perforant path was prominently immunoreactive for mGluR8 in the dentate gyrus and CA3 area. The mossy fiber was labeled for mGluR2, mGluR7a, and mGluR7b, whereas the Schaffer collateral was labeled only for mGluR7a. Electron microscopy further revealed the spatial segregation of group II and group III mGluRs within presynaptic elements. Immunolabeling for the group III receptors was predominantly observed in presynaptic active zones of asymmetrical and symmetrical synapses, whereas that for the group II receptor (mGluR2) was found in preterminal rather than terminal portions of axons. Target cell-specific segregation of receptors, first reported for mGluR7a (Shigemoto et al,., 1996), was also apparent for the other group III mGluRs, suggesting that transmitter release is differentially regulated by 2-amino-4-phosphonobutyrate-sensitive mGluRs in individual synapses on single axons according to the identity of postsynaptic neurons.

Metabotropic glutamate receptors mGluR2 and mGluR5 are expressed in two non-overlapping populations of Golgi cells in the rat cerebellum.

The metabotropic glutamate receptor subtypes mGluR2 and mGluR5, which are thought to be coupled respectively to the inhibitory cyclic adenosine monophosphate (cAMP) cascade and the phosphatidylinositol hydrolysis/Ca2+ cascade, are known to be expressed on Golgi cells in the granular layer of the rat cerebellar cortex. In the present immunohistochemical study with a monoclonal antibody against mGluR2 and a polyclonal antibody for mGluR5, we examined whether or not mGluR2- and mGluR5-like immunoreactivities were both present in single Golgi cells in the rat cerebellar cortex. In double immunofluorescence histochemistry, no Golgi cells showed mGluR2- and mGluR5-like immunoreactivities simultaneously. Of the total number of Golgi cells immunoreactive for mGluR2 or mGluR5, about 90% were mGluR2-like immunoreactive, and about 10% were mGluR5-like immunoreactive. Golgi cells with mGluR2-like immunoreactivity were distributed evenly in the granular layer of all the cerebellar regions, while those with mGluR5-like immunoreactivity were distributed more frequently in the I, II, VII-X lobules of the vermis and the copula pyramidis of the hemisphere than in other cerebellar regions. The results indicate that Golgi cells containing mGluR2 are segregated from those possessing mGluR5. These two populations of Golgi cells, each equipped with a different metabolic glutamate receptor coupled to a different intracellular signal transduction system, may play different roles in the glutamatergic neuronal circuits in the cerebellar cortex.

Presynaptic localization of a metabotropic glutamate receptor, mGluR8, in the rhinencephalic areas: a light and electron microscope study in the rat.

The present study indicated presynaptic localization of a metabotropic glutamate receptor, mGluR8, in projection neurons of the main olfactory bulb of rat. An antibody was produced by using a peptide corresponding to C-terminal 23 amino acids of mouse mGluR8. It was confirmed that the C-terminal 23 amino acids of rat mGluR8 were the same as those of mouse mGluR8 except for one, and that the antibody specifically recognized mGluR8 in the rat rhinencephalon. In layer Ia of the piriform cortex (a target area of projection fibers from the main olfactory bulb), mGluR8-like immunoreactivity (mGluR8-LI) was reduced after transection of the lateral olfactory tract, and mGluR8-LI was observed in axon terminals which were filled with round synaptic vesicles and made asymmetric synapses with dendritic spines.

Immunohistochemical localization of a metabotropic glutamate receptor, mGluR7, in ganglion neurons of the rat; with special reference to the presence in glutamatergic ganglion neurons.

Immunoreactivity for the metabotropic glutamate receptor 7 (mGluR7) and that for phosphate-activated glutaminase (PAG) were examined in the trigeminal (TG), dorsal root (DRG), nodose (NG), superior cervical, celiac, and pelvic ganglia of the rat. Virtually all neuronal cell bodies showed mGluR7-like immunoreactivity (mGluR7-LI) in these ganglia. On the other hand, PAG-like immunoreactivity (PAG) was seen in almost all neuronal cell bodies in the TG, DRG and NG, but not in the other ganglia. Co-existence of mGluR7- and PAG-LI in the TG, DRG and NG was confirmed by a double-immunofluorescence immunohistochemical method. The results indicate that virtually all sensory ganglion neurons are glutamatergic and equipped with mGluR7.

Pre- and postsynaptic localization of a metabotropic glutamate receptor, mGluR2, in the rat brain: an immunohistochemical study with a monoclonal antibody.

A monoclonal antibody against a metabotropic glutamate receptor, mGluR2, was produced by using a glutathione S-transferase (GST) fusion protein containing an N-terminal sequence of rat mGluR2. Intense mGluR2-like immunoreactivity (mGluR2-LI) was seen mainly in neuropil of the cerebral cortical regions, hippocampus, olfactory bulb, some diencephalic nuclei, dorsal cochlear nucleus and cerebellar cortex. In the cerebellar cortex, mGluR2-LI was seen only in Golgi cells. In Ammon's horn, mGluR2-LI was marked in the stratum lucidum of CA3 and the stratum lacunosum-moleculare of CA1-CA3, but not detected in the stratum pyramidale. The results indicate that mGluR2 is located not only presynaptically but also postsynaptically.

Presynaptic localization of a metabotropic glutamate receptor, mGluR7, in the primary afferent neurons: an immunohistochemical study in the rat.

An antibody which recognizes specifically a metabotropic glutamate receptor, mGluR7, was produced by using a trpE fusion protein containing a C-terminal sequence of rat mGluR7. Neuropil in laminae I and II of the dorsal horn of the rat, as well as many neuronal cell bodies in the dorsal root ganglion, showed mGluR7-like immunoreactivity; the immunoreactivity in neuropil was seen in axon terminals, which were filled with round synaptic vesicles and constituted axodendritic and axosomatic asymmetric synapses. The mGluR7-like immunoreactivity in laminae I and II in the dorsal horn was reduced after dorsal rhizotomy. The results indicate that some axon terminals of the primary afferent fibers to laminae I and II of the dorsal horn are provided with mGluR7.

Purification and molecular cloning of chymase from human tonsils.

A chymotrypsin-like protease was purified to homogeneity from human tonsils by a series of chromatographic procedures. The purified enzyme gave a single protein band with an apparent molecular mass of 30 kDa on SDS-PAGE. The sequence of the first 21 amino acids at the N-terminus of the enzyme was determined. A cDNA for the enzyme was cloned by PCR amplification from extracted tonsillar mRNA using a supposed N-terminal oligonucleotide primer and a conserved C-terminal primer of the chymase family. The deduced amino acid sequence of the isolated clone was identical to that of human chymase in connective tissue-type mast cells from heart except for a Ser instead of a Cys at the N-terminal 7th position.

Ipsilateral Coat's reaction in the eye of a child with en coup de sabre morphoea--a case report.

A female child with post-traumatic en coup de sabre type of morphoea (fronto-parietal circumscribed scleroderma) involving the left side of the forehead and face, who developed a Coat's disease-like fundus picture over the following two years, is being reported.