Chronic pyelonephritis in association with neuropathic bladder

Progressive chronic pyelonephritis (CPN) leading to renal failure was, in the past, a mode of death in children with meningomyelocele (MMC). With more sophisticated management modalities, renal failure is now uncommon, but the problem of CPN still remains. In this series of 100 children with MMC, 39% have CPN. It is significantly more common in girls than in boys. There is a strong relationship between CPN and vesico-ureteric reflux (VUR). There is no association with raised bladder pressure. The majority of CPN arises in children under the age of 4 years, but damaged kidneys can continue to deteriorate. Although chronic renal failure is rarely seen in children with MMC, there is a risk that this may merely be postponed into adulthood.

Identification of a new ligand binding domain in the alpha1 subunit of the inhibitory glycine receptor

Four discontinuous extracellular sequence domains have been proposed to form the ligand binding sites of the ligand-gated ion channel receptor superfamily. In this study, we investigated the role of 12 contiguous residues of the inhibitory glycine receptor that define the proposed "loop A" ligand binding domain. Using the techniques of site-directed mutagenesis and patch-clamp electrophysiology, four of the 12 residues were shown to have impaired ligand binding. Three mutants, 193A, A101H, and N102A, resulted in significant (17-44-fold) increases in the agonist EC50 values as compared with the wild-type glycine receptor, whereas Hill coefficients, ImaX values, and antagonist affinity remained largely unaffected. Consideration of receptor efficacy values indicates that these residues are involved in ligand binding rather than channel activation. A fourth mutant, W94A, failed to give rise to any glycine-activated currents, although cell-surface expression was observed, suggesting that this residue may also be involved in agonist binding. These data provide the most extensive characterization of the loop A ligand binding domain available to date and define two new residue locations, Ile93 and Asn102, as contributing to the four-loop model of ligand binding.

Olfactory receptor neurons exist as distinct subclasses of immature and mature cells in primary culture

The processes of neuronal differentiation and survival are key questions in neurobiology. The olfactory system possesses unique regenerative capacity, as its neurons are continually replaced throughout adulthood from a maintained population of precursor cells. Primary cultures of olfactory epithelium enriched in olfactory neurons would provide a useful model to study the processes of neurogenesis, differentiation and senescence. To determine whether immature olfactory neurons could be isolated in primary culture and to investigate the mechanisms underlying these processes, culture conditions which selectively favored the presence of immature olfactory neurons were optimized. Using low plating densities, a population of cells was identified which, by reverse transcription-polymerase chain reaction, demonstrated messages for olfactory neuronal markers, including Golf, olfactory cyclic nucleotide-gated channel and olfactory marker protein, as well as the p75 low-affinity nerve growth factor receptor. Immunocytochemical analysis showed that these putative immature olfactory neurons possessed immunoreactivity to G(olf), neuron-specific tubulin, neural cell adhesion molecule, synaptophysin and neurofilament. These neurons were defined as olfactory receptor neuron-1 cells. Under these conditions, a separate class of rarely occurring cells with different morphology demonstrated immunoreactivity to mature markers, such as adenylyl cyclase III and olfactory marker protein. Electrophysiologically, these cells displayed properties consistent with those of acutely dissociated olfactory receptor neurons. Another class of rarer cells which represented less than 2% of cells in culture demonstrated immunoreactivity to glial fibrillary acidic protein. These cultures can serve as a model for in vitro analysis of olfactory receptor neuronal development and maintenance, and provide a potential substrate for the development of cell lines.

Characterization of hypothalamic neurons expressing a neuropeptide receptor, GALR2, using combined in situ hybridization-immunohistochemistry

Our laboratory is interested in characterizing the neurotransmitter and hormonal phenotype of neurons in the rat hypothalamus expressing novel neuropeptide receptors of the neuropeptide Y and galanin families. In this review, we describe a technique combining nonradioactive in situ hybridization to detect mRNA and fluorescence immunohistochemistry to detect protein antigens. We examined paraffin sections of rat hypothalamus using confocal microscopy to determine whether mRNA for the galanin receptor, GALR2, was colocalized at the cellular level of resolution with somatostatin or tyrosine hydroxylase immunoreactivity. We found that many neurons in the hypothalamus expressed both GALR2 mRNA and either somatostatin or tyrosine hydroxylase immunoreactivity. The simultaneous detection of mRNA and protein immunoreactivity in individual neurons using the confocal microscope for visualization is an excellent tool for the analysis of newly characterized genes in the central nervous system.

Fibroblast activation protein: a cell surface dipeptidyl peptidase and gelatinase expressed by stellate cells at the tissue remodelling interface in human cirrhosis

Fibroblast activation protein (FAP) is a cell surface-bound protease of the prolyl oligopeptidase gene family expressed at sites of tissue remodelling. This study aimed to delineate the expression of FAP in cirrhotic human liver and examine its biochemical activities. Seventeen cirrhotic and 8 normal liver samples were examined by immunohistochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR). Hepatic stellate cells (HSC) were isolated and immunostained. Recombinant FAP and immunopurified, natural FAP were analyzed for protease activities and similarities to dipeptidyl peptidase IV (DPPIV), a structurally related enzyme. FAP-specific messenger RNA and immunoreactivity were detected in cirrhotic, but not normal, livers. FAP immunoreactivity was most intense on perisinusoidal cells of the periseptal regions within regenerative nodules (15 of 15 cases); this pattern coincides with the tissue remodelling interface. In addition, human FAP was expressed by cells within the fibrous septa (10 of 15 cases). Cell morphology, location, and colocalization with glial fibrillary acidic protein (GFAP) indicated that FAP is present on HSC in vivo. Similarly, isolated HSC expressed FAP in vitro. Both natural FAP from cirrhotic liver and recombinant FAP were shown to have gelatinase and dipeptidyl peptidase activities. FAP is a cell-bound, dual-specificity dipeptidyl peptidase and gelatinase expressed by activated HSC at the tissue remodelling interface in human cirrhosis. FAP may contribute to the HSC-induced extracellular matrix (ECM) changes of cirrhosis.

Alterations in expression of the neurotrophic factors glial cell line-derived neurotrophic factor, ciliary neurotrophic factor and brain-derived neurotrophic factor, in the target-deprived olfactory neuroepithelium

Neuronal growth factors play an important role in the development and maintenance of the nervous system. In the olfactory system, neurogenesis and synapse formation occur not only during development but throughout life and it would be expected that growth factors play a significant role in these ongoing processes. We have examined the expression of three neurotrophic factors, glial cell line-derived neurotrophic factor, ciliary neurotrophic factor and brain-derived neurotrophic factor in the normal rat olfactory system and following synaptic target ablation (olfactory bulbectomy). We found that brain-derived neurotrophic factor immunoreactivity was confined to the horizontal basal cells of the olfactory neuroepithelium and was unaltered by bulbectomy. Glial cell line-derived neurotrophic factor immunoreactivity was present in the mature olfactory neurons and also their synaptic target cells in the olfactory bulb. Following bulbectomy, glial cell line-derived neurotrophic factor immunoreactivity was abolished from the neuroepithelium. Ciliary neurotrophic factor was present throughout the olfactory neuronal lineage with strongest immunoreactivity in the horizontal basal cells and mature olfactory neurons as well as several cell types in the olfactory bulb. Postbulbectomy, there was loss of strong ciliary neurotrophic factor immunoreactivity in olfactory neurons, however, low levels persisted in the remaining neuronal population. Horizontal basal cell immunoreactivity persisted over three months. Our results would be consistent with glial cell line-derived neurotrophic factor expression in mature olfactory neurons being dependent upon functional synaptic contact with the olfactory bulb. Alternatively, this factor may be acting as target-derived growth factor for olfactory neurons, a role in keeping with its function in spinal motoneurons and in the nigrostriatal system. Brain-derived neurotrophic factor is implicated in the trophic support of immature neurons. Ciliary neurotrophic factor is clearly important in this unique neuronal system but elucidation of its role awaits further investigation.

Patterns of synaptophysin expression during development of the inner ear in the chick

The onset of active neural connections between the periphery and the central nervous system is integral to the development of sensory systems. This study presents patterns of synaptogenesis in the chick basilar papilla (i.e., cochlea) by examining the immunohistochemical expression of synaptophysin with a specific monoclonal antibody, SBI 20.10. The initial onset of synaptophysin expression occurs in nerve fibers and ganglion cell bodies at a time when neurites reach the basement membrane of the chick cochlea on embryonic day 6-7 (ED 6-7). By ED 8, synaptophysin positive fibers invade the neural side of the entire length of the cochlea, so that by ED 9-10, fibers are forming multiple terminals on the basolateral ends of retracting receptor or hair cells. In contrast, on the abneural side, immunoreactive terminals are seen first as small, punctate contacts and then as large, synaptophysin positive calyceal endings beneath short hair cells. These terminals are sparse during early development, more numerous by ED 17-19, but still incomplete after 2 weeks posthatching. In comparison, hair cells show synaptophysin immunoreactivity in both supra- and infranuclear regions by ED 11-12, a time when efferent innervation is incomplete. Thus, during development, synaptophysin is expressed at both synaptic and nonsynaptic sites, is relatively selective in its regional distribution, and is expressed in hair cells at a time when auditory function begins. Our results present a framework with which to understand the potential role of synaptophysin in early synaptogenesis of the cochlea.

Cytotoxicity of advanced glycation endproducts is mediated by oxidative stress

Non-enzymatic glycation of proteins with reducing sugars and subsequent transition metal catalysed oxidations leads to the formation of protein bound "advanced glycation endproducts" (AGEs). They accumulate on long-lived proteins and are for example structural components of the beta-amyloid plaques in Alzheimer's disease. Since the oxidation of glycated proteins as well as the interaction of AGEs with cell surface receptors produces superoxide radicals, it was tested in BHK 21 hamster fibroblast cells and SH-SY5Y human neuroblastoma cells if AGEs can exert cytotoxic effects on cells. Cell viability was assessed with three independent tests: MTT-assay (activity of the mitochondrial respiratory chain), lactate dehydrogenase assay (release of cytoplasmatic enzymes, membrane integrity) and Neutral Red assay (active uptake of a hydrophilic dye). Two model AGEs, chicken egg albumin-AGE and BSA-AGE, both caused significant cell death in a dose-dependent manner. The cytotoxic effects of AGEs could be attenuated by alpha-ketoglutarate and pyruvate, by antioxidants such as thioctic acid and N-acetylcysteine, and by aminoguanidine, an inhibitor of nitric oxide synthase. This suggests that reactive oxygen species as well as reactive nitrogen species contribute to AGE mediated cytotoxicity. Since AGEs accumulate on beta-amyloid plaques in AD over time, they may additionally contribute to oxidative stress, cell damage, functional loss and even neuronal cell death in the Alzheimer's disease brain.

Alterations in the neurotrophic factors BDNF, GDNF and CNTF in the regenerating olfactory system

Neurogenesis, axonal outgrowth and synapse formation are usually restricted to specific stages during central nervous system development, but the mature olfactory system maintains these capacities. The cycle of neuronal turnover can be experimentally induced by surgical ablation of the olfactory bulb (OB). We are interested in the growth factor regulation of these processes and the trophic role played by the target tissue, the OB. We studied the immunohistochemical expression of three neurotrophic factors, brain derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF) in the rat olfactory neuroepithelium (ON) and OB and in target-deprived ON at 1, 3 and 12 weeks post unilateral bulbectomy. We found BDNF immunoreactivity (IR) was restricted to the basal cells and did not alter postbulbectomy. GDNF-IR was expressed by mature olfactory receptor neurons (ORNs), their axons and target cells in the OB in controls, but was absent from the ON postbulbectomy. Hence, the expression of GDNF by ORNs was found to be target-dependent. CNTF-IR was present in ORNs and their target cells in the OB, in basal cells and in some immature ORNs. Postbulbectomy, CNTF-IR was unaltered in the basal cells, and very low levels were detectable in maturing ORNs in the ON. Our results indicate that these three factors may contribute to the trophic regulation of this neuronal pathway in a coordinated fashion. Previous work has shown that BDNF promotes survival of ORNs in vitro, and TrkB expression has been found in both immature and mature ORNs. Hence, BDNF produced by basal cells may be acting locally on neurons expressing TrkB. Expression of CNTF by both the basal cells and the ORNs suggests that it may play an integral role in this neuronal differentiation pathway. Finally, the expression of GDNF exclusively by mature ORNs in the ON, its presence in the target cells in the OB and abolition of expression by bulbectomy, suggests that it may be target-derived. This provides a major mechanism by which the bulb could exert trophic influences on ORNs.

Increased expression of human type IIa secretory phospholipase A2 antigen in arthritic synovium

OBJECTIVE

To determine the localisation and level of expression of human type IIa secretory phospholipase A2 (sPLA2) in the synovium of rheumatoid arthritis (RA), osteoarthritis (OA), and non-arthritic (NA) patients and to examine the relation between sPLA2 and histological features of inflammation.

METHODS

Immunoperoxidase staining using the anti-sPLA2 monoclonal antibody 9C1 was performed on frozen sections of knee synovium of 10 RA, 10 OA, and 10 NA patients. sPLA2 positive cells were scored on a scale of 0-3 in 10 fields of a representative tissue section from each case. Double labelling immunofluorescence confocal microscopy with antibodies to CD14 or CD45 and 9C1 was used to determine cell type specificity. Inflammation was assessed by semiquantitative scoring of lining layer thickness and mononuclear cell infiltrates (MC) and a cumulative inflammation score, generated by summing the two parameters. Scores in each group were compared using non-parametric statistical analysis.

RESULTS

sPLA2 was localised to endothelium (EC), vascular smooth muscle (VSM), and mast cells (M) in all tissue sections. In RA and OA sections, staining was seen in both macrophage-like and fibroblast-like cells in the synovial lining layer (LL) and subsynovial lining layer (SLL). Perineural cells stained positively. Subintimal lymphoid aggregates (LA) were negative in all sections. The RA group showed significantly greater staining in extravascular synovial tissue (median 3.6, range 1.5-6.0) than the OA (median 1.95, range 0-5.3) or NA (median 0, range 0-5.9) groups (p < 0.05). LL staining was significantly higher in RA than both OA and NA sections (p < 0.05). The OA group showed a trend to higher staining scores than the NA group that did not reach significance. There was a significant correlation between the sPLA2 staining score and inflammation score within the RA patient group (p < 0.05).

CONCLUSIONS

The synovium is a site of increased expression of sPLA2 antigen in both RA and OA relative to NA. Its presence in both fibroblast and macrophage-like cells in the LL and SLL of synovial tissue in RA and OA, but not NA, indicates that the enzyme is specifically induced in these regions in both conditions with expression in the LL being particularly characteristic of RA. The widespread expression of sPLA2 in synovium suggests it is likely to play a significant part in synovial pathology.

The synthesis of sialylated oligosaccharides using a CMP-Neu5Ac synthetase/sialyltransferase fusion

Large-scale enzymatic synthesis of oligosaccharides, which contain terminal N-acetyl-neuraminic acid residues requires large amounts of the sialyltransferase and the corresponding sugar-nucleotide synthetase, which is required for the synthesis of the sugar-nucleotide donor, CMP-Neu5Ac. Using genes cloned from Neisseria meningitidis, we constructed a fusion protein that has both CMP-Neu5Ac synthetase and alpha-2,3-sialyltransferase activities. The fusion protein was produced in high yields (over 1200 U/L, measured using an alpha-2,3-sialyltransferase assay) in Escherichia coli and functionally pure enzyme could be obtained using a simple protocol. In small-scale enzymatic syntheses, the fusion protein could sialylate various oligosaccharide acceptors (branched and linear) with N-acetyl-neuraminic acid as well as N-glycolyl- and N-propionyl-neuraminic acid in high conversion yield. The fusion protein was also used to produce alpha-2,3-sialyllactose at the 100 g scale using a sugar nucleotide cycle reaction, starting from lactose, sialic acid, phosphoenolpyruvate, and catalytic amounts of ATP and CMP.

Advanced glycation endproducts are associated with Hirano bodies in Alzheimer's disease

One of the structural posttranslational modifications contributing to the formation of insoluble, and protease-resistant protein deposits in Alzheimer's disease (AD), such as neurofibrillary tangles (NFT) and beta-amyloid plaques are 'advanced glycation endproducts' (AGE). Using a polyclonal antibody against AGE in frozen sections of fixed brain tissue from Alzheimer's disease patients, AGE were identified in a further characteristic protein deposit in AD, namely in Hirano bodies. AGE are localized to ovoid, spherical, and rod-like Hirano bodies in the hippocampus, particularly numerous in the stratum lacunosum-moleculare of CA1. Since Hirano bodies are known to contain mainly cytoskeletal and cytoplasmic components and are localized within the soma of neurons our study suggests that AGE formation and intracellular protein crosslinking represent early stages during neuronal degeneration.

Cloning, pharmacological characterization and distribution of a novel galanin receptor

The neuropeptide galanin mediates a diverse spectrum of biological activities by interacting with specific G-protein-coupled receptors. Through expression cloning, human and rat GALR1 receptor cDNA clones have previously been isolated and characterized. In this study, we have used homology screening to isolate a rat brain cDNA clone encoding a second galanin receptor subtype, the GALR2 receptor. The isolated cDNA encodes a 372-amino-acid G-protein-coupled receptor that shares 38% overall amino-acid identity with the rat GALR1 receptor. The pharmacological profile of the rat GALR2 receptor is similar to that of the rat GALR1 receptor. The rat GALR2 receptor binds galanin, N-terminal galanin fragments, and the putative galanin receptor antagonists galantide, C7, M35 and M40 with high affinity but it does not bind C-terminal galanin fragments. Galanin increases intracellular inositol phosphate levels in HEK 293 cells expressing the rat GALR2 receptor via a pertussis toxin-insensitive G-protein. The rat GALR2 receptor mRNA is highly expressed in several brain regions, including hypothalamus and hippocampus as well as the anterior pituitary, with lower levels of expression detected in amygdala, and regions of cortex. It is also highly expressed in the GH3 pituitary cell line and in gut tissues, and to a lower extent in spleen, lung, skeletal muscle, heart, kidney, liver and testis. These results suggest that GALR2 receptor mediates galanin's regulation of pituitary hormone secretion and possibly food intake.

Putative odour receptors localize in cilia of olfactory receptor cells in rat and mouse: a freeze-substitution ultrastructural study

Two different polyclonal antibodies were raised to synthetic peptides corresponding to distinct putative odour receptors of rat and mouse. Both antibodies selectively labelled olfactory cilia as seen with cryofixation and immunogold ultrastructural procedures. Regions of the olfactory organ where label was detected were consistent with those found at LM levels. Immunopositive cells were rare; only up to about 0.4% of these receptor cells were labelled. Despite chemical, species, and topographic differences both antibodies behaved identically in their ultrastructural labelling patterns. For both antibodies, labelling was very specific for olfactory cilia; both bound amply to the thick proximal and the thinner and long distal parts of the cilia. Dendritic knobs showed little labelling if any. Dendritic receptor cell structures below the knobs, supporting cell structures, and respiratory cilia did not immunolabel. There were no obvious differences in morphology between labelled and unlabelled receptor cells and their cilia. Labelling could be followed up to a distance of about 15 microns from the knobs along the distal parts of the cilia. When labelled cells were observed, this signal was detectable in two, sometimes three, sections taken through these cells while being consistently absent in neighbouring cells. This pattern argues strongly for the specificity of the labelling. In conclusion, very few receptor cells labelled with the antibodies to putative odour receptors. Additionally the olfactory cilia, the cellular regions that first encounter odour molecules and that are thought to transduce the odorous signal, displayed the most intense labelling with both antibodies. Consequently, the results showed these cilia as having many copies of the putative receptors. Finally, similar patterns of subcellular labelling were displayed in two different species, despite the use of different antibodies. Thus, this study provides compelling evidence that the heptahelical putative odour receptors localize in the olfactory cilia.

Characterization of a recombinant Neisseria meningitidis alpha-2,3-sialyltransferase and its acceptor specificity

The structure and specificity of the recombinant alpha-2,3-sialyltransferase from Neisseria meninigitidis are reported. This enzyme showed an unusual acceptor specificity in that it could use alpha-terminal and beta-terminal Gal residues as acceptors. In addition (beta1-->4)-linked and (beta1-->3)-linked terminal Gal served as acceptors. These properties distinguish the bacterial enzyme from the more widely investigated mammalian equivalents. The protein was expressed as a membrane-associated protein in Escherichia coli at a level of 750 U/l (approximately 250 mg/l). The protein could be extracted with buffers containing 0.2% Triton X-100 and purified to homogeneity using immobilized-metal-affinity chromatography. Electrospray-ionization mass spectrometry of peptides obtained by cleavage with cyanogen bromide and trypsin confirmed over 95% of the deduced amino acid sequence. When used for enzymatic synthesis in coupled reactions with recombinant CMP-Neu5Ac synthetase, the alpha-2,3-sialyltransferase could sialylate fluorescent derivatives of N-acetyllactosamine with N-acetylneuraminic acid, N-propionylneuraminic acid and N-glycoloylneuraminic acid.

Putative odour receptors localize in cilia of olfactory receptor cells in rat and mouse: a freeze-substitution ultrastructural study

Two different polyclonal antibodies were raised to synthetic peptides corresponding to distinct putative odour receptors of rat and mouse. Both antibodies selectively labelled olfactory cilia as seen with cryofixation and immunogold ultrastructural procedures. Regions of the olfactory organ where label was detected were consistent with those found at LM levels. Immunopositive cells were rare; only up to about 0.4% of these receptor cells were labelled. Despite chemical, species, and topographic differences both antibodies behaved identically in their ultrastructural labelling patterns. For both antibodies, labelling was very specific for olfactory cilia; both bound amply to the thick proximal and the thinner and long distal parts of the cilia. Dendritic knobs showed little labelling if any. Dendritic receptor cell structures below the knobs, supporting cell structures, and respiratory cilia did not immunolabel. There were no obvious differences in morphology between labelled and unlabelled receptor cells and their cilia. Labelling could be followed up to a distance of about 15 microns from the knobs along the distal parts of the cilia. When labelled cells were observed, this signal was detectable in two, sometimes three, sections taken through these cells while being consistently absent in neighbouring cells. This pattern argues strongly for the specificity of the labelling. In conclusion, very few receptor cells labelled with the antibodies to putative odour receptors. Additionally the olfactory cilia, the cellular regions that first encounter odour molecules and that are thought to transduce the odorous signal, displayed the most intense labelling with both antibodies. Consequently, the results showed these cilia as having many copies of the putative receptors. Finally, similar patterns of subcellular labelling were displayed in two different species, despite the use of different antibodies. Thus, this study provides compelling evidence that the heptahelical putative odour receptors localize in the olfactory cilia.

Influence of advanced glycation end-products and AGE-inhibitors on nucleation-dependent polymerization of beta-amyloid peptide

Nucleation-dependent polymerization of beta-amyloid peptide, the major component of plaques in patients with Alzheimer's disease, is significantly accelerated by crosslinking through Advanced Glycation End-products (AGEs) in vitro. During the polymerization process, both nucleus formation and aggregate growth are accelerated by AGE-mediated crosslinking. Formation of the AGE-crosslinked amyloid peptide aggregates could be attenuated by the AGE-inhibitors Tenilsetam, aminoguanidine and carnosine. These experimental data, and clinical studies, reporting a marked improvement in cognition and memory in Alzheimer's disease patients after Tenilsetam treatment, suggest that AGEs might play an important role in the etiology or progression of the disease. Thus AGE-inhibitors may generally become a promising drug class for the treatment of Alzheimer's disease.

Cloning of the lipooligosaccharide alpha-2,3-sialyltransferase from the bacterial pathogens Neisseria meningitidis and Neisseria gonorrhoeae

The genes encoding the alpha-2,3-sialyltransferases involved in lipooligosaccharide biosynthesis from Neisseria meningitidis and Neisseria gonorrhoeae have been cloned and expressed in Escherichia coli. A high sensitivity enzyme assay using a synthetic fluorescent glycosyltransferase acceptor and capillary electrophoresis was used to screen a genomic library of N. meningitidis MC58 L3 in a "divide and conquer" strategy. The gene, denoted lst, was found on a 2. 0-kilobase fragment of DNA, and its sequence was determined and then used to design probes to amplify and subsequently clone the corresponding lst genes from N. meningitidis 406Y L3, N. meningitidis M982B L7, and N. gonorrhoeae F62. Functional sialyltransferase was produced from the genes derived from both L3 N. meningitidis strains and the N. gonorrhoeae F62. However, the N. meningitidis M982B L7 gene contained a frameshift mutation that renders it inactive. The expression of the lst gene was easily detected using the enzyme assay, and the protein expression could be detected when an immunodetection tag was added to the COOH-terminal end of the protein. Using the synthetic acceptor N-acetyllactosamine-aminophenyl-(6-(5-(fluorescein-carboxamido)-hexan oic acid amide), the alpha-2,3 specificity of the enzyme was confirmed by NMR examination of the reaction product. The enzyme could also use synthetic acceptors with lactose or galactose as the saccharide portion. This study is the first example of the cloning, expression, and examination of alpha-2,3-sialyltransferase activity from a bacterial source.

Sensory cells of the chick cochlea express synaptophysin

Previous evidence has shown expression of synaptophysin by sensory cells of the auditory and vestibular systems in the human, but not in other mammalian species. Using a monoclonal antibody, SBI 20.10, we investigated the expression of synaptophysin in the sensory cells of the avian cochlea. We present immunohistochemical data showing synaptophysin expression by cochlear hair cells in both late stage embryos and adult chickens. Immunoblotting of cochleae confirmed an antigen with an apparent molecular weight appropriate for synaptophysin that increases with development. Immunoreactivity in the apex of the cochlea occurred in hair cells on both neural and abneural sides, whereas immunoreactivity in the base of the cochlea was relegated to hair cells on the neural side. These observations indicate that, in the avian auditory system, like the human, synaptophysin is expressed in the sensory cells of both the embryo and adult.

The unique extracellular disulfide loop of the glycine receptor is a principal ligand binding element

A loop structure, formed by the putative disulfide bridging of Cys198 and Cys209, is a principal element of the ligand binding site in the glycine receptor (GlyR). Disruption of the loop's tertiary structure by Ser mutations of these Cys residues either prevented receptor assembly on the cell surface, or created receptors unable to be activated by agonists or to bind the competitive antagonist, strychnine. Mutation of residues Lys200, Tyr202 and Thr204 within this loop reduced agonist binding and channel activation sensitivities by up to 55-, 520- and 190-fold, respectively, without altering maximal current sizes, and mutations of Lys200 and Tyr202 abolished strychnine binding to the receptor. Removal of the hydroxyl moiety from Tyr202 by mutation to Phe profoundly reduced agonist sensitivity, whilst removal of the benzene ring abolished strychnine binding, thus demonstrating that Tyr202 is crucial for both agonist and antagonist binding to the GlyR. Tyr202 also influences receptor assembly on the cell surface, with only large chain substitutions (Phe, Leu and Arg, but not Thr, Ser and Ala) forming functional receptors. Our data demonstrate the presence of a second ligand binding site in the GlyR, consistent with the three-loop model of ligand binding to the ligand-gated ion channel superfamily.

Neuronal inositol 1,4,5-trisphosphate receptor localized to the plasma membrane of olfactory cilia

Both the cyclic adenosine 3',5'-monophosphate and the phosphoinositide second messenger systems are involved in olfactory signal transduction. The inositol 1,4,5-trisphosphate receptor is one of the principal intracellular calcium channels responsible for mobilizing stored calcium. The precise location of the 1,4,5-trisphosphate receptor (endoplasmic reticulum vs surface) and its role in the events of olfactory signal transduction need to be defined. By light microscopic and confocal immunohistochemistry we show expression of the olfactory-enriched G-protein, G(olf), associated with cyclic AMP responses, and of the inositol 1,4,5-trisphosphate receptor in the dendritic projections and cilia of essentially all olfactory receptor neurons, indicating that individual neurons express components of both second messenger systems. By immunoelectron microscopy, we demonstrate that the inositol 1,4,5-trisphosphate receptor is localized to the surface membrane of rat olfactory cilia. This is the first morphological demonstration of the surface membrane localization of inositol 1,4,5-trisphosphate receptor in olfactory cilia. Our findings, taken in conjunction with electrophysiological data from other workers, are supportive of the inositol 1,4,5-trisphosphate receptor playing a novel role in regulating calcium flux at the ciliary surface membrane.

CDRK and DRK1 K+ channels have contrasting localizations in sensory systems

Molecular cloning of mammalian potassium channels has revealed an extensively heterogeneous superfamily of potassium channels derived from four basic subfamilies, Shaker, Shaw, Shal and Shab, each with multiple members. The families were first identified in Drosophila, in which subfamily heterogeneity is derived by alternative splicing, while in mammals mainly distinct genes give rise to channel subtypes. Further diversity of mammalian potassium channels is demonstrated by the identification of some which do not belong to any of the four main subfamilies. Although potassium channels are differentiated into fast-inactivating and delayed rectifier types, differential functions of the many mammalian potassium channels are unclear. Moreover, potassium channels function as homotetramers, though in principle heterotetramers might have a physiological role as is the case with heteromers of neurotransmitter receptor subunits. Insight into differential functions of potassium channels may be provided by their regional and subcellular localizations. In the rat brain in situ hybridization and immunohistochemistry have revealed distinct regional localizations for various subfamilies. In one instance a particular subfamily predominated in cell bodies and another in axons. We demonstrated dramatically different localizations for two members of the Shab subfamily, circumvallate papilla delayed rectifier K+ channel (CDRK) and delayed rectifier potassium channel 1 (DRK1), which in major portions of their sequences display more than 90% amino acid identity. In a number of brain regions they occur in distinct neuronal cell types or subcellular compartments, with CDRK predominantly localized diffusely over soma and in fibers and DRK1 most evident in soma and dendritic process.

Contrasting immunohistochemical localizations in rat brain of two novel K+ channels of the Shab subfamily

We have localized CDRK and DRK1, two novel K+ channels of the Shab subfamily by immunohistochemistry. The two channels are closely related in structure with about 90% amino acid identity in the N-terminal and middle portions and 60% identity in the C-terminal region. We observe striking differences in cellular localizations of the two channels. DRK1 tends to localize to cell bodies and proximal dendrites discretely, while CDRK is diffusely present in cell bodies and is also found on fibers in specific brain areas. In the cerebral cortex DRK1 is localized to pyramidal cells, whereas CDRK occurs in small cells, presumably interneurons. These localizations may reflect specialized delayed rectifier functions and targeting properties manifested differentially by K+ channel subfamily members.

Calcium/calmodulin-activated phosphodiesterase expressed in olfactory receptor neurons

We show that calmodulin-dependent phosphodiesterase (CAM-PDE) is selectively expressed in mature olfactory receptor neurons within the olfactory mucosa. Immunocytochemical staining reveals neuronal immunoreactivity that is most pronounced within cilia, dendritic knobs, and axon bundles. Neither sustentacular cells nor basal cells display immunoreactivity. The extent of loss of neuronal immunoreactivity following bulbectomy resembles loss of the neuronal population. High-affinity CAM-PDE activity in olfactory cilia is fivefold greater than in brain, when assayed at low micromolar cAMP. This activity is depleted in turbinates following bulbectomy. Olfactory mucosal PDE activity is composed of a minimum of two major forms. In the absence of Ca(2+), rolipram-sensitive PDE comprises 65% of total activity. Following stimulation by Ca2+, CAM-PDE activity is elevated sixfold to become the predominant form, thereby increasing total activity 300%, with half-maximal effect at 1 microM Ca2+. We propose that Ca2+ stimulation of CAM-PDE may be necessary for termination of olfactory signals.