Refractory giant cell arteritis with spinal cord infarction

We report an elderly patient with aggressive steroid-refractory giant cell arteritis manifesting as myelopathy and bilateral visual loss while on treatment. Pathologically, spinal cord infarction was observed and was due to extensive necrotizing granulomatous arteritis of spinal arteries. Spinal cord damage in giant cell arteritis is rare. One prior autopsy report of spinal cord infarction in giant cell arteritis did not identify vasculitic changes in the spinal arteries.

Differential distribution of Ca2+-activated K+ channel splice variants among hair cells along the tonotopic axis of the chick cochlea

We have cloned from the receptor epithelium of the chick cochlea a family of alternatively spliced cDNAs derived from cslo, which encodes a Ca2+-activated K+ channel like those shown to help determine the resonant frequency of electrically tuned hair cells. Our results from PCRs using template RNAs from both tonotopically subdivided receptor epithelia and single hair cells demonstrate differential exon usage along the frequency axis of the epithelium at multiple splice sites in cslo. We also show that single hair cells express more than one splice variant at a given splice site. Since channel isoforms encoded by differentially spliced slo transcripts in other species are functionally heterogeneous, these data suggest that differential processing of slo transcripts may account, at least in part, for the systematic variation in hair-cell membrane properties along the frequency axis of electrically tuned auditory receptor epithelia.

Identification of a structural constituent and one possible site of postembryonic formation of a teleost otolithic membrane

A gelatinous otolithic membrane (OM) couples a single calcified otolith to the sensory epithelium in the bluegill sunfish (Lepomis macrochirus) saccule, one of the otolithic organs in the inner ear. Though the OM is an integral part of the anatomic network of endorgan structures that result in vestibular function in the inner ear, the identity of the proteins that make up this sensory accessory membrane in teleosts, or in any vertebrate, is not fully known. Previously, we identified a cDNA from the sunfish saccular otolithic organ that encoded a new member of the collagen family of structural proteins. In this study, we examined biochemical features and the localization of the saccular collagen (SC) protein in vivo using polyclonal antisera that recognize the noncollagenous domains of the SC protein. The SC protein, in vivo, was identified as a 95-kDa glycoprotein in sunfish whole-saccule lysate and in homogenates of microdissected saccular OMs. Immunohistochemical analyses demonstrated that the SC protein was localized within one of the two distinct layers of the sunfish saccular OM. The SC protein was also detected within the cytoplasm of supporting cells at the edges of the saccular sensory epithelium, indicating that these cells are a primary site for the synthesis of this structural protein. Further studies of the organization of this matrix molecule in the OM may help clarify the role of this sensory accessory membrane in vestibular sensory function.

Proliferation in the auditory receptor epithelium mediated by a cyclic AMP-dependent signaling pathway

Loss of receptor hair cells in the cochlea accounts for a significant proportion of hearing impairment in the population. Hair cells can be lost as a consequence of viral or bacterial insult, aging, and damage from intense sound or aminoglycoside antibiotics. The generation of replacement hair cells following damage by sound or drugs has been clearly demonstrated in birds; the chick is the best-studied model for auditory hair cell regeneration. New hair cells arise as progeny from an otherwise nondividing supporting cell population induced to proliferate by the damage. Functional recovery of hearing accompanies this cellular recovery process. The signals and pathways responsible for regenerative proliferation are unknown. Here we show that proliferation is induced in the undamaged receptor epithelium by agents that increase cyclic AMP levels, and that following this stimulation hair cells become labeled with proliferation markers. This remarkable proliferative response is blocked by inhibitors of the cAMP-regulated protein kinase A (PKA). In addition we show that the proliferative response induced by in vitro gentamicin damage is also significantly blocked by PKA inhibitors. These observations are the first to identify a signaling pathway that plays a role in regenerative proliferation in the auditory receptor epithelium.

Prion disease (PrP-A117V) presenting with ataxia instead of dementia

Gerstmann-Sträussler-Scheinker disease (GSS) is caused by several different point mutations of the prion protein (PrP) gene, each of which generally produces a distinct clinical phenotype. An ataxic form of GSS is genetically linked to a mutation at codon 102 (CCG-->CTG) leading to the substitution of leucine for proline, while a "telencephalic" variant of GSS, in which dementia is the predominant symptom and ataxia is minimal, has been described in two kindreds with a mutation at codon 117 (GCA-->GTG) resulting in the substitution of valine for alanine. In this report, we present a family with ataxic GSS that has, however, the same mutation at codon 117 as is present in the telencephalic variant of GSS. Other than an additional silent mutation (GCA-->GCG) at codon 117 on the normal allele, there were no other mutations detected. At the polymorphic codon 129, valine was encoded by both alleles in the proband that we studied. Why this family with prion disease (PrP-A117V) should present with ataxia instead of dementia, which was found in two previously identified families with the same PrP gene mutation, remains to be established.

Use of the teleost saccule to identify genes involved in inner ear function

The vertebrate inner ear sensory epithelia contain different types of hair cells and supporting cells. The teleost saccule is anatomically similar to the mammalian saccule and is primarily involved in the detection of translational acceleration and orientation with respect to gravity. To facilitate molecular studies of the teleost saccule cDNA libraries were constructed from microdissected Lepomis macrochirus (bluegill sunfish) saccular maculae. To our knowledge, this is the first report of cDNA libraries constructed from the saccule. In one instance, a non-polymerase chain reaction-based method of amplifying a mRNA population from limited amounts of starting tissue was employed that allowed construction of cDNA libraries from nanogram amounts of tissue mRNA. Conventional cDNA libraries were constructed from the sunfish saccular maculae as well. These cDNA libraries enriched in hair cell and supporting cell transcripts should facilitate molecular biological studies of inner ear sensory epithelia. As an example of their utility, efforts to identify tyrosine kinases expressed in the saccular endorgan using low-stringency hybridization screening of these cDNA libraries and the partial sequence of a cDNA found to encode an erbB-2-related tyrosine kinase are also reported.

Permeation properties and differential expression across the auditory receptor epithelium of an inward rectifier K+ channel cloned from the chick inner ear

The auditory receptor epithelium is an excellent model system for studying the differential expression of ion channel genes. An inward rectifier potassium current is among those which have been measured in only subsets of chick cochlear hair cells. We have cloned and characterized an inward rectifier potassium channel (cIRK1) from the chick cochlear sensory epithelium. cIRK1 functional properties are similar to those of the native channel, and the transcript encoding cIRK1 is limited to the low frequency half of the epithelium. This localization is in agreement with the distribution of the native hair cell current, suggesting that the differential current expression is transcriptionally regulated. The primary structure of cIRK1 is highly homologous to the mouse inward rectifier IRK1. However, we found that cIRK1 exhibited reduced single-channel conductance (17 picosiemens) and lower sensitivity to Ba2+ block (K1/2 = 12 microM). We identified Gln-125 near the putative pore region as being responsible for these differences. Site-directed mutagenesis was used to change Gln-125 to Glu (the residue in IRK1), resulting in a channel with a single-channel conductance of 28 picosiemens and a Ba2+ block of K1/2 = 2 microM. We propose that Gln-125 may form part of the external vestibule of the pore.

Molecular cloning and characterization of an inner ear-specific structural protein

Molecular biological studies of the mammalian inner ear have been limited by the relatively small size of the sensory endorgans contained within. The saccular otolithic organ in teleostian fish is structurally similar to its mammalian counterpart but can contain an order of magnitude more sensory cells. The prospect of the evolutionary conservation of proteins utilized in the vertebrate inner ear and the relative abundance of teleostian saccular sensory tissue made this an attractive system for molecular biological studies. A complementary DNA obtained by differential screening of a saccular complementary DNA library was identified that encodes an inner ear-specific collagen molecule.

Molecular cloning of a chick cochlea cDNA encoding a subunit of DNA replication factor C/activator 1

A chick cochlea cDNA library was constructed to clone molecules involved in peripheral auditory transduction and in the maintenance and regeneration of the sensory neuroepithelium following damage. Characterization of the library showed it to be of high complexity, to contain a high proportion of full-length cDNA inserts, and to contain a representative proportion of clones derived from hair cell transcripts. A cDNA clone encoding the chick homolog of the 40-kD subunit of the human replication factor C (also called activator 1) was isolated and the complete cDNA sequence determined. The predicted amino acid sequence is about 90% identical to that of the human homolog. Expression of the message for this replication factor was detected in brain and liver as well as in the cochlea. Expression levels in the brain are relatively high and are similar in developing and adult chicken nervous tissue. This suggests that replication factor C message expression, unlike that for the functionally associated factor proliferating cell nuclear antigen (PCNA), may be constitutive rather than cell cycle dependent. Although likely to be involved in DNA replication within the receptor neuroepithelium, expression of this replication factor message is not likely to constitute a marker for proliferation.

Herpes zoster ophthalmicus with orbital pseudotumor syndrome complicated by optic nerve infarction and cerebral granulomatous angiitis: MR-pathologic correlation

The authors describe a 41-year-old woman with herpes zoster ophthalmicus and extensive intracranial and orbital involvement as documented by MR and pathologically. MR showed all of the lesions that led to the ophthalmoplegia and pseudotumor syndrome, the periaxial infarct of the distal optic nerve, pontine infarcts, and granulomatous angiitis of the meningeal vessels. MR is useful in both detection and monitoring of the disease.

Metabolic labelling and quantitation of proteins synthesized by single chick cochleas

Molecular studies of the peripheral auditory system are made difficult by the small quantities of tissue available and by their relative inaccessibility. In addition, the cochlea and other hair cell-containing receptor organs are composed of both hair cells and supporting cells, as well as several other cell types. The identification of known proteins and the characterization of specific and novel protein molecules from these tissues require the use of sensitive techniques and a consideration of the complex histology. The chick cochlea was selected as an experimental system since the cochlea is relatively accessible in the bird, the receptor neuroepithelium contains a large number of hair cells compacted in a small area, and the physiology of the auditory periphery has been studied extensively. A general procedure is described for the metabolic radiolabelling of proteins from single cochleas followed by their solubilization, separation by high-resolution two-dimensional gel electrophoresis, and accurate quantitation. The method is highly reproducible and sensitive, and should prove useful in studies of proteins from the specialized cell types of the chick cochlea, including the identification of those whose rates of synthesis are modified in response to acoustic stimulation and sound damage or recovery.

Reactive lymphohistiocytosis with recurrence in the optic chiasm

Histiocytic infiltration of the optic chiasm is rare. We report a patient with a seizure disorder on anticonvulsant therapy, who developed systemic reactive histiocytosis. Treatment with splenectomy, corticosteroids, and anticonvulsant medication change resulted in clinical remission. The patient later developed recurrent lymphohistiocytosis restricted to the optic chiasm. Extensive re-evaluation yielded no evidence for infectious or malignant etiology. Radiation therapy and withdrawal of anticonvulsant therapy resulted in clinical remission. We conclude that both phenytoin and phenobarbital may trigger a lymphohistiocytic process and that infiltration of the visual pathway is possible.

The 28-kDa calbindin-D is a major calcium-binding protein in the basilar papilla of the chick

In previous work we identified a basilar papilla protein (BPP23) that appears to be one of the most abundant soluble proteins in the basilar papilla of the chick cochlea. Here we report the purification of protein BPP23 from chick cochlea and the generation of a specific antiserum. Immunoblotting and immunoprecipitation experiments with this antiserum indicate that BPP23 is a calcium-binding protein very similar, if not identical, to avian calbindin, the 28-kDa vitamin D-dependent calcium-binding protein. Although the basilar papilla contains both receptor hair cells and supporting cells, immunocytochemical studies by others have localized calbindin-like immunoreactivity to the hair cells in the rat auditory receptor epithelium. Our estimates of the abundance of protein BPP23, assuming exclusive localization within the hair cell, indicate a concentration of at least 1 mM. Avian calbindin has four high-affinity (Kd = 0.5 X 10(-6)) calcium-binding sites. The presence of a specific calcium-binding activity at such high levels suggests an important function for cochlear calbindin (BPP23) in hair cell calcium homeostasis and auditory transduction.

Glucokinase in B-cell-depleted islets of Langerhans

Glucose phosphorylation was studied in B-cell-enriched or in B-cell-depleted pancreatic islets from normal or streptozotocin-diabetic rats, respectively, using quantitative histochemical procedures. The data indicate that B-cell-enriched preparations from normal animals and whole islets from normals, diabetics, and insulin-treated diabetic animals have comparable glucokinase activities. Average maximum velocities were (mmol/kg dry tissue/hr) 134.1 +/- 7.3 for whole islets and 125.6 +/- 10.7 for the B-cell-enriched preparations from normal rats, 143.1 +/- 13.6 for B-cell-depleted islets from diabetic rats, and 124.4 +/- 10.7 for B-cell-depleted islets from insulin-treated diabetic animals. The Kmax for glucose of the enzyme in islets from untreated diabetic rats was 16 mM, comparable to the Kmax found for glucokinase from normal rat islets. Mannoheptulose, previously shown to be a competitive inhibitor of glucokinase from liver and normal islets, also inhibited glucokinase in B-cell-depleted islets from diabetic rats. The data indicate that glucokinase is not selectively located in the B-cell, as was previously assumed, but is also found in A- and/or D-cells of diabetic rats. This observation raises significant questions about the functional role of islet glucokinase under control and diabetic conditions.

The developmental appearance of a major basilar papilla-specific protein in the chick

The sensory epithelium of the chick cochlea, the basilar papilla, contains a major protein of approximately 23,000 daltons. This protein was as abundant as actin in the papilla, yet could not be found in significant quantities in any other cochlear tissue. The protein appeared at a time in development when other studies have shown that the chick embryo develops peripheral auditory competence. These observations suggest a role for this protein in cochlear function.

Hydrogen-bonded structure of the complex N-linked fetuin glycopeptide

The conformation of the N-linked complex glycopeptide of fetuin was examined with hydrogen-exchange techniques. The glycopeptide molecule contains eight acetamido hydrogens stemming from five N-acetylglucosamine residues and three N-acetylneuraminic acid residues and also one from the remaining sugar-peptide linkage. The hydrogen-exchange rates of these secondary amides were compared with small molecule model compounds having identical primary structures at their exchangeable hydrogen sites. Differences between the model rates and glycopeptide rates therefore cannot be accounted for by primary structure effects but reflect conformational features of the glycopeptide. Two glycopeptide hydrogens exhibit significantly hindered exchange; the rest exchange at the model rates. Removal of the three N-acetylneuraminic acid residues from terminal positions on the three branches of the glycopeptide removes the slowed hydrogens. The remaining ones continue to exchange at the model rate. These results indicate that two of the eight sugar acetamido hydrogens are involved in intramolecular hydrogen bonds. A likely structure includes two hydrogen bonds between the three N-acetylneuraminic acid residues. These two hydrogens, slowed to a moderate degree, reflect a preferred conformation stabilized by about 1 kcal/mol in free energy. The solution conformation of the glycopeptide suggested by these results is one that is partially ordered and can be easily modulated, owing to the relatively small amount of energy stabilizing the preferred conformation.