Risk factors for decreased bone density and effects of HIV on bone in the elderly

Most studies of bone density in HIV-infected individuals focus on young men. This study compares differences in bone density in elderly HIV positive men and women to HIV negative controls. Bone density was lower in the lumbar spine and hip in the HIV-infected group. Antiretrovirals may be associated with decreased bone mineralization.

INTRODUCTION

Individuals with human immunodeficiency virus (HIV) may be at increased risk for osteoporosis. Prolonged exposures to HIV and/or antiretroviral therapy are possible causes for this association. This study compares differences in bone mineral density (BMD) in elderly HIV positive men and women to HIV negative controls.

METHODS

A cross-sectional study was conducted among 57 HIV-infected and 47 HIV negative subjects over age 55. BMD at the lumbar spine and total hip and markers of bone turnover were compared.

RESULTS

BMD was borderline lower in the lumbar spine and significantly lower in the hip in the HIV-infected group. Controlling for age, sex, race and body mass index, differences between the groups were significant at both sites. There was no difference in markers of bone turnover between the groups. Tenofovir use was significantly associated with decreased BMD at the spine while protease inhibitor use was significantly associated with decreased BMD at the hip.

CONCLUSION

Elderly men and women with HIV have lower bone mass than HIV negative controls. Decreased body mass index was the most important risk factor associated with decreased BMD. Bone demineralization was observed among HIV-infected subjects receiving either tenofovir or a protease inhibitor.

Aspergillus infection limited to renal allograft: case report and review of literature

We report a case of a 28-year-old recipient of a cadaveric renal transplant who developed Aspergillus infection in the allograft without having disseminated disease. We review the previously reported cases of isolated Aspergillus in kidney transplant recipients and discuss the possible route of transmission in our patient. We also discuss the alternate but successful treatment that our patient received.

Biopsies of human olfactory epithelium

It has been shown that olfactory epithelium can be safely biopsied from the living, intact human being. Observations of the ultrastructure of this epithelium shows changes that can then be correlated with the etiology and degree of olfactory loss, allowing a greater understanding of both normal transduction and of the pathology of dysfunction. Examples of the common forms of olfactory dysfunction are presented and discussed. Additionally, the technique will allow additional immuno-histochemical and molecular study of the tissue, will increase the understanding of both normal and pathological function and should translate to new therapeutic regimens.

Variability of position of the P2 glomerulus within a map of the mouse olfactory bulb

Olfactory receptor neurons (ORNs) that express a common odorant receptor molecule target specific glomeruli in the olfactory bulb. We systematically assessed the location of the olfactory glomeruli that receive input from ORNs expressing P2 receptors in the P2-internal ribosome entry site-tau-lacZ mouse. We present a new mapping method that includes an Internet-accessible computer program for generating two- and three-dimensional maps of the glomerular sheet in the olfactory bulbs of mice. Cylindrical coordinates were used to define glomerular location: The coordinates were given as the anteroposterior (AP) distance parallel to the long axis of the bulb (rostrocaudal; RC) and angular measurements with origin defined by the remnant ependymal layer in the center of the granule cell layer in the bulb. Using this method, we can apply rigorous statistical methods to give objective estimates of position and variability. At the 95% confidence interval, the lateral P2 glomerulus lies at coordinates 1,008 microm +/- 306 microm AP x 146 degrees +/- 12 degrees, and the medial P2 glomerulus lies at 1,828 microm +/- 196 microm AP x 204 degrees +/- 8 degrees. We estimate that these coordinates encompass a domain containing 29 and 37 of the 1,800 glomeruli ( approximately 2%) for the lateral and medial glomeruli, respectively. Furthermore, the data reported here demonstrate that the rostrocaudal position of small P2 glomeruli is three times more variable than that of large glomeruli.

Olfactory fingerprints for major histocompatibility complex-determined body odors

Recognition of individual body odors is analogous to human face recognition in that it provides information about identity. Individual body odors determined by differences at the major histocompatibility complex (MHC or H-2) have been shown to influence mate choice, pregnancy block, and maternal behavior in mice. Unfortunately, the mechanism and extent of the main olfactory bulb (MOB) and accessory olfactory bulb (AOB) involvement in the discrimination of animals according to H-2-type has remained ambiguous. Here we study the neuronal activation patterns evoked in the MOB in different individuals on exposure to these complex, biologically meaningful sensory stimuli. We demonstrate that body odors from H-2 disparate mice evoke overlapping but distinct maps of neuronal activation in the MOB. The spatial patterns of odor-evoked activity are sufficient to be used like fingerprints to predict H-2 identity using a novel computer algorithm. These results provide functional evidence for discrimination of H-2-determined body odors in the MOB, but do not preclude a role for the AOB. These data further our understanding of the neural strategies used to decode socially relevant odors.

Characteristics of odorant elicited calcium changes in cultured human olfactory neurons

An important step in establishing and utilizing a cell culture system for the in vitro study of olfaction is assessing whether the cultured cells possess physiological properties similar to those of mature olfactory neurons. Various investigators have successfully established proliferating cell lines from olfactory tissue, but few have demonstrated the characteristics of odor sensitivity of these cells. We successfully established cultured cell lines from adult human olfactory tissue obtained using an olfactory biopsy procedure and measured their ability to respond to odor stimulation using calcium imaging techniques. A subset of the human olfactory cells in culture displayed a distinct morphology and specifically expressed immunocytochemical markers characteristic of mature human olfactory neurons such as OMP, G(olf), NCAM and NST. Under defined growth conditions, these cultured cells responded to odorant mixes that have been previously shown to elicit intracellular calcium changes in acutely-isolated human olfactory neurons. These odorant-elicited calcium responses displayed characteristics similar to those found in mature human olfactory neurons. First, cultured cells responded with either increases or decreases in intracellular calcium. Second, increases in calcium were abolished by removal of extracellular calcium. Third, inhibitors of the olfactory signal transduction cascades reversibly blocked these odorant-elicited intracellular calcium changes. Our results demonstrate that cultures of adult human olfactory cells established from olfactory biopsies retain some of the in vivo odorant response characteristics of acutely isolated cells from the adult olfactory epithelium. This work has important ramifications for investigation of olfactory function and dysfunction using biopsy procedures and in vitro assays of odor sensitivity.

Mature olfactory receptor neurons express connexin 43

The expression of the gap junction subunit connexin 43 was studied in the olfactory epithelium of adult mice. In agreement with conclusions from previous immunohistochemical studies, we observed expression of mRNA encoding for connexin 43 in layers of the epithelium containing nuclei belonging to sustentacular cells. However, we also observed expression of connexin 43 mRNA in the layers containing nuclei belonging to mature olfactory receptor neurons (ORNs), immature ORNs, and basal cells. Connexin 43 mRNA expression was low in dorsomedial regions of the nasal cavity but higher ventrally. This differential regional distribution was consistent with expression in a transgenic mouse of a LacZ reporter gene driven by the proximal 6.5 kb of the connexin 43 promoter. LacZ was expressed in cells colabeled with antibody against olfactory marker protein (OMP), corroborating that mature ORNs express connexin 43. LacZ staining also was observed in sustentacular and basal cells and in immature ORNs. Double-label studies with antibodies against connexin 43 and OMP and expression of connexin 43 in the epithelium of bulbectomized mice were also consistent with expression of connexin 43 in mature ORNs. This is the first report of expression of a connexin subunit in mature ORNs. Our findings of connexin subunits in mature ORNs raise the novel possibility that gap junctions may play a fundamental role in information processing in the olfactory epithelium.

Modulation of odor-induced increases in [Ca(2+)](i) by inhibitors of protein kinases A and C in rat and human olfactory receptor neurons

Protein kinases A and C have been postulated to exert multiple effects on different elements of signal transduction pathways in olfactory receptor neurons. However, little is known about the modulation of olfactory responses by protein kinases in intact olfactory receptor neurons. To further elucidate the details of the modulation of odorant responsiveness by these protein kinases, we investigated the action of two protein kinase inhibitors: H89, an inhibitor of protein kinase A, and N-myristoylated EGF receptor, an inhibitor of protein kinase C, on odorant responsiveness in intact olfactory neurons. We isolated individual olfactory neurons from the adult human and rat olfactory epithelium and measured responses of the isolated cells to odorants or biochemical activators that have been shown to initiate cyclic AMP or inositol 1,4,5-trisphospate production in biochemical preparations. We employed calcium imaging techniques to measure odor-elicited changes in intracellular calcium that occur over several seconds. In human olfactory receptor neurons, the protein kinase A and C inhibitors affected the responses to different sets of odorants. In rats, however, the protein kinase C inhibitor affected responses to all odorants, while the protein kinase A inhibitor had no effect. In both species, the effect of inhibition of protein kinases was to enhance the elevation and block termination of intracellular calcium levels elicited by odorants. Our results show that protein kinases A and C may modulate odorant responses of olfactory neurons by regulating calcium fluxes that occur several seconds after odorant stimulation. The effects of protein kinase C inhibition are different in rat and human olfactory neurons, indicating that species differences are an important consideration when applying data from animal studies to apply to humans.

Expression of mRNAs encoding for two different olfactory receptors in a subset of olfactory receptor neurons

Evidence has accumulated to support a model for odorant detection in which individual olfactory receptor neurons (ORNs) express one of a large family of G protein-coupled receptor proteins that are activated by a small number of closely related volatile chemicals. However, the issue of whether an individual ORN expresses one or multiple types of receptor proteins has yet to be definitively addressed. Physiological data indicate that some individual ORNs can be activated by odorants differing substantially in structure and/or perceived quality, suggesting multiple receptors or one nonspecific receptor per cell. In contrast, molecular biological studies favor a scheme with a single, fairly selective receptor per cell. The present studies directly assessed whether individual rat ORNs can express multiple receptors using single-cell PCR techniques with degenerate primers designed to amplify a wide variety of receptor sequences. We found that whereas only a single OR sequence was obtained from most ORNs examined, one ORN produced two distinct receptor sequences that represented different receptor gene families. Double-label in situ hybridization studies indicated that a subset of ORNs co-express two distinct receptor mRNAs. A laminar segregation analysis of the cell nuclei of ORNs labeled with the two OR mRNA probes showed that for one probe, the histogram of the distribution of the cell nuclei along the depth of the epithelium was bimodal, with one peak overlapping the (unimodal) histogram for the other probe. These results are consistent with co-expression of two OR mRNAs in a population of single ORNs.

Olfactory neuron-specific expression of NeuroD in mouse and human nasal mucosa

Human olfactory neuroepithelium (OE) is situated within the olfactory cleft of the nasal cavity and has the characteristic property of continually regenerating neurons during the lifetime of the individual. This regenerative ability of OE provides a unique model for neuronal differentiation, but little is known about the structure and biology of human olfactory mucosa. Thus, to better understand neurogenesis in human OE, we studied the expression of olfactory marker protein (OMP), TrkB and NeuroD in human nasal biopsies and autopsy specimens and compared these data with those obtained from normal and regenerating mouse OE. We show that NeuroD and TrkB are coordinately expressed in human OE. Thus, by using these markers we have been able to extend the known boundaries of the human OE to include the inferior middle turbinate. In normal mouse OE, TrkB and OMP expression overlap in cells closest to the superficial layer, but TrkB is expressed more strongly in the lower region of this layer. In contrast, NeuroD expression is more basally restricted in a region just above the globose basal cells. These characteristic expression patterns of OMP, TrkB and NeuroD were also observed in the regenerating mouse OE induced by axotomy. These results support a role of NeuroD and brain-derived neurotrophic actor (BDNF), the preferred ligand for TrkB, in the maintenance of the olfactory neuroepithelium in humans and mice.

Odorants suppress a voltage-activated K+ conductance in rat olfactory neurons

Stimulation of olfactory receptor neurons (ORNs) with odors elicits an increase in the concentration of cAMP leading to opening of cyclic nucleotide-gated (CNG) channels and subsequent depolarization. Although opening of CNG channels is thought to be the main mechanism mediating signal transduction, modulation of other ion conductances by odorants has been postulated. To determine whether K+ conductances are modulated by odorants in mammalian ORNs, we examined the response of rat ORNs to odors by recording membrane current under perforated-patch conditions. We find that rat ORNs display two predominant types of responses. Thirty percent of the cells responded to odorants with activation of a CNG conductance. In contrast, in 55% of the ORNs, stimulation with odorants inhibited a voltage-activated K+ conductance (IKo). In terms of pharmacology, ion permeation, outward rectification, and time course for inactivation, IKo resembled a delayed rectifier K+ conductance. The effect of odorants on IKo was specific (only certain odorants inhibited IKo in each ORN) and concentration dependent, and there was a significant latency between arrival of odorants to the cell and the onset of suppression. These results indicate that indirect suppression of a K+ conductance (IKo) by odorants plays a role in signal transduction in mammalian ORNs.

Characterization of inositol-1,4,5-trisphosphate-gated channels in the plasma membrane of rat olfactory neurons

It is generally accepted that inositol-1,4,5-trisphosphate (InsP3) plays a role in olfactory transduction. However, the precise mode of action of InsP3 remains controversial. We have characterized the conductances activated by the addition of 10 microM InsP3 to excised patches of soma plasma membrane from rat olfactory neurons. InsP3 induced current fluctuations in 25 of 121 inside-out patches. These conductances could be classified into two groups according to the polarity of the current at a holding potential of +40 to +60 mV (with Ringer's in the pipette and pseudointracellular solution in the bath). Conductances mediating outward currents could be further divided into large- (64 +/- 4 pS, n = 4) and small- (16 +/- 1.7 pS, n = 11) conductance channels. Both small- and large-conductance channels were nonspecific cation channels. The large-conductance channel displayed bursting behavior at +40 mV, with flickering increasing at negative holding potentials to the point where single-channel currents were no longer discernible. The small-conductance channel did not display flickering behavior. The conductance mediating inward currents at +40 to +60 mV reversed at +73 +/- 4 mV (n = 4). The current traces displayed considerable fluctuations, and single-channel currents could not be discerned. The current fluctuations returned to baseline after removal of InsP3. The power density spectrum for the excess noise generated by InsP3 followed a 1/f dependence consistent with conductance fluctuations in the channel mediating this current, although other mechanisms are not excluded. These experiments demonstrate the presence of plasma membrane InsP3-gated channels of different ionic specificity in olfactory receptor cells.

The use of olfactory receptor neurons (ORNs) from biopsies to study changes in aging and neurodegenerative diseases

A gradual loss of olfactory capability with age and in a number of neurodegenerative diseases is common, and mechanisms underlying these losses are not understood. We determined the feasibility of using ORNs obtained from olfactory epithelial biopsies to identify possible changes in ORN function that may contribute to olfactory impairment in these individuals. ORNs from nine healthy subjects (66-84 yr), three patients with Alzheimer's disease and one with multi-infarct dementia were studied with calcium imaging techniques and two odorant mixtures. Seventy-five viable ORNs were studied; 53% of these were odorant responsive, and twenty percent of these responded to both odorant mixtures. In contrast, 25% of 173 ORNs from younger subjects were odorant responsive, and none of these responded to both odorant mixtures. The proportion of cells responding to each of the odorant mixtures also differed between older and younger subjects. These studies demonstrate the feasibility of this approach to examine age or disease-associated changes in neuronal function. Further, age-related changes in ORN selectivity may contribute to changes in olfactory performance.

Transduction mechanisms in vertebrate olfactory receptor cells

Considerable progress has been made in the understanding of transduction mechanisms in olfactory receptor neurons (ORNs) over the last decade. Odorants pass through a mucus interface before binding to odorant receptors (ORs). The molecular structure of many ORs is now known. They belong to the large class of G protein-coupled receptors with seven transmembrane domains. Binding of an odorant to an OR triggers the activation of second messenger cascades. One second messenger pathway in particular has been extensively studied; the receptor activates, via the G protein Golf, an adenylyl cyclase, resulting in an increase in adenosine 3',5'-cyclic monophosphate (cAMP), which elicits opening of cation channels directly gated by cAMP. Under physiological conditions, Ca2+ has the highest permeability through this channel, and the increase in intracellular Ca2+ concentration activates a Cl- current which, owing to an elevated reversal potential for Cl-, depolarizes the olfactory neuron. The receptor potential finally leads to the generation of action potentials conveying the chemosensory information to the olfactory bulb. Although much less studied, other transduction pathways appear to exist, some of which seem to involve the odorant-induced formation of inositol polyphosphates as well as Ca2+ and/or inositol polyphosphate -activated cation channels. In addition, there is evidence for odorant-modulated K+ and Cl- conductances. Finally, in some species, ORNs can be inhibited by certain odorants. This paper presents a comprehensive review of the biophysical and electrophysiological evidence regarding the transduction processes as well as subsequent signal processing and spike generation in ORNs.

Selectivity and response characteristics of human olfactory neurons

Transduction mechanisms were investigated in human olfactory neurons by determining characteristics of odorant-induced changes in intracellular calcium concentration ([Ca2+]i). Olfactory neurons were freshly isolated from nasal biopsies, allowed to attach to coverslips, and loaded with the calcium-sensitive indicator fura-2. Changes in [Ca2+]i were studied in response to exposure to individual odors, or odorant mixtures composed to distinguish between transduction pathways mediated by adenosine 3'5'-monophosphate (cAMP; mix A) or inositol 1,4,5-trisphosphate (InsP3; mix B). Overall, 52% of biopsies produced one or more odorant-responsive olfactory neurons, whereas 24% of all olfactory neurons tested responded to odorant exposure with a change in [Ca2+]i. As in olfactory neurons from other species, the data suggest that odorant exposure elicited calcium influx via second-messenger pathways involving cAMP or InsP3. Unlike olfactory neurons from other species that have been tested, some human olfactory neurons responded to odorants with decreases in [Ca2+]i. Also in contrast with olfactory neurons from other species, human olfactory neurons were better able to discriminate between odorant mixtures in that no neuron responded to more than one type of odor or mixture. These results suggest the presence of a previously unreported type of olfactory transduction mechanism, and raise the possibility that coding of odor qualities in humans may be accomplished to some degree differently than in other vertebrates, with the olfactory neuron itself making a greater contribution to the discrimination process.

G alpha 9/G alpha 11: immunolocalization in the olfactory epithelium of the rat (Rattus rattus) and the channel catfish (Ictalurus punctatus)

The immunohistochemical localization of G alpha 9/G alpha 11 was studied in the olfactory and respiratory epithelium of two representative vertebrates, the rat and the channel catfish. Localization in the rat was found at the apical surface of cells in the epithelium and within nerve tracts in the lamina propria. Immunostaining of neuronal cilia and supporting cell microvilli was confirmed by electron microscopy. Immunoreactivity on the ipsilateral neuroepithelium was abolished five weeks following unilateral bulbectomy. An emergence of patchy immunoreactivity was found, however, after fifteen weeks. In catfish, G alpha 9/G alpha 11 antigenicity was found at the apical surface of cells within the olfactory epithelium, at supranuclear regions within some cell bodies and in basal nerve tracts of the olfactory rosette. Immunoreactivity was removed with unilateral bulbectomy. Specific labelling in both rat and catfish was eliminated by preincubation of the G alpha 9/G alpha 11 antibodies with the cognate peptide. Proteins were extracted from olfactory tissues of both species and solubilized. Using western blotting, bands corresponding in apparent molecular weight to a 38,000 mol. wt protein were found. These data demonstrate the presence of G alpha 9/G alpha 11 in the olfactory tissues of these vertebrates and suggest a role in olfaction for this class of G-protein.

Induction of differentiation of human olfactory neuroblastoma cells into odorant-responsive cells

Olfactory neuroblastoma is a rare malignancy of the olfactory mucosa that may be derived from the olfactory epithelium. To characterize this tumor, we cultured olfactory neuroblastoma cells in the presence or absence of growth factors (transforming growth factor alpha and basic fibroblast growth factor) known to affect olfactory tissue and assessed their responsiveness to known odorants by measuring changes in intracellular calcium. Untreated cells did not respond to odorants. Basic fibroblast growth factor treatment had cytotoxic effects, and treated cells did not respond to odorants. Transforming growth factor alpha treatment resulted in the induction of odor responsiveness in these cells. Cells responded to odorants at 100 nM to 100 microM concentrations and responded with both increases and decreases in intracellular calcium. Increases in intracellular calcium were mediated by a calcium influx and were reversibly blocked by compounds known to inhibit second messenger pathways in olfactory receptor neurons. The calcium responses of the olfactory neuroblastoma cells were thus specific to the odorants and similar to those found in olfactory receptor neurons. The results support the notion that olfactory neuroblastoma cells may be of olfactory origin and thus they can be used as a model cell line to study human olfaction.

Measurement of membrane potential and [Ca2+]i in cell ensembles: application to the study of glutamate taste in mice

We have studied the spectral properties of the voltage-sensitive dye, 1-(3-sulfonatopropyl)-4-[beta [2-(di-n-octylamino)-6-naphtyl]vinyl] pyridinium betaine (di-8-ANEPPS), and the Ca(2+)-sensitive dye, fura-2, in azolectin liposomes and in isolated taste buds from mouse. We find that the fluorescence excitation spectra of di-8-ANEPPS and fura-2 are largely nonoverlapping, allowing alternate ratio measurements of membrane potential and intracellular calcium ([Ca2+]i). There is a small spillover of di-8-ANEPPS fluorescence at the excitation wavelengths used for fura-2 (340 and 360 nm). However, voltage-induced changes in the fluorescence of di-8-ANEPPS, excited at the fura-2 wavelengths, are small. In addition, di-8-ANEPPS fluorescence is localized to the membrane, whereas fura-2 fluorescence is distributed throughout the cytoplasm. Because of this, the effect of spillover of di-8-ANEPPS fluorescence in the [Ca2+]i estimate is < 1%, under the appropriate conditions. We have applied this method to study of the responses of multiple taste cells within isolated taste buds. We show that membrane potential and [Ca2+]i can be measured alternately in isolated taste buds from mouse. Stimulation with glutamate and glutamate analogs indicates that taste cells express both metabotropic and ionotropic receptors. The data suggest that the receptors responding to 2-amino-4-phosphonobutyrate (L-AP4), presumably metabotropic L-glutamate receptors, do not mediate excitatory glutamate taste responses.

Second messenger signaling in olfactory transduction

Olfactory receptor neurons respond to odorants with G-protein mediated increases in the concentration of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol 1,4,5-trisphospahte (InsP3). These two second messengers directly regulate opening of cAMP- and InsP3-regulated conductances localized to the apical transduction compartments of the cell (cilia and olfactory knob). In the presence of physiological concentrations of extracellular Ca2+, these second messenger regulated conductances mediate influx of Ca2+ into the olfactory neuron resulting in large, localized increases in intracellular Ca2+ ([Ca2+]i). A significant advance in our understanding of the molecular mechanisms of olfaction is the recent realization that this increase in [Ca2+]i plays an important role as a "third messenger" in olfactory transduction. Second messenger dependent increases in [Ca2+]i cause opening of ciliary Ca(2+)-activated Cl-, cation and/ or K+ channels that can carry a large percentage of the generator current, thus amplifying the signal substantially. As a result of this sequence of events, the generator potential in olfactory neurons can be depolarizing, leading to excitation of the neuron, or hyperpolarizing, leading to suppression of basal action potential firing rate. This dual effect of odorants on olfactory neurons may play an important role in quality coding and in the ability to detect low concentrations of odorants, particularly in complex mixtures.

Single taste stimuli elicit either increases or decreases in intracellular calcium in isolated catfish taste cells

Taste cells are specialized epithelial cells that respond to stimulation with release of neurotransmitters onto afferent nerves that innervate taste buds. In analogy to neurotransmitter release in other cells, it is expected that neurotransmitter release in taste cells is dependent on an increase in intracellular Ca2+ ([Ca2+]i). We have studied changes in [Ca2+]i elicited by the taste stimuli L- and D-arginine in isolated taste cells from the channel catfish (Ictalurus punctatus). In a sample of 119 cells, we found 15 cells responding to L-arginine, and 12 cells responding to D-arginine with an increase in [Ca2+]i. The response to L-arginine was inhibited by equimolar D-arginine in cells where D-arginine alone did not cause a change in [Ca2+]i, which is consistent with mediation of this response by a previously characterized L-arginine-gated nonspecific cation channel antagonized by D-arginine [31]. However, we also found that these taste stimuli elicited decreases in [Ca2+]i in substantial number of cells (6 for L-Arg, and 2 for D-Arg, n = 119). These observations suggest that stimulation of taste cells with sapid stimuli may result in simultaneous excitation and inhibition of different taste cells within the taste bud, which could be involved in local processing of the taste signal.