Acetylcysteine has No Mechanistic Effect in Patients at Risk of Contrast-Induced Nephropathy - A Failure of Academic Clinical Science

Contrast‐induced nephropathy (CIN) is a major complication of imaging in patients with chronic kidney disease (CKD). The publication of an academic randomized controlled trial (RCT; n = 83) reporting oral (N)‐acetylcysteine (NAC) to reduce CIN led to > 70 clinical trials, 23 systematic reviews, and 2 large RCTs showing no benefit. However, no mechanistic studies were conducted to determine how NAC might work; proposed mechanisms included renal artery vasodilatation and antioxidant boosting. We evaluated the proposed mechanisms of NAC action in participants with healthy and diseased kidneys. Four substudies were performed. Two randomized, double‐blind, placebo‐controlled, three‐period crossover studies (n = 8) assessed the effect of oral and intravenous (i.v.) NAC in healthy kidneys in the presence/absence of iso‐osmolar contrast (iodixanol). A third crossover study in patients with CKD stage III (CKD3) (n = 8) assessed the effect of oral and i.v. NAC without contrast. A three‐arm randomized, double‐blind, placebo‐controlled parallel‐group study, recruiting patients with CKD3 (n = 66) undergoing coronary angiography, assessed the effect of oral and i.v. NAC in the presence of contrast. We recorded systemic (blood pressure and heart rate) and renal (renal blood flow (RBF) and glomerular filtration rate (GFR)) hemodynamics, and antioxidant status, plus biomarkers of renal injury in patients with CKD3 undergoing angiography. Primary outcome for all studies was RBF over 8 hours after the start of i.v. NAC/placebo. NAC at doses used in previous trials of renal prophylaxis was essentially undetectable in plasma after oral administration. In healthy volunteers, i.v. NAC, but not oral NAC, increased blood pressure (mean area under the curve (AUC) mean arterial pressure (MAP): mean difference 29 h⋅mmHg, P = 0.019 vs. placebo), heart rate (28 h⋅bpm, P < 0.001), and RBF (714 h⋅mL/min, 8.0% increase, P = 0.006). Renal vasodilatation also occurred in the presence of contrast (RBF 917 h⋅mL/min, 12% increase, P = 0.005). In patients with CKD3 without contrast, only a rise in heart rate (34 h⋅bpm, P = 0.010) and RBF (288 h⋅mL/min, 6.0% increase, P = 0.001) occurred with i.v. NAC, with no significant effect on blood pressure (MAP rise 26 h⋅mmHg, P = 0.156). Oral NAC showed no effect. In patients with CKD3 receiving contrast, i.v. NAC increased blood pressure (MAP rise 52 h⋅mmHg, P = 0.008) but had no effect on RBF (151 h⋅mL/min, 3.0% increase, P = 0.470), GFR (29 h⋅mL/min/1.73m², P = 0.122), or markers of renal injury. Neither i.v. nor oral NAC affected plasma antioxidant status. We found oral NAC to be poorly absorbed and have no reno‐protective effects. Intravenous, not oral, NAC caused renal artery vasodilatation in healthy volunteers but offered no protection to patients with CKD3 at risk of CIN. These findings emphasize the importance of mechanistic clinical studies before progressing to RCTs for novel interventions. Thousands were recruited to academic clinical trials without the necessary mechanistic studies being performed to confirm the approach had any chance of working.

Transfer of hepatocellular microRNA regulates cytochrome P450 2E1 in renal tubular cells

BACKGROUND

Extracellular microRNAs enter kidney cells and modify gene expression. We used a Dicer-hepatocyte-specific microRNA conditional-knock-out (Dicer-CKO) mouse to investigate microRNA transfer from liver to kidney.

METHODS

Dicerflox/flox mice were treated with a Cre recombinase-expressing adenovirus (AAV8) to selectively inhibit hepatocyte microRNA production (Dicer-CKO). Organ microRNA expression was measured in health and following paracetamol toxicity. The functional consequence of hepatic microRNA transfer was determined by measuring the expression and activity of cytochrome P450 2E1 (target of the hepatocellular miR-122), and by measuring the effect of serum extracellular vesicles (ECVs) on proximal tubular cell injury. In humans with liver injury we measured microRNA expression in urinary ECVs. A murine model of myocardial infarction was used as a non-hepatic model of microRNA release.

FINDINGS

Dicer-CKO mice demonstrated a decrease in kidney miR-122 in the absence of other microRNA changes. During hepatotoxicity, miR-122 increased in kidney tubular cells; this was abolished in Dicer-CKO mice. Depletion of hepatocyte microRNA increased kidney cytochrome P450 2E1 expression and activity. Serum ECVs from mice with hepatotoxicity increased proximal tubular cell miR-122 and prevented cisplatin toxicity. miR-122 increased in urinary ECVs during human hepatotoxicity. Transfer of microRNA was not restricted to liver injury -miR-499 was released following cardiac injury and correlated with an increase in the kidney.

INTERPRETATION

Physiological transfer of functional microRNA to the kidney is increased by liver injury and this signalling represents a new paradigm for understanding the relationship between liver injury and renal function.

FUNDING

Kidney Research UK, Medical Research Scotland, Medical Research Council.

Direct Detection of miR-122 in Hepatotoxicity Using Dynamic Chemical Labeling Overcomes Stability and isomiR Challenges

Circulating microRNAs are biomarkers reported to be stable and translational across species. MicroRNA-122 (miR-122) is a hepatocyte-specific microRNA biomarker for drug-induced liver injury (DILI). We developed a single molecule, dynamic chemical labeling (DCL) assay to directly detect miR-122 in blood. The DCL assay specifically measured miR-122 directly from 10 μL of serum or plasma without any extraction steps, with a limit of detection of 1.32 pM that enabled the identification of DILI. Testing of 192 human serum samples showed that DCL accurately identified patients at risk of DILI after acetaminophen overdose (area under ROC curve 0.98 (95% CI; 0.96-1), P < 0.0001). The DCL assay also identified liver injury in rats and dogs. The use of specific captured beads had the additional benefit of stabilizing miR-122 after sample collection, with no signal loss after 14 days at room temperature, in contrast to PCR that showed significant loss of signal. RNA sequencing demonstrated the presence of multiple miR-122 isomiRs in the serum of patients with DILI that were at low concentration or not present in healthy individuals. Sample degradation over time produced more isomiRs, particularly rapidly with DILI. PCR was inaccurate when analyzing miR-122 isomiRs, whereas the DCL assay demonstrated accurate quantification. We conclude that the DCL assay can accurately measure miR-122 to diagnose liver injury in humans and other species and can overcome microRNA stability and isomiR challenges.

Safety and Efficacy of the SNAP 12-hour Acetylcysteine Regimen for the Treatment of Paracetamol Overdose

BACKGROUND

Acetylcysteine (NAC) is effective at preventing liver injury after paracetamol overdose. The Scottish and Newcastle Anti-emetic Pre-treatment for Paracetamol Poisoning (SNAP) Study demonstrated that a 12 h NAC regimen was associated with fewer adverse drug reactions compared with the standard 21 h regimen. Here, we describe the clinical effectiveness of the SNAP NAC regimen.

METHODS

The SNAP regimen, consisting of intravenous NAC 100 mg/kg over 2 h then 200 mg/kg over 10 h, was introduced to treat all paracetamol overdose patients at the Royal Infirmary of Edinburgh, the Royal Victoria Infirmary, Newcastle and St Thomas' Hospital, London. Patient data were prospectively and systematically collected before and after the change in treatment (total patients N = 3340, 21 h N = 1488, SNAP N = 1852). Health record linkage was used to determine patient outcome after hospital discharge.

FINDINGS

There was no difference in liver injury or liver synthetic dysfunction between regimens. Hepatotoxicity (peak ALT > 1000 U/L) occurred in 64 (4.3%) and 67 (3.6%) patients, respectively, in the 21 h and SNAP groups (absolute difference - 0.7%, 95% CI - 2.1 to 0.6). Multivariable logistic regression did not identify treatment regimen as an outcome-associated factor. No patients were readmitted to hospital with, or died from, liver failure within 30 days of discharge. Anti-histamine treatment (for NAC anaphylactoid drug reactions) was prescribed for 163 (11.0%) patients with the 21 h regimen and 37 (2.0%) patients with the SNAP regimen (absolute difference 9.0% (95% CI 7.3 to 10.7)).

INTERPRETATION

In clinical use the SNAP regimen has similar efficacy as standard therapy for preventing liver injury and produces fewer adverse reactions.

First-in-Man Demonstration of Direct Endothelin-Mediated Natriuresis and Diuresis

Endothelin (ET) receptor antagonists are potentially novel therapeutic agents in chronic kidney disease and resistant hypertension, but their use is complicated by sodium and water retention. In animal studies, this side effect arises from ETB receptor blockade in the renal tubule. Previous attempts to determine whether this mechanism operates in humans have been confounded by the hemodynamic consequences of ET receptor stimulation/blockade. We aimed to determine the effects of ET signaling on salt transport in the human nephron by administering subpressor doses of the ET-1 precursor, big ET-1. We conducted a 2-phase randomized, double-blind, placebo-controlled crossover study in 10 healthy volunteers. After sodium restriction, subjects received either intravenous placebo or big ET-1, in escalating dose (≤300 pmol/min). This increased plasma concentration and urinary excretion of ET-1. Big ET-1 reduced heart rate (≈8 beats/min) but did not otherwise affect systemic hemodynamics or glomerular filtration rate. Big ET-1 increased the fractional excretion of sodium (from 0.5 to 1.0%). It also increased free water clearance and tended to increase the abundance of the sodium-potassium-chloride cotransporter (NKCC2) in urinary extracellular vesicles. Our protocol induced modest increases in circulating and urinary ET-1. Sodium and water excretion increased in the absence of significant hemodynamic perturbation, supporting a direct action of ET-1 on the renal tubule. Our data also suggest that sodium reabsorption is stimulated by ET-1 in the thick ascending limb and suppressed in the distal renal tubule. Fluid retention associated with ET receptor antagonist therapy may be circumvented by coprescribing potassium-sparing diuretics.

Vasopressin Regulates Extracellular Vesicle Uptake by Kidney Collecting Duct Cells

Extracellular vesicles (ECVs) facilitate intercellular communication along the nephron, with the potential to change the function of the recipient cell. However, it is not known whether this is a regulated process analogous to other signaling systems. We investigated the potential hormonal regulation of ECV transfer and report that desmopressin, a vasopressin analogue, stimulated the uptake of fluorescently loaded ECVs into a kidney collecting duct cell line (mCCD_C11) and into primary cells. Exposure of mCCD_C11 cells to ECVs isolated from cells overexpressing microRNA-503 led to downregulated expression of microRNA-503 target genes, but only in the presence of desmopressin. Mechanistically, ECV entry into mCCD_C11 cells required cAMP production, was reduced by inhibiting dynamin, and was selective for ECVs from kidney tubular cells. In vivo, we measured the urinary excretion and tissue uptake of fluorescently loaded ECVs delivered systemically to mice before and after administration of the vasopressin V2 receptor antagonist tolvaptan. In control-treated mice, we recovered 2.5% of administered ECVs in the urine; tolvaptan increased recovery five-fold and reduced ECV deposition in kidney tissue. Furthermore, in a patient with central diabetes insipidus, desmopressin reduced the excretion of ECVs derived from glomerular and proximal tubular cells. These data are consistent with vasopressin-regulated uptake of ECVs in vivo We conclude that ECV uptake is a specific and regulated process. Physiologically, ECVs are a new mechanism of intercellular communication; therapeutically, ECVs may be a vehicle by which RNA therapy could be targeted to specific cells for the treatment of kidney disease.

Renal extracellular vesicles: from physiology to clinical application

Urinary extracellular vesicles (uEVs) are released from all regions of the kidney's nephron and from other cells that line the urinary tract. Extracellular vesicles retain proteomic and transcriptomic markers specific to their cell of origin and so represent a potential reservoir for kidney disease biomarker discovery. Exosomes, a subtype of uEVs, are distinguished from other vesicles by features related to their biogenesis within cells: mature multi-vesicular bodies fuse with the cellular membrane to liberate exosomes into the extracellular space. uEVs represent a novel cell signalling mechanism because they can be shuttled to a recipient cell and, through a number of proposed mechanisms, affect the recipient cell's proteome and function. Here we review the current evidence for uEV signalling along the nephron, their role in health and disease of the kidney, and their potential for clinical translation as biomarkers and therapeutics.

Observing the NICEties of hypertension management

National Institute for Health and Clinical Excellence guidance for the clinical management of hypertension, published last year, proposes a step change in UK clinical practice.1 Although broadly helpful, there are some concerns about its implementation. Ambulatory blood pressure monitoring for diagnosis of hypertension, though logical, will place an additional financial burden on primary care at a time of austerity. Home blood pressure measurement may be a more practical option. Previous guidance recommended the used of thiazide diuretics as a first-line treatment option.2 Five years later, the new guidelines propose a major change, with an initial emphasis on the use of calcium channel blockers and angiotensin converting enzyme inhibitors/angiotensin receptor blockers, moving the use of thiazide-like diuretics to a third-line option. In addition, bendroflumethiazide, the mainstay of treatment in the UK over many years, has been replaced with chlortalidone, the starting doses of which are not readily available in this country. Cost-effectiveness analysis and a presumed risk of metabolic disorders has guided the rationale for these changes to the therapeutic algorithm, however this may not be robust. Importantly, unless there are special circumstances, reducing the blood pressure in hypertensive patients is more important than the means used to lower it. In future, it will be important to 'personalise' treatment more effectively and base management on lifetime risk.

ASPM and microcephalin expression in epithelial ovarian cancer correlates with tumour grade and survival

BACKGROUND

The clinico-pathological and molecular heterogeneity of epithelial ovarian cancer (EOC) complicates its early diagnosis and successful treatment. Highly aneuploid tumours and the presence of ascitic fluids are hallmarks of EOC. Two microcephaly-associated proteins, abnormal spindle-like microcephaly-associated protein (ASPM) and microcephalin, are involved in mitosis and DNA damage repair. Their expression is deregulated at the RNA level in EOC. Here, ASPM and microcephalin protein expression in primary cultures established from the ascites of patients with EOC was determined and correlated with clinical data to assess their suitability as biomarkers.

METHODS

Five established ovarian cancer cell lines, cells derived from two benign ovarian ascites samples and 40 primary cultures of EOC derived from ovarian ascites samples were analysed by protein slot blotting and/or immunofluorescence to determine ASPM and microcephalin protein levels and their cellular localisation. Results were correlated with clinico-pathological data.

RESULTS

A statistically significant correlation was identified for ASPM localisation and tumour grade, with high levels of cytoplasmic ASPM correlating with grade 1 tumours. Conversely, cytoplasmic microcephalin was only identified in high-grade tumours. Furthermore, low levels of nuclear microcephalin correlated with reduced patient survival.

CONCLUSION

Our results suggest that ASPM and microcephalin have the potential to be biomarkers in ovarian cancer.

Action and interactions at microtubule ends

Microtubule dynamic instability is fundamentally important to the way cells respond to their environment and segregate their genetic material. A disparate class of proteins defined by their localisation to growing microtubule plus ends ('+TIPS') play a key role in controlling microtubule dynamics and organisation. They directly impact upon the behaviour of the microtubule tip and link this structure to interfaces that include kinetochores and the cortex of the cell. Surprisingly, some +TIPs also have important functions at the microtubule minus end. These properties contribute to the important roles played by +TIPs in processes such as mitosis and cell migration. This review examines how recent advances have impacted our understanding of +TIP function in mammalian cells, with emphasis on the emergence of the EB1 family as a core component of +TIP activities. An overview of the use of +TIP imaging as a tool for the cell biologist is also presented.

Adenomatous polyposis coli localization is both cell type and cell context dependent

The adenomatous polyposis coli (APC) tumor suppressor protein is mutated in most colorectal carcinomas. In addition to its role in WNT signaling it is proposed to be involved in both cell migration and mitosis. Although a variety of studies have shown an APC localization along lateral membranes of adjacent epithelial cells the existence of a cortical APC localization in mammalian cells remains controversial. To address this we have used matched rat epithelial (NRK-52E) and fibroblast (NRK-49F) cell lines to investigate the localization of APC. Subconfluent cultures of NRK-52E and -49F cells displayed microtubule-associated APC populations by immunostaining. However, confluent NRK-52E, but not -49F monolayers, exhibited a cortical APC distribution. Cortical APC localized in close proximity to a number of cell junction proteins in a microtubule-independent manner while calcium switch experiments suggested that APC was recruited to the cortex only when junction assembly was complete. Confluent NRK-49F and -52E cells also showed contrasting APC localizations in response to monolayer wounding. Our data suggests APC cortical localization is a feature of confluent epithelioid cells and that the subcellular distribution of APC is therefore dependent upon both cell type and context.

Changes in mitotic rate and GFAP expression in the primary olfactory axis of streptozotocin-induced diabetic rats

Many diabetic individuals develop anosmia but the mechanism(s) causing the dysfunction in the olfactory system is (are) unknown. Glial fibrillary acidic protein expression is reduced in diabetic retinopathy and is also reduced, with unknown consequences, in other brain regions of diabetic rats. We used immunohistochemistry and immunoblotting from untreated control and streptozotocin-induced type 1 (insulin dependent) diabetic rats to investigate main olfactory epithelial mitotic rate and glial fibrillary acidic protein expression in the lamina propria of the sensory epithelium and in the olfactory bulb. Numbers of bromodeoxyuridine-positive cells were significantly lower in the diabetic sensory epithelium compared to non-diabetic controls. Immunohistochemical observations suggested a qualitative difference in glial fibrillary acidic protein expression in both regions examined especially in the olfactory bulb external plexiform layer and the lamina propria. Immunoblot analysis confirmed that the diabetic olfactory bulb and lamina propria expressed less glial fibrillary acidic protein compared to the non-diabetic control group. The lower expression levels in the olfactory bulb external plexiform layer suggested by immunohistochemistry do not reflect a change in the number of astrocytes since the numbers of S100B(+) cells were not different between the two groups.

Nuclear actin is partially associated with Cajal bodies in human cells in culture and relocates to the nuclear periphery after infection of cells by adenovirus 5

Cajal bodies are intra-nuclear structures enriched in proteins involved in transcription and mRNA processing. In this study, immunofluorescence microscopy experiments using a highly specific antibody to actin revealed nuclear actin spots that colocalized in part with p80 coilin-positive Cajal bodies. Actin remained associated with Cajal bodies in cells extracted to reveal the nuclear matrix. Adenovirus infection, which is known to disassemble Cajal bodies, resulted in loss of actin from these structures late in infection. In infected cells, nuclear actin was observed to relocate to structures at the periphery of the nucleus, inside the nuclear envelope. Based on these findings, it is suggested that actin may play an important role in the organization or function of the Cajal body.

Structure and function of long-lived olfactory organotypic cultures from postnatal mice

The first synapse in the olfactory pathway mediates a significant transfer of information given the restricted association of specific olfactory receptor neurons with specific glomeruli in the olfactory bulb. To understand better how this connection is made and what the functional capacities of the participating cells are, we created a long-lived culture system composed of olfactory epithelium and olfactory bulb tissues. Using the roller tube method of culturing, we grew epithelium-bulb cocultures, explanted from 1-4-day-old Swiss Webster mice, on Aclar for periods ranging from 18 hr to 68 days. The explants flattened so that in some areas the culture was only a few cells thick, making individual cells distinguishable. From 107 cultures studied, we identified the following cell types by expression of specific markers (oldest culture expressing marker, days in vitro, DIV): olfactory receptor neurons (neural cell adhesion molecule, 42 DIV); mature receptor neurons (olfactory marker protein, 28 DIV); postmitotic olfactory receptor neurons and olfactory bulb neurons (beta-tubulin, 68 DIV); astrocytes (glial fibrillary acidic protein, glutamate/aspartate transporter, 68 DIV); olfactory horizontal basal cells (cytokeratin, 22 DIV). Neuronal processes formed glomeruli in 2-4-week-old cultures. We also recorded electro-olfactography responses to puffs of vapor collected over an odorant mixture containing ethyl butyrate, eugenol, (+) carvone, and (-) carvone from cultures as old as 21 DIV. These features of our olfactory culture system make this model useful for studying properties of immature and mature olfactory receptor neurons, pathfinding strategies of receptor axons, and mechanisms of information transfer in the olfactory glomerulus.

Tumour-induced apoptosis in human mesothelial cells: a mechanism of peritoneal invasion by Fas Ligand/Fas interaction

Gastrointestinal carcinomas frequently disseminate within the abdominal cavity to form secondary peritoneal metastases. Invasion of the peritoneal mesothelium is fundamental to this process, yet the underlying invasive mechanisms remain unclear. Preliminary in vitro work suggested that tumour cells can induce mesothelial apoptosis, representing a novel mechanism of peritoneal invasion. We examined the role of tumour cell-induced mesothelial apoptosis and explored the role of the death ligand/receptor system, Fas Ligand/Fas, as mediators of the apoptotic process. Cultured human mesothelial cells were used to establish in vitro co-culture models with the SW480 colonic cancer cell line. Tumour-induced mesothelial apoptosis was confirmed by phase-contrast microscopy and apoptotic detection assays. Human mesothelial cells and SW480 tumour cells constitutively expressed Fas and Fas Ligand mRNA and protein as determined by RT-PCR and confocal fluorescent microscopy. Stimulation of human mesothelial cells with anti-Fas monoclonal antibody or crosslinked soluble Fas Ligand-induced apoptosis, confirming the functional status of the Fas receptor. Pretreatment of SW480 cells with a blocking recombinant anti-Fas Ligand monoclonal antibody significantly reduced mesothelial apoptosis, indicating that tumour-induced mesothelial apoptosis may, in part, be mediated via a Fas-dependent mechanism. This represents a novel mechanism of mesothelial invasion and offers several new targets for therapeutic intervention.

Immunohistochemistry of the canine vomeronasal organ

The canine's olfactory acuity is legendary, but neither its main olfactory system nor its vomeronasal system has been described in much detail. We used immunohistochemistry on paraffin-embedded sections of male and female adult dog vomeronasal organ (VNO) to characterize the expression of proteins known to be expressed in the VNO of several other mammals. Basal cell bodies were more apparent in each section than in rodent VNO and expressed immunoreactivity to anticytokeratin and antiepidermal growth factor receptor antibodies. The thin layer of neurone cell bodies in the sensory epithelium and axon fascicles in the lamina propria expressed immunoreactivity to neurone cell adhesion molecule, neurone-specific beta tubulin and protein gene product 9.5. Some neurones expressed growth-associated protein 43 (GAP43): and a number of those also expressed neurone-specific beta tubulin-immunoreactivity. Some axon fascicles were double labelled for those two proteins. The G-protein alpha subunits Gi and Go, involved in the signal transduction pathway, showed immunoreactivity in the sensory cell layer. Our results demonstrate that the canine vomeronasal organ contains a population of cells that expresses several neuronal markers. Furthermore, GAP43 immunoreactivity suggests that the sensory epithelium is neurogenic in adult dogs.

Immunohistochemistry of the canine vomeronasal organ

The canine's olfactory acuity is legendary, but neither its main olfactory system nor its vomeronasal system has been described in much detail. We used immunohistochemistry on paraffin-embedded sections of male and female adult dog vomeronasal organ (VNO) to characterize the expression of proteins known to be expressed in the VNO of several other mammals. Basal cell bodies were more apparent in each section than in rodent VNO and expressed immunoreactivity to anticytokeratin and antiepidermal growth factor receptor antibodies. The thin layer of neurone cell bodies in the sensory epithelium and axon fascicles in the lamina propria expressed immunoreactivity to neurone cell adhesion molecule, neurone-specific beta tubulin and protein gene product 9.5. Some neurones expressed growth-associated protein 43 (GAP43): and a number of those also expressed neurone-specific beta tubulin-immunoreactivity. Some axon fascicles were double labelled for those two proteins. The G-protein alpha subunits Gi and Go, involved in the signal transduction pathway, showed immunoreactivity in the sensory cell layer. Our results demonstrate that the canine vomeronasal organ contains a population of cells that expresses several neuronal markers. Furthermore, GAP43 immunoreactivity suggests that the sensory epithelium is neurogenic in adult dogs.

Microtubule assembly in cultured myoblasts and myotubes following nocodazole induced microtubule depolymerisation

When myoblasts fuse into myotubes, the organisation of the cytoskeleton changes dramatically. For example, microtubules emanate in a radial array form the centrosome in myoblasts, but form linear arrays not linked to a centrosome in myotubes. It is not clear how these linear arrays are formed and nucleated. They could arise in a number of ways: by nucleation and release from centrosomal like structures, cytoplasmic assembly, breakage/severing or nucleation from non-centrosomal sites. To test which of the above mechanisms or combination of mechanisms are responsible we investigated the re-formation of microtubules after depolymerisation by nocodazole, using antibodies against pericentrin, gamma-tubulin, EB1, and tyrosinated alpha-tubulin. In myoblasts, we found that when microtubules were allowed to recover after complete depolymerisation with nocodazole, microtubule recovery began within 1 min and was complete after 5 min. Microtubules grew out from the centrosome, which was positively stained for gamma-tubulin or pericentrin. In untreated myotubes, microtubules were arranged in linear arrays, with EB1 at their ends. The pericentriolar protein, pericentrin was arranged in a band around the nucleus as well as discrete spots in the cytoplasm. In contrast, the microtubule nucleating protein gamma-tubulin was not found in a band around the nucleus, but was found in several punctuate spots throughout the cytoplasm. Further, when microtubules were allowed to recover, after complete depolymerisation with nocodazole, recovery was not as rapid as that seen in myoblasts, and we found that regrowth began with the formation of short microtubule fragments throughout the cytoplasm. Gamma-tubulin was associated with these fragments. These results suggest that in myotubes, nucleation of microtubules can be non-centrosomal.

Evidence that an interaction between EB1 and p150(Glued) is required for the formation and maintenance of a radial microtubule array anchored at the centrosome

EB1 is a microtubule tip-associated protein that interacts with the APC tumor suppressor protein and components of the dynein/dynactin complex. We have found that the C-terminal 50 and 84 amino acids (aa) of EB1 were sufficient to mediate the interactions with APC and dynactin, respectively. EB1 formed mutually exclusive complexes with APC and dynactin, and a direct interaction between EB1 and p150(Glued) was identified. EB1-GFP deletion mutants demonstrated a role for the N-terminus in mediating the EB1-microtubule interaction, whereas C-terminal regions contributed to both its microtubule tip localization and a centrosomal localization. Cells expressing the last 84 aa of EB1 fused to GFP (EB1-C84-GFP) displayed profound defects in microtubule organization and centrosomal anchoring. EB1-C84-GFP expression severely inhibited microtubule regrowth, focusing, and anchoring in transfected cells during recovery from nocodazole treatment. The recruitment of gamma-tubulin and p150(Glued) to centrosomes was also inhibited. None of these effects were seen in cells expressing the last 50 aa of EB1 fused to GFP. Furthermore, EB1-C84-GFP expression did not induce Golgi apparatus fragmentation. We propose that a functional interaction between EB1 and p150(Glued) is required for microtubule minus end anchoring at centrosomes during the assembly and maintenance of a radial microtubule array.

EB1 identifies sites of microtubule polymerisation during neurite development

EB1 is a microtubule associated protein which interacts with the APC tumour suppressor protein and components of the cytoplasmic dynein/dynactin complex. EB1 is also a specific marker of growing microtubule tips. Here we demonstrate that EB1 protein levels are increased during axon but not dendrite formation in differentiated N2A neuroblastoma cells, and that EB1 localises to microtubule tips throughout extending neurites in these cells. In N2A axons, analysis of the ratio of EB1/beta-tubulin fluorescence demonstrated that the distal tip region contained the highest proportion of polymerising microtubules. Time-lapse confocal imaging of an EB1-GFP fusion protein in transfected N2A cells directly revealed the dynamics of microtubule extension in neurites, and demonstrated the existence of unusual, discrete knots of microtubule polymerisation at the periphery of non-process bearing cells which may represent an early event in neurite outgrowth. We conclude that EB1 localisation can be used to identify and analyse sites of microtubule polymerisation at a high resolution during neurite development, a process to which it may contribute.

EB 1 immunofluorescence reveals an increase in growing astral microtubule length and number during anaphase in NRK-52E cells

Spindle positioning in animal cells is thought to rely upon the interaction of astral microtubules with the cell cortex. Information on the dynamics of astral microtubules during this process is scarce, in part because of the difficulty in visualising these microtubules by light microscopy. EB1 is a protein which specifically localises to growing microtubule distal tips. Immunostaining for EB1 therefore represents a powerful method for visualising the distribution of growing microtubule tips within cells. In this study we used EB1 immunostaining in mitotic NRK-52E cells to quantitatively analyse the length and number of growing astral microtubules during metaphase and anaphase. We observed a dramatic increase in growing astral microtubule length and number during anaphase. Furthermore, drug treatments which specifically destroyed astral microtubules resulted in an increase in misaligned anaphase but not metaphase spindles. We suggest that an anaphase-specific increase in growing astral microtubule length and number facilitates the maintenance of a correctly aligned spindle in mitotic NRK-52E cells.

Improving communication among health professionals through education: a pilot study

Communication can be thought of as a message that is sent, received, and understood. Each discipline of the health profession has its own jargon and means of expressing ideas in shorthand. These separate forms of communicating are effective among those of the same background but are often at the root of misunderstandings between professional groups. This article reviews communication theory and traces the difficulties created when inter-disciplinary teams of healthcare try to work together and communicate. As multi-disciplinary teams are increasingly dealing with the complex problems of today's healthcare system, clear communication and understanding has never been more important. If educators could assist in creating an understanding of vocabulary used for decision processes, communication could improve. The authors of this study performed a multi-stage Delphi survey that grouped terms used by administrators and clinicians and produced a lexicon of corresponding terms. An expert panel then reviewed and modified the list. The result is a lexicon that can be useful to assist clinicians and administrators to communicate with each other. By utilizing clinical terminology, or vice versa, instead of management or clinical jargon, some of the translation done by administration or clinicians could be reduced. Examples of how the lexicon can be utilized are provided in the article. This includes using it in health administration education to demonstrate the variances in clinical/managerial terms. It could also be provided as a primer to physicians, nurses, and other health professionals who assume administrative positions to enhance their communication with administrators.

RGS2 regulates signal transduction in olfactory neurons by attenuating activation of adenylyl cyclase III

The heterotrimeric G-protein Gs couples cell-surface receptors to the activation of adenylyl cyclases and cyclic AMP production (reviewed in refs 1, 2). RGS proteins, which act as GTPase-activating proteins (GAPs) for the G-protein alpha-subunits alpha(i) and alpha(q), lack such activity for alpha(s) (refs 3-6). But several RGS proteins inhibit cAMP production by Gs-linked receptors. Here we report that RGS2 reduces cAMP production by odorant-stimulated olfactory epithelium membranes, in which the alpha(s) family member alpha(olf) links odorant receptors to adenylyl cyclase activation. Unexpectedly, RGS2 reduces odorant-elicited cAMP production, not by acting on alpha(olf) but by inhibiting the activity of adenylyl cyclase type III, the predominant adenylyl cyclase isoform in olfactory neurons. Furthermore, whole-cell voltage clamp recordings of odorant-stimulated olfactory neurons indicate that endogenous RGS2 negatively regulates odorant-evoked intracellular signalling. These results reveal a mechanism for controlling the activities of adenylyl cyclases, which probably contributes to the ability of olfactory neurons to discriminate odours.

Regulation and function of the interaction between the APC tumour suppressor protein and EB1

The interaction between the adenomatous polyposis coli (APC) tumour suppressor and the microtubule-associated protein EB1 was examined. Immunoprecipitation suggested that APC and EB1 were not associated in cultures of HCT116 cells arrested in mitosis. The C-terminal 170 amino acids of APC, purified as a bacterial fusion protein, precipitated EB1 from cell extracts, significantly refining the location of the EB1 interaction domain in APC. In vitro phosphorylation of this fusion protein by either protein kinase A or p34cdc2 reduced its ability to bind to EB1. Expression of GFP fusions to C-terminal APC sequences lacking or including the APC basic domain but encompassing the EB1 binding region in SW480 cells revealed a microtubule tip association which co-localized with that of EB1. Expression of the basic domain alone revealed a non-specific microtubule localization. In vitro interaction studies confirmed that the APC basic domain did not contribute to EB1 binding. These findings strongly suggest that the interaction between APC and EB1 targets APC to microtubule tips, and that the interaction between the two proteins is down-regulated during mitosis by the previously described mitotic phosphorylation of APC.

Truncated adenomatous polyposis coli (APC) tumour suppressor protein can undergo tyrosine phosphorylation

Numerous mutations in the adenomatous polyposis coli (APC) gene have been described in colorectal cancer. The vast majority introduce nonsense codons leading to the production of truncated N-terminal APC fragments. Mutations occurring before APC codon 158, have been associated with an attenuated form of familial adenomatous polyposis whereas those occurring at codon 168 or beyond lead to the characteristic form of the disease. These 10 amino acid residues of APC contain a YYAQ motif which appears to constitute a potential SH2 binding domain similar to a sequence present in tyrosine kinase receptors that activate STAT 3 when phosphorylated. We have expressed a recombinant, N-terminal APC fragment in bacterial cells, and shown that it can indeed undergo tyrosine phosphorylation in this domain. We used site-directed mutagenesis to confirm the specificity of the reaction. These observations raise the possibility that tyrosine phosphorylation may be another mechanism involved in controlling APC function.

EB1, a protein which interacts with the APC tumour suppressor, is associated with the microtubule cytoskeleton throughout the cell cycle

The characteristics of the adenomatous polyposis coli (APC) associated protein EB1 were examined in mammalian cells. By immunocytochemistry EB1 was shown to be closely associated with the microtubule cytoskeleton throughout the cell cycle. In interphase cells EB1 was associated with microtubules along their full length but was often particularly concentrated at their tips. During early mitosis, EB1 was localized to separating centrosomes and associated microtubules, while at metaphase it was associated with the spindle poles and associated microtubules. During cytokinesis EB1 was strongly associated with the midbody microtubules. Treatment with nocodazole caused a diffuse redistribution of EB1 immunoreactivity, whereas treatment with cytochalasin D had no effect. Interestingly, treatment with taxol abolished the EB1 association with microtubules. In nocodazole washout experiments EB1 rapidly became associated with the centrosome and repolymerizing microtubules. In taxol wash-out experiments EB1 rapidly re-associated with the microtubule cytoskeleton, resembling untreated control cells within 10 min. Immunostaining of SW480 cells, which contain truncated APC incapable of interaction with EB1, showed that the association of EB1 with microtubules throughout the cell cycle was not dependent upon an interaction with APC. These results suggest a role for EB1 in the control of microtubule dynamics in mammalian cells.

Differences in the intracellular localization and fate of herpes simplex virus tegument proteins early in the infection of Vero cells

The fate of herpes simplex virus 1 (HSV-1) tegument proteins during infection in Vero cells was investigated immunochemically. Input virion-associated VP13/14 and VP16 localized to the nucleus early in infection, while VP1/2 localized to the nuclear envelope of the cell and VP22 could not be detected using monoclonal antibody P43. Western blotting suggested that virion-associated VP13/14, VP16 and VP22 were stable in infected cells whereas VP1/2 appeared to be processed or modified. Further studies showed that P43 recognized a phosphorylation-sensitive epitope in VP22 and suggested that virion-associated VP22 was phosphorylated upon entry to the cell. VP13/14 and VP16 were easily extracted from cells early in infection whereas VP22 was largely insoluble. Phosphatase treatment of soluble extracts caused a shift in the molecular mass of VP16 showing it was phosphorylated. As infection progressed VP16 was observed in discrete nuclear compartments where it co-localized with ICP8 and the capsid-associated protein VP22a. VP13/14 was also observed in the nucleus. P43 immunostaining appeared around 6 h post-infection as punctate nuclear foci which often localized to the edge of VP16-immunoreactive areas. Punctate P43 cytoplasmic staining appeared around 12 h post-infection. By 18 h the nuclear pattern had disappeared and an extensive cytoplasmic stain was observed which closely overlapped that of other tegument proteins. On the basis of these data we suggest that virion-associated VP22 is phosphorylated upon entry of the virus into the cell and that unphosphorylated VP22, which is preferentially recognized by P43, becomes available later in infection, initially in the nucleus, for packaging into virions.

Phosphorylation of structural components promotes dissociation of the herpes simplex virus type 1 tegument

The role of phosphorylation in the dissociation of structural components of the herpes simplex virus type 1 (HSV-1) tegument was investigated, using an in vitro assay. Addition of physiological concentrations of ATP and magnesium to wild-type virions in the presence of detergent promoted the release of VP13/14 and VP22. VP1/2 and the UL13 protein kinase were not significantly solubilized. However, using a virus with an inactivated UL13 protein, we found that the release of VP22 was severely impaired. Addition of casein kinase II (CKII) to UL13 mutant virions promoted VP22 release. Heat inactivation of virions or addition of phosphatase inhibited the release of both proteins. Incorporation of radiolabeled ATP into the assay demonstrated the phosphorylation of VP1/2, VP13/14, VP16, and VP22. Incubation of detergent-purified, heat-inactivated capsid-tegument with recombinant kinases showed VP1/2 phosphorylation by CKII, VP13/14 phosphorylation by CKII, protein kinase A (PKA), and PKC, VP16 phosphorylation by PKA, and VP22 phosphorylation by CKII and PKC. Proteolytic mapping and phosphoamino acid analysis of phosphorylated VP22 correlated with previously published work. The phosphorylation of virion-associated VP13/14, VP16, and VP22 was demonstrated in cells infected in the presence of cycloheximide. Use of equine herpesvirus 1 in the in vitro release assay resulted in the enhanced release of VP10, the homolog of HSV-1 VP13/14. These results suggest that the dissociation of major tegument proteins from alphaherpesvirus virions in infected cells may be initiated by phosphorylation events mediated by both virion-associated and cellular kinases.

Inhibition and enhancement of odorant-induced cAMP accumulation in rat olfactory cilia by antibodies directed against G alpha S/olf- and G alpha i-protein subunits

The odorant-induced accumulation of cAMP can be inhibited by antibodies directed against G alpha s/olf. In contrast, antibodies raised against G alpha i-subunits caused a strong enhancement of the odorant-induced cAMP accumulation. Western blotting and immunoelectron microscopy revealed the presence of both G alpha s/olf- and G alpha i-subunits in rat cilia preparations. The existence of both stimulatory and inhibitory odorant-induced regulation of adenylyl cyclase activity in olfactory cilia may indicate that an initial integration of different odorant stimuli begins at the level of primary reactions in the same effector enzyme.

The cellular distribution of the adenomatous polyposis coli tumour suppressor protein in neuroblastoma cells is regulated by microtubule dynamics

The adenomatous polyposis coli tumour suppressor protein is highly expressed in developing rodent brain, but its function is unclear. Recent studies have suggested a role for this protein in regulating microtubule dynamics. Neuro 2A mouse neuroblastoma cells were previously thought not to express this protein. Using immunochemical techniques, this report corrects this observation. Immunoreactive bands of a size consistent with that of the full-length protein were observed by western blotting. Using immunocytochemistry, punctate immunoreactivity localized to areas of the cell containing microtubules, particularly neurite growth cones, in a distribution suggesting a role in neuritogenesis and growth cone extension. The protein did not localize to actin-rich cellular structures, and perturbation of the actin cytoskeleton had no effect upon this distribution. Treatment of cells with taxol to stabilize microtubules caused the concentration of the immunoreactive puncta to the tips of microtubules and areas along the axis of potential microtubule assembly. Treatment of cells with the microtubule disrupting reagent nocodazole showed that over shorter times the punctate distribution was not dependent upon polymerized microtubules. However, at longer incubation times a decrease in punctate immunostaining was observed. These results indicate that the intracellular distribution of the adenomatous polyposis coli protein is dependent upon microtubule but not actin dynamics. A role for this protein in the regulation of directed microtubule assembly is suggested.

Expression of beta-catenin and the adenomatous polyposis coli tumour suppressor protein in mouse neocortical cells in vitro

Beta-catenin is known to associate with the tumour suppressor protein adenomatous polyposis coli (APC), which is highly expressed in developing brain. We have therefore investigated the distribution of beta-catenin and APC in primary cultures of mouse neocortex. Western blotting demonstrated the presence of a single beta-catenin species in our cultures. Immunocytochemistry showed that beta-catenin was plasma membrane associated and concentrated in growth cones in cultured neurons. The APC tumour suppressor protein was also concentrated in growth cones. In glial cells, beta-catenin was localised at cell-cell contacts in a manner similar to that previously described in other cell types. This data suggests a role for both APC and beta-catenin in neuronal growth cones, and for beta-catenin in the formation of cell to cell contacts between glia.

Processing and intracellular localization of the herpes simplex virus type 1 proteinase

The herpes simplex virus type 1 (HSV-1) capsid protein VP24 (encoded by UL26) was expressed as a GST-fusion protein and used to prepare a group of monoclonal antibodies. These were used to characterize the protein in capsids and virus infected cells and demonstrated that it exists as two polypeptide species. The nature of the relationship between these two species was investigated and found to be associated with disulphide bonding. Under non-reducing conditions a species corresponding to dimers of VP24 was identified in preparations of B capsids, the site of action of the proteinase. Biochemical subcellular fractionation studies suggested that only cleaved forms of UL26 and UL26.5 gene products could be detected in the nucleus of the infected cell at early times post-infection.

An ultrastructural study of glomeruli associated with vomeronasal organs transplanted into the rat CNS

Rat neonate vomeronasal organs were transplanted into the parietal cortex of littermates to examine their survival and the behavior of axon growth into the surrounding host brain parenchyma. After survival times of 10-100 days the brains were processed for ultrastructural examination. The transplanted vomeronasal organs (VNO) formed several vesicles lined with a sensory epithelium. From these sensory epithelia, VNO neurons leave the epithelium and enter the host brain. Transplant neurons grew axons that fasciculated into bundles surrounded by sheath cell processes and formed one or more fiber plexuses containing distinct globose or spherical-shaped glomerular-like structures. The glomeruli consisted of nerve terminals between which existed asymmetric synaptic contacts. Rarely did we observe clear reciprocal synapses. The glomeruli also contained terminals that showed signs of degeneration, such as increased density of the terminals, clumping of mitochondria and multivesicular bodies. The glomeruli were not partitioned or subdivided by glial septa; however, glial profiles were interspersed among the sensory terminals. Transplant glomeruli also lacked periglomerular cells and had no definitive glial envelope. These results suggest that glomerular formation is not dependent on dendrite contribution of second order neurons or glial support, but rather on a complementary population of receptor neurons.

Regeneration of olfactory sensory neurons and reconnection in the aging hamster central nervous system

Olfactory neuron recovery and axon growth was studied in 12-24 month old hamsters after unilateral olfactory nerve transection. At recovery times ranging from 4 to 126 days olfactory nerve regeneration and axon reconnection to the olfactory bulb were examined by anterograde horseradish peroxidase (HRP) neurohistochemistry and electron microscopy. Nerve transection produced immediate retrograde neuron degeneration and there was no HRP reaction product in the bulb at 4 days post transection. By day 35, centrally growing olfactory axons had reached the bulb. Axons formed glomeruli smaller than those in the unoperated control bulb and they were not always confined to the glomerular layer of the bulb. Some animals showed robust fiber growth with axon fascicles penetrating the different layers of the bulb and forming ectopic glomeruli along their path. Second order bulb neurons contained wheat germ agglutinin HRP reaction product, indicating that transneuronal transport had occurred. Electron microscopy confirmed transneuronal transport between olfactory axons and second order bulbar neurons. These results show that the capacity for olfactory neuron recovery and reconnection persists in the hamster well into old age.

Transplantation of postnatal vomeronasal organ in the CNS of newborn rats

The present study was conducted to examine the survival and development of intracerebral transplanted neonatal rat vomeronasal organs (VNs). Complete neonatal (P5-P10) VNs were transplanted into the parietal cortex region of littermates and examined at 10-100 days by light microscopy. The VN survived and was organized into a series of vesicles lined by respiratory and/or sensory epithelia. Sensory neurons grew long axons that fasciculated and invaded the surrounding brain parenchyma. The newly developed axons did not prefer a specific brain region. The axons developed a complex fiber plexus either at the interface between transplant and host tissue or deep within the host brain parenchyma. Vomeronasal axons consistently formed glomerular-like structures within the fiber plexus. Our results suggest that glomerular formation is not dependent on specific target of length of axon development, but rather on a set of complementary axons that display mutual recognition.

Polarized distribution of the trans-Golgi network marker TGN38 during the in vitro development of neocortical neurons: effects of nocodazole and brefeldin A

Neurons are polarized secretory cells whose cytoplasm and plasma membrane are polarized to form two compartments: dendrites and axons. In mature, fully polarized neurons, the microtubule-associated protein Map2 is targeted to dendrites, while tau is mainly restricted to axons. However, the intraneuronal distribution of secretory pathway organelles, such as the endoplasmic reticulum and the Golgi complex, which give rise to all constitutive, regulated and lysosome vesicles, is poorly understood. Thus, to investigate the distribution of the trans-Golgi network during the development and maturation of rat neocortical neurons in vitro, we have utilized an antibody recognizing a 38 kDa trans-Golgi network-specific protein, TGN38, and immunofluorescence microscopy. Before neurons have established polarity. TGN38 immunoreactivity outlines several vesicles dispersed throughout the cell body cytoplasm; these converge close to a major Map2-immunopositive process during the establishment of neuronal polarity, and later merge into a single structure located at the base of a thick Map2-immunopositive process, approximately 18 h after plating. At this stage TGN38 immunoreactivity is located within 45 degrees of the major Map2-immunoreactive process in 54% of neurons, while in only 6% of cells it is located at the opposite pole. After 3 days in vitro, during the segregation of microtubule-associated proteins to either dendrites or axons. TGN38 immunoreactivity clusters continue to be located close to a major dendrite, and in some neurons these clusters begin to enter a major Map2-immunoreactive process. At 10 days in vitro TGN38 immunoreactivity extends into a major dendrite for 5-30 microns in many neurons. Thus, the distribution of TGN38 immunoreactivity becomes polarized, being localized within a single, usually the major, neocortical dendrite. Our results also show that the morphological appearance of TGN38-immunoreactive structures is microtubule-dependent, since nocodazole treatment of polarized neurons induces scattering of TGN38-immunoreactive vesicles throughout the cell body's cytoplasm. Treatment with brefeldin A induces scattering of small TGN38-immunoreactive vesicles throughout the neuronal cytoplasm and processes, a different response to that observed in non-neuronal cells.

Use of recombinant vectors derived from herpes simplex virus 1 mutant tsK for short-term expression of transgenes encoding cytoplasmic and membrane anchored proteins in postmitotic polarized cortical neurons and glial cells in vitro

We constructed three recombinant vectors derived from the herpes simplex virus type 1 mutant tsK, each of which contained a different transgene under the control of the herpes simplex virus type 1 immediate early 3 promoter inserted into the thymidine kinase locus: the prokaryotic enzymes beta-galactosidase and chloramphenicol acetyl transferase, and a fusion gene consisting of human tissue inhibitor of metalloproteinases linked to the last exon of Thy-1, which encodes for a glycosyl-phosphatidyl-inositol membrane anchor. Infection of postmitotic neocortical and hippocampal neurons in low-density primary cultures with these vectors, achieved reliable expression of all three foreign gene products in various neocortical cell types, e.g. pyramidal neurons, non-pyramidal neurons, and glial cells. The percentage of neurons expressing transgenes ranged from 1 to 46% depending on the multiplicity of infection (highest assayed = 5); the percentage of glial cells expressing transgenes ranged from 0.5 to 98% (highest multiplicity assayed = 3.4). Expression of transgenes could be detected for up to three days in approximately 20% of neurons infected at a multiplicity of infection of 1. Infection of neurons with tk K-derived recombinant vectors inhibited their protein synthesis by 40-50% at a multiplicity of infection of 10, but no effect was observed at a multiplicity of infection of 1. Infection of glial cells with the same vectors at a multiplicity of infection of 1 inhibited protein synthesis by more than 90%. Analysis of neuronal viability at different times post-infection indicated that more than 98% of neurons expressing transgenes 48 h post-infection were viable. Thus, low-density neuronal cultures can be used to assess the efficiency of herpes simplex virus type 1-derived gene transfer vectors and transgene expression in developing cortical postmitotic cells, before and after they establish polarity. In addition, we show that two cytoplasmic enzymes, beta-galactosidase and chloramphenicol acetyl transferase, are able to diffuse freely in the cytoplasm reaching even growth cones in young neurons, while the chimeric protein tissue inhibitor of metalloproteinases/Thy-1 is correctly targeted to the plasma membrane via a glycosyl-phosphatidylinositol anchor. This model system should be useful for investigation of cellular and molecular aspects of the development and establishment of neuronal polarity, as well as for analysis of signals involved in protein targeting in postmitotic neurons.

Morphology of olfactory epithelium in humans and other vertebrates

Human olfactory epithelium is similar in organization and cell morphology to that of most vertebrate species. The epithelium has a pseudostratified columnar organization and consists of olfactory neurons, supporting and basal cells. Near the mucosal surface there are also microvillar cells. These cells have neuron-like features and may be chemoreceptors. Human olfactory epithelium is not a uniform sensory sheet. Patches of non-sensory tissue often appear in what was thought to be a purely olfactory region. The significance of these patches has not been determined, but they could reflect exposure to environment agents or changes that occur during the normal aging process. In order to better understand the human olfactory system, further knowledge of the normal structure is necessary. This review addresses the morphology of the human olfactory epithelium and the remarkable plasticity of the vertebrate olfactory system.

Morphology of the human olfactory epithelium

The human olfactory epithelium has been previously studied with scanning electron microscopy; however, most studies have been limited to examining the epithelial surface. In an attempt to examine structures below the surface, we scanned epithelial fractures that occurred during tissue preparation. This made it possible to obtain unique three-dimensional images of cell profiles from the mucosal surface through the full depth of the epithelium. We examined supporting cells, olfactory neurons, basal cells, and a fourth cell type, the microvillar cell. Supporting cells had a microvillar surface and were in close contact with olfactory neurons and their processes. Olfactory neurons were primarily located in the middle and lower epithelial regions. Basal cells occurred alone or in clusters adjacent to the basal lamina. Microvillar cells were always observed in the upper epithelial region. They were flask- or pear-shaped, had a tuft of microvilli that extended into the nasal cavity, and a thin axon-like process that passed basally towards the lamina propria. This study represents the first comprehensive scanning electron microscopy examination of the human olfactory epithelium. Three-dimensional images obtained for each epithelial cell type allowed us to examine cell processes and their close contacts, especially between supporting cells and olfactory neurons. These results also revealed the irregular and patchy distribution of olfactory receptors within the human nasal cavity. Further studies that examine the detailed morphology of the human olfactory epithelium should provide a better understanding of the physiological mechanism and clinical disorders that affect olfactory function in humans.

Scanning electron microscopic study of degeneration and regeneration in the olfactory epithelium after axotomy

The olfactory epithelium of the adult hamster (Mesocricetus auratus) was examined with the scanning electron microscope following olfactory nerve axotomy. Axotomy results in retrograde degeneration of mature olfactory neurons. Maximum degeneration was observed around day 4. During the degeneration period the epithelium consists primarily of supporting and basal cells. Microvillar columnar supporting cells were observed to have fine cellular processes extending from their lateral border to neighbouring cells. Supporting cells extended to the basal lamina where they terminated in foot-like processes of variable shapes (club, splay and hook). Basal cells which gave rise to new replacement olfactory neurons were observed near the basal lamina. They had a rough cellular surface covered with small granules and fine cellular extensions. Bowman's gland duct cells extended unbranched through the epithelium where they formed funnel duct openings covered with microvilli. During early recovery periods (5-30 days) the number of olfactory neurons in the lower epithelium region increased. We observed olfactory neurons with developing axon and dendritic processes. Specialized growth cone structures were seen at the tips. Olfactory neuron growth cones were elongated or club-shaped and had a ruffled membrane surface. Several thin filopodia extended from the growth cone and made contact with adjacent cells. At late recovery periods (35-120 days) there was a marked increase in the number of olfactory neurons within the middle and lower epithelium regions. Numerous dendritic processes extended to the epithelial surface and terminated in knob-like ciliated structures. Olfactory axons passed basally, forming small intra-epithelial bundles that penetrated the basal lamina then fasciculated into larger bundles within the lamina propria. This study provides detailed three-dimensional observations of the olfactory epithelium following neuron injury, and describes neural degenerative changes, replacement of olfactory neurons, development and maturation. In addition, we describe the structure and basal attachment of supporting cells and their glial-like relation with olfactory neurons.

Three-dimensional scanning electron microscopic study of the normal hamster olfactory epithelium

The olfactory epithelium of the adult hamster (Mesocricetus auratus) was studied using the scanning electron microscope. A method that produced fractures in the epithelium exposed structures below the surface and made it possible to examine the morphological and structural relationships among cells. Three cell types were studied: supporting cells, olfactory neurons (receptor cells) and basal cells. Supporting cells were observed spanning the full extent of the epithelium, and had basal foot processes that terminated at or near the basal lamina. Along the lateral margin of supporting cells, cellular processes were observed extending outwards, reaching olfactory neurons and adjacent supporting cells. These cellular contacts among supporting cells and olfactory neurons were present at different levels of the epithelium. Olfactory neurons were located primarily in the middle and lower epithelial regions. Their dendritic processes reached the epithelial surface in a straight or tortuous manner, passing between the supporting cells. Olfactory axons were observed as thin unbranched processes that emerged from a conical hillock region, passed basally, and fasciculated into larger sensory bundles within the lamina propria. Basal cells were observed adjacent to the basal lamina as a row of single cells or clustered in groups. Within the lamina propria connective tissue, blood vessels, axon bundles and Bowman's glands were examined. Bowman's glands were composed of pyramidal secretory cells arranged about a single duct that extended to the epithelial surface. Scanning electron microscopy provided a unique three-dimensional analysis of cell structure within the olfactory epithelium. The results provide new and different observations on the detailed morphology and intimate relationships that exist among epithelial cells, and complement previous light and transmission EM observations.

Experimental studies on the olfactory marker protein. IV. Olfactory marker protein in the olfactory neurons transplanted within the brain

The presence of the olfactory marker protein (OMP) was studied in brain transplants of rat neonatal olfactory mucosa. In all transplants examined, many olfactory neurons were observed inside the transplanted neuroepithelium and within the surrounding brain parenchyma. However, only few neurons were OMP-positive. The absence of proper target and/or the ectopic brain environment are the two possibilities put forward to explain why the olfactory matrix produces cellular elements which do not express OMP even when they seem to reach morphological maturity.