Putative Cerebral Microbleeds in Dogs Undergoing Magnetic Resonance Imaging of the Head: A Retrospective Study of Demographics, Clinical Associations, and Relationship to Case Outcome

BACKGROUND

Cerebral microbleeds (CMBs) are focal intraparenchymal signal voids on gradient-echo magnetic resonance imaging (MRI), corresponding to regions of chronic hemorrhage. In humans, they are associated with systemic disease and shorter survival times. Although similar findings have been identified in dogs, their epidemiology and clinical correlations have not been investigated.

OBJECTIVE

To determine epidemiological features, clinical associations, and associations with outcome for putative CMB-like foci (putative microbleeds [pMBs]) identified by T2*-weighted MRI in dogs.

ANIMALS

Five hundred and eighty-two dogs undergoing 3T brain MRI between 2011 and 2016.

METHODS

Retrospective case-control study. Demographic, diagnostic, and clinicopathological data were obtained from medical records and phone follow-up. Demographic variables were compared between dogs with and without evidence of pMBs. For dogs with such evidence, and a subset of matched controls, associations with clinical presentation, concurrent disease, and survival times were evaluated.

RESULTS

Dogs with pMBs were older (P < .001) and smaller (P = .004) than unaffected dogs. Compared to matched controls, they presented more frequently for vestibular signs (P = .030). Cortical atrophy occurred concurrently with pMBs in 26% (14/54) of dogs. Diagnosed renal disease was not significantly associated with pMBs, but proteinuria was more common in dogs with pMBs than in matched controls (odds ratio = 3.01, P = .005). Dogs with pMBs had a shorter median survival time than did matched controls (P = .011).

CONCLUSIONS AND CLINICAL IMPORTANCE

Putative microbleeds occurred in 54 of 582 (9.3%) of dogs undergoing brain MRI, but may not be a normal consequence of aging. They were associated with shorter survival time and proteinuria in the study population.

Solomon Asch's Legacy for Group Research

Asch's work has had a profound impact on how psychologists think about and study social influence in groups. To appreciate this impact, we must go beyond his classic conformity experiments and consider his broader theoretical framework. This article examines 4 of Asch's ideas that have proven to be particularly influential in later efforts to understand social influence in groups: (a) Social interaction depends on individuals' ability to represent others' positions, define themselves as members of the same group, and regulate their behavior in terms of the norms and values of the group; (b) independence is critical to effective group functioning; (c) independence and conformity are not simply mirror images that can be explained in terms of a unitary psychological process; and (d) change of meaning is an important mechanism of social influence. Finally, Asch's role as a theorist and researcher in the wider area of group dynamics is considered.

Clinical Features and Magnetic Resonance Imaging Findings in 7 Dogs with Central Nervous System Aspergillosis

Background

Systemic aspergillosis is a manifestation of Aspergillus sp. infection that can result in central nervous system (CNS) involvement with marked alterations in CNS function. Information regarding the clinical presentation and magnetic resonance imaging (MRI) findings in cases of aspergillosis with CNS involvement is lacking, resulting in a need for better understanding of this disease.

Hypothesis/Objectives

The primary objectives were to describe the clinical features and MRI findings in dogs with CNS aspergillosis. The secondary objectives were to describe clinicopathologic findings and case outcome.

Animals

Seven dogs with CNS aspergillosis.

Methods

Archived records from 6 institutions were reviewed to identify cases with MRI of CNS aspergillosis confirmed with serum galactomannan enzyme immunoassay (EIA) testing, culture, or supported by histopathology. Signalment, clinical, MRI, clinicopathologic, histopathologic, and microbiologic findings were recorded and evaluated.

Results

Aspergillosis of the CNS was identified in 7 dogs from 3 institutions. The median age was 3 years and six were German Shepherd dogs. Five dogs had signs of vestibular dysfunction as a component of multifocal neurological abnormalities. The MRI findings ranged from normal to abnormal, including hemorrhagic infarction and mass lesions.

Conclusions and Clinical Importance

Until now, all reported MRI findings in dogs with CNS aspergillosis have been abnormal. We document that CNS aspergillosis in dogs, particularly German Shepherd dogs, can be suspected based on neurologic signs, whether MRI findings are normal or abnormal. Confirmatory testing with galactomannan EIA, urine, cerebrospinal fluid (CSF) or tissue culture should be performed in cases where aspergillosis is a differential diagnosis.

A comparison of clinical, magnetic resonance imaging and pathological findings in dogs with gliomatosis cerebri, focusing on cases with minimal magnetic resonance imaging changes(‡)

The primary study objective was to determine whether clinical examination and magnetic resonance imaging (MRI) can underestimate canine gliomatosis cerebri (GC); we also investigated immunohistochemical features. Seven dogs with GC were studied; four recruited specifically because of minimal MRI changes. Neuroanatomic localization and the distribution of MRI, gross and sub-gross lesions were compared with the actual histological distribution of neoplastic cells. In six cases, clinical examination predicted focal disease and MRI demonstrated a single lesion or appeared normal. Neoplastic cells infiltrated many regions deemed normal by clinical examination and MRI, and were Olig2-positive and glial fibrillary acid protein-negative. Four dogs had concurrent gliomas. GC is a differential diagnosis for dogs with focal neurological deficits and a normal MRI or a focal MRI lesion. Canine GC is probably mainly oligodendrocytic. Type II GC, a solid glioma accompanying diffuse central nervous system neoplastic infiltration, occurs in dogs as in people.

Necrotizing meningoencephalitis in atypical dog breeds: a case series and literature review

Background

Canine necrotizing meningoencephalitis (NME) is a fatal, noninfectious inflammatory disease of unknown etiology. NME has been reported only in a small number of dog breeds, which has led to the presumption that it is a breed‐restricted disorder.

Hypothesis/Objectives

Our objective was to describe histopathologically confirmed NME in dog breeds in which the condition has not been reported previously and to provide preliminary evidence that NME affects a wider spectrum of dog breeds than previously reported.

Animals

Four dogs with NME.

Methods

Archives from 3 institutions and from 1 author's (BS) collection were reviewed to identify histopathologically confirmed cases of NME in breeds in which the disease has not been reported previously. Age, sex, breed, survival from onset of clinical signs, and histopathologic findings were evaluated.

Results

Necrotizing meningoencephalitis was identified in 4 small dog breeds (Papillon, Shih Tzu, Coton de Tulear, and Brussels Griffon). Median age at clinical evaluation was 2.5 years. Histopathologic abnormalities included 2 or more of the following: lymphoplasmacytic or histiocytic meningoencephalitis or encephalitis, moderate‐to‐severe cerebrocortical necrosis, variable involvement of other anatomic locations within the brain (cerebellum, brainstem), and absence of detectable infectious agents.

Conclusions and Clinical Importance

Until now, NME has only been described in 5 small dog breeds. We document an additional 4 small breeds previously not shown to develop NME. Our cases further illustrate that NME is not a breed‐restricted disorder and should be considered in the differential diagnosis for dogs with signalment and clinical signs consistent with inflammatory brain disease.

Broadly reactive polymerase chain reaction for pathogen detection in canine granulomatous meningoencephalomyelitis and necrotizing meningoencephalitis

Background

Granulomatous meningoencephalomyelitis (GME) and necrotizing meningoencephalitis (NME) are common inflammatory conditions of the central nervous system of dogs. Infectious pathogens, particularly viruses, are suspected to contribute to the etiopathogenesis of GME and NME.

Hypothesis

Broadly reactive PCR might aid in the identification of infectious agents in GME and NME.

Animals

Sixty‐eight client‐owned dogs evaluated by necropsy at 1 university referral hospital.

Methods

A mixed prospective/retrospective case‐control study was performed. Brain tissue prospectively collected at necropsy from GME, NME, and control cases was evaluated by broadly reactive polymerase chain reaction (PCR) for adenoviruses, bunyaviruses, coronaviruses, enteroviruses, flaviviruses, herpesviruses, paramyxoviruses, and parechoviruses. In addition, these tissues were retrospectively evaluated for the presence of mycoplasmas by PCR, culture, and immunohistochemistry (IHC).

Results

Brain tissue was collected from 11 GME and 27 NME cases and 30 controls. Viral nucleic acids were not identified in the 6 GME cases, 25 NME cases, and 2 controls evaluated by viral PCR. Mycoplasma canis was identified by Mycoplasma genus PCR in 1/5 GME and 4/25 NME cases and subsequently was cultured from 4/5 GME and 4/8 NME cases as well as 2/9 controls. The IHC did not detect M. canis in any of the 11 GME and 27 NME cases or 14 controls evaluated with strain PG14 polyclonal antiserum.

Conclusions and Clinical Importance

The negative results suggest that viral pathogens are not common in the brain tissue of dogs with GME and NME. Further investigation is warranted to determine the importance of M. canis in cases of GME and NME.

Magnetic resonance imaging for the differentiation of neoplastic, inflammatory, and cerebrovascular brain disease in dogs

BACKGROUND

The reliability and validity of magnetic resonance imaging (MRI) for detecting neoplastic, inflammatory, and cerebrovascular brain lesions in dogs are unknown.

OBJECTIVES

To estimate sensitivity, specificity, and inter-rater agreement of MRI for classifying histologically confirmed neoplastic, inflammatory, and cerebrovascular brain disease in dogs.

ANIMALS

One hundred and twenty-one client-owned dogs diagnosed with brain disease (n = 77) or idiopathic epilepsy (n = 44).

METHODS

Retrospective, multi-institutional case series; 3 investigators analyzed MR images for the presence of a brain lesion with and without knowledge of case clinical data. Investigators recorded most likely etiologic category (neoplastic, inflammatory, cerebrovascular) and most likely specific disease for all brain lesions. Sensitivity, specificity, and inter-rater agreement were calculated to estimate diagnostic performance.

RESULTS

MRI was 94.4% sensitive (95% confidence interval [CI] = 88.7, 97.4) and 95.5% specific (95% CI = 89.9, 98.1) for detecting a brain lesion with similarly high performance for classifying neoplastic and inflammatory disease, but was only 38.9% sensitive for classifying cerebrovascular disease (95% CI = 16.1, 67.0). In general, high specificity but not sensitivity was retained for MR diagnosis of specific brain diseases. Inter-rater agreement was very good for overall detection of structural brain lesions (κ = 0.895, 95% CI = 0.792, 0.998, P < .001) and neoplastic lesions, but was only fair for cerebrovascular lesions (κ = 0.299, 95% CI = 0, 0.761, P = .21).

CONCLUSIONS AND CLINICAL IMPORTANCE

MRI is sensitive and specific for identifying brain lesions and classifying disease as inflammatory or neoplastic in dogs. Cerebrovascular disease in general and specific inflammatory, neoplastic, and cerebrovascular brain diseases were frequently misclassified.

Chondroblastoma of the temporal bone: consistent middle fossa involvement

The objective of this study is to describe the presentation and clinical course of two patients with temporal bone chondroblastoma, and to review the literature on temporal bone chondroblastoma to identify characteristic clinical and radiological presentations, and optimal treatment regimens. MEDLINE literature searches covering the period from 1966 to January 1998, in all languages, were performed as well as a review of the bibliographies of the identified studies. Strict inclusion criteria were upheld, In total 18 studies had patients whose data could be analyzed. From the 18 studies, 34 patients were identified, but only 21 cases met the inclusion criteria. Demographic, clinical presentation, radiological, operative and treatment parameters were analyzed in this cohort of patients. Ninety-five percent of patients were found to have invasion of the middle cranial fossa and 76% were found to have erosion into the superior aspect of the external auditory canal by temporal bone chondroblastoma. The characteristic growth pattern of temporal bone chondroblastoma may result from embryonal or cartilagenous rests entrapped in the tympanosquamous suture line in the middle fossa floor. Temporal bone chondroblastoma represents a pathology that does not arise from, or have a growth pattern resembling other pathologies in the temporal bone.

Observer agreement study of cervical-vertebral ratios in horses

REASON FOR PERFORMING STUDY

Different examiners or the same examiner were observed at different times producing slightly different results when obtaining cervical-vertebral ratios. If the difference is substantial, then measurement variability would have an important impact of radiographic interpretation.

OBJECTIVE

To quantify agreement and repeatability of these measurements.

METHODS

An observer agreement study was performed using 75 horses. Measurements were made at C3-4 and C6-7 by a board-certified radiologist and an imaging resident. Intra- and interobserver agreement was quantified using Bland-Altman plots. Repeatability was assessed as the percentage of differences between duplicate measurements by the radiologist that were within ± 2 s.d. of the differences.

RESULTS

At C3-4, the limits of agreement for the intra-vertebral ratio were between -5 and 4% for the intra- and -5 and 6% for interobserver comparison. For the intervertebral ratio, they were between -9 and 8% for the intra- and -10 and 10% for interobserver comparison. At C6-7, the limits of agreement for the intra-vertebral ratio were between -6 and 5% for the intra- and -6 and 8% for interobserver comparison. For the intervertebral ratio, they were between -7 and 7% for the intra- and -6 and 13% for interobserver comparison. At C3-4, all measurements were 95% repeatable (differences typically ≤ 4% and always ≤ 8%) for the intra-vertebral ratio and 96% repeatable (differences typically ≤ 8% and always ≤ 11%) for the intervertebral ratio. At C6-7, all measurements were 98% repeatable (differences typically ≤ 6% and always ≤ 7%) for the intravertebral ratio and 92% repeatable (differences typically ≤ 6% and always ≤ 10%) for the intervertebral ratio.

CONCLUSIONS

Cervical-vertebral ratios typically varied by 5-10% within and between examiners.

POTENTIAL RELEVANCE

When using cervical-vertebral ratios in practice, the impact of measurement agreement should be factored into the interpretation of the test result because measurement variability may lead to misdiagnosis and limit the clinical usefulness of these tests.

Evaluation of brain tissue or cerebrospinal fluid with broadly reactive polymerase chain reaction for Ehrlichia, Anaplasma, spotted fever group Rickettsia, Bartonella, and Borrelia species in canine neurological diseases (109 cases)

BACKGROUND

Vector-transmitted microorganisms in the genera Ehrlichia, Anaplasma, Rickettsia, Bartonella, and Borrelia are commonly suspected in dogs with meningoencephalomyelitis (MEM), but the prevalence of these pathogens in brain tissue and cerebrospinal fluid (CSF) of dogs with MEM is unknown.

HYPOTHESIS/OBJECTIVES

To determine if DNA from these genera is present in brain tissue and CSF of dogs with MEM, including those with meningoencephalitis of unknown etiology (MUE) and histopathologically confirmed cases of granulomatous (GME) and necrotizing meningoencephalomyelitis (NME).

ANIMALS

Hundred and nine dogs examined for neurological signs at 3 university referral hospitals.

METHODS

Brain tissue and CSF were collected prospectively from dogs with neurological disease and evaluated by broadly reactive polymerase chain reaction (PCR) for Ehrlichia, Anaplasma, Spotted Fever Group Rickettsia, Bartonella, and Borrelia species. Medical records were evaluated retrospectively to identify MEM and control cases.

RESULTS

Seventy-five cases of MUE, GME, or NME, including brain tissue from 31 and CSF from 44 cases, were evaluated. Brain tissue from 4 cases and inflammatory CSF from 30 cases with infectious, neoplastic, compressive, vascular, or malformative disease were evaluated as controls. Pathogen nucleic acids were detected in 1 of 109 cases evaluated. Specifically, Bartonella vinsonii subsp. berkhoffii DNA was amplified from 1/6 dogs with histopathologically confirmed GME.

CONCLUSION AND CLINICAL IMPORTANCE

The results of this investigation suggest that microorganisms in the genera Ehrlichia, Anaplasma, Rickettsia, and Borrelia are unlikely to be directly associated with canine MEM in the geographic regions evaluated. The role of Bartonella in the pathogenesis of GME warrants further investigation.

Cerebrospinal fluid myelin basic protein as a prognostic biomarker in dogs with thoracolumbar intervertebral disk herniation

BACKGROUND

Release of myelin basic protein (MBP) into the cerebrospinal fluid (CSF) is associated with active demyelination and correlates with outcome in various neurological diseases.

HYPOTHESIS/OBJECTIVES

To describe associations among CSF MBP concentration, initial neurological dysfunction, and long-term ambulatory outcome in dogs with acute thoracolumbar intervertebral disk herniation (IVDH).

ANIMALS

Fifty seven [corrected] dogs with acute thoracolumbar IVDH and 16 clinically normal dogs.

METHODS

Prospective case series clinical study. Signalment, initial neurological dysfunction as determined by a modified Frankel score (MFS), and ambulatory outcome at >3-month follow-up were recorded. Cisternal CSF MBP concentration was determined by an ELISA. Associations were estimated between CSF MBP concentration and various clinical parameters.

RESULTS

Dogs with thoracolumbar IVDH that did not ambulate at follow-up had a higher CSF MBP concentration (median, 3.56 ng/mL; range, 0.59-51.2 ng/mL) compared with control dogs (median, 2.22 ng/mL; range, 0-3.82 ng/mL) (P=.032). A CSF MBP concentration of >or=3 ng/mL had a sensitivity of 78% and specificity of 76% to predict an unsuccessful outcome based on receiver-operating characteristics curve analysis (area under the curve=0.688, P=.079). Affected dogs with a CSF MBP concentration>or=3 ng/mL had 0.09 times the odds of ambulation at follow-up compared with affected dogs with CSF MBP concentration<3 ng/mL when adjusted for initial MFS (95% confidence interval 0.01-0.66, P=.018).

CONCLUSIONS AND CLINICAL IMPORTANCE

These results would suggest that CSF MBP concentration may be useful as an independent prognostic indicator in dogs with thoracolumbar IVDH.

Native shrub reestablishment in exotic annual grasslands: do ecosystem processes recover?

The impacts of exotic plant species on ecosystem processes are well established, motivating numerous efforts to facilitate native-species recovery. Nonetheless, how the return of native species influences ecosystem processes and how these changes feed back to influence the recovery process are poorly understood. We examined these questions in exotic annual grasslands on Santa Cruz Island, California, USA, where the removal of nonnative herbivores has led to the recovery of the native shrubs Artemisia californica and Eriogonum arborescens. To examine the influence of shrub colonization on nutrient cycling, and the mechanisms by which these changes arise, we measured available nitrogen and phosphorus, and quantified nitrogen mineralization and litterfall rates under shrubs and grasses in the field and in experimental monoculture plots. Both native shrubs altered nitrogen cycling as they colonized the grassland, but they did so in opposite directions. Eriogonum depressed nitrogen pools and mineralization rates via large inputs of nitrogen-poor litter. In contrast Artemisia increased nitrogen and phosphorus pools and nitrogen mineralization rates. Last, to determine if shrub effects on soils favor shrubs or grasses, we conducted a nitrogen and phosphorus fertilization experiment in the field. Only the exotic grass was significantly limited by nitrogen. Thus the depressed nitrogen availability associated with Eriogonum colonization is more harmful to exotic grasses than to the native shrub. By contrast, the elevated nitrogen associated with recovering Artemisia favors grasses over the shrub, possibly hindering recovery of the native. Mechanistic studies of the ecosystem ,impacts of native-plant recovery are useful for managers wishing to predict which native species return ecosystem function, and whether such changes feed back to influence native recovery.

Magnetic resonance imaging characteristics of necrotizing meningoencephalitis in Pug dogs

BACKGROUND

The magnetic resonance imaging (MRI) characteristics of necrotizing meningoencephalitis (NME) are not well documented.

OBJECTIVES

To describe common MRI features of NME, to compare the MRI features to histopathologic findings, and to determine whether or not MRI lesions are predictive of survival time.

ANIMALS

Eighteen Pugs with NME.

METHODS

Retrospective MRI case study of Pugs identified by a search of medical records at 6 veterinary institutions. Eighteen dogs met inclusion criteria of histopathologically confirmed NME and antemortem MRI exam. MRI lesions were characterized and compared with histopathology with the kappa statistic. Survival times were compared with MRI findings by use of Mann-Whitney U-tests and Spearman's rho.

RESULTS

Twelve of 18 lesions were indistinctly marginated with mild parenchymal contrast enhancement. Prosencephalic (17/18) lesion distribution included the parietal (16/18), temporal (16/18), and occipital (16/18) lobes. There were cerebellar (4/18) and brainstem (3/18) lesions. Asymmetric lesions were present in both gray and white matter in all dogs. Falx cerebri shift was common (11/18), and 6 dogs had brain herniation. Leptomeningeal enhancement was present in 9/18 dogs. A moderate positive association was found between parenchymal contrast enhancement and both necrosis (kappa= 0.45; P= .045) and monocytic inflammation (kappa= 0.48; P= .025). Higher MRI lesion burden was correlated with longer time from disease onset to MRI (P= .045). MRI lesion burden did not correlate to survival time.

CONCLUSIONS AND CLINICAL IMPORTANCE

Asymmetric prosencephalic grey and white matter lesions with variable contrast enhancement were consistent MRI changes in Pugs with confirmed NME. While not pathognomonic for NME, these MRI characteristics should increase confidence in a presumptive diagnosis of NME in young Pugs with acute signs of neurologic disease.

Effect of mannitol and hypertonic saline on cerebral oxygenation in patients with severe traumatic brain injury and refractory intracranial hypertension

BACKGROUND

The impact of osmotic therapies on brain oxygen has not been extensively studied in humans. We examined the effects on brain tissue oxygen tension (PbtO(2)) of mannitol and hypertonic saline (HTS) in patients with severe traumatic brain injury (TBI) and refractory intracranial hypertension.

METHODS

12 consecutive patients with severe TBI who underwent intracranial pressure (ICP) and PbtO(2) monitoring were studied. Patients were treated with mannitol (25%, 0.75 g/kg) for episodes of elevated ICP (>20 mm Hg) or HTS (7.5%, 250 ml) if ICP was not controlled with mannitol. PbtO(2), ICP, mean arterial pressure, cerebral perfusion pressure (CPP), central venous pressure and cardiac output were monitored continuously.

RESULTS

42 episodes of intracranial hypertension, treated with mannitol (n = 28 boluses) or HTS (n = 14 boluses), were analysed. HTS treatment was associated with an increase in PbtO(2) (from baseline 28.3 (13.8) mm Hg to 34.9 (18.2) mm Hg at 30 min, 37.0 (17.6) mm Hg at 60 min and 41.4 (17.7) mm Hg at 120 min; all p<0.01) while mannitol did not affect PbtO(2) (baseline 30.4 (11.4) vs 28.7 (13.5) vs 28.4 (10.6) vs 27.5 (9.9) mm Hg; all p>0.1). Compared with mannitol, HTS was associated with lower ICP and higher CPP and cardiac output.

CONCLUSIONS

In patients with severe TBI and elevated ICP refractory to previous mannitol treatment, 7.5% hypertonic saline administered as second tier therapy is associated with a significant increase in brain oxygenation, and improved cerebral and systemic haemodynamics.

Epidemiology of necrotizing meningoencephalitis in Pug dogs

Background: Although the histopathologic features of necrotizing meningoencephalitis (NME) have been described previously, little information is available concerning the signalment, geographic distribution, seasonal onset, treatment, and survival of affected dogs.

Animals: Sixty Pugs with NME and 14 contemporaneous control Pugs with other intracranial diseases (non‐NME group).

Methods: Pugs that were euthanized or died because of intracranial disease were prospectively obtained. All dogs had necropsy, histopathology, and testing for various infectious diseases and were subsequently divided into NME and non‐NME groups. Signalment, geographic distribution, seasonal onset, treatment, and survival were compared between groups.

Results: In Pugs with NME, median age at onset of clinical signs was 18 months (range, 4–113 months). A greater proportion of female dogs were present in the NME group (40/60) compared with the control group (6/14). Pugs with NME had a significantly lower mean weight (7.81 kg) than control Pugs (9.79 kg) (P= .012). Mean survival in Pugs with NME was 93 days (range, 1–680 days), with dogs receiving any form of treatment living significantly longer than those that were not treated (P= .003). Anticonvulsive drugs were the only treatment significantly associated with longer survival (P= .003).

Conclusions and Clinical Importance: NME appears to be a common cause of intracranial signs in Pugs, based on the high proportion of NME dogs reported in this population. Pugs with NME are most commonly young adult female dogs. Although further investigation is needed to determine the optimal treatment of NME, anticonvulsive drugs appear to beneficially affect duration of survival.

Relationship between glaucoma and selenium levels in plasma and aqueous humour

AIM

The aim of the study was to compare selenium levels in plasma and aqueous humour in subjects with and without primary open-angle glaucoma (POAG).

METHODS

Forty-seven POAG cases and 54 controls in this case-control study were recruited from surgery patients at the University Physician's Ophthalmology Clinic in Tucson, Arizona, USA. Aqueous humour and plasma selenium were determined by high-performance liquid chromatography ion channel plasma mass spectrometry (HPLC ICP-MS). Potential confounders were assessed via a questionnaire. Biological samples were collected and processed at surgery and analysed for selenium content after collection was complete. Outcome measures included the odds of glaucoma in relationship to plasma selenium, aqueous humour selenium, and the ratio of levels of aqueous humour selenium to plasma selenium.

RESULTS

Tertile of selenium and its relationship to POAG was examined. After adjustment for common glaucoma risk factors, the odds of glaucoma in the highest tertile of plasma selenium (OR = 11.3; p = 0.03) and the middle tertile of aqueous humour selenium (OR = 0.06; p = 0.02) was significantly associated with glaucoma.

CONCLUSION

Although a causal pathway cannot be inferred from our analysis, our data, added to that of others, suggest that the pathology is selenium-related.

Use of an ankle-foot orthosis in a dog with traumatic sciatic neuropathy

Traumatic unilateral sciatic neuropathy secondary to a gunshot wound was diagnosed in a seven-month-old, intact male golden retriever. Findings on neurological assessment, performed after cardiovascular stabilisation, were incompatible with a return to normal limb function. An ankle-foot orthosis was used to correct excessive flexion of the digits and tarsus. This device greatly improved the dog's willingness to ambulate and could serve as an alternative to amputation in companion animals with severe sciatic axonotmesis or neurotmesis. Complications associated with chronic tibiotarsal hyperflexion necessitated a pantarsal arthrodesis one year after initial presentation; the dog also developed cranial cruciate disease in the affected limb three years after the gunshot injury.

The glial precursor proteoglycan, NG2, is expressed on tumour neovasculature by vascular pericytes in human malignant brain tumours

Glial precursor cells express NG2 and GD3 in the developing brain. These antigens are both over-expressed during neoplasia, which suggests they may have specific functions in the malignant progression of human brain tumours. This study describes the expression of NG2 and GD3 in 28 paediatric and adult brain tumours. Glioblastoma biopsy spheroids were also implanted into nude rats to assess the regional distribution of the molecules within the tumour. These xenografts showed extensive infiltration and growth that mimicked the growth patterns of human gliomas in situ. NG2 was identified in 20 out of 28 brain tumours, where the expression was confined to the main mass of the tumour, and was reduced towards the tumour periphery. NG2 was mainly associated with blood vessels on both the pericyte and basement membrane components of the tumour vasculature. Ki67 (MIB-1) labelling indicated that NG2 expression was associated with areas of high cellular proliferation. Conversely, all the tumours expressed GD3, which was present both in the tumour main mass and throughout the periphery. Thus, the expression of NG2 may be indicative of tumour progression and might be an amenable target for future therapeutic interventions.

Laboratory screening for electrolyte abnormalities and anemia in bulimia nervosa: a controlled study

OBJECTIVE

Abnormal eating patterns and recurrent purging behaviors can result in significant medical complications. The purpose of this study was to assess the frequency of abnormalities in clinical laboratory tests in patients with bulimia nervosa who reported being otherwise in good health.

METHODS

Subjects included nonhospitalized women (N = 74) who met criteria for bulimia nervosa outlined in the 3rd Rev. ed. of the Diagnostic and Statistical Manual of Mental Disorders. They also reported use of self-induced vomiting and/or laxatives as compensatory behaviors (purging subtype). The control group (N = 110) included female volunteers with no history of a psychiatric disorder. All subjects reported being in good medical health, were medication free, and were in a normal weight range. Blood samples were analyzed in the hospital clinical laboratory.

RESULTS

Compared with controls, patients showed more frequent occurrence of low values for serum potassium (6.8% vs. 0.9%; p <.05) and chloride (8.1% vs. 0.9%; p <.02). Electrolyte abnormalities occurred most often in patients with frequent bulimic episodes. Study groups did not differ significantly in frequency of abnormal hemoglobin concentrations.

DISCUSSION

These results help to clarify the expected frequency of electrolyte abnormalities in individuals with bulimia nervosa who report otherwise good medical health. The substantial frequency of hypokalemia and hypochloremia underscores the importance of an appropriate medical assessment for individuals with this disorder.

Deposition of the NG2 proteoglycan at nodes of Ranvier in the peripheral nervous system

The node of Ranvier is a complex macromolecular assembly of ion channels and other proteins that is specialized for the rapid propagation of the action potential. A full understanding of the processes responsible for the assembly and maintenance of the node requires first the identification and characterization of the proteins found there. Here we show that NG2, a structurally unique chondroitin sulfate proteoglycan, is a molecular component of the node of Ranvier in the peripheral nervous system. In adult sciatic nerve, NG2 is (1) associated with thin, elongated fibroblast-like cells, (2) on some but not all basal laminae, and (3) at nodes of Ranvier. At the nodes, NG2 is restricted to the nodal gap and is absent from the paranodal or juxtaparanodal region. In dissociated cell cultures of adult sciatic nerve, perineurial fibroblasts but not Schwann cells express NG2 on their surfaces. Approximately 45% of the total NG2 in peripheral nerves is in a soluble, rather than particulate, subcellular compartment. NG2 is also present in membrane fractions that also contain high levels of voltage-dependent sodium channels, caspr, and neuron-glia related cell adhesion molecule. These medium-density membranes likely correspond to the nodal and paranodal region of the axon-Schwann cell unit. These results suggest a model in which perineurial fibroblasts secrete or shed NG2, which subsequently associates with nodes of Ranvier. The growth-inhibitory and anti-adhesive properties of NG2 may limit the lateral extension of myelinating Schwann cells as nodes mature. NG2 may also participate in the barrier functions of the perineurial linings of the nerve.

Disturbed oligodendrocyte development and recovery from hypomyelination in a c-myc transgenic mouse mutant

The complexity of interactions underlying the elaboration of myelin has been extensively demonstrated. We provide evidence that signals promoting myelination are not confined to the normal developmental time window for myelination and persist well into adult life. The 2-50 mutant, described previously, carries a c-myc transgene regulated by a myelin basic protein promoter. This mutant is characterised by severe hypomyelination and abnormal oligodendrocytes in early life, followed by loss of the phenotype and normal longevity. We show that c-myc expression in early oligodendrocyte development results in a substantial reduction of cells of this lineage. However, apparent complete recovery, associated with loss of c-myc expression, axonal survival, and gradual myelin accumulation, is observed by 4 months of age. Thus, stimulation of myelination continues during adult life until normal myelin levels are established. We propose that this mutant may contribute to the characterisation of oligodendrocyte responses to myelinating signals.

Aldolase C/zebrin II expression in the neonatal rat forebrain reveals cellular heterogeneity within the subventricular zone and early astrocyte differentiation

During late gestational and early postnatal development, proliferating cells in the subventricular zones of the lateral ventricles (SVZ) migrate into the gray and white matter of the forebrain and differentiate into astrocytes and oligodendrocytes. Because the cellular composition and structure of the neonatal SVZ is poorly understood, we performed a differential display PCR screen to identify genes preferentially expressed therein. One highly expressed gene encoded aldolase C. We used a specific monoclonal antibody, aldolase C/zebrin II (ALDC/ZII), in combination with markers of glial lineage and proliferation, to characterize the cells that express this gene. In the neonatal SVZ, ALDC/ZII-positive cells, which are generally polygonal and display several processes, have a nonuniform spatial distribution. They do not express vimentin, GFAP, or NG2. A subset of ALDC/ZII-positive cells incorporates bromodeoxyuridine, but progenitors identified by beta-galactosidase expression after infection with recombinant BAG virus do not show ALDC/ZII immunoreactivity. Outside of the SVZ, beta-galactosidase-positive/ALDC/ZII-positive cells have an astrocytic phenotype, suggesting that immunoreactivity was acquired after exit from the SVZ. These studies demonstrate that the neonatal SVZ is composed of different populations of cells that can be characterized by their antigenic phenotype, their proliferative capacity, and their spatial distributions. Nonrandom distributions of different cell types within the SVZ may permit the formation of microenvironments that stimulate the production of cells with specific potentials at appropriate points in development. Analysis of ALDC/ZII expression by astrocyte lineage cells in the neonatal cerebral cortex and white matter may reveal insights into the phenotype and behavior of undifferentiated astrocyte progenitors.

AN2/NG2 protein-expressing glial progenitor cells in the murine CNS: isolation, differentiation, and association with radial glia

During early neural development, the lineage specification of initially pluripotent progenitor cells is associated with proliferation, differentiation, and migration. Oligodendroglial progenitor cells migrate from their sites of origin to reach the axons that they will myelinate. We have described a cell-surface protein, AN2, expressed by oligodendroglial progenitor cells in vitro and showed that antibodies against AN2 inhibited the migration of cultured primary oligodendroglial progenitor cells, suggesting that the AN2 antigen plays a role in their migration. Recently, results from MALDI mass spectroscopy showed that AN2 is the mouse homologue of the rat NG2 protein. In this study, we have analyzed cells staining with AN2 antibodies during development and in the adult murine central nervous system (CNS), carried out double stainings with antibodies against NG2, and investigated the differentiation potential of cells in vitro after isolation from early postnatal brain using AN2 antibodies. AN2 and NG2 antibodies stained totally overlapping populations of cells in the CNS. AN2/NG2 expressing cells in embryonic and postnatal brain expressed the PDGF-alpha-receptor and in postnatal brain exhibited electrophysiological properties typical of glial progenitor cells. Cells isolated from early postnatal brain using AN2 monoclonal antibody developed into oligodendrocytes in low serum medium or into astrocytes in the presence of fetal calf serum. In the embryonic spinal cord, cells staining with AN2 antibodies were found closely apposed to radial glial cells, suggesting that glial precursors, like neurons, may use radial glia as scaffolds for migration.

Late oligodendrocyte progenitors coincide with the developmental window of vulnerability for human perinatal white matter injury

Hypoxic-ischemic injury to the periventricular cerebral white matter [periventricular leukomalacia (PVL)] results in cerebral palsy and is the leading cause of brain injury in premature infants. The principal feature of PVL is a chronic disturbance of myelination and suggests that oligodendrocyte (OL) lineage progression is disrupted by ischemic injury. We determined the OL lineage stages at risk for injury during the developmental window of vulnerability for PVL (23-32 weeks, postconceptional age). In 26 normal control autopsy human brains, OL lineage progression was defined in parietal white matter, a region of predilection for PVL. Three successive OL stages, the late OL progenitor, the immature OL, and the mature OL, were characterized between 18 and 41 weeks with anti-NG2 proteoglycan, O4, O1, and anti-myelin basic protein (anti-MBP) antibodies. NG2+O4+ late OL progenitors were the predominant stage throughout the latter half of gestation. Between 18 and 27 weeks, O4+O1+ immature OLs were a minor population (9.9 +/- 2.1% of total OLs; n = 9). Between 28 and 41 weeks, an increase in immature OLs to 30.9 +/- 2.1% of total OLs (n = 9) was accompanied by a progressive increase in MBP+ myelin sheaths that were restricted to the periventricular white matter. The developmental window of high risk for PVL thus precedes the onset of myelination and identifies the late OL progenitor as the major potential target. Moreover, the decline in incidence of PVL at approximately 32 weeks coincides with the onset of myelination in the periventricular white matter and suggests that the risk for PVL is related to the presence of late OL progenitors in the periventricular white matter.

p21cip1 is required for the differentiation of oligodendrocytes independently of cell cycle withdrawal

Differentiation of most cell types requires both establishment of G1 arrest and the induction of a program related to achieving quiescence. We have chosen to study the differentiation of oligodendrocyte cells to determine the role of p27 and p21 in this process. Here we report that both p27 and p21 are required for the appropriate differentiation of these cells. p27 is required for proper withdrawal from the cell cycle, p21 is not. Instead, p21 is required for the establishment of the differentiation program following growth arrest. Similar observations were made in vivo. We show that p21-/- cells withdraw from the cell cycle similar to wild-type cells; however, early in animal life, the brain is hypomyelinated, inferring that the loss of p21 delayed myelination in the cerebellum. We found that we could complement or bypass the differentiation failure in p21-/- cells with either PD98059, an inhibitor of Mek1, or by transducing them with a tat-p16ink4a protein. We concluded that the two cdk inhibitors serve non-redundant roles in this program of differentiation, with p27 being responsible for arrest and p21 having a function in differentiation independent of its ability to control exit from the cell cycle.

The oligodendrocyte precursor cell in health and disease

Adult oligodendrocyte precursor cells (OPCs) make up around 5-8% of the glial cell population in the CNS. Their function in the undamaged CNS is largely unknown, but their processes are in contact with nodes of Ranvier and synapses, suggesting a regulatory role at these structures. The cells divide slowly, and constitute approximately 70% of cells labelled following a pulse injection of bromodeoxyuridine. In the injured CNS the cells form a reactive glial population that undergoes hypertrophy and mitosis, probably driven by a variety of growth factors and cytokines. In response to demyelination they divide and are thought to differentiate to provide new oligodendrocytes to replace those that have been lost. However, remyelination fails during the later stages of multiple sclerosis, and it is not clear whether this is as a result of a depletion of adult OPCs, inhibition within the glial scar, or damage to the axons that prevents myelination. Adult OPCs are also activated and proliferate following other forms of CNS damage, such as mechanical injury, excitotoxicity and viral infection. The cells produce several of the chondroitin sulphate proteoglycans that might inhibit axon regeneration.

NG2-expressing cells in the central nervous system: are they oligodendroglial progenitors?

Antibodies against the chondroitin sulphate proteoglycan, NG2, are increasingly being used to identify the widespread population of oligodendrocyte progenitor cells in the adult mammalian CNS. However, the specificity of this marker and the role of NG2-expressing cells in CNS function are still open to question. In this review we consider the evidence that NG2(+) cells in the CNS are part of the oligodendrocyte lineage and whether they can give rise to new oligodendrocytes following demyelination. In both the developing and mature rodent CNS, NG2(+) cells express the established oligodendrocyte lineage marker PDGF-alphaR and from P7, the late progenitor antigen O4, which persists in immature oligodendrocytes. They do not express markers of other CNS populations, such as OX42 or GFAP, at any developmental age. NG2(+) cells represent the major cycling cell population in the normal adult rat CNS, suggesting they have stem cell-like properties. NG2 immunoreactivity is upregulated as a result of physical, viral, excitotoxic and inflammatory insults to the CNS. Following demyelination NG2(+) cell number increases in the immediate vicinity of the lesion and rapid remyelination ensues. NG2 expression has also been investigated in human tissue. Multi-process bearing cells, which morphologically resemble those identified with antibodies against O4, persist in chronically demyelinated multiple sclerosis lesions.

Wound care in the 21st century: lessons from ancient Egypt

Wound care is becoming increasingly important to geriatricians and long-term care providers. Although pressure ulcers have recently taken the spotlight, wound care actually involves many other types of lesions found commonly in the nursing home environment. Physicians of ancient Egypt were experts in the art and science of healing wounds, as revealed by examination of the Smith Papyrus, one of the oldest medical texts in existence. Today, wound healing is no longer emphasized in medical training and practice. However, long-term care physicians and medical directors are in a perfect position to elevate wound care to its formerly preeminent position in medicine. To reach this goal, an agenda needs to be set for physician education on the techniques and tools of wound healing, including prevention, interdisciplinary collaboration, documentation, and correct choice of products.

Species diversity and biological invasions: relating local process to community pattern

In a California riparian system, the most diverse natural assemblages are the most invaded by exotic plants. A direct in situ manipulation of local diversity and a seed addition experiment showed that these patterns emerge despite the intrinsic negative effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At community-wide scales, the overwhelming effects of ecological factors spatially covarying with diversity, such as propagule supply, make the most diverse communities most likely to be invaded.

Neurocan is upregulated in injured brain and in cytokine-treated astrocytes

Injury to the CNS results in the formation of the glial scar, a primarily astrocytic structure that represents an obstacle to regrowing axons. Chondroitin sulfate proteoglycans (CSPG) are greatly upregulated in the glial scar, and a large body of evidence suggests that these molecules are inhibitory to axon regeneration. We show that the CSPG neurocan, which is expressed in the CNS, exerts a repulsive effect on growing cerebellar axons. Expression of neurocan was examined in the normal and damaged CNS. Frozen sections labeled with anti-neurocan monoclonal antibodies 7 d after a unilateral knife lesion to the cerebral cortex revealed an upregulation of neurocan around the lesion. Western blot analysis of extracts prepared from injured and uninjured tissue also revealed substantially more neurocan in the injured CNS. Western blot analysis revealed neurocan and the processed forms neurocan-C and neurocan-130 to be present in the conditioned medium of highly purified rat astrocytes. The amount detected was increased by transforming growth factor beta and to a greater extent by epidermal growth factor and was decreased by platelet-derived growth factor and, to a lesser extent, by interferon gamma. O-2A lineage cells were also capable of synthesizing and processing neurocan. Immunocytochemistry revealed neurocan to be deposited on the substrate around and under astrocytes but not on the cells. Astrocytes therefore lack the means to retain neurocan at the cell surface. These findings raise the possibility that neurocan interferes with axonal regeneration after CNS injury.

Approaches to the sellar and parasellar region: a retrospective comparison of the endonasal-transsphenoidal and sublabial-transsphenoidal approaches

Tumors of the hypophysis are often managed surgically by the neurosurgeon and the otolaryngologist. Three widely used anterior routes to the sella are the endonasal (transcolumellar) transsphenoidal, sublabial transsphenoidal, and transethmoidal approaches. We reviewed the charts of 60 patients who underwent surgery, 42 transcolumellar and 18 sublabial, for sellar and parasellar adenomas and compared the two transsphenoidal approaches. None of the patients in our study underwent the transethmoidal approach. Furthermore, 26 of the patients underwent an extensive interview to assess postoperative progress. Clinically, neither approach had any significant complications, and none of the patients in either group reported significant postoperative morbidity. On the basis of these results, we believe there is minimal difference in patient subjective reports and objective morbidity when comparing the sublabial and transcolumellar approaches.

Serotonin function following remission from bulimia nervosa

Abnormal serotonergic regulation in bulimia nervosa is thought to contribute to recurrent binge eating, depressed mood, and impulsivity. To follow-up on previous studies showing decreased neuroendocrine responses in symptomatic patients, this study assessed serotonin-mediated prolactin responses in individuals who had remitted from bulimia nervosa. Subjects included 21 women with a history of bulimia nervosa and 21 healthy female controls, as well as an additional comparison group of 19 women with current bulimia nervosa. Placebo-controlled neuroendocrine response studies utilized a single oral dose (60 mg) of the indirect serotonin agonist d,l-fenfluramine. For the bulimia nervosa remitted group, the fenfluramine-stimulated elevation in serum prolactin concentration was not significantly different from the response in healthy controls, but was significantly larger than the response in patients with current bulimia nervosa (p < .01). These findings suggest that diminished serotonergic neuroendocrine responsiveness in bulimia nervosa reflects a state-related abnormality. The results are discussed in relationship to recent reports indicating that some alterations in central nervous system serotonin regulation may persist in symptomatically recovered individuals.

Changes in bedrail prevalence during a bedrails-reduction initiative

OBJECTIVE

To examine the prevalence of bedrails and observe whether use of bedrails can be decreased during a bedrails-reduction initiative.

DESIGN

A serial, cross-sectional, observational study of bedrail use.

PATIENTS AND SETTING

An 816-bed not-for-profit nursing facility with academic affiliation and closed medical staff. Median age of residents was 88.1 (range 62-108); 74% were women and 26% were men.

MEASUREMENTS

Observed use of bedrails with classification of bedrail configurations into Enclosure Levels based on percentage of bedsides enclosed; serial census of bedrail use during a restraint-reduction effort.

RESULTS

Bedrail configurations fell into five Enclosure Levels based on percentage of the bed enclosed. Over 9 months, total bedrail prevalence increased from 50 to 56%; however, the highest Enclosure Levels decreased from 7.7 to 3.9%.

CONCLUSIONS

Bedrail configurations can be placed on a continuum of enclosure, and highest Enclosure Levels can be decreased during a bedrails-reduction program.

Activation and proliferation of endogenous oligodendrocyte precursor cells during ethidium bromide-induced demyelination

The adult brain contains a large population of glial cells with the properties of oligodendrocyte precursor cells (OPCs). The functions of this newly recognized class of glial cells in normal animals are unknown. Here, we analyzed the reactions of OPCs to a transient demyelination of the rat brainstem induced by the injection of ethidium bromide (EB) into the fourth ventricle. Within 22 h after EB injection, there is a 21% decrease in the number of OPCs within affected fiber tracts such as the spinal tract of the trigeminal nerve, most likely reflecting the toxic actions of EB. The surviving OPCs had enlarged cell bodies with fewer long processes and many membrane blebs. By 2 days after EB injection, these reactive OPCs had incorporated BrdU and increased in number. The increase in OPC cell number reached a maximum between 6-10 days after EB injection, at which time demyelination was complete. Myelin-specific marker antigens reappeared beginning at 12 days postinjection and the remyelination continued for up to 40 days. During remyelination, OPCs displayed a normal stellate morphology with an increased number of thin processes, many of which were closely associated with neurofilament-positive axonal profiles. The transient increase in the number of reactive OPCs within the demyelinated tissue and subsequent decrease in OPC number during remyelination demonstrates that the endogenous oligodendrocyte precursor population responds rapidly to the pathophysiological state of the brain. Demyelination generates a sufficient number of OPCs to participate in the repair of the demyelinated lesions.

Bedrails: choosing the best alternative

This article discusses the importance of resident assessment in the decision to use bedrails, highlights the importance of an interdisciplinary approach to decision-making, and offers a compendium of care plan interventions and devices that serve as alternatives to bedrails.

Comparing astrocytic cell lines that are inhibitory or permissive for axon growth: the major axon-inhibitory proteoglycan is NG2

Astrocytes, oligodendrocytes, and oligodendrocyte/type 2 astrocyte progenitors (O2A cells) can all produce molecules that inhibit axon regeneration. We have shown previously that inhibition of axon growth by astrocytes involves proteoglycans. To identify inhibitory mechanisms, we created astrocyte cell lines that are permissive or nonpermissive and showed that nonpermissive cells produce inhibitory chondroitin sulfate proteoglycans (CS-PGs). We have now tested these cell lines for the production and inhibitory function of known large CS-PGs. The most inhibitory line, Neu7, produces three CS-PGs in much greater amounts than the other cell lines: NG2, versican, and the CS-56 antigen. The contribution of NG2 to inhibition by the cells was tested using a function-blocking antibody. This allowed increased growth of dorsal root ganglion (DRG) axons over Neu7 cells and matrix and greatly increased the proportion of cortical axons able to cross from permissive A7 cells onto inhibitory Neu7 cells; CS-56 antibody had a similar effect. Inhibitory fractions of conditioned medium contained NG2 coupled to CS glycosaminoglycan chains, whereas noninhibitory fractions contained NG2 without CS chains. Enzyme preparations that facilitated axon growth in Neu7 cultures were shown to either degrade the NG2 core protein or remove CS chains. Versican is present as patches on Neu7 monolayers, but DRG axons do not avoid these patches. Therefore, NG2 appears to be the major axon-inhibitory factor made by Neu7 astrocytes. In the CNS, NG2 is expressed by O2A cells, which react rapidly after injury to produce a dense NG2-rich network, and by some reactive astrocytes. Our results suggest that NG2 may be a major obstacle to axon regeneration.

Transforming Individuals into Groups: Some Hallmarks of the SDS Approach to Small Group Research

During the past 25 years, Davis's social decision scheme (SDS) model, designed to clarify how individual-level characteristics combine to create group-level products, has had a major impact on small group research. Using formal, mathematical models, Davis and his colleagues first construct predictions, or theoretical baselines, about group products based on assumptions about members' characteristics and interactions and then compare these predictions to the performances of real groups. The SDS approach has been valuable in clarifying how group performance is affected by such variables as task characteristics, group size, individual differences (e.g., member status), procedural factors (e.g., straw polling, agendas), and temporal changes in social parameters. Copyright 1999 Academic Press.

Loss of p27Kip1 function results in increased proliferative capacity of oligodendrocyte progenitors but unaltered timing of differentiation

In many tissues, progenitor cells permanently withdraw from the cell cycle prior to commitment towards a differentiated phenotype. In the oligodendrocyte lineage a counting mechanism has been proposed, linking the number of cell divisions to growth arrest and differentiation. A direct prediction of this model is that an increase in the number of cell divisions would result in a delayed onset of differentiation. Since the cell cycle inhibitor p27Kip1 is an essential component of the machinery leading to oligodendrocyte progenitor growth arrest, we examined the temporal relationship between cell cycle withdrawal and expression of late differentiation markers in vivo, in mice carrying a targeted deletion in the p27Kip1 gene. Using bromodeoxyuridine to label proliferating cells, quaking (QKI) to identify embryonic glial progenitors, NG2 to identify neonatal oligodendrocyte progenitors, and myelin basic protein to label differentiated oligodendrocytes, we found an increased number of proliferating QKI- and NG2-positive cells in germinal zones of p27Kip1(−/−) mice at the peak of gliogenesis. However, no delay was observed in these mice in the appearance of the late differentiation marker myelin basic protein in the developing corpus callosum and cerebellum. Significantly, a decrease in cyclin E levels was observed in the brain of p27Kip1 null mice coincident with oligodendrocyte growth arrest. We conclude that two distinct modalities of growth arrest occur in the oligodendrocyte lineage: a p27Kip1-dependent mechanism of growth arrest affecting proliferation in early phases of gliogenesis, and a p27Kip1-independent event leading to withdrawal from the cell cycle and differentiation.

The NG2 chondroitin sulfate proteoglycan: role in malignant progression of human brain tumours

The expression and function of NG2, a transmembrane chondroitin sulfate proteoglycan was studied in human gliomas of various histological types in culture using immunocytochemistry and flow cytometry. NG2 was differentially expressed in the neoplasms, with higher expression in high compared to low-grade gliomas. In acutely isolated cells from human biopsies, NG2 +ve and NG2 -ve populations were morphologically distinct from each other, and NG2 +ve cells were more proliferative than NG2 -ve cells. The mitogens platelet derived growth factor (PDGF-AA) and basic fibroblast growth factor (bFGF) added in combination to serum-free medium (SFM) upregulated NG2 expression on glioblastoma multiforme cells in culture but had little effect on NG2 expression on the anaplastic astrocytoma cells. Furthermore, NG2 was colocalised with the platelet derived growth factor alpha receptor (PDGFalphaR) and antibody blockade of the PDGF-alphaR ablated NG2 expression on the glioblastoma multiforme cells, suggesting that increased NG2 expression in the presence of PDGF-AA is mediated via the PDGF-alphaR. Assays of migration and invasion indicate that NG2 +ve glioma cells migrated more efficiently on collagen IV and that NG2 -ve cells were more invasive than their NG2 +ve counterparts. The results indicate that NG2 may be, respectively, positively and negatively related to the proliferative and invasive capacity of glioma cells. Thus, expression of the NG2 proteoglycan may have major implications for malignant progression in glial neoplasms and may prove a useful target for future therapeutic regimens.

A light and electron microscopic study of NG2 chondroitin sulfate proteoglycan-positive oligodendrocyte precursor cells in the normal and kainate-lesioned rat hippocampus

The adult brain contains a large population of oligodendrocyte precursor cells that can be identified using antibodies against the NG2 chondroitin sulfate proteoglycan. The functions of this newly recognized class of glial cells in the normal or pathological brain are not well understood. To begin to elucidate these functions, we have examined the morphology and distribution of oligodendrocyte precursor cells in the hippocampus and neocortex of normal and kainate-lesioned rats by anti-NG2 immunocytochemistry using light and electron microscopy. Large numbers of oligodendrocyte precursor cells were present in all layers of the neocortex and hippocampus. These cells differed in their morphology from astrocytes, oligodendrocytes and microglia. The processes of these cells often surrounded unlabeled areas of clear cytoplasm. At the electron microscopic level, some of the profiles that were enclosed by oligodendrocyte precursor cell processes contained synaptic vesicles. Other enclosed profiles were dendrites or dendritic spines. NG2-immunopositive processes were also observed to interpose between axon terminals containing round vesicles and dendrites with thick postsynaptic densities. After kainate injection, the NG2-positive oligodendrocyte precursor cells in the hippocampus displayed reactive changes characterized by swollen cell bodies, an increased number of small, filopodial-like processes, and higher levels of immunodetectable NG2. Both viable and degenerating oligodendrocyte precursor cells were observed with electron microscopy. These observations emphasize the dynamic nature of the oligodendrocyte precursor cell and suggest that, in addition to participating in the glial reactions to excitotoxic damage, oligodendrocyte precursor cells may regulate the stability, structure and function of synapses in the normal central nervous system.