Final Outcomes from a Phase 2 Trial of Posoleucel in Allogeneic Hematopoietic Cell Transplant Recipients

Allogeneic hematopoietic cell transplantation (allo-HCT) recipients are susceptible to viral infections. We conducted a phase 2 trial evaluating the safety and rate of clinically significant infections (CSIs; viremia requiring treatment or end-organ disease) following infusion of posoleucel, a partially HLA-matched, allogeneic, off-the-shelf, multivirus-specific T cell investigational product for preventing CSIs with adenovirus, BK virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus-6, or JC virus. This open-label trial enrolled high-risk allo-HCT recipients based on receiving grafts from umbilical cord blood, haploidentical, mismatched, or matched unrelated donors; post-HCT lymphocytes <180/mm3; or use of T cell depletion. Posoleucel dosing was initiated within 15-49 days of allo-HCT and subsequently every 14 days for up to seven doses. The primary endpoint was the number of CSIs due to the six target viruses by week 14. Of the 26 patients enrolled just three (12%) had a CSI by week 14, each with a single target virus. In vivo expansion of functional virus-specific T cells detected via interferon-γ ELISpot assay was associated with viral control. Persistence of posoleucel-derived T cell clones for up to 14 weeks after the last infusion was confirmed by T cell receptor deep-sequencing. Five patients (19%) had acute GVHD grade II-IV. No patient experienced cytokine release syndrome. All six deaths were due to relapse or disease progression. High-risk allo-HCT patients who received posoleucel had low rates of CSIs from six targeted viruses. Repeat posoleucel dosing was generally safe and well tolerated and associated with functional immune reconstitution. www.clinicaltrials.gov NCT04693637.

Phenotypic and functional characterization of posoleucel, a multivirus-specific T cell therapy for the treatment and prevention of viral infections in immunocompromised patients

BACKGROUND

Deficits in T cell immunity translate into increased risk of severe viral infection in recipients of solid organ and hematopoietic cell transplants. Thus, therapeutic strategies that employ the adoptive transfer of virus-specific T cells are being clinically investigated to treat and prevent viral diseases in these highly immunocompromised patients. Posoleucel is an off-the-shelf multivirus-specific T cell investigational product for the treatment and prevention of infections due to adenovirus, BK virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus 6 or JC virus.

METHODS

Herein we perform extensive characterization of the phenotype and functional profile of posoleucel to illustrate the cellular properties that may contribute to its in vivo activity.

RESULTS AND CONCLUSIONS

Our results demonstrate that posoleucel is enriched for central and effector memory CD4+ and CD8+ T cells with specificity for posoleucel target viruses and expressing a broad repertoire of T cell receptors. Antigen-driven upregulation of cell-surface molecules and production of cytokine and effector molecules indicative of proliferation, co-stimulation, and cytolytic potential demonstrate the specificity of posoleucel and its potential to mount a broad, polyfunctional, and effective Th1-polarized antiviral response upon viral exposure. We also show the low risk for off-target and nonspecific effects as evidenced by the enrichment of posoleucel in memory T cells, low frequency of naive T cells, and lack of demonstrated alloreactivity in vitro. The efficacy of posoleucel is being explored in four placebo-controlled clinical trials in transplant recipients to treat and prevent viral infections (NCT05179057, NCT05305040, NCT04390113, NCT04605484).

Characterization of a KDM5 small molecule inhibitor with antiviral activity against hepatitis B virus

Chronic hepatitis B (CHB) is a global health care challenge and a major cause of liver disease. To find new therapeutic avenues with a potential to functionally cure chronic Hepatitis B virus (HBV) infection, we performed a focused screen of epigenetic modifiers to identify potential inhibitors of replication or gene expression. From this work we identified isonicotinic acid inhibitors of the histone lysine demethylase 5 (KDM5) with potent anti-HBV activity. To enhance the cellular permeability and liver accumulation of the most potent KDM5 inhibitor identified (GS-080) an ester prodrug was developed (GS-5801) that resulted in improved bioavailability and liver exposure as well as an increased H3K4me3:H3 ratio on chromatin. GS-5801 treatment of HBV-infected primary human hepatocytes reduced the levels of HBV RNA, DNA and antigen. Evaluation of GS-5801 antiviral activity in a humanized mouse model of HBV infection, however, did not result in antiviral efficacy, despite achieving pharmacodynamic levels of H3K4me3:H3 predicted to be efficacious from the in vitro model. Here we discuss potential reasons for the disconnect between in vitro and in vivo efficacy, which highlight the translational difficulties of epigenetic targets for viral diseases.

Group 1 ILCs regulate T cell-mediated liver immunopathology by controlling local IL-2 availability

Group 1 innate lymphoid cells (ILCs), which comprise both natural killer (NK) cells and ILC1s, are important innate effectors that can also positively and negatively influence adaptive immune responses. The latter function is generally ascribed to the ability of NK cells to recognize and kill activated T cells. Here, we used multiphoton intravital microscopy in mouse models of hepatitis B to study the intrahepatic behavior of group 1 ILCs and their cross-talk with hepatitis B virus (HBV)-specific CD8⁺ T cells. We found that hepatocellular antigen recognition by effector CD8⁺ T cells triggered a prominent increase in the number of hepatic NK cells and ILC1s. Group 1 ILCs colocalized and engaged in prolonged interactions with effector CD8⁺ T cells undergoing hepatocellular antigen recognition; however, they did not induce T cell apoptosis. Rather, group 1 ILCs constrained CD8⁺ T cell proliferation by controlling local interleukin-2 (IL-2) availability. Accordingly, group 1 ILC depletion, or genetic removal of their IL-2 receptor a chain, considerably increased the number of intrahepatic HBV-specific effector CD8⁺ T cells and the attendant immunopathology. Together, these results reveal a role for group 1 ILCs in controlling T cell-mediated liver immunopathology by limiting local IL-2 concentration and have implications for the treatment of chronic HBV infection.

Genome-Wide Reprogramming of Transcript Architecture by Temperature Specifies the Developmental States of the Human Pathogen Histoplasma

Eukaryotic cells integrate layers of gene regulation to coordinate complex cellular processes; however, mechanisms of post-transcriptional gene regulation remain poorly studied. The human fungal pathogen Histoplasma capsulatum (Hc) responds to environmental or host temperature by initiating unique transcriptional programs to specify multicellular (hyphae) or unicellular (yeast) developmental states that function in infectivity or pathogenesis, respectively. Here we used recent advances in next-generation sequencing to uncover a novel re-programming of transcript length between Hc developmental cell types. We found that ~2% percent of Hc transcripts exhibit 5’ leader sequences that differ markedly in length between morphogenetic states. Ribosome density and mRNA abundance measurements of differential leader transcripts revealed nuanced transcriptional and translational regulation. One such class of regulated longer leader transcripts exhibited tight transcriptional and translational repression. Further examination of these dually repressed genes revealed that some control Hc morphology and that their strict regulation is necessary for the pathogen to make appropriate developmental decisions in response to temperature.

Eukaryotic cells alter their developmental programs in response to environmental signals. Histoplasma capsulatum (Hc), a ubiquitous fungal pathogen of humans, establishes unique transcriptional programs to specify growth in either a multicellular hyphal form or unicellular yeast form in response to temperature. Since hyphae and yeast are specialized to function in infectivity or pathogenesis, respectively, Hc provides a clinically relevant system in which to query eukaryotic regulatory processes. Here we used next-generation sequencing approaches to annotate the transcriptomes of four distinct Hc strains in response to temperature. We found that a fraction of Hc transcripts have differential transcript architecture in hyphae and yeast, exhibiting 5’ leader sequences that differ markedly in length between morphogenetic states. To begin to understand the effect of these differential leader sequences on expression, we performed the first ribosome density and mRNA abundance measurements in Hc, thereby uncovering transcriptional and translational control that contribute to cell-type regulation.

N-acetylglucosamine (GlcNAc) triggers a rapid, temperature-responsive morphogenetic program in thermally dimorphic fungi

The monosaccharide N-acetylglucosamine (GlcNAc) is a major component of microbial cell walls and is ubiquitous in the environment. GlcNAc stimulates developmental pathways in the fungal pathogen Candida albicans, which is a commensal organism that colonizes the mammalian gut and causes disease in the setting of host immunodeficiency. Here we investigate GlcNAc signaling in thermally dimorphic human fungal pathogens, a group of fungi that are highly evolutionarily diverged from C. albicans and cause disease even in healthy individuals. These soil organisms grow as polarized, multicellular hyphal filaments that transition into a unicellular, pathogenic yeast form when inhaled by a human host. Temperature is the primary environmental cue that promotes reversible cellular differentiation into either yeast or filaments; however, a shift to a lower temperature in vitro induces filamentous growth in an inefficient and asynchronous manner. We found GlcNAc to be a potent and specific inducer of the yeast-to-filament transition in two thermally dimorphic fungi, Histoplasma capsulatum and Blastomyces dermatitidis. In addition to increasing the rate of filamentous growth, micromolar concentrations of GlcNAc induced a robust morphological transition of H. capsulatum after temperature shift that was independent of GlcNAc catabolism, indicating that fungal cells sense GlcNAc to promote filamentation. Whole-genome expression profiling to identify candidate genes involved in establishing the filamentous growth program uncovered two genes encoding GlcNAc transporters, NGT1 and NGT2, that were necessary for H. capsulatum cells to robustly filament in response to GlcNAc. Unexpectedly, NGT1 and NGT2 were important for efficient H. capsulatum yeast-to-filament conversion in standard glucose medium, suggesting that Ngt1 and Ngt2 monitor endogenous levels of GlcNAc to control multicellular filamentous growth in response to temperature. Overall, our work indicates that GlcNAc functions as a highly conserved cue of morphogenesis in fungi, which further enhances the significance of this ubiquitous sugar in cellular signaling in eukaryotes.

Cholesterol catabolism by Mycobacterium tuberculosis requires transcriptional and metabolic adaptations

To understand the adaptation of Mycobacterium tuberculosis to the intracellular environment, we used comprehensive metabolite profiling to identify the biochemical pathways utilized during growth on cholesterol, a critical carbon source during chronic infection. Metabolic alterations observed during cholesterol catabolism centered on propionyl-CoA and pyruvate pools. Consequently, growth on this substrate required the transcriptional induction of the propionyl-CoA-assimilating methylcitrate cycle (MCC) enzymes, via the Rv1129c regulatory protein. We show that both Rv1129c and the MCC enzymes are required for intracellular growth in macrophages and that the growth defect of MCC mutants is largely attributable to the degradation of host-derived cholesterol. Together, these observations define a coordinated transcriptional and metabolic adaptation that is required for scavenging carbon during intracellular growth.

Elucidation and chemical modulation of sulfolipid-1 biosynthesis in Mycobacterium tuberculosis

Mycobacterium tuberculosis possesses unique cell-surface lipids that have been implicated in virulence. One of the most abundant is sulfolipid-1 (SL-1), a tetraacyl-sulfotrehalose glycolipid. Although the early steps in SL-1 biosynthesis are known, the machinery underlying the final acylation reactions is not understood. We provide genetic and biochemical evidence for the activities of two proteins, Chp1 and Sap (corresponding to gene loci rv3822 and rv3821), that complete this pathway. The membrane-associated acyltransferase Chp1 accepts a synthetic diacyl sulfolipid and transfers an acyl group regioselectively from one donor substrate molecule to a second acceptor molecule in two successive reactions to yield a tetraacylated product. Chp1 is fully active in vitro, but in M. tuberculosis, its function is potentiated by the previously identified sulfolipid transporter MmpL8. We also show that the integral membrane protein Sap and MmpL8 are both essential for sulfolipid transport. Finally, the lipase inhibitor tetrahydrolipstatin disrupts Chp1 activity in M. tuberculosis, suggesting an avenue for perturbing SL-1 biosynthesis in vivo. These data complete the SL-1 biosynthetic pathway and corroborate a model in which lipid biosynthesis and transmembrane transport are coupled at the membrane-cytosol interface through the activity of multiple proteins, possibly as a macromolecular complex.

Quantitative proteomic profiling of host-pathogen interactions: the macrophage response to Mycobacterium tuberculosis lipids

Mycobacterium tuberculosis (M. tuberculosis) is an intracellular pathogen possessing a complex mixture of cell wall lipids that are thought to modulate the activities of host macrophages. In this study, we employed two state-of-the-art quantitative proteomic approaches, metabolic labeling SILAC and chemical isobaric tagging iTRAQ, to study changes in macrophage protein expression in response to exposure to M. tuberculosis lipids. From a total of 1286 proteins identified, 463 were discovered by both isotope-labeling strategies at a high consistency, and the rest of proteins were detected by only one of the two approaches. Upon exposure to mycobacterial cell wall lipids, 166 macrophage proteins showed differential expression. These included proteins involved in the immune response, oxidation and reduction, and vesicle transport, as well as other cellular processes. The response of the macrophage proteome to M. tuberculosis lipids reflects the cell's innate defense mechanisms as well as lipid-induced processes that may benefit the pathogen.

Structural characterization of a novel sulfated menaquinone produced by stf3 from Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis, produces unique sulfated metabolites associated with virulence. One such metabolite from M. tuberculosis lipid extracts, S881, has been shown to negatively regulate the virulence of M. tuberculosis in mouse infection studies, and its cell-surface localization suggests a role in modulating host-pathogen interactions. However, a detailed structural analysis of S881 has remained elusive. Here we use high-resolution, high-mass-accuracy, and tandem mass spectrometry to characterize the structure of S881. Exact mass measurements showed that S881 is highly unsaturated, tandem mass spectrometry indicated a polyisoprene-derived structure, and characterization of synthetic structural analogs confirmed that S881 is a previously undescribed sulfated derivative of dihydromenaquinone-9, the primary quinol electron carrier in M. tuberculosis. To our knowledge, this is the first example of a sulfated menaquinone produced in any prokaryote. Together with previous studies, these findings suggest that this redox cofactor may play a role in mycobacterial pathogenesis.

Function and structure of a prokaryotic formylglycine-generating enzyme

Type I sulfatases require an unusual co- or post-translational modification for their activity in hydrolyzing sulfate esters. In eukaryotic sulfatases, an active site cysteine residue is oxidized to the aldehyde-containing C_α-formylglycine residue by the formylglycine-generating enzyme (FGE). The machinery responsible for sulfatase activation is poorly understood in prokaryotes. Here we describe the identification of a prokaryotic FGE from Mycobacterium tuberculosis. In addition, we solved the crystal structure of the Streptomyces coelicolor FGE homolog to 2.1Å resolution. The prokaryotic homolog exhibits remarkable structural similarity to human FGE, including the position of catalytic cysteine residues. Both biochemical and structural data indicate the presence of an oxidized cysteine modification in the active site that may be relevant to catalysis. In addition, we generated a mutant M. tuberculosis strain lacking FGE. Although global sulfatase activity was reduced in the mutant, a significant amount of residual sulfatase activity suggests the presence of FGE-independent sulfatases in this organism.

Clinical dietetics changes due to cost-reduction activities in healthcare systems

OBJECTIVE

This study was designed to assess changes in clinical dietetics due to cost-reduction activities in healthcare systems.

SUBJECTS

1,200 ADA members who indicated that they were employed by acute care hospitals in ADA Area 2 states.

DESIGN

A questionnaire about changes in clinical dietetics staffing and clinical dietitians' activities and responsibilities was developed based on qualitative research. Descriptive statistics, t tests, analysis of variance, chi2 tests, and correlations were calculated.

RESULTS

A total of 342 usable questionnaires (28.5%) were returned. More than one third (37.9%) of respondents reported reductions in the number of clinical dietitians, and 32.2% reported increases in the number of part-time clinical dietitians. Most respondents indicated that they were more involved with high-risk patient interventions, had limited time for inpatient instruction, and experienced an increased patient caseload. Although 45.4% of respondents reported diminished job satisfaction due to recent changes in healthcare systems, some changes, such as increased high-risk patient intervention and referrals, were positively correlated with perceived job satisfaction.

DISCUSSION

Thorough review of current clinical dietetics activities/responsibilities and planning before cost-reduction, restructuring activities may maximize staff utilization without decreased job satisfaction of clinical dietetics staff.

Schwann cell-induced loss of synapses in the central nervous system

Synaptophysin immunostaining of areas of spinal gray matter occupied by radiation-induced intraspinal Schwann cells revealed a loss of immunoreactivity from the neuropil. In contrast, synaptophysin immunoreactivity was preserved on the somata and proximal dendrites of motor neurons. The present study extended these observations to the ultrastructural level and confirmed the absence not only of synapses but also of astrocytes and small- and medium-sized dendrites. These neural elements were abundant and appropriately organized in contiguous areas of irradiated neuropil not occupied by Schwann cells.

Synaptophysin immunoreactivity in spinal white matter of young adult rats

Patterns of synaptophysin immunoreactivity were examined in the ventral and lateral funiculi of rat lumbosacral spinal cords. In normal young adults, dendrites from neurons in the spinal gray matter extended into the ventral and lateral white matter as finger-like projections, immunopositive for synaptophysin. These projections appeared to diminish in size as they extended peripherally and, in general, did not reach the surface of the spinal cord, so that the outer one-third to one-fourth of the funiculi contained little or no immunoreactivity. The spinal cords of some of the animals studied were X-irradiated on the third postnatal day. When examined 6 weeks to 5 months later, the pattern of synaptophysin immunoreactivity was found to be markedly altered in these animals. In general, the synaptophysin immunoreactivity in the white matter was less organized than in the non-irradiated rat. As a result, the finger-like projections, particularly into the lateral funiculi, were not as distinct, and the immunoreactivity appeared to be more diffusely distributed in the white matter. Further, the immunoreactivity was present throughout the thickness of the white matter in the irradiated animals and subpial concentrations were evident, especially along the lateral aspect of the spinal cord. Ultrastructural evaluation of the synaptic profiles revealed no differences between irradiated and non-irradiated animals. The synapses occurred on both the shafts of the dendrites and on the spines. In general, both dendrites and axon terminals were covered by astrocyte processes except at synaptic sites, and the synaptic complexes were surrounded by astrocyte processes. Although the mechanisms underlying the altered pattern of synaptophysin immunoreactivity are not yet understood, they may be related to radiation-induced effects on the glial populations previously reported by the investigators and/or to radiation-induced alterations in reorganization or maturation of dendritic trees.

Transplantation of sciatic nerve segments into normal and glia-depleted spinal cords

Although peripheral nerves are used as guides in attempts to enhance regeneration in the central nervous system (CNS), surprisingly little is known about the interface that develops between the host tissue and the transplanted or implanted peripheral nerve. This study examines host-nerve interfaces following transplantation of segments of sciatic nerve into the spinal cord under two differing conditions, one in which the spinal cord contains normal numbers of glia and one in which the glial population is reduced. The depletion of the glial population is achieved by exposing the lumbosacral region of the spinal cord in 3-day-old rats to X-rays, a model developed in this laboratory. Twenty days later, segments of fresh or frozen sciatic nerves harvested from other 3-day-old rats were transplanted into the lumbar region of spinal cord in irradiated animals and in their non-irradiated littermate controls. Following a 20-day postoperative period, the interfaces between host spinal cord and sciatic nerves were examined ultrastructurally, and pronounced differences were noted. A distinct scar composed of multiple layers of astrocyte processes completely enveloped the transplant in non-irradiated host spinal cord and confined Schwann cells and fibroblasts to the area enclosed by the scar. Terminals from axons that appeared to have traversed the transplant during this 20-day period ended blindly in the astrocytic scar. In contrast, a complete astrocytic scar failed to form around the transplant in the irradiated, glia-depleted hosts, and Schwann cells intermingled with host tissue. Some Schwann cells migrated away from the transplant, which was placed in the dorsal funiculus, along a perivascular route and extended into the gray matter. In some instances Schwann cells were observed in the ventral gray surrounding blood vessels and motoneurons. From these observations, it is clear that the formation of a distinct astrocytic barrier at the host-graft interface is greatly reduced irradiated host. The effects of astrocyte reduction on enhanced regeneration within the spinal cord are discussed.

Microglia, but not astrocytes, react to sciatic nerve injury in aging rats

Peripheral nerve axotomy activates microglia and astrocytes within regions of brainstem or spinal cord from which the nerve arises. The present study demonstrates that unilateral sciatic axotomy in rats 2 to 18 months of age results in differing responses with age between these two glial populations. By 4 days postaxotomy, both astrocytes and microglia become activated in 2-month-old rats, whereas only the microglial population shows evidence of activation in rats 8 to 18 months of age.

Schwann cell invasion of ventral spinal cord: the effect of irradiation on astrocyte barriers

This study examines a radiation-induced invasion and spread of Schwann cells into ventral gray regions of the lumbar spinal cord. The prevalence of these cells within the gray matter and the time course of their appearance in the ventral spinal cord is quite different from the pattern of Schwann cell development in dorsal spinal cord reported previously. The focus is on 2 possible pathways, each involving astrocytic barriers, by which Schwann cells access the ventral gray matter. The first of these is the glia limitans covering the ventral surface of the spinal cord and the possibility that its integrity has been disrupted by the exposure to x-rays. Comparisons of the glia limitans, including its thickness, between irradiated and nonirradiated rats revealed that exposure to radiation did not result in any morphologically discernible alterations. The second barrier examined was the astrocytic covering of blood vessels. In irradiated animals the astrocyte processes that normally surround blood vessels were missing in some instances, and Schwann cells were observed at these sites. The difference between the dorsal and ventral occurrence of Schwann cells is that, whereas Schwann cells primarily follow axons, specifically dorsal root axons, to access the dorsal spinal cord, it appears that the presence of Schwann cells in the ventral portion of the spinal cord where their location is primarily in the gray matter is associated with the vasculature.

Schwann cells can misdirect regrowing neuronal processes

Studies of potentials for dorsal spinal nerve root axons to regrow into the spinal cord involved placement of the tracer HRP/WGA-HRP on the cut end of the nerve root. Following this procedure, labeled neurons were found within the spinal dorsal gray matter. Analyses revealed that spinal neurons influenced by the presence of radiation-induced intraspinal Schwann cells extend misdirected processes into the dorsal root.

Astrocytes in the aged rat spinal cord fail to increase GFAP mRNA following sciatic nerve axotomy

Aging in the brain is associated with specific changes in the astrocyte population. The present study establishes that similar changes occur in the aging spinal cord. The levels of glial fibrillary acidic protein (GFAP) mRNA were significantly increased 0.4-fold in aged 8- to 17-month-old rats compared to young 2-month-old rats. The ability of astrocytes in the aging spinal cord to respond to a non-invasive CNS injury was compared to young rats 4 days following sciatic nerve axotomy. The level of GFAP mRNA was significantly increased 0.5-fold in the young rats in response to axotomy. In contrast, the level of GFAP mRNA in aged rats did not increase following injury above that present in non-axotomized rats of the same age.

Microglial development is altered in immature spinal cord by exposure to radiation

Previous studies in this laboratory have documented that the microglial environment of the immature spinal cord is altered by exposure to ionizing radiation. As a result, the lumbosacral spinal cord is markedly depleted of both oligodendrocytes and astrocytes, while leaving axons and the overall cytoarchitecture intact. The status of the microglia in the irradiated region is unknown and is of interest given the interactions between microglia and astrocytes recently elucidated by others. This study uses both in vivo and in vitro approaches to examine the microglial population in normal and irradiated immature spinal cord. The lectin, Griffonia (Bandeiraea) simplicifolia, was selected since it marks microglia both in paraffin embedded sections and in cell cultures. Light microscopic examinations of spinal cord sections revealed a reduced microglial population in the irradiated region when compared to littermate controls, and a change in morphology of the remaining microglia to that described by others as "activated". Cultures prepared from lumbosacral spinal cords harvested from 3-day-old rats within 2-4 hr following irradiation were compared with cultures derived from their non-irradiated littermates after 8 days in vitro. Cultures from the irradiated spinal cords revealed trends similar to those observed in vivo, i.e. a reduced microglial population and altered morphology. Although all glial cell types were reduced in cultures from irradiated spinal cords, the few microglia present were usually positioned atop astrocytes. The consistency of reduction in all glial populations in this model shows the microglia to be a novel microenvironment for further studies of roles of microglial within the spinal cord.

Glial-glial and glial-neuronal interfaces in radiation-induced, glia-depleted spinal cord

This review summarises some of the major findings derived from studies using the model of a glia-depleted environment developed and characterised in this laboratory. Glial depletion is achieved by exposure of the immature rodent spinal cord to x-radiation which markedly reduces both astrocyte and oligodendrocyte populations and severely impairs myelination. This glia-depleted, hypomyelinated state presents a unique opportunity to examine aspects of spinal cord maturation in the absence of a normal glial population. An associated sequela within 2-3 wk following irradiation is the appearance of Schwann cells in the dorsal portion of the spinal cord. Characteristics of these intraspinal Schwann cells, their patterns of myelination or ensheathment, and their interrelations with the few remaining central glia have been examined. A later sequela is the development of Schwann cells in the ventral aspect of the spinal cord where they occur predominantly in the grey matter. Characteristics of these ventrally situated intraspinal Schwann cells are compared with those of Schwann cells located dorsally. Recently, injury responses have been defined in the glia-depleted spinal cord subsequent to the lesioning of dorsal spinal nerve roots. In otherwise normal animals, dorsal nerve root injury induces an astrocytic reaction within the spinal segments with which the root(s) is/are associated. Lesioning of the 4th lumbar dorsal root on the right side in irradiated or nonirradiated animals results in markedly different glial responses with little astrocytic scarring in the irradiated animals. Tracing studies reveal that these lesioned dorsal root axons regrow rather robustly into the spinal cord in irradiated but not in nonirradiated animals. To examine role(s) of glial cells in preventing this axonal regrowth, glial cells are now being added back to this glia-depleted environment through transplantation of cultured glia into the irradiated area. Transplanted astrocytes establish barrier-like arrangements within the irradiated cords and prevent axonal regrowth into the cord. Studies using other types of glial cultures (oligodendrocyte or mixed) are ongoing.

Schwann cell-neuron relationships in spinal cord gray matter

Schwann cells develop within the ventral gray matter following exposure of lumbosacral spinal cords to x-rays in early postnatal rats. These ventral gray matter Schwann cell aggregates occurred in about 40% of the animals 8 or more weeks following irradiation. Light microscopically these cells appeared to be apposed to somata of large motor neurons, raising a question regarding the fate of axo-somatic synapses. This study focused on neuron-Schwann cell relationships and demonstrated ultrastructurally that the intraspinal Schwann cells established a variety of relationships with the neuronal somata and primary dendrites. These relationships ranged from direct contact without an intervening basal lamina to the presence of synaptic contacts intervening between neuron and Schwann cell basal lamina. Occasionally, the Schwann cells occupied an intermediate position between neurons and blood vessels, suggesting functions similar to those carried out by astrocytes. In these instances, as in all cases of Schwann cell-blood vessel contact, the vessels lacked their normal investiture by astrocytes. Light microscopic evaluation of synaptophysin-immunostained sections revealed decreased immunoreactivity in neuropil occupied by the Schwann cells but confirmed the presence of synapses on neuronal somata. Possible mechanisms underlying Schwann cell induction in the ventral gray matter are discussed. An understanding of the interactions between Schwann cells and the cellular constituents of the gray matter is important in light of attempts to enhance repair in the central nervous system by transplanting Schwann cells into that environment.

Clinical indicators associated with unintentional weight loss and pressure ulcers in elderly residents of nursing facilities

OBJECTIVE

To monitor adults older than 65 years living in nursing facilities and who experience unintentional weight loss of more than 10% of actual body weight in 6 months or more than 5% in 1 month or who have stage II, III, or IV pressure ulcers.

SUBJECTS

We reviewed 290 medical records for unintentional weight loss and 265 for pressure ulcers.

DESIGN

Two data-collecting instruments were used: one for pressure ulcers and one for unintentional weight loss. Indicators for each instrument were selected to monitor clinical conditions that tend to be problem-prone areas for these two populations.

STATISTICAL ANALYSIS

Descriptive statistics were used to calculate the frequency of each indicator for each population.

RESULTS

Of the 24 indicators for unintentional weight loss, the 6 indicators present most often, in descending order, were reduced functional ability, intake of 50% or less of food served for the past 3 consecutive days, chewing problems, serum albumin level less than 35 g/l with normal hydration status, cholesterol level less than 4.1 mmol/L, and refusal of 50% or more of food replacement for the past 7 days. For the residents with pressure ulcers, the indicator present most often was serum albumin level less than 35 g/L with normal hydration status. The three highest intervention indicators were receives 1.2 g protein per kilogram of actual body weight, receives 120 mg or more of vitamin C daily, and receives 1 1/2 times the energy required based on goal body weight. When serum albumin level was documented in the medical record, it was a valid indicator for both diagnoses.

CONCLUSIONS

Inappropriate dietary intake, disease, and disability place residents in nursing facilities at risk for malnutrition. Thus, it is important to obtain laboratory values when assessing elderly residents and determining their nutritional status.

Glial development in primary cultures established from normal and X-irradiated neonatal spinal cord

The glial population of the lumbosacral spinal cord of the rat can be markedly depleted by exposure to ionizing radiation during the first postnatal week. Identification of specific cell populations which survive the exposure to radiation is difficult in situ; therefore, the present investigation used in vitro approaches to address issues related to specific phenotypes and maturational states of glia in cultures derived from non-irradiated (control) and irradiated (experimental) lumbosacral spinal cords of 3-day-old rats. Cultures were established from the spinal cords 2 to 4 hours following irradiation and were compared to cultures from non-irradiated, littermate controls. By 4 days in vitro (DIV) the numbers of cells in experimental cultures were profoundly reduced when compared to controls, and this reduction persisted through the termination of the study (8 DIV). In addition to reduction in numbers, astrocyte phenotypes were altered in experimental cultures, with greater proportions of the astrocyte population being constituted by the flat angular, large angular, and pancake types and a lesser proportion by stellate cells. The non-astrocytic cell types were dramatically reduced as evidenced by the paucity of oligodendrocytes immunoreactive for galactocerebroside and of small, non-process bearing cells binding the lectin, Griffonia (Bandeiraea) simplicifolia, a marker for microglia. Experimental cultures contained an increased incidence of binucleate astrocytes, an increase not restricted to a particular astrocyte phenotype. This study established the feasibility of utilizing this combined in vivo/in vitro approach in assessment of glial populations in immature spinal cords, and further investigations are in progress using this model.

Regeneration of dorsal root axons into experimentally altered glial environments in the rat spinal cord

Exposure of the lumbar spinal cord of rats to X-rays 3 days after birth results in changes in the composition of central glia. Shortly after irradiation, there is both retardation of central myelin formation and a loss of integrity of the astrocyte-derived glia limitans on the dorsal surface of the cord. Subsequently, Schwann cells invade, undergo division and myelinate axons in the dorsal funiculi in the irradiated region of the cord, creating there an environment similar to that of peripheral nerve. The present study was undertaken to compare the ability of lesioned dorsal root axons to grow back into the altered glial environments that exist within the spinal cord after irradiation. This regrowth was assessed by injecting Fluoro-Gold into the spinal cord and subsequently examining neurons in the dorsal root ganglia (DRG) for the presence of this label. Numbers of retrogradely labeled neurons were counted in the DRG in both injured and contralateral non-injured sides. Non-irradiated control rats had almost no labeled DRG neurons on the injured side, whereas Fluoro-Gold labeled neurons were observed in substantial numbers in the DRG on the injured side of irradiated rats. There was a definite trend in the data, indicating that the longer the interval between irradiation and root injury, the greater the number of labeled neurons. Since the Fluoro-Gold labeling technique does not allow for visualization of the labeled axons within the spinal cord, a few animals were used to assess anterograde labeling with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP/HRP) from the dorsal root into the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Regrowth of dorsal root axons into a radiation-induced glial-deficient environment in the spinal cord

Exposure of the lumbosacral spinal cord of early postnatal rats to X-rays reduces the glial populations within the irradiated region. The present study examines the ability of axons of a dorsal root subjected to a crush-freeze lesion to grow back into this glial-deficient spinal cord environment, in contrast to the non-irradiated rat. Ultrastructural examination of the dorsal root entry zone (DREZ) 60 days after root injury revealed a well-formed astrocytic scar in this zone and adjacent regions of spinal cord in non-irradiated rats. In contrast, scar formation did not occur in irradiated root-lesioned animals in which the astrocytic response was quite limited. Axons were present in the DREZ and underlying spinal cord in irradiated root-lesioned rats at this time but were absent from these regions in the non-irradiated lesioned controls. These ultrastructural findings are highly suggestive that axons are capable of regrowth into the irradiated spinal cord. Axonal regrowth was assessed further by tracing techniques after application of a combination of peroxidase-labeled wheat germ agglutinin and horseradish peroxidase to the cut end of the root distal to the previously injured site. Labeled axons were readily identified within the spinal gray matter in irradiated lesioned but not in the non-irradiated lesioned rats. These data, together with the ultrastructural observations, are supportive of regrowth of the dorsal root axons into the spinal cord. The radiation-induced changes in the glial populations are discussed with regard to conversion of a normally non-permissive environment into one conducive for axonal regrowth.

Patterns of Schwann cell myelination of axons within the spinal cord

Patterns of Schwann cell myelination of long-projecting axons in the spinal cord were studied. The goal was to determine if such axons arising from neurons whose somata and processes are normally confined to the central nervous system can interact effectively with Schwann cells, the myelinating cells of the peripheral nervous system. In one paradigm Schwann cells develop in the dorsal funiculi of the lumbar spinal cord subsequent to radiation-induced alterations in development of the glial populations. Light and electron microscopic evaluations were made in the region of the corticospinal tracts (CSTs), which in the rat occupy the base of the dorsal funiculi. At 90 days following irradiation, larger axons of these tracts (> 1.5 microns in diameter) were myelinated by Schwann cells, and smaller axons were ensheathed by them. In the second paradigm cultured Schwann cells were injected into the medial portions of the ventral funiculi at 13 days post-irradiation when the glial population was markedly reduced. Earlier investigations from this laboratory demonstrated that Schwann cells do not develop in the irradiated ventral funiculi, as they do dorsally. When placed in proximity to long-projecting axons in the medial portion of the ventral funiculi, the Schwann cells either formed compact myelin sheaths or ensheathed axons, depending upon their diameter. Fasciculation and presence of collagen were characteristic of this paradigm but were absent from the Schwann cell-occupied regions of the CSTs. This probably relates to the presence of fibroblasts in the injected cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Standards of Practice criteria: consultant dietitians in health care facilities

Establishment of quality assurance guidelines is becoming increasingly necessary in long-term-care facilities. The Consultant Dietitians in Health Care Facilities (CD-HCF) dietetic practice group of The American Dietetic Association (ADA) developed 27 documentations/outcome-oriented guidelines for quality assurance. The documentations were categorized according to the six Standards of Practice developed by ADA. The six general categories covered establishment of performance criteria, development of individual practice plans, knowledge of nutrition, self-development, research, and use of resources. We surveyed 188 members of the CD-HCF about their levels of agreement in theory with and frequency of completion for each documentation. Of the respondents, 165 (88%) were employed in long-term-care facilities. Respondents had worked as consultant dietitians for a mean of 10 years. Four standards and the total questionnaire had highly significant positive correlations between agreement in theory and frequency of completion. The findings indicate that consultant dietitians agree with the theory of the documentation and frequently complete documentation.

Schwann cell induction in the ventral portion of the spinal cord

Schwann cell development can be induced in a predictable manner in the dorsal aspect of the lumbosacral spinal cord of the immature rat by exposing that structure to ionizing radiation. This development occurs in essentially all animals and becomes evident between 2 and 3 weeks postirradiation (P-I). Occasionally, intraspinal Schwann cells were observed ventrally at later intervals following irradiation, usually more than 45 days P-I. The present study focused on the development of Schwann cells within the ventral portion of the lumbosacral spinal cord in 53 animals followed for periods up to 7 months P-I. Ventrally located intraspinal Schwann cells developed in approximately 40% of these animals, in contrast to the development dorsally in all animals. The ventrally located aggregates were generally smaller than those dorsally and occurred more frequently in gray matter than in white matter. An interesting feature of the ventrally located Schwann cells was that they were often associated with blood vessels, which raised the possibility that these cells developed from undifferentiated cells of the vascular walls or used the vessels as a pathway for migration.

Glial response to dorsal root lesion in the irradiated spinal cord

Exposure of the rat lumbar spinal cord to X-rays during the early postnatal period results in a marked reduction in the glial populations within the irradiated region. The present study was undertaken to determine what effects this reduction of glia, particularly astrocytes, has on the pattern and characteristics of the scar formation that follows root injury in the normal spinal cord. Morphological assessments 60 days following injury of the right L4 dorsal root revealed a distinct difference in the extent of the astrocyte response between the irradiated and the nonirradiated rats. In the nonirradiated animals, a thick astrocytic scar composed of multiple layers of astrocyte processes formed over the dorsal horn and adjacent portions of the dorsal surface of the cord. This astrocytic response was not confined to the surface of the spinal cord but extended also into the root, i.e., into regions normally considered as PNS. In irradiated rats, the astrocytes did not form a thick scar nor did they extend into the injured root. Instead, they formed a glia limitans and were at most only one or two layers thick over the region of cord comparable to that occupied by the thick astrocytic scar in the nonirradiated rats. Mechanisms involved in the glial response of the irradiated spinal cord to dorsal root injury are discussed, particularly with regard to the possible positive effect that this reduction in scar formation may have on regrowth of injured dorsal root axons into the spinal cord environment.

Radial glia give rise to perinodal processes

Nodes of Ranvier in the central nervous system in mammals are characterized by the presence of perinodal astrocytic processes. This study examines the association between processes of radial glia and the axolemma at nodes of Ranvier in the spinal cord of the mature axolotl, an animal in which radial glia represent a large portion of the total glial population. The radial glial cells have their cell bodies located close to the central canal. Those situated dorsal to the canal send long processes to the dorsal surface of the spinal cord. Along this trajectory these processes coalesce into large fascicles in the midline and form the dorsal median septum. Slender branches rise from the processes in these fascicles and extend into the adjacent white matter to terminate in close apposition to the axolemma at nodes of Ranvier. This arrangement provides an intracellular pathway extending from the perinodal region to the surface of the spinal cord. Radial glia ventral to the central canal give rise to processes that project to the glia limitans adjacent to the ventral spinal artery. These ventrally projecting processes appear to be more irregular in their branching pattern than their dorsal counterparts. Multiple slender processes are seen in close apposition to the nodal axolemma of myelinated axons in the ventral white commissure, again providing an intracellular pathway that runs from the perinodal region to the cord surface. In one instance a radial glial process was observed to occupy a pocket formed by the invagination of the nodal axolemma. The axonal cytoplasm adjacent to the invagination contained a variety of organelles, e.g. multivesicular bodies, vesicles and endoplasmic reticulum, suggesting that this relationship between the radial glial process and the axon is more than a passive interaction. These observations are consistent with the view that processes of radial glial cells may regulate the extracellular environment adjacent to the nodal axolemma, and/or play an active role in the maintenance of the nodal membrane. The existence of perinodally-directed processes of radial glial cells in the salamander indicates that this axo-glial specialization reflects an important functional interaction preserved across a large segment of the phylogenetic scale.

Development of the rat corticospinal tract through an altered glial environment

The major corticospinal tract (CST) in the rat is located at the base of the dorsal funiculus. It is a late-developing tract, and the growth of its axons into the lumbosacral region of the spinal cord does not occur until postnatal days 5 and 6. This delay is taken advantage of in this study in order to evaluate the effects of a markedly reduced glial population on ingrowth of the CST axons into the lumbosacral spinal cord. A reduction of the glial population is achieved by exposure of this region of spinal cord to X-radiation at 3 days of age. Growth of CST axons into and through the lumbosacral spinal cord in rats in which this region has undergone a radiation-induced depletion of glial cells is compared with that in their non-irradiated littermate controls by axonal tracing techniques using horseradish peroxidase (HRP). The HRP was applied directly to the motor cortices of normal and irradiated rats, and at all ages studied, there was anterograde filling of CST axons and their growth cones. At 3 days postnatally, the age when the lumbosacral spinal cord was irradiated in the experimental animals, CST axons were present in the more rostral thoracic levels. CST axons were observed in the lumbar region of non-irradiated rats on day 5, and by day 7 they were present at sacral levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Astrocytic reactions in spinal gray matter following sciatic axotomy

Astrocytic responses following unilateral sciatic nerve axotomy were examined in the spinal gray matter. Using an antiserum to glial fibrillary acidic protein (GFAP), immunoreactive astrocytes were studied in both dorsal and ventral gray matter at intervals from 2 days through 34 days post-axotomy. In all axotomized animals, increased numbers of strongly immunoreactive astrocytes were present in the gray matter ipsilateral to the surgery. Such astrocytes were absent from the contralateral intact side and from gray matter bilaterally in adjacent spinal segments not involved in formation of the sciatic nerve. These GFAP-positive astrocytes occurred not only in association with large motor neurons in the ventral gray matter but also in association with central processes of dorsal root ganglion neurons in the dorsal gray matter. The response was quite rapid, being discernible both dorsally and ventrally as early as the second post-operative day. This increased GFAP immunoreactivity persisted throughout the entire observation period, with the perikarya of large ventral motor neurons appearing to become surrounded or encapsulated by the immunoreactive processes. A further alteration noted at the longest post-operative intervals was the presence in the ventral gray matter of astrocytes appearing to be binucleate. The data obtained indicate that the astrocytic response is not related solely to reactions in motor neurons and, furthermore, the rapidity with which it develops in the dorsal gray matter suggests that its induction is not dependent upon transganglionic degeneration, which others have reported to occur weeks after peripheral nerve injury.

Interactions between Schwann cells and CNS axons following a delay in the normal formation of central myelin

Irradiation of the rat spinal cord during the first postnatal week results in a profound reduction of oligodendrocyte myelin formation in the dorsal funiculi (DF). Despite this absence of myelin, however, axons in the irradiated region in the DF increase in diameter and approximate the size distribution seen in the control spinal cord. By 25 days of age Schwann cells are present in the irradiated DF where they undergo cell division and myelinate the axons. During the early stages of this myelin formation, these intraspinal Schwann cells exhibit a relationship to axons that is somewhat different from that seen in the normal developing peripheral nervous system (PNS). For example, within a given region, intraspinal Schwann cells myelinate axons of large diameter prior to ensheathing bundles of small diameter axons. Additionally, during myelination a Schwann cell will surround a single axon with multiple processes which appear to compete for contact with the axolemma. On axons of larger diameter, the elaboration of these processes is so excessive that it is often difficult to trace them back to the parent Schwann cell. Later, when a single process establishes several spirals about an axon, additional processes are no longer elaborated, and the "extra" processes disappear as myelin formation advances to the stage of compact lamellae. Thereafter, the myelin sheath continues to form in a normal manner. Excess processes have been observed during myelinogenesis in the normal developing PNS, but their frequency in that environment is much less than in the irradiated cord. These observations support the hypothesis that the signal(s) to initiate myelin formation are expressed on the axolemmal surface and are controlled by the neuron. In addition, these observations suggest that the delay in myelination results in an affinity or tropism between axons and Schwann cells which exceeds the level existing at the normal time of myelin formation.

Development of NADPH diaphorase-positive pedunculopontine nucleus neurons

Nicotinamide adenine dinucleotide phosphate (NAD-PH) diaphorase histochemistry was used to localize cholinergic neurons in the pedunculopontine nucleus of neonatal and adult rats. Measurements of cell body areas revealed an average area around 200 microns2 at birth, followed by a significant increase to approximately 500 microns2 by 2 weeks of age. Thereafter, there was a decrease in cell area such that by 5 weeks of age the neurons had attained their adult size of around 300 microns2. The marked increase in cell size at the end of 2 weeks of age is discussed in relation to significant events in the development of locomotor and other rhythmic function control systems.

Temporary adhesions between axons and myelin-forming processes

Following irradiation, the dorsal funiculus of the lumbosacral spinal cord in the rat undergoes the following sequence of events: (a) a marked reduction of the normal glial population, (b) an absence of oligodendrocyte myelin formation, (c) the invasion and proliferation of Schwann cells, and (d) the myelination of axons within the cord by Schwann cells. The present study demonstrates that, during the latter process, junctional complexes develop between these intraspinal Schwann cells and the axolemma. These complexes are present at sites of probable initial contact between the two membranes. As the Schwann cell process begins to wrap the axons, these junctional complexes are located between the inner spiraling process of the Schwann cell and the axon. With the advancement of myelin formation to the stage of 8 to 9 compact spirals, these contacts are rarely observed. Spinal cords from normal 8-day-old rats were examined in order to determine if such contacts occur during myelination by oligodendrocytes. Although they are more difficult to detect in the normal animal due to the abundance of glial processes, similar junctional complexes occur between oligodendrocyte processes and axons. These observations suggest that these complexes may serve to stabilize and to guide the myelin-forming process around the perimeter of the axon. Additionally, these junctions may play an active role in the advancement of the inner spiraling process by forming temporary adhesions between the axolemma and the adjacent myelin-forming process. Coated vesicles are commonly observed fused with the axolemma of axons which are in the early stages of myelination. These coated vesicles may be involved in the insertion or the deletion of junctional membrane.

Proliferation of rat intraspinal Schwann cells following tellurium intoxication

A stable population of intraspinal Schwann cells, which developed following early postnatal irradiation of the spinal cord, was challenged by the addition of tellurium (Te) to the diet beginning at 30 days of age. Schwann cells incorporating [3H]thymidine were identified by 1 micron autoradiographs and by conventional electron microscopy of adjacent thin sections. Autoradiographs of areas with Schwann cell myelination showed extensive labelling of cells in the Te-fed animals. In contrast, control animals which were not fed Te showed little evidence of labelled Schwann cells. These data indicate that Schwann cells in the intraspinal environment show a proliferative response to the presence of Te in the rat's diet, as do Schwann cells in their normal extraspinal milieu.

Schwann cell myelination of the myelin deficient rat spinal cord following X-irradiation

The myelin-deficient (md) rat is an X-linked myelin mutant that has an abnormality of oligodendrocytes and a severe paucity of myelin throughout the CNS. This lack of myelin makes it an ideal model in which to study the cellular interactions that occur when "foreign" myelinating cells are induced in the milieu of this nonmyelinated CNS. In this study, Schwann cells were induced in the lumbosacral spinal cord by exposing it to radiation, a technique demonstrated repeatedly in other nonmutant strains of rats. Md rats and their age-matched littermates were irradiated (3,000 to 4,000 R) at 3 days of age and perfused 16-22 days later after pulse labeling with tritiated thymidine. In the md rat, Schwann cell invasion progressed from the area of the spinal cord-nerve root junction and extended into the dorsal columns and adjacent gray matter. Autoradiographic evidence revealed that many of these cells incorporated 3H-thymidine, indicating that they were undergoing proliferation. Ultrastructural observations showed that there was an integration of these intraspinal Schwann cells with the cells normally occurring in this environment, i.e., oligodendrocytes and astrocytes. The extent of migration and division of Schwann cells, as well as their interactions with glial cells, were similar to those seen in the nonmutant irradiated littermates. These studies provide conclusive evidence that md rat axons are normal with respect to their ability to provide trophic and mitogenic signals to myelinating cells.

Cytoplasmic membrane elaborations in oligodendrocytes during myelination of spinal motoneuron axons

The ultrastructure of paranodal oligodendroglial cytoplasm, which is located in proximity to the forming myelin sheath, was studied during maturation of spinal motoneuron axons in rat. At 8 days postnatal, the paranodal oligodendroglial loops contain a network of membrane-bound tubulovesicular elements. These membrane elaborations are most common in oligodendroglial loops attached to the outermost layers of the myelin sheath, i.e., paranodal loops closest to the nodal gap. The number of oligodendroglial cytoplasmic profiles per paranodal loop falls over the course of five to ten sequential paranodal loops, and these profiles are nearly absent in paranodal oligodendroglial cytoplasm located distant from the nodal gap. Oligodendrocytes in spinal cords of 14- and 20-day-old rats and of adult rats did not exhibit networks of tubulovesicular profiles. The appearance of these membrane organelles within oligodendroglial cytoplasm during myelin maturation suggests increased membrane turnover within paranodal cytoplasm located adjacent to the axon that is being myelinated. Membrane turnover within oligodendrocytes may reflect axonal modulation of glial function during myelination.

Effects of delayed myelination by oligodendrocytes and Schwann cells on the macromolecular structure of axonal membrane in rat spinal cord

The macromolecular structure of axonal membrane from dorsal funiculi of control and irradiated spinal cord of 45-day-old rats was examined with freeze-fracture electron microscopy. In control spinal cords, virtually all myelination is mediated by oligodendrocytes, and the internodal axonal membrane of these fibres displays highly asymmetrical partitioning of intramembranous particles (IMPs). The internodal P-face particle density is approximately 2350IMPs per micron 2, whereas the E-face IMP density is approximately 150 per micron 2. In control dorsal spinal roots, myelination is mediated by Schwann cells, and the ultrastructure of the internodal axolemma of the myelinated fibres is similar to that displayed by myelinated fibres of dorsal funiculi. On the internodal P-face of Schwann cell-myelinated fibres the IMP density is approximately 2350 per micron 2, whereas on the E-face the density is approximately 175 per micron 2. Irradiation of the lumbosacral spinal cord at 3 days of age results in a glial cell-deficient region within the spinal cord such that myelination in irradiated dorsal funiculi is delayed and subsequent myelination is mediated by both oligodendrocytes and Schwann cells. By 45 days of age, dorsal funiculi of irradiated spinal cords are well populated with fibres myelinated by oligodendrocytes and Schwann cells. However, fibres myelinated by oligodendrocytes display very thin myelin sheaths whereas Schwann cell-myelinated fibres exhibit myelin sheaths with normal thicknesses. Internodal membrane of fibres myelinated by Schwann cells and oligodendrocytes exhibit similar macromolecular structure, with approximately 2400 IMPs per micron 2 on P-faces and approximately 150 IMPs per micron 2 on E-faces. Occasional large (greater than 1.5 micron diameter) axons without glial-Schwann cell ensheathment are observed. These axons display a high density of P-face particles (approximately 2000 per micron 2) and a moderate density (approximately 350 per micron 2) of E-face IMPs on their fracture faces. These results demonstrate that CNS fibers exhibit similar axonal membrane ultrastructure irrespective of whether they are myelinated by Schwann cells or oligodendrocytes, or whether myelination is delayed. Moreover, when myelination does not occur, the axolemmal E-face IMP density, which may be related to the density of voltage-sensitive sodium channels, is not reduced.

Degenerative changes in rat intraspinal Schwann cells following tellurium intoxication

A diet containing 1.25% elemental tellurium (Te) when fed to rats in week 3 of life produces acute peripheral nervous system (PNS) demyelination. The purpose of this investigation was to determine whether Te has the same neurotoxic effect on Schwann cells and their associated myelin when located within the spinal cord. Schwann cells were induced into the CNS by irradiating the lumbosacral spinal cord of 3 day-old rats with 4000 rads of soft X-rays (Heard & Gilmore, 1980). At 22-28 days of age, a diet containing 1.25% Te was fed to half of these rats, and others were fed on rat chow alone. Non-irradiated rats of the same age were divided into two similarly fed groups. At intervals from 2 to 15 days after the initiation of this diet, the rats were perfused and the irradiated portion of the cord, or comparable level in non-irradiated rats, was trimmed and processed for light and electron microscopy and immunocytochemistry. All rats fed Te became paretic by 6-7 days, and diffuse demyelination with obvious degenerative changes in Schwann cells was seen in the nerve roots. Immunocytochemical localization of Schwann cells and peripheral myelin in the spinal cord was demonstrated using Po antiserum, and in these areas the reduction of astrocytes and their processes was shown using sections incubated with GFAP antiserum. In these areas, as in the roots, there was myelin lamellar separation, and many Schwann cells contained cytoplasmic vacuoles, hypertrophied lysosomal structures and myelin debris. Adjacent oligodendrocytes and CNS myelin were apparently unaffected, confirming a differential susceptibility of oligodendrocytes and Schwann cells. There were no Schwann cell abnormalities in the non Te-fed irradiated rats. This experimental model provides a situation in which other neurotoxic compounds can be evaluated to compare their effects on CNS and PNS myelin in the same milieu.

Dorsal-ventral differences in the glia limitans of the spinal cord: an ultrastructural study in developing normal and irradiated rats

The dorsal and ventral surfaces of the lumbosacral spinal cord were examined in normal and irradiated postnatal rats. In normal rats between three and 13 days postnatal (DP), the glia limitans (GL) of the ventral surface was a more complex structure than the dorsal GL. This greater degree of complexity was manifested in a greater number of subpial astrocytes, a greater number of radial glial processes and a more advanced state in differentiation of its constituents. In rats irradiated at three DP and examined at 13 DP, the ventral GL remained intact and relatively unaffected by the radiation. In contrast, the dorsal GL was disrupted, and Schwann cells were seen within the dorsal funiculus. The ventral GL of the rat lumbosacral spinal cord is a more substantial structure than the dorsal GL during normal development. This factor alone may account for the integrity of the barrier properties of the ventral GL following radiation. However, our observations suggest that subpial astrocytes of the dorsal GL are more susceptible to radiation damage at three DP than the subpial astrocytes and radial glia of the ventral GL.

Perinodal astrocytic processes at nodes of Ranvier in developing normal and glial cell deficient rat spinal cord

This study examined, during normal development and during the development of a glial cell deficient axon population, the nature of astrocyte involvement at the central nodes of Ranvier on spinal cord axons. One condition examined was the ventral funiculus of normal 7-day-old rats. At this age, the lumbar spinal cord underwent an active phase of gliogenesis, and axons were seen in various stages of myelination. Perinodal astrocytic processes were routinely observed at nodes of axons on which myelin sheaths exceeded 8 compact lamellae. Perinodal astrocytic processes were also seen in close proximity to axolemma at most developing nodes. This study also examined the lumbar spinal cords of rats which were X-irradiated on the third postnatal day. This procedure caused a profound reduction in the astrocyte and oligodendrocyte population in 13- and 18-day-old rats, while sparing the neuronal elements. Thus, axo-glial relationships observed in this tissue are unlikely to be random occurrences. Despite the reduction in glial cells, some oligodendrocyte-myelinated axons were observed in the irradiated spinal cords. Perinodal astrocytes were seen at all oligodendrocyte-derived nodes observed in the irradiated cord and appeared to have a specific relationship to the node of Ranvier. The presence of astrocytic processes at the normal, developing node and at the nodes in glial cell deficient spinal cords suggests that astrocytes may be necessary to the function of nodal axolemma. In irradiated spinal cords, where the glial cells are markedly reduced, apposition between astrocytic and oligodendrocytic membrane at the paranode and internode was also seen and was so common that it is highly unlikely to be due to random occurrences. These observations further suggest that in addition to the presumptive role at the nodes, astrocytes may play an inductive or supportive role in the development and maintenance of central myelin.

A comparison of histopathologic changes following X-irradiation of mid-thoracic and lumbosacral levels of neonatal rat spinal cord

Light microscopic changes were studied in the dorsal funiculi of spinal cords from rats irradiated (4000 R) at 3 days of age and killed from 9-60 days postirradiation (P-I). The irradiated site was limited to a 5-mm length of mid-thoracic spinal cord (T only) in one group of rats, to a 5-mm length of lumbosacral spinal cord (L only) in a second group, and to 5-mm lengths of both mid-thoracic and lumbosacral spinal cord (T/L) in the third group. Changes in the lumbosacral regions were essentially the same in both L only and T/L irradiated groups. These changes included a decreased neuroglial population and a concurrent state of hypomyelination from 9-30 days P-I. In contrast, in the mid-thoracic regions of T only and T/L irradiated groups the decrease in the neuroglial population was obvious only through 13 days P-I, and by 30 days this population resembled that of the controls. The irradiated mid-thoracic areas were hypomyelinated, with the fasciculus gracilis showing a greater degree of hypomyelination than the fasciculus cuneatus. By 25 days P-I, myelination appeared to be normal in these areas. Scattered hemorrhages were noted in both lumbosacral and mid-thoracic regions, but necrotic areas occurred only at the lumbosacral level. In general, the mid-thoracic area appeared to be less sensitive to x-radiation at 3 days of age than the lumbosacral area. These data suggest that there may be marked differences in the developmental states of cells at these two levels at 3 days of age.

Membrane ultrastructure of developing axons in glial cell deficient rat spinal cord

In order to investigate axolemmal development in a glial cell deficient environment, normal and irradiated dorsal funiculus in rat lumbosacral spinal cord was examined by freeze-fracture electron microscopy. At 3 days of age, normal fibres are all unmyelinated and of small (less than 0.5 micron) diameter. The unmyelinated axons have a moderate density (approximately 850 microns-2) of intramembranous particles (IMPs) on P-fracture faces and a low IMP density (approximately 300 microns-2) on E-faces. IMPs are homogeneously distributed along both fracture faces. By 19 days of age, the normal dorsal funiculus is well populated with myelinated axons and glial cells, as well as a sizable population of unmyelinated fibres. Nearly all of the myelinated fibres have a large (greater than 1.0 micron) diameter; whereas, most unmyelinated axons are of small (less than 0.5 micron) calibre. The axolemma of unmyelinated axons is relatively undifferentiated, with an asymmetrical distribution of IMPs (P-face: approximately 1100 microns-2; E-face: approximately 450 microns-2). Myelinated fibres show nodal and paranodal regions with P-face and E-face ultrastructure similar to previous descriptions. Internodal axolemma appears relatively homogeneous, with P-faces being highly particulate (approximately 2100 microns-2) and a low IMP density (approximately 200 microns-2) on E-faces. Following irradiation of the lumbosacral spinal cord at 3 days of age, there is a severe reduction in the number of glial cells and myelinated fibres in this region when the tissue is examined at 19 days of age. Despite the deficiency of glial cells in this tissue, axonal and axolemmal development continue. Numerous large (greater than 1.0 micron) diameter axons are present in this irradiated tissue. Large diameter axons show a high (approximately 2000 microns-2) density of IMPs on P-faces; E-face IMP density remains at approximately 440 micron-2. Small calibre axons also have an asymmetrical distribution of particles (P-face: approximately 1100 microns-2; E-face: 280 microns-2). The axolemmal E-faces of some glial cell deprived fibres exhibit regions with greater than normal (approximately 750 microns-2) density of IMPs. These results demonstrate that some aspects of axonal and axolemmal development continue in a glial cell deficient environment, and it is suggested that axolemmal ultrastructure is, at least in part, independent of glial cell association.

Glial proliferation in the irradiated rat spinal cord

The identity of mitotic cells in the ventral half of the irradiated spinal cord in 13-day-old rats was studied by light and electron microscopy. At this post-irradiation interval, astrocytes as well as oligodendrocytes are markedly reduced in both gray and white matter, and few myelin sheaths are present. Earlier studies showed incorporation of 3H-thymidine into cells identified light-microscopically as neuroglia. In the present study, a number of mitotic cells were identified in thick plastic sections. When adjacent thin sections were examined by electron microscopy, these mitotic cells were identified ultrastructurally as astroglia on the basis of the bundles of filaments in their cytoplasm and the irregular outline of the cell body and its processes. It is apparent from this study that astroglia proliferate prior to the delayed myelination that occurs later in the glial cell deprived ventral irradiated cord.

Central canal area in the early postnatal rat: normal development and radiation-induced changes

The spinal central canal area in the early postnatal rat differs markedly in appearance from that in the adult. Dorsally and ventrally, the walls of the canal lack nuclei and appear to be composed of processes from cell bodies at some distance from the lumen. Additionally, a densely packed cluster of cells similar to those in the lateral walls is situated ventral to the canal area. Preliminary data indicated that the cells in this cluster were extremely susceptible to ionizing radiation; the present study: (1) characterizes these cells ultrastructurally in the normal animal; and (2) examines radiation-induced changes. Ultrastructurally, the cells forming this cluster in the normal 3-day-old rat were tightly packed, and their outlines followed the contours of adjacent cells. The cytoplasm, which contained an abundance of organelles, including distinct, wide-bore endoplasmic reticulum with darkly stained cisternae, occasionally surrounded bundles of axons. Synapses and junctional complexes were absent. Both nuclear and cytoplasmic characteristics are those of immature astrocytes. By 6 h following irradiation of the 3-day-old, many cells in this cluster were pyknotic, and by 24 h the cluster had essentially disappeared. The number of cells surrounding the lumen decreased less rapidly than in the cluster. By 10 days post-irradiation (P-I) this number was approximately 39% less than in the control. These changes indicated a differential sensitivity to ionizing radiation between the cells of the ventral cluster and those elsewhere in the central canal area.

Interactions between intraspinal Schwann cells and the cellular constituents normally occurring in the spinal cord: an ultrastructural study in the irradiated rat

Relationships between intraspinal Schwann cells and neuroglia, particularly, astrocytes, were studied following X-irradiation of the spinal cord in 3-day-old rats. Initially, this exposure results in a depletion of the neuroglial population. By 10 days post-irradiation (P-I), gaps occur in the glia limitans, although the overlying basal lamina remains intact. Development of and myelination by intraspinal Schwann cells is well underway by 15 days P-I. These Schwann cell-occupied regions have a paucity of astrocyte processes, a finding which persists throughout the study (60 days P-I), and several types of Schwann cell-neuroglial interfaces are observed, including: (1) astrocyte separation of Schwann cells from oligodendrocyte-myelinated regions; (2) intermingling of Schwann cell-myelinated axons and oligodendrocyte-myelinated axons in the absence of astrocyte processes; and (3) ensheathment of unmyelinated axons by astrocyte processes which separate these axons from the Schwann cells. The gaps in the glia limitans widen as the P-I interval increases. At 45 and 60 days P-I, the basal lamina no longer forms a singular, continuous covering over the spinal cord surface, but follows instead a rather tortuous course over the disrupted glia limitans and the intraspinal Schwann cells. Although the mode of initial occurrence of Schwann cells within the spinal cord is not yet understood, the data indicate that the astrocyte population is involved in that process, as well as in limiting the further development of Schwann cells within the substance of the spinal cord.

Patterns of x-radiation-induced Schwann cell development in spinal cords of immature rats

Schwann cells, Schwann cell myelin, and connective tissue components develop in the spinal cord of the immature rat following exposure to x-rays. For the purposes of this paper, these intraspinal peripheral nervous tissue constituents are referred to as IPNT. A series of investigations are in progress to elucidate factors related to the development of IPNT, and the present study is a light microscopic evaluation of the relationship between the amount of radiation administered (1,000-3,000R) to the lumbosacral spinal cord in 3-day-old rats and the incidence and distribution of IPNT at intervals up to 60 days postirradiation (P-I). The results showed that IPNT was present in only 33% of the rats exposed to 1,000R, whereas its presence was observed in 86% or more of those in the 2,000-, 2,500-, and 3,000R groups. The distribution of IPNT was quite limited in the 1,000R group, where it was restricted to the spinal cord-dorsal root junction and was found in only a few sections within the irradiated area. The distribution was more widespread with increasing amounts of radiation, and IPNT occupied substantial portions of the dorsal funiculi and extended into the dorsal gray matter in the 3,000R group. In all aR mals developing IPNT in the groups receiving 2,000R or more, the IPNT was present in essentially all sections from the irradiated area. Further studies will compare in detail spinal cords exposed to 1,000R in which IPNT is an infrequent, limited occurrence with those exposed to higher doses where IPNT occurs in a more widespread fashion in essentially all animals.