Emergence of three myelin proteins in oligodendrocytes cultured without neurons.

Oligodendrocytes, the myelin-forming cells of the central nervous system, were cultured from newborn rat brain and optic nerve to allow us to analyze whether two transmembranous myelin proteins, myelin-associated glycoprotein (MAG) and proteolipid protein (PLP), were expressed together with myelin basic protein (MBP) in defined medium with low serum and in the absence of neurons. Using double label immunofluorescence, we investigated when and where these three myelin proteins appeared in cells expressing galactocerebroside (GC), a specific marker for the oligodendrocyte membrane. We found that a proportion of oligodendrocytes derived from brain and optic nerve invariably express MBP, MAG, and PLP about a week after the emergence of GC, which occurs around birth. In brain-derived oligodendrocytes, MBP and MAG first emerge between the fifth and the seventh day after birth, followed by PLP 1 to 2 d later. All three proteins were confined to the cell body at that time, although an extensive network of GC positive processes had already developed. Each protein shows a specific cytoplasmic localization: diffuse for MBP, mostly perinuclear for MAG, and particulate for PLP. Interestingly, MAG, which may be involved in glial-axon interactions, is the first myelin protein detected in the processes at approximately 10 d after birth. MBP and PLP are only seen in these locations after 15 d. All GC-positive cells express the three myelin proteins by day 19. Simultaneously, numerous membrane and myelin whorls accumulate along the oligodendrocyte surface. The sequential emergence, cytoplasmic location, and peak of expression of these three myelin proteins in vitro follow a pattern similar to that described in vivo and, therefore, are independent of continuous neuronal influences. Such cultures provide a convenient system to study factors regulating expression of myelin proteins.

The initial events in myelin synthesis: orientation of proteolipid protein in the plasma membrane of cultured oligodendrocytes.

Proteolipid protein (PLP) is the most abundant transmembrane protein in myelin of the central nervous system. Conflicting models of PLP topology have been generated by computer predictions based on its primary sequence and experiments with purified myelin. We have examined the initial events in myelin synthesis, including the insertion and orientation of PLP in the plasma membrane, in rat oligodendrocytes which express PLP and the other myelin-specific proteins when cultured without neurons (Dubois-Dalcq, M., T. Behar, L. Hudson, and R. A. Lazzarini. 1986. J. Cell Biol. 102:384-392). These cells, identified by the presence of surface galactocerebroside, the major myelin glycolipid, were stained with six anti-peptide antibodies directed against hydrophilic or short hydrophobic sequences of PLP. Five of these anti-peptide antibodies specifically stained living oligodendrocytes. Staining was only seen approximately 10 d after PLP was first detected in the cytoplasm of fixed and permeabilized cells, suggesting that PLP is slowly transported from the RER to the cell surface. The presence of PLP domains on the extracellular surface was also confirmed by cleavage of such domains with proteases and by antibody-dependent complement-mediated lysis of living oligodendrocytes. Our results indicate that PLP has only two transmembrane domains and that the great majority of the protein, including its amino and carboxy termini, is located on the extracellular face of the oligodendrocyte plasma membrane. This disposition of the PLP molecule suggests that homophilic interactions between PLP molecules of apposed extracellular faces may mediate compaction of adjacent bilayers in the myelin sheath.

Glutamate acting at NMDA receptors stimulates embryonic cortical neuronal migration.

During cortical development, embryonic neurons migrate from germinal zones near the ventricle into the cortical plate, where they organize into layers. Mechanisms that direct neuronal migration may include molecules that act as chemoattractants. In rats, GABA, which localizes near the target destination for migrating cortical neurons, stimulates embryonic neuronal migration in vitro. In mice, glutamate is highly localized near the target destinations for migrating cortical neurons. Glutamate-induced migration of murine embryonic cortical cells was evaluated in cell dissociates and cortical slice cultures. In dissociates, the chemotropic effects of glutamate were 10-fold greater than the effects of GABA, demonstrating that for murine cortical cells, glutamate is a more potent chemoattractant than GABA. Thus, cortical chemoattractants appear to differ between species. Micromolar glutamate stimulated neuronal chemotaxis that was mimicked by microM NMDA but not by other ionotropic glutamate receptor agonists (AMPA, kainate, quisqualate). Responding cells were primarily derived from immature cortical regions [ventricular zone (vz)/subventricular zone (svz)]. Bromodeoxyuridine (BrdU) pulse labeling of cortical slices cultured in NMDA antagonists (microM MK801 or APV) revealed that antagonist exposure blocked the migration of BrdU-positive cells from the vz/svz into the cortical plate. PCR confirmed the presence of NMDA receptor expression in vz/svz cells, whereas electrophysiology and Ca2+ imaging demonstrated that vz/svz cells exhibited physiological responses to NMDA. These studies indicate that, in mice, glutamate may serve as a chemoattractant for neurons in the developing cortex, signaling cells to migrate into the cortical plate via NMDA receptor activation.

Comparative evolution of carotidynia on ultrasound and magnetic resonance imaging.

Carotidynia is rare and associates neck pain with tenderness to palpation usually over the carotid bifurcation, the diagnosis of which is based on magnetic resonance imaging (MRI). Ultrasounds (US) are also frequently used but their accuracy in predicting the course of the disease is unknown. We are reporting the case of a 52-year-old man who presented a typical carotidynia. Clinical symptoms, ultrasound and MRI imaging evolution were closely correlated. Our case suggest that after a first MRI to set a positive diagnosis of carotidynia and exclude differential diagnoses, US which is more widely available and less expensive could constitute the imaging of reference for the follow-up.

Transient expression of GABA immunoreactivity in the developing rat spinal cord.

The development of GABAergic neurons in the spinal cord of the rat has been investigated by immunocytochemical staining of frozen sections with anti-gamma-aminobutyric acid (GABA) antiserum. In the cervical cord, GABA-immunoreactive fibers first appeared at embryonic day (E) 13 in the presumptive white matter within the ventral commissure, ventral funiculus, and dorsal root entrance zone, and in the ventral roots. There were no GABA-immunoreactive cell bodies detected at this age. By E14, motoneurons, the earliest generated spinal cells, were the first cell population to become GABA-immunoreactive at the cell body level. Thereafter, GABA-immunoreactive neurons increased progressively in number and extended from ventral to dorsal regions. GABA-immunoreactive relay neurons within lamina I of the dorsal horn were initially detected at E17. Interneurons in the substantia gelatinosa, the latest generated cells in the spinal cord, were also the last to express the GABA immunoreactivity at E18. Immunoreactive neurons peaked in intensity and extent at E18 and 19. GABA immunoreactivity was only detectable in neurons within the intermediate and marginal zones 1-3 days after they withdrew from the cell cycle. This contrasts to glutamate decarboxylase immunoreactivity, which is detected in precursor cells in the ventricular zone prior to, or during, withdrawal from the cell cycle. Toward the end of gestation, GABA immunoreactivity declined in intensity and extent. This regression began in the ventral horn of the cervical region and ended in the dorsal horn of the lumbosacral region. During the first week after birth, immunoreactivity in motoneurons and in many other neurons within the ventral horn, intermediate gray, and deeper layers of the dorsal horn disappeared, and only in those neurons predominantly within the superficial layers of the dorsal horn did it persist into adulthood. Thus, the expression and regression of GABA immunoreactivity in the spinal cord followed ventral-to-dorsal, rostral-to-caudal, and medial-to-lateral gradients. These observations indicate that the majority of embryonic spinal neurons pass through a stage of transient expression of GABA immunoreactivity. The functional significance of this transient expression is unknown, but it coincides with the period of intense neurite growth of motoneurons, sensory neurons, and interneurons, and of neuromuscular junction formation, suggesting that the transient presence of GABA may play an important role in the differentiation of sensorimotor neuronal circuits.

Transient increase in expression of GAD65 and GAD67 mRNAs during postnatal development of rat spinal cord.

Gamma-aminobutyric acid (GABA) is thought to be one of the classic neurotransmitters acting as a developmental signal. To understand the role for GABA in development, we investigated the expression of transcripts encoding two forms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD65 and GAD67) in the cervical enlargement of the rat spinal cord at successive postnatal days--P0, P7, P14, P21, and P90 (adult)--by using in situ hybridization histochemistry. Cells hybridized with two oligonucleotide probes designed to detect GAD65 and GAD67 mRNAs were widely distributed in all laminae, except in motoneurons of the spinal cord. The integrated densities of hybridization signals were measured across all layers of the gray matter. The relative number of GAD mRNA-labeled cells was determined within each of four regions: laminae I-III, laminae IV-VI, laminae VII and VIII, and lamina X. There was a transient increase in both the integrated density and the relative number of hybridized cells between P7 and P14, after which there was a marked decline to adult levels (lowest). An overall decrease in the number of GAD mRNA-labeled cells was evident in all layers, but a dramatic drop occurred in a subpopulation of cells within ventral portions of the spinal cord. The distribution patterns and postnatal changes in expression of the mRNAs encoding GAD65 and GAD67 were similar and closely paralleled reported changes in the abundance of GAD65 and GAD67 proteins and their product, GABA. Transient increases in GAD mRNA expression during the early postnatal period coincide with, and may be linked to, synapse formation and synapse elimination of the developing spinal cord.

Neuroepithelial cells in the rat spinal cord express glutamate decarboxylase immunoreactivity in vivo and in vitro.

It is unknown whether neuroepithelial cells in the mammalian central nervous system express neurotransmitter-synthesizing enzymes. In this study, expression of glutamate decarboxylase (GAD), the gamma-aminobutyric acid (GABA)-synthesizing enzyme, was examined in proliferative cells and postmitotic neuroblasts in embryonic rat spinal cord. Immunostaining coronal sections of the embryonic spinal cord with K2 antiserum, which recognizes GAD proteins encoded by the GAD67 gene, revealed intensely stained neuroepithelial cells in the basal plate at embryonic day (E) 13, in the intermediate plate between E 13-16, and last seen in the alar plate at E 16. Nissl counterstaining demonstrated that a small number of these GAD-immunoreactive cells adjacent to the neural tube lumen were mitotic. The ventral-to-dorsal gradient of GAD expression in precursor cells and postmitotic neuroblasts correlates anatomically and temporally with the sequential generation of motoneurons, commissural neurons, and interneurons in the dorsal horn. Some of these GAD-immunoreactive neuroepithelial cells may re-enter the mitotic cycle, while others are postmitotic neuroblasts presumably migrating to the intermediate zone to differentiate into young neurons. Double-immunostaining cells acutely dissociated from E 11-18 spinal cords with K2 and anti-bromodeoxyuridine antisera, following a bromodeoxyuridine pulse in vivo, revealed considerable numbers of DNA-synthesizing cells immunoreactive for GAD. The absolute number of double-stained cells peaked during E 12-15, coinciding with terminal cell division in most spinal neurons. These observations suggest that spinal neuronal precursors can synthesize GAD-related proteins prior to, or during, the terminal cell cycle. Although GAD immunoreactivity revealed by K2 antiserum was detected in proliferative cells and in migrating postmitotic neuroblasts, GABA immunoreactivity was never detectable in these cells. These early embryonic GAD-immunoreactive neuroepithelial cells may either synthesize levels of GABA that cannot be detected immunocytochemically, and/or express enzymatically inactive GAD-related proteins.

Detection of B cell antigens in multiple sclerosis. Use of serum from multiparous women.

Sera from two multiparous wives of patients with multiple sclerosis (MS) were used to detect B cell antigens in other patients. With serum X, 11 of 16 patients were positive as compared with ten of 16 controls (.05 less than P less than .1). With serum Y, a positive response was found in 11 of 16 patients and two of 23 controls (P less than .0005). Ten of the 11 patients who were positive with serum Y were also HLA-Dw2, which suggests that the B cell antigen detected by this serum is linked to Dw2. Three of four Dw2-positive controls were negative with serum Y, which raises two alternative hypothetical possibilities concerning the B cell antigen. These findings indicate that serum from multiparous wives may be an important tool in the investigation of the genetic components associated with MS.

A fractal analysis of cultured rat optic nerve glial growth and differentiation.

Fractal dimension can be used as a quantitative measure of morphological complexity. Separate, enriched populations of oligodendrocytes or type 2 astrocytes derived from neonatal rat optic nerves were allowed to differentiate in vitro. Fractal dimensions of differentiating glial cells were measured over time. The fractal dimension correlated with perceived complexity and increased in value as the glial cells matured. Analysis of the changes in fractal dimension with time revealed unique rates of growth and differentiation for each glial phenotype.

Comparative fractal analysis of cultured glia derived from optic nerve and brain demonstrate different rates of morphological differentiation.

O-2A progenitor cells derived from neonatal rat cerebral hemispheres or optic nerves, were induced to differentiate in culture into either oligodendrocytes or type 2 astrocytes. The fractal dimensions, a measure of morphological complexity, of the differentiating glial cells were measured over time. Analysis of the changes in fractal dimension (D) with respect to time revealed specific rates of growth for each glial phenotype and a specific final D. The time course of these changes is well fit by a simple mathematical model. While brain-derived oligodendrocytes matured faster than the astrocytes, they ultimately attained comparable levels of complexity, with similar maximum fractal dimensions. Oligodendrocytes from nerve also matured faster than nerve derived astrocytes, in contrast, however, they attained a greater morphological complexity than nerve astrocytes. While the brain-derived oligodendrocytes showed a faster rate of maturation than their optic nerve counterparts, astrocytes from both regions had similar rates of morphological differentiation. Self-similarity, a defining property of fractal objects was investigated, by determining the fractal dimension of cells over a range of magnifications. The calculated fractal dimension remained constant over a 10-fold range in optical magnification, illustrating that cultured glial cells exhibit this important characteristic of fractal objects. In addition, we analyzed the branching patterns of glial processes by the Sholl method and found that the results were not as interpretable or meaningful as those of fractal analysis.

Correlation of gp140trk expression and NGF-induced neuroblast chemotaxis in the embryonic rat spinal cord.

During rat embryogenesis, fibers containing nerve growth factor (NGF) are present near the target destinations of migratory spinal neuroblasts, suggesting that diffusible gradients of NGF provide signals to newly generated neurons in the developing cord. In vitro, pM concentrations of NGF induce neuroblast chemotaxis (directed migration along a chemical gradient), indicating evoked motility is mediated by high-affinity receptors. Binding of 125I-labelled NGF to fetal cord cells provides additional evidence that rat spinal neuroblasts express the high-affinity receptors; however, their presence has not been directly demonstrated. In the present study, we used immunocytochemistry to show that the high-affinity NGF receptor protein, gp140trk (trk) is detectable in embryonic spinal tissue sections and in cord dissociates. Correlation of trk expression with NGF-induced chemotaxis revealed that both the receptor protein expression and functional responses to NGF develop along a ventro-dorsal gradient that parallels the in vivo pattern of neurogenesis and migration. Analysis of the temporal changes in trk immunoreactivity demonstrated that expression of gp140trk is bimodal, possibly reflecting multiple effects of NGF during development. Chemotaxis to NGF was blocked by nM concentrations of the kinase inhibitor, K252a, suggesting that NGF stimulates motility via high-affinity receptors coupled to kinase activity. Elevated 3',5'-cyclic adenosine monophosphate (cAMP) also attenuated NGF-induced chemotaxis, presenting preliminary evidence that protein kinase A (PKA) may regulate motility responses to NGF.

Analysis of the anatomical distribution of GAD67 mRNA encoding truncated glutamic acid decarboxylase proteins in the embryonic rat brain.

During development of the central nervous system (CNS) the gene that encodes the 67 kDa form of glutamic acid decarboxylase (GAD) undergoes alternative splicing. The alternatively spliced variants include an exon (referred to as ES, for embryonic stop) that contains a premature stop codon. The detection of mRNA containing the ES exon in embryonic rat brain has been previously reported (Proc. Natl. Acad. Sci., 87 (1990) 8771-8775). We have used in situ hybridization to identify the anatomical distribution of ES mRNA in the embryonic rat brain during two stages of development, embryonic day 17 (E17) and E20. At E17, GAD67 mRNA was expressed in several CNS regions that were destined to contain GABAergic neurons when mature. ES transcripts were predominantly localized to ventricular zones and other regions associated with populations of proliferative cells at E17 and E20. At both ages, however, the alternatively spliced variants were also detected in regions of brain associated with migratory or post-mitotic neurons. GAD67 transcripts that did not include the ES exon were localized to anatomical areas that contained post-mitotic, and often post-migratory neurons. The temporal and spatial disappearance of mRNA containing the ES exon generally followed a caudal-to-rostral gradient which paralleled neuronal terminal mitosis and differentiation.

Many spinal cord cells transiently express low molecular weight forms of glutamic acid decarboxylase during embryonic development.

At early developmental stages in the rat spinal cord (embryonic day 13), when neuronal progenitors are still proliferating, most differentiating neurons express truncated forms of glutamic acid decarboxylase (GAD) (approximately 25 kDa) which are the products of alternative splicing of the GAD67 gene. These truncated proteins do not appear to synthesize gamma-aminobutyric acid (GABA). The amino acid is detected in cells only after alternative splicing of the GAD67 gene generates a full-length, 67 kDa enzymatically active form of GAD. Both the 67 kDa GAD and GABA colocalize and appear diffusely distributed in the cytoplasm of embryonic neurons. GABA does not appear associated with synaptic vesicles until after birth, when its intracellular distribution becomes punctate and it colocalizes with synaptophysin. At this time, it also colocalizes with an immunologically distinct 65 kDa GAD protein encoded by a second GAD gene (GAD65). Expression of different GAD-related proteins with distinct intracellular distributions during development suggests that GABA, the product of these enzymes, may have trophic or metabolic roles during spinal cord differentiation.

Quantitative analysis of transient GABA expression in embryonic and early postnatal rat spinal cord neurons.

GABA expression was investigated using biochemical analysis of spinal cord homogenates and immunocytochemical analysis of cells acutely dissociated from the embryonic and postnatal rat spinal cord. gamma-Aminobutyric acid (GABA) was detected by both methods as early as embryonic day 13 (E13). At E13, the percentage of neurons that were GABA+ was 0.5%. This value increased during embryogenesis, peaked during the first two postnatal weeks to just over 50%, and declined to approximately 20% by the third postnatal week emphasizing the transient nature of GABA expression. At E17 there was a pronounced, positive ventro-dorsal and rostro-caudal gradient of GABA+ cells that persisted until just before birth. At this time the gradients reversed in cervical and lumbosacral regions indicating that GABA immunoreactivity in discrete anatomical regions is also a transient phenomenon. During the embryonic period GABA immunoreactivity was diffusely distributed throughout cell bodies and proximal processes. At E21, both GABA and synaptophysin were present in the same cells. However the two antigens did not co-localize point for point. By postnatal day 21 GABA immunoreactivity appeared in puncta that co-localized entirely with puncta of synaptophysin immunoreactivity. The sizable percentage of neurons that transiently express GABA during development, and the fact that it can be detected prior to the synaptic form of glutamic acid decarboxylase (GAD65), suggest that the amino acid may play a significant role during differentiation before it functions as an inhibitory neurotransmitter.

GABAergic cells and signals appear together in the early post-mitotic period of telencephalic and striatal development.

Single cell suspensions derived from embryonic telencephala taken from embryos of gestational day 13 (E13) as well as rat striatal tissue from E14, 15 and 17 were prepared by tissue digestion with papain. Cell suspensions were analyzed by flow cytometry or plated onto poly-D-lysine-coated culture dishes for either nuclear staining or immunocytochemistry. Experiments on functional Na+ channels and GABAA receptor expression were carried out using a fluorescence-activated cell sorter (FACS) and a negatively charged fluorescent indicator dye (oxonol). FACS analysis of embryonic cell suspensions at E13-17 consistently revealed one major subpopulation accounting for 85-90% of the events and one minor subpopulation (10-15% of the total). When sorted, the major subpopulation consisted of phase-bright cells of 5-7 microns diameter some of which had neurites. The minor population consisted of phase-dark cells and resealed membranes of 0.5-4 microns diameter as well as debris. Almost all the cells obtained in the high FALS (forward-angle light scatter) subpopulation at E17 expressed 200-kDa neurofilament and tetanus toxin antigens while the small diameter cells seldom expressed tetanus toxin and particles never did. A small number of GABA-containing neurons were detected in the telencephalon at E13 (3%) and in the developing striatum at E14 (6%). All of the GABA-containing neurons expressed neurofilament. In the embryonic rat striatum, nanomolar concentrations of muscimol (GABAA agonist) induced depolarizing responses. A small number of cells in the high FALS subpopulation were responsive to muscimol starting at embryonic day 14, and the number of responsive cells increased at E15.(ABSTRACT TRUNCATED AT 250 WORDS)

Sclerosing lipogranulomatosis: a case report of scrotal injection of automobile transmission fluid and literature review of subcutaneous injection of oils.

For nearly a century, physicians and laypersons have attempted to repair, reconstruct, and embellish the human body in numerous ways by injecting various oils beneath the skin. Soon after Gersuny's first reported subcutaneous injection of oil, the local and systemic complications became apparent. Despite this, the practice of oil injections continues. "Medical grade" silicone injection was investigated in the 1960s to 1980s with varied success and complications. While few physicians practice oil injection therapy, some laypersons continue to subject themselves or their clients to the risk of the disfiguring complications of sclerosing lipogranulomata. Accidental high-pressure injection injury of liquids, so-called grease gun injuries, continues to provide a therapeutic challenge for the hand surgeon. Our case of a man who injected automobile transmission fluid into his scrotum illustrates the classical course and proper management of sclerosing lipogranulomata. A subcutaneous inflammatory and fibrosing reaction occurred with regional lymphadenopathy. The need for complete excision of all involved tissue to treat the condition successfully is illustrated. This case also illustrates the tendency of patients to conceal from their doctors the history of self-injection of foreign bodies. In cases of self-injection, psychological counseling might certainly be appropriate.

Major stump trauma following below-knee amputation. Outcome and recommendations for therapy.

Injury to the stump of a below-knee amputation (BKA) may require revision to a higher level of amputation. We undertook a retrospective review of BKAs performed during a 14-year period. Twenty-three patients suffered trauma to their stumps. Most (80%) trauma resulted from a fall. The severity of the trauma was graded on a three-part scale. Operative reclosure was attempted in 8 cases with 2 successes. Closure by secondary intent was successful in 7 of the 12 attempts. A total of 11 patients had revision to above-knee amputation (AKA) as the final outcome. The severity of trauma correlated inversely with the likelihood of eventual stump salvage. We conclude that primary reclosure or closure by secondary intent should be considered, since in 53% of attempts this results in knee preservation. Analysis of noninvasive vascular testing prior to the BKA was not helpful in predicting successful salvage of traumatized stumps.

[Prevalence and risk factors of peripheral arterial disease in an outpatient screening campaign]. / Évaluation de la prévalence et des facteurs de risque de l'artériopathie oblitérante des membres inférieurs dans le cadre d'une campagne de dépistage ambulatoire.

BACKGROUND: Peripheral arterial disease (PAD) is an important predictor of cardiovascular disease with major medico-economic consequences. However, systematic screening of asymptomatic patients free from history of cardiovascular disease is debated. OBJECTIVE: Determining the prevalence, risk factors for PAD in a population of outpatients at intermediate or high-risk of cardiovascular disease, free from history of cardiovascular disease to assess the potential impact of PAD screening in such groups of patients. METHODS: Multicenter 1-day screening program of PAD conducted from 2008 to 2010 in a population defined by diabetes plus age greater than 50 years, positive active smoking status, or age greater than 70 years. PAD was defined as an ankle-brachial index (ABI) less than 0.9 measured as follows: lowest systolic ankle pressure divided by highest systolic arm pressure. RESULTS: Ten thousand six hundred and fourteen patients fulfilled study inclusion criteria: 16.7% (n = 1774) exhibited an ABI less than 0.9 and 3.8% (n = 407) an ABI less than 0.7. ABI greater than 1.3 was found in 7.7% of patients (n = 818). Age greater than 70 years, male gender, active smoking status, hypertension and diabetes (treated) were independent risk factors for PAD. CONCLUSION: Primary prevention outpatient screening of a population with intermediate or high cardiovascular risk can identify numerous patients with PAD. The medical impact in terms of cardiovascular mortality and morbidity of such a screening needs to be assessed.

Analysis of fractal dimension of O2A glial cells differentiating in vitro.

Fractal dimension is a quantitative measure of morphological complexity. Glial cells of the oligodendrocyte-type 2 astrocyte (O2A) lineage exhibit increasing morphological complexity as they differentiate in vitro. Enriched populations of O2A progenitor cells isolated from neonatal rat cerebral hemispheres or optic nerves were allowed to differentiate in vitro, and their fractal dimensions were measured over time. The fractal dimensions of the maturing cells correlated with perceived complexity; cells with elaborate process branching had larger fractal dimensions than cells with a simpler morphology. An analysis of changes in fractal dimension revealed distinct rates of growth for both oligodendrocytes and type 2 astrocytes. The fractal dimension remained constant over a 10-fold range in optical magnification, demonstrating that cultured O2A glial cells exhibit self-similarity, a defining characteristic of fractal objects. These results illustrate that fractal dimension analysis of maturing cell populations is a useful method for quantitatively describing the process of cell differentiation.