Rat White Matter Research Articles

Long-Term Running Exercise Delays Age-Related Changes in White Matter in Rats.

Running exercise, one of the strategies to protect brain function, has positive effects on neurons and synapses in the cortex and hippocampus. However, white matter, as an important structure of the brain, is often overlooked, and the effects of long-term running exercise on white matter are unknown. Here, 14-month-old male Sprague–Dawley (SD) rats were divided into a middle-aged control group (18-month-old control group), an old control group (28-month-old control group), and a long-term runner group (28-month-old runner group). The rats in the runner group underwent a 14-month running exercise regime. Spatial learning ability was tested using the Morris water maze, and white matter volume, myelinated fiber parameters, total mature oligodendrocyte number, and white matter capillary parameters were investigated using stereological methods. The levels of growth factors related to nerve growth and vascular growth in peripheral blood and the level of neurite outgrowth inhibitor-A (Nogo-A) in white matter were measured using an enzyme-linked immunosorbent assay (ELISA). The present results indicated that long-term running exercise effectively delayed the age-related decline in spatial learning ability and the atrophy of white matter by protecting against age-related changes in myelinated fibers and oligodendrocytes in the white matter. Moreover, long-term running exercise prevented age-related changes in capillaries within white matter, which might be related to the protective effects of long-term exercise on aged white matter.

Dl-3-n-butylphthalide promotes remyelination process in cerebral white matter in rats subjected to ischemic stroke

Remyelination has been widely noticed as an important repair mechanism triggered after a stroke-induced white matter injury, but it often fails due to the lack of recruitment of the oligodendrocyte progenitor cells (OPCs) to the demyelinated area and the inadequate differentiation of OPCs. Racemic dl-3-n-butylphthalide (dl-NBP) has been reported to improve the functional recovery in animal models of vascular dementia, Alzheimer’s disease (AD) and ischemic stroke. Dl-NBP (70 mg/kg) by oral gavage for two weeks from day 7 after a stroke was administered in the study, the treatment promoted differentiation and maturation of OPCs in perilesional white matter and enhanced the length of crossing corticospinal tract (CST) fibers into the denervated hemispheres. These effects could be linked to increased expression levels of brain-derived neurotrophic factor (BDNF) and the reduced expression of neurite outgrowth inhibitor (NogoA) in the perilesional area in dl-NBP group. However, dl-NBP did not increase the numbers of neuron/glia type 2 (NG2)-positive and oligodendrocyte lineage transcription factor 2 (Olig2)-positive cells in the subventricular zone. Our data highlight the effects of dl-NBP in the remyelination process and reveal the therapeutic potential of this approach in cerebral ischemia.

Diffusion tensor imaging of brain white matter in rats with ischemia reperfusion injury and its behavioral changes

Objective To investigate the changes of diffusion tensor imaging (DTI) in the cerebral white matter of rats with ischemia-reperfusion injury. Methods Adult SD rats were randomly divided into two groups, sham operation group and model group. The model of ischemia reperfusion injury was made by the Koizumi suture method to occlude the middle cerebral artery. Application of Zea-Longa score was carried out to determine the establishment of modeling, and the modified neurological severity score (mNSS) was used to evaluate the neurological deficit of rats. The Rotarod test instrument was used to observe the motor function of rats by using Rotarod fatigue balance signs, and the DTI sequence scanning observation of brain white matter nerve fiber damage was determined by using Brook 7.0T small animal magnetic resonance imaging system. Track Vis software was used to analyze the distribution of cerebral white matter nerve fibers, and the relative number of nerve fibers in the areas of ROI (region of interest, ROI), sensorimotor areas and striatum were calculated. Results The results showed varying degrees of neurological impairment in rats 2 h after cerebral ischemia reperfusion injury, and the Zea-Longa score and the mNSS score were gradually reduced at the 1 d, 7 d and 14 d after ischemia reperfusion injury. The time of rats retaining on the rotating rod was shortened at the 7 d and 14 d after ischemia reperfusion injury. At the ischemic lateral, nerve fibers decreased significantly, and the number of sensory nerve fiber connections in the sensorimotor areas to striatum was reduced. Nissl staining showed that the cytoplasm of neurons in the sensorimotor cortex and striatum of the ischemic lateral were disappeared and the Nissl bodies were decreased. Conclusions The nerve fibers of sensory motor cortex connecting to striatum were damaged by ischemia reperfusion injury. Key words: Ischemia reperfusion injury; Brain white matter; DTI imaging; Sensorimotor; Striatum

Exercise protects myelinated fibers of white matter in a rat model of depression.

The antidepressive effects of exercise have been a focus of research and are hypothesized to remodel the brain networks constructed by myelinated fibers. However, whether the antidepressant effects of exercise are dependent on changes in white matter myelination are unknown. Therefore, we chose chronic unpredictable stress (CUS) as a model of depression and designed an experiment. After a 4-week CUS period, 40 animals were tested using the sucrose preference test (SPT) and the open field test (OFT). The depressed rats then underwent 4-week running exercise. Next, electron microscopy and unbiased stereological methods were used to investigate white matter changes in the rats. After the 4-week CUS stimulation, body weight, sucrose preference and scores on the OFT were significantly lower in the depression rats than in the unstressed rats (p < .05). After undergoing a 4-week running exercise, the depression rats showed a significantly greater sucrose preference than the depression control rats without running exercise (p < .05). Furthermore, the white matter parameters of the depression rats (including the white matter volumes, the length and volumes of myelinated fibers, and the volumes and thickness of the myelin sheaths) were significantly reduced after the CUS period (p < .05). However, these white matter parameters were significantly increased after running exercise (p < .05). The present study is the first to provide evidence that running exercise has positive effects on white matter and the myelinated fibers of white matter in depressed rats, and this evidence might provide an important theoretical basis for the exercise-mediated treatment of depression.

White matter and SVZ serve as endogenous sources of glial progenitor cells for self-repair in neonatal rats with ischemic PVL

Mounting evidence suggests that endogenous progenitor cells may initiate cerebral WM repair. This study was designed to determine whether endogenous glial progenitor cells derived from either the subventricular zone (SVZ) or the white matter (WM) contribute to WM repair in a neonatal rat model of ischemic periventricular leukomalacia (PVL). Additionally, the role of G protein-coupled receptor 17 (GPR17), recently shown to act as a sensor for WM damage, was explored to assess its potential recruitment and activation of endogenous glial progenitor cells for such WM self-repair. Our in vivo and in vitro models consisted of five-day-old neonatal rats or cultured glial progenitor cells derived from both the SVZ and WM of these rats, randomly divided into sham/control and induced ischemic PVL/oxygen–glucose deprivation (OGD) groups. The WM of all PVL rats showed either mild or severe histopathological changes, with significantly increased in vivo apoptosis and poor myelination compared to those of the sham group. Significantly more apoptotic and necrotic cells were also detected in the OGD glial progenitor cell cultures derived from the SVZ and WM at all time intervals. The glial progenitor cells were significantly increased in both the SVZ (NG2+/GPR17−/BrdU+) and WM (NG2+/GPR17+/BrdU+) within 72h after PVL; preOLs were also increased significantly in both the SVZ (O4+/GPR17−/BrdU+) and WM (O4+/GPR17+/BrdU+) within 7d after PVL in vivo or OGD in vitro. However, the more differentiated CNPase+/GPR17−/BrdU+ and MBP+/GPR17−/BrdU+ OLs in the SVZ and WM remained significantly less than those in the sham groups up to 14d or 21d after OGD or PVL, respectively. Hence, both the WM and SVZ were found to be potential endogenous sources of glial progenitor cells for WM repair in PVL rats. However their endogenous self-repair capacity appeared to be limited, since the more mature OLs did not completely recover from experimental ischemia, even after 14–21d.

Effects of an enriched environment on myelin sheaths in the white matter of rats during normal aging: A stereological study

We found that an enriched environment (EE) could delay the loss of myelinated fibers in the white matter of rats during normal aging. However, the reasons for the protective effects of EE on the myelinated fibers were unclear. In this present study, via the use of stereological methods, we quantitatively investigated the myelin sheaths and the axons of myelinated fibers in the white matter of rats reared in an EE or a standard environment (SE) during the aging process. The results showed that an EE induced significant increases in the lengths of myelinated fibers, the axon volumes and the myelin sheath volumes of aging rats when compared with SE rats and that the enrichment effects, with the exception of the axon volumes, were sex- and age-independent. The mean diameter of the myelinated fibers, the mean perimeter of the myelin sheaths and the mean thicknesses of the myelin sheaths were not significantly changed. The EE-induced increase in myelinated fibers was mostly observed in those of smaller diameter (<1μm) with thinner myelin sheaths (<0.16μm), which had an optimal axon-fiber ratio (g=0.61). Our results suggest that EE-induced an increase in myelinated fibers in the white matter of aging rats primarily due to marked remyelination and some ongoing myelination.

Developmental regulation of group I metabotropic glutamate receptors in the premature brain and their protective role in a rodent model of periventricular leukomalacia

Cerebral white matter injury in premature infants, known as periventricular leukomalacia (PVL), is common after hypoxia-ischemia (HI). While ionotropic glutamate receptors (iGluRs) can mediate immature white matter injury, we have previously shown that excitotoxic injury to premyelinating oligodendrocytes (preOLs) in vitro can be attenuated by group I metabotropic glutamate receptor (mGluR) agonists. Thus, we evaluated mGluR expression in developing white matter in rat and human brain, and tested the protective efficacy of a central nervous system (CNS)-penetrating mGluR agonist on injury to developing oligodendrocytes (OLs) in vivo. Group I mGluRs (mGluR1 and mGluR5) were strongly expressed on OLs in neonatal rodent cerebral white matter throughout normal development, with highest expression early in development on preOLs. Specifically at P6, mGluR1 and mGLuR5 were most highly expressed on GalC-positive OLs compared to neurons, axons, astrocytes and microglia. Systemic administration of (1S,3R) 1-aminocyclopentane-trans-1,3,-dicarboxylic acid (ACPD) significantly attenuated the loss of myelin basic protein in the white matter following HI in P6 rats. Assessment of postmortem human tissue showed both mGluR1 and mGluR5 localized on immature OLs in white matter throughout development, with mGluR5 highest in the preterm period. These data indicate group I mGluRs are highly expressed on OLs during the peak period of vulnerability to HI and modulation of mGluRs is protective in a rodent model of PVL. Group I mGluRs may represent important therapeutic targets for protection from HI-mediated white matter injury.

On the contribution of deoxy-hemoglobin to MRI gray–white matter phase contrast at high field

High field (≥7 T) MRI studies based on signal phase have been used to improve visualization of the fine structure of the brain, most notably the major white matter fiber bundles, the gray–white matter subdivision, and the laminar cortical architecture. The observed contrast has been attributed in part to local variations in magnetic susceptibility arising from iron in storage proteins and tissue lipid. Another contribution could come from the paramagnetic blood constituent deoxy-hemoglobin, the tissue concentration of which may vary through local variations in vascular density. To investigate this possibility, we examined phase contrast between gray and white matter in rats after intravenous administration of a superparamagnetic contrast agent at various dosages. At the maximum dosage (3 mg Fe/kg), which resulted in an estimated paramagnetic susceptibility shift 4–8 times larger than deoxy-hemoglobin, we observed a negligible increase in phase contrast between gray and white matter. This result suggests that endogenous deoxy-hemoglobin has no significant contribution to phase contrast between gray and white matter.

Expression of S100 protein and protective effect of arundic acid on the rat brain in chronic cerebral hypoperfusion

S100 protein is expressed primarily by astroglia in the brain, and accumulates in and around the ischemic lesions. Arundic acid, a novel astroglia-modulating agent, is neuroprotective in acute cerebral infarction, whereas the protective effects remain unknown during chronic cerebral hypoperfusion. Rats undergoing chronic cerebral hypoperfusion were subjected to a bilateral ligation of the common carotid arteries, and were allowed to survive for 3, 7 and 14 days. The animals received a daily intraperitoneal injection of 5.0, 10.0 or 20.0 mg/kg of arundic acid, or vehicle, for 14 days. Alternatively, other groups of rats received a delayed intraperitoneal injection of 20.0 mg/kg of arundic acid or vehicle, which started from 1, 3 or 7 days after ligation and continued to 14 days. The degree of white matter (WM) lesions and the numerical density of S100 protein-immunoreactive astroglia were estimated. In the WM of rats with vehicle injections, the number of S100 protein-immunoreactive astroglia increased significantly after chronic cerebral hypoperfusion as compared to the sham-operation. A dosage of 10.0 and 20.0 mg/kg of arundic acid suppressed the numerical increase in S100 protein-immunoreactive astroglia and the WM lesions. These pathological changes were suppressed with delayed treatment up to 7 days in terms of astroglial activation, and up to 3 days in terms of the WM lesions. The protective effects of arundic acid against WM lesions were demonstrated in a dose-dependent manner, and even after postischemic treatments. These results suggest the potential usefulness of arundic acid in the treatment of cerebrovascular WM lesions.

Protective effect of nimodipine on behavior and white matter of rats with hydrocephalus.

Hydrocephalus, a pathological dilation of the ventricles of the brain, causes damage to periventricular white matter, at least in part, through chronic ischemia. The authors tested the hypothesis that treatment with nimodipine, an L-type calcium channel-blocking agent with demonstrated efficacy in a range of cerebral ischemic disorders, would ameliorate the adverse effects of experimental hydrocephalus. Hydrocephalus was induced in 3-week-old rats by injection of kaolin into the cisterna magna. The rats were treated by continuous administration of nimodipine or control vehicle for 2 weeks, beginning 2 weeks after induction of hydrocephalus. During the treatment period, the animals underwent repeated tests of motor and cognitive behavior. At the end of the treatment period, the rat brains were analyzed by histopathological and biochemical means. Nimodipine treatment prevented the declines in motor and cognitive behavior that were observed in untreated control rats. During the treatment period, ventricular enlargement, determined by magnetic resonance imaging, was equal in the two groups, although the corpus callosum was thicker in the treated rats. Myelin content in white matter and synaptophysin content in gray matter, an indicator of synapses, did not differ. The protective effect of nimodipine is most likely based on improved blood flow, although prevention of calcium influx-mediated proteolytic processes in axons cannot be excluded. Adjunctive pharmacological therapy may be beneficial to patients with hydrocephalus.

Regional Potassium Distribution in the Brain in Forensic Relevant Types of Intoxication: Preliminary Morphometric Evaluation Using a Histochemical Method

A histochemical–morphometric method was used to measure potassium (K +) levels in gray and white matter of rats following sublethal intoxication with 11 different neurotoxic compounds of high forensic significance. Six rats were each given a single substance applied intraperitoneally, the same dosage being given to two animals each. The animals were subsequently killed, the brains immediately frozen, and cryosections cut. K + levels were evaluated morphometrically. A drop in K + levels was used as the criterion for cytotoxic edema. Application of ethanol, atropine, carbromal, carbon monoxide, morphine or triethyltin led to a rise in K + levels in the gray matter and a simultaneous decline in the white matter. By contrast, administration of amitriptyline, glycerin, potassium cyanide, parathion or phenobarbital initiated an increase in K + levels in both gray and white matter. A cytotoxic edema could thus be reliably excluded in these intoxications. Although the study design allows no statistical analysis, these conclusions are supported by the marked differences in K + levels in gray and white matter induced by the different toxicants.

Degeneration of axons in the corticospinal tract secondary to spinal cord ischemia in rats

Occlusion of the thoracic aorta and both subclavian arteries (XC) in the rat model produces spastic paraplegia. In order to characterize the lesion of white matter, 14 male Sprague-Dawley rats underwent XC for 10.5 to 12 min, were observed for 32 days and assessed with a lesion score. A sham group of eight underwent surgical manipulations without XC. The spinal cords were studied by optical microscopy and electron microscopy. An additional group of normal animals (n = 8) underwent spinal cord blood flow measurement with the autoradiographic technique. Optical microscopy showed normal histology in sham operated rats and rats with aortic cross-clamp and lesion score = 2-4 (n = 5), rare changes in the white matter of rats with lesion score = 8 (n = 2), and demyelination of the anterior and lateral tracts of the white matter and motor neuron loss in the gray matter of rats with lesion score = 13-15 (n = 7) and spastic paraplegia. In this last group, electron microscopy disclosed severe axonal degeneration of corticospinal tracts. In the same region spinal cord blood flow was higher than the remaining white matter. This study confirms that spastic paraplegia observed in the rat model after XC is due to degeneration of the pyramidal tracts, perhaps more susceptible to injury due to the high spinal cord blood flow.

Effects of X-irradiation on glial cells in the developing rat brain.

Sprague-Dawley rats were given a single dose of 2 Gy X-rays when 1 or 3 days of age. Dying cells in the germinal layer of the telencephalon reached peak values 6 h after irradiation; dead cells were cleared 48 h later. These effects were almost abolished with the injection of cycloheximide (1 microgram/g body weight) given at the time of irradiation. PCNA-immunoreactive cells (cells in late G1 and S phases of the cell cycle) and PCNA-negative cells were sensitive to X-rays. Long-term effects on glial cell populations in the subcortical white matter of the cingulum were examined in irradiated rats, killed at postnatal day 30 (P30), by means of glial fibrillary acidic protein, vimentin and S-100 immunohistochemistry, as well as with anti-TGF-alpha (transformerly growth factor) antibodies that are used as putative oligodendroglial cell markers in the white matter of rat. The subcortical white matter was reduced in irradiated animals, mainly in rat irradiated at P3, as revealed with myelin basic protein immunohistochemistry. Quantitative studies showed no significant differences in the number of glial cells in animals irradiated at P1 when compared with age-matched controls. However, reduced numbers of vimentin-, S-100-, and TGF-alpha-immunoreactive cells were found in animals irradiated at P3. These features indicate a limited capacity of surviving germinal cells, in animals irradiated at P3, to give rise to normal values of glial cells in the white matter in rat aged 30 days. This limitation mainly affects putative oligodendrocytes and glial cell precursors.

The histochemical identification of microglia

The existence of the microglial cell as an entity, part of the neuroglia of the CNS, is in question. Light-microscopic evidence of their presence, obtained through use of Del Rio-Hortega-type silver impregnation techniques, is plentiful. Evidence through electron microscopy has been equivocal although the balance of opinion favours their authenticity. Also, general histochemical techniques for neuroglia do not easily distinguish microglia. The use of thick (20–25 μm) free-floating cold neutral formalin-fixed sections, and prolonged incubation in the media of Padykula-Herman for adenosine triphosphatase (ATPase) and of Wachstein-Meisel for ATPase and other nucleoside phosphatases, demonstrated selectively in white matter of rats and rabbits neuroglial elements morphologically identical with microglia; in grey matter they were the most prominent elements. These are findings that confirm those previously made by Sjöstrand; uridine diphosphatase demonstrated the microglia just as well as did ATPase. Directly traumatized (stab wound) rat brain demonstrated that local microglia were activated and, with or without haematogeneous elements, took an active part in the formation of lipid-laden gitter cells. There was no evidence that enzymically hyperactive and hypertrophied microglia in grey matter (cerebral cortex) proliferated or migrated some distance from the site of necrosis. On the other hand, in white matter morphological characteristics of these cells strongly suggested that they were actively migrating towards the site of necrosis and gitter cells. Both in normal and activated microglia the best, and almost selective, enzymic markers were ATPase and UDPase. Oligodendrocytes of white matter, unless directly injured, reacted by hypertrophy, enzymic hyperactivity (including acid phosphatase) and proliferation. Such a reaction, seen under other conditions leading to demyelination and thought to be specific, seems, therefore, to be a nonspecific response to injury short of lethal. Nevertheless, direct or indirect transient or incomplete compromise of blood supply to these cells seems to be an important common factor.

Effects of hypothyroidism on the differentiation of neurons and glia in developing rat cerebrum

Microchemical techniques and histologic examination were used to study the somatosensory area of developing cerebral cortex and subcortical white matter in rats made thyroid hormone deficient immediately after birth. The body weight of these animals failed to show the normal growth spurt, achieving levels which were only 40% of age-matched controls by 50 post-natal days. The endocrine imbalance initiated by a lack of thyroid hormone from the day of birth results in a metabolic derangement which disturbs the migration of glial cells from the subependymal zone into cortex between 10 and 50 days of post-natal life. During this same developmental period, the differentiation of neurons is impaired, resulting in decreased formation of axodendritic processes and synapses. Finally, in association with the pathologic development of axons and fewer numbers of well-differentiated interfascicular oligodendroglia, there is a failure of myelin formation. Hence, in rats made hypothyroid at birth, the cerebrum is subjected to drastic alterations in the normally continuous and interdependent process of neuron and glial cell differentiation.

Hexachlorophene Influence on Ultrastructure of The CNS

Histological studies have demonstrated an hexachlorophene induced change of the cerebral white matter in rats (Kimbrough). The following report is an ultrastructural description of the changes as seen in monkeys, with an attempt to explain the molecular mechanism by which the changes develop.A dose of 3 mg of hexachlorophene per kg was administered subcutaneously to four juvenile (3-4 yrs) monkeys (Macaca mulatta) twice daily for 3 months. At the end of the experiment four treated monkeys and two stock control monkeys were sacrificed under anesthesia. The head region was perfused with 2.5% glutaraldehyde in a modified Tyrode's solution and tissues were sampled from spinal cord, superior colliculus, thalamus-callosum, cerebellum and optic nerve, and prepared for electron microscopic examination.Light microscopic examination revealed the development of cystic spaces in the thalamus-callosum samples from all of the treated animals. Optic nerve and spinal cord samples also demonstrated cystic spaces, but not as extensively as in thalamus-callosum.

The correlation between choline acetyltransferase and acetylcholinesterase activity in different areas of the cerebellum of rat and guinea pig.

Abstract— Choline acetyltransferase (ChAc) and acetylcholinesterase (AChE) levels were measured quantitatively in samples from the archi‐ and paleocerebellar vermis (Larsell's Lobules IX c,d,‐X, and Lobules VII‐VIII, respectively) and from the cerebellar peduncles, nuclei and white matter of rat and guinea pig. Lesions to isolate archi‐ or paleocerebellar areas were made in some rats and the effect on enzyme levels and ultrastructure were studied. In the rat there was a striking correlation between the activity of ChAc and AChE in the different areas; thus in the archicerebellar cortex the levels of both enzymes were 3–4 times those in the paleocortex. Deafferentation caused a fall in ChAc and this practically paralleled the fall in AChE in the same area. The reduction in both enzymes was more pronounced in the archi‐ than in the paleocerebellar cortex. In the guinea pig the results were very different. The ChAc activity was much lower than in the rat and was equal in the archi‐ and paleocerebellum. The AChE activity was also uniform in the different areas but, in contrast to ChAc, was higher than in the rat.