Dynamics of oligodendrocyte responses to anterograde axonal (Wallerian) and terminal degeneration in normal and TNF-transgenic mice

Multiple hippocampal transections for intractable hippocampal epilepsy: Seizure outcome

PURPOSE

The purpose of this study was to evaluate the seizure outcomes after transverse multiple hippocampal transections (MHTs) in 13 patients with intractable TLE.

METHODS

Thirteen patients with normal memory scores, including 8 with nonlesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. After confirming hippocampal seizure onset, they underwent MHT. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at approximately 1-cm intervals and spike counting for 5-8min before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and postoperatively for all patients and will be reported separately.

RESULTS

Duration of epilepsy ranged between 5 and 55years. There were no complications. Intraoperatively, MHT resulted in marked spike reduction (p=0.003, paired t-test). Ten patients (77%) are seizure-free (average follow-up was 33months, range 20-65months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another had an additional neocortical seizure focus (as suggested by pure aphasic seizures), and the third had only 2 seizures in 4years, one of which occurred during antiseizure medication withdrawal. Verbal and visual memory outcomes will be reported separately. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173).

CONCLUSIONS

Multiple hippocampal transections provide an effective intervention and a safe alternative to temporal lobectomy in patients with hippocampal epilepsy.

Effect of infliximab combined with methylprednisolone on expressions of NF-κB, TRADD, and FADD in rat acute spinal cord injury

STUDY DESIGN

The possibility to prevent acute spinal cord injury (ASCI) by selective infliximab combined with methylprednisolone (MP) was assessed in experimental ASCI.

OBJECTIVE

To investigate the effects of infliximab, MP, and the combination of these 2 agents on expressions of NF-κB (nuclear factor Kappa B), TRADD (tumor necrosis factor receptor associated death domain), and FADD (fas associated death domain) in a rat model of acute spinal cord injury (ASCI), and to confirm the therapeutic efficacy and possible mechanism of infliximab combined with MP in the treatment of ASCI.

SUMMARY OF BACKGROUND DATA

The theory that SCI can induce tumor necrosis factor-α expression at the injury site has been evaluated. However, there are few data to confirm the therapeutic efficacy of infliximab combinated with MP in the treatment of rat SCI METHODS: One hundred eighty adult male Sprague Dawley rats with 280 to 300 g body weight were allocated randomly and accordingly. We applied Basso, Beattie, Bresnahan locomotor rating scale to assess the hindlimb motor functional score (10 rats × 6 groups), the hematoxylin and eosin stain and immunohistochemistry stain (10 rats × 6 groups) to assay the morphological changes of spinal cord, the arrangement and expressions of NF-κB, TRADD and FADD, and the RT-PCR (10 rats × 6 groups) to evaluate the messenger RNA expressions of NF-κB, TRADD, and FADD.

RESULTS

The results showed that both infliximab and MP could lower the expressions of NF-κB, TRADD, and FADD 24 hours after the ASCI, and increased Basso, Beattie, Bresnahan score on the 14th and the 21st days after ASCI, suggesting possible neuroprotective effectiveness on attenuating the severity of neurological deficits and improving the locomotor function in the rat ASCI model. Moreover, infliximab combined with MP exhibited the more powerful ability to this amelioration.

CONCLUSION

Infliximab combined with methylprednisolone may be an effective treatment for the recovery of ASCI. Further study is needed to determine if this neuroprotective effect is seen for long-term outcomes especially in human ASCI.

Anti-TNF therapy in the injured spinal cord

Spinal cord injury (SCI) has a significant impact on the quality and expectancy of life. It also carries a heavy economic burden, with considerable costs associated with primary care and loss of income. The normal architecture of the spinal cord is radically disrupted by injury. After the initial insult, structure and function are lost through active secondary processes that involve reactive astrocytes, glial progenitors, microglia, macrophages, fibroblasts and Schwann cells. These cells produce chemokines and cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β, which mediate the recruitment of inflammatory cells to the injury site. Targeting of these cytokines represents a potential strategy to reduce the secondary damage in SCI. In this review, we focus on several emerging strategies to neutralize TNF-α, including antibodies, soluble receptors, recombinant TNF-binding proteins, TNF receptor fusion proteins, and non-specific agents (e.g. thalidomide) and discuss their potential as therapy for SCI.

Progesterone influence on neurite outgrowth involves microglia

Progesterone (P4) antagonizes estradiol (E2) in synaptic remodeling in the hippocampus during the rat estrous cycle. To further understand how P4 modulates synaptic plasticity, we used entorhinal cortex lesions, which induce E2-dependent neurite sprouting in the hippocampus. In young ovariectomized rats, the E2-dependent entorhinal cortex lesion-induced sprouting was attenuated by concurrent treatment with P4 and E2. Microglial activation also showed the E2-P4 antagonism. These findings extend reports on the estrous cycle synaptic remodeling without lesions by showing the P4-E2 antagonism during simultaneous treatment with both E2 and P4. Glial mechanisms were analyzed with the wounding-in-a-dish model of cocultured glia and embryonic d-18 cortical neurons from rat. In cocultures of mixed glia (astrocytes plus 30% microglia), P4 antagonized the E2-dependent neurite outgrowth (number and length) and neuron viability in the presence of E2, as observed in vivo. However, removal of microglia (astrocyte-neuron coculture) abolished the antagonism of E2 by P4 on neuron sprouting. The P4 receptor antagonists ORG-31710 and RU-486 blocked the antagonism of P4 on E2-dependent sprouting. These findings suggest a new role for microglia in P4 antagonism of E2 in neuronal plasticity and show its dependence on progesterone receptors. These findings are also relevant to the inclusion of progestins in hormone therapy, which is controversial in relation to cognitive declines during aging and in Alzheimer's disease.

MRI Detection of Secondary Damage After Stroke

Background and Purpose— Iron plays a central role in many metabolic processes. Under certain pathological situations it accumulates, producing negative effects such as increasing damage by oxidative stress. The present study examined long-term iron accumulation in a stroke model with secondary degeneration, using MRI and histological techniques.

Methods— Male Wistar rats (n=22) were subjected to 60 minutes MCA occlusion. MR images (T2- and T2*-weighted) were obtained weekly between weeks 1 and 7 after reperfusion, and at weeks 10, 14, 20, and 24. Histological iron detection and immunohistochemical examination for different markers (NeuN, GFAP, OX-42, HO-1, and APP) were performed at the 3 survival time points (3, 7, and 24 weeks).

Results— Infarcts affecting MCA territory were evident on T2-weighted imaging, and all animals showed deficits on behavioral tests. In the thalamus, T2 hyperintensity was detected 3 weeks after stroke, and disappeared around week 7 when T2*-weighted images showed a marked hypointensity in that area. Histology revealed neuronal loss in the thalamus, accompanied by strong microglial reactivity and microglial HO-1 expression. APP deposits were detected in the thalamus from week 3 on and persisted until week 24. Iron storage was detected in microglia at week 3, in the parenchyma at week 7, and around APP deposits at week 24.

Conclusions— T2*-weighted MRI allows the detection of secondary damage in the thalamus after MCAO. Iron accumulation in the thalamus is mediated by HO-1 expression in reactive microglia.

Structural reorganization of the dentate gyrus following entorhinal denervation: species differences between rat and mouse

Deafferentation of the dentate gyrus by unilateral entorhinal cortex lesion or unilateral perforant pathway transection is a classical model to study the response of the central nervous system (CNS) to denervation. This model has been extensively characterized in the rat to clarify mechanisms underlying denervation-induced gliosis, transneuronal degeneration of denervated neurons, and collateral sprouting of surviving axons. As a result, candidate molecules have been identified which could regulate these changes, but a causal link between these molecules and the postlesional changes has not yet been demonstrated. To this end, mutant mice are currently studied by many groups. A tacit assumption is that data from the rat can be generalized to the mouse, and fundamental species differences in hippocampal architecture and the fiber systems involved in sprouting are often ignored. In this review, we will (1) provide an overview of some of the basics and technical aspects of the entorhinal denervation model, (2) identify anatomical species differences between rats and mice and will point out their relevance for the axonal reorganization process, (3) describe glial and local inflammatory changes, (4) consider transneuronal changes of denervated dentate neurons and the potential role of reactive glia in this context, and (5) summarize the differences in the reorganization of the dentate gyrus between the two species. Finally, we will discuss the use of the entorhinal denervation model in mutant mice.

Unbiased cell quantification reveals a continued increase in the number of neocortical neurones during early post-natal development in mice

The post-natal growth spurt of the mammalian neocortex has been attributed to maturation of dendritic arborizations, growth and myelination of axons, and addition of glia. It is unclear whether this growth may also involve recruitment of additional neurones. Using stereological methods, we analysed the number of neurones and glia in the neocortex during post-natal development in two separate strains of mice. Cell counting by the optical fractionator revealed that the number of neurones increased 80-100% from the time of birth to post-natal day (P)16, followed by a reduction by approximately 25% in the young adult mouse at P50-55. Unexpectedly, at the time of birth less than half of the neurones and at P8 only 65% of the neurones expressed neuronal nuclear antigen (NeuN), a marker of mature post-migratory neurones. In accordance with these observations, NeuN acquisition by neurones in layer VIa was delayed until P16. The number of glia reached its maximum at P16, whereas the number of oligodendroglia, identified using a transgenic marker, increased until P55, the latest time of observation. Neurones continued to accumulate in the developing neocortex during the first 2 weeks of post-natal development, underscoring fundamental differences in brain development in the mouse compared with human and non-human primates. Further, delayed acquisition of NeuN by neurones in the deepest neocortical layers and continued addition of oligodendroglia to the neocortex suggested that neocortical maturation should be regarded as an ongoing process continuing into the young adult mouse.

Tumor necrosis factor and its p55 and p75 receptors are not required for axonal lesion-induced microgliosis in mouse fascia dentata

Tumor necrosis factor (TNF) is a potent pro-inflammatory and neuromodulatory cytokine. In the CNS it is produced primarily by microglia and considered to regulate microglial activation. On the basis of previous observations of increased microglial TNF mRNA synthesis in areas of anterograde axonal and terminal degeneration in mice, we studied the effect of TNF and its p55 and p75 receptors on axonal lesion-induced microglial activation in fascia dentata following transection of the perforant path (PP) projection. Unexpectedly, cell counting showed that the axonal lesion-induced microglial response in TNF and TNF-p55p75 receptor knock out mice and C57BL/6 mice was similar 5 days after the lesion. In addition, the microglial expression of the lysosomal-associated antigen CD68, and the clearance of MBP(+) myelin debris appeared similar in TNF and TNF-p55p75 receptor knock out mice compared to C57BL/6 mice. Quantitative PCR and in situ hybridization showed the expression of TNF mRNA to be maximally upregulated 6 h after the lesion, and confirmed that TNF mRNA was still upregulated 5 days after lesion when microglial numbers, CD11b mRNA level, and cellular TNF-p55 and -p75 receptor mRNA level reached maximum. However, in spite of the induction of TNF mRNA, TNF protein level remained at base-line in fascia dentata using immunohistochemistry and ELISA. In conclusion, the results showed a lower than expected lesion-induced increase in TNF protein, and that neither TNF nor its receptors were required for the axonal lesion-induced microglial morphological transformation and proliferation or for the initial clearance of degenerated myelin in the PP-deafferented fascia dentata.

Nogo-A expression in the human hippocampus in normal aging and in Alzheimer disease

Myelin-associated proteins are involved in the formation and stabilization of myelin sheaths. In addition, they prevent axon regeneration and plasticity in the adult brain. Recent evidence suggests that the expression of certain myelin-associated proteins (e.g. Nogo-A) can be regulated by synaptic activity or by over-expression after neural lesions in brain syndromes such as temporal lobe epilepsy. However, no studies on Alzheimer disease (AD) have been reported in which cell loss and significant synaptic reorganization occurs. In the present study, we analyze in detail the expression of Nogo-A in the hippocampal formation in normal human aging and in AD. Our results indicate that Nogo-A is expressed by oligodendrocytes and neurons in the aged hippocampal formation. In addition, both granule cells and mossy fiber connections are also labeled in the old-aged hippocampi. Interestingly, Nogo-A is over-expressed by hippocampal neurons in AD and is associated with beta-amyloid deposits in senile plaques. Taken together, our results reinforce the hypothesis that Reticulon proteins such as Nogo-A participate in the neuronal responses stemming from hippocampal formation during senescence, and particularly in AD. These findings also indicate that Reticulon proteins could be considered as new putative drug targets in therapies of neurodegenerative disorders.

NG2 upregulation in the denervated rat fascia dentata following unilateral entorhinal cortex lesion

The chondroitin sulfate proteoglycan NG2 is a component of the glial scar following brain injury. Because of its growth inhibiting properties, it has been suggested to impede axonal regeneration. To study whether NG2 could also regulate axonal growth in denervated brain areas, changes in NG2 were studied in the rat fascia dentata following entorhinal deafferentation and were correlated with the post-lesional sprouting response. Laser microdissection was employed to selectively harvest the denervated molecular layer and combined with quantitative RT-PCR to measure changes in NG2 mRNA (6 h, 12 h, 2 days, 4 days, 7 days post-lesion). This revealed increases of NG2 mRNA at day 2 (2.5-fold) and day 4 (2-fold) post-lesion. Immunocytochemistry was used to detect changes in NG2 protein (1 days, 4 days, 7 days, 10 days, 14 days, 30 days, 6 months post-lesion). NG2 staining was increased in the denervated outer molecular layer at day 1 post-lesion, reached a maximum 10 days post-lesion, and returned to control levels thereafter. Electron microscopy revealed NG2 immunoprecipitate on glial surfaces and in the extracellular matrix around neuronal profiles, indicating that NG2 is secreted following denervation. Double labeling of NG2-immunopositive cells with markers for astrocytes, microglia/macrophages, and mature oligodendrocytes suggested that NG2 cells are a distinct glial subpopulation before and after entorhinal deafferentation. BrdU labeling revealed that some of the NG2-positive cells are generated post-lesion. Taken together, our data revealed a layer-specific upregulation of NG2 in the denervated fascia dentata that coincides with the sprouting response. This suggests that NG2 could regulate lesion-induced axonal growth in denervated areas of the brain.

Validation of two reference genes for mRNA level studies of murine disease models in neurobiology

Reverse transcription of extracted cellular RNA combined with real-time PCR is now an established method for sensitive detection and quantification of specific mRNA level changes in experimental models of neurological diseases. To neutralize the impact of experimental error and make quantification more precise, normalization of test gene data using data from a constantly expressed gene, a reference gene that is tested along with the test gene, is required. There is no single gene constantly expressed under all experimental conditions. For a given set of conditions or a given disease model, identification of an unaffected reference gene is necessary. In this report, we present our findings from evaluation and validation of the genes encoding hypoxanthine guanine phosphoribosyl transferase 1 (HPRT1) and glyceraldehyde phosphate dehydrogenase (GAPDH) as individual reference genes in mRNA level studies involving four murine neurological disease models. We find both genes are suitable as a reference gene with these four models, provided quantification of subtle changes are avoided. We furthermore demonstrate that above a certain threshold of test mRNA level changes and given high quality RNA processing, normalization to total RNA alone provides for equally reliable quantitative mRNA level results.

Axonal degeneration stimulates the formation of NG2+ cells and oligodendrocytes in the mouse

Proliferation of the adult NG2-expressing oligodendrocyte precursor cells has traditionally been viewed as a remyelination response ensuing from destruction of myelin and oligodendrocytes, and not to the axonal pathology that is also a characteristic of demyelinating disease. To better understand the response of the NG2+ cells to the different components of demyelinating pathology, we investigated the response of adult NG2+ cells to axonal degeneration in the absence of primary myelin or oligodendrocyte pathology. Axonal degeneration was induced in the hippocampal dentate gyrus of adult mice by transection of the entorhino-dentate perforant path projection. The acutely induced degeneration of axons and terminals resulted in a prompt response of NG2+ cells, consisting of morphological transformation, cellular proliferation, and upregulation of NG2 expression days 2-3 after surgery. This was followed by a reduction of cellular NG2 expression to subnormal levels from day 5 to 7 and reappearance of normal appearing NG2+ cells from day 10. Mice that had received repeated injections of bromodeoxyuridine from 24 to 72 h after surgery contained significant numbers of bromodeoxyuridine-incorporating oligodendrocytes in the areas with axonal degeneration at day 7. The results suggest that axonal degeneration induces a unique sequence of changes of NG2+ cells and that a subpopulation of the newly generated NG2+ cells differentiate into oligodendrocytes.

Overexpression of myelin-associated glycoprotein after axotomy of the perforant pathway

Myelin-associated glycoprotein (MAG) contributes to the prevention of axonal regeneration in the adult central nervous system (CNS). However, changes in MAG expression following lesions and the involvement of MAG in the failure of cortical connections to regenerate are still poorly understood. Here, we show that MAG expression is differently regulated in the entorhinal cortex (EC) and the hippocampus in response to axotomy of the perforant pathway. In the EC, MAG mRNA is transiently overexpressed by mature oligodendrocytes after lesion. In the hippocampus, MAG overexpression is accompanied by an increase in the number of MAG-expressing cells. Lastly, the participation of MAG in preventing axonal regeneration was tested in vitro, where neuraminidase treatment of axotomized entorhino-hippocampal cultures potentiates axonal regeneration. These results demonstrate that MAG expression is regulated in response to cortical axotomy, and indicate that it may limit axonal regeneration after CNS injury.

Microglial cell population dynamics in the injured adult central nervous system

Reactive microgliosis is characteristic of trauma and stroke as well as inflammatory and chronic neurodegenerative disease. A conspicuous feature of the microglial reaction to acute neural injury is a massive expansion of the microglial cell population which peaks a few days following injury. New data based on the use of radiation bone marrow-chimeric mice suggest this expansion also involves recruitment of bone marrow-derived cells, which migrate into the neural parenchyma and differentiate into microglia. Here, we discuss the contribution of bone marrow-derived cells to the injury-induced expansion of the microglial cell population, seen in the dentate gyrus with ongoing anterograde axonal and terminal synaptic degeneration, subsequent to transection of the entorhino-dentate perforant path projection. In this paradigm of minor brain injury, the bone marrow-derived cells are grossly outnumbered by activated resident microglia, which express the stem cell antigen CD34 concurrent to a marked capacity for self-renewal. The observation of a mixed origin of lesion-reactive microglia, consisting of a smaller subpopulation of exogenous bone marrow-derived microglia, and a larger population of activated resident microglia, the majority of which express CD34 and undergo proliferation, suggests that lesion-reactive microglia consist of functionally distinct cell populations. The demonstration of an injury-enhanced recruitment of bone marrow-derived cells into the perforant path-denervated dentate gyrus, raises the possibility of using genetically manipulated cells as vectors for lesion-site-specific gene therapy even in minimally injured areas of the central nervous system.