IKK mediates ischemia-induced neuronal death

The IkappaB kinase complex IKK is a central component of the signaling cascade that controls NF-kappaB-dependent gene transcription. So far, its function in the brain is largely unknown. Here, we show that IKK is activated in a mouse model of stroke. To investigate the function of IKK in brain ischemia we generated mice that contain a targeted deletion of Ikbkb (which encodes IKK2) in mouse neurons and mice that express a dominant inhibitor of IKK in neurons. In both lines, inhibition of IKK activity markedly reduced infarct size. In contrast, constitutive activation of IKK2 enlarged the infarct size. A selective small-molecule inhibitor of IKK mimicked the effect of genetic IKK inhibition in neurons, reducing the infarct volume and cell death in a therapeutic time window of 4.5 h. These data indicate a key function of IKK in ischemic brain damage and suggest a potential role for IKK inhibitors in stroke therapy.

NLRP3 inflammasome is expressed by astrocytes in the SOD1 mouse model of ALS and in human sporadic ALS patients

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of motoneurons in the cerebral cortex, brainstem and spinal cord. Neuroinflammation plays an important role in the pathogenesis of ALS and involves the activation of microglia and astrocytes. Intracellular inflammasome complexes are part of the innate immunity as they sense and execute host inflammatory responses. The best characterized component is the NLRP3 inflammasome comprised of the NLR protein NLRP3, the adaptor ASC and pro-caspase 1. The NLRP3 inflammasome is critical for the activation of caspase 1 and the processing and release of IL1β and IL18. In this study, we investigated the expression, activation and co-localization of the NLRP3 inflammasome in the spinal cord of male SOD1(G93A) mice carrying a mutant human superoxide dismutase 1 (SOD1) variant and regarded as an animal model for ALS as well as in post-mortem tissue of ALS patients. NLRP3 and its molecular components as well as IL1β were already detectable in SOD1 mice at a pre-symptomatic stage after 9 weeks and further increased in 14 week old animals. Spinal cord astrocytes were identified as the major cell type expressing NLRP3 components. In human ALS tissue, we also found increased NLRP3, ASC, IL18 and active caspase 1 levels compared to control patients. Our findings suggest that astroglial NLRP3 inflammasome complexes are critically involved in neuroinflammation in ALS.

Estrogen and the developing mammalian brain

In recent years, the knowledge of how estrogen interferes with mammalian brain functions and development has broadened substantially. In the adult brain, estrogen is not only involved in the neuroendocrine feedback regulation at the hypothalamic and pituitary level but also in the control of motor and cognitive functions. More recently, estrogen was found to act as a protective factor for neurodegenerative disorders such as Parkinson's and Alzheimer's disease. In contrast to these regulatory and protective functions, estrogen plays a different role during neuronal development. After the demonstration that the estrogen-synthesizing enzyme aromatase and both nuclear estrogen receptors are expressed in many brain areas during ontogeny, it was soon realized that estrogen modulates neuronal differentiation, notably by influencing cell migration, survival and death, and synaptic plasticity of neurons. These effects were initially seen in the classical target area for estrogen, the hypothalamus, but successive studies revealed the neurotrophic potential of estrogen also in other brain regions. The focus of this review will be to summarize estrogen formation and the role of estrogen during mammalian brain development. Moreover, cellular mechanisms involved in these neurotrophic effects will be discussed, giving special emphasis to "nongenomic" estrogen signaling and cross-coupling of estrogen signaling with those of growth factors.

Inflammasome: Its role in traumatic brain and spinal cord injury

Traumatic brain injury (TBI) and spinal cord injury (SCI) are pathological events that lead to neuropathological conditions which have in consequence the initiation of pro-inflammatory cytokine production. Neuroinflammation plays a key role in the secondary phase of both TBI and SCI after initial cell death. Activation of cytoplasmic inflammasome complexes is regarded as the essential step of neuroinflammation and a key trigger for neuronal death called pyroptosis. Inflammasome complexes are involved in activation of caspase-1 which catalyzes the cleavage of pro-interleukins into their active forms (including interleukin-18 [IL-18] and IL-1β). The focus of this article is to discuss the time-course and regulation of inflammasome assembly and activation during TBI and SCI and their targeting in designing therapeutic approaches. We particularly focus on the inflammasomes NLRP1 and NLRP3 which play a pivotal function during TBI and SCI in the central nervous system (CNS).

17beta-estradiol and progesterone prevent cuprizone provoked demyelination of corpus callosum in male mice

Sex hormones, for example, estrogen and progesterone, are thought to affect and delay progression of multiple sclerosis (MS) in pregnant women. Although both steroid hormones are neuroprotective in the brain and elevated during pregnancy, only estrogen was tested in clinical trials. To evaluate the role of 17beta-estradiol (E) and progesterone (P) in prevention demyelination, young adult male mice were fed with cuprizone for a defined time interval and simultaneously treated with steroids by repeated injections into the neck region. The status of myelination was analyzed by magnetic resonance imaging and conventional histological staining. The individual application of E and P resulted only in a moderate prevention of demyelination in the corpus callosum (CC). The combined treatment with both steroid hormones counteracted the process of demyelination. Expression of the mature (PLP and MBP) and premature (PDGF-alpha-R) oligodendrocyte markers were significantly increased after hormone application in the affected CC. In addition, both hormones stimulated astrogliosis and the expression of IGF-1. Microglial invasion in demyelinated CC was pronounced and additionally localized in the midline of CC after hormone treatment. These data show that sex steroids can protect the brain from demyelination and stimulate remyelination. It appears that only the administration of both hormones is fully effective. The beneficial steroid effect requires interactions with oligodendrocytes possibly by preventing their degeneration or recruitment from precursor cells which are stimulated to remyelinated fibers. The positive hormonal influence on myelination in the CNS may be a future therapeutically strategy for the treatment of MS.

Regulation of glutamate transporter GLAST and GLT-1 expression in astrocytes by estrogen

Estrogen influences neuronal development and a broad spectrum of neural functions. In addition, several lines of evidence suggest a role as neuroprotective factor for estrogen in the CNS. Neuroprotection can result from direct estrogen-neuron interactions or be mediated indirectly involving the regulation of physiological properties of nonneuronal cells, such as astrocytes and microglia. Increased l-glutamate levels are associated with neurotoxic and neurodegenerative processes in the brain. Thus, the removal of l-glutamate from the extracellular space by astrocytes through the astroglial glutamate transporters GLT-1 and GLAST appears essential for maintaining a homeostatic milieu for neighboring neurons. We have therefore studied the influence of 17beta-estradiol on l-glutamate metabolism in cultured astrocytes from the neonate mouse midbrain using quantitative RT-PCR and Western blotting for both transporters as well as functional l-glutamate uptake studies. The administration of estrogen significantly increased the expression of GLT-1 and GLAST on the mRNA and protein level. Likewise, specific l-glutamate uptake by astrocytes was elevated after estrogen exposure and mimicked by dbcAMP stimulation. Induction of transporter expression and l-glutamate uptake were sensitive to ICI 182,780 treatment suggesting estrogen action through nuclear estrogen receptors. These findings indicate that estrogen can prevent l-glutamate-related cell death by decreasing extracellular l-glutamate levels through an increased l-glutamate uptake capacity by astrocytes.

Pathological supply dependence of O2 uptake during bacteremia in dogs

When systemic delivery of O2 [QO2 = cardiac output X arterial O2 content (CaO2)] is reduced, the systemic O2 extraction ratio [(CaO2-concentration of O2 in venous blood/CaO2] increases until a critical limit is reached below which O2 uptake (VO2) becomes limited by delivery. Many patients with adult respiratory distress syndrome exhibit supply dependence of VO2 even at high levels of QO2, which suggests that a peripheral O2 extraction defect may be present. Since many of these patients also suffer from serious bacterial infection, we tested the hypothesis that bacteremia might produce a similar defect in the ability of tissues to maintain VO2 independent of QO2, as QO2 reduced. The critical O2 delivery (QO2crit) and critical extraction ratio (ERcrit) were compared in a control group of dogs and a group receiving a continuous infusion of Pseudomonas aeruginosa (5 x 10(7) organisms/min). Dogs were anesthetized, paralyzed, and ventilated with room air. Systemic QO2 was reduced in stages by hemorrhage as hematocrit was maintained. At each stage, systemic VO2 and QO2 were measured, and the critical point was determined from a plot of VO2 vs. QO2. The mean QO2crit and ERcrit of the bacteremic group (11.4 +/- 2.2 ml.min-1.kg-1 and 0.51 +/- 0.09) were significantly different from control (7.4 +/- 1.2 and 0.71 +/- 0.10) (P less than 0.05). These results suggest that bacterial infection can reduce the ability of peripheral tissues to extract O2 from a limited supply, causing VO2 to become limited by O2 delivery at a stage when a smaller fraction of the delivered O2 has been extracted.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered localization, abnormal modification and loss of function of Sigma receptor-1 in amyotrophic lateral sclerosis

Intracellular accumulations of mutant, misfolded proteins are major pathological hallmarks of amyotrophic lateral sclerosis (ALS) and related disorders. Recently, mutations in Sigma receptor 1 (SigR1) have been found to cause a form of ALS and frontotemporal lobar degeneration (FTLD). Our goal was to pinpoint alterations and modifications of SigR1 in ALS and to determine how these changes contribute to the pathogenesis of ALS. In the present study, we found that levels of the SigR1 protein were reduced in lumbar ALS patient spinal cord. SigR1 was abnormally accumulated in enlarged C-terminals and endoplasmic reticulum (ER) structures of alpha motor neurons. These accumulations co-localized with the 20s proteasome subunit. SigR1 accumulations were also observed in SOD1 transgenic mice, cultured ALS-8 patient's fibroblasts with the P56S-VAPB mutation and in neuronal cell culture models. Along with the accumulation of SigR1 and several other proteins involved in protein quality control, severe disturbances in the unfolded protein response and impairment of protein degradation pathways were detected in the above-mentioned cell culture systems. Furthermore, shRNA knockdown of SigR1 lead to deranged calcium signaling and caused abnormalities in ER and Golgi structures in cultured NSC-34 cells. Finally, pharmacological activation of SigR1 induced the clearance of mutant protein aggregates in these cells. Our results support the notion that SigR1 is abnormally modified and contributes to the pathogenesis of ALS.

Activation and Regulation of NLRP3 Inflammasome by Intrathecal Application of SDF-1a in a Spinal Cord Injury Model

Stromal cell-derived factor-1 alpha (SDF-1a) or CXCL12 is an important cytokine with multiple functions in the brain during development and in adulthood. The inflammatory response initiated by spinal cord injury (SCI) involves the processing of interleukin-1beta (IL-1ß) and IL-18 mediated by caspase-1 which is under the control of an intracellular multiprotein complex termed inflammasome. Using an SCI rat model, we found improved functional long-term recovery which is paralleled by a reduction of apoptosis after intrathecal treatment with SDF-1a. An intriguing aspect is that SDF-1a changed the number of neuroinflammatory cells in the damaged area. We further examined the cellular localization and sequential expression of several inflammasomes during SCI at 6 h, 24 h, 3 days, and 7 days as well as the role of SDF-1a as a regulatory factor for inflammasomes. Using 14-week old male Wistar rats, spinal cord contusion was applied at the thoracic segment 9, and animals were subsequently treated with SDF-1a via intrathecal application through an osmotic pump. SCI temporally increased the expression of the inflammasomes NLRP3, ASC, the inflammatory marker tumor necrosis factor-a (TNF-a), interleukin-1ß (IL-1β) and IL-18. SDF-1a significantly reduced the levels of IL-18, IL-1b, TNF-a, NLRP3, ASC, and caspase-1. Immunofluorescence double-labeling demonstrated that microglia and neurons are major sources of the ASC and NLRP3 respectivley. Our data provide clear evidence that SCI stimulates a complex scenario of inflammasome activation at the injured site and that SDF-1a-mediated neuroprotection presumably depends on the attenuation of the inflammasome complex.

Myelin debris regulates inflammatory responses in an experimental demyelination animal model and multiple sclerosis lesions

In multiple sclerosis (MS), gray matter pathology is characterized by less pronounced inflammation when compared with white matter lesions. Although regional differences in the cytoarchitecture may account for these differences, the amount of myelin debris in the cortex during a demyelinating event might also be contributory. To analyze the association between myelin debris levels and inflammatory responses, cortical areas with distinct and sparse myelination were analyzed for micro- and astrogliosis before and after cuprizone-induced demyelination in mice. In postmortem tissue of MS patients, leucocortical lesions were assessed for the type and level of inflammation in the cortical and white matter regions of the lesion. Furthermore, mice were injected intracerebrally with myelin-enriched debris, and the inflammatory response analyzed in white and grey matter areas. Our studies show that the magnitude of myelin loss positively correlates with microgliosis in the cuprizone model. In MS, the number of MHC class II expressing cells is higher in the white compared with the grey matter part of leucocortical lesions. Finally, direct application of myelin debris into the corpus callosum or cortex of mice induces profound and comparable inflammation in both regions. Our data suggest that myelin debris is an important variable in the inflammatory response during demyelinating events. Whether myelin-driven inflammation affects neuronal integrity remains to be clarified.

Progesterone therapy induces an M1 to M2 switch in microglia phenotype and suppresses NLRP3 inflammasome in a cuprizone-induced demyelination mouse model

Demyelination of the central nervous system (CNS) has been associated to reactive microglia in neurodegenerative disorders, such as multiple sclerosis (MS). The M1 microglia phenotype plays a pro-inflammatory role while M2 is involved in anti-inflammatory processes in the brain. In this study, CPZ-induced demyelination mouse model was used to investigate the effect of progesterone (PRO) therapy on microglia activation and neuro-inflammation. Results showed that progesterone therapy (CPZ+PRO) decreased neurological behavioral deficits, as demonstrated by significantly decreased escape latencies, in comparison to CPZ mice. In addition, CPZ+PRO caused a significant reduction in the mRNA expression levels of M1-markers (iNOS, CD86, MHC-II and TNF-α) in the corpus callosum region, whereas the expression of M2-markers (Trem-2, CD206, Arg-1 and TGF-β) was significantly increased, in comparison to CPZ mice. Moreover, CPZ+PRO resulted in a significant decrease in the number of iNOS+ and Iba-1+/iNOS+ cells (M1), whereas TREM-2+ and Iba-1+/TREM-2+ cells (M2) significantly increased, in comparison to CPZ group. Furthermore, CPZ+PRO caused a significant decrease in mRNA and protein expression levels of NLRP3 and IL-18 (~2-fold), in comparison to the CPZ group. Finally, CPZ+PRO therapy was accompanied with reduced levels of demyelination, compared to CPZ, as confirmed by immunofluorescence to myelin basic protein (MBP) and Luxol Fast Blue (LFB) staining, as well as transmission electron microscopy (TEM) analysis. In summary, we reported for the first time that PRO therapy causes polarization of M2 microglia, attenuation of M1 phenotype, and suppression of NLRP3 inflammasome in a CPZ-induced demyelination model of MS.

Somato-motor components of the pelvic and pudendal nerves of the female rat

The efferent innervation of the pelvic and pudendal nerves was characterized in this study by identifying the muscles activated by electrical stimulation of the nerves distal to the point at which they bifurcate from the L6-S1 trunk. Pelvic nerve electrical stimulation produced EMG-monitored contraction of the ipsilateral ilio- and pubococcygeus muscles, which was abolished by cutting one ('muscular') branch of the bifurcated nerve. (This 'muscular' branch receives proprioceptive input activated by tail displacement, whereas the other, 'viscero-cutaneous' branch receives sensory innervation from the midline perineal region.) Pudendal nerve electrical stimulation produced contraction of the coccygeus, external anal sphincter, and ischiocavernosus muscles. Movements of the orifice and wall of the vagina were directly visualized during electrical stimulation of the two nerves. Intravaginal pressure measured by balloon was increased by pelvic nerve stimulation and decreased by pudendal nerve stimulation. Reflexive contraction of the ilio- en pubococcygeus muscles was produced by mechanostimulation of the perineum, clitoral sheath and distal vagina. This response was abolished by gentle cervical mechanostimulation. One implication of this finding is that passage of the fetuses through the cervix during parturition may relax the ilio- and pubococcygeus muscles, thereby facilitating delivery.

Inflammatory response and chemokine expression in the white matter corpus callosum and gray matter cortex region during cuprizone-induced demyelination

Brain inflammation plays a central role in multiple sclerosis (MS). Besides lymphocytes, the astroglia and microglia mainly contribute to the cellular composition of the inflammatory infiltrate in MS lesions. Several studies were able to demonstrate that cortical lesions are characterized by lower levels of inflammatory cells among activated microglia/macrophages. The underlying mechanisms for this difference, however, remain to be clarified. In the current study, we compared the kinetics and extent of microglia and astrocyte activation during early and late cuprizone-induced demyelination in the white matter tract corpus callosum and the telencephalic gray matter. Cellular parameters were related to the expression profiles of the chemokines Ccl2 and Ccl3. We are clearly able to demonstrate that both regions are characterized by early oligodendrocyte stress/apoptosis with concomitant microglia activation and delayed astrocytosis. The extent of microgliosis/astrocytosis appeared to be greater in the subcortical white matter tract corpus callosum compared to the gray matter cortex region. The same holds true for the expression of the key chemokines Ccl2 and Ccl3. The current study defines a model to study early microglia activation and to investigate differences in the neuroinflammatory response of white vs. gray matter.

Nongenomic effects of oestrogen: embryonic mouse midbrain neurones respond with a rapid release of calcium from intracellular stores

Evidence is emerging that oestrogen, besides acting via classical nuclear receptors, can rapidly influence the physiology of nerve cells through other mechanisms. Oestrogens have been shown to modulate the differentiation and function of embryonic midbrain dopaminergic neurones by stimulating neurite outgrowth, expression of tyrosine hydroxylase mRNA, dopamine uptake and release in spite of the fact that dopaminergic cells in the prenatal midbrain do not express the classical oestrogen receptor. This study therefore intended to unravel possible signal transduction pathways activated by oestrogen which might be associated with the above oestrogen effects. As a physiological second-messenger mechanism, we studied the influence of oestrogen on fluctuations of intracellular Ca2+ levels [Ca2+]i by microspectrofluorimetry of the Ca2+-sensitive indicator Fura-2, in primary cultures from embryonic mouse midbrains. 17Beta-estradiol (10 nM-1 pM) but not 17alpha-estradiol increased [Ca2+]i within 1-3 s in a dose-dependent way. Removal of extracellular Ca2+ abrogated K+-stimulated Ca2+ rise but did not affect 17beta-estradiol stimulation. Pretreatment of cells with thapsigargin (1 microM, 10 min), an inhibitor of Ca2+-pumping ATPases in the endoplasmic reticulum, abolished the 17beta-estradiol effect but not the K+-stimulated [Ca2+]i rise. Oestrogen effects on [Ca2+]i were completely mimicked by using a membrane-impermeant oestrogen-BSA construct. In order to identify oestrogen-sensitive cells, some cultures were subsequently immunostained for microtubule-associated protein II, tyrosine hydroxylase, or GABA. All oestrogen-sensitive cells were immunocytochemically characterized as neurones, and about half of these responsive neurones was found to be dopaminergic or GABAergic. These results demonstrate that 17beta-estradiol is capable of rapidly modulating physiological parameters of developing midbrain neurones by directly interacting with specific membrane binding sites coupled to a signal transduction mechanism that causes a calcium release from intracellular Ca2+ stores. It is suggested that oestrogen effects on differentiation and function of midbrain dopaminergic neurones are mediated by intracellular Ca2+ signalling.

Nociceptive responses to altered GABAergic activity at the spinal cord

GABA agonists and antagonists were injected intrathecally at the spinal cord, to determine their effect on nociceptive thresholds. Tactile stimulation, applied against the flank by a medium diameter von Frey fiber (5.5 g force), elicited distress vocalizations after, but not before injection of the GABA antagonists, bicuculline MI or picrotoxin (0.25 and 1 microgram dosages). Vocalization threshold to tail shock was significantly reduced by bicuculline MI or picrotoxin. Tail flick withdrawal latency from radiant heat was not altered by GABA antagonists. The GABA agonist, muscimol, significantly elevated vocalization threshold to tail shock at a 5 micrograms dose. At a lower dose level (1 microgram), muscimol significantly reduced vocalization threshold to tail shock. Tail flick latency was significantly prolonged by the 5 micrograms dose of muscimol; however, flaccid paralysis of the hind limbs was also evident. Nociceptive thresholds were not altered by GABA or saline injection. These findings indicate that GABAergic activity contributes to the tonic modulation of nociception at the spinal cord.

Hyperalgesia induced by altered glycinergic activity at the spinal cord

Glycine or its receptor antagonist, strychnine, were administered perispinally to investigate their effect on nociceptive responses elicited by activation of various cutaneous receptors. Strychnine produced dose-dependent sensory and motor disturbances; 1 and 5 micrograms doses were sub-convulsive, eliciting recurrent episodes of coordinated grooming, scratching and biting at the skin, which persisted for approximately 10 minutes post-injection; higher doses (25 and 100 micrograms) increased the intensity and duration of these effects, and produced convulsive motor seizures. Motor disturbances were not elicited by glycine (5, 25, 100 and 400 micrograms). Strychnine treated rats, at all doses, vocalized consistently in response to light cutaneous stimulation; a significant proportion of glycine treated rats also vocalized, but were not as sensitive to mild stimulation. Skin hyperalgesia persisted for at least 30 minutes in both strychnine and glycine treated rats. Both strychnine and glycine significantly reduced vocalization thresholds to tail shock. However, no clear effect on tail flick latency was observed following either strychnine or glycine. These results indicate that glycinergic neurons contribute to the tonic regulation of nociceptive input at the spinal cord.

Rapid stimulation of the PI3-kinase/Akt signalling pathway in developing midbrain neurones by oestrogen

Oestrogen promotes the differentiation of neurones in the central nervous system. In the rodent midbrain, the maturation of dopaminergic neurones appears to be under oestrogen control. This is supported by the fact that dopaminergic cells contain nuclear oestrogen receptors-alpha/beta (ER). Second, aromatase is transiently expressed in the developing midbrain. In previous studies, we have shown that oestrogen increases dopamine synthesis and plasticity of dopamine cells. These effects are transmitted through classical nuclear ER but require also the stimulation of nonclassical signalling pathways involving the activation of membrane receptors. This study attempted to identify nonclassical oestrogen-dependent signalling cascades which might be stimulated downstream of membrane ERs. Using cultured mouse midbrain cells, we could demonstrate by Western blotting, that oestrogen rapidly phosphorylates Akt, a kinase which is implicated in the phosphatidylinositol 3 (PI3)-kinase pathway. This effect was only seen in midbrain neurones but not astrocytes. Oestrogen-induced Akt phosphorylation was time- and dose-dependent, showing highest responses after 30 min and at a steroid concentration of 10(-8) and 10(-6) M. Immunocytochemistry for phosphorylated Akt (pAkt) demonstrated that pAkt is predominantly found in a nuclear/perinuclear position and that oestrogen exposure increased the number of pAkt-positive cells. To investigate the mechanisms which are involved in transmitting oestrogen effects on the cellular level, cells were treated with antagonists for distinct signalling pathways. The application of the nuclear ER antagonist ICI 182 780 did not abolish the oestrogen-induced Akt phosphorylation. In contrast, interrupting intracellular calcium signalling with BAPTA completely prevented this effect. The PI3-kinase inhibitor LY294002 also inhibited the activation of Akt by oestrogen. Our study clearly indicates that oestrogen can rapidly stimulate the PI3-kinase/Akt signalling cascade in differentiating midbrain neurones. This effect requires the intermediate activation of calcium-dependent signalling pathways. In conclusion, oestrogen effects in the developing midbrain appear to be connected with the PI3-kinase/Akt signalling mechanism.

Ontogenetic expression and sex differences of aromatase and estrogen receptor-alpha/beta mRNA in the mouse hippocampus

Estrogen plays an important role during brain development interfering with the maturation of distinct neural systems and, in particular, with the sexual differentiation of brain structures and function. Similar to other brain regions, estrogen is known to influence neuronal differentiation and plasticity in the hippocampus. The present study is concerned with the developmental expression of mRNAs for the estrogen-synthesizing enzyme aromatase and the two known nuclear estrogen receptors (alpha/beta) in the male and female mouse hippocampus. Using semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis, we found that aromatase as well as estrogen receptors (alpha/beta) are already expressed prenatally in the hippocampus of both sexes. Aromatase expression increased during the first two postnatal weeks and decreased, thereafter, to lower levels in adults. Sex differences in aromatase expression were observed postnatally with higher levels in males. Estrogen receptor-alpha/beta mRNAs did not fluctuate obviously throughout pre- and postnatal development but revealed a distinct sex-specific pattern at the end of the first postnatal week. Again, higher expression was detected in males. These findings clearly demonstrate the capacity of estrogen formation and the presence of both estrogen receptor subtypes in the developing hippocampus. Sex differences in aromatase mRNA levels paralleled the sex-specific pattern of estrogen receptor expression. Thus, our data support the idea that the developing hippocampus is a target for estrogen action and estrogen receptor-mediated sexual differentiation.

Estrogen Attenuates Local Inflammasome Expression and Activation after Spinal Cord Injury

17-estradiol (E2) is a neuroprotective hormone with a high anti-inflammatory potential in different neurological disorders. The inflammatory response initiated by spinal cord injury (SCI) involves the processing of interleukin-1beta (IL-1b) and IL-18 mediated by caspase-1 which is under the control of an intracellular multiprotein complex called inflammasome. We recently described in a SCI model that between 24 and 72 h post-injury, most of inflammasome components including IL-18, IL-1b, NLRP3, ASC, and caspase-1 are upregulated. In this study, we investigated the influence of E2 treatment after spinal cord contusion on inflammasome regulation. After contusion of T9 spinal segment, 12-week-old male Wistar rats were treated subcutaneously with E2 immediately after injury and every 12 h for the next 3 days. Behavioral scores were significantly improved in E2-treated animals compared to vehicle-treated groups. Functional improvement in E2-treated animals was paralleled by the attenuated expression of certain inflammasome components such as ASC, NLRP1b, and NLRP3 together with IL1b, IL-18, and caspase-1. On the histopathological level, microgliosis and oligodendrocyte injury was ameliorated. These findings support and extend the knowledge of the E2-mediated neuroprotective function during SCI. The control of the inflammasome machinery by E2 might be a missing piece of the puzzle to understand the anti-inflammatory potency of E2.

Differentiated NSC-34 motoneuron-like cells as experimental model for cholinergic neurodegeneration

Alpha-motoneurons appear to be exceedingly affected in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Morphological and physiological degeneration of this neuronal phenotype is typically characterized by a marked decrease of neuronal markers and by alterations of cholinergic metabolism such as reduced choline acetyltransferase (ChAT) expression. The motoneuron-like cell line NSC-34 is a hybrid cell line produced by fusion of neuroblastoma with mouse motoneuron-enriched primary spinal cord cells. In order to further establish this cell line as a valid model system to investigate cholinergic neurodegeneration, NSC-34 cells were differentiated by serum deprivation and additional treatment with all-trans retinoic acid (atRA). Cell maturation was characterized by neurite outgrowth and increased expression of neuronal and cholinergic markers, including MAP2, GAP-43 and ChAT. Subsequently, we used differentiated NSC-34 cells to study early degenerative responses following exposure to various neurotoxins (H2O2, TNF-α, and glutamate). Susceptibility to toxin-induced cell death was determined by means of morphological changes, expression of neuronal marker proteins, and the ratio of pro-(Bax) to anti-(Bcl-2) apoptotic proteins. NSC-34 cells respond to low doses of neurotoxins with increased cell death of remaining undifferentiated cells with no obvious adverse effects on differentiated cells. Thus, the different vulnerability of differentiated and undifferentiated NSC-34 cells to neurotoxins is a key characteristic of NSC-34 cells and has to be considered in neurotoxic studies. Nonetheless, application of atRA induced differentiation of NSC-34 cells and provides a suitable model to investigate molecular events linked to neurodegeneration of differentiated neurons.

Cuprizone treatment induces demyelination and astrocytosis in the mouse hippocampus

Memory impairment is outstanding within the spectrum of cognitive deficits in multiple sclerosis (MS) patients. Demyelination has been reported in the hippocampus formation of MS patients. The degree of hippocampus lesions in MS strongly correlates with progression of cognitive dysfunction. Because no appropriate animal model for the study of hippocampus demyelination has been established, we used the cuprizone mouse model to investigated demyelination in young adult and aged mice. The myelin status was analyzed by classical histological staining, immunocytochemistry for proteolipoprotein, and electron microscopy. Oligodendrocyte, astroglial, and microglia markers were studied. Cuprizone intoxication induced an almost complete demyelination of distinct hippocampus subregions to a similar extent in young adult and aged male mice. Demyelination was pronounced in a subset of white and gray matter areas, i.e., the stratum lacunosum moleculare containing the perforant path, medial alveus, stratum pyramidale in the cornu ammonis 2/3 region, and hilus region. Besides demyelination, affected areas displayed hypertrophic and hyperplastic astrocytosis. No significant effect on microglia invasion was detected at any investigated time point (0, 3, 5, and 7 weeks). We conclude that cuprizone-induced demyelination provides an adequate animal model to investigate appropriate therapy strategies for the prevention of hippocampus demyelination.

Dopamine regulates brain-derived neurotrophic factor (BDNF) expression in cultured embryonic mouse striatal cells

The differentiation of striatal GABAergic neurons coincides with the perinatal establishment of nigrostriatal dopaminergic synaptic connections. We have shown previously that dopamine stimulates the maturation of striatal GABAergic neurons. Since BDNF also regulates the development of GABAergic cells, we hypothesized that dopamine might affect striatal BDNF expression. The influence of dopamine on BDNF protein/mRNA and trkB mRNA levels was studied in neuronal and astroglia cultures of the mouse striatum. Stimulation with dopamine and a dopamine D1 receptor agonist increased BDNF mRNA and protein but not trkB mRNA in neuronal cultures. Our data indicate a potential role for dopamine in the developmental regulation of striatal BDNF expression and suggest that dopamine effects on GABAergic cells may be intertwined with BDNF action.

Poststroke Inflammasome Expression and Regulation in the Peri-Infarct Area by Gonadal Steroids after Transient Focal Ischemia in the Rat Brain

CNS ischemia results in locally confined and rapid tissue damage accompanied by a loss of neurons and their circuits. Early and time-delayed inflammatory responses are critical variables determining the extent of neural disintegration and regeneration. Inflammasomes are vital effectors in innate immunity. Their activation in brain-intrinsic immune cells contributes to ischemia-related brain damage. The steroids 17β-estradiol (E2) and progesterone (P) are neuroprotective and anti-inflammatory. Using a transient focal rat ischemic model, we evaluated the time response of different inflammasomes in the peri-infarct zone from the early to late phases after poststroke ischemia. We show that the different inflammasome complexes reveal a specific time-oriented sequential expression pattern with a maximum at approximately 24 h after the infarct. Within the limits of antibody availability, immunofluorescence labeling demonstrated that microglia and neurons are major sources of the locally activated inflammasomes NOD-like receptor protein-3 (NLRP3) and associated speck-like protein (ASC), respectively. E2 and P given for 24 h immediately after ischemia onset reduced hypoxia-induced mRNA expression of the inflammasomes NLRC4, AIM2 and ASC, and decreased the protein levels of ASC and NLRP3. In addition, mRNA protein levels of the cytokines interleukin-1β (IL1β), IL18 and TNFα were reduced by the steroids. The findings provide for the first time a detailed flow chart of hypoxia-driven inflammasome regulation in the peri-infarct cerebral cortex. Further, we demonstrate that E2 and P alleviate the expression of certain inflammasome components, sometimes in a hormone-specific way. Besides directly regulating other cellular neuroprotective pathways, the control of inflammasomes by these steroids might contribute to its neuroprotective potency.