Contribution of axonal orientation to pathway-dependent modulation of excitatory transmission by direct current stimulation in isolated rat hippocampus

Transcranial direct current stimulation (tDCS) is a method for modulating cortical excitability by weak constant electrical current that is applied through scalp electrodes. Although often described in terms of anodal or cathodal stimulation, depending on which scalp electrode pole is proximal to the cortical region of interest, it is the orientation of neuronal structures relative to the direct current (DC) vector that determines the effect of tDCS. To investigate the contribution of neural pathway orientation, we studied DCS-mediated neuromodulation in an in vitro rat hippocampal slice preparation. We examined the contribution of dendritic orientation to the direct current stimulation (DCS) neuromodulatory effect by recording field excitatory postsynaptic potentials (fEPSPs) in apical and basal dendrites of CA1 neurons within a constant DC field. In addition, we assessed the contribution of axonal orientation by recording CA1 and CA3 apical fEPSPs generated by stimulation of oppositely oriented Schaffer collateral and mossy fiber axons, respectively, during DCS. Finally, nonsynaptic excitatory signal propagation was measured along antidromically stimulated CA1 axons at different DCS amplitudes and polarity. We find that modulation of both the fEPSP and population spike depends on axonal orientation relative to the electric field vector. Axonal orientation determines whether the DC field is excitatory or inhibitory and dendritic orientation affects the magnitude, but not the overall direction, of the DC effect. These data suggest that tDCS may oppositely affect neurons in a stimulated cortical volume if these neurons are excited by oppositely orientated axons in a constant electrical field.

A new measure of cortical inhibition by mechanomyography and paired-pulse transcranial magnetic stimulation in unanesthetized rats

Paired-pulse transcranial magnetic stimulation (ppTMS) is a safe and noninvasive tool for measuring cortical inhibition in humans, particularly in patients with disorders of cortical inhibition such as epilepsy. However, ppTMS protocols in rodent disease models, where mechanistic insight into the ppTMS physiology and into disease processes may be obtained, have been limited due to the requirement for anesthesia and needle electromyography. To eliminate the confounding factor of anesthesia and to approximate human ppTMS protocols in awake rats, we adapted the mechanomyogram (MMG) method to investigate the ppTMS inhibitory phenomenon in awake rats and then applied differential pharmacology to test the hypothesis that long-interval cortical inhibition is mediated by the GABA(A) receptor. Bilateral hindlimb-evoked MMGs were elicited in awake rats by long-interval ppTMS protocols with 50-, 100-, and 200-ms interstimulus intervals. Acute changes in ppTMS-MMG were measured before and after intraperitoneal injections of saline, the GABA(A) agonist pentobarbital (PB), and GABA(A) antagonist pentylenetetrazole (PTZ). An evoked MMG was obtained in 100% of animals by single-pulse stimulation, and ppTMS resulted in predictable inhibition of the test-evoked MMG. With increasing TMS intensity, MMG amplitudes increased in proportion to machine output to produce reliable input-output curves. Simultaneous recordings of electromyography and MMG showed a predictable latency discrepancy between the motor-evoked potential and the evoked MMG (7.55 ± 0.08 and 9.16 ± 0.14 ms, respectively). With pharmacological testing, time course observations showed that ppTMS-MMG inhibition was acutely reduced following PTZ (P < 0.05), acutely enhanced after PB (P < 0.01) injection, and then recovered to pretreatment baseline after 1 h. Our data support the application of the ppTMS-MMG technique for measuring the cortical excitability in awake rats and provide the evidence that GABA(A) receptor contributes to long-interval paired-pulse cortical inhibition. Thus ppTMS-MMG appears a well-tolerated biomarker for measuring GABA(A)-mediated cortical inhibition in rats.

Strain-specific differences in perinatal rodent oligodendrocyte lineage progression and its correlation with human

Progress in the development of rat models of human periventricular white matter injury (WMI) has been hampered by uncertainty about the developmental window in different rodent strains that coincides with cerebral white matter development in human premature infants. To define strain-specific differences in rat cerebral white matter maturation, we analyzed oligodendrocyte (OL) lineage maturation between postnatal days (P)2 and P14 in three widely studied strains of rat: Sprague-Dawley, Long-Evans and Wistar (W). We previously reported that late OL progenitors (preOL) are the major vulnerable cell type in human periventricular WMI. Strain-specific differences in preOL maturation were found at P2, such that the W rat had the highest percentage and density of preOL relative to the other strains. Overall, at P2, the state of OL maturation was similar to preterm human cerebral white matter. However, by P5, all three strains displayed a similar magnitude and extent of OL maturation that persisted with progressive myelination between P7 and P14. PreOL were the predominant OL lineage stage present in the cerebral cortex through P14, and thus OL lineage maturation occurred latter than in white matter. The hippocampus also displayed a later onset of preOL maturation in all three strains, such that OL lineage maturation and early myelination was not observed to occur until about P14. This timing of preOL maturation in rat cortical gray matter coincided with a similar timing in human cerebral cortex, where preOL also predominated until at least 8 months after full-term birth. These studies support that strain-specific differences in OL lineage immaturity were present in the early perinatal period at about P2, and they define a narrow window of preterm equivalence with human that diminishes by P5. Later developmental onset of preOL maturation in both cerebral cortex and hippocampus coincides with an extended window of potential vulnerability of the OL lineage to hypoxia-ischemia in these gray matter regions.

Reprint of "The developing oligodendrocyte: key cellular target in brain injury in the premature infant"

Brain injury in the premature infant, a problem of enormous importance, is associated with a high risk of neurodevelopmental disability. The major type of injury involves cerebral white matter and the principal cellular target is the developing oligodendrocyte. The specific phase of the oligodendroglial lineage affected has been defined from study of both human brain and experimental models. This premyelinating cell (pre-OL) is vulnerable because of a series of maturation-dependent events. The pathogenesis of pre-OL injury relates to operation of two upstream mechanisms, hypoxia-ischemia and systemic infection/inflammation, both of which are common occurrences in premature infants. The focus of this review and of our research over the past 15-20 years has been the cellular and molecular bases for the maturation-dependent vulnerability of the pre-OL to the action of the two upstream mechanisms. Three downstream mechanisms have been identified, i.e., microglial activation, excitotoxicity and free radical attack. The work in both experimental models and human brain has identified a remarkable confluence of maturation-dependent factors that render the pre-OL so exquisitely vulnerable to these downstream mechanisms. Most importantly, elucidation of these factors has led to delineation of a series of potential therapeutic interventions, which in experimental models show marked protective properties. The critical next step, i.e., clinical trials in the living infant, is now on the horizon.

The clinically available NMDA receptor antagonist, memantine, exhibits relative safety in the developing rat brain

The N-methyl-d-aspartate glutamate receptor (NMDAR) has been implicated in preterm brain injury (periventricular leukomalacia (PVL)) and represents a potential therapeutic target. However, the antagonist dizocilpine (MK-801) has been reported to increase constitutive neuronal apoptosis in the developing rat brain, limiting its clinical use in the developing brain. Memantine is another use-dependent NMDAR antagonist with shorter binding kinetics and has been demonstrated to be protective in a rat model of PVL, without effects on normal myelination or cortical growth. To further evaluate the safety of memantine in the developing brain, we demonstrate here that, in contrast to MK-801, memantine at neuroprotective doses does not increase neuronal constitutive apoptosis. In addition, there are no long-term alterations in the expression of NMDAR subunits, AMPAR subunits, and two markers of synaptogenesis, Synapsin-1 and PSD95. Evaluating clinically approved drugs in preclinical neonatal animal models of early brain development is an important prerequisite to considering them for clinical trial in preterm infants and early childhood.

The developing oligodendrocyte: key cellular target in brain injury in the premature infant

Brain injury in the premature infant, a problem of enormous importance, is associated with a high risk of neurodevelopmental disability. The major type of injury involves cerebral white matter and the principal cellular target is the developing oligodendrocyte. The specific phase of the oligodendroglial lineage affected has been defined from study of both human brain and experimental models. This premyelinating cell (pre-OL) is vulnerable because of a series of maturation-dependent events. The pathogenesis of pre-OL injury relates to operation of two upstream mechanisms, hypoxia-ischemia and systemic infection/inflammation, both of which are common occurrences in premature infants. The focus of this review and of our research over the past 15-20 years has been the cellular and molecular bases for the maturation-dependent vulnerability of the pre-OL to the action of the two upstream mechanisms. Three downstream mechanisms have been identified, i.e., microglial activation, excitotoxicity and free radical attack. The work in both experimental models and human brain has identified a remarkable confluence of maturation-dependent factors that render the pre-OL so exquisitely vulnerable to these downstream mechanisms. Most importantly, elucidation of these factors has led to delineation of a series of potential therapeutic interventions, which in experimental models show marked protective properties. The critical next step, i.e., clinical trials in the living infant, is now on the horizon.

Development of later life spontaneous seizures in a rodent model of hypoxia-induced neonatal seizures

PURPOSE

To study the development of epilepsy following hypoxia-induced neonatal seizures in Long-Evans rats and to establish the presence of spontaneous seizures in this model of early life seizures.

METHODS

Long-Evans rat pups were subjected to hypoxia-induced neonatal seizures at postnatal day 10 (P10). Epidural cortical electroencephalography (EEG) and hippocampal depth electrodes were used to detect the presence of seizures in later adulthood (> P60). In addition, subdermal wire electrode recordings were used to monitor age at onset and progression of seizures in the juvenile period, at intervals between P10 and P60. Timm staining was performed to evaluate mossy fiber sprouting in the hippocampi of P100 adult rats that had experienced neonatal seizures.

KEY FINDINGS

In recordings made from adult rats (P60-180), the prevalence of epilepsy in cortical and hippocampal EEG recordings was 94.4% following early life hypoxic seizures. These spontaneous seizures were identified by characteristic spike and wave activity on EEG accompanied by behavioral arrest and facial automatisms (electroclinical seizures). Phenobarbital injection transiently abolished spontaneous seizures. EEG in the juvenile period (P10-60) showed that spontaneous seizures first occurred approximately 2 weeks after the initial episode of hypoxic seizures. Following this period, spontaneous seizure frequency and duration increased progressively with time. Furthermore, significantly increased sprouting of mossy fibers was observed in the CA3 pyramidal cell layer of the hippocampus in adult animals following hypoxia-induced neonatal seizures. Notably, Fluoro-Jade B staining confirmed that hypoxic seizures at P10 did not induce acute neuronal death.

SIGNIFICANCE

The rodent model of hypoxia-induced neonatal seizures leads to the development of epilepsy in later life, accompanied by increased mossy fiber sprouting. In addition, this model appears to exhibit a seizure-free latent period, following which there is a progressive increase in the frequency of electroclinical seizures.

Sensitive isotope dilution liquid chromatography/tandem mass spectrometry method for quantitative analysis of bumetanide in serum and brain tissue

We have developed and validated a simple and sensitive stable isotope dilution liquid chromatography/tandem mass spectrometric (LC-MS/MS) method for the quantification of bumetanide in human serum. Samples were prepared with a simple acetonitrile based protein precipitation. The supernatant was then analyzed directly using LC-MS/MS. Chromatographic separation was achieved on a C18 reversed phase column using a methanol and water gradient. The detection was performed in selected reaction monitoring (SRM) mode via a positive electrospray ionization (ESI) interface. The method had a lower limit of quantification (LLOQ) of 1 ng/mL, linearity up to 1250 ng/mL, intra- and inter-day precision less than 10%, and accuracy within ±10%. This method was also demonstrated to be suitable for the analysis of bumetanide in rat serum and brain tissue. Bumetanide concentrations in rat serum and brain were determined for samples collected at several intervals following intraperitoneal (i.p.) injection of bumetanide, and were used to calculate bumetanide permeability through the blood-brain barrier.

Epilepsy as a spectrum disorder: Implications from novel clinical and basic neuroscience

Epilepsy is increasingly recognized as a disease that reaches well beyond seizures. Cognitive and psychiatric impairment affect half of all epilepsy patients, and to date there are no specific treatments for these symptoms. It is unclear which of these comorbidities are directly due to seizures and which are due to separable mechanisms that are parallel to those underlying ictal activity. Cellular and molecular mechanisms underlying synaptic modulation are central to both the ictal and nonictal changes in epilepsy. Current diagnostic methods are rapidly advancing to better delineate the nature and extent of ictal activity, and could soon be critical in identifying patterns unique to the cognitive and psychiatric comorbidities.

Does acquired epileptogenesis in the immature brain require neuronal death

Because epilepsy often occurs during development, understanding the mechanisms by which this process takes place (epileptogenesis) is important. In addition, the age-specificity of seizures and epilepsies of the neonatal, infancy, and childhood periods suggests that the processes and mechanisms that culminate in epilepsy might be age specific as well. Here we provide an updated review of recent and existing literature and discuss evidence that neuronal loss may occur during epileptogenesis in the developing brain, but is not required for the epileptogenic process. We speculate about the mechanisms for the resilience of neurons in immature limbic structures to epileptogenic insults, and propose that the type, duration and severity of these insults influence the phenomenology of the resulting spontaneous seizures.

Measures of cortical inhibition by paired-pulse transcranial magnetic stimulation in anesthetized rats

Paired-pulse transcranial magnetic stimulation (ppTMS) is a noninvasive method to measure cortical inhibition in vivo. Long interpulse interval (50-500 ms) ppTMS (LI-ppTMS) provokes intracortical inhibitory circuits and can reveal pathologically impaired cortical inhibition in disorders such as epilepsy. Adaptation of ppTMS protocols to rodent disease models is highly desirable to facilitate basic and translational research. We previously adapted single-pulse TMS (spTMS) methods to rats, but ppTMS has yet to be applied. Specifically, whether ppTMS elicits an inhibitory response in rodents is unknown. ppTMS in rats also requires anesthesia, a setting under which the preservation of these measures is undetermined. We therefore tested, in anesthetized rats, whether anesthetic choice affects spTMS-motor-evoked potentials (MEPs), LI-ppTMS in rats, as in humans, elicits intracortical inhibition of the MEP, and rat LI-ppTMS inhibition is acutely impaired in a seizure model. Rats were anesthetized with pentobarbital (PB) or ketamine-atropine-xylazine (KAX) and stimulated unilaterally over the motor cortex while recording bilateral brachioradialis MEPs. LI-ppTMS was applied analogous to human long interval intracortical inhibition (LICI) protocols, and acute changes in inhibition were evaluated following injection of the convulsant pentylenetetrazole (PTZ). We find that spTMS-evoked MEPs were reliably present under either anesthetic, and that LI-ppTMS elicits inhibition of the conditioned MEP in rats, similar to human LICI, by as much as 58 ± 12 and 71 ± 11% under PB and KAX anesthesia, respectively. LI-ppTMS inhibition was reduced to as much as 53% of saline controls following PTZ injection, while spTMS-derived measures of corticospinal excitability were unchanged. Our data show that regional inhibition, similar to human LICI, is present in rats, can be elicited under PB or KAX anesthesia, and is reduced following convulsant administration. These results suggest a potential for LI-ppTMS as a biomarker of impaired cortical inhibition in murine disease models.

Association of the small GTPase Rheb with the NMDA receptor subunit NR3A

The NMDAR subunit NR3A is most highly expressed during the second postnatal week, when synaptogenesis reaches peak levels. Genetic ablation or overexpression of the NR3A subunit negatively interferes with the maturation of cortical synapses and leads to changes in the shape and number of dendritic spines, the density of which is increased in NR3A knock-out mice and decreased in NR3A-overexpressing transgenic mice. Alterations in spine density have been linked to dysregulation of mTOR signaling and synaptic protein translation. Using a yeast two-hybrid system, we identified the mTOR-activating GTPase Rheb as an interacting protein of the NMDAR subunit NR3A. We confirmed the interaction in mammalian cells by expressing recombinant Rheb and NR3A and showed that Rheb and NR3A could be co-immunoprecipitated from synaptic plasma membranes from the developing rat brain. These data suggest that NR3A sequesters synaptic Rheb and might thus function as a break of the mTOR-dependent synaptic translation of protein.

Neonatal seizures: an update on mechanisms and management

The lifespan risk of seizures is highest in the neonatal period. Current therapies have limited efficacy. Although the treatment of neonatal seizures has not changed significantly in the last several decades, there has been substantial progress in understanding developmental mechanisms that influence seizure generation and responsiveness to anticonvulsants. This article provides an overview of current approaches to the diagnosis and treatment of neonatal seizures, and some of the recent insights about the pathophysiology of neonatal seizures that may provide the foundation for better treatment are identified.

Altered development of glutamatergic synapses in layer V pyramidal neurons in NR3A knockout mice

Expression of the NMDA receptor (NMDAR) subunit NR3A reaches its highest level in layer V of the developing rodent cortex during the second postnatal week, a peak period of synaptogenesis. Incorporation of NR3A leads to the formation of non-canonical, Mg2+-insensitive NMDARs, but it is not known whether they participate in synaptic transmission and maturation. Here we show that in the second postnatal week, layer V pyramidal neurons in the somatosensory cortex of wild type (WT) mice exhibited evoked excitatory postsynaptic currents (eEPSCs) with 3- to 6-fold lower Mg2+ sensitivity than NR3A knockout (KO) mice and their reversal potential was approximately 2 mV more negative compared to KO mice consistent with decreased P(Ca) of NMDARs. Surprisingly, ablation of NR3A also led to a 20-fold reduction of the ratio of AMPAR- to NMDAR-mediated eEPSC amplitudes in KO mice. Insertion of AMPARs at the synapses of layer V pyramidal neurons appears to be facilitated by the expression of Mg2+-insensitive NMDARs. The data indicate that NR3A plays a significant role in the development of excitatory synapses in layer V of the developing neocortex.

17beta-estradiol protects against hypoxic/ischemic white matter damage in the neonatal rat brain

Developing oligodendrocytes (pre-OLs) are highly vulnerable to hypoxic-ischemic injury and associated excitotoxicity and oxidative stress. 17beta-Estradiol plays an important role in the development and function of the CNS and is neuroprotective. The sudden drop in circulating estrogen after birth may enhance the susceptibility of developing OLs to injury. Estrogen receptor (ER)-alpha and ER-beta are both expressed in OLs. We examined the effect of 17beta-estradiol on oxygen-glucose deprivation and oxidative stress-induced cell death in rat pre-OLs in vitro and on hypoxic-ischemic brain injury in vivo. Pre-OLs in culture were subjected to oxygen-glucose deprivation (OGD) or glutathione depletion in the presence or absence of 17beta-estradiol. LDH release, the Alamar blue assay, and phase-contrast microscopy were used to assess cell viability. Hypoxic-ischemic injury was generated in 6-day-old rats (P6) by unilateral carotid ligation and hypoxia (6% O(2) for 1 hr). Rat pups received one intraperitoneal injection of 300 or 600 microg/kg 17beta-estradiol or vehicle 12 hr prior to the surgical procedure. Injury was assessed by myelin basic protein (MBP) immunocytochemistry at P10. 17beta-Estradiol produced significant protection against OGD-induced cell death in primary OLs (EC(50) = 1.3 +/- 0.46 x 10(-9) M) and against oxidative stress. Moreover, 17beta-estradiol attenuated the loss of MBP labeling in P10 pups ipsilateral to the carotid ligation. These results suggest a potential role for estrogens in attenuation of hypoxic-ischemic and oxidative injury to developing OLs and in the prevention of periventricular leukomalacia.

Curing epilepsy: progress and future directions

During the past decade, substantial progress has been made in delineating clinical features of the epilepsies and the basic mechanisms responsible for these disorders. Eleven human epilepsy genes have been identified and many more are now known from animal models. Candidate targets for cures are now based upon newly identified cellular and molecular mechanisms that underlie epileptogenesis. However, epilepsy is increasingly recognized as a group of heterogeneous syndromes characterized by other conditions that co-exist with seizures. Cognitive, emotional and behavioral co-morbidities are common and offer fruitful areas for study. These advances in understanding mechanisms are being matched by the rapid development of new diagnostic methods and therapeutic approaches. This article reviews these areas of progress and suggests specific goals that once accomplished promise to lead to cures for epilepsy.

Talampanel suppresses the acute and chronic effects of seizures in a rodent neonatal seizure model

PURPOSE

To test the efficacy of the novel candidate anticonvulsant talampanel (GYKI 53773) in a rodent model of hypoxic neonatal seizures. Talampanel is a noncompetitive antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid subtype of the glutamate receptor (AMPAR). We have previously shown that AMPARs play a critical role in the generation of acute seizures and later-life seizure susceptibility in this model of neonatal seizures.

METHODS

Seizures were induced in postnatal day (P) 10 Long-Evans rat pups by a 15 min exposure to global hypoxia. Acute seizure activity at P10 and subsequent susceptibility to seizure-induced neuronal injury with a "second-hit" kainate-induced seizure at P30-31 were compared between animals receiving talampanel (1, 5, 7.5, or 10 mg/kg) intraperitoneally (i.p.) versus saline vehicle treatment.

RESULTS

Talampanel treatment suppressed seizures in a dose-dependent manner, with maximal effect at 7.5 and 10 mg/kg. In addition, talampanel treatment 30 min before hypoxia prevented later-life increases in seizure-induced neuronal injury as assessed by in situ DNA nick end-labeling (ISEL).

DISCUSSION

We have previously demonstrated efficacy of other AMPAR antagonists such as NBQX and topiramate in this model. The present finding shows that the novel agent talampanel, under evaluation as an antiepileptic drug in children and adults, may have clinical potential in the treatment of neonatal seizures, particularly those occurring in the context of hypoxic encephalopathy.

Seizure suppression by EEG-guided repetitive transcranial magnetic stimulation in the rat

OBJECTIVE

To test the anticonvulsive potential of a range of repetitive transcranial magnetic stimulation (rTMS) frequencies by novel methods for simultaneous EEG and rTMS in a rat seizure model.

METHODS

Seizures were triggered by intraperitoneal kainic acid (KA; 10mg/kg). Rats (n=21) were divided into three groups in which individual seizures were treated with rTMS trains at one of three frequencies: 0.25, 0.5 or 0.75 Hz. EEG was continuously viewed by an operator who identified each seizure onset. Consecutive seizures in each animal were (1) treated with active rTMS, (2) treated with sham rTMS, or (3) were untreated. EEG was re-analyzed post hoc by visual inspection, and seizure durations were compared within and between treatment groups.

RESULTS

KA-induced seizures were abbreviated by 0.75 Hz (P=0.019) and 0.5 Hz (P=0.033) active EEG-guided rTMS. In contrast, neither active 0.25 Hz rTMS nor the control conditions affected seizure duration (P>0.2).

CONCLUSIONS

We demonstrate that EEG-guided rTMS can suppress seizures in the rat KA epilepsy model, and that the effect is frequency dependent, with 0.75 and 0.5 Hz rTMS being superior to 0.25 Hz rTMS.

SIGNIFICANCE

These data support the use of rat seizure models in translational research aimed at evaluation and development of effective rTMS anticonvulsive protocols. We also offer a proof of principle that real-time analysis of EEG can be used to guide rTMS to suppress individual seizures.

Cell-specific alterations of glutamate receptor expression in tuberous sclerosis complex cortical tubers

OBJECTIVE

Genetic loss of TSC1/TSC2 function in tuberous sclerosis complex (TSC) results in overactivation of the mammalian target of rapamycin complex 1 pathway, leading to cellular dysplasia. We hypothesized that the dysplastic cells in TSC tubers are heterogeneous, including separable classes on a neuronal-glial spectrum, and that these dysplastic cells express glutamate receptor (GluR) patterns consistent with increased cortical network excitability.

METHODS

Surgically resected human cortical tubers and nondysplastic epileptic cortical samples were analyzed by double-label immunocytochemistry for coexpression of neuronal and glial markers, the TSC1/TSC2 pathway downstream molecule phospho-S6 (pS6) and GluR subunits, and compared with control cortical tissue. Western blotting was used to quantify changes in GluR subunit expression in tubers versus controls.

RESULTS

We demonstrate that cortical tubers contain a broad spectrum of cell types including disoriented pyramidal cells, dysplastic neurons, giant neuroglial cells, dysplastic astroglia, and reactive astrocytes. Dysplastic neurons, giant cells, and dysplastic astroglia express high levels of pS6 and demonstrate altered GluR subunit composition, resembling those of normal immature neurons and glia. In contrast, nondysplastic neurons in TSC and non-TSC epileptic lesions express lower pS6 levels and display changes in GluR subunit expression that are distinct from the patterns seen in tuber dysplastic cells.

INTERPRETATION

This work significantly expands the spectrum of abnormal cells recognized in tubers beyond the classic tuber giant cell and demonstrates cell-specific abnormalities in GluR expression that may contribute to seizure pathogenesis in TSC. Furthermore, these results suggest that subunit-specific antagonists may be of potential use in the treatment of epilepsy in TSC.

Minocycline treatment following hypoxic/ischaemic injury attenuates white matter injury in a rodent model of periventricular leucomalacia

AIMS

Periventricular white matter injury in premature infants occurs following hypoxia/ischaemia and systemic infection, and results in hypomyelination, as well as neuromotor and cognitive deficits later in life. Inflammatory infiltrates are seen within human cerebral white matter from periventricular leucomalacia (PVL) cases.

METHODS

In this study, we examine the time course of CD-68+ microglial cell responses relative to cell death within white matter following hypoxia/ischaemia in a rat model of PVL. We also tested the efficacy of the minocycline, an agent that suppresses microglial activation, in this model when administered as a post-insult treatment.

RESULTS

We show that preoligodendrocyte injury in the post-natal day 6 begins within 24 h and continues for 48-96 h after hypoxia/ischaemia, and that microglial responses occur primarily over the first 96 h following hypoxia/ischaemia. Minocycline treatment over this 96 h time window following the insult resulted in significant protection against white matter injury, and this effect was concomitant with a reduction in CD-68+ microglial cell numbers.

CONCLUSIONS

These results suggest that anti-inflammatory treatments may represent a useful strategy in the treatment of PVL, where clinical conditions would favour a post-insult treatment strategy.

Neonatal seizures

In childhood, the risk for seizures is greatest in the neonatal period. Currently used therapies have limited efficacy. Although the treatment of neonatal seizures has not significantly changed in the past several decades, there has been substantial progress in understanding developmental mechanisms that influence seizure generation and responsiveness to anticonvulsants. This review includes an overview of current approaches to the diagnosis and treatment of neonatal seizures, identifies some of the critical factors that have limited progress, and highlights recent insights about the pathophysiology of neonatal seizures that may provide the foundation for better treatment.