Increased Cortical Excitability in Female Migraineurs: A Transcranial Magnetic Stimulation Study Conducted in the Preovulatory Phase.

BACKGROUND AND PURPOSE: The cerebral cortex has been the focus of investigations of the pathogenesis of migraine for a long time. Transcranial magnetic stimulation (TMS) is a safe and effective technique for evaluating cortex excitability. Previous studies of the duration of the cortical silent period (CSP)-a measure of intracortical inhibition-in migraine patients have yielded conflicting results. We aimed to characterize cortical excitability by applying TMS to female migraineurs during the preovulatory phase of the menstrual cycle, in order to eliminate the effects of variations in sex hormones. METHODS: We enrolled 70 female subjects: 20 migraine with aura (MA) patients, 20 migraine without aura (MO) patients, and 30 healthy controls. We measured the CSP, resting motor threshold (rMT), and motor evoked potential (MEP) induced by TMS to evaluate cortical excitability during the preovulatory phase of the menstrual cycle. RESULTS: The CSP was shorter in MA patients (88.93±3.82 ms, mean±SEM) and MO patients (86.98±2.72 ms) than in the control group (109.06±2.85 ms) (both p=0.001), and did not differ significantly between the MA and MO groups (p=0.925). The rMT did not differ significantly among the groups (p=0.088). MEPmax was higher in MA patients than in healthy controls (p=0.014), while that in MO patients did not differ from those in MA patients and healthy controls (p=0.079 and p=0.068). CONCLUSIONS: We detected a shorter CSP in both MA and MO patients. This finding may indicate the presence of motor cortex hyperexcitability, which is probably due to reduced GABAergic neuronal inhibition in migraine.

Role of thalamic diffusion for disease differentiation between multiple sclerosis and ischemic cerebral small vessel disease.

INTRODUCTION: Cerebral small vessel disease (CSVD) and multiple sclerosis (MS) both harbor multiple, T2-hyperintense white matter lesions on conventional magnetic resonance imaging (MRI).We aimed to determine the microstructural changes via diffusion-weighted imaging (DWI) in normal appearing thalami. We hypothesized that the apparent diffusion coefficient (ADC) values would be different in CSVD and MS, since the extent of arterial involvement is different in these two diseases. METHODS: DWI was performed for 50 patients with CSVD and 35 patients with MS along with gender- and age-matched controls whose conventional MRI revealed normal findings. DWI was done with 1.5 Tesla MR devices using echo planar imaging (EPI) for b = 0, 1000 s/mm(2). ADC values were obtained from the thalami which appeared normal on T2-weighted and FLAIR images. Standard oval regions of interest (ROIs) of 0.5 cm(2) which were oriented parallel to the long axis of the thalamus were used for this purpose. RESULTS: The mean ADC value of the thalamus was (0.99 ± 0.16) × 10(-3) mm(2)/s in patients with CSVD, whereas the mean ADC value was (0.78 ± 0.06) × 10(-3) mm(2)/s in the control group. The mean ADC value was significantly higher in patients with CSVD compared to the controls (p < 0.001). The mean ADC values of the thalamus were (0.78 ± 0.08) × 10(-3) mm(2)/s in MS patients, and (0.75 ± 0.08) × 10(-3) mm(2)/s in the control group, which are not significantly different (p > 0.05). CONCLUSION: Our study revealed a difference in the diffusion of the thalami between CSVD and MS. DWI may aid in the radiological disease differentiation.

Sonic hedgehog regulates ischemia/hypoxia-induced neural progenitor proliferation.

BACKGROUND AND PURPOSE: Sonic hedgehog (Shh) protein is required for the maintenance of neural progenitor cells (NPCs) in the embryonic and adult hippocampus. Brain ischemia causes increased proliferation of hippocampal NPCs. We therefore examined whether Shh regulates the increase in proliferation of NPCs after ischemia/hypoxia. METHODS: Male SV129 mice were exposed to a 20-minute middle cerebral artery occlusion; hippocampi were then analyzed for Shh mRNA and protein expression by real-time polymerase chain reaction, immunoblot, and immunohistochemistry. Primary cell cultures of neurons, astrocytes, and NPCs were exposed to 16 hours of hypoxia (1% O(2)) and analyzed by real-time polymerase chain reaction and immunoblot for Shh expression. Proliferation of NPCs, in vivo and in vitro, was measured by bromodeoxyuridine incorporation. RESULTS: Among the cell types examined in vitro, only NPC and neurons increased Shh mRNA under hypoxic conditions. Furthermore, hypoxia increased proliferation of NPCs and this proliferation was enhanced by the addition of recombinant Shh or blocked by the pathway-specific inhibitor, cyclopamine. Middle cerebral artery occlusion was associated with a transient 2-fold increase in the mRNA encoding both Shh and its transcription factor, Gli1, 0.5 days after ischemia. Within the hippocampus, Shh protein was increased approximately 3-fold 3 and 7 days after ischemia and was observed predominantly within cells in the CA3 and hilar regions. Shh was expressed only in mature neurons. In vivo, cyclopamine suppressed ischemia-induced proliferation of subgranular NPCs. CONCLUSIONS: The Shh pathway plays a role in the proliferation of NPCs induced by ischemia/hypoxia and might participate in injury remodeling.

Pericyte contraction induced by oxidative-nitrative stress impairs capillary reflow despite successful opening of an occluded cerebral artery.

Here we show that ischemia induces sustained contraction of pericytes on microvessels in the intact mouse brain. Pericytes remain contracted despite successful reopening of the middle cerebral artery after 2 h of ischemia. Pericyte contraction causes capillary constriction and obstructs erythrocyte flow. Suppression of oxidative-nitrative stress relieves pericyte contraction, reduces erythrocyte entrapment and restores microvascular patency; hence, tissue survival improves. In contrast, peroxynitrite application causes pericyte contraction. We also show that the microvessel wall is the major source of oxygen and nitrogen radicals causing ischemia and reperfusion-induced microvascular dysfunction. These findings point to a major but previously not recognized pathophysiological mechanism; ischemia and reperfusion-induced injury to pericytes may impair microcirculatory reflow and negatively affect survival by limiting substrate and drug delivery to tissue already under metabolic stress, despite recanalization of an occluded artery. Agents that can restore pericyte dysfunction and microvascular patency may increase the success of thrombolytic and neuroprotective treatments.

p27Kip1 constrains proliferation of neural progenitor cells in adult brain under homeostatic and ischemic conditions.

Cell cycle inhibition of neural stem and progenitor cells is critical for maintaining the stability of central nervous system in adults, but it may represent a significant hurdle for neural regeneration after injury. We have previously demonstrated that the cyclin-dependent kinase inhibitor (CKI) p21(cip1/waf1) (p21) maintains the quiescence of neural stem-like cells under cerebral ischemia, as similarly shown for the hematopoietic stem cells. Here, we report the distinct role of another CKI member, p27(kip1) (p27) in neural progenitor cells (NPCs) from adult brain (subventricular zone and hippocampal subgranular zone) under both homeostatic and ischemic conditions. The basal level of NPC proliferation in the p27-/- mice was higher than that in p27+/+ mice. Upon ischemia, the overall proliferation of NPCs continued to be higher in p27-/- mice than that in p27+/+ mice. Moreover, the increase of NPC proliferation in p27-/- mice remained until 2 weeks after ischemia, whereas it resumed back to the basal level in p27+/+ mice. As a result, newly generated neuronal cells in the granular layer of p27-/- brain were more abundant compared with p27+/+ controls. These new data demonstrate that p27 functions as a distinct inhibitor for NPC proliferation under homeostatic as well as ischemic conditions.

Statin potentiates human platelet eNOS activity without enhancing eNOS mRNA and protein levels.

BACKGROUND/AIMS: Experimental studies suggest an enhanced endothelial and platelet nitric oxide (NO) generation after statin treatment, possibly due to increased endothelial NO synthase (eNOS) activity and protein levels. In parallel with experimental research, statins were shown to increase the forearm blood flow independently of serum cholesterol in humans. However, it was not possible to correlate blood flow changes with eNOS levels in these studies due to limitations in obtaining arterial samples. Hence, we investigated changes in eNOS activity, mRNA and protein levels after statin treatment in human platelets, which are readily accessible unlike arteries. METHODS: In vitro bleeding times were measured in 22 patients by stimulating platelets with collagen-epinephrine or collagen-ADP. To assess platelet eNOS activity, the bleeding times were also determined after incubating platelets with L-arginine. The measurements were repeated following 14 days of pravastatin (40 mg/day) treatment. Platelet-rich plasma was collected before and after statin treatment to evaluate eNOS mRNA (semiquantitative RT-PCR) and protein levels (Western blotting). RESULTS: The basal bleeding time was prolonged by 24 +/- 3% (mean +/- SE) when the samples were incubated with 500 microM of L-arginine. The NOS inhibitor L-N(5)-(I-iminoethyl)ornithine reversed this effect, suggesting that it was mediated by NO. After statin treatment, the NO-mediated prolongation of the bleeding time with 500 microM of L-arginine was significantly potentiated (to 44 +/- 10%). Despite enhanced eNOS activity, there was no significant change in platelet eNOS mRNA and protein levels after statin treatment. CONCLUSION: These data demonstrate that platelet eNOS activity is potentiated after statin treatment in humans in parallel with experimental studies.

Distribution of sphingosine kinase activity and mRNA in rodent brain.

Sphingosine-1-phosphate (S1P) is a lipid mediator that exerts multiple cellular functions through activation of a subfamily of G-protein-coupled receptors. Although there is evidence that S1P plays a role in the developing and adult CNS, little is known about the ability of brain parenchyma to synthesize this lipid. We have therefore analyzed the brain distribution of the enzymatic activity of the S1P synthesizing enzyme, sphingosine kinase (SPHK) [EC:2.7.1.91], as well as mRNA distribution for one of the two isoforms of this enzyme, sphingosine kinase 2. SPHK activity, measured by the conversion of [(3)H]sphingosine to [(3)H]S1P, is highest in cerebellum, followed by cortex and brainstem. Lowest activities were found in striatum and hippocampus. Sensitivity to 0.1% Triton-X suggests that this activity is accounted for by SPHK2. RT-PCR and in situ hybridization studies show that mRNA for this isoform has a distribution similar to that of SPHK activity. In vivo and in vitro ischemia increase SPHK activity and SPHK2 mRNA levels. These results indicate that SPHK2 is the predominant S1P-synthesizing isoform in normal brain parenchyma. Its heterogeneous distribution, in particular laminar distribution in cortex, suggests a neuronal localization and a possible role in cortical and cerebellar functions, in normal as well as ischemic brain.

fMRI of delayed albumin treatment during stroke recovery in rats: implication for fast neuronal habituation in recovering brains.

Accumulating experimental and clinical data suggest that albumin may be neuroprotective for stroke. Here, we use functional magnetic resonance imaging (fMRI) to evaluate the therapeutic efficacy of albumin and its effects on the recovery of stimuli-induced cerebral hemodynamics. For this purpose, fMRI activity in the ipsilesional somatosensory (SS) cortex was assessed using a well established rat model of transient 90 min focal ischemia and electrical forelimb stimulation. Rats were treated with either saline or albumin via intracerebroventricular injections at 12 h post-stroke onset. Despite this delayed treatment time, when compared to the saline-treated rats (n=7), there were significant enhancements of the fMRI activation in the albumin-treated rats (n=6) for both blood oxygenation level dependence (BOLD) and functional cerebral blood volume (fCBV) responses. Interestingly, the temporal characteristics of the ipsilesional SS BOLD responses in the albumin-treated rats appeared considerably altered compared to those of contralesional responses while such temporal alterations were not pronounced for the fCBV responses. These characteristic fMRI temporal profiles of the albumin-treated brains may be due to altered neuronal responses rather than altered integrity of neurovascular coupling, which implies an unusually fast habituation of neuronal responses in the lesional SS cortex. The correlation between various MRI-derived structural parameters and the fMRI response magnitude was also characteristic for albumin and control groups. Taken together, these data suggest that restoration of fMRI response magnitudes, temporal profiles, and correlations with structure may reveal the extent and specific traits of albumin treatment associated stroke recovery.