Brain ischemia elicits microglial activation and microglia survival depend on signaling through colony-stimulating factor 1 receptor (CSF1R). Although depletion of microglia has been linked to worse stroke outcomes, it remains unclear to what extent and by what mechanisms activated microglia influence ischemia-induced inflammation and injury in the brain. Using a mouse model of transient focal cerebral ischemia and reperfusion, we demonstrated that depletion of microglia via administration of the dual CSF1R/c-Kit inhibitor PLX3397 exacerbates neurodeficits and brain infarction. Depletion of microglia augmented the production of inflammatory mediators, leukocyte infiltration, and cell death during brain ischemia. Of note, microglial depletion-induced exacerbation of stroke severity did not solely depend on lymphocytes and monocytes. Importantly, depletion of microglia dramatically augmented the production of inflammatory mediators by astrocytes after brain ischemia. In vitro studies reveal that microglia restricted ischemia-induced astrocyte response and provided neuroprotective effects. Our findings suggest that neuroprotective effects of microglia may result, in part, from its inhibitory action on astrocyte response after ischemia.

Brain ischemia inhibits immune function systemically, with resulting infectious complications. Whether in stroke different immune alterations occur in brain and periphery and whether analogous mechanisms operate in these compartments remains unclear. Here we show that in patients with ischemic stroke and in mice subjected to middle cerebral artery occlusion, natural killer (NK) cells display remarkably distinct temporal and transcriptome profiles in the brain as compared to the periphery. The activation of catecholaminergic and hypothalamic-pituitary-adrenal axis leads to splenic atrophy and contraction of NK cell numbers in the periphery through a modulated expression of SOCS3, whereas cholinergic innervation-mediated suppression of NK cell responses in the brain involves RUNX3. Importantly, pharmacological or genetic ablation of innervation preserved NK cell function and restrained post-stroke infection. Thus, brain ischemia compromises NK cell-mediated immune defenses through mechanisms that differ in the brain versus the periphery, and targeted inhibition of neurogenic innervation limits post-stroke infection.

Gonzales, Rayna J., Diana N. Krause, and Sue P. Duckles. Testosterone suppresses endothelium-dependent dilation of rat middle cerebral arteries. Am J Physiol Heart Circ Physiol 286: H552-H560, 2004. First published October 9, 2003 10.1152/ajpheart.00663. 2003Little is known about vascular effects of testosterone. We previously reported chronic testosterone treatment increases vascular tone in middle cerebral arteries (MCA; 300 m diameter) of male rats. In the present study, we investigated the hypothesis that physiological levels of circulating testosterone affect endothelial factors that modulate cerebrovascular reactivity. Small branches of MCA (150 m diameter) were isolated from orchiectomized (ORX) and testosteronetreated (ORXϩT) rats. Intraluminal diameters were recorded after step changes in intraluminal pressure (20-100 Torr) in the absence or presence of N G -nitro-L-arginine-methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor; indomethacin, a cyclooxygenase (COX) inhibitor; and/or apamin and charybdotoxin (CTX); and KCa channel blockers used to inhibit endothelium-derived hyperpolarizing factors (EDHF). At intraluminal pressures Ն60 Torr, arteries from ORXϩT developed greater tone compared with ORX arteries. This difference was abolished by removal of the endothelium but remained after treatment of intact arteries with indomethacin or L-NAME. In addition, testosterone treatment had no effect on cerebrovascular production of endothelin-1 or prostacyclin nor did it alter protein levels of endothelial NOS or COX-1. Endothelium removal after L-NAME/ indomethacin exposure caused an additional increase in tone. Interestingly, the latter effect was smaller in arteries from ORXϩT, suggesting testosterone affects endothelial vasodilators that are independent of NOS and COX. Apamin/CTX, in the presence of L-NAME/indomethacin, abolished the difference in tone between ORX and ORXϩT and resulted in vessel diameters similar to those of endothelium-denuded preparations. In conclusion, testosterone may modulate vascular tone in cerebral arteries by suppressing EDHF. endothelium; vascular tone; endothelium-derived hyperpolarizing factor THE EFFECT OF SEX HORMONES on vascular reactivity is thought to be one of the underlying factors contributing to gender differences in cardiovascular function and disease (30,32). Most studies, however, have focused on the influence of estrogen on the blood vessel wall, so relatively little is known about vascular effects of testosterone (30,32). Several studies (4,5,16,23,35,39) report that acute exposure to testosterone causes vasodilation; however, this effect requires supraphysiological concentrations of the hormone and does not appear to be receptor mediated. In contrast, lower concentrations of testosterone can enhance vasoconstriction (3, 17, 31), but this effect is not seen in all studies (23). Few investigators (9,11,27) have addressed the effects of chronic in vivo exposure to androgens, but available data suggest that in the long term, testosterone increases vascu...

ObjectiveThe present study was undertaken to determine the efficacy of coadministration of fingolimod with alteplase in acute ischemic stroke patients in a delayed time window.MethodsThis was a prospective, randomized, open‐label, blinded endpoint clinical trial, enrolling patients with internal carotid artery or middle cerebral artery proximal occlusion within 4.5 to 6 hours from symptom onset. Patients were randomly assigned to receive alteplase alone or alteplase with fingolimod. All patients underwent pretreatment and 24‐hour noncontrast computed tomography (CT)/perfusion CT/CT angiography. The coprimary endpoints were the decrease of National Institutes of Health Stroke Scale scores over 24 hours and the favorable shift of modified Rankin Scale score (mRS) distribution at day 90. Exploratory outcomes included vessel recanalization, anterograde reperfusion, and retrograde reperfusion of collateral flow.ResultsEach treatment group included 23 patients. Compared with alteplase alone, patients receiving fingolimod plus alteplase exhibited better early clinical improvement at 24 hours and a favorable shift of mRS distribution at day 90. In addition, patients who received fingolimod and alteplase exhibited a greater reduction in the perfusion lesion accompanied by suppressed infarct growth by 24 hours. Fingolimod in conjunction with alteplase significantly improved anterograde reperfusion of downstream territory and prevented the failure of retrograde reperfusion from collateral circulation.InterpretationFingolimod may enhance the efficacy of alteplase administration in the 4.5‐ to 6‐hour time window in patients with a proximal cerebral arterial occlusion and salvageable penumbral tissue by promoting both anterograde reperfusion and retrograde collateral flow. These findings are instructive for the design of future trials of recanalization therapies in extended time windows. Ann Neurol 2018;84:725–736

We have previously demonstrated that arterial, but not venous, vasodilatory responses to endothelium-derived nitric oxide (EDNO)-dependent agonists are enhanced in lungs isolated from rats with chronic hypoxia (CH)-induced pulmonary arterial hypertension. These data suggest that CH is associated with increased endothelial nitric oxide synthase (eNOS) activity within the pulmonary arterial vasculature. In addition, the correlation of increased pulmonary arterial pressure with selectively enhanced arterial responsiveness to EDNO-mediated agonists suggests that arterial hypertension, rather than hypoxia per se, is a contributing factor in this response. Therefore, we hypothesized that 1) CH selectively upregulates eNOS within the pulmonary arterial vasculature and 2) monocrotaline (MC)-induced pulmonary arterial hypertension selectively enhances pulmonary arterial dilation to EDNO-dependent dilators and upregulates arterial eNOS. We examined the responses to the EDNO-dependent dilators arginine vasopressin and ionomycin in U-46619-constricted isolated perfused lungs from control and MC-treated rats. Microvascular pressure was assessed by the double-occlusion technique, allowing calculation of segmental resistances. Lungs from MC-treated rats exhibited augmented arterial dilation to arginine vasopressin compared with control lungs. However, the responses to ionomycin were not different between the two groups. Quantitative immunocytochemistry was used to compare pulmonary eNOS immunoreactivity in vessels from control, CH, and MC-treated rats. eNOS staining was more intense in the arteries of CH and MC-treated rats compared with those of control animals, whereas CH and MC treatment had no effect on eNOS staining in veins. We conclude that pulmonary arterial hypertension, or altered vascular mechanical forces associated with hypertension, may be responsible for the augmented EDNO-dependent arterial dilation and upregulation of arterial eNOS in lungs from CH and MC-treated rats.