Showing papers by "Costantino Iadecola published in 1997"

Cyclo-Oxygenase-2 Gene Expression in Neurons Contributes to Ischemic Brain Damage

Abstract: Cyclo-oxygenase-2 (COX-2), a rate-limiting enzyme for prostanoid synthesis, is induced during inflammation and participates in inflammation-mediated cytotoxicity. Cerebral ischemia is followed by an inflammatory reaction that plays a role in the evolution of the tissue damage. We studied whether COX-2 is induced after cerebral ischemia and if so, whether such expression contributes to ischemic brain damage. The middle cerebral artery was occluded in rats, and the ischemic area was sampled for analysis 3–96 hr later. COX-2 mRNA was determined by the competitive reverse-transcription PCR. COX-2 mRNA was upregulated in the ischemic hemisphere, but not contralaterally, beginning 6 hr after ischemia. The upregulation reached a maximum at 12 hr, at which time a fivefold induction of the message occurred. Twenty-four hours after ischemia, the concentration of prostaglandin E2 was elevated in the injured brain by 292 ± 57% ( n = 6). COX-2 immunoreactivity was observed in neurons at the medial edge of the ischemic area. Administration of the COX-2 inhibitor NS-398 attenuated the elevation in prostaglandin E2 in the postischemic brain and reduced the volume of the infarct by 29 ± 6% ( p < 0.05). Thus, cerebral ischemia leads to upregulation of COX-2 message, protein, and reaction products in the injured hemisphere. The data implicate COX-2 in the mechanisms of delayed neuronal death at the infarct border and provide the rationale for neuroprotective strategies employing COX-2 inhibitors.

Delayed Reduction of Ischemic Brain Injury and Neurological Deficits in Mice Lacking the Inducible Nitric Oxide Synthase Gene

Abstract: Inducible nitric oxide synthase (iNOS), an enzyme that produces toxic amounts of nitric oxide, is expressed in a number of brain pathologies, including cerebral ischemia. We used mice with a null mutation of the iNOS gene to study the role of iNOS in ischemic brain damage. Focal cerebral ischemia was produced by occlusion of the middle cerebral artery (MCA). In wild-type mice, iNOS mRNA expression in the post-ischemic brain begun between 24 and 48 hr peaked at 96 hr and subsided 7 d after MCA occlusion. iNOS mRNA induction was associated with expression of iNOS protein and enzymatic activity. In contrast, mice lacking the iNOS gene did not express iNOS message or protein after MCA occlusion. The infarct and the motor deficits produced by MCA occlusion were smaller in iNOS knockouts than in wild-type mice (p < 0.05). Such reduction in ischemic damage and neurological deficits was observed 96 hr after ischemia but not at 24 hr, when iNOS is not yet expressed in wild-type mice. The decreased susceptibility to cerebral ischemia in iNOS knockouts could not be attributed to differences in the degree of ischemia or vascular reactivity between wild-type and knockout mice. These findings indicate that iNOS expression is one of the factors contributing to the expansion of the brain damage that occurs in the post-ischemic period. iNOS inhibition may provide a novel therapeutic strategy targeted specifically at the secondary progression of ischemic brain injury.

Local and Propagated Vascular Responses Evoked by Focal Synaptic Activity in Cerebellar Cortex

Abstract: Iadecola, Costantino, Guang Yang, Timothy J. Ebner, and Gang Chen. Local and propagated vascular responses evoked by focal synaptic activity in cerebellar cortex. J. Neurophysiol. 78: 651–659, 1997...

Increased susceptibility to ischemic brain damage in transgenic mice overexpressing the amyloid precursor protein.

Abstract: We studied the role of the amyloid precursor protein (APP) in ischemic brain damage using transgenic mice overexpressing APP. The middle cerebral artery (MCA) was occluded in FVB/N mice expressing APP695.SWE (Swedish mutation) and in nontransgenic littermates. Infarct volume (cubic millimeters) was assessed 24 hr later in thionin-stained brain sections. The infarct produced by MCA occlusion was enlarged in the transgenics (+32 +/- 6%; n = 12; p 0.05). The reduction in cerebral blood flow produced by MCA occlusion at the periphery of the ischemic territory was more pronounced in APP transgenics (-42 +/- 8%; n = 9) than in controls (-20 +/- 8%; n = 9). Furthermore, the vasodilatation produced by neocortical application of the endothelium-dependent vasodilator acetylcholine (10 microM) was reduced by 82 +/- 5% (n = 8; p < 0.05) in APP transgenics. The data demonstrate that APP overexpression increases the susceptibility of the brain to ischemic injury. The effect is likely to involve the Abeta-induced disturbance in endothelium-dependent vascular reactivity that leads to more severe ischemia in regions at risk for infarction. The cerebral vascular actions of peptides deriving from APP metabolism may play a role in the pathogenic effects of APP.

Molecular Pathology of Cerebral Ischemia: Delayed Gene Expression and Strategies for Neuroprotection

Abstract: The evidence reviewed in this paper suggests that molecular and cellular events occurring in the late stages of cerebral ischemia (> 6 h) play an important role in the evolution of ischemic brain damage. We focused our inquiry on two inflammation-related genes iNOS and COX-2. iNOS is expressed in inflammatory and vascular cells in the post-ischemic brain. Pharmacological inhibition of iNOS activity ameliorates ischemic damage, whereas knockout mice lacking the iNOS gene are relatively protected from the consequences of cerebral ischemia. COX-2 is expressed in neurons at the infarct border and inhibition of COX-2 activity improves ischemic brain damage. These results indicate that expression of iNOS and COX-2 contributes to the late stages of ischemic brain damage. Consequently, inhibition of iNOS and COX-2 could be a valuable addition to treatment strategies for ischemic stroke. Most efforts to date have targeted the acute phase of cerebral ischemia. Inhibition of iNOS or COX-2 offers the prospect of treatments directed to the late stages of the damage. However, additional preclinical studies would be necessary before these new treatment strategies can be tested in human stroke.

Obligatory role of NO in glutamate-dependent hyperemia evoked from cerebellar parallel fibers

Abstract: Electrical stimulation of cerebellar parallel fibers (PF) increases cerebellar blood flow (BFcrb), a response that is attenuated by glutamate receptor antagonists and NO synthase (NOS) inhibitors. We investigated whether administration of NO donors could counteract attenuation by NOS inhibitors of vasodilation produced by PF stimulation. In halothane-anesthetized rats the cerebellar cortex was exposed and superfused with Ringer solution. PF were stimulated with microelectrodes (100 microA, 30 Hz), and BFcrb was recorded by a laser-Doppler probe. During Ringer superfusion, PF stimulation increased BFcrb by 56 +/- 7% and hypercapnia by 72 +/- 5% (n = 5). Superfusion with the nonselective NOS inhibitor N-nitro-L-arginine (L-NNA, 1 mM) reduced resting BFcrb and attenuated the response to PF stimulation (-47 +/- 5%) and hypercapnia (-46 +/- 7%; PCO2 = 50-60 mmHg). After L-NNA, superfusion with the NO donors 3-morpholinosydnonimine (100 microM, n = 5) or S-nitroso-N-acetyl-penicillamine (5 microM, n = 5) reestablished resting BFcrb (P > 0.05 vs. before L-NNA) and reversed L-NNA-induced attenuation of the response to hypercapnia (P > 0.05 vs. before L-NNA) but not PF stimulation (P > 0.05 vs. after L-NNA). Similar results were obtained when NOS activity was inhibited with the inhibitor of neuronal NOS 7-nitroindazole (50 mg/kg i.p.). Like NO donors, the guanosine 3',5'-cyclic monophosphate analog 8-bromoguanosine 3',5'-cyclic monophosphate (n = 5), administered after L-NNA, restored resting BFcrb and counteracted inhibition of the response to hypercapnia but not PF stimulation. In contrast to NO donors and 8-bromoguanosine 3',5'-cyclic monophosphate, the NO-independent vasodilator papaverine (100 microM, n = 5) had no effect on attenuation of responses to PF stimulation or hypercapnia. Thus NO donors are unable to reverse the effect of NOS inhibition on vasodilation produced by PF stimulation. The data support the hypothesis that the vascular response to PF stimulation, at variance with hypercapnia, requires NOS activation and NO production. Thus NO plays an obligatory role in vasodilation produced by increased functional activity in cerebellar cortex.

Principles and Methods for Measurement of Cerebral Blood Flow: Experimental Methods

Abstract: This chapter elaborates the basic principles and experimental methods for measurement of cerebral blood flow (CBF). Methods for point measurement of CBF using probes are based on the use of probes that detect a signal related to CBF at a single site in brain; CBF can be monitored at multiple sites simultaneously, if more than one probe is used. The thermal clearance method uses a thermistor probe that is inserted into the brain. The probe consists of a heating element and a thermocouple that measures the temperature difference between the heating element and the temperature of the brain; this detects tissue heat clearance, a variable related to CBF. The main advantage of this method is the ability to measure flow continuously. Disadvantages are the need for brain penetration, lack of quantitation, and nonlinearity between heat clearance and flow in some brain regions. Hydrogen clearance method is based on the rate of washout of hydrogen that is either generated locally, using electrochemical means, or inhaled to the point of brain saturation. Laser–Doppler flowmetry technique uses the scatter of laser light by red blood cells to monitor microvascular perfusion.