Lymphocyte infiltration in the injured brain: role of proinflammatory cytokines.

Studies using mouse axotomised facial motoneuron model show a strong and highly selective entry of CD3+ lymphocytes into the affected nucleus, with a maximum at Day 14, which coincides with the peak of neuronal cell death, microglial phagocytosis, and increased synthesis of interleukin-1 beta (IL1beta), tumour necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma). We explored the possible involvement of these cytokines during the main phase of lymphocyte recruitment into the axotomised facial motor nucleus 7-21 days after nerve cut using mice homozygously deficient for IL1 receptor type 1 (IL1R1-/-), TNF receptor type 1 (TNFR1-/-), type 2 (TNFR2-/-) and type 1 and 2 (TNFR1&2-/-), IFNgamma receptor type 1 (IFNgammaR1-/-), and the appropriate controls for the genetic background. Transgenic deletion of IL1R1 led to a 54% decrease and that of TNFR2 to a 44% reduction in the number of CD3+ T-cells in the axotomised facial motor nucleus, with a similar relative decrease at Day 7, 14, and 21. Deletion of TNFR1 or IFNgammaR1 had no significant effect. Deletion of both TNFR1 and 2 (TNFR1&2-/-) caused a somewhat stronger, 63% decrease than did TNFR2 deletion alone, but this could be due to an almost complete inhibition of neuronal cell death. No mutations seemed to inhibit aggregation of CD3+ T-cells around glial nodules consisting of Ca-ion binding adaptor protein-1 (IBA1)+ phagocytotic microglia and neuronal debris. Altogether, the current data show the importance of IL1R1 and TNFR2 as the key players during the main phase of lymphocyte recruitment to the damaged part of the central nervous system.

Loss of microglial ramification in microglia-astrocyte cocultures: involvement of adenylate cyclase, calcium, phosphatase, and Gi-protein systems.

Reduction in microglial branching is a common feature in brain pathology and culminates in the transformation into small, rounded, microglia-derived phagocytes in the presence of neural debris. The molecular factors responsible for this transformation are unknown. Here we explored the effect of different classes of intra- and extracellular stimuli in vitro on the morphology of ramified microglia cultured on a confluent astrocyte substrate. These studies showed a strong dose-dependent effect for the Ca(2+) ionophore calcimycine/A21837 (50 microM) and for dibutyryl-cAMP (1 mM), with a loss of microglial ramification. Direct activation of the adenylate cyclase with forskolin (0.1 mM) also led to the disappearance of microglial branching. Okadaic acid (70 nM), the inhibitor of protein phosphatases 1 and 2A (PP1/PP2A), and pertussis toxin (12.5 microg/ml), a G(i)-protein inhibitor, also showed similar effects. No effect was observed for dibutyryl-cGMP or for UTP; addition of ATP had a moderate effect, but only at very high, probably nonphysiological concentrations (100 mM). Extracellular matrix components such as keratatan-sulfate, integrin receptor blockers, the disintegrins kistrin, echistatin, and flavoridin, or the serine protease thrombin all had no effect. Addition of prostaglandin D(2) (PGD(2)), a molecule produced by activated microglial cells, had a transforming effect, but at concentrations two orders of magnitude higher than that of established PGD(2) receptors. In summary, addition of agents causing intracellular elevation of Ca(2+) and cAMP or inhibition of G(i)-proteins and phosphatases to ramified microglia cultured on top of confluent astrocytes leads to a rapid loss of microglial branching. Signaling cascades controlled by these molecules may play an important role in the regulation of this common physiological process in the injured brain.

MRI predicts area of increased plasminogen activation in permanent focal cerebral ischemia.

To determine if MRI can predict intracerebral plasminogen activation after focal cerebral ischemia (FCI), ischemic regions detected by MRI after 48 h of permanent FCI in rats were compared with areas of increased plasminogen activation, defined by histological zymography after 72 h of ischemia. The overlap between areas of MRI alterations (64.5% +/- 5.4% of total ischemic hemisphere) and areas with increased plasminogen activation (62.2% +/- 3.6%) was significant for the hemisphere (p < 0.001), the cortex (p < 0.05), and the basal ganglia (p < 0.05). Thus, MRI can predict the extent of increased plasminogen activation, which may play a role in BBB-mediated post-ischemic brain edema and secondary hemorrhage.

Tissue-saving infarct volumetry using histochemistry validated by MRI in rat focal ischemia.

Lesion size is an important outcome parameter in experimental stroke research. However, most methods of measuring the infarct volume in rodents either require expensive equipment or render the brain tissue unusable for further analysis. We report on an inexpensive, tissue-saving method for quantifying the infarct volume in small rodents. After 3 h of middle cerebral artery occlusion (MCAO) and 24 h of reperfusion in male Wistar rats, the lesion was first identified using MRI with T2-weighted sequences. The infarct was then visualized in unfixed brain cryosections using microtubule associated protein 2 (MAP2)-immunohistochemistry and silver infarct staining. The lesion areas detected by all three different methods completely overlapped. The infarct volume was calculated for each method from the lesion area size on serial sections and the distance between them. Significant differences in lesion size were found between the individual animals (p = 0.000056), but not between different methods (p > 0.05). MAP2 immunohistochemistry is a convenient and valid method to measure stroke lesion volume; in addition 98% of the brain tissue is saved and available for use in further histological, immunohistochemical, and biochemical analysis.

Microvascular basal lamina injury after experimental focal cerebral ischemia and reperfusion in the rat.

To define the location and extent of microvascular damage of the basal lamina after cerebral ischemia and reperfusion in rats, the authors subjected animals (n = 16) to 3 hours of focal cerebral ischemia and 24 hours of reperfusion using the suture middle cerebral artery occlusion model; sham-operated animals served as controls (n = 6). The Western blot technique was used to define the collagen type IV protein content in various brain regions, whereas immunohistochemistry identified microvascular basal lamina loss (anticollagen type IV staining). The extent of damage was quantified by automatic morphometric video-imaging analysis. Statistical analysis was based on the Mann-Whitney test and the paired Student's t-test. The ischemic hemisphere showed a reduction of the collagen type IV protein content after ischemia and reperfusion in the Western blot (reduction compared with the nonischemic side: total hemisphere, 33% +/- 6%; basal ganglia, 25% +/- 7%; cortex 49% +/- 4%; P < 0.01) [corrected]. There was also a decrease in the number of cerebral microvessels between the ischemic and nonischemic hemispheres (20% +/- 2%), cortical (8% +/- 3%), and basal ganglia areas (31% +/- 3%) (P < 0.001). Besides a reduction of the vessel number, there was also a loss in basal lamina antigen-positive stained area in ischemic areas (hemisphere, 16% +/- 3%; cortex, 14% +/- 3%; basal ganglia, 21% +/- 4%; P < 0.01) [corrected]. Cortical areas had a less pronounced basal lamina loss than basal ganglia (P < 0.05). For the first time, microvascular basal lamina damage, indicated by collagen type IV loss, is proven in rats by biochemical and morphometric analysis. These changes are comparable with those found in nonhuman primates. The authors report novel data regarding microvascular ischemic changes in the cortex. These data provide a basis for future experiments to determine the mechanisms of ischemic microvascular damage and to devise new therapeutic strategies.

Prolonged cerebral transit time in CADASIL: a transcranial ultrasound study.

BACKGROUND AND PURPOSE: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary angiopathy caused by mutations in Notch3. Cerebral microvessels show an accumulation of granular osmophilic material in the vicinity of degenerating vascular smooth muscle cells. In this study, we measured the arteriovenous cerebral transit time (CTT) to identify changes related to the microangiopathy in CADASIL. METHODS: CTT is the time that a contrast agent needs to pass from a cerebral artery to its corresponding vein. CTT was measured in 17 CADASIL individuals (mean age, 50.2+/-12.3 years) and an equal number of age- and sex-matched control subjects (mean age, 48.9+/-13.0 years) with transcranial color-coded duplex sonography. The intensity curves were recorded in the P2 segment of the posterior cerebral artery and the vein of Galen after injection of the ultrasound contrast agent Levovist. RESULTS: CTT was significantly prolonged in individuals with CADASIL (4.4+/-1.9 seconds) compared with control subjects (1.3+/-0.5 seconds, P<0.0001). This difference was also significant when only nondisabled CADASIL individuals (Rankin score=0, n=9) were analyzed (P<0.0001). There was a nonsignificant trend for a correlation between Rankin score and CTT (r=0.39, P=0.11). CONCLUSIONS: The prolonged CTT likely reflects microvascular changes in CADASIL. Measurements of the CTT may be used clinically to disclose small-vessel disease. Studies comparing CADASIL subjects with other patient populations seem warranted to determine possible differences in CTT between different types of small-vessel disease.