In vivo rat closed spinal window for spinal microcirculation: observation of pial vessels, leukocyte adhesion, and red blood cell velocity

Differential responses of porcine anterior spinal and middle cerebral arteries to carbon dioxide and pH

OBJECTIVE

Dysfunction of the anterior spinal arteries (ASAs) may induce paresis or paraplegia after thoracoabdominal aortic aneurysm or spine surgery. However, there have been no reports of the effects of CO2 and pH on ASAs. Information on these effects on ASAs might contribute to the perioperative management or critical care of spinal cord function. Thus, we investigated the effects of CO2 and pH on the vasomotor tone of ASAs and the third branch of the middle cerebral artery (bMCA).

DESIGN

Prospective study of the effects of CO2 and pH on vasomotor response of porcine ASA and bMCA in vitro.

SETTING

University laboratories.

SUBJECTS

Porcine heads and spinal cords obtained from a slaughterhouse.

INTERVENTION

ASAs and bMCAs were isolated, and changes in the intraluminal region of these pressurized arteries ( approximately 80 mm Hg) were observed for 30 minutes after perfusion with a solution saturated with various concentrations of CO2 and pH.

MEASUREMENTS AND MAIN RESULTS

Respiratory acidosis (pH/Pco2 approximately 7.10-7.15/ approximately 60-80 mm Hg) constricted the ASAs, followed by a partial but gradual decrease in tone, whereas the bMCAs were exclusively dilated. The respiratory alkalosis (pH/Pco2 approximately 7.60/ approximately 20 mm Hg) did not influence ASA tone. Vasoconstriction of the ASAs induced by respiratory acidosis was abolished by removal of the endothelium, but not by N-nitro-L-arginine (1 microM). Respiratory acidosis dilated the ASAs in all preparations treated with ONO-3708 (1 microM), a specific thromboxane A2 receptor antagonist, and OKY-046 (1 microM), a specific thromboxane synthase inhibitor. Metabolic acidosis (pH/Pco2 approximately 7.10/ approximately 40 mm Hg) caused dilation of both bMCAs and ASAs, which was abolished by glibenclamide (1 microM).

CONCLUSIONS

CO2-induced endothelium-dependent constriction in porcine ASAs through releasing thromboxane A2-like substance(s). Thus, hypercarbia might not be favorable for the perioperative or critical care management of spinal cord function during thoracoabdominal aortic aneurysm and spine surgery.

Platelet adhesion and arteriolar dilation in the photothrombosis: observation with the rat closed cranial and spinal windows

The mechanism of cerebral infarction, in which thrombus formation and platelet-endothelium interaction play an important part, have not yet been clearly elucidated in vivo. The aim of this study was to observe rolling and adherent platelets and to analyze adherent leukocytes and vessel diameter change in vivo using a photothrombotic vessel occlusion model.A photothrombosis, which is mediated by free radicals, was induced in male Wistar rats in the presence of a photosensitizing dye (Photofrin II) and exposure to a filtered light. Rhodamine 6G-labeled platelets and leukocytes were visualized with intravital fluorescence videomicroscopy through a closed cranial or spinal window. The vessel diameter, photothrombosis and leukocyte adhesion were analyzed. Rolling and adherent platelets were observed during irradiation through the cerebral and spinal window. Before the platelets were recognized, the irradiated arteriole dilated significantly. After the photochemical occlusion of an arteriole, other arterioles also dilated and the adherent leukocytes increased in the venules. The photothrombosis were almost completely composed of platelets according to electron microscopic analysis. The arteriolar dilation rate and the number of adherent leukocytes in the cerebrum were greater than those in the spinal cord. By combining the photochemical thrombus formation and the fluorescence microscope techniques, we were able for the first time to observe rolling and adherent platelets and microvascular responses during photothrombosis in the cerebral and spinal microvasculature. It is suggested that free radicals, which can lead to platelet aggregation, play an important role as a cerebral vasodilator. This model is useful for cerebral and spinal microcirculatory analysis to investigate the platelet-endothelium interaction, the platelet aggregation and the effect of free radicals on cerebral and spinal microcirculation.

Role of nitric oxide in the regulation of spinal arteriolar tone

OBJECTIVE

The important role played by nitric oxide (NO) in the maintenance of cerebral arterial tone, both in the resting state and after injury, has been demonstrated, but the role of NO in spinal arteries is unknown. The aim of this study was to verify, by topical application of a NO synthase inhibitor in vivo, the hypothesis that NO plays an important role in the maintenance of spinal arteriolar tone.

METHODS

Closed spinal windows were prepared at the C6 level, for observation of arteriolar reactivity. Male Wistar rats were divided into four groups in the resting state and three groups in the compressed state (which was produced by increasing the intrathecal window pressure). The control group underwent superfusion of artificial cerebrospinal fluid into the spinal window. The nitro-L-arginine-methyl ester (L-NAME) and nitro-D-arginine-methyl ester groups underwent superfusion of the NO synthase inhibitor L-NAME and its inactive enantiomer nitro-d-arginine-methyl ester, respectively. The L-NAME/S-nitroso-acetylpenicillamine (SNAP) group underwent mixed superfusion of L-NAME and the direct NO donor SNAP, for investigation of the effects of an exogenous NO donor.

RESULTS

In the resting state, the arterioles constricted significantly in the L-NAME group, compared with values before L-NAME superfusion and those for the other groups. In the L-NAME/SNAP group, the arterioles dilated significantly after SNAP superfusion, compared with values before superfusion and those for the other groups. In the compressed state, the arterioles dilated after compression in all three groups but the dilation was significantly attenuated in the L-NAME group, compared with values for the control and nitro-D-arginine-methyl ester groups.

CONCLUSION

It is suggested that NO plays an important role in the maintenance of spinal arteriolar tone in the resting and compressed states of the spinal cord.

Morphological changes of the anterior spinal artery during aortic cross-clamping and effect of prostaglandin E1 with perfusion

This investigation was designed to evaluate the morphological changes of anterior spinal artery (ASA) and its reaction to prostaglandinE1 (PGE1) during aortic cross-clamping. ASA during 30 min cross-clamping was observed with charge-coupled device (CCD) and ASA diameter (ASAD) was measured. Group A: Infrarenal aorta was cross-clamped. Group B: Infrarenal aorta was cross-clamped and aorta above the bifurcation was snared. The aortic segment between clamp and snare was perfused with blood. Group C: PGE1 of 100 ng/kg/min was added to perfusate of Group B. The aortic segmental pressures in group B and C were about 30% of the proximal systolic arterial pressure and were significantly higher than distal pressure of group A. After cross-clamping, ASAD decreased about 80% of before cross-clamping in group A. By segmental perfusion of which pressure was about 30% of proximal systolic arterial pressure, ASAD remained almost 90% in group B. By administration of PGE1, ASAD was significantly increased in group C. The changes of ASAD were significantly different between group A and C, and between group B and C.

Intravital fluorescence videomicroscopy to study tumor angiogenesis and microcirculation

Angiogenesis and microcirculation play a central role in growth and metastasis of human neoplasms, and, thus, represent a major target for novel treatment strategies. Mechanistic analysis of processes involved in tumor vascularization, however, requires sophisticated in vivo experimental models and techniques. Intravital microscopy allows direct assessment of tumor angiogenesis, microcirculation and overall perfusion. Its application to the study of tumor-induced neovascularization further provides information on molecular transport and delivery, intra- and extravascular cell-to-cell and cell-to-matrix interaction, as well as tumor oxygenation and metabolism. With the recent advances in the field of bioluminescence and fluorescent reporter genes, appropriate for in vivo imaging, the intravital fluorescent microscopic approach has to be considered a powerful tool to study microvascular, cellular and molecular mechanisms of tumor growth.

Effects of moderate hypothermia on leukocyte- endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion

Background and Purpose--It has been demonstrated that moderate hypothermia attenuates brain damage, but the mechanism whereby this is achieved has not been clearly shown. Recently, the role of leukocytes as mediators of secondary brain damage after brain ischemia has been discussed. The aim of this study is to examine the effects of moderate hypothermia on leukocyte-endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion (MCAO). Methods--Rhodamine 6G-labeled leukocytes in brain surface were visualized with intravital fluorescence videomicroscopy through a closed cranial window. We analyzed the number of leukocytes adhering to the venular and arteriolar endothelium before ischemic insult and up to 3 hours after reperfusion. Rats were divided into 4 experimental groups. Group I (n=6) consisted of sham-operated animals. Groups II (n=6) and III (n=6) received left MCAO for 1 hour under normothermia (36 degrees C to 37 degrees C, group II) and under moderate hypothermia (30 degrees C to 32 degrees C, group III). Group IV (n=4) received left common carotid artery occlusion for 1 hour under normothermia. Results--The number of adhering leukocytes in venules in groups II and IV increased significantly (P<0.001) after reperfusion compared with the group I, but that in group III did not increase significantly (P>0.05). The number of adhering leukocytes in arterioles in group II increased significantly (P<0.01) compared with the other groups, although the adhering leukocytes were not as numerous as those seen in venules. Conclusions--It is demonstrated that hypothermia attenuates adhering leukocytes in venules and arterioles after reperfusion of MCAO. The inhibition of the leukocyte function may be an important factor in the neuroprotective effect of hypothermia.