Introduction induce vasodilation via the production of vasodilators [43].

Brain Research 883 2000 51–59 www.elsevier.com locate bres Research report Hypoxic modulation of striatal lesions induced by administration of endothelin-1 Laibaik Park , Jim Thornhill Department of Physiology and Saskatchewan Stroke Research Center , University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan, Canada S 7N 5E5 Accepted 22 August 2000 Abstract Levels of endothelin-1 ET-1, a potent endogenous vasoconstrictor, are elevated in plasma and cerebrospinal fluid CSF following cerebral ischemia and reperfusion injury. The present study sought insight into the potential differential vasoactive effects on the cerebral vasculature and resultant neural damage of ET-1 during normoxic vs. ischemic conditions and upon reperfusion. Under normoxic conditions, intrastriatal stereotaxic injection of exogenous ET-1 40 pmol induced a significant P,0.05 reduction 29612 in the regional striatal cerebral blood flow measured by Laser Doppler flowmetry CBF for up to 40 min in halothane-anesthetized male LDF Long–Evans rats. Intrastriatal injection of ET-1 10 min after the onset of hypoxia 12 O , balance N tended to blunt, but not 2 2 significantly, the striatal CBF responses to the 35 min period of hypoxia. ET-1 given during reoxygenation significantly P,0.05 LDF reduced striatal CBF , which was similar to the effect of ET-1 during normoxia. ET-1-induced infarction when administered prior to LDF hypoxia, but not during or post-hypoxia, was significantly P,0.05 exacerbated compared to infarction of ET-1 without hypoxia. These results suggest that exogenous ET-1 administered into the brain parenchyma can induce an infarction associated with modulation of CBF during the normoxic or reoxygenation period, but not during the hypoxic period and that the increased release of ET-1 in any LDF pathological phase of cerebral ischemia contributes to irreversible neural damage with associated hemodynamic disturbances.  2000 Elsevier Science B.V. All rights reserved. Theme : Disorders of the nervous system Topic : Ischemia Keywords : Endothelin; Hypoxia; Laser Doppler flowmetry; Reoxygenation; Neural damage 1. Introduction induce vasodilation via the production of vasodilators [43]. The ET receptors are also expressed on neuronal cell types Endothelin ET family peptides ET-1, ET-2, and ET- such as neurons, glial cells, epithelial cells of choroid 3, originally isolated from the supernatant of cultured plexus, and ependymal cells lining the ventricles of the endothelial cells, are potent vasoconstrictor agents that are brain [2,20]. Astrocytes are activated via ET receptors B present in several species, including human [56]. The [22] and the expression of these receptors was increased in activities of ET peptides are mediated by two types of rat neostriatum when cells were in a fully differentiated heterotrimeric G protein-coupled ET receptors ET and state [16]. A ET [14]. The ET receptors have higher affinity for With global and focal ischemia and during subarachnoid B A ET-1 and ET-2 than ET-3, and are predominantly located hemorrhage of animals and humans, ET peptides are on the cerebrovascular smooth muscle cells to mediate elevated in plasma and CSF [1,3,26,39,58]. The increased vasoconstriction. ET receptors have equal affinity for release of ET-1 in ischemic stroke suggests that this B ET-1, ET-2, and ET-3 and are found on endothelial cells to endogenous peptide may be a contributing factor in the pathogenesis of this disease [15,58], possibly due to its potent vasoconstrictor properties. As ET-1 levels in plas- Corresponding author. Tel.: 11-306-966-6569; fax: 11-306-966- ma, CSF, and brain tissue are phasically increased with 6532. E-mail address : parkduke.usask.ca L. Park. ischemic stroke or subarachnoid hemorrhage, it is specu- 0006-8993 00 – see front matter  2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 2 8 8 4 - 5 52 L lated that elevated ET-1 levels that occur during the fluid replacement of blood taken through arterial catheter. various phases e.g. hypoxic vs. reperfusion periods of Core body temperatures were servo-controlled at ischemic stroke may compromise tissue perfusion of the 3760.28C via a heating pad connected to the temperature ischemic area in different ways. Under normoxic con- controller Acadia Clinical. ditions, topical or intraparenchymal application of ET-1 or ET-3 induces potent and long-lasting vasoconstriction of 2.1.2. Induction of focal cerebral ischemia with ET-1 cerebral vessels to the point of inducing severe ischemia Procedures for the induction of focal cerebral ischemia and consequently irreversible ischemic injury using ET-1 Sigma, St. Louis, MO, USA were modified [9,10,12,32,41,46,52], but the vasoconstrictive property of from those published previously [9,10,52]. After catheteri- ET-1 under hypoxic and reoxygenation conditions is not zation of right femoral artery and vein, experimental known. In addition, pharmacological studies have attempt- animals were placed in a stereotaxic frame David Kopf ed to correlate the hypoperfusion effects of ET-1 during Instruments. An incision was made along the midline of hypoxic-reperfusion periods of the ischemic stroke the scalp. Two burr holes were made, one for a Laser [2,8,35,36,49] with its resultant pathophysiological effects Doppler Pencil Probe P-434 using coordinates of: an- on cerebral tissues during these different phases of is- terior 0.70 mm from bregma, lateral 20.18 mm from chemia, but the correlation remains inconsistent [33,37] midline, and ventral 6.0 mm from dura, according to the and largely unknown. Paxinos and Watson Rat Atlas [38] and the other for the The purpose of the present study was to determine: a 23-gauge guide cannula coordinates noted below in the the vasoactive effects of exogenous ET-1 given intrastriat- right frontal hemisphere. A Laser Doppler probe was ally during normoxic, hypoxic 12 O , or reoxygenation attached to the guide cannula and was 2.0 mm lateral from 2 periods on cerebral blood flow; and b if the timing the guide cannula. Relative changes of striatal cerebral between ET-1 administration and hypoxia altered the blood flow CBF were continuously monitored via the LDF resultant neuronal damage. Laser Doppler perfusion monitor Laserflo Model BPM 403A, TSI, MN, USA throughout the experiment in all groups. After steady state readings were obtained for

2. Materials and methods approximately 2–5 min, baseline control measurements of