The presence or degree of haemodynamic impairment due to occlusive cerebrovascular disease is often inferred from measurements of cerebral blood flow (CBF), cerebral blood volume (CBV), oxygen extraction fraction (OEF) and the cerebral rate for oxygen metabolism (CMRO2). However, the relationship of these variables, in particular CBV, to regional cerebral haemodynamics is not clearly established in humans with subacute or chronic disease. In the present study, we investigated the relationship of CBV to OEF, CBF and CMRO2, and to subsequent stroke risk in patients with unilateral carotid artery occlusion, in order to define better the associated haemodynamic and metabolic changes. We reviewed data from 81 patients with symptomatic carotid occlusion enrolled in a prospective study of haemodynamic factors and stroke risk. Measurements of CBV, CBF, OEF and CMRO2 were made on entry using PET. Patients were divided into groups by hemispheric ratios and absolute ipsilateral values of OEF and CBV, based on comparison with normal controls. Haemodynamic and metabolic values, risk factors and stroke risk were compared between groups. Based on hemispheric ratios, 45 patients had increased ipsilateral OEF; CBV was increased in 19 of these 45 patients. No differences in CBF, CMRO2 or clinical risk factors were found between these 19 patients and the remaining 26 patients with increased OEF and normal or reduced CBV. Thirteen ipsilateral strokes occurred during follow-up, and 10 of the 13 occurred in the 19 patients with increased OEF and CBV (log rank P < 0.0001). Thirty-two of the 68 patients with complete quantitative PET data had increased OEF by absolute ipsilateral values. CBV was increased in 20 of the 32 patients. No differences in CBF, CMRO2 or clinical risk factors were found between these 20 patients and the remaining 12 patients with increased OEF and normal CBV. Seven of the nine ipsilateral strokes that occurred in the 68 patients occurred in those 20 patients with increased OEF and increased CBV (log rank P = 0.003). The higher risk of ischaemic stroke in patients with increased OEF and CBV suggests that their degree of haemodynamic compromise is more severe than those with increased OEF and normal CBV. In patients with chronic carotid occlusion and increased OEF, increased CBV may indicate pronounced vasodilation due to exhausted autoregulatory vasodilation. The physiological explanation for the measurement of normal CBV in patients with increased OEF is less certain and may reflect preserved autoregulatory capacity.

Context.-The relative importance of hemodynamic factors in the pathogenesis and treatment of stroke in patients with carotid artery occlusion remains controversial.Objective.-To test the hypothesis that stage II cerebral hemodynamic failure (increased oxygen extraction measured by positron emission tomography [PET]) distal to symptomatic carotid artery occlusion is an independent risk factor for subsequent stroke in medically treated patients.Design and Setting.-Prospective, blinded, longitudinal cohort study of patients referred from a group of regional hospitals between 1992 and 1996.Patients.-From 419 subjects referred, 81 with previous stroke or transient ischemic attack in the territory of an occluded carotid artery were enrolled. All were followed up to completion of the study, with average follow-up of 31.5 months.Main Outcome Measures.-Telephone contact every 6 months recorded the subsequent occurrence of all stroke, ipsilateral ischemic stroke, and death.Results.-Stroke occurred in 12 of 39 patients with stage II hemodynamic failure and in 3 of 42 patients without (P = .005); stroke was ipsilateral in 11 of 39 patients with stage II hemodynamic failure and in 2 of 42 patients without (P = .004). Six deaths occurred in each group (P = .94). The age-adjusted relative risk conferred by stage II hemodynamic failure was 6.0 (95% confidence interval [CI], 1.7-21.6) for all stroke and 7.3 (95% CI, 1.6-33.4) for ipsilateral stroke.Conclusions.-Stage II hemodynamic failure defines a subgroup of patients with symptomatic carotid occlusion who are at high risk for subsequent stroke when treated medically. A randomized trial evaluating surgical revascularization in this high-risk subgroup is warranted.

No abstract

The multitransmembrane protein Patched (PTCH) is the receptor for Sonic Hedgehog (Shh), a secreted molecule implicated in the formation of embryonic structures and in tumorigenesis. Current models suggest that binding of Shh to PTCH prevents the normal inhibition of the seventransmembrane-protein Smoothened (SMO) by PTCH. According to this model, the inhibition of SMO signaling is relieved after mutational inactivation of PTCH in the basal cell nevus syndrome. Recently, PTCH2, a molecule with sequence homology to PTCH, has been identified. To characterize both PTCH molecules with respect to the various Hedgehog proteins, we have isolated the human PTCH2 gene. Biochemical analysis of PTCH and PTCH2 shows that they both bind to all hedgehog family members with similar affinity and that they can form a complex with SMO. However, the expression patterns of PTCH and PTCH2 do not fully overlap. While PTCH is expressed throughout the mouse embryo, PTCH2 is found at high levels in the skin and in spermatocytes. Because Desert Hedgehog (Dhh) is expressed specifically in the testis and is required for germ cell development, it is likely that PTCH2 mediates its activity in vivo. Chromosomal localization of PTCH2 places it on chromosome 1p33-34, a region deleted in some germ cell tumors, raising the possibility that PTCH2 may be a tumor suppressor in Dhh target cells.

Previous studies of cerebral oxygen metabolism and extraction in patients with subarachnoid hemorrhage (SAH) have yielded conflicting results. We used positron emission tomography (PET) to measure the regional cerebral metabolic rate for oxygen (rCMRO2), oxygen extraction fraction (rOEF), and cerebral blood flow (rCBF) 16 times in 11 patients with aneurysmal SAH. All studies were performed preoperatively; no patient had hydrocephalus or intracerebral hematoma on brain CT. Eight patients with no arteriographic vasospasm who were studied on days 1-4 post-SAH had a significant 25% reduction in global CMRO2 compared to age-matched controls, and no significant change in global OEF, suggesting a primary reduction in CMRO2 caused by SAH. Four patients studied seven times during arteriographic vasospasm had significantly increased rOEF with unchanged CMRO2 in arterial territories affected by arteriographic vasospasm compared to territories without vasospasm, indicative of cerebral ischemia without infarction. No brain regions studied with PET were infarcted on follow-up CT. We conclude that the initial aneurysm rupture produces a primary reduction in CMRO2, and that subsequent vasospasm causes ischemia.

No abstract

The cochlea and vestibular structures of the inner ear labyrinth develop from the otic capsule via step-wise regional and cell fate specification. Each inner ear structure contains a sensory epithelium, composed of hair cells, the mechanosensory transducers, and supporting cells. We examined the spatio-temporal expression of genes in the Notch signaling pathway, Notch receptors (Notch1-4) and two ligands, Jagged1 and Delta1, in the developing mammalian inner ear. Our results show that Notch1 and Jagged1 are first expressed in the otic vesicle, likely involved in differentiation of the VIIIth nerve ganglion neurons, and subsequently within the inner ear sensory epithelia, temporally coincident with initial hair cell differentiation. Notch1 expression is specific to hair cells and Jagged1 to supporting cells. Their expression persists into adult. Notch2, Notch3, Notch4, and Delta1 are excluded from the inner ear epithelia. These data support the hypothesis that Notch signaling is involved in hair cell differentiation during inner ear morphogenesis.

Background and Purpose-The purpose of this experiment was to assess long-term cerebral hemodynamic and metabolic changes in patients with increased oxygen extraction fraction (OEF) in the hemisphere distal to an occluded carotid artery who remain free of stroke. Methods-Ten patients with increased OEF and no interval stroke underwent repeated positron emission tomography examinations 12 to 59 months after the initial examination. Quantitative regional measurements of cerebral blood flow, cerebral blood volume, cerebral rate of oxygen metabolism (CMRO 2 ), and OEF were obtained. Regional measurements of the cerebral rate of glucose metabolism (CMRGlc) were made on follow-up in 5 patients. Statistical significance (PϽ0.05) was measured with t tests and linear regression analysis. Results-The ipsilateral/contralateral OEF ratio declined from a mean of 1.16 to 1.08 (Pϭ0.022). Greater reductions were seen with longer duration of follow-up (Pϭ0.023, rϭ0.707). The cerebral blood flow ratio improved from 0.81 to 0.85 (Pϭ0.021). No change in cerebral blood volume or CMRO 2 was observed. CMRGlc was reduced in the ipsilateral hemisphere (Pϭ0.001 compared with normal), but the CMRO 2 /CMRGlc ratio was normal. Conclusions-Increased OEF improves in patients with carotid occlusion and no interval stroke. This improvement in OEF is due to an improvement in collateral blood flow.