Neuroprotection by hyperbaric oxygenation after experimental focal cerebral ischemia monitored by MRI

BACKGROUND

Hyperbaric oxygenation (HBO) after focal cerebral ischemia reduces infarct size and improves outcome when applied early after stroke. Here, we evaluated effects of HBO on permanent focal cerebral ischemia and applied magnetic resonance imaging (MRI) monitoring to study lesion evolution.

METHODS

Rats underwent permanent middle cerebral artery occlusion (MCAO). Two hours later, animals were treated with HBO (100% O(2)/2 atm; n=17) for 1 hour or treated with room air (n=17). Animals underwent serial MRI studies (DWI, PI, T2) beginning 90 minutes after MCAO. Neuroscore was assessed (5-point rating scale). Animals were euthanized and brains were 2,3,5-triphenyltetrazolium chloride (TTC)-stained for infarct volume calculation 120 hours after MCAO. Immunohistochemistry was performed with antibodies against c-FOS and 4-hydroxy-2-nonenal-modified proteins (HNE) to check for effects of oxidative stress caused by HBO treatment.

RESULTS

HBO reduced infarct volume by 38% (P<0.001). As shown by MRI, neuroprotection began 5 hours after ischemia and remained effective for 5 days. The relative regional cerebral blood flow was not different between groups at 3.5 and 5 hours after occlusion. There was less neurological deficit in HBO-treated animals compared with controls (P<0.05). Lipid peroxidation of cerebral vessels after HBO treatment as measured by HNE staining and pattern of c-FOS induction were not significantly different between groups at 3.5 and 8 hours after ischemia.

CONCLUSIONS

As monitored by MRI HBO treatment reversed ischemic lesion size between 3 and 5 hours after ischemia and achieved a long-lasting neuroprotective effect without significant oxidative damage.

Effect of Brain-Derived Neurotrophic Factor Treatment and Forced Arm Use on Functional Motor Recovery After Small Cortical Ischemia

BACKGROUND AND PURPOSE

Both the administration of growth factors and physical therapy such as forced arm use (FAU) are promising approaches to enhance recovery after stroke. We explored the effects of these therapies on behavioral recovery and molecular markers of regeneration after experimental ischemia.

METHODS

Rats were subjected to photothrombotic ischemia: sham (no ischemia), control (ischemia), brain-derived neurotrophic factor (BDNF; ischemia plus BDNF, 20 microg), and FAU (ischemia plus FAU, 1-sleeve plaster cast ipsilateral limb). Animals survived 1 or 6 weeks and underwent behavioral testing (Rotarod, beam balance, adhesive removal, plantar test, neuroscore). After the rats were killed, brain sections were immunostained for semiquantitative analysis of MAP1B, MAP2, synaptophysin, GFAP expression, and quantification of infarct volumes.

RESULTS

Infarct volumes were not different between the groups 1 or 6 weeks after ischemia. BDNF-treated animals had better functional motor recovery (Rotarod, beam balance, neuroscore) compared with all other groups (P<0.05). There was no significant adverse effect of early FAU treatment on motor recovery, although sensorimotor function (adhesive removal test) was impaired (P<0.05). There were no differences between groups as measured by nociception of the left and right forepaw (plantar test). BDNF treatment transiently induced MAP1B expression in the ischemic border zone and synaptophysin expression within the contralateral cortex 6 weeks after ischemia (P<0.05). Both BDNF and FAU reduced astrogliosis compared with controls (P<0.05).

CONCLUSIONS

Postischemic intravenous BDNF treatment improves functional motor recovery after photothrombotic stroke and induces widespread neuronal remodeling. Early FAU treatment after stroke does not increase infarct size, impairs sensorimotor function, but leaves motor function unchanged. Postischemic astrogliosis was reduced by both treatments.

Energy demand in patients with stroke who are sedated and receiving mechanical ventilation

OBJECT

The purpose of this study was 1) to determine the total energy expenditure (TEE) in patients with acute stroke who are sedated and receiving mechanical ventilation; and 2) to compare the TEE between patients with ischemic and hemorrhagic stroke.

METHODS

Thirty-four consecutive nonseptic patients with stroke requiring sedation and mechanical ventilation were prospectively examined; 13 of the patients had experienced spontaneous intracerebral hemorrhage and 21 cerebral ischemia of the middle cerebral artery territory. The TEE was evaluated using continuous indirect calorimetry during the first 5 days after admission to the intensive care unit. The serum albumin concentration was determined on admission and on Day 5. The TEE varied from 1560 +/- 240 to 1623 +/- 251 kcal/day. A highly significant correlation between the TEE and the basal energy expenditure (BEE), as predicted using the Harris-Benedict equation, was observed in both groups. No significant differences in the TEE were detected between the two groups or among the different study days.

CONCLUSIONS

A highly significant correlation was found between the TEE and the predicted BEE in patients with acute stroke who have been sedated and have received mechanical ventilation. No significant differences were observed between patients with hemorrhagic and ischemic stroke. Further studies are needed to evaluate the effect of tailored feeding on clinical outcome in these patients.

Energy expenditure in ischemic stroke patients treated with moderate hypothermia

OBJECTIVE

To determine total energy expenditure (TEE) in patients with acute ischemic stroke in the territory of the middle cerebral artery (MCA), treated with moderate hypothermia (33 degrees C).

DESIGN AND SETTING

Prospective study in a neurological ICU.

PATIENTS

Ten consecutive patients with severe MCA infarction undergoing moderate hypothermia.

MEASUREMENTS AND RESULTS

Indirect calorimetry was performed continuously over the first 6 days after admission. Mean daily TEE decreased significantly from 1549 before initiation of hypothermia to 1099, 1129, and 1157 on the first, second, and third days of hypothermia, respectively and returned to baseline values after hypothermia was terminated. The ratio of TEE to predicted basal energy expenditure declined from 1.01 before induction of hypothermia to an average of 0.74 during steady state of hypothermia and increased to 1.16 after rewarming.

CONCLUSIONS

We found a significant fall in TEE in sedated, curarized, and ventilated ischemic stroke patients during moderate hypothermia. Indirect calorimetry appears to be a useful tool for measuring energy expenditure in these patients, as predicted basal energy expenditure overestimates the caloric requirements during hypothermia.

Akute Meningitis nach transrektaler Prostatapunktion

Acute meningitis caused by Escherichia coli is a rare disease in adulthood. Medical procedures, e.g. surgical interventions, have been described as a cause. Infection by blood transmission of fecal E. coli is also known. We report a case of acute meningitis after transrectal prostate biopsy. E. coli could be identified both in the cerebrospinal fluid and in the blood culture. A broad initial antibiotic therapy was administered. After cultural isolation of E. coli the therapy was switched to cefotaxime. The initially comatose patient recovered swiftly.

Stroke MRI in intracerebral hemorrhage: is there a perihemorrhagic penumbra?

BACKGROUND AND PURPOSE

Cerebral ischemia has been proposed as a contributing mechanism to secondary neuronal injury after intracerebral hemorrhage (ICH). The search for surrogate parameters that allow treatment stratification for spontaneous ICH continues. We sought to assess the presence and prognostic effect of perihemorrhagic ischemic changes and hypoperfusion in a prospective stroke MRI study.

METHODS

We performed stroke MRI in 32 patients with hyperacute ICH (mean, 16.9+/-17.2 mL) within 6 hours after symptom onset (mean, 3.1+/-1.3 hours). Clinical data at baseline (National Institutes of Health Stroke Scale) and on day 90 (Barthel Index, modified Rankin Scale) were assessed. Perihemorrhagic perfusion- and diffusion-weighted imaging changes were assessed in a 1-cm-wide area around the clot.

RESULTS

Despite a mild perihemorrhagic mean transit time prolongation of 0.7+/-1.1 second, there were no significant perihemorrhagic apparent diffusion coefficient or mean transit time changes indicating irreversible ischemia or hypoperfusion. ICH size, time to imaging, or clinical severity at baseline or outcome were not reflected by changes of relative apparent diffusion coefficient or perfusion-weighted imaging. ICH size correlated with baseline clinical severity (r=0.51, P=0.005). There was a significant association (P=0.0494) and a significant negative correlation (r=-0.468, P=0.0103) of perihemorrhagic perfusion change with time from symptom onset not associated with ICH size.

CONCLUSIONS

Perihemorrhagic hypoperfusion probably is a consequence of reduced metabolic demand (diaschisis) rather than a sign of ischemia. We found no evidence for a perihemorrhagic and potentially salvageable ischemic penumbra in hyperacute ICH. Further studies should address metabolic, toxic, apoptotic, and microvascular aspects.

Exogenous brain-derived neurotrophic factor prevents postischemic downregulation of [3H]muscimol binding to GABA(A) receptors in the cortical penumbra

We have previously shown that exogenous application of brain-derived neurotrophic factor (BDNF) reduces infarct volume in the cortical ischemic penumbra after experimental focal ischemia [Stroke 31 (2000) 2212-2217]. Since BDNF is known to modulate the expression and function of various neurotransmitter receptors, we addressed the question whether BDNF may act via modification of postischemic ligand binding to excitatory NMDA and AMPA and/or inhibitory GABA(A) receptors, respectively. Transient focal cerebral ischemia was induced in male Wistar rats for 2 h using the suture occlusion technique. A period of 30 min after occlusion of the middle cerebral artery, BDNF (300 microg/kg per hour in vehicle; n=5) or vehicle alone (n=5) was continuously infused intravenously for 3 h. Using quantitative receptor autoradiography, postischemic ligand binding of [(3)H]MK-801, [(3)H]AMPA and [(3)H]muscimol was analyzed in the ischemic core, the ischemic cortical penumbra and corresponding regions of the contralateral hemisphere. Transient focal ischemia caused a significant reduction of [(3)H]muscimol binding to GABA(A) receptors within the ischemic cortical penumbra of placebo-treated rats. This was largely prevented by exogenous application of BDNF. [(3)H]MK-801 and [(3)H]AMPA binding values were also reduced in the cortical penumbra and the corresponding area of the contralateral hemisphere. Our data suggest that the neuroprotective effect of BDNF against ischemic damage in the cortical penumbra may be mediated in part by maintained activity of the inhibitory GABAergic system which likely counteracts glutamate induced excitotoxicity.

Neuroprotective effect of granulocyte colony-stimulating factor after focal cerebral ischemia

BACKGROUND AND PURPOSE

The potential neuroprotective effect of the granulocyte colony-stimulating factor (G-CSF) after glutamate-induced excitotoxicity in cell culture and after focal cerebral ischemia in rats was studied. We hypothesized the existence of the G-CSF receptor (G-CSFR) as a main G-CSF effector on neurons, and immunohistochemistry, immunoblotting, and polymerase chain reaction were performed. The G-CSFR-mediated action was studied by activation of signal transducer(s) and activator(s) of transcription-3 (STAT3) in the periphery of the infarction.

METHODS

Neuroprotection of various G-CSF concentrations on glutamate-induced excitotoxicity was studied in cell culture. In vivo, ischemia was induced by use of a suture occlusion model of the middle cerebral artery (90-minute occlusion) in the rat. Thirty minutes after the induction of ischemia, the animals (n=12 per group) received G-CSF at 60 microg/kg body wt IV for 90 minutes or vehicle (saline). Infarct volume was calculated on the basis of 2,3,5-triphenyltetrazolium chloride staining 24 hours after ischemia. Expression of the G-CSFR was studied by immunohistochemistry and verified by reverse transcription-polymerase chain reaction and immunoblotting. Expression of STAT3 was determined by immunohistochemistry.

RESULTS

In cell culture, G-CSF exhibited a significant neuroprotective effect after glutamate-induced excitotoxicity (P<0.05). A G-CSF concentration of 10 ng/mL was maximally effective, resulting in a nearly complete protection. In vivo, G-CSF reduced infarct volume to 47% (132.0+/-112.7 mm3 versus 278.9+/-91.6 mm3 [P<0.05] in the control group). Immunohistochemistry, Western blotting, and reverse transcription-polymerase chain reaction revealed the existence of G-CSFRs in neurons and glial cells. Animals treated with G-CSF significantly upregulated STAT3 in the periphery of the infarction compared with control animals (P<0.05).

CONCLUSIONS

G-CSF achieved a significant neuroprotective effect in cell culture and after intravenous administration after stroke. Increased STAT3 expression in the penumbra of G-CSF-treated rats suggests mediation by G-CSFR.

[Myxedema coma as a rare differential diagnosis of severe consciousness disturbance]

Myxedema coma is a rare and life-threatening complication of untreated hypothyroidism. Therefore, it must be part of the differential diagnosis in comatose patients. We report one patient who presented with CO(2) narcosis,hypothermia, bradycardia,hyporeflexia, tetraparesis, ascitis, pleural effusions, and heart insufficiency. Examination of the CSF, cranial CT, MRI, and MR angiography were normal. In suspicion of myxedema coma,the patient was treated with high dose L-thyroxine and hydrocortisone for preventing secondary adrenal insufficiency. A fast clinical recovery, decreased T4 (7.2 ng/l) and T3 (0.93 ng/l), and increased TSH (20.19 mU/l) together with the following anamnesis of radio iodine therapy and insufficient thyroxine intake confirmed the diagnosis. In conclusion, treatment of the myxedema coma must be started as soon as the laboratory results are confirmatory, since its course depends on the time of initiation of treatment.

Multimodal functional imaging of prolonged neurological deficits in a patient suffering from familial hemiplegic migraine

The case of a patient with familial hemiplegic migraine (FHM) suffering from prolonged right sided hemiparesis and aphasia that persisted for more than 10 days is reported. The symptoms were accompanied by slowing of the magnetoencephalogram over the left hemisphere, which normalized parallel to the clinical improvement. Positron emission tomography obtained on the 6th day revealed glucose-hypometabolism (hemispheric difference > or =10%) in left hemisphere's fronto-basal cortex, caudate nucleus, and thalamus. In contrast, magnetic resonance imaging including perfusion and diffusion weighted imaging was normal and did not show significant alterations of cortical perfusion or water mobility during the episode. We hypothesize that this finding provides evidence for a primary neuronal dysfunction causing the prolonged neurological deficits in FHM.

Early effects of acid-base management during hypothermia on cerebral infarct volume, edema, and cerebral blood flow in acute focal cerebral ischemia in rats

BACKGROUND

Although the frequency for the use of moderate hypothermia in acute ischemic stroke is increasing, the optimal acid-base management during hypothermia remains unclear. This study investigates the effect of pH- and alpha-stat acid-base management on cerebral blood flow (CBF), infarct volume, and cerebral edema in a model of transient focal cerebral ischemia in rats.

METHODS

Twenty Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (MCAO) for 2 h during normothermic conditions followed by 5 h of reperfusion during hypothermia (33 degrees C). Animals were artificially ventilated with either alpha- (n = 10) or pH-stat management (n = 10). CBF was analyzed 7 h after induction of MCAO by iodo[(14)C]antipyrine autoradiography. Cerebral infarct volume and cerebral edema were measured by high-contrast silver infarct staining (SIS).

RESULTS

Compared with the alpha-stat regimen, pH-stat management reduced cerebral infarct volume (98.3 +/- 33.2 mm(3) vs. 53.6 +/- 21.6 mm(3); P > or = 0.05 mean +/- SD) and cerebral edema (10.6 +/- 4.0% vs. 3.1 +/- 2.4%; P > or = 0.05). Global CBF during pH-stat management exceeded that of alpha-stat animals (69.5 +/- 12.3 ml x 100 g(-1) x min(-1) vs. 54.7 +/- 13.3 ml x 100 g(-1) x min; P > or = 0.05). The regional CBF of the ischemic hemisphere was 62.1 +/- 11.2 ml x 100 g(-1) x min(-1) in the pH-stat group versus 48.2 +/- 7.2 ml x 100 g(-1) x min(-1) in the alpha-stat group ( P> or = 0.05).

CONCLUSIONS

In the very early reperfusion period (5 h), pH-stat management significantly decreases cerebral infarct volume and edema as compared with alpha-stat during moderate hypothermia, probably by increasing CBF.

Influence of inspiration:expiration ratio on intracranial and cerebral perfusion pressure in acute stroke patients

OBJECTIVE

We undertook this study to evaluate the influence of the inspiration:expiration (I:E) ratio on intracranial pressure and cerebral perfusion in patients with acute stroke.

DESIGN

Ventilated patients with acute stroke were examined under a protocol involving variations of I:E ratio from 1:2 to 1:1 to 1:2 under positive end-expiratory pressure (PEEP) of 5.3 and - subsequently - 10.6 cmH(2)O. Intracranial pressure was monitored with parenchymal or ventricular catheters. Mean arterial blood pressure, intracranial pressure (ICP), heart rate and peak mean flow velocity of the middle cerebral arteries were continuously recorded.

SETTING

Neurological intensive care unit.

PATIENTS

A total of 45 monitoring sessions were performed in 16 patients (subarachnoid haemorrhage 3, ischemic stroke 13).

RESULTS

No significant changes in any of the parameters monitored were evident in association with the I:E ratio variations under either of the PEEP levels applied. It must be noted, though, that ICP exceeded 15 mmHg in only 5/45 monitoring sessions, and never exceeded 20 mmHg.

CONCLUSIONS

Our preliminary results suggest that variations of the I:E ratio cause no significant changes in intracranial or cerebral perfusion pressure and, thus, can be safely used in patients with acute stroke without intracranial hypertension. The influence of I:E ratio variations on stroke patients with intracranial hypertension remains to be evaluated.

Neuroprotective effect of delayed moderate hypothermia after focal cerebral ischemia: an MRI study

BACKGROUND AND PURPOSE

In contrast to early hypothermia, the effects of delayed hypothermia in focal cerebral ischemia have not been widely addressed. We examined the influence of delayed hypothermia on secondary ischemic injury, MRI lesion size, and neurological outcome after transient focal cerebral ischemia in a rat model.

METHODS

Rats (n=30) were subjected to transient middle cerebral artery occlusion (MCAO, 120 minutes) by use of the intraluminal filament model. Animals of the treatment group (n=12) were exposed to whole-body hypothermia of 33 degrees C for 5 hours starting 3 hours after MCAO, whereas the control group (n=18) was kept at 37 degrees C throughout the whole experiment. The normothermia- and hypothermia-treated animals were investigated daily by using the Menzies neurological score. Serial MRI was performed 1, 3, and 6 hours after MCAO and on days 1, 2, 3, and 5. After the final MRI scan, the rats were euthanized, and brain slices were stained by 2,3,5-triphenyltetrazolium chloride.

RESULTS

Delayed hypothermia resulted in a significant increase of survival rate and a significant improvement of the Menzies score. Moreover, a significant decrease in the extent of hyperintense volumes in T2-weighted scans and a reduction of cerebral edema as calculated from T2-weighted scans throughout the examination period were obvious. The extent of cerebral infarct volume and cerebral brain edema examined by MRI was consistent with 2,3,5-triphenyltetrazolium chloride staining.

CONCLUSIONS

Our results suggest that even delayed postischemic hypothermia can reduce the extent of infarct volume and brain edema after transient focal cerebral ischemia.

[Value of MRI in intracerebral and subarachnoid hemorrhage]

Intracranial hemorrhage (ICH) accounts for 15% of all strokes. In hyperacute emergency assessment, CT is the diagnostic standard for differentiating between hyperacute ICH and ischemic stroke. At this stage, MRI is considered to be of little value for the diagnosis of ICH or subarachnoidal hemorrhage (SAH). We review the current literature and characterize the role of MRI in the diagnosis of ICH and SAH as well as hyperacute stroke in general: While MRI is considered superior to CT in the diagnosis of subacute and chronic ICH/SAH, in hyperacute ICH this is still a matter of debate. MRI signal characteristics of ICH depend on hemoglobin degradation. Deoxyhemoglobin is the MRI substrate for demonstration of blood due to its paramagnetic properties causing signal loss on susceptibility weighted images (T2*-WI). Preliminary data, however, suggest that the sensitivity of modern stroke MRI protocols is sufficiently high for hyperacute ICH and SAH and may render additional information with regard to the etiology of ICH or SAH. Further interest is focused on perihemorrhagic pathophysiologic processes, which may help to improve therapeutic decision making in patients with ICH.

Endovascular cooling for moderate hypothermia in patients with acute stroke: first results of a novel approach

BACKGROUND AND PURPOSE

We undertook this study to evaluate the feasibility of inducing and maintaining moderate hypothermia with the use of endovascular rather than surface cooling.

METHODS

Six patients with severe acute ischemic stroke were treated with moderate hypothermia. This was induced and maintained by circulating temperature-adjusted normal saline in a closed-loop system entailing 3 balloons located near the tip of a central line, which dwelled in the inferior vena cava.

RESULTS

The mean+/-SD initial temperature of the patients was 37+/-1 degrees C (range, 35.5 degrees C to 38.4 degrees C). The pace of cooling was 1.4+/-0.6 degrees C/h, and target temperature was reached after 3+/-1 hours (range, 2 to 4.5 hours). During hypothermia, the maximal temperature observed was 33.4 degrees C, and the minimal temperature was 32.2 degrees C. Temperature deviations >0.2 degrees C or >0.3 degrees C were observed during 21% or 10% of the hours under hypothermia, respectively. Singultus was the only device-related complication encountered. Pulmonary infection, arterial hypotension, bradycardia, arrhythmia, and thrombocytopenia were the most common side effects.

CONCLUSIONS

Induction and maintenance of hypothermia with an intravenous cooling device are feasible. The safety of this approach remains to be evaluated.

Expression and phylogeny of claudins in vertebrate primordia

Claudins, the major transmembrane proteins of tight junctions, are members of the tetraspanin superfamily of proteins that mediate cellular adhesion and migration. Their functional importance is demonstrated by mutations in claudin genes that eliminate tight junctions in myelin and the testis, abolish Mg(2+) resorption in the kidney, and cause autosomal recessive deafness. Here we report that two paralogs among 15 claudin genes in the zebrafish, Danio rerio, are expressed in the otic and lateral-line placodes at their earliest stages of development. Related claudins in amphibians and mammals are expressed in a similar manner in vertebrate primordia such as sensory placodes, branchial arches, and limb buds. We also show that the claudin gene family may have expanded along the chordate stem lineage from urochordates to gnathostomes, in parallel with the elaboration of vertebrate characters. We propose that tight junctions not only form barriers in mature epithelia, but also participate in vertebrate morphogenesis.

Delayed neuroprotective effect of insulin-like growth factor-i after experimental transient focal cerebral ischemia monitored with mri

BACKGROUND AND PURPOSE

Insulin-like growth factor (IGF) treatment has been shown to have trophic and neuroprotective effects in vitro and in vivo in different lesion models. IGF-I has potent neuroprotective effects after hypoxic-ischemic injury and global ischemia. The role of IGF-I in focal cerebral ischemia is only partially understood. Therefore, in the present study, we evaluated, by applying MRI monitoring, whether a clinically relevant systemic administration of IGF-I can achieve a long-lasting neuroprotective effect.

METHODS

Male Wistar rats underwent transient occlusion of the right middle cerebral artery for 1 hour by using the suture occlusion model. Animals then were intraventricularly treated with 33.33 microg IGF-I/d for 3 days (group A, the IGF-I group [n=13]; group B, the placebo group [n=14]) or subcutaneously treated with 200 microg IGF-I/d for 7 days (group D, the IGF-I group [n=10]; group E, the placebo group [n=10]). Groups C and F served as sham-operated controls (n=5 and n=3, respectively). Treatment was begun 30 minutes after occlusion of the middle cerebral artery. Subcutaneously treated animals underwent MRI studies (diffusion-weighted imaging, perfusion imaging, and T2-weighted imaging) beginning 60 minutes after vessel occlusion at 6 hours and at days 1, 2, 5, and 7 after ischemia. The animals were weighed and neurologically assessed daily (rating scale ranged from 0, indicating no deficit, to 5, indicating death). On the third day (intraventricular trial) and on the seventh day (subcutaneous trial), animals were euthanized, and brain sections were stained with triphenyltetrazolium chloride.

RESULTS

The mean infarct volume was 52.9+/-25.2 mm(3) in intraventricularly treated animals versus 146.4+/-62.2 mm(3) in control animals (P<0.01) and 42.2+/-17.9 mm(3) in subcutaneously IGF-I-treated animals versus 73.1+/-38.1 mm(3) in control animals (P<0.05). Apparent diffusion coefficient-derived lesion volume at 60 minutes after occlusion was 40.4+/-23.7 mm(3) versus 38.3+/-19.3 mm(3) (P=NS), increased to 168.3+/-49.55 mm(3) versus 105.5+/-33.8 mm(3) (P<0.05) at 24 hours, and then decreased to 55.8+/-30.3 mm(3) versus 23.3+/-20.2 mm(3) (P<0.05) for control and IGF-I-treated animals, respectively. The T2-weighted-derived ischemic lesion volume at 24 hours after occlusion was 236+/-49.2 mm(3) versus 115.9+/-56.8 mm(3) (P<0.05) and decreased to 115.9+/-26.2 mm(3) versus 75.7+/-35.8 mm(3) (P<0.05) at day 7 for control and IGF-I-treated animals, respectively. The relative regional cerebral blood volume was reduced to 50% before reperfusion in all regions of interest except for region of interest 1 (vessel territory of anterior cerebral artery), recovered during reperfusion, but was not different between the control and the growth factor-treated group at any imaging time point. There was no significant difference in weight loss. There was less neurological deficit after ischemia in intraventricularly and subcutaneously IGF-I-treated animals compared with control animals (P<0.05).

CONCLUSIONS

Continuous treatment with intraventricularly and subcutaneously administered IGF-I achieved a long-lasting neuroprotective effect as early as 24 hours after ischemia as measured by MRI. Therefore, IGF-I may represent a new approach to the treatment of focal cerebral ischemia.

Who does the hair cell's 'do? Rho GTPases and hair-bundle morphogenesis

The mechanosensitive hair bundles of vertebrate hair cells exhibit a remarkable variety of shapes. For a given location in a sensory epithelium, however, the shape and polarity of a hair bundle are specified precisely. Recent findings, in particular with analogous experimental systems of actin polymerization, suggest a model of hair-bundle morphogenesis whereby different Rho guanosine triphosphatases (GTPases) regulate the initiation phase and the elongation phase of local actin-filament assembly at the hair cell's apical membrane.

Hair cell-specific splicing of mRNA for the alpha1D subunit of voltage-gated Ca2+ channels in the chicken's cochlea

The L-type voltage-gated Ca2+ channels that control tonic release of neurotransmitter from hair cells exhibit unusual electrophysiological properties: a low activation threshold, rapid activation and deactivation, and a lack of Ca2+-dependent inactivation. We have inquired whether these characteristics result from cell-specific splicing of the mRNA for the L-type alpha1D subunit that predominates in hair cells of the chicken's cochlea. The alpha1D subunit in hair cells contains three uncommon exons: one encoding a 26-aa insert in the cytoplasmic loop between repeats I and II, an alternative exon for transmembrane segment IIIS2, and a heretofore undescribed exon specifying a 10-aa insert in the cytoplasmic loop between segments IVS2 and IVS3. We propose that the alternative splicing of the alpha1D mRNA contributes to the unusual behavior of the hair cell's voltage-gated Ca2+ channels.

Predominance of the alpha1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea

The voltage-gated Ca2+ channels that effect tonic release of neurotransmitter from hair cells have unusual pharmacological properties: unlike most presynaptic Ca2+ channels, they are sensitive to dihydropyridines and therefore are L-type. To characterize these Ca2+ channels, we investigated the expression of L-type alpha1 subunits in hair cells of the chicken's cochlea. In PCRs with five different pairs of degenerate primers, we always obtained alpha1D products, but only once an alpha1C product and never an alpha1S product. A full-length alpha1D mRNA sequence was assembled from overlapping PCR products; the predicted amino acid sequence of the alpha1D subunit was about 90% identical to those of the mammalian alpha1D subunits. In situ hybridization confirmed that the alpha1D mRNA is present in hair cells. By using a quantitative PCR assay, we determined that the alpha1D mRNA is 100-500 times more abundant than the alpha1C mRNA. We conclude that most, if not all, voltage-gated Ca2+ channels in hair cells contain an alpha1D subunit. Furthermore, we propose that the alpha1D subunit plays a hitherto undocumented role at tonic synapses.

Start site selection at the TATA-less carbamoyl-phosphate synthase (glutamine-hydrolyzing)/aspartate carbamoyltransferase/dihydroorotase promoter

Transcription of the carbamoyl-phosphate synthase (glutamine-hydrolyzing)/aspartate carbamoyltransferase/dihydroorotase (CAD) gene from the Syrian hamster, Mesocricetus auratus, starts at a single major site. We characterized the cis-acting elements that position RNA polymerase II at the correct start site in the CAD promoter. Sequence alignment showed that the CAD promoter lacks a TATA box, but contains a consensus initiator. Mutational analysis of the CAD promoter demonstrated that the sequences between -81 and +26 were sufficient for accurate and efficient transcription in vitro and in vivo; binding sites for the transcription factor Sp1 around -70 and -49 were necessary for transcriptional activity. The binding site at -49 directed initiation about 50 base pairs downstream. A ubiquitous activator protein, Honk, bound to the CAD promoter between -30 and -12, but did not participate in start site selection. The sequences around +1, which contain the consensus initiator, contributed to promoter activity; however, the presence of a consensus initiator in this region was neither necessary nor sufficient for transcription. We concluded from these results that the Sp1 binding site at -49 substituted for the missing TATA box and played a major role in start site selection at the CAD promoter.