Pterygopalatine Artery Research Articles

Cannulation of the internal carotid artery in mice: A novel technique for intra-arterial delivery of therapeutics

We have developed a novel minimally invasive technique for the intra-arterial delivery of therapeutics to the mouse brain. CD-1 mice were anesthetized and placed in a lateral decubitus position. A 10mm midline longitudinal incision was made over the thyroid bone. The omohyoid and sternomastoid muscles were retracted to expose the common carotid artery and external carotid artery (ECA). To maximize delivery of administered agents, the superior thyroid artery was ligated or coagulated, and the occipital artery and the pterygopalatine artery (PPA) were temporarily occluded with 6-0 prolene suture. The ECA was carefully dissected and a permanent ligature was placed on its distal segment while a temporary 6-0 prolene ligature was placed on the proximal segment in order to obtain a flow-free segment of vessel. A sterilized 169μm outer diameter polyimide microcatheter was introduced into the ECA and advanced in retrograde fashion toward the carotid bifurcation. The catheter was then secured and manually rotated so that the microcatheter tip was oriented cephalad in the internal carotid artery (ICA). We were able to achieve reproducible results for selective ipsilateral hemispheric carotid injections of mannitol mediated therapeutics and/or gadolinium-based MRI contrast agent. Survival rates were dependent on the administered agent and ranged from 78 to 90%. This technique allows for reproducible delivery of agents to the ipsilateral cerebral hemisphere by utilizing anterograde catheter placement and temporary ligation of the PPA. This method is cost-effective and associated with a low rate of morbimortality.

Cilostazol prevents retinal ischemic damage partly via inhibition of tumor necrosis factor‐α‐induced nuclear factor‐kappa B/activator protein‐1 signaling pathway

Cilostazol is a specific inhibitor of phosphodiesterase III and is widely used to treat ischemic symptoms of peripheral vascular disease. We evaluated the protective effects of cilostazol in a murine model of ocular ischemic syndrome in which retinal ischemia was induced by 5-h unilateral ligation of both the pterygopalatine artery (PPA) and the external carotid artery (ECA) in anesthetized mice. The effects of cilostazol (30 mg/kg, p.o.) on ischemia/reperfusion (I/R)-induced retinal damage were examined by histological, retinal vascular permeability, and electrophysiological analyses. Using immunoblotting, the protective mechanism for cilostazol was evaluated by examining antiinflammatory effects of cilostazol on the expression of tumor necrosis factors-α (TNF-α) and tight junction proteins (ZO-1 and claudin-5), and the phosphorylations of nuclear factor-kappa B (NF-κB) and c-Jun. The histological analysis revealed that I/R decreased the cell number in the ganglion cell layer (GCL) and the thicknesses of the inner plexiform layer (IPL) and inner nuclear layer (INL), and that cilostazol attenuated these decreases. Additionally, cilostazol prevented the hyperpermeability of blood vessels. Electroretinogram (ERG) measurements revealed that cilostazol prevented the I/R-induced reductions in a-, b-, and oscillatory potential (OP) wave amplitudes seen at 5 days after I/R. Cilostazol inhibited the increased expression of TNF-α and the phosphorylation levels of NF-κB and c-Jun in the retina after I/R. In addition, cilostazol prevented TNF-α-induced reduction of ZO-1 and claudin-5 expression in human retinal microvascular endothelial cells (HRMECs). These findings indicate that cilostazol may prevent I/R-induced retinal damage partly through inhibition of TNF-α-induced NF-κB/AP-1 signaling pathway.

A novel method for efficient delivery of stem cells to the ischemic brain

IntroductionRat middle cerebral artery occlusion (MCAO) model is the most commonly used animal model in ischemic stroke studies. In the model, to increase the amount of stem cells or drugs to enter the brain after delivery into the internal carotid artery (ICA), the pterygopalatine artery (PPA) is occluded. However, PPA occlusion is a technically demanding procedure which often causes complications.MethodsIn this study, we developed an ICA injection needle to facilitate easy and efficient delivery of stem cells to the ischemic brain through the ICA without the need of PPA occlusion. We injected methylene blue and fluorescence dye DiI-labeled human mesenchymal stem cells (DiI-hMSCs) into the ICA in rats with the ICA injection needle (without PPA ligation) or the conventional micro-injection needle (with PPA ligation) and assessed their distributions.ResultsWhen methylene blue was injected, evident blue stains were found in the brain of the injection side particularly the middle cerebral artery (MCA)-supplied areas but not in the PPA supplied areas. Similarly, when DiI-hMSCs were injected, the cells largely appeared in the MCA-supplied tissues, which were similar in quantity compared to conventional micro-injection needle injection with PPA occlusion. Moreover, hMSCs injected with the ICA needle or the micro-injection needle similarly improved the functional recovery of the infarcted brain.ConclusionsOur results indicate that the ICA injection needle is easy to use and efficient in delivering cells to the ischemic brain tissue in rat MCAO model.

Toll-Like Receptor 4 Mediates Retinal Ischemia/Reperfusion Injury Through Nuclear Factor-κB and Spleen Tyrosine Kinase Activation

Inflammatory response has a critical role in neuronal damage after retinal ischemia-reperfusion (I/R) injury, and is regulated tightly by the toll-like receptor (TLR) 4. This study aimed to determine whether TLR4 is involved with injury in an ocular ischemic syndrome mice model and to clarify the downstream pathway of TLR4. To cause retinal ischemia, we ligated the unilateral external carotid artery and the pterygopalatine artery of mice for 5 hours. Five days after reperfusion, retinal histologic analysis was performed. To examine the downstream pathway of TLR4, we analyzed the changes in phosphorylation of nuclear factor-κB (NF-κB) by Western blotting. In addition, we evaluated the expression of phosphorylated spleen tyrosine kinase (Syk), which is an adaptor protein of TLR4, and the effects of a Syk inhibitor (piceatannol) against the retinal ischemic damage and TLR4 signaling. TLR4 knock-out (KO) mice significantly inhibited the histologic damage induced by I/R compared to wild-type mice. The expression of TLR4 was upregulated after I/R in wild-type mice. The phosphorylation level of NF-κB after I/R in TLR4 KO mice was decreased compared to that in wild-type mice. The phosphorylated Syk expression was upregulated after I/R, and the upregulation was inhibited in TLR4 KO mice. Piceatannol inhibited the histologic and functional retinal damage, and reduced the phosphorylation level of NF-κB induced by I/R. These data indicate that TLR4 has a pivotal role in the pathogenesis of ocular ischemic syndrome, and Syk and NF-κB are key molecules in TLR4 signaling in retinal ischemia.

Crocetin, a carotenoid derivative, inhibits retinal ischemic damage in mice

Crocetin, an aglycone of crocin, is found both in the saffron crocus (Crocus starus L.) and in gardenia fruit (Gardenia jasminoides Ellis). We evaluated the protective effects of crocetin against the retinal ischemia induced by 5h unilateral ligation of both the pterygopalatine artery (PPA) and the external carotid artery (ECA) in anesthetized mice. The effects of crocetin (20mg/kg, p.o.) on ischemia/reperfusion-induced retinal damage were examined by histological, electrophysiological, and anti-apoptotic analyses. Data for anti-apoptotic analysis was obtained by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Using immunohistochemistry and immunoblotting, the protective mechanism mediating the effects of crocetin was evaluated by examining crocetin's effects on the expression of 8-hydroxy-2-deoxyguanosine (8-OHdG; used as a marker of oxidative stress) and on phosphorylations of mitogen-activated protein kinases [MAPK; viz. extracellular signal-regulated protein kinases (ERK), c-Jun N-terminal kinases (JNK) and p38], and the redox-sensitive transcription factors nuclear factor-kappa B (NF-κB) and c-Jun. The histological analysis revealed that ischemia/reperfusion (I/R) decreased the cell number in the ganglion cell layer (GCL) and the thickness of inner nuclear layer (INL), and that crocetin inhibited GCL and INL. ERG measurements revealed that crocetin prevented the I/R-induced reductions in a- and b-wave amplitudes seen at 5 days after I/R. In addition, crocetin decreased the numbers of TUNEL-positive cells and 8-OHdG-positive cells, and the phosphorylation levels of p38, JNK, NF-κB, and c-Jun present in the retina after I/R. These findings indicate that crocetin prevented ischemia-induced retinal damage through its inhibition of oxidative stress.

P4‐294: MR imaging of arterial dysfunction in a mouse model of Alzheimer's disease

Arterial spin labeling (ASL) magnetic resonance imaging (MRI) has demonstrated regional cerebral hypoperfusion in Alzheimer's disease (AD) patients, as well as murine models of AD. It is well-recognized that cerebral arteries undergo microstructural changes in AD, including deposition of β-amyloid (i.e. cerebral amyloid angiopathy) and loss of smooth muscle cells, resulting in cerebrovascular dysfunction. While compromised arterial function can be assessed in mouse brain by several techniques, these methods are restricted to focal regions of the cortical surface. In order to assess the entire arterial system, we have employed a novel, non-invasive, quantitative approach based on in vivo 3D MRI data. MR image volumes were acquired from 3–5 month-old (young) and 18–20 month-old (aged) APP transgenic (TG) and wild-type (WT) mice. Whole-brain anatomical images and 3D MR arteriograms were acquired on a 7T animal MRI system. The MRI data was processed using a fully-automated pipeline. In order to derive quantitative information from the arteriogram, we utilized a region-of-interest (ROI)-based approach. The ROI labels (vessel segments) were mapped from a standardized atlas in reference space to each mouse brain MRI volume in native space via atlas-based segmentation. We then derived a quantitative measure, the “arterial index”, which is related to the apparent arterial cerebral blood volume (CBV a), for each ROI. Young APP TG mice demonstrated significantly reduced arterial indices relative to WT mice in the distal segments of major cerebral arteries, including middle cerebral, posterior cerebral, and azygos pericallosal arteries (with the exception of the retrosplenial branch), while the proximal segments and the internal carotid were largely unaffected. The pterygopalatine artery demonstrated a higher arterial index in the young TG relative to WT mice. The retrosplenial branch of the azygos pericallosal artery showed greater age-related reduction in the arterial index in TG compared to WT mice. We have demonstrated regional differences in arterial function as a function of genotype (TG vs. WT) and age (young vs. aged). The arterial index may complement conventional ASL perfusion MRI measures, and could potentially serve as a powerful, novel imaging biomarker for the assessment of disease evolution and therapeutic intervention in pre-clinical and clinical studies.

Ligation of the Pterygopalatine and External Carotid Arteries Induces Ischemic Damage in the Murine Retina

This study aimed to characterize the functional and morphologic changes in a murine model of ocular ischemic disease caused by vascular occlusion. Retinal ischemia was induced by unilateral ligation of the pterygopalatine artery (PPA) and the external carotid artery (ECA) in anesthetized mice. Changes in ocular blood flow and retinal circulation were evaluated by three different methods: laser speckle blood flow imaging, fundus imaging, and fluorescein isothiocyanate angiography. Five days after reperfusion following 3- or 5-hour ischemia, an electroretinogram (ERG) was recorded, and the retinal histology was examined and quantified. The effects of a free radical scavenger, edaravone, using the model were evaluated by ERG and histologic analysis. The ligation of both the PPA and the ECA significantly reduced ocular blood flow and narrowed the blood vessels. Five hours of ischemia reduced the a-wave, b-wave, and oscillatory potential amplitudes of the ERG. The number of cells in the ganglion cell layer and the thickness of both the inner plexiform layer and the inner nuclear layer were reduced in the ischemic group. Retinal ischemia caused an increase in terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells in the inner layer after 21-hour reperfusion following 3-hour ischemia and 19-hour reperfusion following 5-hour ischemia. Edaravone (1 mg/kg, administered intraperitoneally) significantly reduced the retinal ischemic damage. These findings indicate that the murine model in which both the PPA and the ECA are ligated may be useful to clarify the pathologic mechanisms of retinal ischemic diseases and to evaluate neuroprotective drugs that target retinal ischemic injury.

Microvascular decompression of the pterygopalatine ganglion in patients with refractory cluster headache

Cluster headache is an invalidating form of headache. Although cluster headache can be managed pharmacologically, some patients require surgical treatment with varying results. Microvascular decompression of the pterygopalatine ganglion could be an alternative to traditional surgical management in patients with cluster headache. Microvascular decompression of the pterygopalatine ganglion was performed in three patients with refractory cluster headache. The pterygopalatine artery was ligated and a temporal muscle graft was placed between the artery and the ganglion. No differences were found between the presurgical period and 1 week, 1 month, 3 months, and 6 months postoperatively with respect to attack duration and frequency, visual analogue scale score during attacks and in remission periods, duration of remissions, and quality of life. These preliminary data suggest that microvascular decompression of the pterygopalatine ganglion does not provide pain reduction or improvement of quality of life in patients with refractory cluster headache.

Association Between Changes in Weight and Cerebral Arteries in Rats

The objective of the study was to gain a better understanding of brain artery diameters and anatomical variations for precise modification of cerebral blood supply in ischemic stroke models. Sprague-Dawley rats (n = 35) were used for the experiment. Rats were perfused and resin replicas of cerebral arteries were created using a corrosion casting technique. Resin replicas were measured and analyzed for correlation of vessel lumen with animal sex and weight. A strong correlation between root of aorta diameter and weight was observed (p < 0.0001). We also observed a significant correlation between weight, internal carotid arteries, right external carotid artery, and pterygopalatine arteries. For the common carotid artery, a significant difference between the left and right branches was observed even though there was no association with weight. There was no significant association observed between animal sex and vessel size independent of weight. A better knowledge of vessel lumen in relation to animal sex and weight is essential for adequate blockage of an intracranial artery to induce cerebral ischemia in a rat model of stroke. This study provides a viable reference for choice of rat size in relation to the size of embolic agents such as filaments, microwires, or in vitro thrombus used in ischemic stroke experiments.

Novel rat middle cerebral artery occlusion model: Trans-femoral artery approach combined with preservation of the external carotid artery

We developed a novel trans-femoral artery approach to the rat middle cerebral artery occlusion model (TF-MCAO) without sacrificing the external carotid artery (ECA) with/without the pterygopalatine artery, which is important for chewing food. To make the TF-MCAO we first dissect the left common carotid artery (CCA), ECA, and internal carotid artery (ICA). Transient occlusion clips are applied to the proximal ECA and the pterygopalatine artery; we never sacrifice the ECA branch. A 24-gage catheter is inserted into the left femoral artery. We insert a slightly bent 0.014in. hydrophilically coated guide wire via a haemostasis valve. Anatomically, the left common carotid artery is located rostral to the descending aorta, permitting a straight-forward, blind approach to the CCA. The guide wire is gently advanced about 17mm from the bifurcation of the CCA until slight resistance is encountered. The guide wire and temporary occlusion clips are withdrawn after 90min. Rats were sacrificed 24h after reperfusion. Eleven rats were examined. One rat died before occlusion due to deep anesthesia. The success rate for producing infarction was 80%. The mean infarction volume of the basal ganglia was 94.4mm3±9.4 se and mean infarction volume of the cerebral cortex was 124.2mm3±21.6 se. No rat died due to cerebral infarction and no rat suffered subarachnoid hemorrhage. We conclude that TF-MCAO was useful for producing a cerebral infarction.

Blocking pterygopalatine arterial blood flow decreases infarct volume variability in a mouse model of intraluminal suture middle cerebral artery occlusion

The mouse model of intraluminal suture middle cerebral artery occlusion (MCAO) is still associated with several issues, such as variability of infarction volume and survival. Thus, the method is far from standardization. The effect of blood flow in the pterygopalatine artery (PPA) in the mouse MCAO model remains obscure. While producing mouse MCAO models using commercially available silicone-coated monofilaments, we temporarily occluded the common carotid artery (CCA) or PPA to determine whether cerebral blood flow (CBF) values, infarct size and the stability of the model would be affected. Forty male C57BL/6 mice were divided into 3 groups: MCAO with blocked CCA blood flow (MCAO-C; n=12), MCAO with blocked PPA blood flow (MCAO-P; n=16) and MCAO without either CCA or PPA blood flow blockage (MCAO-U; n=12). We found that the CBF values were significantly higher during occlusion in the MCAO-U than in the other two groups (p<0.001). We stained whole brains from each group at 24h after reperfusion with 2% 2,3,5-triphenyltetrazolium chloride. Although mean infarct volume did not obviously differ between the MCAO-U and other two groups, infarct volumes varied significantly more within the MCAO-U, than in the other two groups (p<0.05). We concluded that collateral circulation from the PPA to the brain significantly influences the MCAO model, and cannot be ignored. An approximately consistent mouse MCAO model can be generated using commercially available silicone-coated sutures while blocking PPA blood flow during occlusion.

Novel Mouse Model of Monocular Amaurosis Fugax

Retinal ischemia is a major cause of visual impairment and is associated with a high risk of subsequent ischemic stroke. The retina and its projections are easily accessible for experimental procedures and functional evaluation. We created and characterized a mouse model of global and transient retinal ischemia and provide a comprehensive chronologic profile of some genes that display altered expression during ischemia. Ischemia and reperfusion were assessed by observing flat-mounted retinas after systemic fluorescein injection. The temporal pattern of gene expression modulation was evaluated by quantitative reverse transcription-polymerase chain reaction from the occurrence of unilateral 30-minute pterygopalatine artery occlusion until 4 weeks after reperfusion. Electroretinograms evaluated functional sequelae 4 weeks after the ischemic episode and were correlated with histologic lesions. This model is the first to reproduce the features of transient monocular amaurosis fugax resulting from ophthalmic artery occlusion. The histologic structure was roughly conserved, but functional lesions affected ganglion cells, inner nuclear layer cells, and photoreceptor cells. We observed an early and strong upregulation of c-fos, c-jun, Cox-2, Hsp70, and Gadd34 gene expression and a late decrease in Hsp70 transcript levels. A murine model of transient retinal ischemia was successfully developed that exhibited the characteristic upregulation of immediate-early genes and persistent functional deficits. The model should prove useful for investigating mechanisms of injury in genetically altered mice and for testing novel neuroprotective drugs.

129Xe spectra from the heads of rats with and without ligation of the external carotid and pterygopalatine arteries

After rats inhaled hyperpolarized (129)Xe gas, in vivo spectra from their heads revealed a dominant peak around 195 ppm, another easily resolvable peak near 189 ppm, a broad peak around 210 ppm, and two minor peaks around 198 ppm and 192 ppm. However, the source of each peak remains controversial. To further study the origin of each peak, we compared spectra obtained from the heads of normal rats with spectra taken from the heads of rats that had undergone ligation of the external carotid (ECA) and pterygopalatine (PPA) arteries, the major feeding vessels of nonbrain tissue in the rat head. The amplitude of the peak at around 189 ppm was greatly reduced in the ECA/PPA-ligated rats, while the peak around 195 ppm persisted. We conclude that the signal that originates from the rat brain after inhalation of (129)Xe gas is overwhelmingly dominated by the single resonance at 195 ppm.

Characterization of a new double-filament model of focal cerebral ischemia in heme oxygenase-2-deficient mice.

Variations in vascular anatomy in knockout mouse strains can influence infarct volume after middle cerebral artery (MCA) occlusion (MCAO). In wild-type (WT) and heme oxygenase-2 gene-deleted (HO2-/-) mice, infarcts were not reproducibly achieved with the standard intraluminal filament technique. The present study characterizes a double-filament model of MCAO, which was developed to produce consistent infarcts in both WT and HO2-/- mice. Diameters of most cerebral arteries were similar in WT and HO2-/- mice, although the posterior communicating artery size was variable. In halothane-anesthetized mice, two 6-0 monofilaments with blunted tips were inserted into the left internal carotid artery 6.0 and 4.5 mm past the pterygopalatine artery junction to reside distal and proximal to the origin of the MCA. The tissue "volume at risk" determined by brief dye perfusion in WT (59 +/- 2% of hemisphere; +/-SE) was similar to HO2-/- (62 +/- 4%). The volume of tissue with cerebral blood flow <50 ml.min(-1).100 g(-1) was similar in WT (35 +/- 9%) and HO2-/- (36 +/- 11%) during MCAO and at 3 h of reperfusion (<2%). After 1 h MCAO, infarct volume was greater in HO2-/- (44 +/- 6%) than WT (25 +/- 3%). After increasing MCAO duration to 2 h, the difference between HO2-/- (47 +/- 4%) and WT (36 +/- 3%) diminished, but infarct volume remained substantially less than the volume at risk. Infusion of tin protoporphyrin IX, an HO inhibitor, during reperfusion after 1 h MCAO increased infarct volume in WT but not significantly in HO2-/- mice, although infarct volume remained less than the volume at risk. Thus greater infarct volume in HO2-/- mice is not attributable to a greater volume at risk, lower intraischemic blood flow, or poor reflow, but rather to a neuroprotective effect of HO2 activity. The double-filament model may be of use as an alternative in other murine knockout strains in which the standard filament model does not yield consistent infarcts.

New simple methods for isolating baroreceptor regions of carotid sinus and aortic depressor nerves in rats.

We developed new methods for isolating in situ baroreceptor regions of carotid sinus and aortic depressor nerves in halothane-anesthetized rats. After ligation of the root of the external carotid artery, the internal carotid and pterygopalatine arteries were embolized with two ball bearings of 0.8 mm in diameter. Bilateral carotid sinus pressures were changed between 60 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between aortic and carotid sinus pressures in 11 rats indicated the maximum gain of the carotid sinus baroreflex to be -2. 99 +/- 0.75 at 120 +/- 5 mmHg. An in situ isolation of the baroreceptor area of the right aortic depressor nerve could be made by ligation of the innominate, common carotid, and subclavian arteries in 9 rats. Pressure imposed on the subclavian baroreceptor was altered between 40 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between the aortic depressor nerve activity and imposed pressure showed that the baroreceptor gain peaked at 118 +/- 4 mmHg. We established an easy approach to the rat baroreflex and baroreceptor research.

Effect of mannitol on local cerebral blood flow after temporary complete cerebral ischemia in rats

The effects of pretreatment with mannitol on local cerebral blood flow (CBF) after permanent or temporary global cerebral ischemia were evaluated with 14C-iodoantipyrine autoradiography in rats under halothane-N2O endotracheal anesthesia. Blood pressure, pulse rate, arterial blood gas levels, and electroencephalographic (EEG) tracings were monitored throughout the experiments. After permanent occlusion of the basilar artery and both external carotid and pterygopalatine arteries, severe global ischemia was induced by permanent occlusion of the common carotid arteries (CCA's) or by a 30-minute temporary CCA occlusion followed by 5 minutes of reperfusion. Intravenous mannitol (25%, 1 gm/kg) or saline solution was administered 5 minutes before occlusion of the CCA's. Cerebral blood flow was measured in 24 anatomical regions. The EEG tracings flattened within 2 to 3 minutes after the onset of ischemia, and no recovery was observed during reperfusion. In the mannitol-treated rats and the saline-treated controls, autoradiographic studies after permanent occlusion showed no CBF in the forebrain or cerebellum, although brain-stem and spinal cord CBF values were normal. After 5 minutes of reperfusion, CBF in the cortex, basal ganglia, and white matter was 100% to 200% higher in mannitol-treated rats and 50% to 100% higher in saline-injected rats than in the nonischemic anesthetized control group. Heterogeneously distributed areas of no-reflow were seen in all saline-injected rats but were observed in none of the mannitol-treated rats. Pretreatment with mannitol prevented postischemic obstruction of the microcirculation during 5 minutes of recirculation after 30 minutes of severe temporary ischemia, but the EEG signals did not recover. Further studies of the functional and morphological responses to longer periods of postischemic recirculation are needed to verify the extent to which these mannitol-induced effects are protective.

Chapter 29: Tracer uptake by circumventricular organs — a relative measure of blood supply to the brain

The permeability difference between “tight brain regions” and “leaky brain structures” is illustrated by example, in which the tritiated adenosine analog N -ethylcarboxamidoadenosine was injected intracarotidally. The radioactivity was in this case revealed by autoradiography. The tracer amount accumulated in a given experiment by the blood–brain barrier (BBB)-protected, tight brain regions frequently shows a rather pronounced fluctuation from one animal to another. One main reason for this is that the portion of the bolus injected into the common carotid artery that distributes to the brain via the internal carotid artery varies, because of the variable amounts of the bolus diverted largely to the external carotid and pterygopalatine arteries. To be able to disregard interindividual uptake differences in the tight brain regions caused by such a differing tracer supply, it has proved useful to relate the measured accumulation values to the corresponding values obtained for the circumventricular organs. Because of the leakiness of their capillaries, the tracer uptake by these regions indicates very well the actual tracer supply to the brain.

Development and evolution of the carotid circulation in geomyoid rodents in relationship to their craniomorphology

The diversity in cranial morphology of living geomyoids, including pocket gophers (Thomomys), spiny pocket mice (Heteromys and Liomys), desert pocket mice (Chaetodipus and Perognathus), and kangaroo rats and mice (Dipodomys and Microdipodops) is accompanied by only a few differences in their cephalic arterial circulation. The principal difference is the origin of the pterygopalatine artery, which serves the orbit and rostrum. In dipodomyines and perognathines it originates as a stapedial branch of the internal carotid artery and passes through the middle ear en route to the braincase. In geomyines and heteromyines it originates as an internal maxillary branch of the external carotid artery and enters the braincase directly. Either geomyines and heteromyines are convergent in this respect, or the currently recognized family Heteromyidae is paraphyletic. The stapedial artery is the same size in early embryos of T. bottae and D. merriami, but in the former species it fails to grow and disappears in juveniles. Comparison of developmental series of D. merriami and T. bottae revealed that the decline of the artery in the latter species is preceded by a greater degree of arterial coarctation, or narrowing, as it passes though the developing stapes. The loss of the stapedial artery is correlated with an enlarged masseter profundus muscle in T. bottae and with an unusually small stapes in T. bottae, H. desmarestianus, and L. salvini. I hypothesize that the primitive condition for geomyoids is the presence of both stapedial and internal maxillary arteries, that the stapedial artery was lost in geomyines and heteromyines because of the constraint on its size posed by the stapes, and that the stapedial artery was retained in dipodomyines because enlargement of the stapes accompanied bullar inflation in these taxa and lifted the constraint on the size of the stapedial artery.

Thrombolytic therapy in stroke — A rat model

Sprague-Dawley male rats 250–350 grams were used. Previous to the experiments, the animals had free access to water and food. Anaesthesia was accomplished by fentanyl 0.06 mg/kg i.m., fluanisone 3.0 mg/kg i.m., diazepam 2.5 mg/kg i.p., and atropine 0.05 mg/kg s.c. followed by 350 units heparin i.p. The right carotid bifurcation was isolated, peripheral branches of the external carotid artery ligated, and the pterygopalatine artery ligated at the base of the skull, just after retrograde insertion of a thin catheter, which tip was near the point of origin of the external carotid artery. Through the surgical procedure PaCO 2, PaO 2, pH and MAP did not exceed physiological limits, and body temperature was kept normal. Regional cerebral blood flow (rCBF) was measured with 133Xenon, intraarterial injection and extracranial scintillation detection of 133Xenon clearance. It was found that injection of a 0.1–0.2 ml autologous blood clot produced a clinical hemiparesis — very comparable to human apoplexia, and a 90% reduction of rCBF in the affected hemisphere, whereas control animals (without injection of clots) have normal flow and postoperative behavior. This model is probably suitable in a study of the effects of thrombolytic therapy after embolic arterial occlusion.

Kinetic analysis of cerebrovascular transport based on indicator diffusion technique.

The indicator diffusion method was used for studies of the blood-brain barrier in rats and [131I]iodoantipyrine (IAP) was used as a highly diffusable model test substance. Interlaminar (Taylor) diffusion and effects of red cell carriage were studied with 57Co-diethylene-triaminepentaacetic acid (DTPA), 125I-human serum albumin, and 46Sc-microspheres (15 microns diameter). Vascular shunting from the pterygopalatine artery (PPA) into the torcula sinus was observed in some animals, and ligation of the PPA was required to obtain reliable data. Dilution curve of the reference compound was corrected to compensate for any difference in interlaminar diffusion and red cell plus protein carriage of the test substance. Apparent extraction ratio of IAP was calculated for each torcula sinus sample and found to increase during the initial phase of the dilution curve, reach a peak of approximately 0.85, and fall during the latter portion of the curve. These results suggest a heterogeneity of intravascular transit times in the cerebral circulation and a rapid efflux of IAP from brain into venous blood. Because of the topography of cerebral capillaries, we developed a modification of the distributed model for intravascular transit and capillary exchange proposed by Goresky et al. (J. Clin. Invest. 52: 991-1009, 1973) and Rose and Goresky (Circ. Res. 34:541-554, 1976); this modification included a well-mixed tissue compartment, as suggested by Johnson and Wilson (Am. J. Physiol. 210: 1299-1303, 1966) and is named the tissue homogeneity model. The experimental data was analyzed by both the tissue homogeneity and Goresky models. The estimated mean extraction E (0.95 and 0.94) and the estimated permeability-surface area product of influx (PS)1 (3.1 and 2.8 ml.min-1.g-1) for IAP in a whole blood injectate were similar using the two different models. The efflux rate constant (k2) for IAP was consistently smaller when the tissue homogeneity model was used (0.13 +/- 0.02 s-1) vs. that obtained with the Goresky model (0.18 +/- 0.02 s-1). Model simulations also indicated that the efflux parameter k2 was most sensitive to the choice of kinetic models, but we could not discriminate between the two model analyses on the basis of the "quality of fit." Nevertheless, from anatomical considerations, we suggest that the tissue homogeneity model may be more appropriate fro brain.