Theoretical interpretation of extraction (in brain) of peptides including concentration variations

The transport properties of several peptides across blood-brain barrier (BBB) have been investigated theoretically in terms of simple diffusion and facilitated diffusion processes. Comparison of the calculated results from the simple diffusion and the experimental data reveals the presence of the facilitated diffusion of these substances which we have conceived of as a carrier-mediated process. The values of the partition coefficients f for these peptides were in the range7 × 10⁻⁴ f 200 × 10⁻⁴. The calculated f values gave permeabilities, P_s, in lipids between10⁻⁷ P_s 14 × 10⁻⁷cm/s. These values were then used to estimate the extraction for peptides from simple diffusion alone which vary from 0.3 to 3.5% compared with the experimental extraction (0.4–12%) indicating the inadequacy of the simple diffusion alone to explain the experimental data. As for the carrier-mediated facilitated diffusion process we have used the activated-complex theory. The extraction in this case depends on the maximal rate of transport (T_max)_f and the reciprocal of the affinity constantK_t for the transport of peptides through BBB. We have deduced that(T_max)_f 0.46 × 10⁻³pmol/g·s and K_t 0.35 nM for Met-enkephalin (Met-ENK), Leu-enkephalin (Leu-ENK), glutathione, carnosine, α-MSH and MIF and(T_max)_f 10 × 10⁻³pmol/g·s andK_t 7nM for AVP, βLT, βE and αE to explain the observed results. We have also obtained the quantitative variation of extraction with concentration of peptides in the brain-capillary and have established that the extraction decreases with increasing concentration of peptides, tending to a small constant value at high concentrations. It has been inferred that carrier-mediated facilitated diffusion is important for the transport of peptides across BBB.     

Connexin43 promotes angiogenesis through activating the HIF-1α/VEGF signaling pathway under chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion, a major vascular contributor to vascular cognitive impairment and dementia, can exacerbate small vessel pathology. Connexin43, the most abundant gap junction protein in brain tissue, has been found to be critically involved in the pathological changes of vascular cognitive impairment and dementia caused by chronic cerebral hypoperfusion. However, the precise mechanisms underpinning its role are unclear. We established a mouse model via bilateral common carotid arteries stenosis on connexin43 heterozygous male mice and demonstrated that connexin43 improves brain blood flow recovery by mediating reparative angiogenesis under chronic cerebral hypoperfusion, which subsequently reduces the characteristic pathologies of vascular cognitive impairment and dementia including white matter lesions and irreversible neuronal injury. We additionally found that connexin43 mediates hypoxia inducible factor-1α expression and then activates the PKA signaling pathway to regulate vascular endothelial growth factor-induced angiogenesis. All the above findings were replicated in bEnd.3 cells treated with 375 µM CoCl₂ in vitro. These results suggest that connexin 43 could be instrumental in developing potential therapies for vascular cognitive impairment and dementia caused by chronic cerebral hypoperfusion.     

Lack of correlation between cholinergic-induced changes in chemosensory activity and dopamine release from the cat carotid body in vitro

We studied the effects of nicotine, acetylcholine (ACh) and dopamine (DA) on the frequency of chemosensory discharges (f_x) and catecholamine (CA) efflux in the cat carotid body superfused in vitro. CA efflux was measured by changes in CA concentration (ΔCA) determined by chronoamperometry with nafionated carbon-fiber microelectrodes inserted in the carotid body, while f_x was recorded simultaneously from the carotid (sinus) nerve. Nicotine (10–20 μg) and ACh (>100 μg) increased f_x in all carotid bodies (n=16), but produced a delayed ΔCA (0.65 μM) in only half of them. Eserine potentiated ACh-evoked increases in f_x and CA effluxes. Nicotine and ACh-induced ΔCA were rapidly reduced upon repeated administration. While f_x increases evoked by low doses of nicotine or ACh were reduced or abolished by prior administration of exogenous DA (>100 μg), CA effluxes were enhanced and hastened. Thus, cholinergic-induced changes in f_x are dissociated from CA efflux.     

Feasibility of oscillating and pulsed gradient diffusion MRI to assess neonatal hypoxia-ischemia on clinical systems

Diffusion-time- (t_d) dependent diffusion MRI (dMRI) extends our ability to characterize brain microstructure by measuring dMRI signals at varying t_d. The use of oscillating gradient (OG) is essential for accessing short t_d but is technically challenging on clinical MRI systems. This study aims to investigate the clinical feasibility and value of t_d-dependent dMRI in neonatal hypoxic-ischemic encephalopathy (HIE). Eighteen HIE neonates and six normal term-born neonates were scanned on a 3 T scanner, with OG-dMRI at an oscillating frequency of 33 Hz (equivalent t_d ≈ 7.5 ms) and pulsed gradient (PG)-dMRI at a t_d of 82.8 ms and b-value of 700 s/mm². The t_d-dependence, as quantified by the difference in apparent diffusivity coefficients between OG- and PG-dMRI (ΔADC), was observed in the normal neonatal brains, and the ΔADC was higher in the subcortical white matter than the deep grey matter. In HIE neonates with severe and moderate injury, ΔADC significantly increased in the basal ganglia (BG) compared to the controls (23.7% and 10.6%, respectively). In contrast, the conventional PG-ADC showed a 12.6% reduction only in the severe HIE group. White matter edema regions also demonstrated increased ΔADC, where PG-ADC did not show apparent changes. Our result demonstrated that t_d-dependent dMRI provided high sensitivity in detecting moderate-to-severe HIE.     

Atrial natriuretic peptide augments the blood-brain transfer of water but not leucine and glucose

Recent evidence predicts an effect of atrial natriuretic peptide (ANP) on the blood-brain transfer of water. To test this prediction, we measured the blood-brain transfer of water, l-leucine, and d-glucose in 9 brain regions of male rats after intravenous injection of 10 pmol ANP. The peptide elicited an increase of the permeability-surface area (P_aS) product of labeled water by 28–108% while the P_aS products of leucine and glucose remained unchanged. Cerebral blood flow incresed 15–48% while cardiac output and plasma volume in brain did not alter, indicating no change of capillary surface area (CSA). Regionally, the CSA varied from 63 cm²/g (striatum) to 97 cm²/g (colliculi) and the fraction of capillaries contributing to the total vascular volume varied from 29% (olfactory bulb/lobe) to 62% (striatum). The blood-brain barrier (BBB) permeability to water (5.7 μm/s) was an order of magnitude higher than to glucose (0.4 μm/s) or to leucine (0.3 μm/s).     

Size-dependent blood-brain barrier opening demonstrated with [C]sucrose and a 200,000-da [H]dextran

The reclosure of the blood-brain barrier following osmotic opening was investigated by determining the product of permeability times surface area for two neutral, water-soluble compounds differing widely in molecular size. [¹⁴C]Sucrose (M_r 340 Da, radius 5 Å) and [³H]dextran (M_r 200,000 Da, radius 100 Å) were simultaneously injected i.v., and their regional permeability times surface areas were calculated at 6, 10, 35, and 55 min after the blood-brain barrier was opened by a 30-s infusion of 1.8 m l(+)-arabinose into the right external carotid artery. The control permeability times surface area product was about 10⁻⁵ cm³ s⁻¹ g⁻¹ brain for sucrose and negligible for dextran. It increased to 4 × 10⁻⁴ cm³ s⁻¹ g⁻¹ brain for sucrose and dextran, respectively, at 6 min after opening of the blood-brain barrier. Thereafter, permeability-surface area products for both substances declined. Dextran had significantly lower (P < 0.05) values than sucrose at all times. The ratios of permeability times surface areas of [¹⁴C]sucrose to those to [³H]dextran were consistent with restricted diffusion through pores or slits at 35 and 55 min after blood-brain barrier opening, but at 6 and 10 min these ratios were less than the ratio of their free diffusion coefficients, indicative of bulk fluid flow with solute drag from blood to brain. A previously measured increase in brain water content following opening of the blood-brain barrier together with the present results, suggest the creation of slits approximately 400 Å in width after osmotic treatment. Reduction in bulk fluid flow from blood to brain appears to be the major cause for the reduction of permeability times surface areas for both sucrose and dextran as the blood-brain barrier recloses.     

The effects of ketamine–xylazine anesthesia on cerebral blood flow and oxygenation observed using nuclear magnetic resonance perfusion imaging and electron paramagnetic resonance oximetry

Ketamine–xylazine is a commonly used anesthetic for laboratory rats. Previous results showed that rats anesthetized with ketamine–xylazine can have a much lower cerebral partial pressure of oxygen (P_tO₂), compared to unanesthetized and isoflurane anesthetized rats. The underlying mechanisms for the P_tO₂ reduction need to be elucidated. In this study, we measured regional cerebral blood flow (CBF) using nuclear magnetic resonance (NMR) perfusion imaging and cortical P_tO₂ using electron paramagnetic resonance (EPR) oximetry in the forebrain of rats under isoflurane, ketamine, ketamine–xylazine and isoflurane–xylazine anesthesia. The results show that in ventilated rats ketamine at a dose of 50 mg/kg does not induce significant changes in CBF, compared to isoflurane. Ketamine–xylazine in combination causes 25–65% reductions in forebrain CBF in a region-dependent manner. Adding xylazine to isoflurane anesthesia results in similar regional reductions in CBF. EPR oximetry measurements show ketamine increases cortical P_tO₂ while xylazine decreases cortical P_tO₂. The xylazine induced reduction in CBF could explain the reduced brain oxygenation observed in ketamine–xylazine anesthetized rats.     

Evidence for two types of nicotinic receptors in the cat carotid body chemoreceptor cells

Current concepts on the location and functional significance of nicotinic receptors in the carotid body rest on α-bungarotoxin binding and autoradiographic studies. Using an in vitro preparation of the cat carotid body whose catecholamine deposits have been labeled by prior incubation with the tritiated natural precursor [³H]tyrosine, we have found that nicotine induces release of [³H]catecholamines in a dose-dependent manner (IC₅₀=9.81 μM). We also found that mecamylamine (50 μM) completely abolished the nicotine-induced release, while α-bungarotoxin (100 nM; ≈20 times its binding K_d) only reduced the release by 56%. These findings indicate that chemoreceptor cells, and perhaps other carotid body structures, contain nicotinic receptors that are not sensitive to α-bungarotoxin and force a revision of the current concepts on cholinergic mechanisms in the carotid body chemoreception.     

Antioxidants prevent depletion of [Mg]i induced by alcohol in cultured canine cerebral vascular smooth muscle cells: Possible relationship to alcohol-induced stroke

Low serum concentrations of Mg²⁺ ions have been reported, recently, in patients with coronary disease, atherosclerosis, and stroke as well as in patients with cerebral hemorrhage. The aim of the present study was to determine whether potent antioxidants [α-tocopherol and pyrrolidine dithiocarbamate (PDTC)] can prevent or ameliorate intracellular Mg²⁺ ([Mg²⁺]_i) depletion associated with cerebral vascular injury induced by alcohol. Exposure of cultured canine cerebral vascular smooth muscle cells to alcohol (10–100 mM) for 24 h induced marked depletion in [Mg²⁺]_i (i.e., 30–65%, depending upon alcohol concentration). Treatment of the cultured cells with either PDTC (0.1 μM) or α-tocopherol (15 μM) for 24 h, alone, failed to interfere with basal [Mg²⁺]_i levels. However, preincubation of the cells with either α-tocopherol or PDTC for 24 h completely inhibited the depletion of [Mg²⁺]_i induced by exposure to 10–100 mM ethanol. These results indicate that α-tocopherol and PDTC prevent decreases in [Mg²⁺]_i produced by ethanol. Moreover, these new results suggest that such protective effects of α-tocopherol and PDTC on cerebral vascular cells might be useful therapeutic tools in prevention and amelioration of cerebral vascular injury and stroke in alcoholics.     

Cerebral oxygen metabolism of rats using injectable 15O-oxygen with a steady-state method

To develop a less-stressful and simple method for measurement of the cerebral metabolic rate of oxygen (CMRO₂) in small animals, the steady-state method was applied to injectable ¹⁵O₂-PET (¹⁵O₂-positron emission tomography) using hemoglobin-containing vesicles (¹⁵O₂-HbV). Ten normal rats and 10 with middle cerebral arterial occlusion (MCAO) were studied using a small animal PET scanner. A series of ¹⁵O-PET scans with C¹⁵O-labeled HbV, H₂¹⁵O, and ¹⁵O₂-HbV were performed with 10 to 15 minutes intervals to measure cerebral blood volume (CBV), cerebral blood flow (CBF), and CMRO₂. Positron emission tomography scans were started with a tracer injection using a multiprogramming syringe pump, which provides a slowly increasing injection volume to achieve steady-state radioactivity for H₂¹⁵O and ¹⁵O₂-HbV scans. The radioactivity concentration of ¹⁵O rapidly achieved equilibrium in the blood and whole brain at about 2 minutes after H₂¹⁵O and ¹⁵O₂-HbV administration, which was stable during the scans. The whole brain mean values of CBF, CBV, and CMRO₂ were 54.3±2.0 mL per 100 g per minute, 4.9±0.4 mL/100 g, and 2.8±0.2 μmoL per g per minute (6.2±0.4 mL per 100 g per minute) in the normal rats, respectively. In the MCAO model rats, all hemodynamic parameters of the infarction area on the occlusion side significantly decreased. The steady-state method with ¹⁵O-labeled HbV is simple and useful to analyze hemodynamic changes in studies with model animals.     

A Quantitative Spatial Analysis of the Blood–Spinal Cord Barrier: I. Permeability Changes after Experimental Spinal Contusion Injury

Blood–spinal cord barrier (BSB) permeability was measured using quantitative autoradiography following contusion injury to the rat spinal cord. Permeability was assessed by calculating blood-to-tissue transfer constants (K_ivalues) for the vascular tracer [¹⁴C]-α-aminoisobutyric acid (AIB) in injured (3, 7, 14, and 28 days postinjury), laminectomy control, and uninjured control animals. Permeability was quantitated using four separate imaging techniques in gray and white matter throughout the rostro-caudal extents of the forming lesion. Away from the epicenter, gray matter permeability was further differentiated within discrete spinal lamina using computerized templates. Regardless of the type of analysis used, increased AIB permeability (K_ivalues) was noted at all survival times in all tissue regions with respect to both uninjured and laminectomy control groups. The data indicate a large increase in individualK_ivalues throughout the dorsoventral axis of the spinal cord at 3 days postinjury (≈6–9 ml/kg/min). By 7 days,K_ivalues were quantitatively smaller (≈4–5 ml/kg/min) in all regions compared with 3-day tissues. Despite further attenuation of AIB uptake in the gray matter at 14 and 28 days postinjury, circumferential white matter tracts showed a secondary increase in permeability compared to 7-day tissue. Permeability in the white matter at 14–28 days postinjury (≈5–6 ml/kg/min) was comparable to that at 3 days postinjury (6–7 ml/kg/min). Measurements of the axial distribution of AIB permeability indicate increased BSB permeability over several segments rostral and caudal to the lesion epicenter (≈3 cm in both directions). Secondary elevations of AIB transfer in the spinal white matter between 14 and 28 days were colocalized with zones of immunohistochemically defined microglial clusters. The known plasticity of this cell type in response to changes in the extracellular microenvironment suggests that the spinal white matter at later survival times (14–28 days postinjury) is an area of dynamic vascular and/or axonal reconstruction. The implications of increased permeability to both tissue injury and neural regeneration are discussed.     

-DOPA transport properties in an immortalised cell line of rat capillary cerebral endothelial cells, RBE 4

The present study aimed to determine the kinetics of -3,4-dihydroxyphenylalanine ( -DOPA) uptake in an immortalised cell line of rat capillary cerebral endothelial cells (clones RBE 4 and RBE 4B), to define the type of inhibition produced by -5-hydroxytryptophan ( -5-HTP), 2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid (BHC) and N-(methylamino)-isobutyric acid (MeAlB) and its sodium dependence. Non-linear analysis of the saturation curves for -DOPA and -5-HTP revealed in RBE 4 cells K_m values (in μM) of 72 and 102 and in RBE 4B cells K_m values (in μM) of 60 and 118, respectively. IC₅₀ values for -5-HTP (RBE 4, 1026 μM; RBE 4B, 831 μM) obtained in the presence of a nearly saturating (250 μM) concentration of -DOPA were almost 5-fold those obtained when non-saturating (25 μM) concentrations of -DOPA were used. IC₅₀ values for BHC obtained in the presence of a nearly saturating (250 μM) concentration of -DOPA were also 6- to 5-fold those obtained when non-saturating (25 μM) concentrations of -DOPA were used. MeAlB (up to 2.5 mM) was found not to interfere with the uptake of -DOPA. In RBE 4 cells, V_max values for -DOPA uptake were identical in the absence and the presence of 150 μM -5-HTP or 150 μM BHC, but K_m values (μM) were significantly greater (P<0.05) when -DOPA uptake was studied in the presence of -5-HTP or BHC. Similar findings were observed when RBE 4B cells were used. Uptake of (250 μM) -DOPA in the absence of sodium in the incubation medium was similar to that observed in the presence of increasing concentrations of sodium (20 to 140 mM). It is concluded that RBE 4 and RBE 4B cells are endowed with the L-type amino acid transporter through which -DOPA and -5-HTP can be taken up, and suggested that this immortalised cell line of rat capillary cerebral endothelium might constitute an interesting in vitro model for the study of BBB mechanisms, namely those concerning solute and nutrient transfer across the brain capillary endothelium.     

Effect of reduced flow on blood–brain barrier transport systems

Pathological states (i.e. stroke, cardiac arrest) can lead to reduced blood flow to the brain potentially altering blood–brain barrier (BBB) permeability and regulatory transport functions. BBB disruption leads to increased cerebrovascular permeability, an important factor in the development of ischemic brain injury and edema formation. In this study, reduced flow was investigated to determine the effects on cerebral blood flow (CBF), pressure, basal BBB permeability, and transport of insulin and K⁺ across the BBB. Anesthetized adult female Sprague–Dawley rats were measured at normal flow (3.1 ml min⁻¹), half flow (1.5 ml min⁻¹), and quarter flow (0.75 ml min⁻¹), using bilateral in situ brain perfusion for 20 min followed by capillary depletion analysis. Reduction in perfusion flow rates demonstrated a modest reduction in CBF (1.27–1.56 ml min⁻¹ g⁻¹), a decrease in pressure, and no significant effect on basal BBB permeability indicating that autoregulation remained functional. In contrast, there was a concomittant decrease in BBB transport of both insulin and K⁺ with reduced flow. At half and quarter flow, insulin transport was significantly reduced (R_Br%=17.2 and R_Br%=16.2, respectively) from control (R_Br%=30.4). Additionally, a significant reduction in [⁸⁶Rb⁺] was observed at quarter flow (R_Br%=2.5) as compared to control (R_Br%=4.8) suggesting an alteration in ion homeostasis as a result of low flow. This investigation suggests that although autoregulation maintains CBF, BBB transport mechanisms were significantly compromised in states of reduced flow. These flow alterations may have a significant impact on brain homeostasis in pathological states.     

Nitric oxide donor-induced increase in permeability of the blood–brain barrier

The goal of the present study was to determine the effect of nitric oxide (NO) donors on the permeability of the blood–brain barrier in vivo. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood–brain barrier was quantitated by calculating the clearance of fluorescent-labeled dextran (M_w=10 000 Da; FITC–dextran-10K) during suffusion with vehicle, S-nitroso-N-acetylpenicillamine (SNAP; 100 μM) and 3-morpholinosydnonimin (SIN-1; 100 μM). In addition, we examined changes in arteriolar diameter during suffusion with vehicle, SNAP and SIN-1. During suffusion with vehicle, clearance of FITC–dextran-10K from pial vessels and diameter of pial arterioles remained relatively constant during the experimental period. In contrast, suffusion with SNAP or SIN-1 markedly increased clearance of FITC–dextran-10K from the cerebral microcirculation and produced a rapid, sustained dilatation of pial arterioles. Thus, NO donors increase the permeability of the blood–brain barrier and produce pronounced dilatation of cerebral arterioles. In light of evidence suggesting that NO donors may produce their effect by the simultaneous release of NO and superoxide anion to form peroxynitrite, we elected to examine the role of superoxide anion in increases in permeability of the blood–brain barrier in response to SNAP and SIN-1. We found that suffusion with tiron (1 mM) did not alter basal permeability of the blood–brain barrier, but significantly inhibited increases in permeability of the blood–brain barrier in response to SNAP and SIN-1. In addition, tiron did not alter baseline diameter of cerebral arterioles, or SNAP- and SIN-1-induced cerebrovasodilatation. The findings of the present study suggest that NO donors produce an increase in permeability of the blood–brain barrier which appears to be related to the presence of NO and superoxide anion, to presumably form peroxynitrite. We suggest that increases in NO formation observed during brain trauma may contribute to disruption of the blood–brain barrier.     

Maximal densities of μ, δ, and κ receptors are differentially altered by focal cerebral ischaemia in the mouse

Though opioids are known to have neuroprotective properties, little information is available on the functional state of opioidergic receptors following focal cerebral ischaemia. The present study investigated the evolution of the B_max and K_d for [³H]DAMGO, [³H]DADLE, and [³H]U69,593, respectively, for the μ, δ, and κ opioidergic receptors after permanent focal cerebral ischaemia in mice. While the various K_d were unchanged, μ and δ B_max values were precociously decreased in frontoparietal cortices, earlier than κ receptors, reflecting infarct extension with time. The B_max values for μ and δ receptors were also altered in non-infarcted tissues, such as tissues at risk (e.g., temporal auditory cortex) and exofocal (e.g., contralateral and non-infarcted) cortices. These results suggest that, in non-infarcted areas, the observed changes reflect functional modifications to focal ischaemia.     

Changes in tissue oxyhaemoglobin concentration measured using multichannel near infrared spectroscopy during internal carotid angiography

OBJECTIVE—To develop an in vivo model fortesting spatially resolved spectroscopy and quantified near infraredspectroscopy (NIRS) cerebral blood flow measurements.
METHOD—Multiple detector NIRS has been used tostudy changes in tissue oxyhaemoglobin (O₂Hb) concentrationduring selective internal carotid angiography. A significant reductionin O₂Hb occurred in tissue interrogated by detectorssituated between 0.7 and 4.1cm from the NIRS light source.
RESULTS—The time course of O₂Hbconcentration change was consistent with displacement of oxygenatedblood by the radiocontrast medium from vascular beds of differing flowand NIR light attenuation. Increasing changes in O₂Hbconcentration per unit photon path length—predicted to occur atgreater emitter-detector separations if those changes had occurredpredominantly in cerebral tissue—were found in the first four secondsafter injection of radiocontrast medium. However, later changes(6-10 s) were larger and were not proportional to emitter-detector separation.
CONCLUSION—The findings indicate that simpleassumptions regarding the distribution of the internal carotid arteryblood supply to cerebral and extracerebral tissues, the photon pathlength through those tissues, and their relative contributions toattenuation of NIR light may not be justified.

     

Cortical spreading depression-associated hyperemia in rats: involvement of serotonin

We investigated whether the vasoactive neurotransmitter serotonin (5-HT) is involved in cortical spreading depression (CSD)-associated hyperemia in the rat. We focused on the 5-HT₂ receptor, which is engaged in 5-HT induced small arteriolar relaxation in cats, as well as on the 5-HT_1D/1B receptor, the binding site of the potent antimigraine drug sumatriptan. In male barbiturate anaesthetized Wistar rats (n=25) CSDs were elicited by brain topical application of 1 M KCl, and the DC-potential and regional cerebral blood flow (rCBF, by Laser Doppler flowmetry) were measured over the same hemisphere through dura and thinned bone, respectively. Intravenous application of 8 mg/kg of the 5-HT_2A/2C receptor antagonist ritanserin (group I; n=8) significantly reduced the hyperperfusion amplitude during CSD by 44% (p<0.05, from 342±124 to 194±97%, baseline before CSD=100%), and prolonged its duration by approx. 30%. Vehicle alone (group II; n=4) did not affect CSD hyperperfusion. The highly selective 5-HT_1D/1B receptor agonist 311C90 was given in two doses: 100 μg/kg i.v. (n=5) had no effect on CSD hyperperfusion, while 800 μg/kg (n=5) increased hyperperfusion significantly (p<0.05, from 224±86 to 310±148%). We conclude that serotonin is, probably via 5-HT₂ receptors, involved in the modulation of the regional cerebral blood flow increase during CSD. Novel highly selective receptor antagonists may help to discriminate the differential contribution of various 5-HT receptor subspecies.     

Estradiol enhances brain glucose uptake in ovariectomized rats

This study was designed to investigate the effects of 17β-estradiol benzoate (E₂B) on brain glucose uptake and transport across the blood-brain barrier (BBB). Both a time- and dose-response evaluation of the effect of E₂B on glucose uptake in the central nervous system (CNS) were conducted. E₂B, in doses ranging from 1 to 100 μg/kg body weight, was injected subcutaneousy at 2 to 24 h prior to evaluation. The 4h time point and 10 μg/kg dose of E213 produced the most widespread increases in glucose uptake. Six regions responded to E213 with elevated glucose uptake by as much as 120% when compared to oil-treated controls. We then evaluated the effects of E213 on transport of glucose across the BBB. E₂B significantly increased the extraction of labeled sugar across the BBB by 40% without affecting extraction of the internal standard. Collectlvey, these studies indicate that physiological levels of estradiol (E₂) may play an important role in modulating cerebral glucose homeostasis.     

Stimulation of an intracranial trigeminally-innervated structure selectively increases cerebral blood flow

The cranial circulation, both extracerebral and cerebral, is innervated by fibers from the trigeminal nerve. This system is known as the trigeminovascular system. The large venous sinuses and dura mater are pain-sensitive and are innervated primarily by branches of the ophthalmic division of the trigeminal nerve. Studies were conducted in the α-chloralose anaesthetised cat to examine bulk carotid and cerebral blood flow responses to electrical stimulation of the trigeminal ganglion and superior sagittal sinus. Bulk carotid blood flow was measured using an ultrasonic flow probe and meter applied to the common carotid artery while cerebral blood flow was measured using laser Doppler flowmetry. Vascular resistance was calculated using simultaneously collected blood pressure data. Stimulation of the trigeminal ganglion resulted in a frequency-dependent reduction in both bulk carotid and cerebral vascular resistance. The mean maximal reduction was 39±5% at 20/s for the carotid bed and 37±6% at 20/s for the cerebral circulation. Stimulation of the superior sagittal sinus resulted in a frequency-dependent reduction in resistance that involved the cerebral circulation with little effect on bulk carotid resistance. The mean maximum reduction was 37±6% at 20/s for the cerebral circulation and 11±3% at 2/s for bulk carotid resistance. The more focused effects of superior sagittal sinus suggest a highly organised somatotopic arrangement of the trigeminal innervation of the cranial circulation. Such a physiological schema fits the known anatomy as reflected by the differential peptidergic innervation from the trigeminovascular system to cranial vessels and may be important in understanding the pathophysiology of migraine, cluster headache and subarachnoid haemorrhage. ©1997 Elsevier Science B.V. All rights reserved.     

Blockade of K(ATP) channels with glibenclamide does not alter functional activation of cerebral blood flow in the unanesthetized rat

Possible involvement of ATP-sensitive K⁺ (K_ATP) channels in the cerebral blood flow (CBF) response to neuronal functional activation was investigated in unanesthetized rats. Glibenclamide (1, 2, or 10 μmol/l), a specific inhibitor of K_ATP channels, was infused intracisternally continuously for 30 min prior to and during the 1-min period of measurement of CBF. Unilateral functional activation was maintained throughout the measurement of CBF by continuous stroking of the vibrissae on the left side of the face. Local CBF was determined bilaterally by the quantitative autoradiographic [¹⁴C]iodoantipyrine method in four structures of the whisker-to-barrel cortex pathway and in 18 structures unrelated to the pathway. Glibenclamide tended to lower baseline CBF in almost all regions examined, statistically significantly (P<0.05) in the cerebellar lobules with all doses, in the cerebellar cortex with 10 μmol/l, in the pontine nuclei with 2 and 10 μmol/l, and in the spinal trigeminal nucleus of the unstimulated side with all doses. Vibrissal stimulation increased CBF unilaterally in all the stations of the pathway, but the percent increases were not statistically significantly affected by the glibenclamide treatment, except in the spinal trigeminal nucleus where it was reduced statistically significantly (P<0.05) only by 2 μmol/l glibenclamide. These results indicate that K_ATP channels may play a role in the tonic regulation of baseline CBF in some regions but provide no support for their role in the increases in CBF evoked by functional activation.