Isolated brain microvessels: preparation, morphology, histamine and catecholamine contents

A novel multicolor flow-cytometry application for quantitative detection of receptors on vascular smooth muscle cells

There is a need to develop new techniques for quantitative measurement of receptors expression on particular vasculature cells types. Here, we describe and demonstrate a novel method to measure quantitatively and simultaneously the expression of endothelin B receptor (ETB) on vascular smooth muscle cells (VSMC). We isolated cells from male rat tissues such as: brain pial, brain intraparenchymal and retina vessels. To analyze solid tissues, a single-cell suspension was prepared by a combined mechanic and enzymatic process. The cells were stained with Fixable Viability Dye, followed by fixation, permeabilization and antibodies staining. The expression of ETB receptors on VSMC was measured by flow-cytometry and visualized by fluorescence microscopy. We obtained a high percentage of viable cells 87.6% ± 1.5% pial; 84.6% ± 4.3% parenchymal and 90.6% ± 4% retina after isolation of single cells. We performed a quantitative measurement of ETB receptor expression on VSMC and we identified two subpopulations of VSMC based on their expression of smooth muscle cells marker SM22α. The results obtained from pial vessels are statistically significant (38.4% ± 4% vs 9.8% ± 3.32%) between the two subpopulations of VSMC. The results obtained from intraparenchymal and retina vessels were not statistically significant. By specific gating on two subpopulations, we were able to quantify the expression of ETB receptors. The two subpopulation expressed the same level of ETB receptor (p = 0.45; p = 0.3; p = 0.42) in pial, parenchymal and retina vessels, respectively. We applied our method to the animals after induction of subarachnoid hemorrhage (SAH). There was statistically significant expression of ETB receptor (p = 0.02) on VSMC between sham 61.4% ± 4% and SAH 77.4% ± 4% rats pial vessels. The presented technique is able to quantitatively and selectively measure the level of protein expression on VSMC. The entire technique is optimized for rat tissue; however the protocol can also be adapted for other species.

Purification of Mouse Brain Vessels

In the brain, most of the vascular system consists of a selective barrier, the blood-brain barrier (BBB) that regulates the exchange of molecules and immune cells between the brain and the blood. Moreover, the huge neuronal metabolic demand requires a moment-to-moment regulation of blood flow. Notably, abnormalities of these regulations are etiological hallmarks of most brain pathologies; including glioblastoma, stroke, edema, epilepsy, degenerative diseases (ex: Parkinson's disease, Alzheimer's disease), brain tumors, as well as inflammatory conditions such as multiple sclerosis, meningitis and sepsis-induced brain dysfunctions. Thus, understanding the signaling events modulating the cerebrovascular physiology is a major challenge. Much insight into the cellular and molecular properties of the various cell types that compose the cerebrovascular system can be gained from primary culture or cell sorting from freshly dissociated brain tissue. However, properties such as cell polarity, morphology and intercellular relationships are not maintained in such preparations. The protocol that we describe here is designed to purify brain vessel fragments, whilst maintaining structural integrity. We show that isolated vessels consist of endothelial cells sealed by tight junctions that are surrounded by a continuous basal lamina. Pericytes, smooth muscle cells as well as the perivascular astrocyte endfeet membranes remain attached to the endothelial layer. Finally, we describe how to perform immunostaining experiments on purified brain vessels.

Pharmacologic magnetic resonance imaging (phMRI): imaging drug action in the brain

The technique of functional magnetic resonance (fMRI), using various cognitive, motor and sensory stimuli has led to a revolution in the ability to map brain function. Drugs can also be used as stimuli to elicit an hemodynamic change. Stimulation with a pharmaceutical has a number of very different consequences compared to user controllable stimuli, most importantly in the time course of stimulus and response that is not, in general, controllable by the experimenter. Therefore, this type of experiment has been termed pharmacologic MRI (phMRI). The use of a drug stimulus leads to a number of interesting possibilities compared to conventional fMRI. Using receptor specific ligands one can characterize brain circuitry specific to neurotransmitter systems. The possibility exists to measure parameters reflecting neurotransmitter release and binding associated with the pharmacokinetics and/or the pharmacodynamics of drugs. There is also the ability to measure up- and down-regulation of receptors in specific disease states. phMRI can be characterized as a molecular imaging technique using the natural hemodynamic transduction related to neuro-receptor stimulus. This provides a coupling mechanism with very high sensitivity that can rival positron emission tomography (PET) in some circumstances. The large numbers of molecules available, that do not require a radio-label, means that phMRI becomes a very useful tool for performing drug discovery. Data and arguments will be presented to show that phMRI can provide information on neuro-receptor signaling and function that complements the static picture generated by PET studies of receptor numbers and occupancies.

Zolantidine (SK&F 95282) is a potent selective brain-penetrating histamine H2-receptor antagonist

1. The novel benzthiazole derivative zolantidine (SK&F 95282) is a potent antagonist of histamine at H2-receptors in guinea-pig atrium and rat uterus. Only apparent pA2 values of 7.46 and 7.26 respectively could be calculated since the slopes of the Schild plots were significantly less than unity. 2. Zolantidine is equally potent as an antagonist at histamine H2-receptors in guinea-pig brain. The compound inhibited histamine stimulated adenylate cyclase (pKi 7.3) and dimaprit stimulated adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation (approx pA2 7.63), and competed with [3H]-tiotidine binding (pKi 7.17). 3. Zolantidine is at least 30 fold more potent at H2-receptors than at other peripheral and central receptors investigated. 4. Infusion of zolantidine into rats produces a brain concentration greater than the plateau blood concentration (brain/blood ratio 1.45). 5. Zolantidine is thus characterized as a potent selective brain-penetrating H2-receptor antagonist, and will be a valuable pharmacological tool for investigating possible physiological and pathological roles for histamine in the central nervous system.

Vasomotor responses of cerebral arterioles in situ to putative dopamine receptor agonists

The vasomotor responses of individual cerebral pial arterioles on the convexity of the cerebral cortex to subarachnoid perivascular micro-injections of dopamine and the putative dopamine receptor agonists, apomorphine, SKF 38393 and LY 141865, have been examined in 38 anaesthetized cats. The perivascular microapplication of dopamine (10(-9)-10(-3)M) effected dose-dependent reductions in pial arteriolar calibre, with the maximum reductions in calibre (22 +/- 2% from preinjection levels: mean +/- s.e.) being observed at 10(-3)M. The cerebrovascular constriction produced by dopamine (10(-5)M) could be significantly attenuated by the concomitant perivascular administration of phentolamine (10(-6)M) or methysergide (10(-6)M). The perivascular microapplication of apomorphine (10(-8)-10(-4)M) effected dose-dependent increases in arteriolar calibre, with the maximum increase (31 +/- 6%) being observed with apomorphine (10(-5)M). The perivascular administration of the putative dopamine D1-receptor agonist, SKF 38393 (10(-9)-10(-4)M) increased arteriolar calibre, with the maximum response (24 +/- 3%) being observed with injection of 10(-7)M. The putative dopamine D2-receptor agonist, LY 141865, also increased cerebral arteriolar calibre, but only at high concentrations (maximum calibre increase 25 +/- 6.1 with 10(-4)M). The cerebrovascular dilatations elicited by apomorphine and by SKF 38393 were markedly attenuated by the concomitant perivascular microapplication of the putative dopamine D1-receptor antagonist, SCH 23390 (10(-8)M). The perivascular administration of SCH 23390 (10(-9)-10(-5)M) per se did not alter arteriolar calibre nor the arteriolar dilatation provoked by microinjections of acidic cerebrospinal fluid. These results point to the presence on cat cerebral arterioles of dopamine receptors (probably of D1 subtype) mediating dilation.

Distribution and localization of histamine in bovine and rabbit eye

Histamine (HI) is present in various structures of the bovine and rabbit eye (retina, choroid, sclera) and in the optic nerve of both species. The amine levels in particular structures of either cow or rabbit are highly differentiated, as well as profile of HI distribution which differs markedly between both species, except only the retina structure (HI levels were between 70-80 ng per g tissue). In the bovine retina HI is stored in non mast cell compartment, while in the optic nerve at least 50% of the amine is of mast cell origin. Approximately 90% of the retinal HI was recovered in the P1 subcellular fraction. HI in the bovine retina is metabolized by methylation. The data are discussed in terms of a possible physiological role of HI in the retina.