Cerebral Ventricles: Four CSF-filled (see CEREBROSPINAL FLUID) cavities within the cerebral hemispheres (LATERAL VENTRICLES), in the midline (THIRD VENTRICLE) and within the PONS and MEDULLA OBLONGATA (FOURTH VENTRICLE).Injections, Intraventricular: Injections into the cerebral ventricles.Fourth Ventricle: An irregularly shaped cavity in the RHOMBENCEPHALON, located between the MEDULLA OBLONGATA; the PONS; and the isthmus in front, and the CEREBELLUM behind. It is continuous with the central canal of the cord below and with the CEREBRAL AQUEDUCT above, and through its lateral and median apertures it communicates with the SUBARACHNOID SPACE.Cisterna Magna: One of three principal openings in the SUBARACHNOID SPACE. They are also known as cerebellomedullary cistern, and collectively as cisterns.Heart Ventricles: The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.Shivering: Involuntary contraction or twitching of the muscles. It is a physiologic method of heat production in man and other mammals.Cerebral Arteries: The arterial blood vessels supplying the CEREBRUM.Injections: Introduction of substances into the body using a needle and syringe.Body Temperature: The measure of the level of heat of a human or animal.Lateral Ventricles: Cavity in each of the CEREBRAL HEMISPHERES derived from the cavity of the embryonic NEURAL TUBE. They are separated from each other by the SEPTUM PELLUCIDUM, and each communicates with the THIRD VENTRICLE by the foramen of Monro, through which also the choroid plexuses (CHOROID PLEXUS) of the lateral ventricles become continuous with that of the third ventricle.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Cerebrospinal Fluid: A watery fluid that is continuously produced in the CHOROID PLEXUS and circulates around the surface of the BRAIN; SPINAL CORD; and in the CEREBRAL VENTRICLES.Pempidine: A nicotinic antagonist most commonly used as an experimental tool. It has been used as a ganglionic blocker in the treatment of hypertension but has largely been supplanted for that purpose by more specific drugs.Hypothalamus: Ventral part of the DIENCEPHALON extending from the region of the OPTIC CHIASM to the caudal border of the MAMMILLARY BODIES and forming the inferior and lateral walls of the THIRD VENTRICLE.Ependyma: A thin membrane that lines the CEREBRAL VENTRICLES and the central canal of the SPINAL CORD.Cerebral Infarction: The formation of an area of NECROSIS in the CEREBRUM caused by an insufficiency of arterial or venous blood flow. Infarcts of the cerebrum are generally classified by hemisphere (i.e., left vs. right), lobe (e.g., frontal lobe infarction), arterial distribution (e.g., INFARCTION, ANTERIOR CEREBRAL ARTERY), and etiology (e.g., embolic infarction).Hypnosis, Anesthetic: Procedure in which an individual is induced into a trance-like state to relieve pain. This procedure is frequently performed with local but not general ANESTHESIA.Body Temperature Regulation: The processes of heating and cooling that an organism uses to control its temperature.Physostigmine: A cholinesterase inhibitor that is rapidly absorbed through membranes. It can be applied topically to the conjunctiva. It also can cross the blood-brain barrier and is used when central nervous system effects are desired, as in the treatment of severe anticholinergic toxicity.Cerebral Ventricle Neoplasms: Neoplasms located in the brain ventricles, including the two lateral, the third, and the fourth ventricle. Ventricular tumors may be primary (e.g., CHOROID PLEXUS NEOPLASMS and GLIOMA, SUBEPENDYMAL), metastasize from distant organs, or occur as extensions of locally invasive tumors from adjacent brain structures.Hexamethonium Compounds: Compounds containing the hexamethylenebis(trimethylammonium) cation. Members of this group frequently act as antihypertensive agents and selective ganglionic blocking agents.Tranylcypromine: A propylamine formed from the cyclization of the side chain of amphetamine. This monoamine oxidase inhibitor is effective in the treatment of major depression, dysthymic disorder, and atypical depression. It also is useful in panic and phobic disorders. (From AMA Drug Evaluations Annual, 1994, p311)Cats: The domestic cat, Felis catus, of the carnivore family FELIDAE, comprising over 30 different breeds. The domestic cat is descended primarily from the wild cat of Africa and extreme southwestern Asia. Though probably present in towns in Palestine as long ago as 7000 years, actual domestication occurred in Egypt about 4000 years ago. (From Walker's Mammals of the World, 6th ed, p801)Third Ventricle: A narrow cleft inferior to the CORPUS CALLOSUM, within the DIENCEPHALON, between the paired thalami. Its floor is formed by the HYPOTHALAMUS, its anterior wall by the lamina terminalis, and its roof by EPENDYMA. It communicates with the FOURTH VENTRICLE by the CEREBRAL AQUEDUCT, and with the LATERAL VENTRICLES by the interventricular foramina.Subarachnoid Space: The space between the arachnoid membrane and PIA MATER, filled with CEREBROSPINAL FLUID. It contains large blood vessels that supply the BRAIN and SPINAL CORD.Cerebral Palsy: A heterogeneous group of nonprogressive motor disorders caused by chronic brain injuries that originate in the prenatal period, perinatal period, or first few years of life. The four major subtypes are spastic, athetoid, ataxic, and mixed cerebral palsy, with spastic forms being the most common. The motor disorder may range from difficulties with fine motor control to severe spasticity (see MUSCLE SPASTICITY) in all limbs. Spastic diplegia (Little disease) is the most common subtype, and is characterized by spasticity that is more prominent in the legs than in the arms. Pathologically, this condition may be associated with LEUKOMALACIA, PERIVENTRICULAR. (From Dev Med Child Neurol 1998 Aug;40(8):520-7)Cerebrovascular Circulation: The circulation of blood through the BLOOD VESSELS of the BRAIN.Consciousness: Sense of awareness of self and of the environment.Histamine Agents: Drugs used for their actions on histaminergic systems. Included are drugs that act at histamine receptors, affect the life cycle of histamine, or affect the state of histaminergic cells.Middle Cerebral Artery: The largest of the cerebral arteries. It trifurcates into temporal, frontal, and parietal branches supplying blood to most of the parenchyma of these lobes in the CEREBRAL CORTEX. These are the areas involved in motor, sensory, and speech activities.Perfusion: Treatment process involving the injection of fluid into an organ or tissue.Pyrogens: Substances capable of increasing BODY TEMPERATURE and cause FEVER and may be used for FEVER THERAPY. They may be of microbial origin, often POLYSACCHARIDES, and may contaminate distilled water.Serotonin: A biochemical messenger and regulator, synthesized from the essential amino acid L-TRYPTOPHAN. In humans it is found primarily in the central nervous system, gastrointestinal tract, and blood platelets. Serotonin mediates several important physiological functions including neurotransmission, gastrointestinal motility, hemostasis, and cardiovascular integrity. Multiple receptor families (RECEPTORS, SEROTONIN) explain the broad physiological actions and distribution of this biochemical mediator.Hydrocephalus: Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, INTRACRANIAL HYPERTENSION; HEADACHE; lethargy; URINARY INCONTINENCE; and ATAXIA.Choroid Plexus: A villous structure of tangled masses of BLOOD VESSELS contained within the third, lateral, and fourth ventricles of the BRAIN. It regulates part of the production and composition of CEREBROSPINAL FLUID.Norepinephrine: Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers and of the diffuse projection system in the brain arising from the locus ceruleus. It is also found in plants and is used pharmacologically as a sympathomimetic.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)Phentolamine: A nonselective alpha-adrenergic antagonist. It is used in the treatment of hypertension and hypertensive emergencies, pheochromocytoma, vasospasm of RAYNAUD DISEASE and frostbite, clonidine withdrawal syndrome, impotence, and peripheral vascular disease.Lysergic Acid Diethylamide: Semisynthetic derivative of ergot (Claviceps purpurea). It has complex effects on serotonergic systems including antagonism at some peripheral serotonin receptors, both agonist and antagonist actions at central nervous system serotonin receptors, and possibly effects on serotonin turnover. It is a potent hallucinogen, but the mechanisms of that effect are not well understood.Drinking: The consumption of liquids.Rats, Wistar: A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain.Cerebral Angiography: Radiography of the vascular system of the brain after injection of a contrast medium.Parasympathomimetics: Drugs that mimic the effects of parasympathetic nervous system activity. Included here are drugs that directly stimulate muscarinic receptors and drugs that potentiate cholinergic activity, usually by slowing the breakdown of acetylcholine (CHOLINESTERASE INHIBITORS). Drugs that stimulate both sympathetic and parasympathetic postganglionic neurons (GANGLIONIC STIMULANTS) are not included here.Infarction, Middle Cerebral Artery: NECROSIS occurring in the MIDDLE CEREBRAL ARTERY distribution system which brings blood to the entire lateral aspects of each CEREBRAL HEMISPHERE. Clinical signs include impaired cognition; APHASIA; AGRAPHIA; weak and numbness in the face and arms, contralaterally or bilaterally depending on the infarction.Injections, Intravenous: Injections made into a vein for therapeutic or experimental purposes.Malaria, Cerebral: A condition characterized by somnolence or coma in the presence of an acute infection with PLASMODIUM FALCIPARUM (and rarely other Plasmodium species). Initial clinical manifestations include HEADACHES; SEIZURES; and alterations of mentation followed by a rapid progression to COMA. Pathologic features include cerebral capillaries filled with parasitized erythrocytes and multiple small foci of cortical and subcortical necrosis. (From Adams et al., Principles of Neurology, 6th ed, p136)Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Reserpine: An alkaloid found in the roots of Rauwolfia serpentina and R. vomitoria. Reserpine inhibits the uptake of norepinephrine into storage vesicles resulting in depletion of catecholamines and serotonin from central and peripheral axon terminals. It has been used as an antihypertensive and an antipsychotic as well as a research tool, but its adverse effects limit its clinical use.Cerebral Veins: Veins draining the cerebrum.Pentobarbital: A short-acting barbiturate that is effective as a sedative and hypnotic (but not as an anti-anxiety) agent and is usually given orally. It is prescribed more frequently for sleep induction than for sedation but, like similar agents, may lose its effectiveness by the second week of continued administration. (From AMA Drug Evaluations Annual, 1994, p236)Atropine: An alkaloid, originally from Atropa belladonna, but found in other plants, mainly SOLANACEAE. Hyoscyamine is the 3(S)-endo isomer of atropine.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Brain Ischemia: Localized reduction of blood flow to brain tissue due to arterial obstruction or systemic hypoperfusion. This frequently occurs in conjunction with brain hypoxia (HYPOXIA, BRAIN). Prolonged ischemia is associated with BRAIN INFARCTION.Fever: An abnormal elevation of body temperature, usually as a result of a pathologic process.Cerebral Hemorrhage: Bleeding into one or both CEREBRAL HEMISPHERES including the BASAL GANGLIA and the CEREBRAL CORTEX. It is often associated with HYPERTENSION and CRANIOCEREBRAL TRAUMA.Depression, Chemical: The decrease in a measurable parameter of a PHYSIOLOGICAL PROCESS, including cellular, microbial, and plant; immunological, cardiovascular, respiratory, reproductive, urinary, digestive, neural, musculoskeletal, ocular, and skin physiological processes; or METABOLIC PROCESS, including enzymatic and other pharmacological processes, by a drug or other chemical.Naloxone: A specific opiate antagonist that has no agonist activity. It is a competitive antagonist at mu, delta, and kappa opioid receptors.Respiration: The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration (= OXYGEN CONSUMPTION) or cell respiration (= CELL RESPIRATION).Rats, Inbred Strains: Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Ventricular Function: The hemodynamic and electrophysiological action of the HEART VENTRICLES.Arginine Vasopressin: The predominant form of mammalian antidiuretic hormone. It is a nonapeptide containing an ARGININE at residue 8 and two disulfide-linked cysteines at residues of 1 and 6. Arg-vasopressin is used to treat DIABETES INSIPIDUS or to improve vasomotor tone and BLOOD PRESSURE.Sheep: Any of the ruminant mammals with curved horns in the genus Ovis, family Bovidae. They possess lachrymal grooves and interdigital glands, which are absent in GOATS.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Prostaglandins: A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes.Stimulation, Chemical: The increase in a measurable parameter of a PHYSIOLOGICAL PROCESS, including cellular, microbial, and plant; immunological, cardiovascular, respiratory, reproductive, urinary, digestive, neural, musculoskeletal, ocular, and skin physiological processes; or METABOLIC PROCESS, including enzymatic and other pharmacological processes, by a drug or other chemical.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Vasopressins: Antidiuretic hormones released by the NEUROHYPOPHYSIS of all vertebrates (structure varies with species) to regulate water balance and OSMOLARITY. In general, vasopressin is a nonapeptide consisting of a six-amino-acid ring with a cysteine 1 to cysteine 6 disulfide bridge or an octapeptide containing a CYSTINE. All mammals have arginine vasopressin except the pig with a lysine at position 8. Vasopressin, a vasoconstrictor, acts on the KIDNEY COLLECTING DUCTS to increase water reabsorption, increase blood volume and blood pressure.Carbachol: A slowly hydrolyzed CHOLINERGIC AGONIST that acts at both MUSCARINIC RECEPTORS and NICOTINIC RECEPTORS.Electroencephalography: Recording of electric currents developed in the brain by means of electrodes applied to the scalp, to the surface of the brain, or placed within the substance of the brain.Prostaglandins E: (11 alpha,13E,15S)-11,15-Dihydroxy-9-oxoprost-13-en-1-oic acid (PGE(1)); (5Z,11 alpha,13E,15S)-11,15-dihydroxy-9-oxoprosta-5,13-dien-1-oic acid (PGE(2)); and (5Z,11 alpha,13E,15S,17Z)-11,15-dihydroxy-9-oxoprosta-5,13,17-trien-1-oic acid (PGE(3)). Three of the six naturally occurring prostaglandins. They are considered primary in that no one is derived from another in living organisms. Originally isolated from sheep seminal fluid and vesicles, they are found in many organs and tissues and play a major role in mediating various physiological activities.Myocardium: The muscle tissue of the HEART. It is composed of striated, involuntary muscle cells (MYOCYTES, CARDIAC) connected to form the contractile pump to generate blood flow.Epinephrine: The active sympathomimetic hormone from the ADRENAL MEDULLA. It stimulates both the alpha- and beta- adrenergic systems, causes systemic VASOCONSTRICTION and gastrointestinal relaxation, stimulates the HEART, and dilates BRONCHI and cerebral vessels. It is used in ASTHMA and CARDIAC FAILURE and to delay absorption of local ANESTHETICS.Heart: The hollow, muscular organ that maintains the circulation of the blood.Corticotropin-Releasing Hormone: A peptide of about 41 amino acids that stimulates the release of ADRENOCORTICOTROPIC HORMONE. CRH is synthesized by neurons in the PARAVENTRICULAR NUCLEUS of the HYPOTHALAMUS. After being released into the pituitary portal circulation, CRH stimulates the release of ACTH from the PITUITARY GLAND. CRH can also be synthesized in other tissues, such as PLACENTA; ADRENAL MEDULLA; and TESTIS.Behavior, Animal: The observable response an animal makes to any situation.Morphine: The principal alkaloid in opium and the prototype opiate analgesic and narcotic. Morphine has widespread effects in the central nervous system and on smooth muscle.Ischemic Attack, Transient: Brief reversible episodes of focal, nonconvulsive ischemic dysfunction of the brain having a duration of less than 24 hours, and usually less than one hour, caused by transient thrombotic or embolic blood vessel occlusion or stenosis. Events may be classified by arterial distribution, temporal pattern, or etiology (e.g., embolic vs. thrombotic). (From Adams et al., Principles of Neurology, 6th ed, pp814-6)Acetylcholine: A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system.Dopamine: One of the catecholamine NEUROTRANSMITTERS in the brain. It is derived from TYROSINE and is the precursor to NOREPINEPHRINE and EPINEPHRINE. Dopamine is a major transmitter in the extrapyramidal system of the brain, and important in regulating movement. A family of receptors (RECEPTORS, DOPAMINE) mediate its action.Eating: The consumption of edible substances.Sympathetic Nervous System: The thoracolumbar division of the autonomic nervous system. Sympathetic preganglionic fibers originate in neurons of the intermediolateral column of the spinal cord and project to the paravertebral and prevertebral ganglia, which in turn project to target organs. The sympathetic nervous system mediates the body's response to stressful situations, i.e., the fight or flight reactions. It often acts reciprocally to the parasympathetic system.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Anterior Cerebral Artery: Artery formed by the bifurcation of the internal carotid artery (CAROTID ARTERY, INTERNAL). Branches of the anterior cerebral artery supply the CAUDATE NUCLEUS; INTERNAL CAPSULE; PUTAMEN; SEPTAL NUCLEI; GYRUS CINGULI; and surfaces of the FRONTAL LOBE and PARIETAL LOBE.Injections, Intraperitoneal: Forceful administration into the peritoneal cavity of liquid medication, nutrient, or other fluid through a hollow needle piercing the abdominal wall.Cerebral Amyloid Angiopathy: A heterogeneous group of sporadic or familial disorders characterized by AMYLOID deposits in the walls of small and medium sized blood vessels of CEREBRAL CORTEX and MENINGES. Clinical features include multiple, small lobar CEREBRAL HEMORRHAGE; cerebral ischemia (BRAIN ISCHEMIA); and CEREBRAL INFARCTION. Cerebral amyloid angiopathy is unrelated to generalized AMYLOIDOSIS. Amyloidogenic peptides in this condition are nearly always the same ones found in ALZHEIMER DISEASE. (from Kumar: Robbins and Cotran: Pathologic Basis of Disease, 7th ed., 2005)Brain Diseases: Pathologic conditions affecting the BRAIN, which is composed of the intracranial components of the CENTRAL NERVOUS SYSTEM. This includes (but is not limited to) the CEREBRAL CORTEX; intracranial white matter; BASAL GANGLIA; THALAMUS; HYPOTHALAMUS; BRAIN STEM; and CEREBELLUM.Posterior Cerebral Artery: Artery formed by the bifurcation of the BASILAR ARTERY. Branches of the posterior cerebral artery supply portions of the OCCIPITAL LOBE; PARIETAL LOBE; inferior temporal gyrus, brainstem, and CHOROID PLEXUS.Angiotensin II: An octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the C-terminal by ANGIOTENSIN CONVERTING ENZYME. The amino acid in position 5 varies in different species. To block VASOCONSTRICTION and HYPERTENSION effect of angiotensin II, patients are often treated with ACE INHIBITORS or with ANGIOTENSIN II TYPE 1 RECEPTOR BLOCKERS.Subarachnoid Hemorrhage: Bleeding into the intracranial or spinal SUBARACHNOID SPACE, most resulting from INTRACRANIAL ANEURYSM rupture. It can occur after traumatic injuries (SUBARACHNOID HEMORRHAGE, TRAUMATIC). Clinical features include HEADACHE; NAUSEA; VOMITING, nuchal rigidity, variable neurological deficits and reduced mental status.Brain Edema: Increased intracellular or extracellular fluid in brain tissue. Cytotoxic brain edema (swelling due to increased intracellular fluid) is indicative of a disturbance in cell metabolism, and is commonly associated with hypoxic or ischemic injuries (see HYPOXIA, BRAIN). An increase in extracellular fluid may be caused by increased brain capillary permeability (vasogenic edema), an osmotic gradient, local blockages in interstitial fluid pathways, or by obstruction of CSF flow (e.g., obstructive HYDROCEPHALUS). (From Childs Nerv Syst 1992 Sep; 8(6):301-6)Cerebral Ventriculography: Radiography of the ventricular system of the brain after injection of air or other contrast medium directly into the cerebral ventricles. It is used also for x-ray computed tomography of the cerebral ventricles.Myocardial Contraction: Contractile activity of the MYOCARDIUM.Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.Intracranial Pressure: Pressure within the cranial cavity. It is influenced by brain mass, the circulatory system, CSF dynamics, and skull rigidity.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Cerebrovascular Disorders: A spectrum of pathological conditions of impaired blood flow in the brain. They can involve vessels (ARTERIES or VEINS) in the CEREBRUM, the CEREBELLUM, and the BRAIN STEM. Major categories include INTRACRANIAL ARTERIOVENOUS MALFORMATIONS; BRAIN ISCHEMIA; CEREBRAL HEMORRHAGE; and others.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Ventricular Function, Right: The hemodynamic and electrophysiological action of the right HEART VENTRICLE.Double Outlet Right Ventricle: Incomplete transposition of the great vessels in which both the AORTA and the PULMONARY ARTERY arise from the RIGHT VENTRICLE. The only outlet of the LEFT VENTRICLE is a large ventricular septal defect (VENTRICULAR SEPTAL DEFECTS or VSD). The various subtypes are classified by the location of the septal defect, such as subaortic, subpulmonary, or noncommitted.Intracranial Embolism and Thrombosis: Embolism or thrombosis involving blood vessels which supply intracranial structures. Emboli may originate from extracranial or intracranial sources. Thrombosis may occur in arterial or venous structures.Dominance, Cerebral: Dominance of one cerebral hemisphere over the other in cerebral functions.Heart Defects, Congenital: Developmental abnormalities involving structures of the heart. These defects are present at birth but may be discovered later in life.Intracranial Aneurysm: Abnormal outpouching in the wall of intracranial blood vessels. Most common are the saccular (berry) aneurysms located at branch points in CIRCLE OF WILLIS at the base of the brain. Vessel rupture results in SUBARACHNOID HEMORRHAGE or INTRACRANIAL HEMORRHAGES. Giant aneurysms (>2.5 cm in diameter) may compress adjacent structures, including the OCULOMOTOR NERVE. (From Adams et al., Principles of Neurology, 6th ed, p841)Heart Atria: The chambers of the heart, to which the BLOOD returns from the circulation.Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Cerebral Revascularization: Microsurgical revascularization to improve intracranial circulation. It usually involves joining the extracranial circulation to the intracranial circulation but may include extracranial revascularization (e.g., subclavian-vertebral artery bypass, subclavian-external carotid artery bypass). It is performed by joining two arteries (direct anastomosis or use of graft) or by free autologous transplantation of highly vascularized tissue to the surface of the brain.Ventricular Function, Left: The hemodynamic and electrophysiological action of the left HEART VENTRICLE. Its measurement is an important aspect of the clinical evaluation of patients with heart disease to determine the effects of the disease on cardiac performance.Cerebrum: Derived from TELENCEPHALON, cerebrum is composed of a right and a left hemisphere. Each contains an outer cerebral cortex and a subcortical basal ganglia. The cerebrum includes all parts within the skull except the MEDULLA OBLONGATA, the PONS, and the CEREBELLUM. Cerebral functions include sensorimotor, emotional, and intellectual activities.Endocardium: The innermost layer of the heart, comprised of endothelial cells.Vasospasm, Intracranial: Constriction of arteries in the SKULL due to sudden, sharp, and often persistent smooth muscle contraction in blood vessels. Intracranial vasospasm results in reduced vessel lumen caliber, restricted blood flow to the brain, and BRAIN ISCHEMIA that may lead to hypoxic-ischemic brain injury (HYPOXIA-ISCHEMIA, BRAIN).Blood Volume: Volume of circulating BLOOD. It is the sum of the PLASMA VOLUME and ERYTHROCYTE VOLUME.Ventricular Dysfunction, Right: A condition in which the RIGHT VENTRICLE of the heart was functionally impaired. This condition usually leads to HEART FAILURE or MYOCARDIAL INFARCTION, and other cardiovascular complications. Diagnosis is made by measuring the diminished ejection fraction and a depressed level of motility of the right ventricular wall.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Neuroprotective Agents: Drugs intended to prevent damage to the brain or spinal cord from ischemia, stroke, convulsions, or trauma. Some must be administered before the event, but others may be effective for some time after. They act by a variety of mechanisms, but often directly or indirectly minimize the damage produced by endogenous excitatory amino acids.Models, Cardiovascular: Theoretical representations that simulate the behavior or activity of the cardiovascular system, processes, or phenomena; includes the use of mathematical equations, computers and other electronic equipment.Hypoxia, Brain: A reduction in brain oxygen supply due to ANOXEMIA (a reduced amount of oxygen being carried in the blood by HEMOGLOBIN), or to a restriction of the blood supply to the brain, or both. Severe hypoxia is referred to as anoxia, and is a relatively common cause of injury to the central nervous system. Prolonged brain anoxia may lead to BRAIN DEATH or a PERSISTENT VEGETATIVE STATE. Histologically, this condition is characterized by neuronal loss which is most prominent in the HIPPOCAMPUS; GLOBUS PALLIDUS; CEREBELLUM; and inferior olives.Pericardium: A conical fibro-serous sac surrounding the HEART and the roots of the great vessels (AORTA; VENAE CAVAE; PULMONARY ARTERY). Pericardium consists of two sacs: the outer fibrous pericardium and the inner serous pericardium. The latter consists of an outer parietal layer facing the fibrous pericardium, and an inner visceral layer (epicardium) resting next to the heart, and a pericardial cavity between these two layers.Tomography, Emission-Computed: Tomography using radioactive emissions from injected RADIONUCLIDES and computer ALGORITHMS to reconstruct an image.Transposition of Great Vessels: A congenital cardiovascular malformation in which the AORTA arises entirely from the RIGHT VENTRICLE, and the PULMONARY ARTERY arises from the LEFT VENTRICLE. Consequently, the pulmonary and the systemic circulations are parallel and not sequential, so that the venous return from the peripheral circulation is re-circulated by the right ventricle via aorta to the systemic circulation without being oxygenated in the lungs. This is a potentially lethal form of heart disease in newborns and infants.Blood-Brain Barrier: Specialized non-fenestrated tightly-joined ENDOTHELIAL CELLS with TIGHT JUNCTIONS that form a transport barrier for certain substances between the cerebral capillaries and the BRAIN tissue.Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.Xenon Radioisotopes: Unstable isotopes of xenon that decay or disintegrate emitting radiation. Xe atoms with atomic weights 121-123, 125, 127, 133, 135, 137-145 are radioactive xenon isotopes.Stroke: A group of pathological conditions characterized by sudden, non-convulsive loss of neurological function due to BRAIN ISCHEMIA or INTRACRANIAL HEMORRHAGES. Stroke is classified by the type of tissue NECROSIS, such as the anatomic location, vasculature involved, etiology, age of the affected individual, and hemorrhagic vs. non-hemorrhagic nature. (From Adams et al., Principles of Neurology, 6th ed, pp777-810)Image Processing, Computer-Assisted: A technique of inputting two-dimensional images into a computer and then enhancing or analyzing the imagery into a form that is more useful to the human observer.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Basilar Artery: The artery formed by the union of the right and left vertebral arteries; it runs from the lower to the upper border of the pons, where it bifurcates into the two posterior cerebral arteries.Cerebral Aqueduct: Narrow channel in the MESENCEPHALON that connects the third and fourth CEREBRAL VENTRICLES.Heart Septum: This structure includes the thin muscular atrial septum between the two HEART ATRIA, and the thick muscular ventricular septum between the two HEART VENTRICLES.Reperfusion: Restoration of blood supply to tissue which is ischemic due to decrease in normal blood supply. The decrease may result from any source including atherosclerotic obstruction, narrowing of the artery, or surgical clamping. It is primarily a procedure for treating infarction or other ischemia, by enabling viable ischemic tissue to recover, thus limiting further necrosis. However, it is thought that reperfusion can itself further damage the ischemic tissue, causing REPERFUSION INJURY.Tomography, Emission-Computed, Single-Photon: A method of computed tomography that uses radionuclides which emit a single photon of a given energy. The camera is rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer is then used to reconstruct the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the organ. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as size and volume of the organ. The disadvantage is that, unlike positron-emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of many available photons and hence degrades the image.Pia Mater: The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the ARACHNOID and the DURA MATER.Magnetic Resonance Angiography: Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in CEREBRAL ANGIOGRAPHY as well as for studies of other vascular structures.Spectroscopy, Near-Infrared: A noninvasive technique that uses the differential absorption properties of hemoglobin and myoglobin to evaluate tissue oxygenation and indirectly can measure regional hemodynamics and blood flow. Near-infrared light (NIR) can propagate through tissues and at particular wavelengths is differentially absorbed by oxygenated vs. deoxygenated forms of hemoglobin and myoglobin. Illumination of intact tissue with NIR allows qualitative assessment of changes in the tissue concentration of these molecules. The analysis is also used to determine body composition.Hypertrophy, Right Ventricular: Enlargement of the RIGHT VENTRICLE of the heart. This increase in ventricular mass is often attributed to PULMONARY HYPERTENSION and is a contributor to cardiovascular morbidity and mortality.Heart Septal Defects, Ventricular: Developmental abnormalities in any portion of the VENTRICULAR SEPTUM resulting in abnormal communications between the two lower chambers of the heart. Classification of ventricular septal defects is based on location of the communication, such as perimembranous, inlet, outlet (infundibular), central muscular, marginal muscular, or apical muscular defect.