Parenchymal Arterioles Research Articles

P-484 - Observation of spontaneous rhythmic contractions and pharmacological responsiveness in brain parenchymal arterioles in organ culture - a new method using computer-aided image analyzer

P-484 - Observation of spontaneous rhythmic contractions and pharmacological responsiveness in brain parenchymal arterioles in organ culture - a new method using computer-aided image analyzer

Effects of HA 1077, a novel calciumantagonistic spasmolytic agent on intracerebral arterioles of rats

The effects of the new spasmolytic agent HA1077, which belongs to the calciumantagonists but acts by mechanisms different from those of conventional calcium channel blockers, on the cerebral microcirculation were studied in rats using isolated and cannulated intracerebral (parenchymal) arterioles of 50 microns average diameter. After the vessels had developed spontaneous tone, increasing concentrations of HA1077 were applied extraluminally. HA1077 induced vasodilation in a dose-dependent manner with a maximal increase of vessel diameter of 73.9 +/- 5.1% (mean +/- SEM, n = 5) at 10(-4) M and with half-maximal responses (ED50) of 1.00 x 10(-6) M. The extent of maximal vasodilation achieved by HA1077 was significantly greater than that induced by such conventional calcium channel blockers as diltiazem, verapamil, nifedipine and nimodipine (about 50% each in a previous report from our laboratory). Vasoconstriction induced by synthetic thromboxane A2 (10(-9) M to 10(-5) M) which is through to be highly dependent on intracellular calcium, was completely inhibited by 10(-4) M HA1077, whereas both verapamil and nimodipine at a concentration at maximal vasodilation effects (10(-5) M and 10(-7) M respectively) only partially inhibited such vasoconstriction. These results suggest that HA1077 may exert a more potent vasodilator effect on the cerebral microcirculation than do conventional calcium channel blockers.

Spontaneous tone of cerebral parenchymal arterioles: a role in cerebral hyperemic phenomena.

An isolated cerebral arteriole preparation was used to test the hypothesis that a temporary reduction in transmural pressure causes a subsequent vasodilation mediated by mechanisms intrinsic to the vessel wall. Thirty-five cerebral vessels of 44.7 +/- 1.4 microns (+/- standard error of the mean) mean diameter were cannulated in vitro and pressurized at a transmural pressure of 60 mm Hg: after an equilibration period the vessels developed spontaneous tone. When transmural pressure was decreased to 0 mm Hg for a period of 4 minutes then returned to 60 mm Hg, vessels dilated to 155.1% +/- 6.8% of control diameter before gradually redeveloping spontaneous tone in 5.5 +/- 0.7 minutes. Varying the duration of the period during which transmural pressure was at 0 mm Hg had no significant effect on the degree of vasodilation. Conversely, varying the level of decreased transmural pressure between 0 and 20 mm Hg significantly affected both the magnitude of vasodilation and the time course of spontaneous tone recovery. These findings indicate that a temporary period of decreased transmural pressure may result in a loss of spontaneous tone in the resistance vessels of the cerebral microcirculation. Mechanisms intrinsic to the vessel wall may play a significant role in the early stage of post-reperfusion hyperemia. Such mechanisms could also be implicated in other hyperemic phenomena affecting the cerebral circulation, such as the rapid increase in intracranial pressure after subarachnoid hemorrhage, the development of the normal perfusion pressure breakthrough phenomenon, and the initiation of intracranial pressure plateau waves.

Effects of inhibitory and excitatory amino acid neurotransmitters on isolated cerebral parenchymal arterioles

The vasoactive properties of inhibitory (γ-aminobutyric acid (GABA), glycine) and excitatory (glutamate, aspartate) amino acid neurotransmitters were studied in isolated rat cerebral parenchymal arterioles. None of these neurotransmitters had a significant effect on vessel diameter at concentrations between 10 −9 and 10 −3 M, except for 10 −3 M glycine. These amino acid neurotransmitters are unlikely to play a role in regulation or pathophysiology of the cerebral microcirculation by directly changing vascular diameter.

Effect of intracarotid hyperosmolar mannitol on cerebral cortical arterioles--a morphometric study.

The morphometric response of cerebral cortical arterioles to intracarotid hyperosmolar mannitol was assessed utilizing a technique of rapid freezing of rat brain tissue in vivo. A significant decrease in the wall to lumen (W/L) ratio was noted in the small parenchymal arterioles (20-49 mu) (p less than .0001) ipsilateral to the mannitol infusion. Larger arterioles showed a decreased W/L ratio but this change was not significant. Control infusion of 0.9% NaCl resulted in no change in arteriolar caliber. These results indicate that intracarotid hyperosmolar mannitol causes a direct vasodilatory response in small cerebral cortical arterioles.

Enzymes related to monoamine transmitter metabolism in brain microvessels.

The activities of tyrosine hydroxylase, aromatic L-aminoacid decarboxylase, monoamine oxidase, and catechol-O-methyltransferase were measured in microvessel (capillaries and venules), parenchymal arterioles, and pial vessels from rat brains, and the decarboxylase activity was compared in brain microvessels from rabbit, cat, dog, pig, cow, baboon, and man. Cranial sympathectomy was performed to estimate the neuronal contribution to the enzyme activities. All vascular regions had substantial activities of the various enzymes studied. The activity of aromatic L-aminoacid decarboxylase in cerebral microvessels was high in rat, dog, pig, cow, and man; intermediate in rabbit and cat; and low in baboon. In addition to this enzyme, cerebral microvessels also contained tyrosine hydroxylase and monoamine oxidase. Aromatic aminoacid decarboxylase and monoamine oxidase serve an enzymatic barrier function at the microvascular level, whereas the main function of tyrosine hydroxylase is probably to synthesize monoamines within nerve terminals that remain in close association with microvessels under the conditions used for preparation of the microvascular fraction. In larger intracerebral and pial vessels monoamine oxidase was present both in the wall itself and in perivascular sympathetic nerves; the remaining two enzymes had a primarily neuronal localization. The latter types of vessels also contained catechol-O-methyltransferase in their walls.

A histochemical study on the innervation of the cerebral blood vessels in the carp.

Adrenergic and cholinergic innervation of the cerebral blood vessels were studied in the carp using fluorescence and cholinesterase histochemistry. Most of the major cerebral and pial arteries were densely innervated with both nerves. Moreover, both nerves, being probably of central origin, were observed frequently on the walls of parenchymal arterioles and capillaries in the sections of the inferior lobe but were only rarely found in the other brain sections.

A histochemical study on the innervation of cerebral blood vessels in the bullfrog

Specific histochemical techniques for the demonstration of catecholamine and acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves on the cerebral blood vessels of bullfrog, Rana catesbeiana. The adrenergic nerve meshworks on the cerebral arteries of bullfrog were less dense, had a more elongate appearance along the arterial axis as compared with those of mammals and were rather similar to those of snakes. The nerve plexuses on the cerebral carotid artery and its main branches were somewhat denser than those on the basilar artery. The most characteristic feature of innervation in the bullfrog cerebral vessels was that no acetylcholinesterase-positive fibres were observed on the extraparenchymal arteries, whereas, in all higher vertebrates investigated so far, the cerebral arteries have been found to be dually innervated although differences in the density of innervation of the two nerves may exist. This suggests that the peripheral adrenergic innervation on the cerebral blood vessels appeared earlier than the cholinergic one in the evolution of vertebrates. On the other hand, both adrenergic and acetylcholinesterase-positive fibres were observed in close contact with parenchymal arterioles and capillaries suggesting the possible existence of a dual central innervation. This feature, however, was by no means common. Thus, the central neurons have a significant influence on the cerebral circulation in the bullfrog is somewhat equivocal. Most of the pial and the parenchymal small vessels and the parenchymal capillaries exhibited a heavy acetylcholinesterase activity on the vascular walls. Although the significance of the enzyme is obscure as yet, this has to be considered in relation to the regulatory mechanism of the cerebral circulation.

A histochemical study of the innervation of cerebral blood vessels in the turtle.

Specific histochemical techniques for the demonstration of noradrenaline and of acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves to the cerebral blood vessels of turtle, Geoclemys reevesii. The major and medium-sized cerebral arteries were supplied with dense adrenergic nerve plexuses, the plexuses were particularly dense in the medium-sized pial arteries of very thick vascular wall, indicating the functional significance of these arteries in the cerebral circulation. The parenchymal arterioles and capillaries were also supplied with adrenergic nerves. On the other hand, the cholinergic innervation was less dense than the adrenergic one and the acetylcholinesterase activity of the nerve fibres was remarkably weak. By contrast, the parenchymal small arterioles and capillaries exhibited heavy acetylcholinesterase activity on the vascular wall and, in addition, the capillaries were supplied with the well-stained acetylcholinesterase-positive nerve fibres. These fibres and also the adrenergic fibres associating with the capillaries appear to be of central origin. It is suggested that the cholinergic mechanisms in the parenchymal small vessels also play an important role in the cerebral circulation. The basophil leucocytes observed abundantly in the blood of turtle emitted an intensive greenish yellow fluorescence after formaldehyde gas-treatment.

A histochemical study of the innervation of cerebral blood vessels in the snake.

Dual innervation of snake cerebral blood vessels by adrenergic and cholinergic fibres was demonstrated with the use of histochemical methods. Although the nerve plexuses are somewhat less dense, the essential features of innervation of the blood vessels are similar to those of mammals with the exception that the adrenergic plexuses are more prominent than the cholinergic plexuses. The major arteries of the cerebral carotid system have a rich nerve supply. However, the innervation is less rich in the basilar and poor in the spinal (vertebral) arteries. Although the arteries supplying the right side of head are poorly developed, three pairs of arteries, cerebral carotids, ophthalmics and spinals, supply the snake brain. The carotids and ophthalmics are densely innervated and are accompanied by thick nerve bundles, suggesting that the nerves preferentially enter the skull along those arteries. Some parenchymal arterioles are also dually innervated. Connection between the brain parenchyma and intracerebral capillaries via both cholinergic and adrenergic fibres was observed. In addition cholinergic nerve fibers, connecting capillaries and the intramedullary nerve fibre bundles, were noticed. Capillary blood flow may be influenced by both adrenergic and cholinergic central neurons. The walls of capillaries also exhibit heavy acetylcholinesterase activity. This may indicate an important role for the capillary in the regulation of intracerebral blood flow.

On the Special Structure of the Salivary Glands in the Golden Hamster

The present paper dealt with the problems of blood-vessels and nerve-endings in the salivary glands, with the special reference to the duct system. Using the salivary glands in the golden hamster, as in the previous studies, the specimens were treated by a method of the injection with India ink and the silver-impregnation method of SUZUKI.1. The parenchymal arterioles, which are derived from interlobular arteries, ramify to form close capillary networks around the ducts and alveoles. Among the parts of the salivary glands, the striated ducts are supplied most abundantly by capillary networks with elongated meshes.2. In general the capillary network around the striated duct is of epilemmal character, but some capillaries derived from them pass through the basement membrane to form hypolemmal network among cells lining the duct.3. In preparats stained with Azan the figures of red-stained substance attached to the inner wall of the hypolemmal capillary could often be observed. The origin of this substance could also be traced back to the cytoplasm of the duct cell.4. The blood of the capillaries both in hypo- and epilemmal networks is collected into the venules in the parenchym, and carried away from the gland by interlobular veins.5. Forming delicate terminal reticulum with CAJAL's interstitial cells and unmyelinated nerve-fibers, the nerve elements in vegetative nature supply the whole salivary glands. The nervous terminal reticulum, as reported by many other investigators, situate for the greater parts in the connective tissues surrounding the ducts and alveoli.6. Very delicate nerve fibrils of unmyelinated nature derived from the reticulum pass through the basement membrane of the striated duct, and run waving, without any influence of the running directions of the ducts, among the cells in their hyponuclear regions.7. The nerve fibrils supplying the granular duct terminate to the so-called intercalated cells in the duct. In other words, the granular duct receives the nervous stimuli from two different nerve reticuli. one with intercalated cells lies inside the basement membrane, another outside the duct with CAJAL's cells.