Stimulation of the nucleus basalis of Meynert increases cortical cerebral blood flow without influencing diameter of the pial artery in rats.

The effects of focal electrical stimulation of the nucleus basalis of Meynert (NBM) and hypercapnia on diameter of the pial artery and regional cerebral blood flow (CBF) in the parietal cortex were examined in urethane-anesthetized rats. The diameter of pial artery was measured using the video microscope and cortical CBF was measured using the laser Doppler flowmetry. Hypercapnia at 10% of end-tidal CO2 concentration caused significant increases in diameter of the pial artery and cortical CBF.

Cerebral microcirculation: heterogeneity of pial arterial network controlling microcirculation of cerebral cortex.

Analysis of the functional behaviour of pial arterial ramifications feeding small areas of the cerebral cortex of rabbits uncovered well-defined heterogeneity of vascular responses during development of functional hyperemia. In the network of the smaller pial arteries, under 100 microns in diameter, the most active segments, the sphincters of offshoots of smaller arterial branches from larger trunks and the precortical arteries just before their penetration as the radial arteries into the cerebral cortex, have been discovered. The frequency of their dilatation was found to be higher, the latent periods of the vascular responses significantly shorter, and the degree of vasodilatation greater than of the adjacent arterial segments.

[The function of the precortical arteries].

In anesthetized adult rabbits, the responses of pial and precortical arteries to retinal photostimulation and the application of 0.5% strychnine solution to the brain surface were studied, as well as the distribution of cholinergic and adrenergic nerve fibres in these microvessels. The precortical arteries showed the highest degree of dilatation and frequency of responses.

[The variously directed reactions of the pial and cortical arterial branches in postischemic hyperemia in the cerebral cortex].

In adult rabbits, functional behaviour of pial and cortical (radial) arteries was rather different: the pial arteries showed regular dilatation while the lumen of the cortical arteries underwent regular reduction. Despite the different responses of the arterial segments, the vascular resistance diminished entailing an increase of local blood flow in the cerebral cortex.

[Features of physiologic mechanisms regulating microcirculation in the cerebral cortex of birds and mammals].

The responses of pial arteries to increased activity of the cerebral cortex as well as their innervation at various stages of phylogenic development, were studied with the aid of serial photomicrography with subsequent frame-to-frame analysis in adult rabbits and hens. Following the application of 0.5% isotonic strychnine solution to brain surface, the dilatation of all the segments of the pial artery ramifications was considerably more obvious in rabbits than in hens.

[Ultrastructural characteristics of branch sphincters and precortical arteries in the rabbit pial arterial system].

Structural peculiarities of pial arteries and their active microvascular segments-sphincters in offshoots and precortical arteries have been investigated, using electron and light microscopy. Our studies have revealed that these vascular segments, which can independently change their lumen, possess multiple myoendothelial junctions, as well as neuro-muscular contacts. This gives evidence of their independent responses that might be determined by structural peculiarities and innervation of their walls.

[Response of active microvascular segments in the pial artery system to photostimulation of the ey in the rabbit].

Photomicrography revealed the dynamics of pial ertarial responses, their active segments in particular: the sphincters at offshoots of minor arteries from the larger vessels, and the precortical arteries. On retinal photostimulation, the precortical arteries were found to dilate quite often (72%); the sphincters at offshoots in 50%, and the minor arteries in 38% of cases, while the larger pial arteries showed no dilatation at all. The dilatation was most pronounced in the precortical arteries and in the sphincter areas (25% of the control diameter), and less significant in minor pial arteries (10%).

[Spread of the dilatational reactions in the pial artery system to the microapplication of strychnine to the surface of the brain].

In anesthetized adult rabbits, organization of pial arterial bed and responses of its elements to microapplication of strychnine, were studied. The pial arterial responses were primarily related to the vessels' structural and functional features. The most considerable dilatation was characteristic of the precortical arteries.

[Dynamics of local vascular reactions during increased brain activity].

The dynamics of dilatant responses of the pial microvascular system was investigated under conditions of increased cortical activity due to direct application of suprathreshold concentrations of strychnine in experiments on adult rabbits using direct cinemicrography. The diameter of the following interconnected segments of pial arteries was measured in every frame of the film: comparatively large pial arteries (LPA), sphincters at off-shoots of smaller branches (SO), minor pial arteries (MPA), and precortical arteries (PCA). The experiments showed that the order of values of dilatant responses was: PCA greater than SO greater than MPA greater than LPA.

[Effect of sympathectomy on responses of pial arteries during acute deficiency of cerebral blood supply].

The dilatatory responses of small pial arteries including their active segments (sphincters at off-shoots, precortical arteries), to blood supply deficiency in the cerebral cortex were compared in control and sympathectomized rabbits. The sympathectomy resulted in complete disappearance of histochemically detected adrenergic and a considerable decrease of cholinergic nerve fibers in the pial arterial walls. The vasodilatation was much less obvious in sympathectomized than in control animals.

Pattern and innervation of pial microvascular effectors which control blood supply to cerebral cortex.

In experiments with adult rabbits the active microvascular segments located at particular sites of the minor pial arterial ramifications were investigated. These appeared as sphincters at off-shoots of the arterial branches, the precortical arteries, and the arterial microanastomoses. The sphincters and the precortical arteries were found plentifully supplied with the cholinergic and adrenergic nerves, but the innervation of the microanastomoses was not considerably different from that of the adjacent arterial branches.

[Histochemical studies of the microvascular effectors regulating blood supply to the cerebral cortex].

The innervation of the pial arteries as well as the activity of enzymes (phosphorylase I, II, III, succindehydrogenase, lactate dehydrogenase, ATPase, GTPase and CTPase) responsible for vascular smooth muscle function were studied histochemically on total microscopic preparations of rabbit pia matter. An especially rich adrenergic and cholinergic innervation was found around the active microvascular effectors - sphincters of pial and precortical arterial off-shoots. The nerve fibers followed the radial arteries entering the cerebral cortex.

[Reactions of pial microvascular effectors in regulating adequate cortical blood supply to neuronally isolated cerebral cortex].

Responses of pial arteries were studied in experiments on adult rabbits with the use of serial photomicrography of the cerebral surface under conditions of the enhanced activity of the brain cortex, induced by application of 0.5% strychinine. No significant differences in the responses of smaller and larger pial arteries as well in those of the sphincters at their off-shots and precortical arteries were found after dissection of all neural pathways of the vascular responses are neurogenic, the feed-back should operate locally, inside the appropriate cortical areas.

On the control of microcirculation in the cerebral cortex during and following ischemia.

The aim of the present study was the elucidation of the functional behaviour of the pial arteries and their microvascular effectors which are responsible for the microcirculation in the cerebral cortex - large and small pial arteries (PA), sphincters at the offshoots at the pial arteries (SOPA), precortical arteries (PCA) and pial arterial microanastomoses (PAMA) - both under ischemic and postischemic conditions. During ischemia the majority of the studied microvessels underwent dilatation which under conditions of decreased intravascular pressure seems to be active and should be aimed at compensating for the defficiency of the blood supply to the cerebral tissue. Besides, a constriction of some microvessels, especially of SOPA and PCA, was also observed, the amount of such responses of SOPA being increased in the postischemic period.

[Functioning of the microvascular mechanisms in the pial artery system].

In rabbits, the functional behavior of the pial arterial offshoots (PAO), the pial arterial anastomoses (PAA), and the precortical arteries (PCA), was studied. In functional and postischemic hyperemia, as well as on changes of cerebral blood flow (caused by changes of the systemic arterial pressure), dilatatory and constrictory responses of the active portions of the microvessels suggest that the PAO and PAA participate mainly in the regulation of blood supply to the cerebral cortex adequate to its metabolic demands, while the PCA get involved during superfluous inflow of blood to the cerebral cortex.

[Characteristics of the functional behavior of different cerebral arteries and angiospasm location in them].

For the major arteries of the brain, when their tone is normal, the constrictory responses are much greater than the dilatory ones while the tendency to dilation of the pial arteries is considerably greater than their tendency to constriction; some luminal contraction and no dilation of the intracerebral arteries (in the depth of the cortex) appears even at an increased blood flow. The tendency to a spasm of the cerebral arteries is corroborated by the peculiarities of their functional behavior: the spasm-like constriction of the major arteries of the brain occurs much easier than that of the pial arteries; a spasm of the intracerebral arteries may develop, but only under some local effect.