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. Electrical stimulation of the NBM (with parameters of 200 microA, 50 Hz, 0.5 ms, for 1 min) produced a significant increase in cortical CBF, but did not influence the diameter of pial artery. The results suggest that cholinergic fibers originating in the NBM do not contribute to neural vasodilatation of the pial artery, although they induce neural vasodilation of parenchymal blood vessels which results in an increase in CBF in the parietal cortex.

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. An abundant amount of cholinergic nerve plexuses (containing the cholinesterase) was found in the walls of these active vascular segments, and microapplication of atropine resulted in a considerable decrease of their dilatation. These experimental results indicate the involvement of the cholinergic neurogenic mechanism in the functional vasodilatation, as distinct from the largely accepted effect of the humoral mechanism accomplished by diffusion of active vasodilatory substances from tissue elements to the walls of the feeding arterial branches.

[The function of the precortical arteries]. / Funktsiia prekortikal'nykh arterii.

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. Dense innervation was mostly in evidence in the precortical arteries. Upon atropin application, the response suppression was also more obvious in the precortical arteries. The data suggest that the precortical arteries play an important role in regulation of the adequate blood supply to the brain tissue.

[The variously directed reactions of the pial and cortical arterial branches in postischemic hyperemia in the cerebral cortex]. / Raznonapravlennye reaktsii pial'nykh i korkovykh arterial'nykh vetvlenii pri postishemicheskoi giperemii v kore golovnogo mozga.

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]. / Osobennosti fiziologicheskogo mekhanizma regulirovaniia mikrotsirkuliatsii v kore golovnogo mozga ptits i mlekopitaiushchikh.

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. The latencies of the vascular responses differed in a similar way. Histochemical studies revealed a considerably richer adren- and cholinergic innervation in rabbit pial arteries as compared with those of hens. The vascular responses and the neurogenic control of the pial arterial bed seem to become steadily refined, together with its anatomy, in the course of evolutionary development.

[Ultrastructural characteristics of branch sphincters and precortical arteries in the rabbit pial arterial system]. / Ul'trastrukturnye osobennosti sfinkterov otvetvlenii i prekortikal'nykh arterii v pial'noi arterial'noi sisteme u krolikov

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]. / Reaktsiia aktivnykh mikrososudistykh segmentov v sisteme pial'nykh arterii pri fotostimuliatsii glaza u krolikov.

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%). The data obtained indicate that the precortical arteries are the basic vascular effectors of regulation of adequate microcirculation in the cerebral cortex.

[Spread of the dilatational reactions in the pial artery system to the microapplication of strychnine to the surface of the brain]. / Rasprostranenie dilatatornykh reaktsii po sisteme pial'nykh arterii pri mikroapplikatsii strikhnina k poverkhnosti golovnogo mozga.

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. The reactions of sphincters of offshoots and smaller pial arteries were almost similar. The least dilatation occurred in larger pial arteries (over 100 mu in diameter). The limits of the vasodilatation were the microanastomoses which separated individual "terminal microvascular units" in the pial arterial bed. The data obtained show that the anatomy of the pial arterial bed provides a possibility for relatively independent regulation of microcirculation in rather small areas of cerebral neocortex.

[Dynamics of local vascular reactions during increased brain activity]. / Dinamika mestnykh sosudistykh reaktsii v usloviiakh povysheniia aktivnosti golovnogo mozga.

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. The order of the latencies was: PCA less than SO less than MPA less than LPA. The revealed behaviour of the pial microvascular system maintains the adequacy of local blood supply as well as the elimination of the "steal phenomenon" in the neighbouring cortical areas.

[Effect of sympathectomy on responses of pial arteries during acute deficiency of cerebral blood supply]. / Vliianie simpatéktomii na reaktsii pial'nykh arterii pri ostrom defitsite krovosnabzheniia golovnogo mozga.

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. This was associated with (and probably caused by) a considerable rise in histochemically detected serotonin activity of the pial arteries walls. After recovery of blood supply to the brain the constriction of the pial arterial active segments restricting the excessive cerebral blood flow, was significantly reduced due, probably, to the sympathetic deprivation. Therefore, the sympathetic control plays an important part in pial arterial responses regulating the adequate blood supply of the cerebral cortex.

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. The nerves of the precortical arteries were in direct connection with the nerve fibers of the arterial branches located inside the cerebral cortex. The pattern of distribution and innervation of the active vascular portions in pial microvascular bed suggests the probability of a neurogenic control of the blood supply to the smallest areas of the cerebral cortex.

[Histochemical studies of the microvascular effectors regulating blood supply to the cerebral cortex]. / Gistokhimicheskie issledovaniia mikrovaskuliarnykh éffektorov regulirovaniia krovosnabzheniia kory golovnogo mozga.

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. No differences were detected between the pial arteries and active microvascular effectors in the enzyme activity.

[Reactions of pial microvascular effectors in regulating adequate cortical blood supply to neuronally isolated cerebral cortex]. / Reaktsii pial'nykh mikrovaskuliarnykh éffektorov regulirovaniia adekvatnogo krovosnabzheniia kory mozga v usloviiakh ee neíronal'noi izoliatsii.

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.