Jan Kåhrström

Calcitonin gene-related peptide is present in mammalian cerebrovascular nerve fibres and dilates pial and peripheral arteries

Calcitonin gene-related peptide (CGRP) is a novel 37-amino acid peptide occurring in neurones within sensory ganglia, in brain stem, as well as in the walls of blood vessels of peripheral organs. Pial arteries of cat showed a well-developed supply of CGRP-positive nerve fibres. The peptide was found to be a potent dilator of both pial and peripheral vessels of rabbit and cat, and of pial vessels from man. The dilatory effect was independent of the vascular endothelium and was not mediated through adrenergic, cholinergic or histaminergic smooth muscle receptors. The neurogenic vasoconstriction induced by electrical field stimulation was temporarily inhibited by CGRP, as studied in central ear arteries from rabbits. The results suggest that CGRP is a transmitter or modulator playing a role in the regulation of vascular tone.

Selective electrical stimulation of postganglionic cerebrovascular parasympathetic nerve fibers originating from the sphenopalatine ganglion enhances cortical blood flow in the rat

Recently, the origins and pathways of cerebrovascular acetylcholine- and vasoactive intestinal polypeptide-containing nerves have been elucidated in detail in the rat: The sphenopalatine ganglion is the major source for postganglionic parasympathetic fibers to the vascular beds of the cerebral hemispheres. To clarify the functional role of the nerves on cerebral blood vessels in vivo, brain cortical microvascular blood flow was measured in rats during electrical stimulation of these particular postganglionic fibers. Animals were subjected to transection of the right nasociliary nerve 2 weeks before the flow measurements to eliminate activation of peptidergic sensory fibers. Relative change in microvascular blood flow was continuously recorded by a laser-Doppler flowmeter system under α-chloralose anesthesia. The postganglionic fibers were electrically stimulated just proximal to the ethmoidal foramen by a bipolar platinum electrode (5 V; 0.5 ms; 3, 10, 30, 60 Hz; as a continuous stimulation for 90 s). Stimulation at 10 Hz induced a marked increase of the cortical blood flow (CoBF) on the ipsilateral side, whereas no change was observed on the contralateral side. It reached a maximum mean value of 42.5% at 46 s, and then slightly declined during the remaining stimulation period. No significant changes were observed in the mean arterial blood pressure or blood gases during or after stimulation. Both atropine and scopolamine failed to alter this flow increase. Electrical stimulation of the postganglionic fibers at different frequencies revealed a maximal increase in the CoBF at 30 Hz in the control situation (47.2%), but at 10 Hz after scopolamine administration (51.6%). This provides the first report showing that selective postganglionic stimulation of the parasympathetic nerve fibers markedly enhances blood flow in the brain, and it supports the view that the neurogenic vasodilatation is primarily noncholinergic.

Neuropeptide Y Co-Exists with Vasoactive Intestinal Polypeptide and Acetylcholine in Parasympathetic Cerebrovascular Nerves Originating in the Sphenopalatine, OTIC, and Internal Carotid Ganglia of the Rat

Neuropeptide Y co-exists with noradrenaline in the majority of the sympathetic nerves supplying cerebral blood vessels. However, after sympathectomy in the rat the number of cerebrovascular neuropeptide Y nerve fibers are only reduced in number despite a complete disappearance of the adrenergic markers. The origin of these non-sympathetic neuropeptide Y fibers was studied by nerve transections and retrograde axonal tracing utilizing True Blue. Three days after bilateral superior cervical sympathectomy, the number of neuropeptide Y-containing nerve fibers decreased to about 40% of that in non-treated animals. One week after True Blue application on the proximal portion of the middle cerebral artery, the tracer accumulated in neurons of the sphenopalatine, otic, and internal carotid ganglia. Of these cells 80%, 95% and 5%, respectively, were neuropeptide Y-positive. Some of the True Blue/neuropeptide Y-positive cells displayed immunoreactivity for vasoactive intestinal polypeptide and some were positive for choline acetyltransferase. Two weeks after bilateral removal of the sphenopalatine ganglion or transection of postganglionic fibers from the ganglion reaching the pial vessels through the ethmoidal foramen, together with subsequent sympathectomy, no neuropeptide Y-containing nerve fibers could be observed on the anterior cerebral and internal ethmoidal artery or the distal portion of the middle cerebral artery, whereas a few nerve fibers remained on the proximal portion of the middle cerebral artery, internal carotid artery, and the rostral portion of the basilar artery. In conclusion, neuropeptide Y in cerebrovascular nerves is co-stored not only with noradrenaline in sympathetic nerves from the superior cervical ganglion, but also with acetylcholine (reflected in the presence of choline acetyltransferase) and vasoactive intestinal polypeptide in parasympathetic nerves originating in the sphenopalatine, otic, and internal carotid ganglia.

P1- and P2-purine receptors in brain circulation

As there is increasing evidence that purines are involved in cerebral vasodilatation, purine receptors were characterized pharmacologically in pial arteries from rabbit, cat and man, and compared with purine receptors in various non-cerebral vascular beds. Use of agonists and antagonists allows purine receptors to be divided into P1 and P2 receptors. The location of these receptors on the surface of the various cells in the cerebrovascular wall was determined. P1 receptors, stimulated primarily by adenosine, are located on the smooth muscle cells, causing relaxation. P2 receptors, stimulated primarily by ADP and ATP, are located on endothelial cells and cause relaxation, and are also found on smooth muscle cells where they cause contraction. Slowly degradable ATP analogues were considerably more potent constrictors than ATP but not equally potent as dilators, which might indicate minor differences between the P2 receptors on smooth muscle and on endothelium. The P1 receptor was further subclassified into the A2 type. Adenosine may also reach an intracellular purine receptor, via an uptake process, to cause additional relaxation, as was shown with an intracellular purine receptor agonist in cat pial arteries. Brain vessels were found to be considerably more sensitive to purines than most non-cerebral vessels studied.

Endothelin Is a Potent Constrictor of Human Intracranial Arteries and Veins

Endothelin, a peptide produced in endothelial cells, was found to be a potent constrictor of human pial arteries through a direct, slow action on the smooth muscle cell, with a pD2 value of 8.54. It was less potent as a constrictor in pial veins (pD2 7.80) and in branches of the middle meningeal artery and superficial temporal artery (pD2 7.61 and 7.77). The major component of the contractile response in the arteries comprises an effect on potential-operated calcium channels, as evidenced by tests with nimodipine. Endothelin may regulate intracranial vessels tonically during physiological as well as pathophysiological conditions.

Blood-brain barrier leakage and brain edema in stroke-prone spontaneously hypertensive rats. Effect of chronic sympathectomy and low protein/high salt diet

SummaryBrain edema associated with severe chronic hypertension was studied in stroke-prone spontaneously neously hypertensive rats (SHRSP), 5 to 9 months of age. Blood-brain barrier (BBB) leakage sites and intracerebral spreading pathways for plasma proteins were delineated by an intravenously (i.v.) injected exogenous dye tracer (Evans blue), known to form a complex with albumin in blood, and by immunohistochemical visualization of extravasated endogenous plasma proteins. The tissue content of edema fluid was estimated by measuring the specific gravity of selected brain regions, stained or unstained by the tracer dye, on a bromobenzene-kerosene gradient column. Multifocal BBB leakage sites were macroscopically detected within the cerebral cortex and the deep gray matter after i. v. circulation of Evans blue-albumin for 30 min. After 24 h of i.v. circulation the dye tracer had spread not only locally in the gray matter but also into the adjacent white matter, where it was widely distributed. Immunohistochemically visualized plasma proteins showed similar distribution. Unilateral superior cervical ganglionectomy performed at 4 weeks of age neither increased the incidence of major BBB opening to Evans blue-albumin nor altered the specific gravity of the ipsilateral cerebral hemisphere in grown-up SHRSP, furthermore, the blood pressure remained unchanged. The lack of significant effect on BBB function may possibly be attributed to the extensive reinnervation of the cerebral arteries, verified in the grown-up SHRSP using the Falck-Hillarp fluorescence method for visualization catecholaminergic nerve fibers. In SHRSP raised on a low-protein and high-salt diet the mean arterial blood pressure was 212 mm Hg compared to 195 mm Hg in controls (P<0.05) and the incidence of BBB opening was 72% compared to 25% in controls (P<0.05). After 24 h of i.v. circulation of Evans blue-albumin, brain regions stained by the dye tracer showed significantly reduced specific gravity (P<0.001), while unstained regions had normal values. Thus the brain edema fluid spread, as revealed by specific gravity measurements, corresponded to the intracerebral distribution of extravasated plasma proteins.

Studies of protective actions of nicotine on neuronal and vascular functions in the brain of rats: comparison between sympathetic noradrenergic and mesostriatal dopaminergic fiber systems, and the effect of a dopamine agonist.

Neuroprotective and possible trophic actions of nicotine were studied in two types of experimental models: (1) one in which the meso-striatal dopamine system was subjected to partial hemitransection, and regional glucose utilization (using 2-[3H]deoxyglucose) and blood flow (using [14C]iodoantipyrine) were measured by computer-assisted quantitative autoradiography based on a double-isotope technique; and (2) another where the sympathetic cranial nervous system supplying the brain vasculature was subjected to decentralization, axotomy, and partial or complete ganglionectomy, and the neuronal survival and fiber regeneration were elucidated by fluorescence histochemistry of noradrenaline, tyrosine hydroxylase, and neuropeptide Y. Continuous nicotine infusion for 4 weeks failed to significantly affect the neuronal response to the surgical interference of the sympathetic noradrenergic system. The same nicotine treatment for 2 weeks significantly improved glucose utilization and blood flow in caudate-putamen on the side in which the meso-striatal dopamine system had been transected, thus eliminating the 16% side-to-side asymmetry in the metabolism caused by the axotomy. The dopamine agonist, EMD 23,448, was without significant effect on this asymmetry. The hemitransection produced marked reduction in metabolism and flow also in the ventro-lateral thalamus. In substantia nigra, glucose utilization was markedly elevated--perhaps as a consequence of a regenerative increase in protein synthesis--opposite to a considerable reduction in nigral blood flow. Little or no effect of the hemitransection was seen in hippocampus or nucleus accumbens. In neither of these four regions did nicotine (or EMD 23,448) have any overt influence on glucose metabolism or blood flow. It is concluded that nicotine, mainly through its protective action on the meso-striatal dopaminergic system, is able to improve striatal glucose utilization and associated blood flow, probably reflecting a tendency to amelioration of neurotransmission function of surviving terminals belonging to the nigro-striatal dopamine neurons.

Endothelium-dependent relaxation by uridine tri- and diphosphate in isolated human pial vessels.

Uridine triphosphate (UTP) and uridine diphosphate (UDP) are present in platelets, probably linked to storage organelles. In several animal species, UTP is a powerful constrictor of cerebral arteries, with no detectable dilatory component, which was confirmed in the present study. When testing the vasomotor effects of UTP and UDP in precontracted isolated segments of human pial arteries it was found that these nucleotides were powerful, transient dilators in the concentration range 10(-7)-10(-5) M in the majority of vessels studied. At higher doses a contractile response supervened. Uridine monophosphate and uridine were without effect. Removal of the vessel endothelium mechanically or by perfusion with Triton abolished the dilatory response, and now the contraction appeared already at 3 X 10(-6) M. The present findings add UTP and UDP among the group of endothelium-linked biogenic vasodilators. This may be of pathophysiological importance in the maintenance of an adequate brain circulation in disorders involving platelet dysfunction.

Galanin-positive nerves of trigeminal origin innervate rat cerebral vessels

(GAL)-positive nerve fibers in rat cerebral vessels were demonstrated by immunohistochemistry, and their origin in the trigeminal ganglia and pathway in the nasociliary nerve to the vessels was shown by retrograde tracer technique and nerve transection. Some fibres in the vertebrobasilar system appear to originate in extracranial sources. With the antiserum used only few GAL fibers could be seen in the vessels, mostly in the vertebrobasilar system. In neonatally sympathectomized animals a rich network could be visualized in most pial arteries - still particularly in the vertebrobasilar system - probably as a result of a diminished competition for nerve growth factor. No vasomotor effect of GAL could be detected in isolated segments of pial arteries, neither in normal nor in sympathectomized animals, which rules out a direct postsynaptic effect on vascular tone. GAL did not display prejunctional modulatory action on the adrenergic nerves present in the vascular preparations. A sensory function of GAL is discussed.

Amine-induced responses of pial and penetrating cerebral arteries: evidence for heterogeneous responses.

Middle cerebral arteries (MCAs) of rabbits were compared with two types of small branches (<100-µm outer diameter), penetrating arteries (PAs) and surface arteries (SAs), by determining their mechanical reactivity to several amines and standard contractile agents. Two techniques were employed: (a) measurement of isometric tension of 1-mm rings (MCA, PA, or SA); (b) measurement of perfusion pressure of segments consisting of essentially MCA or essentially PA. Both techniques revealed similar reactivity of the different types of vessel to acetylcholine, i.e., relaxations to a maximum of 52–78%, and similar strong contractile responses to histamine, although the MCA was more sensitive. Under H1 blockade, histamine dilated the PA (both techniques) and the MCA (perfusion technique), but not the SA. Relatively weak contractile responses to serotonin were observed in the MCA (both techniques) and the PA (perfusion technique), but not the SA (isometric tension only); no dilative responses could be elicited. Responses to noradrenaline varied with the vessel considered: The MCA contracted only, whereas the PA weakly contracted or relaxed at basal tone, and many preparations relaxed after precontraction with uridine triphosphate; the SA did not react. Relaxation of precontracted PA by noradrenaline occurred at relatively low concentrations and was antagonized by propranolol at 3 × 10− 7 or 3 × 10− 6 M. These results reveal very significant differences in the segmental reactivity to amines and suggest that noradrenaline released from sympathetic fibers might have opposing actions in the major pial arteries and the smaller penetrating branches.